.3 r

Pubii

cations

•L INST OF STAND & yECH

A111Q7 ElOb^fi

31

1

NBS BUILDING SCIENCE SERIES 104

Window Design Strategies

to Conserve Energy

U.S. DEPARTMENT OF COMMERCE • NATIONAL BUREAU OF STANDARDS

A
Library of Congress Catalog Card Number: 77-600018

National Bureau of Standards Building Science Series 104

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 104, 209 pages Gune 1977)

CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

For sale by the Superintendent o£ Documents, U.S. Government Printing Office, Washington, D.C. 20234

(Order by SD Catalog No. 013.29/2:104) Stock No. 003-003-01794-9 Price $3.75 (Add 25 jxrcent additional for other than U.S. mailing)
TABLE OF CONTENTS

ABSTRACT

INTRODUCTION

GLOSSARY

SI CONVERSION

1. SITE

1.1 WINDBREAKS /Air Tightness, Insulation, Ventilation 1-1

1.2 SHADE TREES /Shading, Insulation 1-9

1.3 GROUND SURFACES /Daylighting, Solar Heating 1-15

1.4 ORIENTATION TO SUN/ Solar Heating, Shading 1-21

1.5 ORIENTATION TO WIND/Ventilation, Air Tightness 1-31

2. EXTERIOR APPENDAGES

2.1 SUN SCREENS /Shading, Insulation 2-1

2.2 EXTERIOR ROLL BLINDS / Shading , Insulation 2-9

2.3 ARCHITECTURAL PROJECTIONS /Shading 2-15

2.4 EXTERIOR SHUTTERS/ Shading, Insulation, Air Tightness 2-21

2.5 AWNINGS /Shading 2-27

3. FRAME

3.1 FRAME VENTILATORS/Ventilation 3-1

3.2 WEATHERSTRIPPING/Air Tightness 3-7

3.3 THERMAL BREAK/ Insulation 3-11

3.4 TYPE OF OPERATION/Ventilation, Air Tightness 3-17

3.5 WINDOW TILT /Solar Heating 3-23

3.6 SIZE, ASPECT RATIO/Air Tightness 3-33

4. GLAZING

4.1 MULTIPLE GLAZING/ Insulation 4-1

4.2 HEAT-ABSORBING GLAS

S

/ Shading , Solar Heating 4-9

4.3 REFLECTIVE GLASS /Shading 4-17

4.4 APPLIED FILMS /Shading, Insulation 4-23

4.5 REDUCED GLAZING/ Insulation, Shading 4-27

4.6 GLASS BLOCK/Insulation, Solar Heating, Daylighting 4-31

4.7 THRU-GLASS VENTILATORS/Ventilation 4-37

5. INTERIOR ACCESSORIES

5.1 VENETIAN BLINDS / Shading , Daylighting

5.2 DRAPERIES / Shading , Insulation

5.3 FILM SHADES /Insulation, Solar Heating, Shading

5.4 OPAQUE ROLL SHADES /Shading, Solar Heating

5.5 INSULATING SHUTTERS/ Insulation

6. BUILDING INTERIOR

6.1 FIXTURE CIRCUITING/Daylight 6-1

6.2 TASK LIGHTING/Daylighting 6-5

6.3 AUTOMATIC SWITCHING/Daylighting 6-9

6.4 INTERIOR COLORS /Daylighting 6-13

6.5 THERMAL MASS/ Solar Heating 6-17

CONCLUSION C-1

ACKNOWLEDGMENTS C-2

iii

iv

V

ix

X

5-1

5-7

5-13

5-19

5-25
ABSTRACT

A multitude of design strategies are available to achieve energyefficient windows. Opportunities for improving window performance

fall into six groups: site, exterior appendages, frame, glazing,

interior accessories, and building interior. Design strategies

within these groups can improve one or more of the six energy

functions of windows: solar heating, daylighting, shading, insulation, air tightness, and ventilation. Included in this report

are 33 strategies; an explanation of the physical phenomena responsible for each strategy's energy performance, summarized energy and

non-energy advantages and disadvantages; aesthetic considerations;

cost approximations; example installations, laboratory studies, or calculations by the authors; and references. Intended readers

include professional designers, lessees and owners of commercial

space, home buyers and owners, window component manufacturers, and

researchers. The report's purpose is to draw attention to the wide

range of options currently available to conserve energy with windows.

Key Words: Air-tightness; daylighting; energy conservation;

insulation; shading; solar heating; ventilation; windows.

iv
INTRODUCTION

Windows can substantially alter the amount of purchased energy

required to maintain comfort. Well-designed, they can actually

provide a net energy gain; poorly designed, they can be an enormous energy burden. This report provides design strategies to make

windows energy conserving. Each strategy is directed at improving

one or more of the six energy functions of windows, which are:

providing winter solar heat, providing year-round daylighting,

rejecting summer solar heat, providing insulation and air tightness

during periods of heating or air conditioning, and providing natural ventilation during temperate weather.

Window design strategies to conserve energy need not be limited to

the frame and glazing. Site strategies can minimize adverse climatic forces and/or amplify beneficial climatic forces; exterior

appendages and interior accessories can supplement the capabilities

of the window frame and glazing; and buildiAg interior strategies can insure maximum benefit is derived from the energy assets the

window provides.

In order to facilitate successful use of design strategies, this

report includes a cursory explanation of the physical phenomena

responsible for each stategy's performance. This is followed by a list summarizing the energy, as well as non-energy, advantages and

disadvantages of each strategy. Then, since windows and their

accessories can drastically affect the quality of the building

exterior, as well as the character of the building exterior, aesthetics are discussed. Brief price inquiries are reported to

provide estimates of first costs. Installation was not included in

most cost figures because of the wide variation installation situations introduce. More precise dollar figures should be obtained

from local distributors before life-cycle costing is calculated for an actual building. Finally, the references used in writing and

illustrating each strategy, and sources for further information, are listed.

Selection of individual strategies should be based on the importance

of each of the window's energy functions, considering the local

climate, the time of day and/or seasons the building is most used,

and the environmental requirements of the activities being housed.

The strategy/ function cross-reference table following the introduction is provided to help select strategies addressing the energy

functions determined to be most important for a specific project.

Final evaluation requires recalculation of the total window system,

since the performance of strategies in combination may differ from

the sum of each individual's performance.

V
The report is not only intended for the professional designer , but

also for the researcher, to suggest further investigation of the

many energy-conservation potentials of windows; the manufacturer,

to encourage further refinement of the energy-conservation qualities

of his product(s); and the commercial lessee or home buyer, with

the hope that more energy-efficient windows will result as a consequence of demand from a consuming public better informed of the

range of energy-conserving options available.

Work on this report has been conducted within the framework of an National Bureau of Standards interdisciplinary research project on the energy-related performance of windows. The work on this project

was partially in support of' the development of Building Energy

Performance Standards. It was jointly supported by the Energy

Research and Development Administration (Contract E(49-l) 3800) , by

the United States Department of Housing and Urban Development

(Contract No. RT 193-12), and by the National Bureau of Standards.

The content of the report draws heavily upon research and data

published by private industry. In referencing this material, NBS

in no way endorses specific manufacturers or products. Professional

judgment must be exercised in assessing the capabilities of strategies singly or in combination for specific building projects.

vi
1.

2.

3.

STRATEGY /Function CROSS-REFERENCE TABLE

Solar Daylighting Shading Insu Heating

lation Air

Tightness

Ventilation

SITE

WINDBREAKS X X X

SHADE TREES X X

GROUND SURFACES X X

ORIENTATION TO SUN X X

ORIENTATION TO WIND X

EXTERIOR APPENDAGES

SUN SCREENS X X EXTERIOR ROLL BLINDS X X ARCHI. PROJECTIONS X X

EXTERIOR SHUTTERS X X X AWNINGS X

FRAME

FRAME VENTILATORS X

WEATHERSTRIPPING X

THERMAL BREAK X TYPE OF OPERATION X X WINDOW TILT X

SIZE, ASPECT RATIO X

4. GLAZING

MULTIPLE GLAZING X

HEAT-ABSORBING X X

REFLECTIVE GLASS X APPLIED FILMS X X REDUCED GLAZING X X GLASS BLOCK X X X THRU-GLASS VENTILATORS X

5. INTERIOR ACCESSORIES

VENETIAN BLINDS X X DRAPERIES X X FILM SHADES X X X

OPAQUE ROLL SHADES X X INSULATING SHUTTERS X

6. BUILDING INTERIOR

FIXTURE CIRCUITING X

TASK LIGHTING X

AUTOMATIC SWITCHING X

INTERIOR COLORS X

THERMAL MASS X

vii
LATITUDES OF THE UNITED STATES

viii
GLOSSARY

SOLAR HEATING : Total Solar Transmittance = the amount of solar energy transmitted through the window configuration divided by the

total energy incident (striking) on the outside surface.

(Given as a percentage.)

Latitude: f or the convenience of the reader a map of the U . S

.

with latitudes is provided on the opposite page.

DAYLIGHTING ;

Visible Transmittance = the amount of visible light transmitted

through a window configuration divided by the amount of

visible light incident on the outside surface. (Given

as a percentage.)

SHADING :

Shading Coefficient = the total amount of heat transmitted by

a window configuration divided by the total amount of heat

transmitted by a single pane of double strength (1/8")

glass.

INSULATION :

Btu = amount of heat required to raise the temperature of one pound of water at its maximum density one degree Farenheit

.

U-value = the amount of heat conducted from the inside air,

through the window configuration to the outside air, or vice versa, in the summer. A 15-mph outside wind is assumed

in the winter, a 7 1/2-mph outside wind is assumed in the

summer. The air inside is assumed still summer and winter.

(Given in Btu/square foot, hour degree Farenheit difference

between outside and inside temperatures.) For example, a U-value of 0.50 means 0.50 Btu's pass through each square

foot of window configuration for every hour and, for each

Farenheit degree difference existing between the inside

and outside temperature.

R-value = the resistance a material offers to the flow of heat

from one surface to another. The resistance between the

surface to the air is considered separately. The reciprocal

of the Sum of the Resistances equals the U-value. U=l/

(R,+R„+. . .R )

.

AIR TIGHTNESS, VENTILATION : Volume of air passing through an opening = cubic feet of air

for a given time period divided by crack length (for

infiltration) or divided by open area of sash (for

ventilation) . -
SI CONVERSION

In view of present accepted practice in this country in this

technological area, common U.S. units of measurement have been

used throughout this paper. In recognition of the position of

the USA as a signatory to the General Conference on Weights and

Measures, which gave official status to the metric SI system of

units in 1960, we assist readers interested in making use of the

coherent system of SI units by giving conversion factors applicable to U.S. units used in this paper.

Length

1 in = 0.0254 meter* (m)

1 ft = 0.3048 meter* (m)

Area

2 2

1 ft = 0.0929 square meter (m )

Volume

1 ft^ = 0.0283 cubic meter (m"^)

Mass

1 lb = 0.453 kilogram (kg)

Mass/Volume (Density)

1 Ib/ft"^ = 16.02 kilogram/meter-^ (kg/m^^)

Temperature

degree Celsius ("C) = 5/9 (°F - 32)

Volume/Time (Flow)

3 3

1 cfm = 0.000472 meter /second (m /s)

Velocity

1 mph = 0.447 meter/ second (m/s)

Quantity of Heat

1 Btu = 1055.87 joule (J)

Thermal Resistance

2 2 1 °F h ft /Btu = 0.176 square meter degree Celsius/Watt (m .°C/W)

* exactly

X

1. SITE

Two key site considerations are the siting of a building

to provide favorable window orientation to the sun and

favorable window orientation to prevailing winds. Landscaping can also improve window performance. Shade trees

can seasonally control direct radiation from the sun;

ground surfaces can control reflected radiation; planted

ground cover can moderate air temperature; and windbreaks

can diminish the force of the wind.

In general, there are two advantages to improving window

performance through site design. First, adverse climatic

forces are moderated at a distance. Residual forces are

then dissipated before encountering the windows. Second,

climatic moderation is likely to improve the performance

of adjacent walls and roofs, as well as windows.

The effectiveness of improving the energy performance of

windows through site design is apparent if heat-gain/heatloss calculations are first computed with unadjusted regional

climatic statistics, then recalculated considering the

tempering of sun, wind and air temperature possible through

site design. The site-moderated window performance should

be the basis for making trade-offs in window design.

1-0
1.1 WINDBREAKS/Air Tightness, Insulation, Ventilation

STRATEGY

:

Install a fence and/or row of trees or shrubs as a wind barrier

to reduce wind pressure on windows.

PHENOMENA:

1) Air infiltration through windows can be reduced by diminishing wind pressure by means of a windbreak. The most

effective location for a windbreak is upwind a distance of

1 1/2 to 2 1/2 times the height of the building. At this

distance, the wind will be deflected up and well over the

building, reducing the pushing action on the building's

windward side and the pulling action on its leeward side.

V

h

Figure 1 . Windbreak Distance

1-1
2) A windbreak is more effective If It allows part of the wind

to penetrate. A solid windbreak creates a low pressure area

on its leeward side with resulting strong eddy currents.

These may be as destructive as direct wind in eroding the

still air film at the surface of the window. Allowing a portion of the wind to pass through the windbreak tends to

relieve this leeward suction. This is illustrated in the

following comparison between a solid wall and an open fence.

Solid Fence Fence with Slatted Openings

Figure 2. Airflow vs. Fence Design

1-2
3) Heat transmission through windows can be reduced by diminishing the amount of wind flowing across the glass.

Glass is a good conductor of heat and therefore affords

little impediment to heat flow. However, a still layer of

air at the surface of the glass does retard heat flow.

Blocking the wind will protect this boundary layer of air

from the scouring force of wind. The importance of the

boundary layer of air is illustrated below:

STILL

INSIDE

AIR

SINGLE

GLASS

OUTSIDE

AIR

U = R =.68 + R = .03 -t- R

R

R

.68(0mph)

.25(7.5mph)

.17(15mph)

0.72 U VALUE

1.04 U VALUE

1.13 U VALUE

Figure 3. Heat Flow Through Glass vs. Wind Velocity

4) Prevailing winter winds come from a different direction than

prevailing summer winds in much of the U. S. Therefore, a windbreak can be placed to divert winter wind away from a building without interfering with summer breezes.

1-3
ADVANTAGES

:

1) Reduced air infiltration through cracks around windows.

2) Reduced heat loss through the glass by diminished wind erosion

of the insulating boundary layer of air at the glass surface.

3) Partial protection from the summer sun on east and west

orientation when the sun is low in the sky.

4) Privacy.

5) Improved natural ventilation when the windbreak geometry

funnels breezes.

6) Snowdrift control (snow will collect at the leeward side).

7) Slight reduction in noise from sources beyond the windbreak.

DISADVANTAGES

:

1) Possible need of pruning, fertilizing, watering, and

insecticides

.

2) Difficult to establish where windbreak is most likely to be

effective in built-up areas due to complex wind patterns.

3) Possible increased chance of burglary when windbreak impairs

surveillance of windows by neighbors or pedestrians.

AESTHETICS:

1) Windbreaks and shrubs can improve the overall aesthetic

character of a neighborhood.

2) Windbreaks can be used to physically or implicitly define the

boundaries between public and private space.

3) Windbreaks can obstruct distant views.

1-4
COSTS:

A three-foot-tall American Arborvitae costs $6 delivered,

according to a Washington, D. C, nursery. Spaced 3 feet

apart, this amounts to $2 a linear foot.

A six-foot-high fence consisting of boards staggered on either

side of a 2 X 4 costs $33 per eight-foot section (including one post) delivered, according to one Washington, D. C,

lumber yard. This amounts to $4.13 per linear. foot.

EXAMPLES

:

1) George Mattingly and Eugene Peters of Princeton University are studying the effects of wind on a group of townhouses at Twin

Rivers, New Jersey. Results from scale models in a wind

tunnel suggest that a five-foot-high wooden fence would reduce

air infiltration 26 to 30 percent; a single row of evergreen

trees as tall as the house would reduce air infiltration 40

percent; and a combination of the two would reduce air infiltration 60 percent. The best location for a windbreak was at

a distance of 1 1/2 to 2 1/2 windbreak heights upwind from the

house. The results of the wind tunnel tests are now being

studied in a full-scale field experiment at Twin Rivers.

(75, Mattingly ,p37) = (year, author, page)

2) Another experiment was conducted by the Lake State Forest

Experimental Station in Nebraska on two identical houses. One was fully exposed to the wind, and the other was protected by

dense shrubbery. The exact fuel consumption for maintaining

an indoor temperature of 70° F in each house was measured. A

savings of 23 percent was recorded for the protected house.

(63,01gyay,p99)

Similar results are reported in a study conducted in South

Dakota. A fully exposed electrically heated house required

443 kWh to maintain an inside temperature of 70°F from January

17 to February 17. An identical house sheltered by a windbreak required only 270 kWh. The difference in average energy

requirements for the whole winter was 33.92 percent.

(74,Flemer,p2)

3) Following the References are two wind maps of the U. S.

showing the direction and mean velocity of wind for July

and January. (68,ESSA,p73)

1-5
REFERENCES:

ASHRAE, Handbook of Fundamentals , American Society of Heating,

Refrigerating and Air Conditioning Engineers, Inc.,

New York, 1972.

Caborn, J. M., Shelterbelts and Windbreaks , Faber and Faber,

Ltd., London, 1965.

ESSA, Climate Atlas of the United States , U. S. Dept. of

Commerce, Environmental Science Service Admin. , Washington,

D. C. , June 1968.

Flemer, William III, Energy Conservation with Nature's Growing

Gifts , American Association of Nurserymen, Washington, DC,

1974.

Geiger, Rudolf, The Climate Near the Ground , Harvard University Press, Cambridge, MA, 1966.

Jensen, Martin, Shelter Effect , The Danish Technical Press,

Copenhagen, 1961.

Mattingly, George E. and Peters, Eugene F., Wind and Trees - Air Infiltration Effects on Energy in Housing , The Center for

Environmental Studies, Princeton, NJ, 1975.

Olgyay, Victor., Design with Climate: Biocllmatic Approach

to Architectural Regionalism , Princeton University Press,

Princeton, NJ, 1963.

Robinette, Gary 0. , Plants/People/and Environmental Quality , U. S. Department of the Interior, National Park Service in

Association with American Society of Landscape Architects

Foundation, Government Printing Office, Washington, DC, 1972.

Rosenbrug, Norman J., Microclimate: The Biological

Environment , John Wiley and Sons, New York, 1974.

Vandervort, Donald W. , How to Build Fences and Gates , Lane

Magazine and Book Co., Menlo Park, CA, 1971.

1-6
U.S. Dept. of Commerce, Environmental Science Services Admin., Washington, D.C.

1-7

1.2 SHADE TREES/Shading, Insulation

STRATEGY

:

Plant deciduous trees to provide shade in the summer and admit

sunlight in the winter. Plant evergreens to provide shade in

the summer and to reduce window heat loss to the night sky in

the winter.

PHENOMENA:

1) Deciduous trees provide shade in summer, then lose their

leaves and admit sunlight in the winter. A tree-shaded,

south-facing window receives less solar heat than an unshaded,

north-facing window. (The north window receives diffused

radiation from clouds.) This solar protection increases

continuously throughout the summer, as shown below.

(65, Forest Service, p77)

TYPE OF FOREST PERCENT OF LIGHT PENETRATION

Evergreen

Deciduous

April

8

51

May

7 23

Sept,

4

5

2) Trees not only reduce window heat gain by blocking direct

sunlight penetration but also by lowering the ground surface

temperature. In a test conducted at Indiana University, when

the air temperature was 84° F, concrete exposed to the sun was

108° F while concrete shaded by a maple tree was only 88° F.

(75,FEA,p3) The heat gain through a tree-shaded window is

therefore diminished both by reduced heat radiation from the

ground and correspondingly cooler air temperatures.

1-9
3) The sun's path is lower in the sky in the winter than in the

sununer. Therefore the sun's rays may be low enough to angle

below the branch structure of a tree adjacent to a window.

Summer Winter

Figure 4. Seasonal Sun Angle vs. Tree Interference

4) On a winter night the outside surface of the window radiates

heat to the terrain and the sky. The winter sky has a much

colder average temperature compared to the ground which re- radiates heat accumulated during the hours of sunlight.

An evergreen tree in close proximity to a window will obstruct

the winter night sky. The temperature of the tree will approximate the air temperature. Radiant heat loss from the window

to the tree will therefore be less than to the much colder

night sky. This phenomena is illustrated by frost appearing

on open fields earlier than under trees.

ADVANTAGES

:

1) Reduced summer solar heat gain with only slightly decreased

winter solar heat gain when deciduous trees are used. (Trees

with foliage low to the ground are especially effective on

east and west exposures where roof overhangs provide no protection from low angle sunrays.)

1-10
2) Reduced summer solar heat gain and reduced winter night-sky

heat losses with the use of evergreens.

3) Reduced or eliminated glare from the sun and bright sky.

4) Protection of windows from driving rain or hail.

DISADVANTAGES

:

1) Required maintenance, including not only fertilizing, pruning

deadwood, and possibly spraying to control insects, but also

removal of leaves from grounds and rainwater gutters.

2) Increased likelihood of storm damage due either to lightning

or wind-broken tree limbs.

3) Possibility of root blockage of underground sewer pipes.

4) Beneficial winter solar heat gain blocked by evergreens.

AESTHETICS

:

1) The quality of light under trees is much different from the

quality of light under a roof overhang. Light under a roof

overhang is principally "blue light" diffused from the blue

sky. The light under deciduous trees is principally "red

light" filtered through the leaves. This effect is greater

with deciduous trees than coniferous trees. (65, Forest

Service ,p65) . In addition to the difference in color quality,

trees may dapple a window with a pattern of sunflecks penetrating the canopy of leaves or needles. This pattern moves

with breezes and changes density with the seasons.

2) Trees may be selected for their softness and irregularity or their natural or pruned shapes to complement the hard-edged

geometry of the building. For example, maple and ash provide

a circular massing in summer and an ascending open branch

pattern in winter. The linden is spherical also, but in

winter it has a dense, twiggy branch pattern. Honey locust

and tulip trees are vertical oblongs in form, while white oaks are horizontal oblongs. Poplars are column-like in shape and

American elms are vase-shaped. (73,01gyay,p76)

3) Trees can provide an effective unifying element to a complex

of buildings.

4) Trees can affect the scale of the setting in which a building

is seen. 1-11
COST:

A Washington, DC, nursery quoted the following prices for

trees delivered in small quantity (price does not include

planting). A 6-foot oak or maple costs $8 to $10. Prices of

taller trees vary with their growth rate: a 20-foot maple

costs $70, a 20-foot oak costs $300 to $350. A 6-foot hemlock

costs $25, a 10-hemlock costs $50.

EXAMPLES

:

The following diagram illustrates the calculated effectiveness

of a shade tree on the east or west side of a house in reducing

the air temperature in the shaded area. (74 ,Weatherwise

Gardening, p 32)

Figure 5. Shade Tree Effectiveness vs. Orientation

1-12
REFERENCES:

American Society of Landscape Architects, Site Planning

for Solar Energy Utilization .

FEA, Smith Family Used Living Insulation , Energy Reporter,

Federal Energy Administration, Washington, DC, Aug/Sept. 1975.

FEA/NBS, Energy Conservation with Landscaping , Federal Energy

Administration, Washington, DC, 1976.

Forest Service, Radiant Energy in Relation to Forests , Tech.

Bui. 1344, U. S. Department of Agriculture, Washington, DC,

Dec. 1965.

Olgyay, Victor, Design with Climate , Princeton Univ. Press,

NJ, 1973.

Reifsnyder, William E. and Lull, Howard W. , Radiant Energy in

Relation to Forests , Tech. Bui. No. 1344, Forest Service,

Washington, DC, Dec. 1965.

Weather-wise Gardening , Ortho Book Division, Chevron Chemical

Company, San Francisco, CA, 1974.

1-13

1.3 GROUND SURFACES/Daylighting, Solar Heating

STRATEGY:

Use light-colored ground surfaces to reflect sunlight into

windows, dark-colored surfaces to absorb sunlight and raise

outside temperatures, or planted surfaces to absorb both

sunlight and lower outside temperatures.

PHENOMENA:

1) Light reflected from the ground represents 10 to 15 percent

of the total daylight transmitted by a first floor window on

the sunlit side of a building, and may account for more than

half of the total daylight on the non-sunlit side. The amount

of light reflected through the window is even greater when

adjacent ground surfaces are light in color. The following is

a list of common ground surfaces and the percentage of incident light they reflect. (72,IES,p75)

MATERIAL

PERCENT

REFLECTED

White paint (new)

(old)

Snow (new)

(old)

55

74

64

55

45

40

48

30

25

18

75 percent

Concrete

Marble (white)

Granite

Brick (buff)

(dark glazed)

Vegetation (average)

Macadam

1-15
Ground-reflected light transmitted through windows strikes the

ceiling. This is beneficial for daylighting in two respects.

First, the light is projected deeper into the room than is

direct sunlight. Second, ceilings are usually light-colored

and, hence, reflect light better than darker floors, carpets,

or furniture. .

Ground-Reflected Sun

Figure 6. Ceiling Reflected Ground Light

The addition of ground reflected light to direct sunlight

increases the ability of a window to provide supplemental

winter heat. (The additional light becomes additional heat.)

Dark-colored surfaces absorb more light than light-colored

surfaces and therefore become warmer in sunlight. A window

will radiate less heat in the winter when adjacent ground

surfaces are warm. Also, on a calm winter day, the air

temperature over dark-colored ground surfaces will be warm,

further reducing window heat losses. Conversely, during the

summer, light-colored surfaces are beneficial because they

absorb less light than dark-colored surfaces and are con- sequently cooler. The following is a list of common ground

surfaces and their sunlit surface temperatures when the air

temperature is 84° F. (75,FEA,p4)

MATERIAL SURFACE TEMP. DEV. FROM AIR

Dark Asphalt 124 +40

Light Asphalt (dirty) 112 +28

Concrete 108 +24

Short grass (1-2 inches) 104 +20

Bare ground 100 +16

Tall grass (36 inches) 96 +12

1-16
4) Plant cover absorbs sunlight, yet has a lower surface temperature than paving. Evaporative cooling occurs during the

transpiration life process of plants. The net heat gain from

the sun is rapidly dissipated by the enormous surface area of

leaves. Very little heat is stored in vegetation because of

its minimal mass. Night air temperatures over grass, for

example, are therefore cooler than over paving. The lower day

temperatures and lower night temperatures of planted surfaces

result in less window heat gain and a reduced air conditioning

burden compared to the situation of having paved surfaces

adjacent to windows.

ADVANTAGES

:

1) Increased daylight penetration when light-colored ground

surfaces occur adjacent to windows.

2) Reduced window heat loss in the winter when dark-colored

ground surfaces occur adjacent to windows.

3) Reduced heat gain in the summer, both day and night when

planted surfaces occur adjacent to windows. Likelihood of

glare reduced also.

DISADVANTAGES

:

1) Increased light admitted into the building. When absorbed,

the resulting heat is a disadvantage in summer.

2) Increased likelihood of glare with light-colored ground

surfaces.

3) Ineffectiveness of ground surfaces to improve the performance

of windows several stories above the ground.

4) Increased reflection of sound through windows when hard paved

surfaces are used.

AESTHETICS

:

1) Brick, cobblestone, asphalt paving blocks, gravel, stone

slabs, and textured concrete are a few of many options which

can be used in a multitude of patterns to reinforce the geometry of a building scheme.

1-17
2) Lawn, ground cover, or shrubbery strategically placed to

reduce the ground heat and glare adjacent to windows can enhance both the view out and provide an attractive setting

for a building.

1) T. Kusuda, at the National Bureau of Standards, measured the

surface temperature of five different ground surfaces (bare

soil, black top, long grass, short grass, and white paint

over black top) for two years. He found that asphalt had an average yearly temperature 8° F higher than grass. The daily

maximum surface temperatures of the asphalt paving reached

140° F, whereas the bare soil seldom exceeded 100° F. Even

during the morning on an average summer day, asphalt surfaces

were warmer than ambient air temperatures, while bare soil was

10° F cooler than ambient air temperatures. Painting the

asphalt paving white reduced its surface temperature con- siderably, even during the second year when the paint had

faded. Temperatures of the painted surface never exceeded

105° F. The following graph gives a breakdown of surface

temperatures of different surfaces by month. (76, Kusuda, p297)

EXAMPLES

:

140 -

P^tch Surface Surface "

120 ——• 1 Black Asphalt —— 2 Asphalt Painted White 3 Long Grass

' Air 100 -

20

JFMAMJJASOND

Month

Figure 7. Monthly Ground Surface

Temperatures

1-18
2) Measurements have been made comparing temperatures over Merion

Blue Grass, artificial turf and asphalt paving. When the air

temperature was 90° F, relative humidity 40 percent, and wind

1.1 mph, the grass was 100° F, the asphalt paving 140° F, and

the artificial turf was 162° F. It was expected that grass

would be cooler than artificial turf because of evaporative

cooling. While this was the case, the temperature difference

was also influenced by the light absorption characteristics of

the different surfaces. The absorption of sunlight was: by

grass, 78.4 percent; by asphalt, 87 percent; and by artificial

turf, 92.7 percent. The grass is therefore cooler, not only

due to evaporative cooling but also due to the fact that it

reflects almost three times more sunlight than artificial turf

and nearly two times more sunlight than asphalt paving.

(71, Taylor, p2-43) The following figure shows how much warmer

the air was at various heights above artificial turf compared

to Merion Blue Grass.

9 Feet 1op 3op 3op 3op .2op 30 p

5.5 Feet 3 3 3 -2 3 -1

3 Feet 2 5 5-3-2

3 In. 9 6 3 6 6

945 10=° 11 =° -| 30 33°

Time of Day

6

440

Figure 8. Air Temperature Differences Between

Artificial Turf and Merion Blue Grass

1-19
3) A terrace surfaced in a dark material, facing south and east on the inside corner of an L-shaped building, is a very

effective sun pocket. A temperature of 70° F (21.1° C) has

been recorded in such a corner, while out in the wind the

temperature read 30° F (-1.1° C) . (50, Fitch, p97).

REFERENCES:

FEA, Smith Family Uses Living Insulation , Energy Reporter,

Federal Energy Administration, Washington, DC, Aug/Sept. 1975.

Fitch, James Marsten, American Building , Houghton Mifflin

Publ., Boston, 1966.

Geiger, Rudolf, The Climate Near the Ground , Harvard University Press., Cambridge, 1966.

Griffeth, J. W. , Wengler, 0. F. and Conover, E. W., The

Importance of Ground Reflection in Daylighting , Illuminating

Engineering, Vol. 48, No. 1, Illuminating Engineering Society,

New York, Jan. 1953.

lES, lES Lighting Handbook , Illuminating Engineering Society,

NY, 1972.

Kusuda, T., The Effect of Ground Cover on Earth Temperature , The Use of Earth Covered Buildings , NSF-RA-760006 National

Science Foundation, Washington, DC, July 1975.

Taylor, Elwynn and Pingel, Gerald, Green Grass That's Not So

Green, New York Times, NY, April 11, 1971.

1-20
1.4 ORIENTATION TO SUN/Solar Heating, Shading

STRA.TEGY

:

Provide the largest window area on the side where the sun exposure minimizes combined mechanical heating and cooling

needs

.

PHENOMENA:

1) Sunlight transmission through windows will be a net benefit on an annual basis if winter solar heat gain exceeds winter

window heat loss and summer solar heat gain.

2) What percentage of the incident solar energy a window transmits for any given day depends upon the angle at which rays of

sunlight intercept the window and how many hours the window

receives sunlight. The angle at which sunlight intercepts the

window affects the amount of solar energy transmitted in two

ways: by determining the proportion of light reflected,

absorbed and transmitted; and by determining the projected

area of the window measured perpendicular to the rays of

light.

The proportion of light reflected or absorbed increases

gradually from the minimum when the angle between the light

rays and the glass is 90° up to approximately 45°. Thereafter, the amount reflected or absorbed increases drastically

until no light is transmitted. (See Strategy: Window Tilt)

The projected area is the area of a window projected onto a plane perpendicular to the rays of light. The projected area becomes smaller as the angle at which the light intercepts the

glass becomes smaller. The amount of light transmitted is

therefore reduced due to the decreased area exposed as shown

below.

Actual Width 4^ I = Sun Intercept Angle

Proj. Width = COSZ^ I x Actual Width

Figure 9. Projected Window Width

1-21
3) How many hours a window receives direct sunlight, as well as the angle of the rays of sunlight, is determined by the path

of the sun across the sky. The path of the sun varies with

the seasons and with the latitude. The summer sun rises north

of east and sets north of west. The winter sun rises south of

east later in the morning, travels in a lower arc, and sets

south of west earlier in the evening. The further north a site is, the greater are the seasonal northerly and southerly

shifts of sunrises and sunsets, the lower the arc of the sun across the sky, and the more hours the sun is above the horizon

in summer and the fewer hours it is above the horizon in

winter. This phenomenon is illustrated below for latitudes of

42° and 34°. (50,AIA,p35) (51,AIA,p2-16)

s s

42° N Lat (Boston) 34°N Lat. (Atlanta)

Figure 1 0. Plan View of Sunrise and Sunset

1-22
Figure 1 2. Daily Path of the Sun Viewed Looking East

1-23
Because of the lower and more southerly path of the winter sun across the sky, a south-facing window receives sunlight at a more direct angle and for more hours of the day than an eastor west-facing window. A south-facing window receives the sun obliquely at sunrise, almost perpendicularly at noon and again

obliquely at sunset. By comparison, an east- or west-facing

window receives the sun obliquely and for less than half the

number of hours the sun is above the horizon. A north-facing

window receives no direct sun in the winter and, hence, has

only the minimal heat gain from daylight to offset conducted

heat losses.

Because of the higher and more northerly path of the summer

sun across the sky, a south-facing window gets no direct sun at sunrise or sunset, and in the middle of the day the sun intercepts the windows at a glancing angle. This results in a much reduced projected window area with much of the light

being reflected. Furthermore, the high position of the summer

sun permits modest building projections to totally shade the

window. (While permitting the lower winter sun to penetrate.)

East and west exposures receive the summer sun for more hours

of the day and at a more direct angle than south exposures.

Hence, east and west are more difficult to shade. The north

exposure also receives summer sun, but for only a short period

of the day and at very oblique angles. The thermal conse- quences of north-facing windows in the summer are therefore

minimal. The solar gains for the different orientations are shown below. (76,Kusuda)

AVERAGE DAILY BTU/SQ FT/DAY

S E or W N

Lat 42° N (Boston)

Jun 22 786 1026 638

Dec 22 757 286 143

Lat 34° N (Atlanta)

Jun 22 681 1105 681

Dec 22 1050 458 220

From these values, it can be seen that the further north a site is, the more winter sunlight the south exposure receives

in comparison to the east or west exposures. The further

south a site is, the less summer sunlight the south exposure

receives in comparison to the east or west exposures.

1-24
Therefore, buildings located in southern latitudes should have

window areas concentrated on the north and south exposures

(ideally with a projecting, horizontal shading device over south-facing windows) to minimize the air conditioning burden.

To obtain the greatest benefit from the sun as a winter heat

source, buildings located in northern latitudes should have

window areas concentrated on the south (with minimal window

areas to the north)

.

5) The arrangement of rooms relative to their window orientation

will determine their natural daily temperature cycle. By

matching the times rooms are likely to be occupied with the

hours they receive sunlight, solar heating can be better

utilized and dependence on mechanical heating reduced.

ADVANTAGES:

1) Increased winter solar heat gain. Properly sized and oriented

windows can gain more heat from the sun than they lose by conduction. (75, Berman) This can translate into reduced heating

costs

.

2) Decreased summer solar heat gain. Properly oriented and

shaded windows can result in a savings in initial cost and

subsequent operation of one ton of air conditioning per

100 square feet of glass compared to poorly oriented unshaded

windows. ('66,Callender,p. 749)

DISADVANTAGES

:

1) Fading fabrics due to exposure to sunlight.

2) Winter overheating possible with large south-facing windows

for small room:S within light-weight construction buildings.

3) Reflected sunlight from light-colored ground surfaces or adjacent buildings may reduce effectiveness of glass orientation relative to direct sunlight.

1-25
AESTHETICS:

Properly oriented windows will result in rooms having a shaded

character in summer and a sunny, bright character in winter.

The orientation of a window will determine the path of the

patch of direct sunlight projected onto the floor and/or

walls. The patch of sunlight may be attractive if it spotlights a geranium, or bothersome if it results in glare on a work surface.

The orientation of a window will determine whether the outward

view is shaded or j^unlit. A window oriented to admit the sun

(e.g., south-facing) provides a view of the shaded side of

outside objects. A window on the shaded side of a building

(e.g., north-facing) provides a view of the sunlit side of

outside objects. East or west-facing windows offer the advantage of a view with the light source changing direction

between morning and afternoon.

Proper orientation of windows does not presume increasing the

total window area. The issue is the distribution of the

window area. Therefore, proper orientation need not result in

additional construction costs.

Proper orientation of windows may even reduce construction

costs, by minimizing the amount of expensive shading required

by adverse orientation, and reducing the required capacity of

the heating and cooling mechanical systems.

1) The following is a study of the effect of window orientation

on heating costs. The window areas for a conventional house

in Boston are revised as follows:

COSTS:

EXAMPLES:

WINDOW AREA IN FT

2

CONVENTION

REVISED

S 100

180

N

100

20

E

50

50

W

50

50

TOTAL

300

300

1-26
Occupancy was considered to be a family of four, lighting and

appliance heat gains were considered at about 20 kWh per day,

and room temperature was to be maintained at 70° F (21° C)

.

Solar data were taken from ASHRAE and outside temperature data

from the U. S. Weather Bureau. U-values for the building

envelope were FHA minimum: Roof 0.053, walls 0.085, doors

0.65, floors 0.084, windows 0.65. Air infiltration was assumed at 1 change per hour.

The conventional house was calculated to require 92 million

Btu per year from the heating system. By merely shifting 80

square feet of windows from the north to the south sides of

the house, the heating requirement was reduced to 83 million

Btu for a net savings of 9 million Btu. (76, Bliss, p34)

The cooling loads resulting from different window orientations

have been studied with scale models at the Building Research

Station at Haifa, Israel. In one experiment, four identical

models were constructed. The walls consisted of light-weight

concrete 150 mm (5.9 in) thick. One side contained a closed

window. The models were oriented so that the windows faced

each of the four cardinal directions. Before sunrise, the

inside air temperatures were all approximately equivalent.

Four hours after sunrise, the inside air temperature of the

east-facing model had risen 8° C (14.4° F) above the outside

air temperature.

The model with the west-facing window had the largest insideto-outside temperature difference. The difference reached

11° C (19.8° F) in the afternoon.

The models with south- and north-facing windows showed the

smallest inside/outside temperature differences ranging from

3° to 5° C (5.4° to 9° F). (69,Givoni,p201)

Measured data documenting the effect of orientation on inside

temperatures of actual buildings were collected in a study by

the city of Davis, California, in 1974. The energy requirements of a newly constructed but not yet occupied apartment

complex were recorded. The apartments were two- and threestory buildings built to conventional standards and oriented

north, south, east, and west.

The study found that top floor apartments facing east or west

were the hottest, reaching a maximum of 99° F (37.2° C) . The same apartment model facing north or south reached a maximum

temperature of 85° F (29.4° C) . (76, Cole, no pages)
The following graph by Victor Olgyay differentiates total

solar gain during the cooling season (overheated period)

from total solar gain during the heating season (underheated

period) in New York City. (73, Olgyay, p58)

Figure 1 3. Orientation vs. Yearly Solar Radiation in New York

The most favorable orientation occurs where the positive

difference (the solar gain during the cooling season subtracted

irom solar gain during the heating season) is greatest. For

New York City this is 17 1/2 degrees east of south.

A study by Samuel M. Berman of Stanford University provides

data quantifying the yearly effect of solar energy on the

energy balance of a window. Calculations were made for several

cities and considered a variety of window glazing and shading

options. The example shown below assumes the window includes

a storm sash or is double glazed, and that, during the summer,

a standard white window shade or Venetian blind is lowered

when the window is in sunlight. No external shading of the

window is assumed. The calculations show the amount of

indoor climate control energy expenditure due to the window in

KBtu per square foot of window for the season. A positive

value represents a net energy gain, a minus value represents

a net energy expenditure. (75, Berman, p65)

SOUTH EASTft) WEST NORTH

Winter Summer Winter Summer Winter Summer

DALLAS-FT. WORTH +107 -41 +48 -61 +9 -34

NEW YORK CITY +71 -18 +14 -24 -25 -13

l-2a
The above values show that the solar benefit in the winter

more than offsets the solar detriment in the summer for

south-facing windows in regions with hot summers such as Dallas, or cold winters like New York. Also noteworthy is

the fact that east and west-facing exposures nearly break

even. Finally, it must be realized that the net gain or loss of a window may be advantageous or detrimental, depending

on the configuration of the mechanical heating and cooling

systems

.

1-29
REFERENCES

:

AIA, Regional Climate Analysis and Design Data , The House

Beautiful Climate Control Project, Bulletin of the AIA,

Washington, DC, 1950 & 1951.

Berman, Samuel and Silverstein, Seth, Energy Conservation

and Window Systems , National Technical Information Service,

Springfield, VA, Jan. 1975.

Bliss, Raymond W. , and Williams, Robert H. (editor). Why Not

Just Build the House Right in the First Place? , Bulletin of

the Atomic Scientists. Educational Foundation for Nuclear

Science, Chicago, IL, 1976.

Callender, John Hancock, Time Saver Standard , McGraw Hill, NY,

1966.

Cole, Robert S., Solar Cost Reduction Through Window and

Building Orientation , Solar Engineers , Solar Engineering

Publishers, Inc., Dallas, TX, April 1976.

Givoni, B., Man, Climate and Architecture , Elsevier Publishing

Company, New York, NY, 1969.

Griffith, J. W. , Design of Windows , Solar Effects on Building

Design , Publication No. 1007, BRI, Inc., Washington, DC, 1963,

pp. 95-101.

Knowles, Ralph C, Energy and Form , The MIT Press, Cambridge,

M, 1974.

Kusuda, T., Calculations , National Bureau of Standards,

Washington, DC.

Markus, Thomas A., Window Design in Europe: A Review of Recent

Research , Solar Effects on Building Design , Publication No. 1007,

BRI, Inc., Washington, DC, 1963, pp. 119-140.

Nickerson, David. Best Ways to Gain From a Solar House , Washington Post, Washington, DC, Sept. 5, 1976.

Olgyay, Victor, Design with Climate , Princeton University

Press, Princeton, NJ, 1973, p. 53.

Peter, John, Design with Glass , Reinhold Publishing Corp.,

New York, NY, 1964.

Total Environmental Action, Inc., Solar Energy Home Design in

Four Climates , Total Environmental Action Press, Harrisville,

NH, 1975.

1-30
1.5 ORIENTATION TO WIND/Ventilation, Air Tightness

STRATEGY

Provide "cross-ventilation" with windows out of alignment

with the direction of the wind to improve overall ventilation.

PHENOMENA:

1) When window placement on opposite sides of an interior space

is possible, the building should be oriented slightly askew to

the direction of the wind. When window placement on opposite

sides of a space is not possible but placement on adjacent

sides is possible, the building should face directly into the

wind. The reason for this is illustrated in the following

plan view of window locations:

Windows on Opposite Sides

Good Overall Circulation Local Circulation

Windows on Adjacent Sides

Good Overall Circulation Local Circulation

Figure 1 4. Window Location vs. Air Circulation

1-31
2) From this figure, it can be seen that if the wind encounters

an inlet and outlet in alignment with its outside direction it

will pass through the intervening space in a narrowly defined,

high velocity stream. Very little ventilation will occur beyond that narrowly defined stream. However, if the wind is

forced to change direction in transit between inlet and outlet,

a turbulence within the room will develop. A circular current

will encompass the sides and corners of the room. The maximum

air speed is reduced compared to windows in direct alignment

with the wind, but the average velocity of air movement within

the entire space will be greater. Overall ventilation is

subsequently superior.

3) Where the building interior is subdivided into a series of

interconnected spaces, placement of interior partitions can provide the disruption of the otherwise straight path of air

flow between upwind and downwind windows.

ADVANTAGES

:

1) Increased volume of room ventilation when windows properly

located

.

2) Decreased annoyance from local high velocity drafts.

3) Reduced demand for air conditioning and mechanical ventilation.

DISADVANTAGES

:

1) Effectiveness unreliable if wind direction is unpredictable

and subject to wide variation.

2) Diminished effectiveness if the wind is very weak. Air circulation within a space will be so dissipated as to be beyond

perception.

3) Potential conflict between orientation relative to the wind,

orientation to the sun, and orientation to the view.

4) Untenable where extreme air or noise pollution prevails.

1-32
AESTHETICS:

1) Opened window may provide pleasant sounds and smells to enter

a room, providing variation to the quality of the interior.

2) A strategically directed breeze through a window may be more

psychologically effective than an equal rate of air changes

per hour ducted through a register.

3) Open windows generally require insect screens, which affect

the exterior character of the fenestration.

COSTS:

The cost of locating windows on opposite or adjacent sides of an interior space is not likely to be higher than locating the same number of windows on only one side of the space.

EXAMPLES

:

The following table illustrates the calculated effect of

window location relative to the wind upon the average inside

air velocities, given as a percent of the outside wind

velocity. (69, Givoni,p261)

Wind Perpendicular

Windows on opposite sides 35%

Windows on adjacent sides 45%

Wind at an Angle

42%

37%

REFERENCES

:

Givoni, B., Man, Climate and Architecture , Elsevier Publishing

Co., New York, NY, 1969.

Olgyay, Victor, Design with Climate: Bioclimatic Approach to

Architectural Regionalism , Princeton Unit. Press, Princeton,

NJ, 1963.

1-33

\\^

XTERIOR

APPENDAGES

SUN SCREENS

EXT. ROLL BLINDS

ARCHITECTURAL PROJECTIONS

EXT. SHUTTERS

AWNINGS
2. EXTERIOR APPENDAGES

The energy performance of a window can be greatly Improved

with external appendages which are part of the window system

or part of the wall or roof system. For example, shading

can be effectively accomplished by louvered sun screens,

blinds, awnings, brise soleils, or roof overhangs.

Such devices often provide secondary energy benefits in

addition to their primary function. For example, sun screens,

in addition to providing shade in the summer, preserve the

air film at the exterior surface of the glass, thus reducing

winter heat losses. External roll blinds, by providing a

trapped air space, perform similarly to storm windows in

reducing heat loss in the winter, as well as affording sun

protection in the summer.

The general advantage of using exterior appendages to improve

window performance is that they mitigate climatic problems

before they enter the building. Also, although to a lesser

extent than site strategies, external appendages allow some

of the residual forces, such as summer solar heat or winter

winds, to be dissipated before encountering the window.

2-0
2.1 SUN SCREENS/Shading, Insulation

STRATEGY

:

Install a screen of mini-louvers outside a window to shade

direct sunlight, yet provide a view out from inside the

building.

PHENOMENA:

1) The effectiveness of a solar screen in shading a window depends

on its geometry and its reflectivity as a material. The

geometry determines how high the sun must be above the horizon

before the louvers block all the direct sunlight. The reflectivity of the louvers determine how much light penetrates

indirectly by being reflected off the surface of the louvers.

If the slats have a reflective surface, part of the light

striking the top of one slat will be reflected directly

through the window and part will be directed to the underside

of the slat above, and then directed through the window.

Thus, highly absorptive surfaces improve the effectiveness of sunscreens. The following is an example of the geometry and

effectiveness of a sun screen reported by one manufacturer.

(76 ,Koolshade,p6)

Amount

of Direct

Figure 1 5. Sun Penetration Through A Sun Screen vs. Sun Angle

2-1
2) The potential heat burden of sunlight penetrating a sunscreen

early in the morning or late in the afternoon is small,

because the sun's intensity is diminished at these times.

This is due to the increased distance through the atmosphere

which the light must travel. (68 , Pennington, p88) This is

illustrated below.

Sunset

Figure 1 6. Distance Through Atmosphere vs. Sun Angle

3) An external sun screen installed close to a window creates a layer of virtually still air, thus preserving the layer of air

at the surface of the glass. This benefit results in a reduction in the winter U-value of a single glazed window with a sun screen from 1.13 to 0.85 (74, ASHRAE,p407) . (See STRATEGY:

Windbreak for discussion of air films at the surface of glass.)

4) An external sun screen blocks a window' s exposure to the

winter night sky, which tends to be colder than ground

surfaces

.

ADVANTAGES

:

1) Reduced summer solar heat gain which reduces average interior

temperatures as well as reducing local overheating on the

sunlit side of the building.

2) View and concurrent shading. Visibility, looking out through

a sun screen, can be as high as 86 percent as through an unprotected window. (75, Koolshade,pl6) The visibility is

greatest when the sight line is parallel to the angle.

2-2
3) Daytime privacy without eliminating the view out.

4) Unobstructed night-time surveillance of building interior

through windows with sun screens.

5) Reduced direct and reflected glare. Sun screens block light

reflected from the ground or adjacent buildings more effectively than awnings, roof overhangs, or wall fins.

6) Reduced heat loss in winter due to protection of air film at

the surface of the window, and due to reduced heat radiation

to the cold night sky.

7) Protection of glass from projectiles thrown by vandals.

(Replacement of the sun screen may cost more than replacement

of the glass, but likelihood of injury from breakage is

greatly reduced.)

8) Prevention of insect intrusion. Conventional insect screening

is commonly a mesh of 16 x 18 per inch. One type of sun screen is equivalent to a mesh of 23 x 2 per inch and, hence,

is likely to be suitable for insect screening.

9) May provide solar heating in the future. An experimental unit

is under development which incorporates a sun screen in an air

space between two layers of glass. In the summer the air

space is vented outdoors at the top and bottom, and in the

winter it is vented indoors to take advantage of the solar

heat build-ups.

DISADVANTAGES

:

1) Reduced solar benefit in the winter when sun screens are left

in place.

2) No night-time privacy. In the night, the direction of transparency reverses - the screen appears opaque to occupants

while allowing passersby an uninhibited view in. For residences, this necessitates the installation of drapes or blinds

for privacy.

3) Interference with outswing windows.

4) Interference with window washing.

5) Impeded egress in the event of fire.

2-3
AESTHETICS:

1) Louver ed sun screens make windows appear blackened on the

facade. This increases their visual impact as a design

element.

2) Louvered sun screens somewhat darken the view out of a window.

3) Louvered sun screens striate the view. The direction of the

visual striation depends on whether the horizontal elements or the vertical elements are thicker for a given viewing angle.

COSTS:

Prices of louvered sun screens constructed of aluminum horizontal slats held with twisted bronze wire and finished with a black heat absorbing coating are approximately:

$6.00 per square foot for large windows.

$6.50 for smaller windows (less than 4 foot x 5 foot).

$5.00 delivered price to "do it yourself homeowners"

The price of an expanded metal sun screen made from a sstamped

single sheet is lower, at the expense of reduced transparency.

The price ranges from $3 to $3.50 per square foot.

EXAMPLES

:

1) The Department of Public Works for Buck County, PA, installed

louvered sun screens on its administration building at a cost

of $36,000. Annual savings in operating costs were estimated

to be 35% or $16,283. Thus, the costs of the sun screens were

amortized in just over two years. (76,ACHR,p .29)

2) Following the references are photographs of sun screen installations illustrate the daytime outside appearance,

the effect on view out from the inside, and the night-time

outside appearance of a sun shade. (76,Koolshade)

2-4
REFERENCES:

ACHR News, Screening Windows from Sun Helps Cut Cooling Costs

35 Percent; Heating Costs 28 Percent , Air Conditioning,

Heating, and Refrigeration News, Birmingham, MI, Oct. 29,

1976; Oct. 29, 1973.

ASHRAE, ASHRAE Handbook of Fundamentals , ASHRAE, Inc., New

York, NY, 1974.

Halleck, Edward, personal communications. Construction

Specialties, Cranford, NJ, Jan. 5, 1976.

Kaiser, Louver ed Aluminum for Solar Control , Kaiser Aluminum,

Oakland, CA, 1956.

Koolshade, Shades Save Power , Koolshade Corp., Solana Beach,

CA, 1976.

Pennington, C. W., How Louvered Sun Screens Cut Cooling , Heating Loads , Heating, Piping, and Air Conditioning, Reinhold

Publishing Co., Stamford, CT, Dec. 1968.

2-5
Kool Shade Corp., 722 Geneviewe St., Solatia Beach, CA 92075

2-6


2.2 EXTERIOR ROLL BLINDS/Shading, Insulation

STRATEGY

:

Install exterior roll blinds to provide sun summer and to reduce winter heat flow.

shading in the

PHENOMENA:

1) Horizontal slats on a roller at the head of a window can be

lowered to provide an opaque barrier to the summer sun,

blocking both direct and diffuse sunlight. One manufacturer

reports up to a 35-percent reduction in air conditioning costs

with the use of roll blinds. (76,Frowein,pl) The following

figure illustrates the installation of an exterior roll blind.

Slats Operating Strap

Housing Box

Side Rail

Bottom Slat

Figure 1 7. Installation of an External

Roll Blind

2) When the slats are in the lowered position but not yet resting

one on top of the next, horizontal slots between the slats

permit air to circulate through the blind.

3) If the roll blind tracks are hinged, the entire lowered roll

blind can be projected out from the window during the day to

provide natural ventilation concurrent with shading.
4) Light colored roll blinds more effectively keep rooms cooler,

because the blind reflects incident sunlight and remins cooler

than would be the case with a dark-colored blind.

5) During the winter, when the blind is lowered and the slats

rest one on top of another, the resulting layer of air trapped

between the blind and the window acts as insulation. Exterior

roll blinds provide the most effective insulating air space of

all the exterior strategies reported, because of the tight

joints between the slats and the seal provided at the top and

sides. One manufacturer reports the following U-values for

roll blinds in combination with various types of windows.

(76, Pease, p2)

GLASS TYPE SEASON GLASS

ALONE

GLASS +

1/2 X 2"

ROLL BLIND

SLATS

GLASS +

1/8 X 1 3/8"

ROLL BLIND

SLATS

SINGLE WINTER 1.13

SUMMER 1.06

0.405

0.395

0.568

0.550

DOUBLE WINTER 0.58

(1/2" AIR SPACE) SUMMER 0.56

0.301

0.297

0.384

0.376

SINGLE +

STORM SASH

WINTER

SUMMER

0.56

0.54

0.297

0.290

0.376

0.366

5) Since the coldest hours of the day occur during the hours of

darkness, using a roll shade during the night provides increased

insulation during the period of greatest potential heat loss.

In New York City, for example, 70 percent of the degree-days

occur during hours of darkness. (76, Claridge,p. 57) Furthermore, a lowered roll blind obstructs a window's exposure to

the cold night sky, further reducing heat loss.

ADVANTAGES

:

1) Shading during summer days with the roll blind lowered, and

unimpeded ventilation at night with the roll blind rolled up

into the head of the window.

2) Insulation from winter heat losses with the roll blind lowered

at night, and unimpeded solar gain through the window with the

roll blind raised during the day.

2-10
3) Independent control of the shading of each individual window,

and ability to partially shade a window in the case of the sun striking only part of the window, or where it is desirable to

shade only a portion of a room.

4) Protection of glass from vandalism and wind storms when shade

lowered

.

5) Deterrence to burglars entering through windows when shade

lowered.

6) Impediment to spread of flames out a window and up the side of

the building. (Metal Roll Shades)

7) Reduction in noise transmissiop with blinds lowered. One

manufacturer reports a noise reduction from 100 DBA to 60 DBA

or a STC value of 40. (Mar 76,Frowein,p. 1)

DISADVANTAGES

:

1) Slats cannot be tilted Venetian blind fashion to provide shade

and view.

2) Delayed egress in the event of a fire.

3) Maintenance required for operating hardware,- and for slats if

wooden.

4) Limited to maximum single span of 12 feet for vertical windows

(less for sloped windows) , and a maximum height of approximately 10 feet. Large size exterior roll shades should be

motor operated.

AESTHETICS

:

1) In the raised mode, the slats are rolled into a concealed

pocket in the head of the window.

2) In the lowered mode, a roll blind has the appearance of an opaque panel with horizontal grroves on the facade. They are available in colors; in wood, vinyl, or aluminum; and in

different slat sizes.

2-11
3) In the lowered position where the slats do not yet come in

contact with each other, the effect from the interior is a series of horizontal slits of light. When the blind is locked

down, it appears as a solid opaque panel blocking almost all

daylight. In this lowered mode, if the frame assembly is

hinged, it can be cranked out like an awning. Ground-reflected

light will illuminate the ceiling of the room. If the window

is above the second floor, the activity on the street or grounds below can be viewed through the resulting opening.

COSTS:

The cost of a roll blind per square foot decreases with larger

units, because much of the cost of manufacturing the unit is

in the roller assembly. The following prices are for a unit

without installation: (76,Sinnock)

APPLICATION WIDTH HEIGHT $/FT^ TOTAL $

WINDOW 3'-0" X 3"-6" 10.12 106.26

SL. GL. DOOR 6'-0" x 7'-0" 7.20 302.40

SL. GL. DOOR ll"-6" x 7'-0" 6.00 483.00

EXAMPLES:

1) Roll blinds have been used extensively in Europe for several

decades. Today they are used on approximately 25% of all

European residential buildings and commercial high-rise

buildings

.

In the United States, designers have only in the last three or four years begun to use roll blinds.

Following the references are two photographs illustrating a roll blind viewed from the inside and viewed from the outside.

(76,Frowein)

2) Because of their effectiveness in reducing winter heat loss

and summer heat gain, roll blind devices have been included in

two recent demonstration energy conserving houses: the Zero

Energy House built by the Technical University of Denmark, and

the NASA Technology Utilization House in Hampton, Virginia.

2-12
REFERENCES:

Claridge, David, Window Management and Energy Savings , Efficient Use of Energy in Buildings, LBL 4411, Lawrence

Berkley Laboratories, Berkley, CA, 1976.

Frowein, Onno J., personal communication, ROTO International,

Essex, CN, March 15, 1976.

Frowein, Onno J., Letter, ROTO International, Essex, CN, March

17, 1976.

Harboe, Knud Peter and Koch, Soren, Zero Energy House - a model in 1:1 , Rapport No. 114, Insitute for Husbygning,

Polytekniske Laereanstalt , Lyngby, Denmark, 197 6.

NASA, NASA Technology Utilization House , Tech. Brief LAR-12134,

NASA Langley Research Center, Hampton, VA, 23665, 1976.

Pease, Amrol Exterior Rolling Shutters Conserve Fuel, Provide

Privacy and Security , Pease Company, New Castle, IN, 1976

Sinock, Pomeroy, Telephone conversation. Pease Co. , New Castle,

IN, Dec. 14, 1976.

Steuff, Horst, Konstruktlve Moeglichkeiten im Rolladenbau , Bundesverband Deutscher Rolladenherstelle, 516 Deuren, Alte

Jeulicher St. 105, Postfach 210, West Germany, 1971 (in

German)

.

Roto International, P.O. Box 73, Essex, CT 06426

2-13
Roto International, P.O. Box 73, Essex, CT 06426

2-14
2.3 ARCHITECTURAL PROJECTIONS/Shading

STRATEGY:

Design architectural projections to shade windows from summer

sun

.

PHENOMENA:

1) Horizontal or vertical plane(s) projecting out in front

of or above a window can be designed to intercept the summer sun, admit much if not all the winter sun, and

allow a view out. If the plane projects far enough from

the building a single projection may be sufficient as in

the case of generous roof overhangs or windows recessed

deeply between vertical fins. Alternatively, more modest

projections can be equally effective in shading but they

must be more closely spaced.

2) East and west-facing windows are more effectively shaded

by vertical projecting planes, south-facing windows are more effectively shaded by horizontal projecting planes.

3) For shading effectiveness the color of the .proj ection

should be dark to reduce the light reflected off the

projection and through the window. The light absorbed by

this dark color is converted to heat and then dissipated

to the outside air without becoming an air conditioning

load. A separating gap between the shading device and

the window is important to provide free circulation of

the air to insure this heat dissipation.

4) For daylighting effectiveness the underside of a horizontal

projection should be light colored to reflect indirect

ground reflected light into the room.

5) The further south a building is located, the more important

shading east and west-facing windows becomes and the less

important shading south-facing windows becomes. This is

due to the high position of the summer sun in southern

latitude with the resulting decrease in direct sunlight

transmitted by the south-facing windows. (See Strategy,

Orientation to Sun)

2-15
ADVANTAGES:

1) Reduced summer solar heat gain. If air can circulate

between the shading device and the window, and the window

is completely shaded from direct sunlight the solar heat

gain of the window can be reduced by as much as 80 percent.

('67,ASHRAE,p.485)

2) Reduced glare on work surfaces adjacent to windows.

3) Reduced winter heat loss to the sky.

4) Possible shelter from winter winds with corresponding

reduction in heat conduction losses at the surface of the

glass and reduction in infiltration.

5) Simplified window washing where wide horizontal projections

can secondarily serve as a working platform.

DISADVANTAGES:

1) Possible impediment to window washing in the case of

narrow closely spaced shading planes.

2) Possible impediment to fire egress in the case of narrow

closely spaced shading planes.

3) Obstruction of view.

4) Increased maintenance. Horizontal planes will collect

dirt, bird droppings, and ice.

AESTHETICS:

1) A single overhead projection with a light colored underside will cut off the blue light from the sky but admit

the red or green light of ground reflected light

.

2) Vertical projections from either side of the window

narrow the peripheral view from the window.

3) Deeply recessed windows afford a framed view to the

outside with sight lines quickly cut off when the viewer

moves away from the center of the window.

2-16
4) Closely spaced horizontal or vertical planes may begin to

dominate the view out of a window and in any case change

the scale of the window. The proportion of the space

divided by the shading planes becomes as important as the

overall window proportion in determining the aesthetic

effect of the fenestration.

5) Horizontal projections can provide a sense of security

in the instance of floor to ceiling windows in tall

buildings

.

COSTS:

Generally, custom design and therefore not subject to cost

generalizations.

EXAMPLES:

1) The ASHRAE Handbook of Fundamentals (73 , ASHRAE , p409) contains

a table which gives the distance a horizontal projection

must extend out from the wall to shade an area up to 10 feet

below the projection from April through September. Projections

are given for eight orientations and for latitudes from 24 to

56°N in 8 degree increments. The projections are calculated

for each hour.

2) The following photographs illustrate:

a) Closely spaced horizontal shading projections.

b) Deeply recessed windows providing vertical and horizontal

shading projections.

c) Closely spaced vertical shading projections.

REFERENCES:

ASHRAE, ASHRAE Handbook of Fundamentals , American Society of Heating,

Refrigeration and Air Conditioning Engineers, Inc., New York,

1967 and 1973.

Olgyay, Victor and Aladar, Solar Control and Shading Devices , Princeton Univ. Press, Princeton, N. J., 1957.

2-17
Belinda Collins, Sensory Env. Sect. NBS, Washington, D.C. 20234

2-18
Belinda Collins, Sensory Env. Sect., NBS , Washington, D.C.

2-19

20234

2.4 EXTERIOR SHUTTERS/Shading, Insulation, Air Tightness

STRATEGY

:

Install louvered, operable shutters outside a window to

provide shade in the summer during the day and reduce heat

loss and infiltration in the winter during the night.

PHENOMENA:

1) An exterior shading device effectively blocking all

direct sunlight can reduce solar heat gain through a window up to 80 percent. (undated, NBS ,p2) The shading

performance of closed exterior shutters depends upon how

well the heat absorbed by the shade itself is dissipated

to the outside air. Operable louvers adjusted to block

the sun but let air circulate improve the shutter's

ability to keep out heat. Similarly, light colored

shutters which reflect much of the sunlight rather than

absorb it are more effective. (Actual shading coefficients quantifying performance could not be located.)

2) Heat loss through a window with closed shutters is reduced

because the air space between the shutter and the glass

provides additional resistance to the flow of heat to the

outside. How effective the shutter is in reducing heat

loss depends upon the air tightness of the space between

the shutter and the glass. A shutter with pivoting

louvers which can be closed is beneficial to this end.

However, even louvers fixed in an open configuration

reduce heat loss through the window by substantially

sheltering the insulating film of air at the outer surface

of the glass from the scouring action of the wind, and by

reducing infiltration through window cracks.

ADVANTAGES:

1) Reduced solar heat gain in the summer.

2) Management by the occupant on an individual basis to

permit control of shading, light level within the room,

and view out.

2-21
3) Protection from rain penetration through windows opened

for ventilation.

4) Reduced night heat loss in the winter.

5) Protection of windows from storm damage, vandalism, or intrusion

.

6) Privacy.

DISADVANTAGES:

1) Operation requires reaching outside the window which

necessitates insect screen or storm sash being mounted

inside the window and being openable.

2) Subject to wind damage if not secured properly.

AESTHETICS:

Shutters are considered by many residential designers and

apparently the home buying public, mandatory dressing of

windows. Regretfully, the fact that shutters can serve valuable energy conserving functions as well as cosmetic

functions has been forgotten. If their potential benefit is

again realized, perhaps operable shutters will again be an option to more home buyers in the future.

COSTS:

Primed, wooden shutters with fixed open louvers are commonly

available at lumber yards. A sample of prices in Washington,

D. C. is given below. Hardware to make exterior shutters

operable is not commonly available as such but can be devised

simply from gate hinges.

- 15 X 39 inches $12.00 per pair

X 47 $15.00

X 51 — — $19.00

X 55 ' $25.00

2-22
Wooden shutters with adjustable-tilt slats could not be found

to obtain sample costs. The common interior shutter for

Interior use is not heavy enough construction to be recommended for exterior use.

Prefinished aluminum shutters with fixed open slats are also

available. The following are a sample of retail prices in the

Miami area. (See EXAMPLES for a description of the types

given below.

)

- Bahama $4.25 per sq. ft.

- Sarasota $4.50

- Rolling $5.00

- Side-hinged $6.00

Vinyl shutters are frequently used to dress windows . These

are not appropriate for use as operable shutters if they are molded to be seen only from one side or are molded with

continuous simulated louvers with no open space between the

slats.

EXAMPLES:

1) Several types of operable shutters are common in the

southern regions of the U. S. The following are examples

of various modes of operation and associated generic

names

:

2-23
Rolling Shutters Side-hinged Shutters

Figure 1 8. Types of Shutters

2) The photographs following the references illustrate

installations of Bahama and Sarasota types of operable

shutters as seen from the outside and the quality of

light penetrating a closed rolling shutter as seen from

the inside, (76,Wilk)

REFERENCES

:

NBS, "Home Energy Saving Tips". National Bureau of Standards,

Washington, D. C. , undated.

Wilk, James A., personal communication, Willard Shutter Co. Inc., Miami,

Fla., Nov. 5, 1976.

2-24
2-25
2-26
2.5 AWNINGS/Shading

STRATEGY:

Install an awning with provision for air to circulate between it

and the window to provide shade without heat build-up

.

PHENOMENA:

1) How well an awning shades a window is dependent on how

opaque the material is to both direct sunlight and diffuse

light from the sky. The following table gives the transmittances (amount of light penetrating/ total incident light)

of several common awning constructions: (58 ,Ozisik,p463)

SOLAR TRANSMITTANCES OF AWNING MATERIALS & CONSTRUCTIONS

Material Direct Diffuse

_ transmit tance transmit tance

Canvas 0.0% 0.0%

Plastic 0.25 0.15

Aluminum'^

(separated slats) 0.0 0.20

Note:

1. Source: (76,Stolz) See the figure at the end of the

strategy for an illustration of an aluminum awning.

2) The surfaces of the awning exposed to the sun should be a light color to minimize the amount of sunlight absorbed.

Sunlight absorbed by the awning raise its temperature. Much

of this heat may be transferred to the window in two ways

:

by radiation, and by raising the temperature of the air

between the awning and the window. Light colored awning

materials are therefore more effective because they stay

cooler and transfer less heat to the window. For example, a white canvas awning or a slatted, white aluminum awning

reflects between 70 and 91 percent of the sunlight depending

on how clean it is (dirt absorbs light). By comparison, a dark green canvas awning reflects only 21 percent, and a dark green plastic awning reflects 27 percent of the sunlight. (58,0zisik,p466)

2-27
3) The heat from sunlight absorbed by a dark-colored fabric

will build-up under the awning and be transferred to the

window unless air is permitted to circulate behind the

awning. Fabric awnings are commonly installed with a narrow

continuous gap between the top of the awning and the wall to

prevent hot air from being trapped under the awning.

Slatted aluminum awnings inherently provide air circulation

by virtue of the gaps (ranging from 1/4 inch to 3/4 inch)

between the horizontal slats.

4) In order for an awning to be effective, it must be designed

to provide adequate coverage of the window area for the

specific orientation of the window. A south-facing window

requires only a minimal horizontal projection to be com- pletely shaded all summer, all day. An east or west-facing

window needs an awning which extends down a substantial

percentage of the window height in order to provide protection from the low sun angles of early morning or late

afternoon. In addition, the sides of the awning should be

closed to prevent sunlight from angling in behind the awning

on south-facing windows. The follbwing table illustrates

the sunlit area of glass beneath awnings of various con- figurations in Cleveland, Ohio. (58, Ozisik, p472)

PERCENTAGE OF GLASS AREA SUNLIT FOR VARIOUS AWNING CONFIGURATIONS

orientation solar with side panels open sides

timeI

AWNING DROP^ AWNING DROP

2 0.65 0.60 0.55 0.65 0.60 0.55

SOUTH 8 a.m. 4 p.m. 4 8 % 13% 7% 14% 22%

9 a.m. 3 p.m. 2 4 7 5 11 18

10 a.m. 2 p.m. 2 5 2 5 7

EAST 7 a.m. 5 p.m. 7 13 22 7 13 22

WEST 8 a.m. 4 p.m. 7 15 7 15

Note:

1) Solar time approximates clock time half-way across a time zone. Clock time at the western extreme of the

time zone will be approximately one-half hour earlier

than solar time, and clock time at the eastern

extreme of a time zone will be approximately onehalf hour later than solar time.

2-28
2) The awning drop equals the distance the awning

extends down the window divided by the total window

height.

5) The net effectiveness of an awning in reducing the summer solar heat gain of windows is given below for a design

day representing August 1 at 40 degrees latitude. Heat

gain is totaled for the period from 8 a.m. to 4 p.m. for

the south exposure and noon to 5 p.m. for the west

exposure. The awnings have a 70 percent drop and provision to vent air at the top. A dark foreground is

assumed. For a light foreground the heat gain could be

as much as approximately twice the amount shown due to

light reflecting up beneath the awning. (58 ,Ozisik,p474)

HEAT GAIN THROUGH SINGLE GLAZED WINDOWS WITH AWNINGS

ORIENTATION

OF

WINDOW

TYPE OF AWNING

HEAT GAIN PER

100 SQ FT. GLASS

SURFACE

,

BTU/DAY

HEAT EXCLUDED

BY THE AWNING

PERCENT

BTU/DAY REDUCTION

SOUTH No awning

White canvas awning

Dark green canvas awning

Dark green plastic

awning

WEST No awning

White canvas awning

Dark green canvas awning

Dark green plastic

awning

62,200 0 0

22,500 39700 64

27,700 34500 55

35,600 26600 43

84,200 0 0

19,500 64700 77

23,900 60300 72

34,800 49400 59

ADVANTAGES:

1) Reduced summer solar heat gain by up to 55 to 65 percent

on south-facing windows and 72 to 77 percent on westfacing windows. (58, Ozisik,p475)

2) Reduced glare.

3) Rain protection for windows opened to provide ventilation.

4) Unobstructed view out in a downward direction.

5) Removable in winter to let sunlight in and prolong the

life of fabric awnings.

2-29
DISADVANTAGES:

1) Subject to wind damage.

2) Periodic replacement of fabric due to weathering deterioration. (Canvas: 4 to 6 years, vinyl coated canvas and

plastic: 6 to 8 years)

3) Reduced effectiveness if ground surfaces and/or adjacent

vertical surfaces are highly reflective.

4) Horizontal view out partially obstructed, view of sky

largely or completely obstructed.

5) Rainwater run-off from large awnings can cause splash

problems on the ground.

AESTHETICS:

1) Awnings are available in a variety of colors and patterns.

They can be a bright, cheerful addition to an otherwise

drab facade.

2) Awnings will drastically darken the building interior by

eliminating the sun and bright sky as two sources of

illumination. Any sunlight which does penetrate at the

bottom of the window area does not project any depth into

a room.

COSTS:

In the Washington, D. C. area the following is a sample of the

installed cost of an awning covering a 3 ft. by 5 ft. high

residential window:

2-30
COST OF

COST OF FABRIC FABRIC

MATERIAL CONFIGURATION AND FRAME REPLACEMENT

Painted Canvas No side panels $60 $40

w/side panels $70 $50

Vinyl-coated

canvas 10 percent more than painted canvas

or vinyl-coated

dacron

Acrylic treated

acrilan

Enameled aluminum

20 percent more than painted canvas

solid panels $100

open slatted $120

EXAMPLES:

1) The following example illustrates first cost savings

possible with awnings on residential windows. Calculations are for a room with 400 square feet of floor area,

and two normal-sized, unshaded windows facing west. If

awnings are installed over the two windows the reduced

heat load permits the use of a 3/4 HP motor to drive the

a/c compressor instead of a 1 HP motor. The smaller size

also permits the use of the standard 110 volt electrical

service rather than separate wiring providing 220 or 230

volts. Thus, the use of awnings saves $60 to $100 in the

purchase price of the air conditioner and $50 to $100 in

installation costs for separate wiring. (Ogden,p4)

2) An example of first-cost savings possible with canvas awnings on a commercial application is the newly constructed

Administration Building at North East Missouri State

University. By using an opaque, acrylic awning over the

windows, less expensive gray, tinted glass could be substituted for reflective glass and the size of the air conditioning system could be reduced due to the reduced solar load.

Operating costs of the heating system as well as the air

conditioning system are expected to be lower (due to the

winter solar gain admitted when the awnings are removed)

in comparison to reflective glass which rejects sun yearround. (76, Keller)

2-31
Operating cost savings can be calculated for an example

case using the table listed under the PHENOMENA (number

5) . White canvas awnings are installed on the west side

of a house in New York City. (40°-46' lat.) There are six west-facing windows totaling 100 square feet . The

awnings would reduce the cooling load by 64,700 BTUs per

day. Assuming an air conditioning system consumes one KWH

to remove 6826 BTUs, 9.5 KWH would be saved. At $0.04/KWH

the savings amount to $0.38. This represents August 1, a day when the air conditioning load is likely to be greater

than a day in the beginning or end of the air conditioning

season. However, the amount of daily solar radiation (the

heat source awnings reduce) in August is actually less

than the average for the period of May through September.

Therefore, the savings calculated for August 1 are a conservative estimate of daily savings possible during the

air conditioning season.

Following the REFERENCES is an example of a roller awning

used on an office building, (75 , Avery , pi) and a slatted,

aluminum awning used on a residence. (Alcan,p2)

The following are examples of common awning configurations

2-32
Roller Awning

(self -storing)

2 -33
REFERENCES

:

Alcan, "Flexalum Awnings", Alcan Building Products, Cleveland, Ohio,

undated

.

Avery, "Queensland Sunblind", J. Avery & Co. Ltd., 82-90 Queensland

Road, Holloway, England., February, 1975.

Buckingham, Donald. Telephone conversations, Washington Shade and

Awning Co., Gaithersburg, Md., Dec. 27, 1976.

CPAI, "The Utility and Distinction of Design in Canvas", Canvas

Products Assoc. Int., Saint Paul, Minn., 1964.

Glen Raven, "Sunbrella Outdoor Decorating Guide", Glen Raven Cotton

Mills Inc., Glen Raven, N. C, undated.

Grehan, Arthur, Correspondence, American Canvas Institute, Memphis,

Tenn., July 31, 1975.

Keller, William, telephone conversation, John Steffen Assoc.,

consulting engineers to Ittner and Bauersox, Architects, St.

Louis, Mo., Dec. 29, 1976.

Ogden, J. B., "Air Conditioners Will Help You Sell Awnings", Air

Conditioning Dept., RCA Inc., Chicago, 111., undated.

Ozisik, Necati, and Schutrum, L. F., "Heat Gain Through Windows

Shaded by Canvas Awnings", ASHRAE Transactions , Vol. 64 ASHRAE

Inc., New York, N. Y., 1958.

P.G & E. , "Window Awnings Save Energy", Pacific Gas and Electric

Co., San Francisco, Ca. , undated.

Schultz, Kenneth, "Solar Shading with Canvas Awnings", Canvas Products

Review , Canvas Products Assoc. & Int., St. Paul, Minn., March

1965.

Stolz, Ivan, telephone conversation. Aluminum Awning Industries,

Stockton, Cal., Dec. 27, 1976.

2-34
J. Avery S Co., 82-90 Queensland Rd., Holloway N7 7AW, England

Alcan Building Products, P.O. Box 511, Warren, Ohio 44482 Mr. Aiknis

2-35

/ /

FRAME

FRAME VENTILATORS

WEATHERSTRIPPING

THERMAL BREAK

TYPE OF OPERATION

WINDOW TILT

SIZE, ASPECT RATIO
3. FRAME

The window frame can enhance or detract from the beneficial

energy attributes of a window. The material from which it is

constructed can be insulating or highly conductive of precious

winter heat and prone to condensation problems. Weatherstripping between operable sash and the frame can substantially

impede infiltration through joint cracks at the perimeter of

the window. The perimeter can be kept minimal by adjusting

the proportion of the window. Temperate breezes can be captured

and their flow into a building directed by the choice of

operating window type. Finally, the winter solar heat gain

can be increased and summer solar gain rejected by merely

tilting the window frame.

3-0
3.1 FRAME VENTILATORS/Ventilation

STRATEGY

:

Specify window frames with a provision for controlled admittance

of outside air through the frame section into the building

interior

.

PHENOMENA:

Small openings can be incorporated in the head or sill section

of the frame to admit fresh air without rain or insect penetration. A weatherstripped shutter can provide tight closure

when ventilation is not desired.

ADVANTAGES

:

1) Occupant control of the ventilation.

2) Ventilation at window where security or cost preclude

operable sash.

DISADVANTAGES:

Lack of centrally controlled admittance of outside air.

AESTHETICS:

A deeper head or sill frame section to accommodate the ventilation

openings is required.

COST:

Including through the frame ventilation increases the frame

cost between 15 and 20 percent depending upon the unit selected.

3-1
EXAMPLES

:

Following the references are examples of frame ventilators.

REFERENCES

:

Kawneer, "Kawneer Has Just Re-Invented the Window", Kawneer Architectural

Products, Niles, Mich., 1976.

Roto International, "Unitas-Dauerluf tung" Roto International, Essex,

Conn. 1975.

Wausau Metals Corp., "Aluminum Windows and Curtain Wall", Wausau Metals

Corp., Wausau, Wise, Jan. 1975.

3-2
Kavmeer Architectural Products, Country Club Rd., Harrisonburg, VA 22801

3-3
Roto International, P.O. Box 73, Essex, CT

3-4
Wausau Metals Corp., 1415 West Sheet, Wausau, WI 54401

3-5

3.2 WEATHERSTRIPPING/Air Tightness

STRATEGY

:

Install weatherstripping to reduce air leakage through windows.

PHENOMENA:

1) Infiltration is one of the primary ways that energy is

lost through windows. Every three feet of edge of

operable sash may lose as much energy as one square foot

of glass. (74, Professional Builders ,pl54)

.

2) Air leakage through cracks only occurs when there is a difference in air pressure between the inside and outside

of the building. There are two fundamental causes of

this air pressure difference: 1) outside wind induced

pressure and or inside mechanical system induced pressure.

2) air density difference due to inside and outside air

temperature difference. These two causes can tend to

cancel each other or can be compounding.

3) The air tightness of a window depends upon the initial

size of the crack between the frame and sash necessary

for the sash to be movable and to accomodate fabrication

tolerances; and upon the change in the crack size with

aging due to general wear, distortions of the frame due

to external stresses transferred from the building, and

shrinking or warping of the components. Air leakage

through the perimeter joints of operable sash can be

effectively reduced with weatherstripping because of the

ability of weatherstripping to accommodate changing joint

sizes

.

4) ASHRAE estimates the effectiveness of weatherstripping

for, various types of windows as follows: (65 , ASHRAE ,p459)

3-7
CUBIC FEET OF AIR INFILTRATION PER FOOT OF CRACK, HOUR

Wind Speed (mph)

Wood double hung 5 10 15 20 25

(average fit, unlocked)

non-weatherSt ripped 7 21 39 59 80

weather stripped 4 13 24 36 49

average reduction 38 percent reduction due to weatherstripping

(poor fit, unlocked)

non-weather stripped 27 69 111 154 199

weatherstripped 6 19 34 51 71

average reduction 70 percent reduction due to weatherstripping

Metal Double hung

(unlocked)

non-weatherstripped 20 47 74 104 137

weatherstripped 6 19 32 46 60

average reduction 60 percent reduction due to weatherstripping

ADVANTAGES

:

1) Reduced infiltration of outside air on the windward side

of a building and reduced loss of conditioned air on the

leeward side of a building.

2) Elimination of uncomfortable drafts.

3) Increased resistance to water and snow prentration.

4) Improved sound insulation.

DISADVANTAGES:

1) Deteriorates from physical aging or wearing.

2) Cannot compensate for gross frame distortions.

3-8
EXAMPLES:

1) An analysis was performed on a hypothetical five bedroom

bungalow with 998 square feet of floor area, 12 windows

with a combined area of 221 sq. ft., two doors with a combined area of 37 sq. ft., and 4 inches of insulation

in the walls and ceiling. The windows were average

fitted and had rib-type metal weather str ipping . The

interior temperature was to be maintained at 70°F. The

following table summarizes the calculated reduction in

winter heating costs due to weatherstripping the windows

of the hypothetical bungalow located in various cities.

The costs have been recalculated by the authors for

natural gas at $0.21 per 100 cubic feet (Nov 76 price in

Washington, D. C), 1000 Btu/cubic foot, and a furnace

efficiency of 80 percent. (52, Lund, p4)

FUEL COST SAVINGS FROM WEATHERSTRIPPING

Fuel Cost due

Infiltration

to Total : Cost

Fuel

City

Degree Days Non

W.S. W.S. Savings

Non

W.S. W.S

Washington, D. C. 4,561 55.23 19.40 35.83 149.72 113 .89

New York City 5,280 63.93 22.47 41.46 173.30 131 .85

Chicago, 111. 6,282 76.06 26.72 49.34 206.20 156 .86

Minneapolis, Minn. 7,966 96.46 33.89 62.57 261.50 198 .92

Grand Forks, N. D. 9,871 119.53 41.99 77.54 324.03 246 .49

W.S. = Weatherstripped windows

non-W.S. = non-weatherstripped windows

2) The following section through a double hung window illustrates

one manufacturer's weatherstripping method.

3-9
Figure 20. Cut-away Section of a Weatherstripped Window

REFERENCES

:

ASHRAE, ASHRAE Guide and Data Book , American Society of Heating,

Refrigeration and Air-Conditioning Engineers, New York, 1965.

Lund, M. S., Peterson, W. T. Air Infiltration Through Weatherstripped

and Non-Weatherstripped Windows , Bulletin No. 35, University of

Minnesota, Minneapolis, Minn. 1952.

Professional Builder, "Stop Housing's Biggest Energy Drain", Professional

Builder , Chicago, 111., April 1974.

Tamura, G. T. , "Measurement of Air Leakage Characteristics of

House Enclosures", ASHRAE Transactions No. 2329 , ASHRAE Inc.,

New York, N. Y.

3-10
3.3 THERMAL BREAK/lnsulation

STRATEGY

:

Provide a thermal break in the path of heat flow through metal

window frames to reduce winter heat loss and summer heat gain.

PHENOMENA:

1) Aluminum conducts heat 1,770 times better than wood and

therefore offers little resistance to unwanted flow of heat.

(75, Kern, p. 47) This inherent disadvantage of metal window

frames can be alleviated by thermally separating the inside of

the frame from the outside of the frame. There are presently

two methods of providing a thermal separation:

a) pouring poly-urethane in a slot in the metal frame; then

after it has bonded and set, sawing away the metal

bridging the slot.

b) providing two separate frames linked together with a rigid vinyl insert.

2) The effectiveness of the thermal break depends upon the

insulating value of the material used and the thickness of the

material in the path of the heat flow.

An aluminum frame with a good thermal has a U-value similar to

insulating glass (U=0.58) and performs substantially

better than an aluminum frame with no thermal break as shown below: (76, Kolbishop)

Frame U-Value

2 inch thick aluminum frame - no break U = 1.18

2 inch thick aluminum frame - with break U = 0.60

3) The benefit of providing a thermal break in the frame is

proportional to the amount of frame area. The frame area

can be as high as 20 percent of the total window area.

In such a case, if the window is glazed with insulating

glass, it is important that the frame not provide a "short

circuit" for the heat flow. A thermal break in the frame

prevents this.

3-11
ADVANTAGES

:

1) Reduction in winter heat loss and summer heat gain through the

window frame.

2) Elimination of condensate or ice forming on the frame except

in the most extreme conditions.

3) Elimination of wall deterioration due to run-off from condensate.

DISADVANTAGES

:

1) Possible degradation of the thermal break from sun exposure if

the frame section does not provide protection.

2) Imposition of stress on the thermal break if it is bonded to

both sides of long sections of aluminum subject to wide

inside/outside temperature differences and extreme summer/

winter temperature ranges.

For example, the temperature of the outer frame, if it is

anodized a dark color, can range from 160°F (71°C) when exposed

to sunlight in the summer to below zero (-17.7°C) on cold

winter nights. The frame inside the thermal break will stay

much closer to room temperature, especially if the window has

reflective or heat absorbing insulating glass. The wide

seasonal temperature range of the outside section will cause

it to expand and contract while the inner section changes

relatively little in length. (76,Hetman) This phenomena

requires the use of a resilient material for the thermal break

and a good bonding agent. (76,Roehm)

3) Increased aluminum cross section size required for structural

integrity if the thermal break allows free slippage between

the two frame parts.

AESTHETIC CONSEQUENCES:

1) The frame sections can be detailed to obscure the thermal

break from view or the thermal break can be colored to blend

with the frame.

2) A more massive frame section may be necessary to accommodate

the thermal break and still have adequate structural integrity

if the thermal break does not bond the two sections together.

3-12
COSTS:

The cost of installing window frames with a thermal break depends

upon the complexity of the frame. For simple fixed glass frame

sections, a thermal break adds approximately 10 percent to the

material cost of the frame. For openable windows, a thermal break

will cost considerably more because there are more frame components

and they must withstand the stresses of operation.

1) A manufacturer has calculated the energy and resulting cost

savings for installing windows with a thermal break in a new

office building in Lincoln, Nebraska. (6,671 heating degree

days, 1,282 cooling degree days) All windows were to be

double glazed and non-operable. The building had 1,350 sq.

ft. of inside window frame area. Oil heating with an efficiency of 70 percent was assumed. Based upon an improvement

in the frame U-value from 1.18 to 0.60 it was calculated

that 1,270 gals oil could be saved. At $0.40 per gallon

this amounts to $508 saved per heating season. Additional

savings are expected from reduced air conditioning costs.

The thermal break interrupts the conduction from the sun- heated outside surface of the frame. The additional cost

of providing window frames with a thermal break was $1080.

("'6,K0BISH0P)

2) The following illustrations show how poured poly-urethane

thermal breaks can be included in window frame sections.

EXAMPLES

:

High Structural

Strength Polyurethane

Neoprene

Weather-stripping

3-13
3) The following photograph illustrates the effectiveness of a thermal break in reducing heat loss through the frame. A

piece of dry ice is placed in contact with the outside face

two window frames. The frame section to the right has no thermal break and ices-up, the frame section on the left

contains a thermal break and does not ice-up on the inside.

(76,Devac,p5)

Devac, Inc., 10130 State Highway 55, Minneapolis, Minn. 55441

3-14
REFERENCES

:

Hetman, Frank, telephone call by author, Devac, Inc., Minneapolis,

Minn., Dec. 2, 1976.

Kern, Ken, The Owner Built House . Charles Scribner Sons, New York,

1975.

Kobishop, Peter, correspondence addressed to author. Wausau Metals

Corp., Wausau, Wisconsin. Nov. 24, 1976.

Roehm, John, telephone call by author. Architectural Aluminum Manufacturing Assoc. Chicago, 111., Dec. 3, 1976.

3-15

3.4 TYPE OF OPERATION/Ventilation, Air Tightness

STRATEGY

:

Select a type of operating window considering its ability to draw

in outside breezes and direct incoming air.

PHENOMENA:

1) Outward projecting casement windows can scoop in and exhaust

air when the wind is parallel to the wall. (55 , Jones ,p4)

Wind

Figure 21 . Plan View of Casement Windows _

2) Top hinged, bottom hinged, center pivoting, and jalousie

windows can angle the incoming air stream upward in the plane

of the sash. (73,01gyay ,plll) This helps relieve the

tendency of hot air to stagnate near the ceiling.

Figure 22. Section Through Horizontal PivotingiWindows

3-17
3) Double hung windows provide slight ventilation, even on windless days, due to the difference in density between warm

and cool air. When the outside air is cooler than room

temperature, warm, less dense room air exits out the top

window opening while cool, more dense outside air is drawn in

through the bottom window opening replacing the exiting warm

air. If the outside air is warmer than room air the process

reverses. Because this effect increases with increasing

vertical separation of the top and bottom openings, tall, narrow windows are more effective ventilators. (74 , Grandjean,

p211)

U

Outside

Temp. eO'^F

—^ 80°F

^^^^

J

;r —^ 60°F

Outside

Temp. 80°F

a

Figure 23. Air Circulation Througli Double-Hung

Windows Shown in Section

4) Horizontally sliding windows with both halves operable may

provide more circulation of air in what might otherwise be

dead air spaces. Also, the option of opening one side, the

other side, or both affords more flexibility for furnishing a room and more options for the room occupant to direct the air

flow.

Z3 I

f

/

/

/

Both Sashes

Operable

\ One Sash

Operable

Figure 24. Plan View of Air Movement Through

Horizonal Sliding Windows Shown in Plan

3-18
ADVANTAGES

:

1) More effective overall ventilation of a room.

2) Ventilation during rain possible with out-swing awning, inswing hopper, and jalousie windows.

3) 100 percent of window area is openable with pivoting and

hinging type windows compared to a maximum of 50 percent with

vertically or horizontally sliding windows.

4) Greater ease in window washing possible when outside glass

surfaces can be reached through opened sash, when sash can be

pivoted nearly 180°, or when sash can be lifted out of tracks.

5) Occupant control. Option to have greater variation of room

temperature and ventilation than likely with mechanical system

alone.

DISADVANTAGES:

1) Possible wind damage when opened, hinged, or pivoting sash

catch gusts.

2) More parts to require maintenance with vertically or horizontally pivoting sash compared to sliding sash,

3) Possible entry for burglars by removing glass slats of

jalousie windows.

4) Interference with inside draperies, roll shades, or Venetian

blinds with in-swing windows, and interference with outside

sun screens, roll blinds, or canvas awnings with out-swinging

windows

.

The following table summarizes several of the above advantages and

disadvantages of window operating types:

3-19
WINDOW TYPES

horizontal

sliding

double

hung

double

hung

(reversed)

casement

(out)

casement

(in)

pivoted

(vertical)

Ipivoted

(horizontal)

top

hinged

(out)

bottom

hinged

(in)

fixed

sash

ialousie

ADVANTAGES

provides 100% vent opening X X X X X X X

diverts inflowing air upward X X X

will deflect drafts X X X X X

offers rain protection while partly open X X X X

screen and storm sash easy to install X X X X X X

easy to wash with proper hardware X X X X X X

DISADVANTAGES

only 50% of area openable X X X

does not protect from rain when open X X X X X X

inconvenient operation when over an obstruction X X X X X

presents a hazard if vent low and close to walkways X X X X

hard to wash X X

X X

interferes V7ith furniture, drapes, blinds, etc.

X X X X

screens-storm windows difficult to provide X X X

sash has to be removed for washing X X X X

3-20
AESTHETICS:

1) Subdivision of a window to provide operable as well as fixed

portions reduces the scale of the fenestration and may reduce

dimensions to a more human scale.

2) With a large facade, occupant discretion in having the windows

closed, partially open, or completely open will provide a constantly changing pattern to the composition of the fenestration.

3) An open window, unlike a ventilation register delivering

"processed" air, allows a sense of contact with the outdoors,

both visually, acoustically, and olefactorily

.

4) Horizontal window meeting rails must be designed with eye

level, sight-lines, and view considered in order that annoying

view obstruction be avoided.

5) Too much subdivision of the glass area can distract from an attractive view, as with jalousie windows.

COST:

The additional cost of selecting the correct but more expensive

type of window to ventilate a room versus selecting the least

expensive type of window is small relative to the total building

cost. Providing double hung versus single hung results in minimal

if any additional costs. Often the track and separate sash are already existant, only the operating hardware need be provided.

Casement windows are more expensive than horizontally or vertically

sliding windows but afford complete opening of the window area. Jalousie are more expensive than casement windows but afford 100

percent openable area plus rain protection.

EXAMPLES

:

An unusual type of operating window is available which can be

hinged at the side like an in-swing casement, or by shifting a lever control, hinged at the bottom like an in-swing hopper window.

3-21
When the sash is hinged at the bottom and the heat register or radiator is located below the window the rising hot air will be

directed into the room while being mixed with a controlled amount

of outside fresh air. Drafts are minimal in this situation. When

the sash is hinged from the side 100 percent of the window area is

available for air circulation. Washing is facilitated by simplyswinging the window into the room in the side hinged mode.

The in-swing allows the installation of external storm windows,

insect screens, solar screens, or awnings. However, it does

interfere with interior window accessories, e.g. draperies, Venetian

blinds, or shades as well as limiting the placement of furniture

near the window. (75 , Architects Journal, p488)

REFERENCES:

Architects Journal, "Windows Tech. Study No-. 1, Hanging and Operation,

Ironmongery", Architects Journal , Architectural Press Ltd., London,

Eng., Sept. 3, 1975.

Becket and Godfrey, Windows , Van Nostrand, Reinhold Co., N. Y., 1974.

Grandjean, E., Ergonomics of the Home , Hals ted Press, N. Y., 1974.

Jones, R. A. et.al., "Selecting Windows", Small Homes Council, Urbana,

111., 1955.

Olgyay, Victor, Design with Climate , Princeton University Press, Princeton,

N. J., 1973.

"Roto-Tilt and Turn Windows", Roto International, Essex, Conn., 1976.

3-22
3.5 WINDOW TILT/Solar Heating

STRATEGY

:

Design windows tilted slightly towards the ground to reduce

summer solar heat gain without appreciably affecting winter

solar heat gain.

PHENOMENA:

1) Reflection of sunlight at the surface of glass varies

considerably depending on the incident angle at which the

light strikes the glass (i.e. the angle between the light

ray and a perpendicular line from the surface of the

glass as shown in the figure below) . At incident angles

^

Line Perpendicular to window plane

A — Angle between sun and

window in plan view

B — Angle between sun and ground plane (Altitude)

C — Incident angle

Figure 25. Incident Angle Illustrated

3-23
less than 57° small changes in the incident angle have

little affect on the amounts of light transmitted or reflected. At incident angles greater than 57° the amount of

direct sunlight reflected increases at an increasing rate

and the amount of light transmitted decreases correspondingly.

(77 ,Cellarosi) This is illustrated in the following graph.

(74,Yellot,p22)

0 30 60 90

Incident Angle

Figure 26. Light Transmitted and Reflected by

Glass vs. incident Angle

3-24
2) During the suramer when the sun is high in the sky, the

incident angle of the sun on vertical glass is likely to be

well above 57°. For example, at 42° latitude at noon on June 22 the incident angle of sunlight on a vertical plane

of glass facing south is 71.45°. This is so far in excess

of 57° that any increase in the incident angle, (i.e.

tilting the glass outward) will greatly increase the amount

of light reflected and reduce the solar heat gain correspondingly.

During the winter, when the sun is low in the sky, the

incident angle of sunlight on vertical glass is likely to be

less than 57°. For example, at 42° latitude, on Dec. 22 at

noon the incident angle between the sun and a south-facing

window is 24.55°. At this low sun angle, a slight tilt

downward to the glass will not appreciably decrease the

amount of sunlight transmitted in comparison with vertical

glass. Thus, the potential benefit of winter solar heat

gain is not appreciably decreased. This seasonal variation

is illustrated in the following figure.

Altitude at Noon 42°N Lat. Altitude at Noon (§) 34°N Lat. (Boston) (Atlanta)

June 22 = 71.45° June 22 = 79.45°

Dec 22= 24.55° Dec 22 = 32.55°

Figure 27. Seasonal Sun Angle Variation For Two Cities

3-25
From the previous figure it can also be seen that closer

to the equator (e.g., 34°N latitude) the sun is higher

in the sky in both summer and winter. Thus, less tilt

of the window is required to achieve the same reduction

in summer sun transmission as is possible with more

tilt in more northern latitudes.

3) The amount of summer sunlight transmitted through a tilted window is not only reduced because more of the

light is reflected but it is still further reduced because the horizontal outward projection of the tilt also

reduces the area of glass exposed to the sun. The geometry

is the same as if there were a horizontal projection

shading vertical glass. This shading effect becomes

negligible in the winter when the sun is at a lower angle

in the sky.

Figure 28. Glass Exposure to Sun jShown in Section View

3-26
ADVANTAGES:

1) Reduced summer solar heat gain without obstructing view

out

.

2) Little reduction of winter solar heat gain.

3) Reduction in exposure to cold winter night sky.

4) No management of the window required to achieve these

effects

.

5) Reduced glare.

6) Less prone to soiling from birds.

7) Protection of opened sash section from rain penetration.

DISADVANTAGES:

1) Increased exterior surface area for same floor area provides greater potential heat loss.

2) Not effective on east or west exposures when sun is low

in the sky. (The more off of a true N.S.E.W. orientation

a building is, the more effect tilting the glass will

have on increasing the incident angle for the easterly or westerly exposures.)

3) Reduced effectiveness when ground surfaces are reflective.

4) Dust more prone to collecting on inside surface of the

glass.

5) Washing tilted windows may be more difficult than washing

vertical windows.

6) Stronger roll blinds required for non-vertical windows

because the slats, when not vertical, may tend to bow

from their own weight.

3-27
AESTHETIC CONSEQUENCES:

1) During the day the projection of a building outward

towards an observer may instill a sense of overbearing

dominance. The effect during the night will be minimal.

2) The greater building perimeter at the top of the windows

compared to the base of the windows results in a greater

expanse of ceiling which may give a sense of spaciousness.

However, there is no increase in floor area.

3) Installation of draperies will result in an odd relationship between the "hang" of the drapes and the slope of

the glass. With Venetian blinds, the slope may create

operating difficulties.

COSTS:

Tilting the glass increases the area of glass for a given

height of window opening . This will increase the material and

the installation costs.

EXAMPLES

:

1) The North Carolina Blue Cross and Blue Shield Headquarters

in Orange County, N. C. is oriented with its long axis

running east/west with sloping reflective glass on the

north and south sides to reduce summer solar heat gain.

Wind acceleration was a concern during the design stages

but wind tunnel tests showed no adverse wind conditions.

Air conditioning costs are said to be significantly

reduced as a result of the shape of the building and use

of reflective glazing. (71,P .A. ,pl29)

3-28
Libbey-Owens-Ford Co., 811 Madison Ave., Toledo, Ohio

3-29
In the Tempe Municipal Building of Tempe, Arizona the

glass slopes at 45 degrees to similarly act as its own sunshade and reduce heat gain by reflecting sunlight due

to the increased angle of incidence. Heat absorbing

glass and draperies are used to further reduce heat gain.

The area immediately behind the glass is isolated from

offices and the heat that does penetrate is carried away

by the air handling system. The end result is that only

18 percent of the available solar heat reaches the

occupied areas of the building. (71, P .A. , pill)

City of Tempe, P.O. Box 5002, Tempe, Ariz. 85281

3-30
Dulles Airport Terminal Building in Fairfax County, VA is

another example. The glazing tilts outward, consistant

with the formal lines of the building, providing effective

solar heat gain reduction. The long tilted sides are oriented facing south and north. East and west sides are vertical to facilitate future building expansion.

Untinted single pane glazing is used without any internal

draperies, shades or blinds.

Robert Wehrli, Arch. Research Sect., NBS, Washington, D.C. 20234

3-31
Robert Wehrl i , Arch. Research Sect., NBS, Washington, D.C. 20234

REFERENCES

:

American Society of Heating, Refrigeration and Air Conditioning

Engineers, ASHRAE Handbook of Fundamentals , ASHRAE, New York,

1974.

Cellarosi, Mario, telephone conversation. National Bureau of

Standards, Washington, D. C, March 29, 1977.

Latta, J. K. , Walls, Windows and Roofs for the Canadian Climate , Division of Building Research, Ottawa, Canada, 1973.

P.A. , "Shaped for Savings", Progressive Architecture , Reinhold

Publishing Co., Inc., Stamford, Conn., Oct. 1971.

Stephenson, D. G. and Mitalas, G. P., "An Analog Evaluation of

Methods for Controlling Solar Heat Gain Through Window", Research

Paper No. 154, Division of Building Research, Ottawa, Canada,

April 1962.

Yellot, John I., "Solar Radiation and Its Uses on Earth", Energy

Primer , Protola Inst., Menlo Park, Ca. , 1974.

3-32
3.6 SIZE, ASPECT RATIO/Air Tightness

STRATEGY

:

Proportion windows so they approach a square and use fewer but

correspondingly larger window to minimize window perimeter,

thereby reducing the potential for infiltration.

PHENOMENA:

1) Window infiltration occurs at three joints:

a) the perimeter joint between the frame and the wall.

b) the perimeter joint between the sash and the frame.

c) the perimeter joint between the glass and the sash.

Insulating glass conduction losses are greatest at the

perimeter where metal or glass edging bridges the insulating air space.

2) It is possible to decrease the perimeter of a given area

of window merely by making it closer to a square in

proportion. As can be seen in the following figure, less

perimeter occurs for any given area the smaller the width

to height ratio is. Also the smaller the area, the more

pronounced this phenomena is

.

3-33
1:1 1:2 1:3 1:4 1:5 1:6

Figure 29. Aspect Ratio

3) Regardless of the size of the area, the amount of perimeter

for any given area increases at an increasing rate up to a width to height ratio of 1:3. Thereafter, the amount of

perimeter increases at a decreasing rate. Thereafter, if

non-energy criteria dictate a window narrower than a 1:3

ratio varying its slenderness has decreasing energy

relevance.

4) Using fewer but larger windows rather than more but smaller

windows reduces the perimeter for a given window area. For example, two square windows each 3 ft. on a side

provide, a total area of 18 sq. ft. with a perimeter of 24

ft. A single square window 4.25 feet on a side provides

the same area but the perimeter is only 17 ft.

ADVANTAGES

:

1) Reduced potential infiltration due to reduced perimeter.

2) Reduced conducted heat loss through the edges of insulating

glass

.

3) Less time required to clean a few large windows compared

to many smaller windows.

3-34
4) Reduced maintenance cost of painting and caulking.

5) Reduced potential for water penetration.

DISADVANTAGES

:

1) Less uniform distribution of daylight with a few large

windows compared to more windows placed at intervals.

2) Fewer options for varying the sourced daylight and natural

ventilation with fewer but larger windows.

3) Increased physical effort required to operate large windows.

4) Increased cost for replacement of broken glass due to

vandels or storm damage.

AESTHETIC CONSEQUENCES

:

1) Larger and square shaped windows may pose a problem if

classical proportions are dictated in traditional design

situations.

2) Larger windows affect the scale of the building.

3) Fewer but larger windows may result in a clearer delineation of wall areas and window areas.

COSTS:

1) The total delivered cost of fewer but larger windows is

lower

.

2) The costs of framing and installing fewer but larger

windows is apt to be less within certain ranges. One

constraint is the limit of what a carpenter can handle.

Secondly, the cost of framing the wall opening increases

in discrete increments as the depth of the header increases

in nominal increments.

3-35
EXAMPLES

:

The figure below illustrates the proportions calculated in the

table following the references for the two extremes of: area =

1, and area = 5.

Area - 5.00

II 1.00

I

_i

o

o

II CO0)

\- <

r

1:1 1:2 1:3 1:4 1:5 1:6

P1 = 4.00 Pl = 4.24 Pl = 4.62 Pl = 5.00 Pi- 5.37 Pl = 5.72

P5 = 8.94 P5 = 9.49 P5 = 10.33 P5 = 11.2 P5 = 12.0 P5 = 12.8

Figure 30. Aspect Ratios

REFERENCES

:

Rehm, Ronald, meeting, Mathematics Division, National Bureau of

Standards, Washington, D. C. Dec. 10, 1976.

3-36
The following table illustrates changes in perimeter and perimeter

HJ dl. t-d 1.C1L.XWO do ^ "Fi iTt r* t" 1 nn of aspect ratios from 1 to 1

f~bT"mip"b 1 t n 6 for ATGas of 1 throu^;h 5.

AKhA = l.UUUU

ASPECT WIDTH PER APER PER/A APER/

1 X 1.0 1.000 4.000 4.000

1 X 2.0 . 707 4.243 .111 4.243 .111

1 X 3.0 .577 4.619 . 376 4.619 .376

1 X 4.0 . 500 5.000 .381 5 . 000 . 381

1 X 5.0 .447 5.367 .367 5.367 .367

1 X 6.0 .408 5.715 .349 5.715 .349

AREA = 2.0000

ASPECT WIDTH PER APER PER/A APER/

1 X 1.0 1.414 5.657 2.828

1 X 2.0 1.000 6.000 .158 3.000 .079

1 X 3.0 .816 6.532 .532 3.266 .266

1 X 4.0 .707 7.071 .539 3.536 .270

1 X 5.0 .632 7.589 .518 3.795 .259

1 X 6.0 .577 8.083 .493 4.041 .247

AREA = 3,0000

ASPECT WIDTH PER

1 X 1.0 1.732 6.928

APER PER/A

2.309

APER/A

1 X

1 X

2.0

3.0

1 X 4.0

1 X 5.0

1 X 6.0

AREA = 4,0000

ASPECT

1 X 1.0

1 X 2.0

1 X 3.0

1 X 4.0

1 X 5.0

1 X 6.0

1.225 7.348 .193 2.449 .064

1.000 8.000 .652 2.667 .217

.866 8.660 .660 2.887 .220

.775 9.295 .635 3.098 .212

.707 9.899 .604 3.300 .201

WIDTH PER ZlvPER PER/A APER,

2.000 8.000 2.000

1.414 8.485 .223 2.121 .056

1.155 9.238 .752 2.309 .188

1.000 10.000 . 762 2.500 .183

.894 10.733 .733 2.683 .183

.816 11.431 .698 2.858 .174

AREA = 5.0000

ASPECT WIDTH PER

1 X 1.0 2.236 8.944

APER PER/A

1.789

APER/A

1 X 2.0 1.581 9.487 .249 1.897 .050

1 X 3.0 1.291 10.328 .841 2.066 .168

1 X 4.0 1.118 11.180 .852 2.236 .170

1 X 5.0 1.000 12.000 .820 2.400 .164

1 X 6.0 .913 12.780 .780 2.556 .156

3-37

GLAZING

MULTFLE GLAZING

HEAT-ABSORBING GLASS

APPLIED FILMS

REDUCED GLAZING

GLASS blog: . THRUGLASS VENTILATORS
4. GLAZING

The type of glass installed in the window will determine

the amount of sunlight transmitted into the building's

interior and the amount of the building's heat conducted

to the outside. These two factors will establish the

heat gain or heat loss through glass for given interior

and exterior climatic conditions. Insulating glass,

multiple glazing (storm sash) , and low-emissivity

coatings are extremely effective at reducing the conducted heat flow through glass. Reflective or tinted

glasses are capable of stopping much of the sunlight

from penetrating into the building. In selecting

glass, the orientation of the window, the length and

severity of the seasons, and the heat gain from lighting,

equipment, and people must be considered. For example,

clear double glass on a south exposure may be effective

for locations with long severe winters, while reflective

single glass may be appropriate for locations with

long, hot summers.

4-0
4.1 MULTIPLE GLAZING/lnsulation

STRATEGY:

Install insulating glass and/or storm windows to provide an insulating air space(s), reducing conducted heat losses.

PHENOMENA:

1) Glass is a good conductor of heat, be it indoor heat conducted

outward in the winter, or outdoor heat conducted inward in

the summer. The high conductivity of glass can be appreciated

when compared to another material. For example, glass, as a material, conducts heat 9 times better than plywood. This

rate of heat flow is so great that merely adding layers of

glass in contact with each other is of negligible thermal

benefit. However, if the layers. of glass are separated by

air spaces, the path of conduction is interrupted, and the

rate of heat flow is reduced. To traverse the air spaces,

heat must be transferred by radiation and convection.

2)' The width of the air space affects its thermal performance.

Up to approximately 5/8inch, the wider the air space, the

greater the reduction in heat flow. An air space narrower

than 3/16 inch begins to be ineffective. Across such a short distance, heat is readily conducted by the air. At

the other extreme, increasing the air space width beyond

approximately 5/8 inch does not substantially reduce the Uvalue below that of the 5/8 inch separation (although it can substantially improve the acoustic insulation) . This is

due to a wider space, allowing the air to circulate freely.

Air in contact with the warm sheet of glass rises, air in

contact with the cold sheet of glass settles, and a cyclic

air movement is established. This moving air transports the

heat from the warm glass to the cold glass. The increased

heat loss due to such convection currents offsets the

decreased losses by conduction through the air. The net

effect is shown in the following graph of U-values for

different air space widths. The upper three curves show the

combined heat transfer for convection and conduction for

three temperature differences across the air space. (54,

Robinson, pll)

4-1
1/2 1 2 3

Width of Air Space (inches)

Figure 31 . U-Valved Insulation Glass

vs. Separation

3) Three layers of glass separated by air spaces are more effective than two separated layers of glass of the same overall

width. Triple glazing with two 1/4-inch air spaces has a U-value of 0.47 compared to 0.58 for double glazing with a single 1/2-inch air space. (74, ASHRAE , p370) Installing storm

windows over double-glazed windows is another means of

achieving triple glazing.

4) The mix of gases in the air space affects the rate of heat

transfer. For example, heat flow through an insulating glass

unit (in a 12-mph wind, an outside temperature of 28° F and an indoor temperature of 70° F) will be reduced 14 percent when

the air space is filled with Krypton. (75 , Herman, p33) As

much as an 18- to 20-percent reduction in U-value may be

possible with carbon dioxide. (75,PRITSKER)

5) The heat absorbing and radiating characteristics (characterized by the termed emittance) of the two surfaces of glass

facing toward the air space will affect the rate at which heat

is radiated across the cavity. A coated film, such as tin

oxide or indium oxide, or pure metals, such as gold, silver,

or copper, applied to either of the glass surfaces facing the

cavity reduce the heat transfer by radiation. Examples of the

effectiveness of such coatings is given in the following table.

(74, ASHRAE, p370)

4^2
Type of Insulating Glass Winter U-value

(1/2" air space)

effective emittance =0.8 (untreated). . . 0.58

effective emittance =0.60 0.52

effective emittance =0.40 0.45

effective emittance =0.20 0.38

Note that the U-value for glass having the lowest emittance

coating is comparable to uncoated triple glazing separated by

two 1/2-inch air spaces (U = 0.36). (74,ASHRAE,p370)

Reflective coatings applied to the inside surface of the outer

sheet can also reduce the emissivity of the glass surface and,

hence, reduce the radiation across the air space. A highly

reflective glass can thus reduce the U-value to as low as 0.29. (77,PPG,pl5)

The benefit of such coatings in reducing winter heat conduction outward must be balanced against a loss in daylight

transmittance and loss of natural solar heating and illumination.

Too great a difference between body temperature and the

temperature of nearby surfaces results in a high rate of

radiant heat loss and resulting discomfort. A study in

England indicates that people in a room feel uncomfortable

near surfaces having a temperature 8° C (14.4° F) above or below the average temperature of all other surrounding surfaces. (75 ,McIntyre,p6) Because the heat flow is substantially reduced, the inside surface temperature of insulating

glass is much closer to room temperature than is the case with

single glass, and so discomfort near windows is alleviated.

This benefit is also realized with storm windows.

In the summer, multiple glazing reduces the amount of heat

conduc<"ed from the outdoors inward. The U-value for summer conditions is slightly lower for single glass, and higher for

insulating glass, due to changes in air-space convection at

higher temperatures, because a lower wind speed is assumed.

However, multiple glazing reduces the amount of sunlight

transmitted. Because glass is not 100-percent transparent,

some of the sunlight is absorbed and converted to heat within

the glass. This heat is then dissipated to the air at both

surfaces of the glass and radiated from both surfaces. The

heat which is dissipated to the outdoors is heat with which

the air conditioning system never has to contend.

4-3
Shading coefficients are a relative measure of the total solar

heat transferred to the interior. The performance of single

sheet glass (of double strength) is used as the basis of

comparison and hence has a shading coefficient of 1.00. The

shading coefficient of a window with a storm sash or insulating

glass is reduced to approximately 0.90. This can further be

reduced by using reflective or tinted glasses in the outer

glazing. For example, heat absorbing glass could reduce the

shading coefficient to 0.56. (74, ASHRA.E,p400) If the outer

sheet is reflective glass the shading coefficient is reported

to be as low as 0.17. (75,LOF,pl9)

ADVANTAGES

:

1) Reduced conducted heat loss in winter, both during the night

and during the day, when the window can perform as a solar

collector.

2) Slightly reduced solar transmission and hence slight reduction

in air conditioning load.

' 3) • Improved winter comfort. The inside surface of the glass is

closer to room temperature, so it is no longer uncomfortable

to be near the window.

'4) Elimination of condensate or ice forming on the glass except

in extreme weather.

5) Reduced sound transmission. (75, Sabine, p. 27)

6) Reduced infiltration possible with storm sash.

DISADVANTAGES

:

1) Greater weight compared to single glass windows. The two

layers of glass make the window nearly twice as heavy. This

makes installation more difficult, and removal of sash for

cleaning more awkward.

2) Unsightliness , if the seal becomes leaky condensate will form

on the inaccessible glass surfaces within the air space.

(Manufacturers guarantees against such leakage for a specified

period of time.)

3) Replacement of broken glazing is more costly and time consuming

when non-stock sizes necessitate special ordering.

4-4
4) No reduction in infiltration by installing insulating glass,

as contrasted to installing storm windows, which provide an additional layer to resist infiltration.

5) Increased likelihood of thermal breakage due to the higher

glass temperature in the presence of sunlight. (Manufacturers'

recommendations for installation must be carefully adhered

1) The presence of insulating glass instead of a single pane of

glass is nearly indiscernable visually. A storm sash, if the

frame is the same color and is congruent with the underlying

window, is unobtrusive but does reduce the setback of the

glass on the facade.

2) Low emission, heat absorbing, or reflective glass used in the

outer sheet of insulating glass changes the light transmission

characteristics of the window. Various tints may be specified, ranging from grays to bronzes. The visual and other

effects of these glasses are discussed more completely in the

section on reflective glasses.

to.)

AESTHETICS:

COSTS:

The following is a comparison of glazing costs based upon

estimates in the Washington, DC, area, for small quantities

without installation.

Single glazing 3/16" thick $1.00/ft^

Double glazing 5/8" overall $4.50/ft 2

Storm sash

Prime window

Storm sash with frame

3/16" thick $1.00/ft2

single strength $2.00/ft

Triple glazing

Prime window

Storm sash with frame

5/8" overall $4.50/ft2

single strength $2.00/ft

$6.50/ft^
It should be noted that although there is a substantial

difference in glazing costs when multiple glazing is specified, the cost of the total window does not increase proportionally. Typically, a total window unit consisting of

frame, sash, and glazing increased in price approximately 25

percent for double versus single glazing, and approximately 45

percent for triple versus single glazing.

EXAMPLES

:

1) A study by the Edison Electric Institute indicates that a typical, well-insulated, all-electric, ranch style house could

save 3,266 kWh of electricity with insulating glass instead of

single glass in a climate area such as Indianapolis (5,611

degree days). At an electric rate of $0.04/kWh, this amounts

to $130.64 per year. This represents savings for heating

costs only. (76,PPG,p4)

2) A computer study of two Fairfax County, Virginia, schools

indicates a 13-percent and 10-percent savings for two buildings

reglazed with insulating glass. (74,Grif f in,p67)

3) A study in Sweden calculated the energy savings from triple

glazing compared to double glazing. The study was based on

' a hypothetical office module with other offices above, to

the sides, behind, and below. The glass area was 2.24 m^

(24.1 ft2). The office was occupied by two people from 0800

' to 1600 hours. Their heat output combined with electrical

equipment was assumed to be 300W. Ventilation was supplied at

a rate of 80 m^/hr (2825 ft^/hr). Room temperature is kept at

22° C (68° F) . The following table summarizes the average

daily energy saved, triple versus double glass.

(75, Adamson,pll)

4-6
Orientation Place kWh for Energy Saved

double triple kWh/yr kWh/yr

per window per m'^ (ft'^)

North Malmo 3490 3290 200 89 (8.3)

Stockholm 4140 3910 230 103 (9.6)

Lulea 5880 5550 330 147 (13.7)

East Malmo 3110 2940 170 76 (7.1)

Stockholm 3770 3570 200 89 (8.3)

Lulea 5400 5120 280 125 (11.6)

South Malmo 2650 2530 120 54 (5.0)

Stockholm 3320 3150 170 76 (7.1)

Lulea 4950 4710 240 107 (9.9)

Note: Malmo: 6,900 degree days.

Stockholm: 7,700 degree days.

Lulea: 11,000 degree days.

(77,Helander)

REFERENCES

:

Adamson, Bo and Kallblad, Kurt, Time for Triple Glazing , Department of Building Science, Lund Institute of Technology,

Lund, Sweden, 1975.

American Society of Heating, Refrigerating and Air Conditioning Engineer, ASHRAE Handbook of Fundamentals , ASHRAE,

Inc., NY, 1972.

Anques, J. and Croiset, M. , Thermal Comfort Requirements

Adjacent to Cold Walls - Application to Glazed Openings , Centre Scientifique et Technique du Batiment, Paris, France,

English translation: NBS Technical Note 710-4, NBS, Washington,

DC, 1972.

Berman, Samuel, Energy Conservation and Window Systems . N.T.I.S., Springfield, VA, 1975.

Griffin, C. W. , Energy Conservation in Buildings : Techniques

for Economical Design , Construction Specifications Institute,

Washington, DC, 1974.

Helander, Lars, telephone conversation. Scientific Attache,

Swedish Embassy, Washington, DC, Feb. 15, 1977.

4-7
Libbey-Owens-Ford Co., Glass for Construction , LOF Co.,

Washington, DC, 1975.

Mclntyre, D. A. , Radiant Draughts , Electricity Council

Research Centre, Capenhurst, Chester, England, 1975.

PA, Technics; High-performance Glass , Progressive Architecture, Reinhold Publications, Stamford, CT , June 1976.

PPG Industries, Inc., Architectural Glass Products , PPG

Industries, Inc., Pittsburgh, PA, 1977.

PPG Industries, Inc., Energy Effective Windows for Cost

Savings and Conservation , PPG Industries, Inc., Pittsburgh,

PA, 1976.

Robinson, H. E. and Powelitch, F. J., "The Thermal Insulation

Value of Air Spaces", Housing Research Paper No. 32, Housing

and Home Finance Agency, Washington, DC, April 1954.

Pritsker, Theodore, Assoc. Dallas Laboratories, Dallas, Texas,

Telephone conversation, Dec. 3, 1975.

Robinson, Henry E,, Editor, Calculation of Pane-to-Pane

Temperature Difference, Durability of Insulating Glass , BSS 20, National Bureau of Standards, Washington, DC, 1970.

Sabine, Hale and Myron, Lacker. Acoustical & Thermal Performance of Exterior Residential Walls, Doors, and Windows , NBS BSS 77, 1975.

Shand, E. B., Glass Engineering Handbook, McGraw Hill Book

Co., NY, 1958, p. 27.

Stephenson, D. G. , Heat Transfer at Building Surfaces , Canadian Building Digest, National Research Council of Canada,

Ottawa, April 1964.

4-8
4.2 HEAT-ABSORBING GLASS/Shading, Solar Heatmg

STRATEGY:

Install glass which absorbs more solar energy than clear glass to

reduce solar heat gain.

PHENOMENA:

1) Visible light represents only a part of the total solar

radiation. Solar energy at sea level is comprised of

approximately 3 percent ultraviolet, 44 percent visible, and

53 percent infrared energy. (74, ASHRAE,p387) All of this

energy, when absorbed, is converted to heat. Therefore, it

is the amount of total solar energy transmitted which determines the amount of heat gain, and the amount of visible

light transmitted which determines the amount of illumination

provided.

2) Adding a metallic oxide to the ingredients of glass during

its manufacture increases its absorptivity of visible and

near infrared solar energy. The greater absorptivity occurs

in the near infrared range. This characteristic distinguishes

heat absorbing glass from glass which is merely tinted.

(73 jLATTA, p61) This is an advantage in that the visible

light from the sun provides illumination which must otherwise

be provided by more heat intensive electric lighting.

3) The solar energy absorbed by the glass becomes heat which is

radiated and convected to the outdoors and indoors proportional to the temperatures, air movements, and the surface

characteristics of either side of the glass, ( if different)

.

Unfortunately, on a still, sunny, summer day more heat is

dissipated indoors because the air conditioned building

interior is cooler. Conversely, in the winter more heat is

dissipated to the outdoors because the outside temperatures

are lower than the inside temperature. The following figure

shows that heat-absorbing glass is an improvement over single

glass but still admits much of the summer suns heat. The

percentages given in the figure are for an example case and

will vary as the sun angle varies. (64 , Ulrey , pl68)

4-9
1 00%

Incident

Energy

46.2%

Transmitted

100% r

Incident \ A

Energy

82.3%

Transmitted

5.3%

Reflected 5.2%

Reradiated

24.2%

Reradiated

24.3%

Reradiated 87.5% Total

Admitted

70.5% Total

Admitted

Figure 32. Solar Energy Transmission Through Heat-Absorbing

Single Glazing vs. Clear Glass (SUMMER)

3) lihen heat absorbing glass is used as the outer sheet of

glass in double glazing, its performance is substantially

improved compared to its use as single glazing. In order

for the heat in the glass to enter the building it must

first bridge the trapped air space by radiation and

convection, be conducted through the inner sheet of

glass, and then be radiated and convected into the building interior. More heat will be dissipated to the outside air which is in direct contact with the heat absorbing

glass. Furthermore, the outward rate of heat dissipation

greatly accelerates .if there is any wind. (73 ,LATTA,t)60)

Incident Solar }

Heat-Absorbing Glass

Radiation , I A /4" Plate Glass

I cno/ /Trans b50% 'co/'i

[Absorption J

Reradiation and Convection

44% ^ I /I / I 1/ 1/ J ^ 11%

Rejected Admitted

51% 49%

Figure 33. Solar Energy Transmission

Heat Absorbing Insulating Glass

4-10
The following statistics are examples of the performance

of heat-absorbing glass in single and double glazing

configurations as reported by one glass manufacturer.

(75,LOF,pl9) Exact values will vary depending on the

composition of the glass.

PERFORMANCE OF HEAT-ABSORBING GLASS

GLASS VISIBLE

TRANSM

TOTAL

SOLAR

TRANSM

SHAD.

COEFF

1/4" CLEAR 88% 77% 0.93

1/4" HEAT ABS. 75 47 0.70

1" CLEAR INSUL. 77 59 0.79

1" HEAT ABS. INSUL. 66 36 0.56

If heat-absorbing, double glass is installed in a reversible sash, the heat absorbing sheet of glass can face the

outside in summer to dissipate heat outward, then be

reversed in the winter so that the heat-absorbing glass

faces the inside dissipating its heat into the building.

The effectiveness of this configuration could be even

further increased by providing closable vents above and

below the heat-absorbing glass. In the winter, during

the hours of sunlight, the vents could be opened to

circulate the heated air between the two sheets of glass

into the building interior, then closed at night to

preserve the insulating value of the air space. In the summer with the sash reversed, the heated air between the

glass sheets could be discharged to the outdoors further

reducing the amount of heat which enters the building.

The following diagram illustrates the effects of seasonally

reversed sash.

4-11
Summer Winter

Figure 34. Reversible Sash With HeatAbsorbing Double Glass

6) Since sunlight absorbed in heat-absorbing glass almost

immediately raises its temperature, the time lapse

between windcw exposure to sunlight and room temperature

rise is very short. Alternatively, with clear glazing

most of the sunlight is transmitted through the window

and absorbed by the walls, floor, and furniture within

the room. Thus the room temperature rise is delayed

while heat from the transmitted sun is absorbed into the mass of these objects. (See STRATEGY: Thermal Mass)

7) Closed draperies, roll shades, or blinds can reflect

much of the sunlight which has penetrated heat-absorbing

glass back at the glass. This double exposure of the

heat-absorbing glass to sunlight, substantially increases

the glass temperature. Similarly, when heat absorbing

glass is used in double glazing, the inner sheet of

clear glass reflects part of the sunlight back to the

outer sheet of heat-absorbing glass increasing its

temperature. These high temperatures create large

stresses within the glass.

ADVANTAGES

:

1) Reduced summer solar heat gain largely by absorption of

non-visible solar radiation and to a lesser extent by

absorption of visible light which provides illumination

and view.

4-12
2) Reduced fading of fabrics due to greater absorption of

ultraviolet solar radiation compared to clear glass.

3) Winter solar collection, summer solar rejection with

reversible, double glazed sash with clear and heatabsorbing glass and provision for operable venting at

the top and bottom of the sash.

DISADVANTAGES:

1) Partial dissipation of heat to the indoors in the summer

and to the outside in winter when heat-absorbing glass

used in single glazing.

2) Possible breakage of heat-absorbing glass when drapes or shades drawn in the summer. The strength of the glass

at the edges is especially critical in such instances.

3) Increased temperature of glass increases radiation of

heat which increases likelihood of discomfort for occupants near windows.

AESTHETICS:

1) Which of the many available metallic additives are added

to the ingredients of the glass during its manufacture

determines the tint it will have. For example, iron

oxide imparts a bluish green color. Nickel and cobalt

oxides and selenium give a gray or bronze tint. (75,

Architects Journal, pl263) The designer must consider

both how this tint will alter the colors of the building

interior and, how the glass color will harmonize with

the other colors of the building exterior,

2) The view out through heat-absorbing glass is dimmer than

through clear glass but brighter than many of the reflec

glasses.

3) The thickness of heat-absorbing glass will affect its

color since the tinting is caused by an ingredient

dispersed throughout the glass rather than occurring

only at the surface as with reflective glass. This

means that if various window sizes dictate different

glass thicknesses for reasons of strength, the colordensity variation as viewed from the outside, and the

brightness variation as viewed from the inside, must be

considered in the architectural composition, otherwise

the thicker size should be used throughout.

4-13
COSTS:

Heat-absorbing glass costs approximately 1/3 to 1/2 more than

clear glass.

EXAMPLE:

The effectiveness of heat-absorbing glass, though superior to

clear glass in many instances, is generally inferior to

reflective glass for the purpose of shading solar radiation.

The following study done in Switzerland compares the performance of single clear, single heat-absorbing, and double

reflective glazing with plastic draperies. Six south-west

facing rooms comparable in every respect were used in the

study. Each room had 146 sq. ft. of floor area with a 9.25

ft. ceiling height, 102 sq. ft. of outside wall area, and 46

sq. ft. of window area divided between two windows (approximately 50 percent window to outside wall ratio) . The outside

air temperature ranged from 20 to 23°C (68-74°F) . Average

room air temperatures and inside glass surface temperature

were recorded for September 10, 11, and 12 of 1969. (74,

Granjean,p206)

Glass

Clear

Room air temp.

29.9° - 35.4°C

(86° - 96°F)

Glass temp.

35.8° - 39.6°C

(97° - 103°F)

Heat Absorbing 28.7° - 32°C 38.3° - 46.2°C

(84° - 90°F) (101° - 115°F)

Double Reflective 23° - 27°C 24° - 34°C

(74° - 81°F) (75° - 94°F)

The performance of the heat-absorbing glass would be better

if it were double glazing as was the case with reflective

glazing. The room temperatures would be less extreme in all cases if the building had more thermal mass (the building

studied was light-weight construction)

.

REFERENCES

:

A. J., "Window Glass Design Guide", The Architects Journal , Architectural Press Ltd., London, Jan. 1976.

4-14
Dubin, Fred, "Energy for Architects", Architecture Plus , Informat

Publishing Corp., New York, N. Y., July 1973.

Grandjean, E., The Ergonomics of the Home , Halsted Pr., N. Y.

1974.

Latta, J. K. , Walls, Windows and Roofs for the Canadian Climate , Division of Building Research, National Research Council

Canada, Ottawa, Canada, 1973.

LOF, "Glass for Construction", Libbey-Owens-Ford Co., Toledo,

Ohio, 1975.

Persun, Charles I., "Gray Glass", Progressive Architecture , Reinhold Publishing Company, Stamford, Conn., April 1958.

Stephenson, D. G., and Mitalas, G. P., "An Analog Evaluation of

Methods for Controlling Solar Heat Gain through Windows"

Research Paper No. 154, Division of Building Research, National

Research Council Canada, April 1962.

Ulrey, Harry F., Audels Architects and Builders Guide , Theodore

Audel and Co. Indianapolis, Ind., 1964.

4-15

4.3 REFLECTIVE GLASS/Shading

STRATEGY

:

Install glass with a reflective surface to reduce summer

solar heat gain.

PHENOMENA:

1) Solar energy striking a window is either reflected,

absorbed, or transmitted. By increasing the amount of

solar energy reflected, the amounts absorbed and transmitted are reduced. Solar energy absorbed in the glass,

or transmitted and absorbed within the building, becomes

heat. Reflective glass, by increasing the amount of

solar energy reflected at the window, therefore, reduces

the eventual air conditioning load within the building.

2) Reflective glass used as the outer sheet of insulating

glass is more effective at keeping out the sxin's heat

than reflective glass used as single glazing. This is

due to the fact that reflective glass absorbs more sunlight than clear glass and its temperature rises. When

this heat is concentrated in the outer sheet of insulating glass it is more easily dissipated to the outside

air, especially if there is a breeze. Additionally, the

trapped air space acts as insulation impeding the inward

flow of heat. The following table illustrates the

effectiveness of reflective glass used as single glazing

and as the outer sheet of insulating glass compared to

the performance of clear single and double glass.

(75,LOF,pl9)

TYPE OF GLASS

1/4" clear single

1/4" gray reflective single

1" clear insul.

1" gray reflec. insul.

VISIBLE TOTAL SHAD.

TRANSM. SOLAR COEFF.

TRANSM

.

88% 77% 0.93

34 36 0.60

77 59 0.79

30 29 0.47

4-17
3) The importance of the reflective coating or film occuring

on the outer sheet of insulating glass is illustrated in

the following figure. (73 ,LATTA,p60)

Incident Solar

Radiation

1/4" Plate Glass

^/^ReflectingN\

Incident Solar

Radiation^

1 /4" Plate Glass

Transmission 1 6%

['48% M \i

eradiat

Transmission 1 6%

_ _ 48% Reflection 14% ...

Absorption^v^ 1^22% Absorptionls^^

^„ Rera'diation and Convection Reradiation and Convection

Rejected Admitted

71% 29%

Rejected

78%

Admitted

22%

Figure 35. Effect of Film Location

on Heat-Gain

4) The use of certain types of reflective coatings on one of

the sheets of insulating glass can reduce the radiation

of heat across the air space and hence reduce winter heat

losses. The winter U-value of clear insulating glass

with a 1/2 inch air space is 0.58 versus as low as 0.28

for insulating glass with the outer sheet of reflective

glass. (76,PPG,pl5) (See STRATEGY: Applied Films.)

ADVANTAGES:

1) Reduced summer solar heat load.

2) Reduced likelihood of glare.

3) Reduced heat loss in the winter for certain types of

reflective glass.

DISADVANTAGES:

1) Decreased transmitted solar energy in the winter and

decreased daylight illumination year-round.

4-18
2) Care required to avoid scratching reflective coating when

washing windows. Reflective single glazing frequently

has the reflective coating on the inside surface of the

glass

.

3) Caution required in selecting a sealant to avoid problems

due to lack of bonding with reflective coating of the

glass. (Single glazing only.)

4) Increased replacement cost in the event of breakage by

vandals, storm damage, or other causes. (Also true for

insulating glass and heat-absorbing glass.)

5) Caution required in detailing the setting of reflective

glass to avoid thermal breakage. The higher solar

absorptivity of reflective glass compared to clear glass

results in higher surface temperatures, especially with

insulating glass. If the glass is installed in a massive

material such as concrete, the slowness of the concrete

to heat up in comparison to the glass when sunlit will

result in extreme center to edge temperature differences

and edge stresses in the glass. One means of reducing

these stresses is to seat the glass in a rubber gasket.

The rubber serves as an insulation which reduces the

conduction losses at the edge of the glass and allows the

edges to be closer to the temperature of the center areas

of glass. It is also extremely important that if glass

must be cut in the field, special provisions be taken to

insure a clean cut edge. (See Manufacturer's literature for

instructions on cutting glass)

AESTHETICS:

1) Because an outside viewer looks at reflective glass

rather than through it distortion is more critical than

is the case with clear glass. Trees and clouds, because

of their soft geometry is less problematic than reflection of adjacent buildings. Full scale mock-ups on the

site are worthwhile for studying the visual appearance of

reflective glass and whether distortion is bothersome or not. (77,Skolnik,p93)

2) A reflective glass building may create glare for the

occupants of adjacent buildings as well as pedestrians

and drivers.

4-19
3) Reflective glazing of isolated individual windows may

appear awkward. Reflective glazing tends to be more

visually effective in expanses, either as a series of

windows in continuous band, or a single large area.

4) Where the fenestration carries around a corner or occurs

on opposite sides of narrow parts of a building, such as elevator lobbies or bridging corridors, building the

transparency achieved with clear glass is not possible

with reflecting glass.

5) Reflective glass darkens the view out by virtue of the

reduction in light transmission. Colors may also tint

the view as in the case of bronze or other tinted reflective glasses. This darkening of the view and slight

tinting are not likely to be distracting unless a window

with clear glass is in the vicinity, or unless the coated

surface of the reflective glass is scratched.

COSTS:

EXAMPLE:

In the design of the Toledo Edison Building the architects,

along with the glass manufacturer, conducted a detailed computer

study of the effects of a variety of glasses on the buildings'

construction and operating costs. They selected a chromiumcoated, dual-wall insulating glass which increased the first

cost of the glass by $122,000 compared to conventional 1/4"

float glass (float glass has largely replaced plate glass)

.

However, offsetting this first cost of the glass was a savings

of $123,000 in initial costs for the heating and cooling

equipment and ductwork. (A 64.7 percent reduction in the

capacity of the central refrigeration system, a 53.2 percent

reduction in the capacity of the central heating equipment and

a 67.9 percent reduction in the capacity of the distribution

system.) Resulting energy consumption savings were calculated

to be 729.4 kilowatts per hour which translates to a savings

in yearly operating cost of approximately $40,000. (73,NBS,p84)

REFERENCES:

American Society of Heating, Refrigerating & Air Conditioning

Engineers, ASHRAE Handbook of Fundamentals , ASHRAE Inc., N. Y.,

1974.

4-20
C-E Glass, "C-E Glass", Combustion Engineering, Inc., Pennsauken,

N. J., 1975.

Latta, J. K. Walls, Windows and Roofs for the Canadian Climate,

Division of Building Research, Ottawa, Canada, 1973.

LOF, "Glass for Construction", Libbey-Owens Ford, Toledo, Ohio,

1975.

Kusuda, T. and Ishii, K. Hourly Solar Reduction Data for the

Average Days National Bureau of Standards, Wash., D. C, 1976.

NBS, "Technical Options for Energy Conservation Buildings." NBS

Tech. Note 789 National Bureau of Standards, Wash., D. C, 1973.

PA, "Technics: High-performance Glass", Progressive Architecture , Reinhold Publications, Stamford, Conn., June 1976.

PPG Industries, Inc., "Architectural Glass Projects", PPG Industries,

Inc., Pittsburgh, Pa., 1976.

Skolnik, Alvin D., "Aesthetic Evaluation of Glass", Progressive

Architecture , Reinhold Publishing Co., Stamford, Conn., Jan.

1977.

4-21

4.4 APPLIED FILMS/Shading, Insulation

STRATEGY:

Apply a reflective or low-emissivity film to the inside surface

of glass to reflect sunlight back out a window but let the view

in.

PHENOMENA:

1) Metalic oxides deposited on transparent plastic films are available which reflect much of the incoming solar energy

while still permitting a view out. The shading coefficient

of such reflective films can be as low as approximately

0.24.

2) Other types of film coatings are available which increase

the window's reflectivity of room temperature infrared heat

while only minimally reducing the window's transparency to

the beneficial incoming solar energy. The net effect of

such "low-emissivity" films is a reduction in the winter Uvalue of the window from 1.13 to as low as 0.74. (75,

Berman, p61)

3) Solar reflective films and to a lesser extent low-emissivity

films have the disadvantage of reducing the beneficial

aspect of incoming solar energy in the winter. The following

table illustrates the seasonal benefit (+) or detriment (-)

of single glazing compared to glazing with applied lowemissivity or reflective films in a southern and northern

city. (75,Berman,p64)

WINDOW ENERGY DEMAND BY ORIENTATION (KBTU/SQ. FT. )

CITY NORTH EAST SOUTH WEST

Wntr Sumr Wntr Sumr Wntr Sumr Wntr Sumi

Dallas

No Film -24 -95 +26 -156 +102 -118 +26 -185

Low-emissivity -7 -80 +35 -135 +107 -101 +38 -161

Reflective -46 -41 -33 -56 -14 -46 -33 -63

New York

No Film -84 -43 -38 -76 +29 -59 -38 -81

Low-emissivity -43 -39 -2 -68 +58 -53 -2 -73

Reflective -105 -11 -93 -19 -76 -15 -93 -20

4-23
4) From the table in the previous paragraph it is evident

that the annual energy effectiveness of low-emissivity

or reflective films will be very dependent on whether air

conditioning or heating is dominant, and which direction

a window faces

.

Due to the dominance of air conditioning in Dallas reflective films conserve energy on north, east, and westfacing windows while in New York may be are only minimally

conserving for these orientations. In both Dallas and

New York reflective films would appear to result in

increased energy consumption when applied to south-facing

windows

.

Low-emissivity films appear to be more energy conserving

than no film or reflective film only on south-facing

windows in Dallas but on all exposures in New York.

ADVANTAGES:

1) Reduced summer solar heat gain with reflective films

.

2) Reduced glare without obscuring view.

3) Can be applied to existing windows.

4) Reduced fabric fading.

5) Reduced winter heat loss with "low-emissivity" films.

6) May hold glass together in event of shattering

thickness adequate)

.

(if film

DISADVANTAGES:

1) Reduced benefit of daylight and solar heat gain in winter

with reflective and to lesser extent selective films.

2) Replacement of film is costly, difficult, and likely to

be required after nine to twelve years.

3) Additional care required in washing to avoid scratching

surface of films which are softer than glass.

4) Reduced effectiveness of selective coatings when applied

to single glazing because the need for abrasion resistance

necessitates a protective coating over the selective

coating

.

4-24
5) Possible cause of breakage when installed as a retrofit

item. (See disadvantages listed under Strategy:

Reflective Glass)

AESTHETICS:

1) Reflective films require the same aesthetic judgment as discussed in the strategy: "Reflective Glass".

2) Selective films may impart a slight tint to the outside

view.

COSTS:

1) Reflective films cost approximately $0.40 to 0.50 per

square foot depending on the properties and quantity

specified. Installation ranges from $0.70 to 0.90 on the same basis. (75,GSC,p9)

2) Low-emissivity films have not been used as widely in

window applications but the product is commercially

available. A polyester film with a gold coating is one potentially effective product currently marketed by at

least two manufacturers for other uses. The price is

approximately $1.20/square foot. (76 , Sierracin,pl)

(76 ,Levy , telephone)

EXAMPLES:

1) A reflective film applied to windows in an office building

in Silver Spring, Maryland resulted in a 50 percent

reduction in the air conditioning load. The average air

conditioner operation cycle was reduced for 24 hours per

day during peak summer periods to 12 hours per day.

Winter heat loss reductions were also observed but not

quantified. (75, Groves)

2) A five mil, polyester film with a coating of gold is

currently available which transmits up to 80 percent of

the visible light but reflects over 95 percent of room temperature heat back into the room. The material is

currently being marketed for space suit visers and ski

goggles. (76 , Sierracin)

4-25
REFERENCES

:

Berman, Samuel M., "Energy Conservation and Window Systems", PB243-117, National Technical Information Service, Springfield,

Va., Jan. 1975.

Cellarosi, Mario, telephone conversations. Physical Properties of

Glass Section, National Bureau of Standards, Washington, D. C,

Dec. 10, 1976.

F.E.A., UCAN Manual of Conservation Measures , Conservation Paper

Nr. 35, Federal Energy Administration, Washington, D. C, Nov.

1975.

GSC, "Solar Master Controls Heat, Glare & Fade", General Solar

Corp., Rockville, Md., 1975.

Groves, Roy L., Letter to General Solar Corp. Rockville, Md., L. L.

Rust Co., Washington, D. C, May 1, 1975.

Levy, Donald, telephone conversation about "Lockspray-Gold", Lockheed

Corp., Palo Alto, Cal., Dec. 13, 1976.

Levy, D. J., "The Lockspray-Gold Process, A technical Bulletin",

Lockheed Palo Alto Research Laboratory, Palo Alto, Cal., April,

1966.

Levy, D. J. and Momyer, W. R., "Spray Deposition of Low Emittance

Gold Thermal Control Coatings", SAMPE Journal , Society for

Advancement of Material & Process Engineering Inc., Azusa, Cal.,

Apr/May 1969.

Sierracin, "Sierracin Intrex, Electrically Conductive Film Components",

Sierracin Corp., Sylmar, Cal., 1976.

4-26
4.5 REDUCED GLAZING/lnsulation, Shading

STRATEGY:

Reduce the glass area in the wall opening by substituting an insulating panel in a portion of the window.

PHENOMENA:

1) Single glazing has a U-value of 1.13, double glazing

approximately 0.58, and opaque, insulated panels as low

as 0.10. (76,PPG,pl8) By replacing part of the glass

with an opaque, insulated panel the outward flow of heat

in the winter is reduced. Also, air conditioning costs

may be lowered due to the reduced admittance of sunlight.

2) The benefit of reduced outward heat flow must be compared

against the loss of beneficial winter solar heat and

beneficial day lighting. Opaque, insulated panels might

be beneficial on north-facing windows but detrimental on south-facing windows. Climate and orientation are important factors.

3) Opaque, insulated panels are commonly installed in the

upper section (s) of windows. The high portion of a window provides the deepest penetration of daylight into

a room. Thus, the panels not only reduce the amount of

glass area admitting daylight but also reduce the depth

the daylight penetrates into a room. Heat loss reductions must, consequently, be considered against the

possible additional cost of continuous as opposed to

periodic use of electric lighting.

ADVANTAGES:

1) Reduced heat loss in winter, sunlight transmission in summer

.

2) Reduced window area to wash and maintain.

DISADVANTAGES

:

1) Reduced winter solar heat gain.

4-27
2) Reduced amount and penetration of daylight.

3) Possible loss of means of egress during fire.

AESTHETICS:

1) Reduced view of outside. The sky portion of the view is

cut when panels are installed in upper window sections.

2) Introduces another material to the facade.

3) Changes the perceived proportion of windows.

COSTS:

An insulated, opaque panel consisting of a sheet of heat

strengthened glass with a ceramic color fused to the rear

surface, and backed with one-inch fiber glass insulation and a foil vapor barrier cost approximately the same as clear double

glazing. Aluminum or enameled steel clad panels cost approximately 30 percent less than clear insulating glass. (76,

Hiltman)

EXAMPLE:

A school in Big Fork, Minnesota was expanded from 47,000 to

63,370 square feet and new windows were installed in both the

new wing and throughout the original building . The new window

units consisted of a reduced glass area glazed with insulating

glass and an insulated porcelain panel in the top portion of

the window. As a result of the installation of the new windows,

the total cost to heat the 63,370 square feet with new windows

is lower than the cost of heating the original 47,000 square

feet of school with old windows. (74 , Sandstrom,p58) The

following photograph shows the new window system with insulating,

opaque panels in the upper portion of the window. (76,Devac,p4)

4-28
Devac, Inc., 10130 State Highway 55, Minneapolis, MN 55441

Further analysis is required to separate the savings realized

by the insulated porcelain panels from the savings accrued

from the more air-tight frames and double glazing. However,

the frequency of outside temperatures of minus 20°F and below

in Big Fork, Minnesota suggest that the conduction losses of

the glass are not offset by solar heat gains and therefore,

the insulating panels used to reduce glass area contribute to

the lower operating costs of this particular school. In less severe climates orientation is likely to be a critical determinant of energy savings or even losses realized from replacing

glass with opaque insulating panels.

REFERENCES

:

Devac, "Devac Windows Cut This Buildings Fuel Bill 34 Percent",

Devac Window Co., Minneapolis, Minn.

4-29
Hiltman, Michael., telephone conversation, Stolle Corp., Sydney,

Ohio, Dec. 9, 1976.

PPG, "Architectural Glass Products", PPG Industries, Inc., Pittsburgh, Pa., January, 1976.

Sandstrom, Harvey E., "Replacement Windows Help Reduce Fuel Bills

34 Percent", American School & University , North American

Publishing Co., Philadelphia, Pa., February, 1974.

4-30
4.6 GLASS BLOCK/lnsulation, Solar Heating, Daylighting

STRATEGY

:

Install glass block to admit sunlight and daylight with

minimal building heat loss.

PHENOMENA:

1) Glass blocks are hollow, masonry units molded in two

halves which are then fused together at a high temperature. When cooled, the permanently sealed air becomes

exceptionally dry preventing condensate from forming

within the cavity. This air space results in glass

blocks having a low U-value, yet admitting approximately

50 to 60 percent of the incident solar energy including

78 to 84 percent of the visible light. (64,Ulrey ,pl75)

2) The larger the block face dimensions the lower the Uvalue is. This is due to the fact that the larger size

requires the use of fewer blocks for a given area. Heat

loss is greatest at the edges of a block because the

glass bridges the air space. The following U-values show

how larger glass blocks provide better insulation:

(75,PC,plO)

NOMINAL SIZE U-VALUE U-VALUE

(single cavity) (double cavity)

4 X 12 inch 0.60 0.52

6 inch sq. 0.60

8 inch sq. 0.56 0.48

12 inch sq. 0.52 0.44

Note that glass blocks are available with double cavities

with the same overall block depth - usually a nominal

four inches.

3) The greater mass of glass block compared to window glass

results in a lag in time between when the sun first falls

on the block and when the room temperature rises. The

heat gain for west-facing glass block windows is conse4-31
quently delayed in the morning and conversely, the heat

gain of east-facing glass block windows will be elevated

in the afternoon. To approximate this lag the solar heat

gain factor from the previous rather than the current

hour can be used in calculating heat gain. This product

plus the heat gain or loss through the block (U-value

multiplied by the inside/outside temperature difference)

equals the net heat gain or loss. (74,ASHRAE,p487)

The shading coefficient of glass block can be lowered by

contouring the glass surface (s) and/or by fusing various

types of inserts between the two halves before they are joined in the manufacturing process.

The following table illustrates the effectiveness of

several means of reducting the shading coefficients for

nominal 8x8 inch glass blocks. Multiply the coefficients by 1.15 for 12 x 12 inch blocks or by 0.85 for 6 x

6 inch glass blocks. (74,ASHRAE,p408)

TYPE SHADING COEFFICIENT

(Window glass)

Clear block

EXPOSED TO

SUN

1.00

0.65

SHADED SHADED

N, NW, W, SW NE. E, SE

0.40 0.60

Clear with glass

fiber insert 0.44 0.34 0.51

Contoured outer

surfaces

Prismatic inside

surfaces and

glass fiber insert

0.33 0.27 0.41

Same as above plus

Ceramic coating on insert or gray glass

used for block or prismatic glass fiber

insert

.

0.25 0.18 0.27

Note: Shading glass block windows from direct sunlight

substantially reduces heat gain. By providing roof

overhangs calculated to obstruct the summer sun and admit

the winter sun, glass block can be used to the best

thermal advantage.

4-32
5) Glare from glass blocks can be reduced with various types

of inserts. White opal glass is an example of a glare

reducing insert which has the additional benefit of

making the block a more uniform brightness. Glare can also be reduced by pressing a grid surface into the glass

to diffuse the light.

6) Penetration of light into a room can be increased by

casting the inside surfaces of the glass blocks in a prism configuration to direct the light up onto a reflective ceiling. (64 ,Ulrey ,pl77)

7) Operating glass units can be composed into glass block

panels to provide ventilation.

ADVANTAGES

:

1) Solar heat gain and daylighting with greatly reduced heat

loss compared to single glazed windows.

2) Control of direction of incoming light with potential to

increase penetration into rooms with prism surface blocks.

3) Reduced glare with use of inserts or diffusing surface

treatment of block.

4) Privacy with diffusing or glare reducing glass blocks.

5) Reduced sound transmission ranging from 35.3 db at 128

cycles per second to 47.5 db at 2048 cycles per second.

(64,Ulrey,pl75)

6) Vandal resistant. Projectiles which would shatter window

glass are deflected by glass block.

7) Forced entry greatly impeded.

8) Fire rated at up to 1 1/2 hours depending upon block

type. (75,PC,p8)

DISADVANTAGES:

1) Possible Summer or even Spring and Fall overheating of rooms with large expanses of unshaded glass block and

inadequate provision for natural ventilation.

4-33
2) Distortion or elimination of view out with most glass

block types.

3) Elimination of security surveillance of building interior

through glass block windows.

AESTHETICS:

1) Glass block are available in clear units affording only

slight distortion to view, and in a variety of patterns

which can be combined and arranged in an almost endless

number of compositions.

2) Diffusing blocks effectively increase the ambient light

level of a room.

3) The joints of glass block impart a grid effect to the

fenestration. The scale of the ^rid can be adjusted by

the size and proportion of the block,

COSTS:

The following are a sample of the price of delivered clear

glass block:

SIZE UNIT COST SQ. FT. COST

6x6 $1.75 $7.00

8x8 2.25 5.06

12 X 12 4.50 4.50

EXAMPLES;

1) The following two examples illustrate the light penetration with glass block on a south exposure compared to

glass block on both a south and north exposures 90 feet

apart. Both cases are for 40 degrees N. latitude at 10 a.m. and 2 p.m. on March 21. (66 , lES ,p7-ll)

4-34
12'-0'

3'-

Ceiling Reflectance — 70%

Light

Directional Block

12'-0"

Light

Diffusi Blockng Working Plane

Floor Reflectance — 15%

500 r

400

300 h

200

100

80

60

50

40

30

% 20

10

8

6

5

4

3

2

1 J. J_

3'-4"

3'-0" i_

Light

Directional Block

Light

Diffusing

Block

Ceiling Reflectance

-5^

•70%

4

Working Plane

500

«400

1

Floor Reflectance -15%

1 I

X J I I I 0 10 20 30 40 50 60 70 80

Distance from Fenestration (Feet)

0 10 20 30 40 50 60 70 80 90

Distrance from South Fenestration (Feet)

Figure 36. Glass Block on One Exposure vs. Two Exposures

2) Glass block is effective on north exposures to increase

the ambient light level of a room while providing a fairly low U-value for heat loss. The following illustration shows the use of glass block to increase the

light level of a room and reduce glare from clear glass

windows. (75,PC,pl5)

4-35
Gwathmey Siegel, 154 W 57th St., N.Y. 10019

REFERENCES:

ASHRAE, ASHRAE Handbook of FundaTnentals , American Society of

Heating, Refrigeration, and Air Conditioning Engineers, Inc.,

New York, 1974.

Boyd, Robert Allen, "The Development of Prismatic Glass Block and

the Daylighting Laboratory", Engineering Research Bulletin Nr.

32 , University of Michigan, Ann Arbor, Mich., 1951.

Holton, John K. , "Daylighting of Buildings - A Compendium and Study

of Its Introduction and Control." NBSIR 76-1098, National

Bureau of Standards, Washington, D. C, 1976.

lES, lES Lighting Handbook , Illuminating Engineers Society, New

York, 1966.

P.C., "Glass Block - Decorative and Functional Units for New

Construction and Remodeling", Pittsburgh Corning Corp., Pitts

burgh. Pa. , Dec. 1975.

Smith, W. A., and Pennington, C. W. "Shading Coefficients for Glass

Block Panels", ASHRAE Journal , ASHRAE Inc., New York, N. Y.,

Dec. 1964.

Ulrey, Harry F,, Architect's and Builder's Guide , T. Audel Co.,

Indianapolis, Ind., 1964.

4-36
4.7 THRU-GLASS VENTILATORS/Ventilation

STRATEGY

:

Install a transparent wind-driven rotor with a closable louver

in a hole cut in a fixed glass window to provide controlled

ventilation.

PHENOMENA:

The transparent rotor spins admitting or exhausting air into

or out of a room as a result of air pressure differences

between the inside and outside. Operable louvers allow the

air flow to be stopped entirely when ventilation is not

desired

.

ADVANTAGES

:

1) Ventilation possible with fixed glass windows.

2) Reduction of strong sudden drafts during gusty winds.

3) Security. A six or eight inch diameter hole in a fixed

glass window limits the size of burglars who can gain

entrance.

DISADVANTAGES:

1) Minimal natural ventilation compared to operable windows

or even compared to an equal diameter unobstructed hole

cut in the glass

.

2) Cannot be installed in factory sealed double or tripple

glazed windows, nor in existing tempered glass windows by

the homeowner or contractor in the field.

AESTHETICS:

A transparent rotor unit interferess with the view compared to an uninterrupted expanse of glass. However, the opening,

small as it is, provides a strong contact with the outside in

4-37
terms of admitting the "smell" of fresh air and the sounds of

the outdoors. These qualities are largely lost with normal

fixed glass windows.

COSTS:

The retail cost of a thru-glass ventilator varies with its

size: approximately $7.00 for an 8 inch unit, $5.75 for a 6-

1/2 inch unit, and $3.50 for a 5 inch unit. (Prices do not

include shipping.) Installation entails simply scribing and

tapping out a round hole in the glass. Units are available

which lock into place without screws.

EXAMPLES

:

The following photograph illustrates" one model of a thru-glass

ventilator. (76 , Simon, pi)

George Roach Co., 8010 24th Ave. NW, Seattle, WA 98107

REFERENCES

:

Simon Ltd., "It Runs on Air", George W. Roach Co., Seattle, Wash.,

1976.

4-38
INTERIOR

ACCESSORIES

VENETIAN BLINDS

DRAPERIES

FILM SHADES

OPAQUE ROLL SHADES

INSULATING SHUTTERS
5. INTERIOR ACCESSORIES

The principal advantage of energy-conserving interior accessories

is their accessibility and hence ease of management as outside

conditions change or as the use of the interior changes.

Interior accessories such as draperies, roll shades, and Venetian

blinds are effective in reducing heat gain in the summer as

well as reducing heat loss in the winter. The principal disadvantage of interior accessories is the fact that in reducing

heat gain, the heat absorbed in the device is radiated into the

building interior. Also, interior accessories when being used

for shading may limit the opening of in-swing windows when

shading and ventilation are desired. In reducing heat loss, if

the device does not effectively trap air between itself and the

window, the insulative value is minimal. However, if it is

initially installed to provide tight closure and it is subsequently used conscientiously, an interior accessory can greatly

improve the performance of a window.

5-0
5.1 VENETIAN BLINDS/Shading, Daylighting

STRATEGY:

Install Venetian blinds to reflect the suiraner sun back out the

window, or to direct daylight to the ceiling for deeper light

penetration into a room.

1) Slatted horizontal or vertical blinds can be tilted to

provide maximum reflection of sunlight back out the window

in the summer. At a 45 degree tilt with sunlight perpendicular to the slats, blinds have the following properties:

(74,ASHRAE,p403)

PHENOMENA:

Properties of Venetian Blinds

TYPE TRANS. REEL. ABSORBED

.

Light-Colored Horizontal

Medium-Colored Horizontal

White (closed) Vertical

0.05

0.05

0.00

0.55

0.35

0.77

0.40

0.60

0.23

These characteristics translate into the following shading

coefficients for blinds in conjunction with different

glazing types: (74,ASHRAE,p402)
SHADING COEFFICIENTS OF VENETIAN BLINDS

TYPE OF

GLASS

Single

Single

Single

Double

Double

Double

Clear

Heat-AB

Refl.-*-

SC=0.30

=0.40

=0.50

=0.60

Clear

Heat-AB"^

Reflective

SC=0.20

=0.30

=0.40

NOTES;

SOLAR TRANS

OF GLASS

0.87

0.46

MEDIUM

HORIZONTAL

0.64

0.57

0.25

0.33

0.42

0.50

0.57

0.39

0.19

0.27

0.34

LIGHT

HORIZONTAL

0.55

0.53

0.23

0.29

0.38

0.44

0.51

0.36

0.18

0.26

0.33

WHITE

vertical'

0.29

0.25

0.22

1) Shading coefficients (SC) under the reflective glass

column indicate the performance of the glass without

interior shading for the purpose of identifying glass

types

.

2) White vertical blind performance is rated for tightly

closed blinds in conjunction with glass having a solar transmittance between 0.71 and 0.80.

3) Heat absorbing glass for outer sheet of glass, clear

glass for inner sheet of glass.

5-2
2) Venetian blinds are an effective means of variably controlling the amount of daylight admitted into a room. The

slats can be adjusted to block all direct beam sunlight

while admitting diffuse daylight. With a light-colored

ceiling, the slats can even be tilted to reflect part of

the direct beam sunlight up to the ceiling where it can be

reflected back down to work surfaces. The amount of light

transmitted to the work surface is greatly diminished in

the process but glare is eliminated. Automated control

systems are available to adjust the tilt and even raise

and lower the blinds as the outdoor light level varies.

(See AUTOMATIC SWITCHING /Daylight ing)

ADVANTAGES:

1) Minimal space used to store blinds when open and they

stack with a minimal obstruction of the window area.

2) Can be selectively tilted to direct daylight to the ceiling

or directly onto the work surface.

3) Can be partially lowered to eliminate sunlight from only a portion of a room.

DISADVANTAGES:

1) Cleaning tedius.

2) Maintenance of lifting and tilting hardware and cord

replacement

.

3) Decreased effectiveness in reducing winter heat loss

compared to shades or tight-fitting drapes due to cracks

between each slat.

COSTS:

The following are a few sample retail prices for vertical

Venetian blinds in the Washington, D. C. area for several

widths and lengths.

5-3
NARROW CONVENTIONAL VERTICAL

SLAT 1" SLAT 2" BLIND

36 W X 60 H 51.72 18.75 43.00 - 53.00

36 W X 84 H 66.80 26.25 51.00 - 64.50

72 w X 60 H 94.04 37.50 75.50 - 94.00

72 w X 84 H 122.36 52.50 90.00 - 116.50

EXAMPLES

:

A study by Arthur Rosenfeld and Stephen Selkowitz proposes the use of reflective Venetian blinds in conjunction with clerestory

windows to increase the usefulness of beam sunlight in providing

illumination. The light entering through high windows is

reflected by the blinds up to the ceiling then down to the work

surface. It is believed that such a system could provide

adequate illumination throughout much of the year. Efficiency

could be further improved by coupling the blinds with electric

lighting controls. (See Strategy, Automatic Switching.)

The payback period for such a system is illustrated with

calculations for a small office of 150 square feet with a 12

foot wide south exposure. A clerestory window the full width

of the office would accommodate 12 square feet of beam daylighting blinds. The clerestory with blinds would deliver an average of 100 lumens per square foot for eight hours on average clear days. Assuming that daylighting could be utilized

80 percent of the occupied hours and the sun shined 65 percent

of the time, beam daylight would be viable for 50 percent of

the 2,000 annual working hours. (80% x 65%). Assuming 2W/sq.

ft, for electric lighting the lighting load is 300W for the

office of 150 sq. ft. If the clerestory-blind system provided

adequate illumination for half the time, this would then represent a saving of 300 KWH/per year or at 3c/KWH, $9.00/year.

(50 percent of 2,000 hrs x 300W) . If the utility company has

peak period billing, the savings occur during the peak period

and the dollar savings might then be $13 /year. A timed light

5-4
switch is assumed to pay for itself in approximately a year

from night and weekend savings. Reflection blind might cost

$2.00 per square foot or $24. The payback period for the

system is therefore $24/$13 per year or slightly less than two

years. (76 ,Dean,p46)

REFERENCES

:

ASHRAE, ASHRAE Handbook of Fundamentals , ASHRAE Inc., New York,

N. Y., 1974.

Alcan, "Aluminum Window Blinds for Solar and Light-Control", Alcan

Building Products, South Kearny, N. J., 1976.

Avery, "Sundrape Vertical Blind", J. Avery & Co. Ltd., 82-90 Queensland Road, Holloway, London. N7 7AW, April 1976.

Dean, Edward and Rosenfeld, Arthur, Efficient Use of Energy in

Buildings , LBL 441, Lawrence Berkeley Laboratories, Berkeley,

Calif. , 1976.

Dix, Rollin C, and Zalman, Lavan, "Window Shades and Energy Conser

vation". Illinois Institute of Technology, Chicago, 111., Dec.

1974.

Levolor, "Window Magic", Levolor Lorentien Inc. Hoboken, N. J.,

1976.

Marathon Carey-McFall , "Bali-Architect Venetian Blinds", Marathon

Carey-McFall Co., Philadelphia, Pa., 1974.

Stephenson, D. G. and Mitalas, G. P., "Solar Transmission through

Windows with Venetian Blinds", Research Paper No. 310, Division

of Building Research, National Research Council, Ottawa, Canada,

April 1967.

5-5

5.2 DRAPERIES/Shading, Insulation

STRATEGY:

Install draperies sealed against the wall or window frame at

the sides and extending down in contact with the floor or window sill to insulate the window in the winter and provide

shade in the summer.

PHENOMENA:

1) Heat loss through windows with tight fitting closed

draperies is substantially reduced compared to the heat

loss of an uncovered window. The effectiveness of a closed drapery as an insulator is greatly impaired if

conditioned air is free to circulate between the drapery

and the window. When room air comes in contact with the

cold glass, it is cooled and cascades back into the room

at the bottom of the drapery. Under such conditions, the

winter U-value of a single glazed window is only reduced

from 1.13 to 1.06. (74 ,Dix,pl3) . By contrast, the winter

U-value of a tight-fitting, tight-weave closed drapery and

single glazed window can be assumed to be as low as 0.88.

(calculated from 74 ,ASHRAE,p395)

2) In the winter the draperies should be opened when the

window is sunlit to allow the sunlight to penetrate into

the room, warming more massive materials and remote

surfaces. The heat will then radiate to other interior

surfaces rather than directly back to the glass. The

drapery track should extend a sufficient distance to

either side of the window to permit the draperies to stack

clear of the window to allow all the sunlight to penetrate

into the room.

3) Comfort near windows with drawn draperies will be improved

compared to uncovered windows . This is due to the draperies

being much closer to room temperature than the glass with

a corresponding reduction in body heat loss by radiation.

Tight-weave fabrics are more effective for improving

comfort

.

5-7
Summer heat gain can be reduced with draperies. The

effectiveness of the drapery is mainly determined by three

factors: the amount of incoming solar energy reflected

back at the glass, the amount of solar energy absorbed by

the fabric, and the amount of solar energy transmitted

through the fabric and through the openings of the weave.

To a lesser extent, the insulation value of the drapery

also affects how much outdoor heat is added to the air

conditioning load. For single glazed windows with tight

fitting draperies, the summer U-value can be as low as 0.81 compared to 1,06 for the uncovered window. (74,

ASHRA.E,p395) The shading coefficient of single glazed

windows (1/4" plate) with draperies ranges from 0.80 down

to 0.35, the low value representing a highly reflective

tightly woven drapery material. (74,ASHRAE,p405) . The

window heat gain can be calculated by adding the solar

heat gain and the conducted heat gain. The solar heat

gain equals the amount of solar energy transmitted plus

the amount of solar energy absorbed by the configuration

and dissipated into the building interior. The conducted

heat gain equals the U-value multiplied by the inside

outside temperature difference. (See 74 ,ASHRAE,p388)

The use of tight fitting draperies with insulating glass even further reduces the summer U-value as shown below:

(74,ASHRAE,p395)

DOUBLE GLASS WITH INTERIOR

(width of air space) NO SHADING SHADING

single glazing 1.06 0.81

3/16" air space 0.66 0.54

1/4" air space 0.65 0.52

1/2" air space 0.59 0.48

The use of double draperies, two layers of draperies

separated by an air space, further improves the thermal

performance of windows. A summer U-value of 0.65 is

possible for single glazed windows assuming the same degree of air tightness for both layers of trapped air.

Assuming a better degree of air tightness between the two

layers of drapery than between the drapery and the window

results in the even lower calculated U-value of 0.57.

(Pennington, p2)
7) Draperies should be installed such that conditioned air

blows on the room side of the drapery and not between the

drapery and the window. Where the register is directly

below or above the window, retrofit deflectors are readily

available which divert the air into the room rather than

up or down the window surface.

ADVANTAGES

:

1) Decreased winter heat loss and summer heat gain.

2) Improved comfort near window possible when draperies

closed.

3) Glare control.

4) Privacy

5) Noise absorption. Noise within a room is absorbed by

draperies rather than reflected as from uncovered glass.

Also, outside noise transmitted through the glass is

partially absorbed. The denser the weave and heavier the

drapery, the more effective it is in reducing noise

transmission. The following graph illustrates the effect

of the openness of the weave on sound reduction. (74,

ASHRAE,p406)

0 10 20 30 40

Openness Factor of Fabric (Percent)

Figure 37 Drapery Type vs. Noise

Reduction
DISADVANTAGES:

1) Periodic cleaning required.

2) Obstruction of view when closed.

3) Possible breakage of glass when used in conjunction with

heat-absorbing glass. (Also true for any reflective

interior shading device.) The glass and the way it is set

should be designed to withstand the additional heat-buildup from sunlight being reflected back at the glass from

the closed drapery.

AESTHETICS:

The desire for an airy open weave drapery conflicts with the

thermal effectiveness of draperies both summer and winter.

COSTS:

The price ranges largely with the cost of the fabric. A ready-

- made drapery can range in price from $0.85 to $1.50 per square

foot. Custom made draperies may range much higher in price.

The traverse rod is frequently available in various length

increments which are expandable to any size up to the next size

increment. A 12 to 15 foot traverse rod can range from $12 to

$18.

EXAMPLES:

A series of tests were conducted by the Illinois Institute of

Technology to determine the percentage of energy that could be

saved by using shades, drapery, or Venetian blinds. The tests

were conducted in two rooms with a window mounted between them.

One room had its temperature varied from 20 to 50°F (-6.7 to

10°C) for winter test and from 85 to 95°F (29.4 to 35°C) for summer test. The other room was maintained at 75°F (23.9°C).

Solar radiation levels typical of the mid-west were introduced

using heat lamps for the summer test. All cracks were sealed

5-10
around the window to prevent infiltration. The draperies were

hung two Inches out from the wall so they completely covered

the window opening. The study concluded that a medium colored

drapery with a white plastic backing reduced conducted heat

loss in the winter by 6 to 7% (74,Dix,pii) and conductive and

radiant heat gains in the summer by 33% (74,Dix,p21)

REFERENCES

:

ASHRAE, ASHRAE Handbook of Fundamentals , American Society of Heating,

Refrigeration, and Air Conditioning Engineers, New York, 1974.

Dix, Rollin C. and Zalman, Lawan, "Window Shades and Energy Conservation", Mechanics Mechanical and Aerospace Engineering Dept.,

Illinois Institute of Technology, Chicago, 111., Dec. 1974.

Keys, M. W. "Analysis and Rating of Drapery Materials Used for

Indoor Shading", ASHRAE Transactions , Vol. 73, Part I, ASHRAE

Inc., New York, N. Y., 1967.

Morrison, Clayton A. et.al, "An Experimental Determination of Shading

Coefficients for Selected Insulating Reflective Glasses and

Draperies", No. 2382 R132, Mechanical Engineering Dept., University

of Florida, Gainesville, Fla., undated.

Ozisik, N. and Schutrum, L. F., "Solar Heat Gain Factors for Windows

with Drapes", ASHRAE Transactions . Vol. 66, ASHRAE Inc., New

York, N. Y., 1960.

PA, "Window Coverings", Progressive Architecture , Reinhold Publishing

Co., Stamford, Conn., Nov. 1966.

Pennington, C. W. , et.al, "Experimental Analysis of Solar Heat Gain

Through Insulating Glass with Indoor Shading", ASHRAE Journal , ASHRAE Inc., New York, N. Y., Feb. 1964.

Pennington, C. W. , et.al, "Analysis of Double Drape Fenestration

Configurations", Dept. of Mechanical Engineering, Univ. of

Florida, Gainesville, Fla.

PPG, "The Feneshield System", PPG Industries, Pittsburgh, Pa., Jan.

1974.

Yellott, J. I., "Drapery Fabrics and Their Effectiveness in Sun

Control", ASHRAE Transactions , Vol. 71, Part 1, ASHRAE Inc., New

York, N. Y., 1965.

5-11

5.3 FILM SHADES/lnsulation, Solar Heating, Shading

STRATEGY:

Install clear or coated transparent film shades—singly or in

separated multiple layers and sealed at the sides and bottom to

provide insulation, improved air tightness, solar heating,

and /or shad ing

.

PHENOMENA:

1) A roll shade sealed against the perimeter of a window

frame will create an insulating layer of air. This effect

can be multiplied by providing several consecutive layers

of shades and air spaces. One such system is reported to

provide a U-value for the window of 0.55 with one shade

pulled down, 0.31 with two shades pulled down, and 0.18

with three shades pulled down. ( 76,Insealshaid,p4)

2) A roll shade sealed at the edges also impedes infiltration.

3) A heat-absorbing film shade in sunlight can have a surface

temperature above room temperature and thereby provide a warm radiant surface improving comfort.

4) A low-emissivity film shade can reduce the window's absorption of heat radiated from interior wall surfaces, furniture,

and people. This can result in a heat-loss reduction of

57 to 64 percent from single glazed windows without a shade. (75 ,Dahlen, "Summary" p 2)

5) A reflective film shade can reflect as much as 60 percent

of the incoming sunlight back out through the window.

(76 , Joanna, p2)

6) A selective transmissivity film shade can transmit 75

percent of the visible light but only 55 percent of the

total solar radiation. This allows usable daylight to

enter but blocks much of the invisible radiation, thereby

reducing heat gain. (7 6, Doyle)

5-13
ADVANTAGES

:

1) Reduced summer solar heat gain and winter night losses

with a reflective or selective film, singly or in com- bination with clear film.

2) Reduced winter heat loss with shade configurations which

provide insulating, trapped-air space (s).

3) Reduced Infiltration provided by obstructing flow of

incoming air with a film shade sealed at the edges.

4) Increased comfort near windows because less body heat is

radiated to an inside film shade than to a cold window.

5) Elimination, with a heat-absorbing film, of ultra-violet

radiation and its resulting fading of carpets and furniture.

6) Reduced sky glare with heat-absorbing films.

7) Night visibility into building for security surveillance,

(e.g., shops, schools, or banks).

8) Daytime privacy with reflective film shades.

9) Self-storing when not in use.

DISADVANTAGES:

1) Required management of shade by occupants of building.

2) Difficult to install on other than right angled window

areas

.

3) Lack of glare control from direct sunlight.

4) Lack of privacy with clear shades or reflective shades at

night

.

5) Reduced winter solar heat gain through low emissivity film

shades installed to reduce heat losses. Calculation of

the net heat gain or loss for a given location may suggest

that low emissivity film shades are effective on north,

east, and west orientations and transparent uncoated film

shades are effective on south orientations.

5-14
AESTHETICS:

Film shades may become unattractive after several years due to

scratches and wrinkles, especial at the edge of the shade.

However, replacement of the film is substantially less expensive than the initial installation of the complete system.

A light filtering or reflective film shade mounted on a roller

costs approximately:

3 X 5 ft. window $32.50 ($2.16/sq.ft,)

5 X 6/8 patio door $57.50 = ($1.72/sq.ft.)

The estimated installed cost for single-layer shade system of

either a clear or a reflecting film with a magnetic edge seal

is:

$1.50/sq.ft. on large job (e.g., 100 windows)

$2.00/sq.ft. on small job (e.g., 10 windows)

It may be possible to develop a do-it-yourself magnetically

sealed shade system for the homeowner at a cost of less than

$1.00 per square foot.

The estimated installed cost of a multiple shade system con- sisting of clear film, heat-absorbing film, and reflective film

with sealed edges and automatic venting is:

$4.00/sq.ft. for large windows

$6.00/sq.ft. for small windows

COST:

Delivered Film Cost:

Reflecting Film (3m)

Clear Film

Absorbing Film

20c/sq.ft

.

18c/sq.ft

30c/sq.ft.

5-15
EXAMPLES:

1) One company manufactures a low-emissivity film shade with

a magnetic edge tape for sealing the perimeter to an Iron

oxide tape adhered to the jamb and sill. Test were con- ducted on a school In Minneapolis on November 24, 1974.

Measurements were made, using an Infrared temperature

sensor and thermocouple, on five adjacent windows on the

first floor classroom. One window was uninsulated while

the other four received various retrofit options.

Infrared photographs were then taken on December 1, 1975

to confirm the measurements. The tests showed the insulating effectiveness of the various windows as follows:

(75,Dahlen,p2)

Percent Heat Loss Reduction

(comparison to single glazed windows)

(1) Conventional roll shade plus a 28-36%

blackout shade for movie projecting.

(2) Clear plastic film shade with 36-43%

all perimeter sealed.

(3) Wooden frame exterior storm window. 50-57%

(4) Low heat emitting film shade sealed 57-64%

on bottom and sides only.

2) Another company manufacturers a system of three shades: a reflective film shade near the window, a heat-absorbing

film shade near the room, and a clear shade in the middle.

The shades are operated within frame guides to seal the

sides and bottom.

In the winter during the day, the occupant should lower

the clear shade and the heat-absorbing shade. The clear

shade creates an insulating air space between itself and

the window. The heat-absorbing shade heats the air in

the space between Itself and the clear shade. When the

trapped air temperature becomes warm enough, a bi-metalic

thermostat opens flaps covering slots at the bottom of

the shade frame. Room air is then drawn in at the bottom,

heated by the warm, heat-absorbing film surface, and

convected back into the room at the top. In the winter

during the night, all three shades are lowered to provide

three Insulating, dead-air spaces.

5-16
In the sununer during the day, the outer reflective film

is pulled down to reflect 80% of the sunlight and the

middle clear film is pulled dovm to provide insulation.

(76,Insealshaid, p6)

The Sectional drawings following the references illustrate combinations of roll shades possible with such a system.

REFERENCES:

Dahlen, R. R. , Doyle, J. S., Klaenhamma, B. L,, "Summary of Window

Insulation Tests for Double-Hung School Windows." 3M Company,

St. Paul, Minneapolis, December 1975.

Dahlen, R. R. "Laboratory Measurements of Window Shade Thermal

Performance", 3M Company, St. Paul, Minneapolis.

Dahlen, R. R. "Window Air Infiltration Measurements in School

Classroom", 3M Company, St. Paul, Minneapolis.

Doyle, James S. and Dahlen, R. R. Meeting at NBS

.

Insealshaid, "The More Windows You Have, the More You Need Insealshaid .

Ark-tic-seal Systems Inc. Butler, Wis., 1976.

Joanna Western Mills, "The Money Saving Way to Daytime Comforts",

Joanna Western Mills Co., Chicago, 111., 1976.

5-17
Winter Day

Clear and Heat Absorbing

Winter Night

Reflective & Clear & Heat absorbing

Summer Night

None

Summer Day

Reflective & Clear

Figure 38. Use Modes of a Multiple

Shade System

5-18
5.4 OPAQUE ROLL SHADES/Shading, Solar Heating

STRATEGY

:

Install an opaque or translucent roll shade to reflect sun back out the window in the summer , and , if the shade has a dark side and is reversible, absorb solar energy in the

winter

.

PHENOMENA:

1) Summer solar heat gain through windows can be reduced by

lowering an opaque, white roll shade to reflect much of

the incoming solar energy back out through the glass.

The color of the shade and its opacity greatly affect

performance as can be seen in the following table:

(74,ASHRAE,p403)

CHARACTERISTIC TRANSMITTED REFLECTED ABSORBED

Light-color, translucent 25% 60% 15%

White, opaque 0 80 20

Dark, opaque 0 12 88

As is evident from the table, a shade's ability to reflect

sunlight is badly impaired if it is a dark color.

The light absorbed by the shade raises the shade temperature,

Heat is then dissipated into the room by radiation to

room surfaces, and by convection of room air in contact

with the warm shade surface.

2) The effectiveness of roll shades in combination with

various types of glass is shown below in terms of shading

coefficients: (74,ASHRAE,p403)

5-19
GLASS SOLAR

TRANSM.

SHADING COEFFICIENT

OPAQUE TRANSLUC

WHITE LIGHT

OPAQUE

DARK

Single Clear

Single Heat-Ab.

Double Clear

Double Heat-Ab.

87%

35*

69*

28*

0.59

0.45

0.60

0.40

0.25

0.30

0.25

0.22

0.39

0.36

0.37

0.30

* (75,L0F,pl9)

3) Roll shades a^Lso reduce heat flow through a window both

in winter and summer. The U-value of a roll shade with a moderately close fit to the window opening in the wall

will achieve a summer U-value of approximately 0.88.

(Calculated from 74, ASHRAE, p395)

4) A roll shade can have a dark color on one side which

effectively absorbs sunlight and a white surface on the

reverse side which effectively reflects sunlight. By

simply reversing the shade from dark side facing out in

winter to reflective side facing out in summer, the shade

can perform as a solar collector or shading device varying

with the season. (Silverstein, p63)

ADVANTAGES:

1) Reduced solar heat gain in summer.

2) Reduced conducted heat loss during winter nights.

3) Privacy.

4) Glare control.

5) Self-storing.

DISADVANTAGES:

1) Maintenance. Spring mechanism will fatigue or jamb with time

and need replacement.

2) View out and shading at the same time Impossible.

3) Impeded ventilation from the top opening of double hung

windows when the shade is lowered.

5-20
AESTHETICS:

A roll shade is a simple, inobtrusive element which does not

complicate the appearance of a window.

COSTS:

The following are a sample of retail prices for roll shades in

the Washington, D. C. area:

SHADE TYPE OF SHADE

WIDTH OPAQUE TRANSLUCENT

36 inches $5.00 $3.70

60 inches 20.00 17.00

EXAMPLES

:

The following example illustrates the summer and winter energy

benefit or expenditure attributable for one square foot of

window without and with a roll shade in New York City. The summer calculated energy results plus the solar data, degree

days, and window U-values are taken from a report by Samuel

Berman. (75 , Herman, p47) The winter energy data and total

energy data are not from Berman. These calculations differ

from his report in order to consider the window with a lowered

roll shade during winter nights. Three orientations are calculated with west being assumed similar to east.

The following values are used in the calculation:

Winter U-Values

Type of Glass Shade Up Shade Down

Single glass 1.13 0.88

Storm/double 0.55 0.49

5-21
Type of Glass Winter Solar Heat Gain (WSHG)

(KBTU/winter, sq.ft.)

single

double

N

45

39.6

E,W

91

80.1

S

159

139.9

The shading coefficient for double glass is assumed to be

0.88.

Heat loss for the winter was calculated with the shade lowered

12 hours per day. The heating season used was 4714 degree

days (d) for a period from October to April.

q = (WSHG X SC) - (12 X U , , x d) + (12 x U ^ ^ x d) shade no shade

Using these assumptions the following winter and summer energy expenditures or benefits result from one square foot of

window.

SEASONAL ENERGY EXPENDITURE FOR A WINDOW IN NEW YORK CITY

( K^BTU/SQ.FT.) (- denotes energy input required from mechanical system)

GLAZING SHADING NORTH EAST SOUTH

Wint. Sumr

.

Wint. Sumr

.

Wint. Sumr

.

Single None -84 -43 -38 -76 +29 -59

Single roll shade -69 -15 -23 -26 +45 -20

Savings 15 28 15 50 16 39

Storm/double None -25 -37 +14 -65 +71 -51

Storm/double roll shade -19 -13 +21 -23 +81 -18

Savings 6 24 7 42 10 33

Savings roll shade + 65 30 17 53 52 41

double compared to no roll shade + single

5-22
REFERENCES:

ASHRAE, ASHRAE Handbook of Fundamentals , ASHRAE Inc., New York,

N. Y., 1974.

Barman, Samuel and Silvers tein, Seth, "Energy Conservation and

Window Systems" National Technical Information Service, Springfield, Va. Jan. 1975.

Dix, Rollin C. and Lavan Zalman, "Window Shades and Energy Con^

servation" Illinois Institute of Technology, Chicago, 111., 1974.

Land, C. E., "Effect of Reflective Window Shades in Reducing the

Heat Transfer through Windows", University of Minnesota, Minneapolis, Minn., 1957.

LOF, "Glass for Construction", Libbey-Owens Ford Co., Toledo,

Ohio, 1975.

Olgay, Victor and Olgyay, Aladar, "Design with Climate", Princeton

University Press, Princeton, N. J., 1963.

Ozisik, N. and L. F. Schutrura, "Heat Flow through Glass with Roller

Shades", No. 1696, ASHRAE Transactions , Vol. 65, ASHRAE Inc.,

New York, N. Y. , 1959.

Silverstein, Seth B., "A Dual-Made Internal Window Management Device

for Energy Conservation", General Electric Co., Schenectady,

N . Y .

, undated

.

5-23

5.5 INSULATION SHUTTERS/lnsulation

STRATEGY

:

Provide hinged or removable opaque insulating shutters to

reduce night-time winter heat loss.

PHENOMENA:

1) The winter heat loss through a window can be reduced by

covering the window with an insulating panel in contact

with the glass. The heat loss is then reduced in proportion to the insulating value of the panel measured as resistance to heat flow per inch thickness of material.

The U-value for a window with a one inch insulating panel

against it can be approximated as follows:

"total - % ^ R

U .

T panel

glass alone

This assumes equivalent values for the air film at the

surface of the panel and at the interior surface of the

glass, or an R-value of 0.68 in both cases.

The following table lists several common rigid insulating

materials, their resistances (74 ,ASHRAE ,p361) , and the

winter U-value of a single glazed window with the panel

in contact with the glass. All values are for one inch

thick panels.

5-25
INSULATING VALUES OF VARIOUS INSULATING PANEL MATERIALS

Material

(for

Resistance

• 1" thickness)

U-value of

window with

1" panel

U-value of

window with

2" panel

Expanded polystyrene,

extruded, plain

4.00 0.20 0.11

Expanded polystyrene,

molded beads

3.57 0.22 0.12

Expanded polyurethane 6.25 0.14 0.07

Cork (3/4 inch) 1.68-^ 0.39^

Cork/paper bd/cork (3/4) 2.56-^ 0.29"^ —

Plywood (3/4 inch) 0.93 0.55

2) If a gap exists between the insulating panel and the

glass and air can circulate from the room behind the

panel and across the glass, the effectiveness of the

panel in reducing heat loss will be drastically reduced.

However, if the panel fits tightly to the perimeter of

the wall opening (so that air cannot circulate into the

room) , a separation of the panel from the glass will

increase the panel's effectiveness by providing an insulating layer of trapped air.

ADVANTAGES:

1) Reduced winter heat loss at night.

2) Improved comfort near windows at night.

3) Reduced sound transmission at night.

4) Privacy at night.

5-26
DISADVANTAGES

:

1) Bulky to store during the summer and during day if

demountable panels are used

.

2) Easily crushed in the case of polystyrene or polyurethane

necessitating periodic replacement.

3) Polystyrenes and polyurethanes are flamable and give off

highly toxic gases in the event of fire. A protective

cladding of metal is essential.

AESTHETICS:

Rigid insulating panels can be covered with decorator fabrics

to enhance the character of the window. Cork or other insulating materials are attractive in their natural condition in

many interior design schemes. In deep window openings, the

window may be sufficiently recessed to accommodate half the

width of the window, in which case, thermal panels can be

pivoted at either side without projecting out into the room.

In new construction a pocket can be detailed in the wall

adjacent to the window into which sliding insulating panels

can be stored out of sight. Foam panels should be clad

with sheet metal. The metal skin would eliminate the

problem of panels becoming unsightly due to the vulnerability

of unprotected foam. The skin must also provide protection

from the toxic fumes given off by certain types of foam

insulation in the presence of a fire.

COSTS:

The following table is a sample of retail prices for various

insulating materials:

Material Cost/sq. ft.

1" extruded polystyrene $0.35

1" expanded polystyrene 0.38

3/4" sheet cork 0.50

1/2" pressed paper

board with 1/8" cork

facing both sides

1.51

5-27
EXAMPLES

:

1) An insulating panel which reduces a single glazed window's

U-value to 0.38 or less, is twice as insulating as residential double glass (1/4 inch air space) with a U-value

of 0.65. Thus, if the panels are closed only during the

hours of darkness, approximately twelve hours per day,

they will achieve energy savings comparable to insulating

glass. Furthermore, the difference between outside day

and night temperatures is likely to be greater than the

difference between day and night thermostat settings.

Therefore, even with night-time thermostat set back the

insulating shutters can effectively conserve heating

energy

.

2) A study in Sweden calculated the difference in energy

flow between insulated glass windows with thermal shutters

open all the time and with the shutters closed when

conductivity and infiltration losses exceed solar gain.

The following table gives the annual energy saved by

using the shutters in BTUs x 10^ per square foot. (Converted to English Units from 75,Hagman,p2)

LOCATION DEGREE

DAYS NORTH

ORIENTATION

SOUTH EAST/WEST

Lulea 11000 142 125 135

Stockholm 7700 106 89 99

Malmo 6900 93 79 87

NOTES

:

1) The case of closing the shutters whenever the window

loses more heat than it gains would necessitate

closing the shutters the entire day during December

in Malmo and Stockholm, and November through January

in Lulea.

2) The window with a closed shutter was assumed to have

an equivalent U-value of 0.09 considering both con- duction and infiltration. With the shutter open,

the window alone, considered to be an average

tightness, double glazed unit, the U-value assumed

to be equivalent to 0.53.

5-28
REFERENCES

:

ASHRAE, ASHRAE Handbook of Fundamentals , ASHRAE Inc., New York, N. Y.,

1974.

Hagman, Folke, "The Window as an Energy Factor, Insulating Shutters,

Function Construction, Economy", Report R43: 1975, National

Swedish Council for Building Research, S-111 84 Stockholm,

Sweden, 1974.

5-29

BUILDING

INTERIOR

FIXTURE CIRCUITING

TASK LIGHTING

AUTOMATIC SWITCHING

INTERIOR COLORS

THERMAL MASS
6. BUILDING INTERIOR

The design of the building interior will determine how useful

the energy admitted by the window will be. Distribution of

the incoming energy beyond the immediate vicinity of a window

is one basic objective. The color, location and height of

partitions will determine how deeply daylight penetrates into

a room. The mechanical air circulation system may provide a

means of circulating the winter solar heat beyond the immediate vicinity of the window. Another objective of interior

strategies is to store solar heat during periods of excess

to be re-radiated later when the room temperature drops.

A massive floor and wall in the path of the sunlight can

effectively perform this function. Still another objective

of building interior strategies is to facilitate occupant's

use of daylight as a substitute for electric lighting,

thereby reducing energy consumption by both the lighting

and air conditioning systems.

In summary, the design of the illumination and mechanical

systems, the design and color selection of room surfaces, and

the placement of massive building components will determine

how much the energy gained by windows can reduce illumination,

air conditioning, and heating energy costs.

6-0
6.1 FIXTURE CIRCUITING/Daylight

STRATEGY

:

Provide separately switched circuits for lights in a building's

peripheral zone to facilitate substituting daylighting for

electric lighting.

PHENOMENA:

1) Daylight penetrates a finite distance into an interior

space. The illumination level can be calculated and a zone defined where daylight provides an acceptable level

of illumination with no artificial lighting needed.

2) The amount of daylight penetrating a given space varies

according to cloud cover, time of day, and time of year,

as well as the visible light transmission of the glazing.

Providing separate switching for two rows of light, one near the window and one deeper in the room, would permit

the outer row to be switched off when daylight is adequate

near the window.

3) Daylighting, when excesses are controlled, poses less of a heat load on the air conditioning system than even fluorescent lighting. Therefore, the capability of

switching on only the row of lighting needed on a hot

overcast day saves electricity both in terms of lighting

and air conditioning.

ADVANTAGES

:

1) Reduced electric consumption during the time of the day

when demand on the generating plant is at a peak. Where

electric rates are higher during peak periods, dollar

savings are even greater.

DISADVANTAGES:

1) Potential glare and greater variation in light level

compared to complete reliance on artificial illumination.

2) Overheating if excesses not controlled with shading .

6-1
AESTHETICS:

1) Turning off only the light fixtures in the area receiving

daylighting may provide a more uniform lighting level

throughout the space.

COST:

Additional first costs include the material and installation of

additional footage of wiring and additional switches.

EXAMPLES

:

1) The following figure illustrates the amount of light

theoretically available from a window in an office space.

The clear sky curve assumes the sun is directly overhead.

If the sun were lower in the sky as in the winter, the

light level in the office would be still higher than shown.

If the sun were behind the building, the light level would

approach the curve for the overcast sky. (74,Vild, p3)

The actual illumination in any office may be substantially

lower than these curves . Lower values would actually be

better as the illumination levels shown are excessive.

Figure 39. Usable Daylight at Desk- Top Height vs. Distance from the Window
2) The following example shows how much electricity can be

conserved when daylight would suffice to provide adequate

illumination for half the office six hours a day.

Window Window

I 1

I I

I I

!

1

J I

I I

I -J

t I I [

!

1 I

i h—

J

I

! i

I I

1

N

r r

r rI u .J

I T 1

f r 1

( L — 1

Office "A" Office "B'

Figure 40. Lighting Fixture Circuiting

8 fixtures

2 - 40W tubes each

Assume

:

8 fixtures 4 fixtures 4 fixtures

9 hrs/day 9 hrs/day 3 hrs/day

5.76 KWH/work day 2.88 KWH/work day +0.96 KWH/work day =3.84

$1.15 /work week $0.7 7 /work week

Savings = $0.38/work week

6-3
REFERENCES

:

Vild, Don, "Benefits of Daylight ing in Terms of Energy Savings",

Libbey-Owens Ford Corp., Toledo, Ohio, 1974.

6-4
6.2 TASK LIGHTING/Daylighting

STRATEGY:

Provide task lighting switched separately from ambient lighting to facilitate the use of daylighting for ambient lighting.

PHENOMENA

:

1) Ambient lighting in addition to adequate lighting on a task is necessary to avoid extreme contrast and resulting

eye fatigue. However, the ambient lighting can be only

approximately 1/3 the level of the task lighting.

(75 ,GSA,p6-6) By providing high levels of lighting only

at the task rather than uniformly high levels of light,

considerable electricity can be saved, both from reduced

lighting consumption and reduced air conditioning burden.

By providing separate switching for task and ambient

lighting, the ambient lighting can be turned off when

daylight is adequate, further increasing the savings.

ADVANTAGES

:

1) Reduced electricity consumption when daylighting is

adequate for background lighting.

2) Individual discretion in selecting lighting for a task.

With conventional uniform lighting, if one person feels

he needs more light he must switch on the lighting for

everyone.

3) No electricity, including the resulting increase in air

conditioning load, is wasted by lighting work areas of

individuals who are absent for part or all of the day.

4) Depending on the mounting system an individual can vary

the distance and orientation of the luminaire, relative

to his task, to suit his personal preference.

DISADVANTAGES:

1) Possible glare from the task lighting reflected off the

work surface into the eyes of the worker.

6-5
2) Interference with work task by fixture base if the task

lighting fixtures are on the work table.

3) Less flexibility in terms of relocating the task at a future date if task lighting fixtures are mounted in the

ceiling.

AESTHETICS:

1) In illuminating the task area more brightly than the

background, attention is focused on the work surface.

2) Introducing different levels of illumination within a space makes it more interesting than if it were lighted

uniformly.

3) Task luminaires can be an attractive addition to the

furnishing of a space.

COSTS:

An incandescent drafting lamp can be purchased for $19.00.

EXAMPLES

:

The office of the Pilkington Environmental Advisory Service;

Lancashire, England was experimentally retrofitted with task

lighting and daylighting was relied upon to provide background lighting as much as possible. This was accomplished

by providing desk lamps or drafting lamps and removing nearly

three-quarters of the fluorescent lighting tubes selectively

from the ceiling. Desks were faced towards the darker center

of the space with daylight then coming from behind the desk

rather than from in front of it . This reduced "veiling

reflection". (Glare from light reflected by the pages reducing

the contrast between the ink and the paper.) The following

table summarizes the lighting wattages in the original overall illumination system and the retrofitted task lighting and

daylight ambient lighting system. (75 , Cuttle, p24)

6-6
COMPARISON OF ORIGINAL AND RETROFITTED LIGHTING

Installation Original Retrofitted

Total lighting (W) 5130 2866

Lighting load W/m^ 24.4 13.6

2 Density of occupancy (m /person) 15 15

Background lighting load (W) — 95

Total lighting load/desk worker (W) 365 149

Total lighting load/illustrator (W) 365 205

REFERENCES:

Architectural Record, "Task/Ambient Lighting, An Idea Whose Time

Has Come, But Whose Implications Need to Be Better Understood",

Architectural Record , McGraw Hill Publishing Co. New York,

N. Y., Mid August, 1976.

Cuttle, A. and Slater, A. I. "A Low Energy Approach to Office

Lighting", Light and Lighting . Illuminating Engineering Society,

119 Westminister Bridge Road, London, England. Jan/Feb. 1975.

GSA, Energy Conservation Design Guidelines for New Office Buildings , Public Building Service, Government Services x\dministration.

Washington, D. C, July, 1975.

6-7

6.3 AUTOMATIC SWITCHING/Daylighting

STRATEGY

:

Control light switching with photo-electric light sensors or timers to reduce electric lighting usage during periods of

adequate daylight.

PHENOMENA:

1) Silicon cells generate a small electric current which

varies directly with the light level. By measuring this

current or measuring the change in resistance to a current passed through a silicon or selenium cell,

changes in light levels can be sensed electrically.

This information can be used by control systems to

regulate electric lighting automatically according to

need

.

2) Silicon cells are more stable and faster responding than

selenium cells. Silicon cells are therefore better

suited for controlling interior illumination. (Selenium

cells are acceptable for less critical tasks such as switching security lighting.) (76 ,Zalewski)

3) A timer can be built into the lighting circuit to limit

the use of certain electric lights to night-time.

ADVANTAGES:

1) Elimination of the situation of a cloud reducing the

daylight level, the room occupant switching the lights

on, and then leaving them on the remainder of the day.

2) Reduced electricity demand for lighting and associated

air conditioning.

3) Elimination of night-time workers forgetting to turn out

lights and daytime workers not noticing unneeded lights

left on.

6-9
DISADVANTAGES:

1) Difficulty in purchasing "off the shelf" light-sensing

systems. Only a few manufacturers are involved in their

production. Furthermore, installation requires careful

analysis on a case by case basis. A number of prototype

systems were installed in the late 1950 's and early

60' s, but inexpensive energy greatly extended the amor- tization of first costs. The end of inexpensive energy

now provides an incentive for installing light-sensing,

light switching systems. Several manufacturers have

already identified a market and are mass producing—or have in final design development—highly sophisticated,

light-sensing switching systems.

2) Need for the sensors to be kept clean. This may require

maintenance if they are mounted on the roof or outside

walls

.

3) Directional sensitivity of outdoor sensors. This requires

careful analysis in predicting what the indoor illumination level will be for the outdoor light level at

which the sensor responds by switching on or off indoor

lights.

4) Greater variation in indoor light level when daylight is

depended upon. Variation may be considered a disadvantage

or an advantage depending on personal preference.

AESTHETICS:

1) The light sensor component of the control system can readily be made inconspicuous in the ceiling system or building facade.

2) Changes from side daylighting to overhead electric

lighting during the course of a day provides a change in

the character of the interior space. Interior forms are highlighted in a different manner and the direction and

def initiveness of shadows change.

6-10
COSTS:

1) In addition to the hardware cost of the actual control

system, consulting costs are incurred because lighting

specialists must balance the system. Predicting daylight is a difficult problem because the absorption and

reflection characteristics of both indoor and outdoor

surfaces must be evaluated as well as the variability in

the direction and intensity of the light source.

2) Circuiting the lights to additional switching controls

is an added cost.

EXAMPLES:

1) A skylight manufacturer offers a daylight sensing, light

control system. A time delay is built into the relay

system so that a change in daylight level must last

longer than ninety seconds. This reduces rapid cycling

when clouds pass in front of the sun. A counter is also

included to lock the lights on for a period of an hour

if the lights are switched on and off more than three

times in less than ten minutes. A clock can be included

to provide automatic (as well as manual) over-ride to

the system during weekends, holidays, evenings, lunch

hours, and custodial hours. (76,Commendo)

2) A recent development is a solid state, dimming control

system which varies the output of fluorescent or mercury

vapor lighting according to the availability of daylight.

When a silicon cell senses the daylight level, the

control system varies the electric lighting output con- tinuously (rather than incrementally). (76 ,Longenderfer)

3) A photo activated interior Venetian blind is manufactured

in Great Britain. Banks of up to 30 blinds can be

operated from one photo-cell unit . The control can be

restricted to only tilting of the blind, raising or lowering being accomplished manually, or the entire

operation of the blind system can be automated. (74,

Beckett and Godfrey, p295)

4) An experimental system was installed in two classrooms

of Heather Drive Elementary School in Aurora, Illinois.

A sensor at the window turned off the row of lights

6-11
nearest the interior wall when the outdoor light level

exceeded 1500 foot candles. A second row was turned off

at 1000 foot candles, third at 850 foot candles, fourth

at 700, fifth at 600, and the sixth (nearest windows) at

500. After carefully measuring the electric consumption

for an entire semester, it was found that two unautomated

classrooms (used as an experimental control) used 46

percent more electricity than did the classrooms with

automated switching. (63, Chapman, pl9 3)

5) New office space in a San Francisco building has been

provided with ancillary lighting in certain areas which

is controlled by a photo-cell override which limits its use to non-daylight hours only. (76 , Architectural

Record, pl20)

6) One floor of the Manchester Federal Office Building is

equipped with automatic switching. The three perimeter

rows of lighting are connected to photo-electric cells

adjacent to each row of lighting. When daylighting is

adequate, each row is independently switched off. A 30

second time delay prevents the lights from rapidly

switching on or off as would be the case with a cloud

momentarily blocking the sun. (75 , Isaak,p23)

REFERENCES:

Architectural Record, "Task Ambient Lighting", Architectural

Record, McGraw-Hill Publishing Co., New York, N. Y., Mid

August, 1976.

Beckett, H. E. and Godfrey, J. A., Windows, Performance, Design,

and Installation , Van Nostrand Reinhold Co., New York, 1974.

Chapman, William P., "Automatic Controls Can Cut Lighting Costs",

Architectural Record , McGraw-Hill Publishing Co., New York, May

1963.

Commendo, John, telephone conversation, Naturalite Skylights,

Garland, Texas, June 1, 1976.

Isaak, Nicholas and Andrew, Designing an Energy Efficient Building , General Services Administration, Public Building Service,

Washington, D. C, Sept. 1975.

Longenderfer , John, telephone conversation, Lutron Co., Allentown,

Pa., June 9, 1976.

Zalewski, Edward, telephone conversation. Metrology Section,

National Bureau of Standards, Washington, D. C, May 20, 1976.

6-12
6.4 INTERIOR COLORS/Daylighting

STRATEGY

:

Paint interior surfaces a light color to increase the light

level possible from daylighting

.

PHENOMENA:

1) Light colored surfaces reflect light increasing the

ambient light level for a given amount of available

light. Dark surfaces absorb light decreasing the

ambient light level. The following table gives typical

reflection factors for different colors; (75 ,Kern,p336)

REFLECTION FACTORS OF COLORS

COLOR REFLECTION FACTOR

White

Pale yellow, rose

Pale beige, lilac

Pale blue, green

Mustard yellow

Medium brown

Medium blue, green

Black

80 to 90 percent

80

70

70 to 75

35

25

20 to 30

10

Note: Reflection factor = reflected light/incident

light given as a percentage.

The exact reflection factors for a given color can be

determined by matching it to a standard system of colors

called "Munsell Colors" and using a conversion table to

determine the reflectivity. (72 , lES ,p5-16)

6-13
2) The following are example reflection factors desirable

for different surfaces of a room: (75 ,Kern,p336)

DESIRABLE REFLECTION FACTORS FOR INTERIOR SURFACES

SURFACE REFLECTION FACTOR

Ceilings 80 percent

End walls:

in poorly lighted rooms 70

in well lighted rooms 25

Walls containing window (s) 80

Floors 25

Note:

The use of light reflective colors on the wall(s) con- taining window (s) decreases the contrast between the

windows and the surrounding surfaces. For the same

reason, the window frame, sash, and muntins should also

be a light color. Light colors on surfaces adjacent to

or opposite windows should have a matte finish to

alleviate the potential problem of reflected glare.

3) The likelihood of a room being adequately daylit is

lessened if it is furnished with dark-colored draperies,

carpeting, wall hangings, and furniture.

ADVANTAGES:

1) Increased availability of daylight for task illumination

or ambient illumination.

2) Decreased likelihood of glare from excessive contrast

between bright windows and dark surroundings.

DISADVANTAGES:

Dirt, fingerprints, and scuff marks are more conspicuous on light-colored surfaces.

6-14
AESTHETICS:

Selected colors can have interesting effects upon people. A

"rule of thumb" is to use warm colors (yellows, oranges,

reds) in north-facing rooms receiving little or no sun, and

cool colors (greens, blues, and violets) in rooms receiving

plentiful sunlight.

COSTS:

The cost of light colored paints versus dark colored paints

is the same or insignificantly different.

EXAMPLES:

The following table illustrates the improvement in illumination

both in uniformity and brightness possible with increasing

reflectances of walls, floors, and ceilings. The illumination

at the rear of a room with very dark surfaces is used as the

basis of comparison. The room is 30 x 32 x 12 ft. high with

6 ft. directional glass block the full 32 ft. length. (66,

IES,p7-10)

EFFECT OF SURFACE REFLECTANCE UPON REL. ILLUMINATION

Reflectance Factor Relative Illumination at various

(percent) distances from fenestration

Walls Floor Ceiling 3 feet 15 feet 17 feet

6 6 6 6.57 2.66 1.00

28 28 28 8.55 3.62 1.60

62 28 62 11.98 5.75 3.16

REFERENCES

:

lES, lES Lighting Handbook , Illuminating Engineering Society, New

York, N. Y., 1966.

Kern, Ken. The Owner Built House , Charles Scribner's Sons Inc.,

New York, N. Y. , 1975.

6-15

6.5 THERMAL MASS/Solar Heating

STRATEGY:

Locate massive materials directly in the path of winter sunlight

transmitted through windows in order to store part of the

incoming solar heat, avoid overheating, and provide re-radiated

heat during non-sunlit hours

.

1) Large window areas, especially in small rooms, can transmit

so much solar energy that overheating may occur during

periods of peak solar intensity. This can be partially

remedied with the use of heavy, massive materials. If the

sunlight entering a room falls on the surface of a massive

material, such as a slate floor, part of the energy is

reflected as light, and part of the energy is absorbed and

becomes heat. This heat raises the surface temperature of

the material. When the internal temperature of the material

is lower than the room air temperature, the heat is con- ducted inward into the mass of the material . When the room

temperature later begins to drop and becomes lower than the

surface temperature of the material, the heat accumulated

within the material flows outward. The heat is returned to

the room by convection at the surface of the material, and

by radiation from the surface of the material to opposite

and adjacent room surfaces with a lower temperature.

2) How effective a material is in storing heat can be judged

from its ability to absorb sunlight, conduct surface heat

into its mass (conductivity), and hold the resulting heat.

The ability of a material to absorb sunlight is largely

determined by its color and texture. The following

table provides an approximation of the percent of solar

radiation absorbed by different colors. (65 ,ASHRAE ,plPHENOMENA:

6)

COLOR PERCENT ABSORPTION

white, smooth surfaces 25 to 40 percent

gray to dark gray

green, red, brown

dark brown, blue

dark blue, black

40 to 50

50 to 70

70 to 80

80 to 90

6-17
3) The ability of a material to hold heat can be judged by its

"thermal capacity" which equals its density multiplied by

its specific heat. (Density: Pounds per cubic foot or kilograms per cubic meter; Specific heat: BTU/lb°F or KJ/Kg°C.)

The greater the thermal capacity, the better the material

is for storing heat. If two materials have a similar

thermal capacity, the material with the higher conductivity is a better storage medium. The following table

provides information on both solar absorption and thermal

capacity of several common materials. (Calculated from 67,

Baumeister ,p4-ll and 6-8)

SUITABILITY OF MATERIALS FOR STORING HEAT FROM SUNLIGHT

CONDUCMATERIAL-COLOR TOTAL PERCENT THERMAL CAPACITY TIVITY

SOLAR ABSORBED^ (BTU/°F,f t .3) BTU/hr ft°F

Brick - glazed white 0.26 24.6

0.4

Brick - common, red 0.68 24.6

Marble - white 0.44 35.7

1.5

Marble - dark 0.66 35.7

Granite - reddish 0.55 32.2

Slate - blue gray 0.87 37.8

Slate - dark gray, rough 0.90 37.8

Concrete - 0.65 22.5 0.54

Wood - white pine 18.1 0.06

Wood - white oak 27.4 0.10

Steel - enamel red 0.81 58 .8 26.2

Water 62.0 0.35

NOTES

:

1. Source: (65,ASHRAE,pl-61)

2. Conductivities are given without regard to color in

72,ASHRAE,p570.

4) The following table can be used as a guideline to roughly

approximate how much mass should be provided to store a window's solar heat gain. (Square feet of material per

6-18
square foot of window.) Different areas of material are given for different thickness of materials, for different

amounts of daily solar heat gain, and for different

average inside-outside temperature differences. (74,

Anderson, p46) The inside-outside temperature difference

is important because it determines how much heat is

needed to maintain a comfortable room temperature. Not

given is the resistance to outward heat flow afforded by

the building envelope. A well insulated double glazed

residence would require less mass.

AREA OF CONCRETE REQUIRED TO STORE WINDOW SOLAR HEAT GAIN (SQ.FT. )

Average Daily

Solar Heat Gain

Through the Window-^

500 Btu/ft'

Allow. Inside

Taap. Swing

750 Btu/ft'

1000 Btu/ft'

1250 Btu/ft'

1500 Btu/ft'

1750 Btu/ft'

THICKNESS OF CONCRETE^

2" 4" 8" 1 on

X z

5 25.00 12.50 6.25 4.17

10 12.50 6.25 3.13 2 .08

4 17 £m9 • 08\J\J 1 39

20 6 25 3 13 1.57 1 04

25 5 on 2 50 1.25 0 83

5 31 .50 18.75 9.38 6.25

10 18.75 9.38 4.69 3.13

12 50 6 .25 3 .13 2 08

20 9 38 4 .69 2 .35 1 .56

2 5 7 50 3 .75 1 .87 1 .25

5 50.00 25.00 12.50 8.33

10 25.00 12.50 6.25 4.17

16 67 8 .34 4 .17 2 .78

90 1 2 50 6 25 3 13 2 08

9 5 1 0 on 5 00 2 50 1 .67

69 S9 X • ^ -/ 15 63 10 49

10 31.25 15.63 7.81 5.21

15 20.83 10.42 5.21 3.47

20 15.63 7.81 3.92 2 .60

25 12.50 6.25 3.13 2.08

5 75.00 37.50 18.75 12 .50

10 37.50 18.75 9.37 6.25

15 25.00 12.50 6.25 4.17

20 18.75 9.37 4.68 3.12

25 15.00 7.50 3.75 2 .50

5 62.52 31.26 15.63 10.42

10 31.26 15.63 7 .81 5.21

15 20.83 10.42 5.21 3.47

20 15.63 7.81 3.92 2.60

25 12.50 6.25 3 .13 2.08

6-19
Notes:

1) The average daily solar heat gain for a specific

region and orientation can be found on pages 388

through 392 of the 1972 edition of the ASHRAE

Handbook of Fundamentals .

2) To estimate the area of other monolithic materials

required, multiply the areas given in the table by

the following values:

5) Massive materials may be effective during the summer, if

the night temperatures are substantially lower than into

the daytime temperature. Outdoor night air allowed to

enter through open windows and passing over a massive

material will lower its surface temperature. Subsequently

5

the internal heat will be drawn out of the material.

During the day, if the outside air temperature is greater

than the indoor air temperature, the windows are closed

and shaded. As the room air temperature rises, heat is

absorbed back into the cooler massive material. The

rate at which the room air temperature rises is thereby

reduced

.

6) The geometry of a building material will also affect its

ability to store winter solar heat or summer evening

coolness. Steel is a good storage material due to its

high density (in spite of its low specific heat)

.

However, if the material occurs in a shape with a great

deal of surface area such as a wide flange beam, there

is very little thickness where the heat can be stored

unless for a short period of time. The large surface- area to volume ratio limits the ability of the beam to

store heat.

7) The effectiveness of a massive material in augmenting the

heating or cooling system can be increased by embedding air

ducts or copper tubing in the material and routing the heat

transport medium of the mechanical system through the slab.

ADVANTAGES

:

1) Increased utility of solar energy transmitted through windows.

2) Delayed day time temperature rise during the summer.

3) Reduced frequency of heating or cooling system cycling

(switching on and off) due to the "thermal inertia" of the

massive material.

4) Reduced sound transmission when massive materials are used

between spaces to be acoustically separated.

6-20

wood

brick

1.00

0.86

stone

water

0.83

0.38
DISADVANTAGES:

1) Decreased responsiveness of room temperatures to the

heating or cooling system.

2) Increased reverberation of sounds within the room due

to the surface hardness common to dense, massive

materials.

3) Decreased flexibility in furniture arrangement

.

4) Decreased flexibility in repartitioning floor space

when massive materials are used in the interior wall

construction.

5) Increased loading which must be carried by the structural

system. (However, the massive material may be part of

the structural system as with load bearing interior

masonry walls.)

AESTHETICS:

1) Massive walls, floors, or ceilings give a sense of

permanence

.

2) The hard surfaces of massive materials may be smooth

or textured to reduce their harshness.

3) Tapestries, rugs, and other coverings must be located

so as not to reduce the effectiveness of massive

materials

.

COSTS:

The cost of massive materials such as concrete, marble,

slate, or brick flooring may be justified on an aesthetic,

durability, or structural basis with the thermal mass considered a supplemental benefit.

EXAMPLES

:

1) The National Concrete Masonry Association, using the

National Bureau of Standards Computer Program (NBSLD)

to evaluate the effects of mass on the size of air

6-21
conditioning equipment, calculated a 16 percent reduction

in peak cooling load could be achieved through the use

of massive materials. In the first series of computer

runs a 2-story building was exposed to a 24-hour-cycle

of temperatures ranging from 76°F to 94°F. For the

first computer run the walls were assumed to be composed

of wood studs and insulation having a weight of 8 lbs.

per square foot and U-value of 0.10. Results of the

analysis indicated that maintaining 75 °F would require

air conditioning equipment with a peak cooling load

capacity of 40,500 Btu per hour. For the second

computer run the walls were changed from insulated

wood frame to insulated concrete masonry with the same U-value, but the weight was increased to 40 lbs. per

square foot (8" light-weight concrete block) . The

peak load was then calculated to be 34,000 Btu, or a savings of 6,500 Btu, a reduction of 16 percent.

(75,NCMA-TEK,p2)

A house in Santa Fe, New Mexico is entirely heated

from solar heat transmitted through 384 sq. ft. of

south-facing double glazed windows. To absorb the

heat and keep the room temperature comfortable, the

house has a large amount of interior mass. Walls are 14-inch adobe, floors are brick with 24 inches of

underlying adobe, and several benches in the path of

the incoming sunlight contain 55 gallon drums of

water. This mass is capable of keeping the home

comfortable for three to four sunless days. (76 ,Cole,p22)

A vacation house in Illinois built by the owners for

approximately $10,000 is capable of achieving temperatures up to 100 degrees with window solar heating

(37.8°C) when the outside temperature is five degrees

(-15°C). One of the key components of the system is

the provision of heat storage. Two 16 cubic feet

insulated steel tanks filled with water are located in

the path of sunlight entering through side windows and

skylights. Opened reflective panels outside the

window reflect additional sunlight through the skylights

during the heat collection period, then the panels are closed at night to help reflect the heat radiating

from the storage tanks back into the room. In the summer the process is reversed : the panels are closed

during the day then opened at night to allow the heat

accumulated in the water from the room to be dissipated

to the night sky. (75, House and Garden, pl34)

6-22
REFERENCES:

Anderson, Bruce, et.al. Solar Energy House Design in Four

Climates , Total Environmental Action, Harrisville, N. H., May

1975.

Balcomb, J. D., Hedstrom, J. C. Simulation Analysis of Passive

Solar Heated Buildings , LA-UR-76-89, Los Alamos Scientific

Laboratory, Los Alamos, N. M., 1976.

Baumeister, Theodore (Ed.) Standard Handbook for Mechanical

Engineers , McGraw Hill, New York, N. Y., 1967.

"Energy and Buildings - Thermal Analysis: Part 2" Architects

Journal , 9 Queen Anne's Gate, London, England, March 2A,

1976.

Loudon, A. G., "Window Design Criteria to Avoid Overheating by

Excessive Solar Heat Gains", Building Research Station;

Garston, Watford, England, April 1968.

NCMA-TEK, "New Findings on Energy Conservation with Concrete

Masonry", National Concrete Masonry Assoc., McLean, Va.,

1975.

PCA, "The Concrete Approach to Energy Conservation", Portland

Cement Assoc., Skokie, 111., 1974.

Total Environmental Action, Solar Energy Home Design in Four

Climates. Total Environmental Action, Harrisville, N. H.,

1975.

"Vacation House Warmed by Sun Power", House and Garden, Conde

Nast Pub., New York, N. Y., 1975.

6-23

CONCLUSION

A window can be a solar collector introducing valuable

energy which can lower winter heating costs; a source of illumination which can substitute for artificial lighting to lower

electricity expenditure; and a means of natural ventilation which

can postpone the need for air conditioning- in the spring and

fall, and substitute for air conditioning on cool summer evenings.

Numerous design strategies can improve these capabilities of

a window. The solar energy a window receives can be increased by

light-colored adjacent ground surfaces and by favoring southern

exposures. The usefulness of sunlight inside the building can be

increased by providing mass to store part of the sun's heat. The

utility of daylight can be increased by providing light-colored

walls and ceilings, and by facilitating the substitution of

daylight for electric light. Examples include separate switching

of perimeter lighting, task lighting separate from ambient

lighting, and automatic control systems driven by light sensors and/or timers. Finally, the ability of windows to provide ventilation can be improved through proper orientation to prevailing

winds and by selecting operating window types which effectively

direct the entering and exiting air stream. Even when fixed

glass is required opportunities for admitting outside air are available with frame ventilators or thru-glass ventilators.

Design strategies can likewise minimize the window thermal

load on mechanical systems. Winter heat loss through windows can be reduced with double glazing, storm sash, or edge-sealed transparent roll shades. Night-time heat loss can be minimized with

tight-fitting draperies, opaque roll shades, or insulating shutters

Leakage of unconditioned outside air in and conditioned inside

air out through window cracks can be greatly reduced by initially

installing good quality windows, by providing weatherstripping

,

and by landscaping and exterior appendages which reduce the force

of the wind. Finally, there are numerous means of blocking solar

heat gain in the summer, the most effective solutions being

exterior appendages or site solutions.

Window design strategies can provide occupants with more

freedom in managing their individual environments, and when

effectively used, they can improve comfort, and reduce purchased

energy expenditures.

C-1
ACKNOWLEDGMENTS

N.B.S.

Reviewers

:

Bibliographic

Assistance:

Graphic

Assistance:

Belinda Collins

Porter Driscoll

Tamami Kusuda

Donald Quigley

Nancy Starnes

Heinz Trechsel

Robert Wehrli

Elsie Cerutti

Elizabeth Warner

Nan Stephens

Jerry McKay

Typing: Cheryl Talley
»(HS-n4A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS BSS 104

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

WINDOW DESIGN STRATEGIES TO CONSERVE ENERGY

5. Publication Date June 1977

6. Performing Organization Code

7. AUTHOR(S)

S. Robert Hastings and Richard W. Crenshaw

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Energy Research and Development Administration

Washington, D. C. 20001 ; U.S. Department of Housing and Urban Development

Washington, D. C. 20i.l0

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 77-600018

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.) A multitude of design strategies are available to achieve energy-efficient windows.

Opportunities for improving window performance fall into six groups: site, exterior

appendages, frame, glazing, interior accessories, and building interior. Design

strategies within these groups can improve one or more of the six energy functions

of windows: solar heating, daylighting, shading, insulation, air tightness, and

ventilation. Included in this report are 33 strategies; an explanation of the physical

phenomena responsible for each strategic 's energy performance, suimnarized energy and

non-energy advantages and disadvantages; aesthetic considerations; cost approximations;

example installations, laboratory studies, or calculations by the authors; and referenc(;

Intended readers include professional designers, lessors and owners of commercial

space, home buyers and owners, window component manufacturers, and researchers. The

report's purpose is to draw attention to the wide range of options currently available

to conserve energy with windows

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Air-tightness; daylighting; energy-conservation; insulation; shading; solar-heating;

ventilation; windows.

18. AVAILABILITY [Xl Unlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

1 ! For Official Distribution. Do Not Release to NTIS UNCLASSIFIED

209

[_XJ Order From Sup. of Doc, U.S. Government Printing

Washington. D.C. 20402. SD Cat. No. C13 . 2Q/2i

Office 20. SECURITY CLASS

(THIS PAGE)

22. Price

1

1 Order From National Technical Information Service

Springfield, Virginia 22151

(NTIS)

UNCLASSIFIED

Price S3.75
IIKKteHeat

Manayeimnt

Goiileliook

A typical plant can save about 20 percent of its fuel—just by installing waste heat recovery equip- ment. But with so much equipment on the market,

how do you decide what's right for you?

Find the answers to your problems in the Waste

Heat Management Guidebook, a new handbook

from the Commerce Department's National Bureau

of Standards and the Federal Energy Administration.

The Waste Heat Management Guidebook is designed to help you, the cost-conscious engineer or manager, learn how to capture and recycle heat

that is normally lost to the environment during in- dustrial and commercial processes.

The heart of the guidebook is 14 case studies of companies that have recently installed waste heat

recovery systems and profited. One of these applications may be right for you, but even if it doesn't

fit exactly, you'll find helpful approaches to solving

many waste heat recovery problems.

In addition to case studies, the guidebook contains

information on:

• sources and uses of waste heat • determining waste heat requirements

• economics of waste heat recovery

• commercial options in waste heat recovery

equipment

• instrumentation • engineering data for waste heat recovery • assistance for designing and installing waste

heat systems

To order your copy of the Waste Heat Management

Guidebook, send $2.75 per copy (check or money

order) to Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

A discount of 25 percent is given on orders of 100

copies or more mailed to one address.

The Waste Heat Management Guidebook Is part of the EPIC industrial energy management program

aimed at helping industry and commerce adjust to the increased cost and shortage of energy.

U.S. DEPARTMENT OF COMMERCE/National Bureau of Standards

FEDERAL ENERGY ADMINISTRATION/Energy Conservation and Environment

•irU.S. GOVERNMENT PRINTING OFFICE: 19 7 7-2 40- 848 /2 04
ANNOUNCEMENT OF NEW PUBLICATIONS IN

BUILDING SCIENCE SERIES

Superintendent of Documents,

Government Printing Office,

Washington, D.C., 20402

Dear Sir:

Please add my name to the announcement list of new pubHcations to be

issued in the series: National Bureau of Standards Building Science Series.

Name

Company

Address

City State Zip Code.

(Notification key N-339)





NBS TECHNICAL PUBLICATIONS

PERIODICALS JOURNAL OF RESEARCH reports National Bureau

of Standards research and development in physics,

mathematics, and chemistry. It is published in two

sections, available separately:

• Physics and Chemistry (Section A)

Papers of interest primarily to scier* orking in these fields. This section covers a br .ige of physical and chemical research, wif" jt emphasis on

standards of physical measu*- ^if* , fundamental constants, and properties of m' ^o* '-rfSued six times a year. Annual subscription: D' ^^^c, $17.00; Foreign, $21.25. • Mathematical Sci'- ^Section B)

Studies and com'-' .is designed mainly for the mathematician and .Q<v*c;tical physicist. Topics in mathematical statis<''^^£;i?^.ieory of experiment design, numerical

analysi'" ->J^jretical physics and chemistry, logical de- sign programming of computers and computer syst'" -X^jnort numerical tables. Issued quarterly. Annual

si^ ocription: Domestic, $9.00; Foreign, $11.25.

DIMENSIONS/NBS (formerly Technical News Bulletin) —This monthly magazine is published to inform

scientists, engineers, businessmen, industry, teachers,

students, and consumers of the latest advances in science and technology, with primary emphasis on the work at NBS. The magazine highlights and reviews

such issues as energy research, fire protection, building

technology, metric conversion, pollution abatement,

health and safety, and consumer product performance.

In addition, it reports the results of Bureau programs

in measurement standards and techniques, properties of matter and materials, engineering standards and services, instrumentation, and automatic data processing.

Annual subscription: Domestic, $12.50; Foreign, $15.65.

NONPERIODICALS

Monographs—Major contributions to the technical liter- ature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and

industrial practice (including safety codes) developed

in cooperation with interested industries, professional

organizations, and regulatory bodies. Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other

special publications appropriate to this grouping such

as wall charts, pocket cards, and bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists, engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides

quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a world-wide

program coordinated by NBS. Program under authority

of National Standard Data Act (Public Law 90-396).

NOTE: At present the principal publication outlet for these data is the Journal of Physical and Chemical

Reference Data (JPCRD) published quarterly for NBS

by the American Chemical Society (ACS) and the American Institute of Physics (AIP). Subscriptions, reprints,

and supplements available from ACS, 1155 Sixteenth

St. N.W., Wash. D. C. 20056. Building Science Series—Disseminates technical infor- mation developed at the Bureau on building materials,

components, systems, and whole structures. The series presents research results, test methods, and performance criteria related to the structural and environmental

functions and the durability and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete

in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other

government agencies.

Voluntary Product Standards—Developed under proce- dures published by the Department of Commerce in Part

10, Title 15, of the Code of Federal Regulations. The

purpose of the standards is to establish nationally rec- ognized requirements for products, and to provide all concerned interests with a basis for common understanding of the characteristics of the products. NBS

administers this program as a supplement to the activities of the private sector standardizing organizations.

Consumer Information Series—Practical information,

based on NBS research and experience, covering areas

of interest to the consumer. Easily understandable language and illustrations provide useful background knowledge for shopping in today's technological marketplace.

Order above NBS publications from: Superintendent

of Documents, Government Printing Office, Washington,

D.C. 20i02. Order following NBS publications—NBSIR's and FIPS

from the Natioiial Technical Information Services,

Springfield, Va. 22161. Federal Information Processing Standards Publications

(FIPS PUBS)—Publications in this series collectively constitute the Federal Information Processing Standards Register. Register serves as the official source of information in the Federal Government regarding stand- ards issued by NBS pursuant to the Federal Property

and Administrative Services Act of 1949 as amended.

Public Law 89-306 (79 Stat. 1127), and as implemented

by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS for

outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Services (Springfield, Va. 22161) in paper copy or microfiche form.

BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey

bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service. A

literature survey issued biweekly. Annual subscription: Domestic, 825.00 ; Foreign, 830.00'. Liquified Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00.

Superconducting Devices and Materials. A literature survey issued quarterly. Annual subscription: $.W.00 . Send subscription orders and remittances for the pre- ceding bibliographic services to National Bureau of Standards, Cryogenic Data Center (275.02) Boulder,

Colorado 80302.
U,S. oePARTMENT OP COMMERCE

National Buraau of Sktndards

Washinflton. D C. 20234

OFFICIAL BUSINESS

Penalty far Private Use, S300

POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE

COM>218

SPECIAL FOURTH-CLASS RATE BOOK