NATIONAL BUREAU OF STANDARDS REPORT

2929

THE KEATING AND VENTILATING SYS TEN AT REFLECTION POINT

by

P 0 Ro Achenbach

So D„ Cole

Report to

Division of Housing Research

Housing and Horae Finance Agency

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STAUPAKPS REPOUT

ms PROJECT NBS REPORT

1003-20-1014 November 19 , 1953 2929

THE HEATING AND VENTILATING SYSTEM AT REFLECTION POINT

by

P, R. Achenbach

Sc D. Cole

Heating and Air Conditioning Section

Building Technology Division

to

Division of Housing Research

Housing and Home Finance Agency

<NBS>

0. S. DEPARTMENT OF COilERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprint

unless permission isobt; 25.D.C, Such permit)

cal ly prepared If that

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

art, Is prohibited

irds, Washington

has been spoclfit for Its own use,

HEATING AND VENTILATING SYSTEM AT REFLECTION POINT

by

Po Ro Acbenbach and So Do Cole

A3STRACT

An unconventional heating and ventilating system

in a prototype bouse, known as Reflection Point,

in Cincinnati, Ohio, was investigated during a

field test to study the methods of heat transfer

from the heat source to the room surfaces and to

determine whether the use of reflective materials

on walls and ceiling resulted in any decrease in

heat requirements,, The heating system employed

electric heaters in coves near the ceiling, reflective paper on walls and ceilings, reflective

draperies, and special floor coverings „ Forced

ventilation was used with an electrostatic precipitator for air cleaning „ A continuous test

of 20 hours duration at low outdoor temperatures

indicated that inadequate heating capacity was

provided for design conditions, that this house

had practically the same heat loss for a given

indoor-outdoor temperature difference as it would

have with non-reflective furnishings and a conventional heating system, and that wall and roof

constructions of lower heat transmittance should

he used for economy in heating 0 The tests further

indicated that this heating system would satisfactorily,'- heat a house of moderate heat loss, that

it produced a greater radiant heat flux in the

living space than a plastered ceiling heating panel,

and that it had the characteristics of a multidirectional source of radiant energy and would

probably warm the floor of a house ar.d the lower

extremities of the occupants better than a plastered ceiling heating panel. The forced ventilation

eliminated much of the random infiltration of outdoor air except during very windy weather

„

I. INTRODUCTION

At the request of the Housing and Home Finance Agencyfield tests were made of an experimental heating and ventilating system at Reflection Point in Cincinnati , 0hio o The

system in this house was unconventional in that electric

heating elements in coves near the ceiling were employed,

walls and ceilings were covered with reflective wallpaper,

special reflective drapery materials were used at the windows,

portions of the floor were covered with aluminum foil and an

embossed rubber pad beneath the rugs, and a ventilating blower

pressurized the house by introducing unheated outdoor air

through the perforated ceiling of a central hallo

The tests were made to provide information as follows

in regard, to this heating and ventilating system:

(1) Evaluate the emissivities of the wall coverings and

draperies

o

(2) Evaluate the heating element temperatures

»

(3) Determine whether or not less heat was required to produce a given air temperature in this house than for

houses with conventional wall coverings of higher

emissivity and with conventional heating systems 0

(4) Determine whether or not the reflective drapery

materials reduced the heat loss through the windows e

(5) Evaluate the relation between surface and air temperature at exterior walls, interior walls, floor, furniture, etCo

(6) Determine whether or not comfort was attainable at appreciably lower air temperatures than for conventional

heating methods

»

(7) Evaluate the amount of forced ventilation and its effect

on house temperatures and comfort 0

II„ DESCRIPTION OF HOUSE

The prototype house was a one-story structure built on

a bluff overlooking the city of Cincinnati, Qhio a The living

room, dining room, kitchen, and entrance foyer were built on

a concrete floor slab on grade whereas the bedrooms and study

were built over a small basement and double garage „ The gross

floor area of the house was about 2000 sq 0 ft 0 and the ceiling height was 9 feet except in the kitchen, interior hall,

and bath adjoining the study 0 The significant areas and

volumes of the various rooms are summarized in Table 1 0


.

V ,
TABLE 1 - ROJM SIZES AND VOLUMES AT REFLECTION POINT

Room

Length

oi Cola

Wall

.

Ceiling

Height,

ft

Gros; Cole Wall

Ar^e

,

ft4-

Window

Area

i t

f

Door

Area

»

ft

?

Net Cold

Wall

Ai tp,

ftr

Other Heat Celling Floor

Transmitt 1 Area, Area. Partitions,

ft1

- ft ft

Crack

Length

ft

Room

, Volume

ft^

Living Room 39.6 9 356 100 0 256 0 377 377 0 3393

Dining Room 27.8 9 250 73 0 172 0 189 139 21 1701

Kitchen end Utility 29.0 s 232 66 18 146 0 254 254 51 2032

Fo; er n.2 9 161 51 20 30 0 176 17S 19 1534

Interior Hall 5.5 7.9 43 8 20‘ 15 113^ o* 233 37° 1841

North Becroom 26.2 9 236 53 0 178 0 160 160 96 l44o

Sout'r Bedroom 2S.9 9 2b0 68 0 132 0 23s 238 5° 2142

Study i4 .e 9 131 53 r\ 73 0 l?9 129 6-3 ll6l

Large Bath 7.0 8 56 6 0 -0 49r 57 57 11 4^6

Small Bath 0.0 10 21 0 18c 0 23 24 0 240

Whole House 169.8 - l 63 f 433 53 1135 162 lfios 13376 294 13930

Partitions adjacent to basement stairwell

^ Fresh air inlet

C Walls for ekyligit

Total enclosed Hot area for whole house was 1986 ft^

3

Several special construction features were incorporated

in the house which were related primarily to the heating,

ventilating, and air conditioning of the structure 0 The more

important of these features are summarized below:

1„ Coves extending about one foot downward from the ceiling

and one foot from the sidewalls were used to support,

partl}^ enclose, and conceal from view sheathed electric

heating elements and copper tube refrigerant circuits,

used to heat and cool six rooms of the house, respectivelv„ The hallway, bathrooms, and part of the kitchen

were heated by high temperature sheathed electric heaters mounted on the walls near the ceiling,, The cove

heaters totalled about 60% of the installed heating

capacity,,

2 0 Embossed aluminum foil paper in various colors was used

for interior coverings on most of the wall and ceiling

area 0

3 c Fabrics i^ith moderate reflective properties were used for

draperies at many of the large windows

„

4„ The concrete floors were covered with aluminum foil with

the reflective surface upward, a waffle-design foam

rubber mat and wall-to-wall nylon carpeting in the living

room, dining room, den, and one bedroom,, Cork floor covering was used under the aluminum foil for the portion of

the floor over the basement and garage 0

5o Forced ventilation with filtered outdoor air was provided

using a blower and electrostatic precipitator to reduce

random infiltration at doors and windows „ The ventilating

air was introduced through a perforated ceiling in the hall

without special means for preheating it„

6„ Large picture windows were used in every room of the house,

totalling about one third of the gross exterior wall area.

Most of the windows were of fixed plate glass with no provision for opening them„

7„ The electric heaters in each room were divided into several

circuits o Four thermostats with stepped settings were

used to add increments of heating capacity in each room as

the air temperature decreased,.

Inspection of the house construction during the tests and

published descriptions of the house indicate that the following

materials were used:

Walls:

- 4 -

Embossed aluminum foil wallpaper on 3/$ in 0 gypsum

board on 2x4-in 0 studs with 3 ft in Q plywood sheathing and 25/32 in G redwood vertical tongue -and -groove

sidingo

No insulation in the stud spaces,,

Roof: 7x12- in o wooden beams spaced $ ft„ on centers , carrying l/4 in 0 plywood ceiling, 2x6 in Q tongue-and-groove

planking covered with 6 layers of roofing felt Q The

ceiling was covered with embossed aluminum foil paper 0 (There was a layer of about l/2-in„ of ice frozen on

the roof surface during the tests) 0 Floor: On grade , there was a layer of gravely a concrete slab

with aluminum foil covering, waffle-design sponge

rubber mat, and nylon carpet ing Q Over the basement

and garage there was a 5/l6~in 0 layer of cork tile

between the concrete slab and the aluminum foilo

III* TEST PROCEDURE

Two and one-half days were spent in the house studying the

performance of the heating system 0 The first twenty-four hours

were used to become acquainted with the electric heating circuits in the house, installing thermocouples, and preparing for

specific measurements of temperature and heat consumption » This

period of preparation was followed by a continuous test of 20

hours duration from 4:00 P.M„ on February/ 7 until noon of the

following day during which the outdoor temperature decreased to

2o5°F and the wind velocity attained 14 mph for one minute intervals at various times 0 Shielded thermocouples were installed at the 30-in 0 level

in the center of each room„ Thermocouples were also placed on

three wall surfaces of the living room at the 30-in o level;

in the air one inch from the wall- surface thermocouples in the

living room; at the fresh-air inlet in the hall; on the rug,

rubber mat, and aluminum foil on the floor of the study, respectively; on the rug at the center of the living room; on

the window surface in the living room; and on the sheath of the

electric heating elements at two places „ In addition an unheated £-inch black globe was used at the center of the living room

to obtain a radiation-convection temperature, and an ordinary

mercury-in-glass thermometer was installed at the same station 0 Outdoor temperatures were measured with a mercury thermometer

and wind velocities were observed with a vane anemometer for

one minute intervals each hour 0 Hourly readings were taken of

all watthour meters used to integrate electrical energy consumption,,
' - . * \ . * . . -
- 5 -

Because the outdoor temperature was low, all of the installed

electric heaters were energized during the entire 20-hour continuous testo During the seven-hour period from 5° 00 P 0 Me to

midnight all of the Venetian blinds were raised and all of the

draperies were drawn away from over the windows 0 During the

next four hours all of the blinds were in the lowered positions

and all drapes were drawn over the windows 0 From 4° 00 AJf 0 to

£°00 AoKo all of the windows remained covered and the ventilating air blower was stopped 0 During the course of the test the ceiling surface temperatures and interior and exterior wall surface temperatures in

the living room were observed at small distance intervals by

means of a taped thermocouple 0 The air delivery of the ventilating blower was also measured with an anemometer 0 Samples of all the different reflective wallpapers and

fabrics were secured from surplus rolls stored in the house

for measurement of emissivity 0 IV o TEST RESULTS

Emissivity of the Wall Coverings and Draperies

The total thermal radiation emissivity was measured for

samples of each of the kinds and colors of reflective wallpaper

and for the milium fabric and the woven nylon with foil yarn

used as drapery materials 0 The total emissivities at a temperature of 212 °F and the thicknesses of the wall coverings and

drapery materials are summarized in Table 2 0 Because the thicknesses of the materials affect the surface temperatures of the

specimens during the tests the true values of emissivity at

2i2°F are probably about one percent higher than the tabulated

values for the wallpapers and from 3 to 5 percent higher than

the tabulated value for specimen 10, the nylon fabric 0 The table shows that the emissivity of the wallpaper varied

somewhat with color, ranging from a low value of 0 o 26 for the

bronze color to a high value of 0 o 40 for the red color 0 The

average of the values for the eight specimens was 0 o 32 o An

emissivity of 0 o 05 was measured for a specimen of the red wallpaper with the red paint removed which is in the range expected

for polished aluminum,,

The emissivities of the drapery fabrics were in the range

from 0„5$ to 0 o 69 which is lower than for most fabrics in common

use for this purpose,,
4 ' ( • , '
Table 2

EMISSIVI TY AND THICKNESS CF

WALL COVERINGS AND DRAPERIES

Specimen Thickness Emissi'

#1 - Red Daisy ,0056 . 40

#2 - Gra}?- Poinsettia .0053 • 31

#3 - Bronze Dai S 3

;' .0056 . 26

#4 - Green Poinsettia 0 OO36 .34

#5 - Blue Daisy .0053 .30

#6 - Gra3

.; Daisy .0060 .32

#6 - Gray Daisy reversed, white

paper side out .0060 .7$

#7 - Gray Stipple .0063 .30

#8 - Yellow Dais?/ .0060 .35

#9 - Gray Cloth (Milium fabric) .0061 o5S

#9 - Gray Cloth Reversed

(Milium fabric) .65

#10 .= Aluminum Cloth

(Nylon with foil 3;arn) .0170 .69

#6 - Gray Daisy (Paper removed) .0015 .31

#1 - Red Daisy (Red paint removed

surface bright) 05

6 -

Heating; Element Temperatures

Measurements were made of the heating element temperatures

at two locations, one on the south side of the living room and

the other on the west side of the south bedroom by securing fine

wire thermocouples to the metallic sheath of the electric elements.

For constant heating at full capacity the living room heater element had an average temperature of 430°F whereas that in the

south bedroom averaged 500°F, There were small deviations of

±10°F from the above averages caused by voltage variations and

changes in average room temperature

,

At these temperatures the sheathed electric heating elements would act very much like black body radiators emitting

energy in all wave lengths with a maximum intensity at a wave

length of about 5,6 microns

,

Heat Loss

Because of the low outdoor temperature prevailing during

the 20-hour continuous test all of the installed electric heater

capacity was energized continuously throughout the test. Thus

the heat input was uniform at a rate of 27,9 KW, equivalent to

95,300 Btu/hr,

The temperatures observed in the house during the tests are

summarized in Table 3 for three time periods, namely, (a) from

8 P,M. to midnight when all windows were uncovered, (b) from midnight to 4 AoMo when all windows were covered with drapes or

Venetian blinds, and (c) from 4 A,M„ to 8 A,M, when all the

windows were covered but the ventilating blower was not running.

The indoor air temperature at the room centers, the outdoor

temperature and wind velocity and the indoor-outdoor temperature

difference are shown graphically in Fig, 1 for the 20 hours of

the test.

The computed heat transmission coefficients for the several

building elements are listed in Table 4 with adjustments having

been made to the outside surface coefficient in accordance with

the observed average wind velocity during the three time periods

previously mentioned. The computed heat loss of the house for

each of the three test conditions and for the design conditions

of 70 degree indoor-outdoor temperature difference and 15 mph

wind has been summarized in Table 4o
.
Table 3

OBSERVATIONS IN HOUSE AT REFLECTION POINT

DURING FIELD TEST

Time Peri od

7 PM 12 M 4 AM

to to to

12 M 4 AM 7 AM

Average Outdoor Temp. , °F 7.3 6.5 3.4

Average Wind Velocity, mph 7.5 5.4 3.9

Indoor-Outdoor Temp. Diff 0

, deg. F 45.9 46.1 50.6

Temp, at Room Centers, 30-in . level

Living Room, Unheated Globe, °F 57oO 56.2 57.7

Living Room, Shielded Thermocouple, O 77 53 ol 52.6 54 .0

Dining Room, ft ff °F 51 o4 50.7 51.7

Kitchen, fr TT op 54.7 52.7 54.4

Foyer ,

?? Tf °F 52.3 50.6 53.1

N. Bedroom, ff ?T °F 54.

4

52.7 53.6

So Bedroom, ?T ,T op 56.2 54.5 55.5

Large Bath, " 11 °F 57.0 54.1 55.

8

Study, T? op 73.6 77.3 77.6

Average, ?t rT op 54.2 52.6 54.0

Exterior Wall Surface, Living Room, °F 46 .

4

44

.

,r 44.5

Air 1-in. from Wall " " °F 51 cl 49.6 50.3

Interior Wall Surface, TT n °F £ O O

J l O ~ 55.7 56.2

Air 1-in. from Wall, TT ,f °F 55.7 54.7 55.4

Fresh Air at Hall Ceiling, °F 33d 31.3

Window Surface, Living Room, °F 29c 5 22.7 24.3

Rug Surface, Living Room Center, °F 61.0 59.9 60.0

Rug Surface, Study, °F 6^ 0 6 69.7 69. 7

Upper Rubber Mat Surface, Stud}’, °F 65.7 65.6 66.3

Aluminum Foil Surface, Study, °F 57.

8

57.9 58.4

Heating Element Temp. , Living Room, °F 437 42 5 425

Heating Element Temp., 3. Bedroom, °F 50F 495 494

Heat Input Rate, Btu/hr 95*300 95,300 95*3'

a Study not included

CO

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uj q:

ce: lu

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a:uj

CL

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UJ

_i

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h-

° ^ o

_J

UJ

>

o

z

TEMPERATURE

,°F

WIND

VELOCITY,

MILES

PER

HOURS

HEATING SYSTEM PERFORMANCE AT REFLECTION POINT CINCINNATI

CONSTANT HEAT

INDOOR ! TEMPERATURE

SHIELDED THERMOCOUPl I

TEMPpI

TDOOR

.OUTpl TEMPI'ERATUHI

10 II I2M I 2

TIME IN HOURS

TPTrr

Table 4

COMPUTED TRANSMISSION COEFFICIENTS

AND HEAT LOSSES AT REFLECTION POINT

COMPUTED TRANSMISSION COEFFICIENTS , BTU/HR (FT2 )(°F)

Wind Velocity, mph

15 7.5 5.4 3.9

Ceiling 0.326 0.315 0.310 0.306

Outside Walls 0.312 0.303 0.297 0.294

Windows and Doors 1.13 1.02 0.96 0.92

Floor over Basement 0.33 0.33 0.33 0.33

Inside Partitions 0.37 0.37 0.37 0.37

COMPUTED HEAT L OSS OF LIVING SPACE, BTU/HR

Indoor-Outdoor Temp 0 Diff . °F 70 45 0 9 46.1 50.6

Wind Velocity, mph 15 7.

5

5.4 3.9

Outside Walls 24,700 i 5 750 15,720 17,150

Windows and Doors 42,300 24,020 23,730 25,100

Inside Partitions 1,350 geo 900 990

Ceiling ;'c,4°oa 36,350 39,600 40,600

Floor over Basement 7,360 4,170 3,920 3,920

Slab on Ground 4 s 470 2,920 2,970 3,260

Infiltration*) /s /

S' j J 13,220 13,270 14,570

Total 153,740 100 9 120 100,120 105,620

aBased on 100 Deg. F c Temperature difference between

ceiling surface and outdoor air

’D 8ased on one air change per hour

- 7

A comparison of the data in Tables 3 and 4 shows that a

heat input rate of 95 9 300 Btu/hr produced an average indooroutdoor temperature difference of 45°9°F for the period from

8 PoM„ to midnight whereas the computed heat loss using conventional methods was 100 ,,120 Btu/hr « That is, the observed

heat loss was 95 .1$ of the computed value Q This is considered good agreement in view of several uncertainties in the

heat loss calculations such as the reverse heat loss from

the heated coves , the two kinds of foundation construction,

the variable ceiling temperatures, the effect of radiant

heat on the window losses, and the infiltration rate D An agreement between observed and computed heat losses

with less than 5 % disparity is not to be expected with any

kind of heating system 0 This comparison between observed

and computed heat loss indicates that a heat loss calculation made by conventional methods would be a good guide in

selecting the heating capacity required for the type of heating system and construction used since the heat is introduced

into the living space without significant losses 0 The computed heat loss of the structure was 77° 5 Btu/hr

per sq 0 ft» of enclosed floor area at design outdoor weather

conditions which is a higher heat loss rate than for most

present-day dwelling constructions 0 It will be noted in

Table 4 that the ceiling heat loss accounts for 34 to 39 percent of the total computed loss of the house 0 This is an unreasonably high percentage considering the relative ease with

which a ceiling can be insulated „ These percentages indicate

that more heat was lost through the ceiling than was probably

absorbed by the ceiling surface from the direct radiation of

the electric heaters 0 In the six rooms of the house heated from coves at the

ceiling the gross heat input was 56,500 Btu/hr or 44° 5 Btu/hr

per sq 0 ft„ of ceiling area under the test conditions „ Assuming that about 3$ percent of the total heat input was lost

through the roof, the net heat transfer downward from the ceiling was approximately 28 Btu/hr per sq 0 ft D of ceiling area Q Effect

When the Venetian blinds were lowered and the drapes

drawn over the windows for the period from midnight to 4 A 0 M„

,

there was practically no change in the indoor-outdoor temperature difference for the same heat input rate 0 During this
.
period the heat input rate of 95 ? 300 Btu/hr produced an indooroutdoor temperature difference of 46 0 1°F 0 The computed heat

loss was the same for this period because both the average wind

velocity and temperature decreased,, As compared to the first

four-hour period of the test 9 the indoor temperature decreased

1„6°F and the outdoor temperature decreased 1„8°F during the

second four-hour period,, The infiltration heat loss computation

during both periods was based on one air change per hour and

the observed temperature difference between room air and outdoor air s Table 3 shows that the window surface temperature in the

living room decreased 6»7°F after covering the windows whereas

the outdoor temperature decreased only 1 0 8®F 0 This decrease in

window temperature indicates a lower window heat loss at the

thermocouple location but may not be indicative of the average

change for all windows 0 A drapery in front of a window produces

a chimney effect that probabl}?- increases air circulation adjacent to the window pane as compared to an undraped window,,

The decreased window heat loss, if it existed , was partly or

wholly counterbalanced by the greater loss through that portion

of the wall that was covered by the drapes when they were drawn

back since there was no appreciable increase in indoor-outdoor

temperature difference caused by covering the windows

„

Wall, Floor, and Ceiling Temperatures

The temperatures observed on the exterior wall surface and

one inch from the wall surface, as summarized in Table 3 S indicate that the wall surface was 4o$°F colder than the air for

the period from midnight to 4 A„M0 For the same wall construction and indoor-outdoor air temperature difference, but with

non-reflective wallpaper on all interior surfaces and a convection heating system the wall surfaces would be about $°F colder

than the room air„ This comparison indicates that enough

radiant heat was incident upon and absorbed by the reflective

wallpaper to raise its temperature about 3°F above that expected with non-reflective wallpaper in a convection-heated house

„

The actual rise of the reflective wallpaper temperature

may not have been quite as great as 3®F because the cellulose

tape used to secure the thermocouple to the wall may have absorbed enough additional radiation to locally warm the thermocouple o However, a similar thermocouple on an interior wall

averaged only 1 0 1°F warmer than the air one inch from the wall

so this represents an approximate upper limit to the error

caused b^r the tape on the outside wall„ This rise in exterior

wall surface temperature caused by the absorption of radiant

o _

energy would cause a greater loss of heat through the exterior

wall for the same indoor-outdoor air temperature difference

than for a non-reflective wall without radiant sources in the

room e For the conditions existing during the test the increase

of the wall heat loss from this cause would be about 5%, for a

2 degree warmer wall surface temperature,,

The rug surface at the center of the living room averaged

7 to £°F warmer than the air at the 30 in 0 level « The rug,

being a good absorber, received radiant heat from the ceiling

and walls and served as a source of convection heating for the

air in the room.

The temperatures of an interior and exterior wall and the

ceiling of the living room were observed at 6-inch and one-foot

intervals between 7 and £ A , M * when the ventilating blower was

not running 0 These temperatures are indicated on an outline

vertical section of the room in Fig* 2„ The rug surface temperature and air temperature at the 30-in * level are also shown* A

vertical gradient in exterior wall surface temperature of 13

to 14°F was observed

o

The pattern of ceiling surface temperature shown in Fig *2

is plotted against distance in Fig* 3 to indicate the shape

of the temperature curve* The arithmetical average of the

ceiling temperatures shown in Fig* 3 is about £6°F* for the

ceiling surface between the edges of the coves* The heat input

rate iri the living room was 17,065 Btu/hr during this period

of the test and the temperature of the unheated globe at the

center of the living /room was 57*7°F* Thus an average of 45°3

Btu/hr per sq* ft. of ceiling area was transmitted from the

electric heating elements in the living room for a difference

of 2£*3°F between the average ceiling temperature and that of

the unheated globe*

Computation indicates that the heat loss of the ceiling in

the living room was about £,700 Btu/hr or just about half of

the heat input into the living room* Thus, about half of the

energy transferred from the heating elements in the living room

was lost through the roof and a substantial portion of this

upward heat loss represents heat that was not available for

reflection or radiation to the room from the ceiling surface*

Therefore, the average heat emission and reflection of the

ceiling surface to the room may have been as low as 22.6 Btu/hr

per sq* ft* under the conditions described above* It is probable,

however, that the heat radiated from the ceiling was greater

than this value because some of the £,700 Btu/hr heat loss of

the roof must have been provided by warm air in contact with



FIG. 2



PATTERN OF CEILING SURFACE TEMPERATURE IN LIVING ROOM

• SOUTH WALL COOLII COVE

- 10 -

the cooler central area of the living room ceiling or by reflected energy from the walls . The measured heat output of

a plastered, ceiling heating panel containing embedded copper

tubes , for the same difference between average ceiling temperature and an unheated globe temperature at the 30-in, level,

were found during other studies to range from 27° 5 to 32 Btu/hr

per sq 0 ft. of panel area depending on the tube spacing.

Thus* it would appear that the coves and reflective ceiling

surface at Reflection Point and a non-reflect ive ceiling panel

heating surface might be about equally effective per unit area

in transmitting heat to a living space for the same temperature difference between ceiling surface and an unheated globe.

If the roof had been better insulated, thus decreasing the

upward heat loss, the effectiveness of the cove and reflective

ceiling system would have been proportionately increased.

Comfort

It was impossible to make any precise observations regarding what constituted comfort conditions in the test house

during a brief field trip. However, during the day preceding

the 20-hour test summarized in Table 3 and Fig, 1, outdoor

temperatures were considerably higher and the interior of the

house was warmer. Specific note was taken by the observers

during this first day that an air temperature of about 67 or

6£°F was required for comfort while they were moving about in

the house and clothed in ordinary business suits. Of course,

it is possible that other individuals would be comfortable at

lower air temperatures.

At no time during the 20-hour test from 4 PoM, on February 7 to 12 N on February $ was the house comfortably warm

when the air temperatures ranged from a high value of 63 °F in

the living room at 4 P,M, down to 50°F in the dining room and

foyer at 4 A,M, A portable electric heater was used to warm

the study to a higher temperature during the test to provide

a comfortable location for the observers when data were not

being ta'ken , However, the electric energy used by this portable heater was not included in the heat input used for computation purposes and the air temperature in the study was

not included in the average for the house.

Obviously, portable electric heaters could be used to make

any small area in the house comfortable during severe weather

even though the general level of temperature in the house was

uncomfortably low. However, resort to "spot heating" with a resultant saving in overall heat usage is a possibility with

any heating system and should not be considered as one of the

special features of this particular house.

- 11

The data in Table 3 show that the radiation-convection

temperature measured with the unheated globe was 4o2°F higher

than that indicated by a shielded thermocouple at the same

station o For the conditions of the test and. an 0 in. globe,

the mean radiant temperature was computed to be 2.5°F above

the globe temperature 0 The difference between air temperature and mean radiant temperature would probably increase at

greater heat input rates and decrease at lower heat input

rates 0 For equal comfort, the mean radiant temperature in

a convection-heated room will always be a little lower than

the air temperature whereas for this system the mean radiant

temperature would always be expected to be higher than the

air temperature o Thus, comfort would probably be attained

with the heating system used in this house at an air temperature several degrees lower than for a convection heating

system with no high temperature sources of radiation present.

This difference in air temperature might approach 10% of the

indoor-outdoor temperature difference at design conditions.

However, it was impossible to deduce from the data taken that

the reduction in heat loss resulting from lower air temperature would not be offset by the greater heat loss to the walls

and windows due to the greater radiant flux in the rooms.

It is concluded. , therefore, that the saving of heat would

probably be less than 10% for the heating method employed as

compared to a convection heating system entirely/ enclosed in

the living space.

In the Test Bungalow a ceiling panel heating system produced a radiation-convection temperature in an 0-xn. unheated

globe 2.1°F above the air temperature at the same station with

non-refl ective surfaces on walls and ceiling when the outdoor

temperature was 32°F and the average heat transfer rate from

the ceiling was about 20 Btu/hr per sq. ft. of panel area.

If it is assumed that the heat transfer rate from the reflective

ceiling at Reflection Point was also of the order of 20 Btu/

sq. ft. of ceiling area during the 20-hr test heretofore described, then it is concluded that the radiant heat flux intercepted by the unheated globe was about twice as great at Reflection Point as in the Test Bungalow because the temperature

difference between globe and air was about twice as great at

Reflection Point.

In the Test Bungalow using a plastered ceiling panel heating system comfort was experienced by most observers with summer weight clothing at an air temperature of 67°F to 60°F except for some coolness around the feet and lower part of the

legs after several hours exposure. The floor surface temperature at the center of the room was equal to the air temperature

at the 30-in. level ±1°F In most cases. At Reflection Point

the rug surface temperature was 7 to 0 degrees warmer than

- 12 -

the air at the 30-in . level 0 This indicates that appreciably greater radiant heat flux reached the floor at

Reflection Point 0 The comparison is not ideal because the

Test Bungalow had an unheated basement whereas the living

room floor at Reflection Point was on grade „ However, the

comparison is believed to be significant because sub-floor

temperatures have been shown to have only a small effect

on floor surface temperatures in buildings with uninsulated

wallso These comparisons suggest that comfort might be obtained in a room with a plastered ceiling heating panel at

about the same air temperature as in a room with reflective

walls and ceiling of the t 3rpe used in the house at Reflection

Point except that the former would approach more nearly a unidirectional heat source and would not radiate as much heat

to the lower parts of the occupants of the room as the latter.

Forced Ventilation

The volume of air delivered by the ventilating blower

was measured near the outlet of the electrostatic precipitator., The observed air deliver}*- after being corrected to the

density of the house air wa s 370 cfm 0 This represents about

I, 4 air changes per hour for the house

»

During the period of the test from midnight to 4 A.K,

when the outdoor temperature averaged 6*5°F the ventilating

air entered the living space at the perforated ceiling in

the hall at an average temperature of 31°3°F* This caused

the hall to feel undesirably cold. It is believed that the

hall would still have felt too cold if the remainder of the

house had been at a comfortable temperature and the ventilating air were brought in without tempering*

When the ventilating air blower was stopped the temperature difference between indoors and utdoors increased about

5 degrees indicating that the natural ventilation with an

average wind velocity of 4 mpb was less than the forced ventilation rate* During the period from midnight to 4 Adi about

14,600 Btu/hr were required to warm the ventilating air from

the temperature at the precipitator outlet to the average room

temperature* The remaining $0,700 Btu/hr of the gross electric

heat input were available for heat transmission loss correspond

ing to an average of 1750 Btu/hr per degree indoor-outdoor

temperature difference* Since the indoor-outdoor temperature

difference increased ,5°F when the blower was stopped an additional $,750 Btu/hr was used to offset heat transmission loss

and the remaining 5, $50 Btu/hr represents the heat required

to warm the natural air leakage* This represents about

115 cfm or 0*43 air change per hour*

13

It was observed during the earl]/- part of the test

when the wind velocity was higher that outdoor air leaked into the house around the doors on the windward side

of the house even when the ventilating blower was running,.

IV. DISCUSSION AND CONCLUSIONS

The experience gained during the field test at Reflection

Point and analysis of the data obtained indicates the following conclusions:

(1) Disregarding the cost for electric heating, a house

of moderate heat loss can be comfortably heated by

using radiant heat sources in coves at the ceiling

and reflective papers on the walls and ceiling such

as were used at Reflection Point. However, the test

house was inadequately heated by the electric heating units usedo All of the installed capacity produced an indoor-outdoor temperature difference of

about 46 °Fo

(2) Reflective ceiling and wall surfaces used with a

source of radiant heat in coves at the ceiling,

appeared to increase the radiant heat flux in the

living space as compared to most other heating

methods; had the characteristics of a multi-directional

source of radiant energy; and appeared to warm the

floor of the house and the lower extremities of the

occupants better than an ordinary ceiling heating

panel would <51 o, even though the surfaces had emissivities no lower than 0 0 3 «

(3) In the opinion of the observers an air temperature

of about 6?°F to 6$°F was required in this house

for comfort when the observers were engaged in light

activity and clothed in conventional business suits.

The mean radiant temperature of the living room in

the house was about ?°F higher than the air temperature during the test.

(4) The test results did not indicate positively that

an]/ saving in heat resulted from the use of reflective celling and wall coverings. It Is reasonably certain that the saving, if any, would be less

than 10% as compared to some other convection and

radiant heating systems entirely contained in the

living space. It is believed that the greater savings claimed by the owner are dependent partly on

- 14 -

maintaining lower air temperatures than were

considered comfortable by the observers; partly on the saving of heat possible during sunny

weather in any house with large window areas

on the east, south and west exposures because

of solar heating; and possibly by some use of

spot heating with portable heaters

.

(5) Because the heating system used at Reflection

Point did not significantly reduce the heat

loss of the house as compared to a conventional system, it is just as important to provide

low heat transmission values in the roof and

exterior wall construction with this t 3^pe of

heating system as with any other . The heat

transmission coefficients of the roof and exterior walls were considered to be undesirably

high 0

(6) With radiant heaters in a cove near the ceiling,

a reflective ceiling would have lower ceiling

surface temperatures and lower ceiling heat loss

than a non-reflective ceiling. It is probable

that a non-reflective ceiling surface would be

adversely affected by the high temperature near

the coves if it were made of plaster or wood

.

However, a house with a reflective ceiling

could probably be warmed satisfactorily with

either reflective or non-reflective wall coverings by means of radiant heaters in coves near

the ceiling of the type used at Reflection Point,,

(?) Ceiling surface temperatures were higher near the

perimeter of the rooms than near the center.

While this pattern of temperature is desirable

near the exterior walls from a comfort standpoint,

excessive ceiling temperatures tend to make the

ceiling paper brittle and might adversely affect

wood or plaster surfaces if these materials were

used as a base for the reflective paper on the

ceiling. These considerations might dictate a limiting heat loss which this type of distribution

system could accommodate. ' There was some evidence

of brittleness of the paper on the ceiling of the

test house even though the heating system had not

been in operation one full heating season at the

time of the tests. Ceiling surfaces temperatures

of 125°F were observed near the coves during the

test even when the heat input rate was inadequate

for the house.

(?) The special drapery materials had emissivity coefficients in the range from 0®5'~' to 0®69 and

their use over the large windows did not significantly change the heat loss of the house,, The

temperature difference between the air and an

unheated globe at the center of the living room

was increased only 0®3°F as a result of drawing

drapes and blinds over all the windows,, This

does not represent any considerable change in

the comfort in the living room

(9)

The nylon rugs, foam rubber mats, aluminum foil

and cork tile were considered to be adequate

floor coverings,. As used, the aluminum foil was

only partial^ effective as reflective insulation because about half of the surface was in

contact x-vith the rubber mat „ In our opinion,

other satisfactory floor coverings could be found

for houses using this type of heating s^vstem®

(10) Consideration of the importance of radiant heat

transfer in the heating system at Reflection

Point indicates the necessity for the type of

step-control or modulating control of the heat

sources that was used to avoid uncomfortable

periods that would occur with an on-off type of

control®

(11) Forced ventilation of the test house presumably

eliminated much of the random air leakage except on the windward side and promoted interior

cleanliness although the latter feature was not

directly observed during the field test® The

natural ventilation rate of the house was quite

low when the blower was not running® The introduction of untempered ventilating air through

the hall ceiling caused coolness in local areas

nearb}?-® Tempering of the ventilating air before

introduction would eliminate such discomfort and

would not add to the cost of heating the house®

THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

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Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

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found in NBS Circular 483, Testing by the National Bureau of Standards (25 cents). Both are

available from the Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of Standards, Washington 25, D. C.
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