Reference

iii

NBS

Publi

cations

U.S. Department of Commerce

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Washington, D.C. 20234

NBSIR 81-2248

A Regional Economic

Assessment of Selected

Window Systems

I

Rosalie T. Ruegg

Robert E. Chapman

NBSIR 81-2248

A REGIONAL ECONOMIC

ASSESSMENT OF SELECTED

WINDOW SYSTEMS

NATIONAL BURKA

or standards

library

SEP 1 6 1981

U C(s,

nc %(-

i4%l

Rosalie T. Ruegg

Robert E. Chapman

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Economics and Regulatory Technology Division

Washington, DC 20234

July 1981

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Director
'.••• V

r v

'

i "M

.

'
PREFACE

The background work for preparing this report was conducted within the

framework of a National Bureau of Standards (NBS) interdisciplinary research

project on the energy-related performance of windows. This effort was supported jointly by NBS and U.S. Department of Energy (Mode 2 of Contract E

(49-1) 3800), and by the U.S. Department of Housing and Urban Development

(Contract No. Rt 193012), as a portion of the Building Energy Performance

Standards Program.

This report is the fifth in a series of publications resulting from this NBS

interdisciplinary project on windows. The economic model for evaluating

window performance is described in an earlier report, Economic Evaluation of

Windows in Buildings: Methodology [1]. The thermal model used to compute

energy gains and losses through windows is described in Simplified Analysis of

Thermal and Lighting Characteristics of Windows; Two Case Studies [ 2

]

.

The

window systems examined in this report, as well as many additional window

systems not examined here, are described in Window Design Strategies to Conserve Energy [3]. An overview of findings from the interdisciplinary project

was reported in A New Look at Windows [4], An earlier NBS report, Retrofitting

Existing Housing for Energy Conservation: An Economic Analysis [5], applied an economic optimization model to a group of energy conservation techniques, and

identified the minimum sizes of storm windows which would be cost effective for

a variety of climates and a range of current energy prices. That study, however, considered a single-family residence only, and, unlike this report, did

not take into account other window choices, such as orientation, size of the

primary window, the use of wind management devices such as blinds and shutters,

nor the potential of using windows for daylighting.

A recent NBS report, Daylighting, Window Management Systems, and Lighting

Controls [6], provides empirical data on daylight availability and interior

illumination which support a finding of this report that economic savings from

daylighting are potentially great.

The reader is cautioned that the quantitative results of this report are based

on specific assumptions and incomplete data. The results are offered despite

their limitations, in the hope that they will focus attention on the possibilities for saving energy and reducing long-term costs through the considered

selection and use of windows in buildings.

iii
ACKNOWLEDGMENTS

The authors wish to thank all of those persons who contributed to the

preparation of this report. Special appreciation is extended to Dr. Harold

Marshall, Leader of the Applied Economics Group, for his assistance throughout

the project; to Dr. Belinda Collins, Mr. Stephen Treado, and Mr. William Hall

for their helpful comments; to Ms. Kimberly Barnes for her assistance with the

computer work, and to Ms. Cynthia Broussalian, Ms. Debbie Rodgers, and

Mr. Philip Decker for their assistance in preparing the tables and manuscript.

Credit for the cover design goes to Ms. Nan Stephens.

iv
SI CONVERSION

Length

1 in = 0.0254 meter

1 ft = 0.3048 meter

Area

1 in2 = 6.4516 x 10“^ meter2

1 ft 2 = 0.0929 meter2

Volume

1 in2 = 1.638 x 10-2 meter2

1 gal (U.S. liquid) = 3.785 x 10“2 meter2

1 liter = 1.000 x 10-2 meter2

Energy

1 Btu (International Table) = 1.055 x 102 joule

Power

1 Btu/hr = 0.2930 watt

Temperature

°F = ( 9 °C) + 32

5

Illumination

1 ft candle = 10.76 lux

U-value

1 Btu/hr ft 2 F « 5.678 W/m2 K

v
ABSTRACT

This study, the fifth in a series of reports from the National Bureau of

Standards' interdisciplinary project on windows, provides guidance in selecting

and using windows in buildings for greater cost effectiveness. It presents the

life-cycle costs of selected window systems used in a room of a representative

residence and in an office module of a representative commercial office building for nine cities in the United States, representing five heating zones and

four cooling zones. The cities covered are Miami, Florida; Atlanta, Georgia;

Washington, D.C.; Portland, Maine; Indianapolis, Indiana; San Antonio, Texas;

Los Angeles, California; Bismarck, North Dakota; and Seattle, Washington. The

results of the regional analyses are summarized, and the implications of these

results are considered, both for selecting windows in new buildings and for

managing windows in existing buildings. The emphasis of this report is on conveying the research findings to builders, designers, and building owners

and operators — those involved immediately with the building process. The

research method is described in an earlier companion report. Economic

Evaluation of Windows in Buildings: Methodology .

Key Words: building economics; daylighting; energy conservation; engineering

economics; life-cycle costs; passive solar; regional analysis;

thermal efficiency; windows.

vi
TABLE OF CONTENTS

Page

PREFACE iii

ACKNOWLEDGMENTS iv

SI CONVERSION v ABSTRACT vi

LIST OF TABLES ix

LIST OF FIGURES xiv

1. INTRODUCTION 1

2. RESIDENTIAL CASE STUDIES FOR NINE CITIES 9

2.1 Description of the Building and Window Systems 9

2.2 Miami, Florida 9

2.3 San Antonio, Texas 15

2.4 Los Angeles, California 20

2.5 Atlanta, Georgia 23

2.6 Washington, D.C 23

2.7 Seattle, Washington 32

2.8 Indianapolis, Indiana 36

2.9 Portland, Maine 39

2.10 Bismarck, North Dakota 42

3. COMMERCIAL CASE STUDIES FOR NINE CITIES 51

3.1 Description of Commercial Building and Window Systems 51

3.2 Miami, Florida 53

3.3 San Antonio, Texas 55

3.4 Los Angeles, California 61

3.5 Atlanta, Georgia 61

3.6 Washington, D.C 65

3.7 Seattle, Washington 70

3.8 Indianapolis, Indiana 75

3.9 Portland, Maine 75

3.10 Bismarck, North Dakota 81

4. SUMMARY AND GENERAL CONCLUSIONS 88

4.1 Residential Windows Summary 89

4.2 Commercial Window Summary 95

4.3 General Conclusions 99

SELECTED REFERENCES 102

APPENDIX A: Estimated Costs of Purchase, Installation, Maintenance, and

Repair for the Selected Window Systems in the Single-Family

Residence 103

vii
TABLE OF CONTENTS (Continued)

APPENDIX B Estimated Costs of Purchase, Installation, Maintenance, and

Repair for the Selected Window Systems in the Commercial

Office Building

Page

107

viii
LIST OF TABLES

Page

1.1 Window Alternatives, Key Assumptions, and Economic Performance

Measures 5

2.1 Miami, Florida, Residential Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 12

2.2 Miami, Florida, Residential Case Study: Life-Cycle Costs for a Window System — Evaluated With Window Management and

Day lighting 14

2.3 Miami, Florida, Residential Case Study: Least-Cost Window

Systems — 200 Heating Degree Days, 2400 Cooling Hours 16

2.4 San Antonio, Texas, Residential Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 17

2.5 San Antonio, Texas, Residential Case Study: Life-Cycle Costs for a Window System — Evaluated With Window Management and

Day lighting 18

2.6 San Antonio, Texas, Residential Case Study: Least-Cost Window

Systems — 1550 Heating Degree Days, 2000 Cooling Hours 19

2.7 Los Angeles, California, Residential Case Study: Life-Cycle Costs

for a Window System — Evaluated Without Window Management and

Without Daylighting 21

2.8 Los Angeles, California, Residential Case Study: Life-Cycle Costs

for a Window System — Evaluated With Window Management and

Daylighting 22

2.9 Los Angeles, California, Residential Case Study: Least-Cost Window

Systems — 1350 Heating Degree Days, 550 Cooling Hours 24

2.10 Atlanta, Georgia, Residential Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 25

2.11 Atlanta, Georgia, Residential Case Study: Life-Cycle Costs for a Window System — Evaluated With Window Management and

Daylighting 26

2.12 Atlanta, Georgia, Residential Case Study: Least-Cost Window

Systems — 2950 Heating Degree Days, 1000 Cooling Hours 27

ix
LIST OF TABLES (Continued)

Ha£e 2.13 Washington, D.C., Residential Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 29

2.14 Washington, D.C., Residential Case Study: Life-Cycle Costs for a Window System — Evaluated With Window Management and

Daylighting 30

2.15 Washington, D.C., Residential Case Study: Least-Cost Window

Systems—4200 Heating Degree Days, 1000 Cooling Hours 31

2.16 Seattle, Washington, Residential Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 33

2.17 Seattle, Washington, Residential Case Study: Life-Cycle Costs for a Window System — Evaluated With Window Management and

Daylighting 34

2.18 Seattle, Washington, Residential Case Study: Least-Cost Window

Systems — 4400 Heating Degree Days, 100 Cooling Hours 35

2.19 Indianapolis, Indiana, Residential Case Study: Life-Cycle Costs for

a Window System — Evaluated Without Window Management and Without

Daylighting 37

2.20 Indianapolis, Indiana, Residential Case Study: Life-Cycle Costs for

a Window System — Evaluated With Window Management and

Daylighting 38

2.21 Indianapolis, Indiana, Residential Case Study: Least-Cost Window

Systems — 5700 Heating Degree Days, 750 Cooling Hours 40

2.22 Portland, Maine, Residential Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 41

2.23 Portland, Maine, Residential Case Study: Life-Cycle Costs for a Window System — Evaluated With Window Management and Daylighting .. 43

2.24 Portland, Maine, Residential Case Study: Least-Cost Window

Systems — 7600 Heating Degree Days, 250 Cooling Hours 44

2.25 Bismarck, North Dakota, Residential Case Study: Life-Cycle Costs

for a Window System — Evaluated Without Window Management and

Without Day lighting 45

x
LIST OF TABLES (Continued)

Page

2.26 Bismarck, North Dakota, Residential Case Study: Life-Cycle Costs

for a Window System — Evaluated With Window Management and

Daylighting 47

2.27 Bismarck, North Dakota, Residential Case Study: Least-Cost Window

Systems — 8850 Heating Degree Days, 450 Cooling Hours 48

3.1 Miami, Florida, Commercial Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 54

3.2 Miami, Florida, Commercial Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management but With

Daylighting 56

3.3 Miami, Florida, Commercial Case Study: Least-Cost Window Systems —

200 Heating Degree Days, 2400 Cooling Hours 57

3.4 San Antonio, Texas, Commercial Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 58

3.5 San Antonio, Texas, Commercial Case Study: Life-Cycle Costs for

a Window System — Evaluated Without Window Management but With

Daylighting 59

3.6 San Antonio, Texas, Commercial Case Study: Least-Cost Window

Systems — 1550 Heating Degree Days, 2000 Cooling Hours 60

3.7 Los Angeles, California, Commercial Case Study: Life-Cycle Costs

for a Window System — Evaluated Without Window Management and

Without Day lighting ^ 62

3.8 Los Angeles, California, Commercial Case Study: Life-Cycle Costs

for a Window System — Evaluated Without Window Management but

With Daylighting 63

3.9 Los Angeles, California, Commercial Case Study: Least-Cost Window

Systems — 1350 Heating Degree Days, 550 Cooling Hours 64

3.10 Atlanta, Georgia, Commercial Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 66

3.11 Atlanta, Georgia, Commercial Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management but With

Daylighting 67

xi
LIST OF TABLES (Continued)

Page

3.12 Atlanta, Georgia, Commercial Case Study: Least-Cost Window

Systems — 2950 Heating Degree Days, 1000 Cooling Hours 68

3.13 Washington, D.C., Commercial Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 69

3.14 Washington, D.C., Commercial Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management but With

Daylighting 71

3.15 Washington, D.C., Commercial Case Study: Least-Cost Window

Systems — 4200 Heating Degree Days, 1000 Cooling Hours 72

3.16 Seattle, Washington, Commercial Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 73

3.17 Seattle, Washington, Commercial Case Study: Life-Cycle Costs for

a Window System — Evaluated Without Window Management but With

Daylighting 74

3.18 Seattle, Washington, Commercial Case Study: Least-Cost Window

Systems — 4400 Heating Degree Days, 100 Cooling Hours 76

3.19 Indianapolis, Indiana, Commercial Case Study: Life-Cycle Costs for

a Window System — Evaluated Without Window Management and Without

Day lighting 77

3.20 Indianapolis, Indiana, Commercial Case Study: Life-Cycle Costs for

a Window System — Evaluated Without Window Management but With

Daylighting 78

3.21 Indianapolis, Indiana, Commercial Case Study: Least-Cost Window

Systems — 5700 Heating Degree Days, 750 Cooling Hours 79

3.22 Portland, Maine, Commercial Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management and Without

Daylighting 80

3.23 Portland, Maine, Commercial Case Study: Life-Cycle Costs for a Window System — Evaluated Without Window Management but With

Daylighting 82

3.24 Portland, Maine, Commercial Case Study: Least-Cost Window

Systems — 7600 Heating Degree Days, 250 Cooling Hours 83

xii
LIST OF TABLES (Continued)

j Page

3.25 Bismarck, North Dakota, Commercial Case Study: Life-Cycle Costs

for a Window System — Evaluated Without Window Management and

Without Daylighting 84

3.26 Bismarck, North Dakota, Commercial Case Study: Life-Cycle Costs for

a Window System — Evaluated Without Window Management but With

Daylighting 85

3.27 Bismarck, North Dakota, Commercial Case Study: Least-Cost Window

Systems — 8850 Heating Degree Days, 450 Cooling Hours 86

4.1 Summary: Cost-Effective Choices for the Selected Residential

Window Systems 90

4.2 Summary: Cost-Effective Glazing for the Selected Residential

Windows 91

4.3 Summary: Cost-Effective Choices for the Selected Commercial

Window Systems 96

4.4 Summary: Cost-Effective Glazing for the Selected Commercial Windows 97

A.l Acquisition Costs of a Window in Excess of the Cost of a Non-Windowed Wall 104

A. 2 Cost of Window Accessories 105

A. 3 Window Maintenance and Repair Costs 106

B. l Commercial Case Study: Acquisition Costs 108

B.2 Commercial Case Study: Cost of Window Accessories 109

B.3 Commercial Case Study: Cleaning and Insurance Costs 110

xiii
LIST OF FIGURES

Page

1.1 Locations Studied for Window Systems 2

2.1 Schematic Diagram of Housee with Shaded Study Module 10

2.2 Window Sizes in Relationship to the Size of the Exterior Wall of

the House 11

3.1 Window Sizes in Relationship to the Size of the Exterior Wall of

the Office Module 52

xiv
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XV

1 . INTRODUCTION

The energy crisis has stimulated increased interest in the impact of windows on

the energy costs of buildings. Building energy requirements are significantly

affected by window size, orientatioon, thermal resistance, accessories, and use

for daylighting [1].^ But in the concern for energy costs, other costs should

not be overlooked. From an economic standpoint, it is important that buildings,

including their windows, be as cost effective as possible taking into account

all significant effects over the relevant time period of building use.

This report provides some of the information on windows needed for the

construction and operation of cost-effective buildings. It does this by estimating and comparing the life-cycle costs of selected choices of window size,

glazing, orientation, accessories, and use, and by then formulating general

guidelines for cost-effective windows based on the numerical results.

It should be recognized that the choices examined are limited, the findings are dependent on specific assumptions, and the resulting guidelines are far from

comprehensive. Yet, on a more positive note, many cases are treated here, and

a range of dollar estimates is provided to reflect some of the uncertainty. To

reflect variation in costs due to differing geographical regions and building

types, window costs are examined for nine geographical regions of the United

States and for two types of buildings. The nine cities selected for study and

their locations are shown on the heating and cooling zone maps in figure 1.1.

Five different heating zones and four different cooling zones are included.

The buildings selected for study are a one-story, single-family, brick rambler

and a five-to-ten story commercial office building with curtain wall construction. The focus is on a window in one room of each building: the familyroom/kitchen of the residence and an office module of the commercial building.

It is assumed that windows are located on a single exterior wall of the subject

room, and the orientation of the windows is changed by rotating the entire

building. It is further assumed that there are no heat flows to adjoining

spaces

A range of sizes of a selected window design are examined for each of the two

types of buildings in each climatic region. For the residence, the type of

window selected for study is a wooden, double-hung, weatherstripped, well-fitted

window. For the office building, the type of window selected is a fixed, nonoperable area of glazing in an anodized aluminum frame. For the residence,

window sizes of up to 60 ft^ (5.57 m^) are examined, and for the office, sizes

of up to 90 ft^ (8.36 m^). As a basis of comparison, costs associated with

a windowless room are estimated for both the residence and the office. For

1 Numbers in brackets refer to bibliographic materials listed at the end of

part 4.

1
Portland

This mao taken from Madeleine Jacobs and Steve Petersen’s “Making the Most of Your Energy Dollars in Home Heating and Cooling,” NBS Consumer Information Series 8, 1975 [7 ], is approximate only. For a more ex

tensive listing of cooling hour data, see Insulation Manual-Homes!Apartments, NAHB Res. Found. Inc.,

1971, pp. 23-35 [8].

Washington,

D.C.

Miami

Washington,

D.C.

Miami

Portland

Hawaii

O'

Los

Angeles

l.l.b Summer Cooling

San Antonio

Hours Over 80°F

Los

Angeles

Figure 1.1 Locations Studied for Window Systems

1.1a Normal Heating Degree Days (Base 65°F)

(Zone 6)

Alaska

(Zone 5)
each window size and orientation, the cost effectiveness of single and multiple

glazing is evaluated.

Each alternative window system is examined for two different modes of use. For

the residential windows, the two modes are as follows:

(1) Windows are "unmanaged" and not used for daylighting. That is, windows

are left bare without accessories for reducing undesired heat gains and

losses, the thermostat is not adjusted at night for energy conservation,

and lighting requirements are met by electric lights.

(2) Windows are "managed" and used for daylighting. That is, they are equipped

with Venetian blinds to reduce summer daytime heat gain and thermal shutters to reduce winter nighttime heat loss, the thermostat is lowered at

night during the heating season and raised at night during the cooling

season to conserve energy, and daylight from the windows provides part or all of the specified lighting requirements.

For the commercial windows the two modes of use are as follows:

(1) Windows are unmanaged and not used for daylighting (like mode 1 for

residential windows).

(2) Windows are unmanaged, but used for daylighting. That is, they are

not accessorized for reducing undesired heat gains and losses, the

thermostat is not adjusted at night for energy conservation, but

daylight from the windows does provide part or all of the specified

lighting requirements (unlike mode 2 for residential windows).

The modes of use listed for each building type are selected for presentation

from a total of four modes evaluated by the study. The modes presented give

the worst and the best results, respectively, in both the residential and

commercial applications. The four modes of window use that were examined for

both the residential and commercial applications, from which the worst and

best are selected, are the following: (a) unmananged, not used for daylighting, (b) managed, used for daylighting, (c) unmanaged, used for daylighting,

and (d) manged, not used for daylighting.

While the mode of use giving the "worst case" results is the same for

residential and commercial applications, the mode for the "best case" differs.

For the commercial window, the most favorable results are for the unmanaged

window. That is, window management is not found to be cost effective for the

commercial applications, as it is for the residential cases. This finding

reflects the high purchase and installation costs estimated for thermal

shutters for the office building. It would be inappropriate to conclude from

this finding, however, that management strategies in general are not cost

1 Note that the adjustment of the thermostat affects the windowless room, as well as the room with windows of varying sizes.

3
effective for commercial buildings, nor that Venetian blinds and nighttime

thermostat adjustment, the two management factors grouped with shutters, would

not alone be cost effective. Other management strategies were not evaluated,

and separate analysis was not performed for each factor included in the

"management package."

The results pertain primarily to windows in new buildings, because the

acquisition costs of the windows used in the analyses are estimated for new

construction. However, some of the results also pertain to windows in existing

buildings. The cost-effectiveness results for window management should hold

equally for new and existing buildings, other conditions being equal. The

results from the evaluation of double glazing, on the other hand, would to

apply only to new buildings. The results tend not to hold for existing buildings because the costs are based on new construction. In an existing building,

it would be necessary to replace the entire window in order to obtain double

glazing, whereas in a new building, double glazing would be considered an optional feature available at the time the overall window system is selected.

In that case, it would be necessary to take into account only the differential

costs between double glazing and single glazing, as is done in these analyses.

Table 1.1 summarizes (1) the window alternatives that are examined for each of

the nine regions, (2) the main economic assumptions, and (3) the measures of

economic performance that are provided. The estimates of purchase and installation costs and maintenance and repair costs that are combined with estimates

of energy costs to derive life-cycle costs are given in appendices A and B.

The evaluation is performed using a life-cycle cost model that takes into

account over an estimated life of 25 years the costs of purchasing and installing the windows, Venetian blinds, and thermal shutters (over and above the

costs of a solid wall); the costs of maintenance, repair, and replacement; and

the costs of energy for heating, cooling, and lighting the room. To reflect

the great uncertainty about future energy prices and the importance of energy

costs to window performance, lower and upper bounds of zero and 12 percent real

growth, compounded annually, are assumed for future energy prices.

As was explained in earlier studies [1, 2], a deficiency of the thermal model

is that it does not take into account the possibilities for natural ventilation.

It is also important to note that south-facing windows are considered here

without the thermal storage feature customarily included in direct-gain passive

solar energy systems. Hence, the thermal performance of the south-facing windows is significantly poorer than would normally be expected of south-facing

windows employed in a well designed passive solar energy system. Rather,

performance is intended to be more typical of the windows in conventional "nonsolar" buidings. Additionally, the costs and benefits associated with psychological and aesthetical effects of windows are not included. At the time these

case studies were performed, a further deficiency was that the portion of the

thermal model used to estimate the energy effects of daylighting had not yet

4
TABLE 1.1

WINDOW ALTERNATIVES, KEY ASSUMPTIONS, AND ECONOMIC PERFORMANCE MEASURES

FEATURE ALTERNATIVES EXAMINED

Window type Residential: Wood, Double-Hung and Weatherstripped

Commercial : Anodized Aluminum with Thermal Break

Window Accessories Venetian Blinds during Summer Days and Thermal Shutters during Winter Nights

Building Application 18' x 15' x 8' Family-Room/Kitchen of Single-Family Brick Rambler; Block

(5.49 m x 4.57 m x 2.44 m) with Brick Veneer; 3 1/2" (8.89 cm) Insulation; U = 0.07

(1.21 W/(m«K)); Exterior Wall Area of 144 ft 2 (13.38 ra 2

)

12* x 15' x 10* Office Module of Commercial Office Building,

(3.66 m x 4.57 m x 3.05 m) Curtain Wall Construction

Window Sizes Residential: 0, 12, 18, 30, 60 ft 2 (0, 1.11, 1.67, 2.79, 5.57 Commercial : 0, 12, 30, 60, 90 ft 2 (0, 1.11, 2.79, 5.57, 8.36

m2

) m2

)

Orientation S, E/W, N

Glazing Type Single, Double, Triple

Mode of Window Use Residential: (1) Bare, Not Used for Daylighting; (2) Managed, Used for Daylighting

Commercial : (1) Bare, Not Used for Daylighting; (2) Bare, Used for Daylighting

Internal Energy Loads Lights Equipment Air Leakage People

Residential: 0.65 watts/ft 2 (7 watts/m2

)

0.52 watts/ft 2 (5.6 watts/m2

) 0.50 Air Changes /hr 0.5 people at 260 Btu/hr

(76.2 W)

Commercial: 3.25 watts/ft 2 0.50 watts/ft2 (34.98 watts/m2

) (5.38 watts/m2) 0.25 Air Changes /hr 1.8 people at 260 Btu/hr

(76.2 W)

Boiler Efficiency Cooling COP Thermostat Adjustment

System Operation Residential: 0.65 2.0 72° to 62° F Winter Nights

(22.2° to 16.7°C)

Commercial : 0.65 3.0 78° to 84° F Summer Nights

(25.6° to 28.9°C)

Economic Assumptions Gas Heating at $0.30 per Therm; Electric Cooling and Lighting at $0.03 per kWh

(Estimated U.S. average 1978 Prices) 3 Energy Price Escalation Rates of 0% and 12%, compounded annually not including

Inflation Window Acquisition and Maintenance Costs, estimated 1978 prices^ (See Appendices, A and B) Discount Rate of 8%, Not Including Inflation Depreciation of Commercial Investment Costs Over 25 Years Using a 150% Declining

Balance Method

After Taxes/Before Inflation Analysis

Study Period of 25 years

Economic Performance Measures Life-Cycle Cost of Each Combination of Alternatives

Least-Cost Window Size, Orientation, Glazing, Mode of Use, and Overall Window System

Net Life-Cycle Savings for the Least-Cost System

Years to Payback for Least-Cost System Breakeven Rate of Energy Price Escalation

a Although these energy prices are for 1978, the built-in price escalation rate of 12 percent (upper bound) brings

them closely in line with current (1981) energy prices. For example, at 12 percent per annum compound interest, a $0.30 per therm price for gas in 1978 is equivalent to $0.45 per therm in mid-1981. This price may be compared

with current Department of Energy U.S. average price estimates for mid-1981 of $0.44 per therm for residential

purchases, $0.40 for commercial purchases, and $0.35 for industrial purchases. At 12 percent interest, a $0.03 per kWh price for electricity in 1978 is equivalent to $0,045 per kWh in mid-1981. This price may be compared with

current Department of Energy U.S average price estimates for mid-1981 of $0,057 per kWh for residential purchases,

$0,058 per kWh for commercial purchases, and $0,042 for industrial purchases [12]. Note that energy costs related to windows may be affected by utility component pricing, not reflected in these assumptions. For example, daylightng may reduce building peak power consumption, thereby reducing utility demand

changes [10].

k The first costs of windows and window accessories relative to initial energy prices 1978 have not changed

significantly, from those assumed for 1978. Therefore, the results based on 1978 window and energy

costs should be comparable to results based on 1981 costs.

5
been verified by laboratory and field testing [2]. However, a recent NBS study

supports the validity of the daylight estimates [6].^

The next two parts, 2 and 3, present in detail the life-cycle cost analysis of

windows for each of the nine locations, first for the residential building and

then for the commercial building. Part 4 concludes the report with a summary

of the findings and a discussion of the implications of these findings. Part 4

may be used independently of parts 2 and 3 as a general reference. Those who

prefer an overview may wish to proceed directly to part 4; those who are interested in the results for a particular city may wish to go directly to the

section in part 2 or 3 dealing with that city.

1 Nevertheless, it should be noted that the evaluation of monetary benefits from

daylighting is based on the assumption of conventional electric lighting as the alternative; while, in a more comprehensive analysis of building system

tradeoffs, lamp replacement might be another option for reducing electric

lighting costs [9, 10]. The use of energy conserving lamps would then lessen

the cost advantage of using daylighting. Other factors that are not taken

into account here but which may be important in evaluating the benefits of

daylighting are the potential loss of work resulting from unscheduled downtime of mechanical systems in windowless spaces, differences in the quality

of lighting provided by different lighting sources, and the cost and reliability of controlling electric lighting in order to derive the energy savings

from daylighting [6, 9, 11].

6
D3.ylighting From Well Managed Windows Can Reduce Electric Lighting

Requirements and Greatly Improve the Cost Effectiveness of Windows

7
8

Double-hung

Wood

Windows

Such

as

Those

Assumed

in

the

Residential

Window

Analysis

are

Widely

Used

in

Residential

Construction
2. RESIDENTIAL CASE STUDIES FOR NINE CITIES

2.1 DESCRIPTION OF BUILDING AND WINDOW SYSTEMS 1

The residential module is assumed to be a family room/kitchen in a one-story

rambler with a full basement. The overall dimensions of the house are 28 feet

wide by 50 feet 6 inches long (8.53 m x 15.39 m) , and the total floor area is

1414 square feet (131.36 m^). The layout of the house including the location

of windows and doors is shown in the floor plan in figure 2.1. The family

room/kitchen shown shaded in the floor plan is the subject of the analysis.

The windows assumed for the economic analysis are wooden and double hung, in

four sizes. Figure 2.2 shows the four window sizes in relationship to the

size of the exterior wall. (Other assumptions are given in table 1.1 and in

appendix A.)

All assumptions other than geographical location and window costs^ are identical

for each of the nine residential case study, and a common format is used for

each: Tables of life-cycle window costs, estimated both for constant energy

prices and for rapidly rising energy prices, are given. These tables show

results both for single and double glazing. A separate table is given for each

mode of window use: the first being for windows that are unmanaged and not

used for daylighting, and the second, for windows that are both managed and

used for daylighting. A third table for each city identifies the least-cost

window system for each orientation.

2.2 MIAMI, FLORIDA

In Miami, where heating loads are very low (200 heating degree days) the

effects of a dominant cooling load (2,400 cooling hours) on life-cycle costs

are significant.

Table 2.1 gives the total estimated life-cycle costs of purchasing and

installing the windows, cleaning and repairing them, and heating and cooling

the room with the window system in place. The costs are based on the first

mode of window use, neither managing it nor using it for daylighting.

1 This information, taken in abbreviated form from the companion methodological

report, Economic Evaluation of Windows in Buildings: Methodology [1], is

provided here for the convenience of the reader.

o Location Modifiers are applied to window costs to account for regional

variation in labor and material costs. See appendix A for the basic window

cost data.

9
50'-6"(l5.4m)

10

Figure

2

. 1

Schematic

Diagram

of

House

with

Shaded

Study

Module.

(From

Ruegg,

Rosalie

T.

and

Chapman,

Robert

E.

Economic

Evaluation

of

Windows

in

Building:

Methodology,

National

Bureau

of

Standards

Building

Science

Series

119,

April

1979.)
o o

ro v£>

— CM

cm Tail

Figure

2.2

Window

Sizes

in

Relationship

to

the

Size

of

the

Exterior

Wall

of

the

House
TABLE 2.1

MIAMI, FLORIDA, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTINGa

Window

(FT 2

)

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

' Area

(m2

) S

Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0 0 864 868 854 864 868 854

12 1.11 993 1016 965 1011 1032 985

18 1.67 1052 1084 1015 1074 1103 1040

30 2.79 1158 1235 1130 1227 1272 1176

60 5.57 1510 1606 1410 1594 1679 1502

Part B (FPE b = 12%)

0 0 3357 3375 3319 3357 3375 3319

12 1.11 3689 3777 3581 3677 3758 3576

18 1.67 3855 3979 3712 3831 3944 3699

30 2.79 4201 4395 3988 4167 4343 3972

60 5.57 5060 5431 4671 4993 5326 4638

a Life-cycle costs include the present value costs of (1) purchasing and installing

the windows (in excess of the costs of a brick wall section of equal size),

(2) cleaning, recaulking and repainting the windows on a regular basis, and

(3) the energy costs for heating, cooling, and lighting the designated family

room/kitchen of the house described in section 2. They are not the life-cycle

costs for the entire house. Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate.”

12
Part A of table 2.1 shows that if energy prices remain constant in real dollars,

life-cycle building costs are raised by both single- and double-glazed windows

of all sizes examined and for all orientations.*- However, single-glazed windows are less costly than double-glazed windows. A consequence of the heavy

cooling load requirement is that windows facing east or west raise life-cycle

cost more than windows facing north.

2

Part B of table 2.1 shows that life-cycle costs are substantially higher if

energy prices rise at a real rate of 12 percent compounded annually. Costs

increase sharply as window area is increased. With the rise in energy prices

and without window management—double glazing is slightly more cost effective

than single glazing (i.e., the net losses^ are lower) for all window sizes

and orientations.

Table 2.2 shows the total estimated life-cycle costs if daylight utilization

and window management are practiced. Part A of the table shows that life-cycle

costs are lower with a window than without it for window areas up to and including 18 ft^ (1.67 m^) in size, if real dollar energy prices remain unchanged.

The savings from the 18 ft2 (1.67 m2) south-facing, single-glazed window exceed

$100. However, as the window area is increased beyond about 30 ft^ (2.79 m2),

the extra capital costs for management devices and window acquisition together

with the poorer thermal performance more than offset the extra energy savings

from increased daylighting and net losses grow rapidly.

Part B of table 2.2 shows life-cycle costs if energy prices rise at a real rate

of 12 percent compounded annually. A pattern of declining life-cycle costs for

windows up to 18 ft2 (1.67 m2) in size is revealed. Net savings are much

larger than those shown in part A of the table for the same range of window

size. The use of thermal shutters results in little cost difference between

single and double glazing.

* The reader is reminded that the benefits of natural ventilation are not

taken into account in the evaluation.

2 The temperature and solar radiation figures presented in Kusuda, T. and

Ishii, K., Hourly Solar Radiation Data for Vertical Surfaces on Average

Days in the United States and Canada [13], are useful for understanding why

cooling loads for east-west orientations are higher than those for the

other orientations.

3 "Net savings" is defined as the positive dollar difference found by

subtracting from the life-cycle costs associated with the windowless room,

the costs associated with the room when it has a given window system. If

this difference is negative, then "net losses" are said to result from the

window. For the purpose of these comparisons, a window system is designated

"cost effective" if its life-cycle cost is at all lower than that of the

alternative. In the summary of section 4, however, a cost difference of

less than five percent is treated as relatively insignificant.

13
TABLE 2.2

MIAMI, FLORIDA, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM -- EVALUATED WITH WINDOW MANAGEMENT AND WITH DAYLIGHTING3

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

Window

(FT2

) Area

(m2

) S Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0C 0 860 864 850 860 864 850

12 1.11 734 742 705 756 763 729

18 1.67 756 766 717 783 793 748

30 2.79 896 909 838 947 959 894

60 5.57 1276 1298 1170 1378 1398 1282

Part B (FPEb = 12%)

0

C 0 3342 3360 3305 3342 3360 3305

12 1.11 2483 2514 2370 2486 2516 2381

18 1.67 2470 2508 2319 2468 2504 2330

30 2.79 2645 2697 2420 2648 2696 2442

60 5.57 3255 3342 2842 3261 3340 2887

a Life-cycle costs include the present value costs of (1) purchasing and installing

the windows (in excess of the costs of a brick wall section of equal size),

(2) purchasing the Venetian blinds and shutters, (3) cleaning, recaulking and

repainting the windows on a regular basis, and (4) the energy costs of the

designated room for heating, cooling, and lighting. Base-year prices are for 1978.

b FPE abbreviates "fuel escalation rate."

c Note that the life-cycle costs for all window sizes, from 0 to 60 ft 2 (5.57 m2 ),

reflect the adjustment of the thermostat for energy conservation; hence, the costs

for the zero window case in this table are slightly lower than in the preceding

table which did not assume an adjustment in the thermostat.

14
Table 2.3 shows the least-cost window system for each orientation, and the

least-cost system of all orientations. Part A of table 2.3 shows that the

least-cost window system when energy prices are constant is single glazed,

12 ft^ (1.11 m2) in area, and oriented to the north. Part B of table 2.3 indicates that when energy prices are rising sharply, the least-cost window system

is also single glazed and located on the north, but is somewhat larger in size

(18 ft^ or 1.67 m^) due to the greater benefit of daylighting when electricity

prices are high. (In either case, however, single glazing is only slightly

preferred to double glazing.) It is estimated that if energy prices escalate

rapidly, the savings in lighting and cooling costs will allow the window system

to pay for itself in three to four years.

2.3 SAN ANTONIO, TEXAS

The cooling load requirement (2,000 cooling hours) in San Antonio is somewhat

smaller than in Miami, while the heating load (1,550 heating degree days) is

larger, though still relatively modest.

Table 2.4 shows that with either level or rising constant dollar energy prices,

the windows examined raise life-cycle building costs regardless of glazing

type, window size, or orientation. If energy prices rise at a real rate of 12

percent compounded annually, estimated net losses are more than triple the

estimated losses at constant energy prices. The table shows single glazing to

be more cost effective than double glazing if energy prices are constant, net

losses for single glazing averaging almost 20 percent lower than for double

glazing. With the higher energy prices, the life-cycle costs for single and

double glazing are nearly identical, although double glazing may offer a small

advantage for larger windows. Since the cooling load requirements dominate,

windows with an easterly or westerly exposure tend to have higher life-cycle

costs than windows with other exposures.

As shown in table 2.5, the addition of window management and daylight utilization

significantly alters the results. Part A of table 2.5 shows that with thermal

shutters, Venetian blinds, and thermostat adjustment, and level constant dollar

energy prices, net savings are possible for all single-glazed window areas up

to and including 30 ft^ (2.79 m2) and for all double-glazed window areas up

to and including 18 ft^ (1.67 m2). At constant energy prices, single glazing

is estimated to be somewhat more cost effective than double glazing.

Part B of table 2.5 shows that window management and daylighting increase the

potential saving from windows if real energy prices rise. Estimated net savings

over the 25 year period approximate $1000 for window areas smaller than 30 ft^.

The net savings from single glazing averages 5 to 10 percent higher than from

double glazing.

Part A of table 2.6 shows that the window system which minimizes life-cycle

costs in San Antonio under constant energy prices and other stated conditions

is single glazed, north facing, and 12 ft^ in area. (However, the difference

in life-cycle costs is modest both between the 12 and 18 ft^ (1.11 and 1.67

m^) window areas, and between the single- and double-glazed window areas.) The

least-cost window system is estimated to result in net life-cycle savings

15
MIAMI,

FLORIDA,

RESIDENTIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS

--

200

HEATING

DEGREE

DAYS,

2400

COOLING

HOURS |

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16

FPE

abbreviates

"fuel

price

escalation

rate
TABLE 2.4

SAN ANTONIO, TEXAS, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTING3

Window

(FT2

)

Life -Cycle Costs in Dollars

Single Glazed Double Glazed

Area

(m2

) S

Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0 0 770 776 764 770 776 764

12 1.11 864 889 852 885 907 874

18 1.67 905 938 890 931 961 917

60 5.57 1244 1361 1240 1323 1414 1296

Part B (pp£b = 12 %)

0 0 2996 3016 2969 2996 3016 2969

12 1.11 3201 3296 3154 3204 3291 3159

18 1.67 3297 3428 3242 3297 3417 3242

30 2.79 3503 3726 3457 3507 3693 3434

60 5.57 4079 4534 4061 4018 4371 3913

3 Life-cycle costs include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) cleaning,

recaulking and repainting the windows on a regular basis, and (3) the energy costs

for heating, cooling, and lighting the designated family room/kitchen of the house

described in section 2. They are not the life-cycle costs for the entire house.

Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

17
TABLE 2.5

SAN ANTONIO, TEXAS, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A

WINDOW SYSTEM -- EVALUATED WITH WINDOW MANAGEMENT AND DAYLIGHTINGa

Window

(FT2

)

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

Area

(m2

) S Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0

C 764 769 757 764 769 757

12 620 630 612 647 656 639

18 625 637 617 660 671 652

30 718 734 711 780 795 771

60 985 1019 985 1108 1133 1100

Part B (FPEb = 12%)

0

C 2971 2991 2944 2971 2991 2944

12 2067 2105 2037 2094 2129 2064

18 1990 2037 1958 2025 2068 1993

30 2007 2068 1979 2067 2126 2032

60 2236 2368 2235 2348 2445 2316

a Life-cycle costs include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) purchasing

the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows

on a regular basis, and (4) the energy costs of the designated room for heating,

cooling, and lighting. Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

c Note that the life-cycle costs for all window sizes, from 0 to 60 ft 2 (5.57 m

2 ),

reflect the adjustment of the thermostat for energy conservation; hence, the costs for

the zero window case in this table are slightly lower than in the preceding table which

did not assume an adjustment in the thermostat.

18
SAN

ANTONIO,

TEXAS,

RESIDENTIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS —

1550

HEATING

DEGREE

DAYS,

2000

COOLING

HOURS

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19
of $145 and to pay for itself in four years. Part B of table 2.6 shows that

the window system which minimizes life-cycle costs in the face of higher real

energy prices is 18 ft 2 (1.67 m2

) in size, single glazed, and located on the

north side. The least-cost window area is expected to recover its investment

costs in about three years and to save nearly $1000 over the life cycle.

2.4 LOS ANGELES, CALIFORNIA

In Los Angeles the cooling load of 550 cooling hours is lower than in the

preceding three cities. The heating load of 1350 heating degree days is

slightly lower than in San Antonio, but higher than in Miami. Both heating

and cooling load requirements are modest.

As in the previous cases, net losses result from both single- and double-glazed

windows of all sizes and all orientations when windows are unmanaged and not

used for daylighting. Single glazing appears in all cases somewhat more cost

effective than double glazing. Orientation appears to have little effect on

cost

A comparison of Parts A and B of table 2.7 shows that net losses attributable

to windows actually decrease slightly if the real rate of energy price escalation is raised from 0 to 12 percent per year, though life-cycle costs for the room in general (both with and without windows) are greatly increased. The

smaller losses can be explained in terms of the climate conditions in Los

Angeles, which cause a windowed room to require slightly less energy than a windowless room, even if daylight is not used as an alternative light source.

The life-cycle costs of the windowed room are nevertheless higher than those

of the windowless room, as shown by table 2.10, because the higher acquisition

and maintenance costs of the windows more than offset their lower energy costs.

The room with a double-glazed window requires almost exactly the same amount

of energy as the windowless room so that net losses reflect primarily the

extra expenses of window acquisition and maintenance.

Part A of table 2.8 shows that if energy prices were to remain level in constant

dollars and if window management and daylighting were practiced, net savings

would result for all single-glazed windows up to and including 30 ft 2 (2.79 m

2

) and for all double-glazed windows up to and including 18 ft 2 (1.67 m2

).

Part B of table 2.8 shows that if energy prices were to rise at a real rate of

12 percent per year, a single-glazed window of any of the sizes examined would

save about $1000 over the life, provided it were properly managed and

used for daylighting. Savings are estimated at approximately 10 to 30 percent

less with double-glazed windows.

^ From Kusuda, T. and Ishii, K., Hourly Solar Radiation Data for Vertical and

Horizontal Surfaces on Average Days in the United States and Canada [13], it can be determined from climate data that conduction losses or gains are frequently beneficial in Los Angeles.

20
I

TABLE 2.7

LOS ANGELES, CALIFORNIA, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM -- EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTING3

Window

(FT2

)

Life--Cycle Costs in Dollars

Single Glazed Double Glazed

Area

(m2

) S

Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0 0 697 702 691 697 702 691

12 1.11 757 764 750 795 801 788

18 1.67 779 786 771 830 837 822

30 2.79 839 848 829 930 938 920

60 5.57 981 998 982 1162 1174 1150

Part B (FPE b = 12%)

0 0 2709 2729 2686 2709 2729 2686

12 1.11 2750 2775 2721 2804 2829 2776

18 1.67 2762 2790 2730 2837 2865 2806

30 2.79 2802 2836 2764 2934 2966 2898

60 5.57 2894 2961 2900 3158 3203 3110

a Life-cycle costs include the present value costs of (1) purchasing and installing

the windows (in excess of the costs of a brick wall section of equal size), (2) cleaning,

recaulking and repainting the windows on a regular basis, and (3) the energy costs

for heating, cooling, and lighting of the designated family room/kitchen of the house

described in section 2. They are not the life-cycle costs for the entire house.

Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

•21
TABLE 2.8

LOS ANGELES, CALIFORNIA, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR

A WINDOW SYSTEM — EVALUATED WITH WINDOW MANAGEMENT AND DAYLIGHTINGa

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

Window

(FT2

) Area

(m2

) S

Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

'

0

C 0 689 694 683 689 694 683

12 1.11 564 570 558 604 610 598

18 1.67 568 574 562 622 628 615

30 2.79 644 671 657 759 766 753

60 5.57 945 956 956 1131 1139 1123

Part B (FPEb = 12%)

0

C 0 2680 2700 2657 2680 2700 2657

12 1.11 1777 1799 1752 1838 1860 1814

18 1.67 1678 1702 1652 1764 1787 1738

30 2.79 1633 1660 1606 1783 1809 1757

60 5.57 1748 1791 1788 2026 2057 1996

a Life-cycle costs include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) purchasing

the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows

on a regular basis, and (4) the energy costs of the designated room for heating,

cooling, and lighting. Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

c Note that the life-cycle costs for all window sizes, from 0 to 60 ft 2 (5.57 m2 ),

reflect the adjustment of the thermostat for energy conservation; hence, the costs

for the zero window case in this table are slightly lower than in the preceding table

which did not assume an adjustment in the thermostat.

22
Part A of Table 2.9 shows that with unchanging real energy prices, the window

system which minimizes life-cycle costs is 12 ft^ and single glazed. Orientation makes little difference to costs. The least-cost window system is

expected to save about $125 over the life cycle and pay for itself in five to

six years.

Part B of table 2.9 shows that, with rapidly rising real energy prices, the

window area which minimizes life-cycle costs is 30 ft^ and single glazed. It

is just slightly less expensive if located on the north side. These windows

are estimated to save more than $1000, net, and to pay for themselves in six

and a half years.

2.5 ATLANTA, GEORGIA

Atlanta has not only a substantial cooling load requirement, but also a moderate heating load requirements (2950 heating degree days, 1000 cooling

hours). The balance between the two energy requirements is similar to that

for Los Angeles except that the magnitudes are significantly increased.

Table 2.10 shows net losses for both single- and double-glazed windows of all

sizes and for all orientations. Part A shows that with constant real energy

prices, single glazing is in all cases more cost effective than double glazing,

its losses averaging about 20 percent lower than double glazing.

If energy prices escalate at a real rate of 12 percent per year, part B of

table 2.10 shows that net losses rise to as high as about $800. With higher

energy costs, double glazing becomes somewhat more cost effective than single

glazing.

Part A of table 2.11 shows that with constant real energy prices, and by

combining daylight utilization with window management, all single-glazed windows

up to 30 ft^ (2.79 m^) and all double-glazed windows up to 18 ft^ (1.67 m2)

lower life-cycle costs. Part B of table 2.14 shows that net savings are much

higher if energy prices increase at a real rate of 12 percent per year than if

they are constant. All of the window areas result in sizable net savings.

The life-cycle savings are not substantially different for single and double

glazing.

Table 2.12 shows that the least-cost window system is single glazed and 12 ft^

(1.11 m^) in size if energy prices are constant in real dollars and singleglazed and 18 ft2 (1.67 m2) if prices rise rapidly. Costs are slightly less

if the window system is located on the south side. The windows are estimated

to pay for themselves in about three to four years.

2.6 WASHINGTON, D.C.

Washington, D.C. has approximately 4200 heating degree days and 1000 cooling

hours which means that the effect of windows on both heating and cooling is

relatively important.

23
LOS

ANGELES,

CALIFORNIA,

RESIDENTIAL

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STUDY:

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WINDOW

SYSTEMS —

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24
TABLE 2.10

ATLANTA, GEORGIA, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTINGa

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

Window

(FT2

) Area

(m2

) S Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0 0 720 724 715 720 724 715

12 1.11 780 792 787 802 809 800

18 1.67 809 825 821 831 842 832

30 2.79 884 904 904 918 933 923

60 5.57 1075 1107 1113 1125 1151 1141

Part B (FPE b = 12%)

0 0 2798 2816 2781 2798 2816 2781

12 1.11 2878 2924 2904 2886 2916 2881

18 1.67 2932 2991 2978 2919 2961 2924

30 2.79 3066 3146 3146 3021 3078 3043

60 5.57 3439 3565 3588 3279 3382 3343

I

! a Life-cycle costs include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) cleaning,

recaulking and repainting the windows on a regular basis, and (3) the energy costs

for heating, cooling, and lighting of the designated family room/kitchen of the house

described in section 2. They are not the life-cycle costs for the entire house.

Base-year prices are for 1978.

k FPE abbreviates "fuel price escalation rate.”

25
TABLE 2.11

ATLANTA, GEORGIA, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITH WINDOW MANAGEMENT AND DAYLIGHTING3

Window

(FT2

) Area

(m2

)

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

S

Orientation

E/W N S

Orientation

E/W N

Part A (FPE = 0%)

0b 0 712 716 707 712 716 707

12 1.11 565 579 577 590 603 597

18 1.67 572 587 587 603 617 612

30 2.79 662 680 685 719 736 731

60 5.57 920 948 969 1028 1052 1048

Part B (FPE = 12%)

0

b 0 2767 2785 2751 2767 2785 2751

12 1.11 1863 1916 1909 1883 1933 1911

18 1.67 1795 1854 1854 1817 1874 1854

30 2.79 1811 1882 1899 1853 1920 1902

60 5.57 2026 2135 2218 2091 2183 2169

3 Life-cycle costs include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) purchasing

the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows

on a regular basis, and (4) the energy costs of the designated room for heating,

cooling, and lighting. Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

c Note that the life-cycle costs for all window sizes, from 0 to 60 ft2 (5.57 m2 ), reflect

the adjustment of the thermostat for energy conservation; hence, the costs for the zero window case in this table are slightly lower than in the preceding table which did not assume an adjustment in the thermostat.

26
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27
Table 2.13 shows that life-cycle costs are lower with no windows than with

windows if they are unmanaged and not used for daylighting. When fuel prices

are assumed to remain level in constant dollars (Part A) , adding a 12 ft

(1.11 m2) single glazed window on the south side-*- is estimated to add $89 to

the life-cycle costs of the building; an 18 ft 2 (1.67 m2

) window, $130; a 30 ft 2 (2.79 m2

) window $225; and a 60 ft 2 (5.57 m2

) window, $468. With a

12 percent real escalation rate in fuel prices (FPE) (Part B), window performance is substantially worse: a 12 ft2 (1.11 m2

) single-glazed, south-facing

window is estimated to add $171 to life-cycle costs and a 60 ft 2 (5.57 m2

) window, nearly $1,000. Comparing the costs for double-glazed windows with

those for single-glazed windows, it may be seen that double glazing is cost

effective for larger north-facing windows even if fuel prices remain constant,

and it is cost effective for all window orientations if fuel prices escalate

rapidly.

The data in table 2.14 reflect the effects of window management and daylighting

on total life-cycle costs. From the table it may be seen that windows, effectively managed and used for daylighting, can lower life-cycle costs of the

building. The faster the rise in energy prices, the more favorable the window

becomes in this mode of use, because the savings in reduced lighting costs

(electricity) and cooling costs (electricity) more than offset the increased

costs for heating (gas).

When thermal shutters are used, double glazing is less likely to be needed.

The life-cycle cost results in table 2.14 show, in fact, that double glazing is

not estimated to be cost effective if energy prices remain constant in real

terms. It does become cost effective, however, for north-facing windows and

for large window areas if energy prices escalate rapidly. For smaller windows

facing south, east, or west, the thermal shutters are estimated to provide an adequate substitute for double glazing.

Table 2.15 shows the least-cost window system for each orientation, and the

least-cost system overall. For both constant and rapidly increasing fuel

prices, a single-glazed window of a small-to-moderate size facing south, managed

and used for daylighting, is the most cost effective. This window is estimated

to save $89 and to pay for itself in 6.6 years with constant fuel prices. When

fuel prices are estimated to increase at a 12 percent real rate, the savings

may be as much as $774, with only 4.9 years to payback. This window would be

cost effective even if fuel prices were to decline somewhat.

1 The reader is reminded that this assessment of the performance of

south-facing windows does not include the provision of winter thermal storage

capacity nor summer shading, both customary practices in passive solar energy

design; that is, the poor performance of the bare, unmanaged window is not

contradictory to the potential success of the window as a passive solar

energy collector.

28
TABLE 2.13

WASHINGTON, D.C., RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTINGa

Life--Cycle Costs in Dollars

Single Glazed Double Glazed

Window Area Orientation Orientation

(FT2

) (m2

) S E/W N S E/W N

Part A (FPE b = 0%)

0 0 719 725 718 719 725 718

12 1.11 808 821 824 820 830 824

18 1.67 849 863 870 857 870 865

30 2.79 944 963 980 963 980 975

60 5.57 1187 1219 1260 1214 1239 1234

Part B (FPE b = 12%)

0 0 2794 2819 2793 2794 2819 2793

12 1.11 2965 3014 3025 2924 2963 2942

18 1.67 3055 3112 3138 2976 3028 3008

30 2.79 3251 3322 3388 3121 3188 3167

60 5.57 3774 3897 4058 3474 3572 3550

a Life-cycle costs include the present value costs of (1) purchasing and installing

the windows (in excess of the costs of a brick wall section of equal size), (2) cleaning,

recaulking and repainting the windows on a regular basis, and (3) the energy costs

for heating, cooling, and lighting of the designated family room/kitchen of the house

described in section 2. They are not the life-cycle costs for the entire house.

Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

29
TABLE 2.14

WASHINGTON, D.C., RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITH WINDOW MANAGEMENT AND DAYLIGHTING3

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

Window

(FT2

) Area

(m2

) S Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0

C 0 695 700 693 695 700 693

12 1.11 606 618 625 630 642 640

18 1.67 621 636 649 652 665 664

30 2.79 738 757 780 790 807 809

60 5.57 1054 1083 1135 1153 1179 1185

Part B (FPEb = 12%)

0

C 0 2703 2721 2693 2703 2721 2693

12 1.11 1974 2020 2046 1982 2027 2020

18 1.67 1930 1985 2037 1936 1986 1982

30 2.79 2000 2074 2166 2003 2067 2075

60 5.57 2333 2446 2649 2313 2412 2438

3 Life-cycle costs include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) purchasing

the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows on

a regular basis, and (4) the energy costs of the designated room for heating, cooling,

and lighting. Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

c Note that the life-cycle costs for all window sizes, from 0 to 60 ft 2 (5.57 m2 ), reflect

the adjustment of the thermostat for energy conservation; hence, the costs for the zero window case in this table are slightly lower than in the preceding table which did not assume an adjustment in the thermostat.

30
WASHINGTON,

D.C.,

RESIDENTIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS —

4200

HEATING

DEGREE

DAYS,

1000

COOLING

HOURS o O & w ^ O o o O o o

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"fuel

price

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rate.
2.7 SEATTLE, WASHINGTON

In Seattle the effects of a dominant heating load (4400 heating degree days,

100 cooling hours) on window selection and use are apparent.

Table 2.16 shows that higher life-cycle costs result from both single- and

double-glazed windows of all sizes and with all orientations when windows are

not managed and not used for daylighting. If energy prices remain unchanged

in constant dollar terms, the life-cycle costs for single- and double-glazed

windows are nearly equal, although single glazing is slightly preferred for

windows with a southerly exposure and for small windows with other exposures.

Double glazing is less costly for moderate to large windows with a northerly

exposure. These results indicate that with constant real energy prices the

net losses for large windows average in excess of $500 and may run as high as $600 on northerly exposures.

Double glazing becomes more cost effective than single glazing for all windows

and orientations if energy prices rise at real annual rate of 12 percent.

Raising the real rate of increase in energy prices from 0 to 12 percent

increases the net losses attributable to windows by 30 to 50 percent for

double glazing, and in most cases by more than 100 percent for single

glazing.

Table 2.17 shows a less dramatic turnaround for window cost effectiveness from

adding management devices and daylight utilization than was seen in the previous

case studies. If energy prices remain level in constant dollars, only small

window areas of 12 ft^ (1.11 m^) are estimated to be cost effective, except on

the south where single-glazed windows as large as 18 ft^ (1.67 m^) result in

net savings. Net losses rise rapidly as window area is increased. As in the

preceding case, the costs for single- and double-glazed windows are nearly

equal, with the savings in energy from double glazing being more or less

offset by the higher costs of the windows.

Part B of table 2.17 shows windows to be somewhat more attractive economically

if energy prices rise sharply. For all but the largest windows, savings in

electric lighting costs from daylighting more than offset the higher heating

costs, resulting in net savings. With higher energy prices, double glazing is more cost effective than single glazing in every case.

Part A of table 2.18 shows that if real energy prices were to remain constant,

life-cycle costs would be minimized by having a 12 ft^ (1.11 m^) single-glazed

window, managed and used for daylighting, on the south side. Because the net

savings of even the least-cost window are small, the payback period ranges

from 10.8 years for a small single-glazed window on the south side to 16.7

years for the same window on the north.

Part B of table 2.18 shows that if energy prices rise rapidly, double-glazed

windows of 18 ft^ minimize life-cycle costs for all but northerly orientations.

On the north side, a window size of 12 ft^ is least costly. The least-cost

windows are expected to save between $500 and $600, and are estimated to pay

for themselves in 7.4 to 7.9 years.

32
I

TABLE 2.16

SEATTLE, WASHINGTON, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTINGa

1 Life-Cycle Costs in Dollars

i

II Single Glazed Double Glazed

Window Area Orientation Orientation

(FT 2

) (m2) S E/W N S E/W N

Part A (FPE b = 0%)

0 0 625 628 625 625 628 625

12 1.11 722 734 737 735 740 739

18 1.67 764 781 791 776 782 783

30 2.79 871 898 915 888 897 900

60 5.57 1141 1191 1233 1155 1173 1187

Part B (FPE b = 12%)

0 0 2430 2443 2431 2430 2443 2431

12 1.11 2616 2662 2675 2576 2596 2591

18 1.67 2708 2773 2812 2634 2658 2662

30 2.79 2936 3039 3106 2784 2821 2832 —60 5.57 3536 3729 3894 3155 3224 3277

a Life-cycle costs include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) cleaning,

recaulking and repainting the windows on a regular basis, and (3) the energy costs

for heating, cooling, and lighting of the designated family room/kitchen of the house

described in section 2. They are not the life-cycle costs for the entire house.

Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

33
TABLE 2.17

SEATTLE, WASHINGTON, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITH WINDOW MANAGEMENT AND WITH DAYLIGHTING3

Window Area

(FT2

) (m2)

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

S

Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0

C 0 612 612 608 612 612 608

12 1.11 573 589 603 593 601 606

18 1.67 607 626 646 623 633 643

30 2.79 761 789 822 789 801 817

60 5.57 1161 1210 1267 1207 1225 1256

Part B (FPEb = 12%)

0

C 0 2379 2380 2365 2379 2380 2365

12 1.11 1819 1878 1933 1805 1835 1854

18 1.67 1837 1912 1989 1779 1821 1859

30 2.79 2027 2136 2264 1919 1966 2028

60 5.57 2621 2812 3033 2366 2434 2554

3 Life-cycle <:osts include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) purchasing

the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows on

a regular basis, and (4) the energy costs of the designated room for heating, cooling,

and lighting. Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

c Note that the life-cycle costs for all window sizes, from 0 to 60 ft 2 (5.57 m2

) reflect the adjustment of the thermostat for energy conservation; hence, the costs

for the zero window case in this table are slightly lower than in the preceding

table which did not assume an adjustment in the thermostat.

34
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35
2.8 INDIANAPOLIS, INDIANA

Indianapolis was selected for case study because it has not only a relatively

heavy heating load requirement (5700 heating degree days), but also a moderately

heavy cooling load requirement (750 cooling hours). It is somewhat similar to

Washington, D.C. (4200 heating degree days, 1000 cooling hours), a previous case examined. However, the additional heating load requirement of Indianapolis

exerts a strong influence on the comparative costs of single and double glazing

and results in important differences in window selection in the two cities.

Without window management and without daylight utilization, both single- and

double-glazed windows of all sizes and with all orientations result in increased

life-cycle costs. As shown by part A of table 2.19, with constant real energy

prices, costs are raisqd more than $500 by the 60 ft^ (5.57 m^) window area,

whether single or double glazed. Double-glazed windows are somewhat more cost

effective, particularly for northerly exposures.

Part B of table 2.19 shows that if energy prices rise at a real rate of 12

percent compounded annually, net losses for single-glazed windows are more than

double those experienced with constant real energy prices, rising higher than

$1500 for northerly exposures. With double glazing, the net losses are about

50 percent higher than those experienced at constant energy prices. Double

glazing is in all cases more cost effective than single glazing. The net losses

associated with double-glazed windows range from 30 to 50 percent lower than

losses associated with single-glazed windows. However, even with double-glazed

windows, life-cycle costs climb steadily and may exceed $800 for large windows.

The addition of management devices and daylight utilization alters these

results dramatically. From part A of table 2.20 it can be seen that, with constant real energy prices, net savings are estimated for all windows up to and

including 18 ft^ (1.67 ra^) in area. On the south side, the thermal shutters

appear to eliminate a need for double glazing, and single glazing is cost

effective. On the north side, the energy savings from adding double glazing

to the thermal shutters are matched almost exactly by the higher acquisition

costs, and it makes little difference from an economic standpoint whether or

not double glazing is used in addition to the shutters.

If energy prices rise at a real rate of 12 percent per year, net savings are estimated for all sizes of double-glazed windows and for all single-glazed

windows, except for 60 ft^ (5.57 m^) areas facing east, west, or north. In

36
TABLE 2.19

INDIANAPOLIS, INDIANA, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTING3

I Life-Cycle Costs in Dollars

Window

(FT2

)

Single Glazed Double Glazed

Area

(in2

) S

Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0 0 722 729 725 722 729 725

12 1.11 826 839 844 829 838 835

18 1.67 870 887 899 869 879 877

30 2.79 978 1001 1025 976 989 989

60 5.57 1244 1289 1340 1231 1250 1257

Part B (FPE b = 12%)

0 0 2809 2836 2817 2809 2836 2817

12 1.11 3039 3092 3111 2968 3004 2992

18 1.67 3149 3214 3259 3034 3075 3066

30 2.79 3395 3486 3579 3194 3244 3243

60 5.57 4024 4200 4397 3583 3656 3684

: a Life-cycle costs include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) cleaning,

recaulking and repainting the windows on a regular basis, and (3) the energy costs

for heating, cooling, and lighting of the designated family-room/kitchen of the house

described in section 2. They are not the life-cycle costs for the entire house.

Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."
TABLE 2.20

INDIANAPOLIS, INDIANA, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITH WINDOW MANAGEMENT AND DAYLIGHTINGa

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

Window

(FT2)

Area

(m2

) S

Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0c 0 691 698 692 691 698 692

12 1.11 629 643 651 649 658 658

18 1.67 645 665 680 670 680 683

30 2.79 763 792 822 806 819 827

60 5.57 1099 1145 1208 1164 1185 1206

Part B (FPEb = 12%)

0

C 0 2688 2712 2690 2688 2712 2690

12 1.11 2075 2129 2162 2071 2105 2107

18 1.67 2039 2117 2175 2028 2066 2076

30 2.79 2130 2242 2359 2099 2151 2181

60 5.57 2568 2745 2992 2428 2512 2593

a Life-cycle costs include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) purchasing

the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows

on a regular basis, and (4) the energy costs of the designated room for heating,

cooling, and lighting. Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation."

c Note that the life-cycle costs for all window sizes, from 0 to 60 ft 2 (5.57 m2

) reflect the adjustment of the thermostat for energy conservation; hence, the costs

for the zero window case in this table are slightly lower than in the preceding table

which did not assume an adjustment in the thermostat.

38
every case double glazing is more cost effective than single glazing,

particularly for large, north-facing windows.

1

Part A of table 2.21 shows that with constant real energy prices the window

which minimizes life-cycle costs is single glazed, 12 ft^ (1.11 m2), located on

the south side of the house, managed, and used for daylighting. This window

system is estimated to pay for itself in seven to eight years.

As shown by part B of table 2.21, a double-glazed, 18 ft^ (1.67 m^) window area

on the south side, managed and used for daylighting, is least cost if energy

prices rise rapidly. This window system is estimated to pay for itself in six

to seven years and to save in excess of $600 as compared with a windowless

room.

2.9 PORTLAND, MAINE

The climate of Portland, Maine results in a heavy heating load requirement

(7600 heating degree days), and a very modest cooling load requirement (250

cooling hours). In Portland, Maine, as well as the next city to be explained,

Bismarck, North Dakota, the use of triple glazing to minimize winter heat loss

will be considered. Triple glazing is assumed to be obtained by fitting a storm sash over a sealed double-glazed window.

From part A of table 2.22 it can be seen that without management and daylight

utilization and with constant real energy prices, net losses result for single-,

double-, and triple-glazed windows of all sizes and with all orientations.

With the heavy heating load, single glazing is less cost effective than either

double or triple glazing even if energy prices are constant in real terms. Net

losses exceed $700 for large single-glazed windows with northerly exposures.

The life-cycle costs associated with double and triple glazing are nearly equal

to one another, with triple glazing slightly lower in costs for a northerly

exposure. Net losses for large double- and triple-glazed windows average

about $500.

Part B of table 2.22 shows that if energy prices rise at a real rate of 12

percent per year, net losses for large windows on the north exceed $2000 for

single glazing, $1000 for double glazing, and approach $800 for triple glazing.

With the higher future energy costs, triple glazing is the most cost-effective

glazing type. For large windows on the north, triple glazing reduces net

1 The higher heating load requirements for Indianapolis as compared with

Washington result in the following key differences in window cost effectiveness if energy prices rise rapidly: (1) In Washington all windowed areas managed and used for daylighting are estimated to produced net savings;

whereas in Indianapolis, large single-glazed windows facing east, west, or north are estimated to produce a net increase in life-cycle costs. (2) In

Washington single glazing is estimated to be cost effective for windows

18 ft2 (1.67 m2) and smaller which do not have a northerly exposure; whereas,

in Indianapolis, double glazing appears better for these windows.

39
INDIANAPOLIS,

INDIANA,

RESIDENTIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS

5700

HEATING

DEGREE

DAYS,

750

COOLING

HOURS e3

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40

FPE

abbreviates

"fuel

price

escalation

rate
TABLE 2.22

PORTLAND, MAINE, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM -- EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTING3

Life-Cycle Costs in Dollars

Single Glazed Double Glazed Triple Glazed

Window Area

(FT2

) (m2) Orientation

S E/W N

Orientation

S E/W N

Orientation

S E/W N

Part A (FPE b = 0%)

0 0 703 712 713 703 712 713 703 712 713

12 1.11 818 839 860 806 818 827 807 818 822

18 1.67 870 897 926 844 859 872 845 859 864

30 2.79 990 1027 1078 949 970 989 951 968 977

60 5.57 1291 1359 1461 1199 1230 1265 1199 1227 1242

Part B (FPE b = 12%)

0 0 2734 2767 2772 2734 2767 2772 2734 2767 2772

12 1.11 3024 3108 3188 2902 2950 2985 2870 2915 2930

18 1.67 3170 3276 3390 2974 3033 3081 2925 2976 3000

30 2.79 3480 3626 3824 3145 3226 3299 3064 3129 3163

60 5.57 4286 4550 4945 3573 3693 3831 3394 3500 3559

a Life-cycle costs include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) cleaning,

recaulking and repainting the windows on a regular basis, and (3) the energy costs for

heating, cooling, and lighting of the designated family room/kitchen of the house

described in section 2. They are not the life-cycle costs for the entire house.

Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

41
losses 28 percent below those of double glazing, and 64 percent below those of

single glazing.

Table 2.23 shows the life-cycle costs associated with the windows when they are managed and used for daylight. Part A of table 2.23 shows that window management and daylighting result in modest net savings for small windows, except

those on the north, if real energy prices remain constant. With thermal shutters, single glazing is slightly more cost effective for southerly exposures;

double glazing for most northerly exposures. Triple glazing is estimated to

be slightly more cost effective than single glazing and slightly less cost

effective than double glazing for northern exposures.

From part B of table 2.23 it can be seen that with rapidly rising energy prices

all but the largest windowed areas yield net savings provided they are either

double or triple glazed, managed, and used for daylighting. In every case examined, triple glazing appears to be the most cost-effective type of glazing.

If energy prices rise at about the rate of general price inflation (i.e., no increase in real dollars), it appears from part A of table 2.24 that small,

single-glazed windows on the south side of the house are the cost-effective

choice. But if energy prices rise at a rate 12 percent faster than the rate

of general price inflation, part B of table 2.24 shows that the window system

which minimizes life-cycle costs is triple glazed with an area of 18 ft^

(1.67 m^). The least-cost, triple-glazed window system is expected to save nearly $500 in present value dollars, and to pay for itself in seven to eight

years. These results suggest that even in a climate with a heavy heating

load, windows which are well designed thermally, appropriately sized, oriented,

and equipped with accessories, and which take advantage of natural lighting can accomplish significant reductions in life-time building costs.

2.10 BISMARCK, NORTH DAKOTA

The last city treated in the residential case studies is Bismarck, North

Dakota. Bismarck has the highest heating load requirement (8850 heating degree

days) of the cities examined, as well as a higher cooling load (450 cooling

hours) than the other cold winter city, Portland, Maine. It offers an interesting contrast to the case study for Miami, where the cooling load requirement

was very high.

Table 2.25 shows that without management or daylight utilization, windows cause life-cycle costs to rise, regardless of the type of glazing, the size, or the

orientation. Part A of the table shows that, as in the previous case study,

single glazing is not cost effective, even with constant real energy prices.

Net losses exceed $800 for large single-glazed windows with northerly exposures. There is little difference in the life-cycle costs of double and triple

glazing, although triple glazing is slightly preferred.

Part B of table 2.25 shows that if energy prices rise at a real rate of 12

percent per year, net losses for large windows on the north side of the room

may exceed $2500 for single-glazing, $1200 for double glazing, and $900 for

triple glazing. In all cases triple glazing is the most cost-effective type

42
TABLE 2.23

PORTLAND, MAINE, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM -- EVALUATED WITH WINDOW MANAGEMENT AND DAYLIGHTING3

Life-Cycle Costs in Dollars

Single Glazed Double Glazed Triple Glazed

Window Area Orientation Orientation Orientation

(FT2

) (m2) S E/W N S E/W N S E/W N

Part A (FPE b = 0%)

0C 0 671 680 681 671 680 681 671 680 681

12 1.11 642 665 694 656 670 683 665 678 687

18 1.67 670 698 738 681 698 716 693 708 720

30 2.79 795 835 899 818 837 865 835 854 871

60 5.57 1126 1194 1316 1158 1186 1237 1193 1219 1245

Part B (FPEb = 12%)

0

C 0 2610 2644 2648 2610 2644 2648 2610 2644 2648

12 1.11 2161 2253 2362 2143 2195 2249 2141 2192 2225

18 1.67 2180 2289 2445 2126 2192 2264 2121 2180 2224

30 2.79 2333 2487 2738 2245 2319 2427 2222 2296 2359

60 5.57 2837 3100 3575 2608 2714 2912 2562 2661 2764

3 Life-cycle costs include the present value costs of (1) purchasing and installing

the windows (in excess of the costs of a brick wall section of equal size),

(2) purchasing the Venetian blinds and shutters, (3) cleaning, recaulking and

repainting the windows on a regular basis, and (4) the energy costs of the

designated room for heating, cooling, and lighting. Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

c Note that the life-cycle costs for all window sizes, from 0 to 60 ft 2 (5.57 m2

) reflect the adjustment of the thermostat for energy conservation; hence, the costs

for the zero window case in this table are slightly lower than in the preceding

table which did not assume an adjustment in the thermostat.

43
PORTLAND,

MAINE,

RESIDENTIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS

--

7600

HEATING

DEGREE

DAYS,

250

COOLING

HOURS s3

44

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co3O

33e

COo01 Ml

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44
TABLE 2.25

BISMARCK, NORTH DAKOTA, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTING3

Life-Cycle Costs in Dollars

Single Glazed Double Glazed Triple Glazed

Window Area Orientation Orientation Orientation

(FT 2

) (m2) S E/W N S E/W N S E/W N

Part A (FPE b = 0%)

0 0 753 764 766 753 764 766 753 764 766

12 1.11 882 913 938 861 880 893 861 877 885

18 1.67 941 981 1017 904 926 944 902 921 932

30 2.79 1073 1129 1191 1016 1043 1072 1011 1035 1052

60 5.57 1405 1507 1631 1281 1322 1379 1270 1307 1337

Part B (FPE b = 12%)

0 0 2927 2971 2980 2927 2971 2980 2927 2971 2980

12 1.11 3271 3391 3488 3115 3186 3238 3074 3137 3169

18 1.67 3442 3595 3735 3197 3282 3354 3135 3208 3251

30 2.79 3797 4016 4253 3393 3499 3613 3283 3376 3441

60 5.57 4710 5108 5590 3870 4028 4250 3641 3783 3902

3 Life-cycle costs include the present value costs of (1) purchasing and installing

the windows (in excess of the costs of a brick wall section of equal size), (2)

cleaning, recaulking and repainting the windows on a regular basis, and (3) the

energy costs for heating, cooling, and lighting of the designated family-room/

kitchen of the house described in section 2. They are not the life-cycle costs

for the entire house. Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate."

45
of glazing. With triple glazing, net losses are estimated to be less than

half what they are with single glazing, and only about three-fourths what they

are with double glazing.

Table 2.26 shows that managing the windows and using daylight in all cases improves the economic performance of the windows; however, attention to sizing,

orientation, and glazing is also necessary to realize net dollar savings from

them. If energy prices are level in constant dollars and thermal shutters are used, single glazing appears slightly more cost effective for southerly exposures, double glazing for easterly/westerly exposures, and either double or triple glazing for northerly exposures.

Part B of table 2.26 shows the impact of rapidly rising energy prices on window

costs when the windows are managed and used for daylighting. With 12 percent

real escalation in energy prices, it is possible to realize sizable net savings

from windows, provided they are kept small to moderate in size and are either

placed on the south or are double or triple glazed. For all window sizes and

orientation, triple glazing is the most cost-effective type of glazing. Savings

average more than $400 for triple-glazed windows 12 to 18 ft^ (1.11 to 1.67 m2)

in area.

As shown by part A of table 2.27, none of the window systems examined produces

net savings on the north side if real energy prices are constant. For southerly

exposures, the least-cost window system is 12 ft^ (1.11 m2) and single glazed.

For easterly-westerly exposures, the least-cost window systems is 12 ft^

(1.11 m^) and double glazed. In both cases, net savings are trival in amount.

From part B of table 2.27, it can be seen that the window system which minimizes

life-cycle costs when energy prices escalate rapidly is triple glazed, 18 ft^

(1.67 m^), and located on the south side. On the north side, the least-cost

window system is 12 ft2 (1.11 m2) in area and triple glazed. Net savings from

the least-cost window system for each orientation vary from just under $400 on

the north side to almost $500 on the south, and the expected time to payback

is about eight years.

46
TABLE 2.26

BISMARCK, NORTH DAKOTA, RESIDENTIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM -- EVALUATED WITH WINDOW MANAGEMENT AND DAYLIGHTING3

Life-Cycle Costs in Dollars

Single Glazed Double Glazed Triple Glazed

Window Area Orientation Orientation Orientation

(FT2

) (m2) S E/W N S E/W N S E/W

Part A (FPE b = 0%)

0

C 0 721 732 734 721 732 734 721 732 734

12 1.11 698 731 764 710 730 748 719 737 749

18 1.67 725 766 813 735 758 783 746 767 784

30 2.79 854 912 986 873 901 938 891 916 939

60 5.57 1193 1296 1440 1226 1265 1335 1258 1293 1334

Part B (FPEb = 12%)

0

C 0 2804 2847 2852 2804 2847 2852 2804 2847 2852

12 1.11 2373 2501 2627 2343 2420 2490 2341 2409 2456

18 1.67 2383 2545 2726 2325 2414 2510 2312 2394 2458

30 2.79 2545 2771 3058 2439 2547 2692 2414 2512 2604

60 5.57 3060 3461 4021 2827 2979 3251 2767 2903 3065

a Life-cycle costs include the present value costs of (1) purchasing and installing the

windows (in excess of the costs of a brick wall section of equal size), (2) purchasing

the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows

on a regular basis, and (4) the energy costs of the designated room for heating,

cooling, and lighting. Base-year prices are for 1978.

b FPE abbreviates "fuel price escalation rate.”

c Note that the life-cycle costs for all window sizes, from 0 to 60 ft 2 (5.57 m2 ),

reflect the adjustment of the thermostat for energy conservation; hence, the costs for

the zero window case in this table are slightly lower than in the preceding table

which did not assume an adjustment in the thermostat.

47
BISMARCK,

NORTH

DAKOTA,

RESIDENTIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS —

8850

HEATING

DEGREE

DAYS,

450

COOLING

HOURS E CJ 3e w /-s o o

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48
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49

Windows

are

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element

in

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commercial

building

facade.

i

3. COMMERCIAL CASE STUDIES FOR NINE CITIES

3 . 1 DESCRIPTION OF COMMERCIAL BUILDING AND WINDOW SYSTEMS 1

The focus of the commercial case studies is an office module in a 5-to-10 story

office building with conventional curtain wall construction. The exterior wall

of the office building consists of a dark glass spandrel panel with one inch of

rigid fiberglass insulation applied with a mastic. The mullions which hold the

spandrel panels are dark anodized aluminum with a thermal break. The interior

surface of the exterior wall is cut out and installed. The size of the cutout

is determined by the size and type of glazing. The U value of the non-windowed

wall is approximately 0.15.

The windows are assumed to be fixed. The framing is dark anodized aluminum

with a thermal break. It is assumed that no tints or low emissivity coatings

are used. All glazing is erected from the inside of the building as a stick

wall; elastomeric gaskets^ (dryset) are used on all windowed areas. Both

single and double glazing are examined. Window sizes range from 0 to 90 square

feet (0 to 5.57 m^). Figure 3.1 illustrates the shape of the office module

and the window sizes in relationship to the size of the exterior wall.

The floor area of the office module is 180 square feet (16.72 m^) and the

volume of the module is 1800 cubic feet (50.97 m^). It is assumed that two

people are assigned to the office during the normal working hours of 9:00 a.m.

to 5:00 p.m. Their occupancy is averaged over the day and the resultant

figure of 1.8 persons is used in the computer model to calculate heat loads

generated by the occupants. The calculation of expected heat gains also takes

into account the effects of office equipment, such as typewriters, electric

adding machines/desk calculators, and computer time-sharing terminals, as well

as lighting. Additional assumptions, such as lighting requirements and heating

and cooling system efficiencies, are given in table 1.1, and costs of the

window systems are given in appendix B.

The cities are those used for the residential case studies: Washington, D.C.;

Miami, Florida; Atlanta, Georgia; Portland, Maine; Indianapolis, Indiana; San

Antonio, Texas; Los Angeles, California; Bismarck, North Dakota; and Seattle,

Washington. (Their locations and climatic zone designations are shown on the

map in figure 1.1.)

1 This information, taken from the companion report, Economic Evaluation of

Windows in Buildings : Methodology [1], is repeated here for the convenience

of the reader.

2 The use of elastomeric gaskets reduces the likelihood of repairs which would

probably result from chemical sealants applied at the site. The elastomeric

gaskets are assumed to perform satisfactorily throughout the 25 year life

cycle .

51
52

Figure

3.1

Window

Sizes

in

Relationship

to

the

Size

of

the

Exterior

Wall

of

the

Office

Module
Like the residential case studies, these commercial case studies do not include

special passive solar energy features for south-facing windows to increase

solar absorption and thermal storage. Also like the residential cases, energy

savings from natural ventilation are not included; however, this is appropriate

for the commercial cases since the windows are assumed fixed. It should also

be noted that energy savings from daylighting requires its effective substitution for electric lighting, probably a difficult goal to achieve in an office

building without the use of an automatic switching device ^ or employee energy

awareness or incentive program, the cost and effectiveness of which are not

included in this analysis. Regarding the utilization of solar heat gains

through the windows, the following should be noted: if the thermal analysis

indicates a need for heat in the office module, calculated solar heat gains

through the window are treated as beneficial up to the limits of the heating

requirements, ignoring the problems of overheating and the need to distribute

the heat through the space.

The format in this section is the same as that in the previous section for the

residential case studies. For each city, tables of life-cycle costs are given,

first, for the least economically favorable mode of use examined, and, second,

fbr the most favorable mode of use. These two tables are followed by a third

table identifying the least-cost window systems. The first mode of window

use—identical to that for the residential case studies—is unmanaged windows,

not used for daylighting. The second mode—unlike that for the residential

case studies—is unmanaged windows, used for daylighting .

3.2 MIAMI, FLORIDA

Let us look first at the less advantageous results for windows: those not used

for daylighting. We see from table 3.1 that in Miami, with its dominant cooling load of 2400 cooling hours, the lowest cost penalty from windows in face of

rapidly rising real energy prices is for small, single-glazed windows located

on the north. With constant real energy prices, windows are estimated to add

little to long-run costs, regardless of their size or orientation. The higher

acquisition cost of the double glazing is not estimated to be a worthwhile

expense for the office window in Miami.

1 The use of photo-sensitive lighting controls to reduce lighting energy while

maintaining required illumination through daylighting has been investigated

by Treado and Kusuda [6].

^ Although the particular window management considered here was found not to

be cost effective for the commercial windows, the reader is reminded that

this finding reflects the large estimated acquisition cost for commercialgrade shutters, and does not mean that blinds and thermostat adjustment are

not cost effective. It is also important to keep in mind that there are many other forms of window management, not considered here, which may

be cost effective.

53
TABLE 3.1

MIAMI, FLORIDA, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTING3

Window

(FT2

) Area

(m 2

)

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

S

Orientation

E/W N S OrientationE/W N

Part A (FPEb = 0%)

0 0 1219 1222 1215 1219 1222 1215

12 1.11 1255 1262 1243 1321 1327 1309

30 2.79 1284 1298 1259 1404 1417 1381

60 5.57 1408 1433 1362 1624 1646 1582

90c 8.36 1297 1333 1230 1587 1620 1527

Part B (FPEb = 12%)

0 0 1871 1879 1856 1871 1879 1856

12 1.11 1972 1996 1927 2029 2051 1987

30 2.79 2100 2147 2011 2197 2240 2115

60 5.57 2387 2475 2226 2557 2636 2411

90c 8.36 2440 2567 2207 2661 2776 2451

3 Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

mullions, and interior curtain wall; (2) annual cleaning costs over 25 years;

(3) annual insurance costs over 25 years; and (4) annual energy costs for heating,

cooling, and lighting the office module over 25 years, with (5) all costs adjusted

for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than

for 60 ft 2 (5.57 m

2

) of area, due to estimated lower framing costs for the larger area

.

54
Table 3.2 shows the total life-cycle costs when daylight utilization is

practiced. Part A of the table shows that small net savings result for most of

the window sizes if real energy costs remain level and single glazing is used.

On the other hand, all double-glazed window areas examined are estimated to

produce net losses.

Part B of table 3.2 shows at least small estimated savings for all

single-glazed windows, except large east and west-facing windows, if energy

prices rise at a real rate of 12 percent compounded annually. The largest

savings result from moderately sized, north-facing, single-glazed windows.

Double glazing is not estimated to be cost effective relative to single-glazing;

however, savings are estimated for moderately sized double-glazed windows.

Table 3.3 shows that rising real energy prices in Miami increase the potential

net savings from daylighting, but constrain the size of the least-cost window

to 30 ft^ (2.79 m^ ) . The dominant cooling load in Miami dictates the north

side of the building as the least-cost window orientation.

3.3 SAN ANTONIO, TEXAS

Tables 3.4 through 3.6 give the life-cycle cost results for San Antonio. These

results are quite similar to those for Miami, although there is less difference

in San Antonio in the costs of north- and south-facing windows. Due to the

somewhat lower cooling load and higher heating load in San Antonio relative to

Miami (2000 versus 2400 cooling hours, and 1550 versus 200 heating degree days,

respectively), north and south orientations are about equal in life-cycle costs

for San Antonio, whereas in Miami, there was a cost advantage to orienting windows to the north. Like the Miami case, orienting windows to the east or west

raises costs, as does the use of double glazing.

Also like the Miami case, windows in the San Antonio office are in general

estimated to raise life-cycle costs unless they are used for daylighting. This

cost increase is quite small if real energy prices remain constant and if

single glazing is used, and is relatively modest even if energy prices rise

rapidly. Single glazing is estimated to be lower in cost than double glazing

even if energy prices rise at 12 percent per year, but the advantage of single

glazing is diminished as energy prices rise, and would be lost if energy prices

were to rise much faster than 12 percent per year.

Daylight utilization significantly alters the life-cycle cost results. Part A

of table 3.5 shows small net savings for most of the single-glazed windows if

real energy prices are constant, but no savings for double-glazed windows.

Part B of table 3.5 shows that with rapidly rising energy prices, the potential

for savings through daylighting is increased. Single glazing continues to be

more cost effective than double glazing.

Part A of table 3.6 shows that if real energy prices are level, the window

system which minimizes life-cycle costs is 90 ft^ (8.36 m^) in size, south

facing, and single glazed. Part B of the table shows that higher energy prices

raise potential savings — the increase due to greater reductions in electric

55
TABLE 3.2

MIAMI, FLORIDA, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT BUT WITH DAYLIGHT INGa

Window

(FT2

) Area

(m2

)

Life -Cycle Costs in Dollars

Single Glazed Double Glazed

S

Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0 0 1219 1222 1215 1219 1222 1215

12 1.11 1216 1223 1203 1282 1288 1270

30 2.79 1153 1167 1128 1273 1285 1250

60 5.57 1260 1285 1214 1476 1498 1434

90° 8.36 1171 1208 1105 1461 1494 1401

Part B (FPEb = 12%)

0 0 1871 1879 1856 1871 1879 1856

12 1.11 1745 1768 1700 1801 1823 1759

30 2.79 1548 1596 1459 1645 1689 1564

60 5.57 1744 1832 1583 1914 1994 1768

90c 8.36 1814 1941 1580 2035 2150 1825

a Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

mullions, and interior curtain wall; (2) annual cleaning costs over 25 years;

(3) annual insurance costs over 25 years; and (4) annual energy costs for heating,

cooling, and lighting the office module over 25 years, with (5) all costs adjusted

for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than

for 60 ft 2 (5.57 m

2

) of area, due to estimated lower framing costs for the larger

area

.

56
MIAMI,

FLORIDA,

COMMERCIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS —

200

HEATING

DEGREE

DAYS,

2400

COOLING

HOURS 536

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57
TABLE 3.4

SAN ANTONIO, TEXAS, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTINGa

Window

(FT2

)

Life -Cycle Costs in Dollars

Area

(m2

)

Single Glazed Double Glazed

S

Orientation

E/W N S

Orientation

E/W N

Part A (FPEb = 0%)

0 0 1111 1115 1110 1111 1115 1110

12 1.11 1138 1149 1137 1210 1221 1209

30 2.79 1155 1177 1153 1301 1320 1298

60 5.57 1257 1295 1255 1545 1572 1531

90c 8.36 1145 1198 1146 1543 1581 1521

Part B (FPEb = 12%)

0 0 1719 1733 1717 1719 1733 1717

12 1.11 1780 1820 1777 1843 1881 1839

30 2.79 1851 1928 1844 1978 2043 1965

60 5.57 2048 2181 2043 2307 2404 2260

90c 8.36 2035 2219 2038 2391 2523 2312

a Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

mullions, and interior curtain wall; (2) annual cleaning costs over 25 years;

(3) annual insurance costs over 25 years; and (4) annual energy costs for heating,

cooling, and lighting the office module over 25 years, with (5) all costs adjusted

for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than

for a 60 ft 2 (5.57 m

2

) of area, due to estimated lower framing costs for the larger

area.

58
TABLE 3.5

SAN ANTONIO, TEXAS, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT BUT WITH DAYLIGHTINGa

Window

(FT2

)

Life-Cycle Costs in 1Dollars

Single Glazed Double Glazed

Area

(m2) S

Orientation

E/W N S

Orientation

E/W N

Part A (FPE b = 0%)

0 0 1111 1115 1110 1111 1115 1110

12 1.11 1103 1115 1102 1176 1186 1175

30 2.79 1036 10-59 1041 1183 1201 1179

60 5.57 1119 1167 1140 1406 1434 1400

90c 8.36 1026 1094 1055 1424 1462 1411

Part B (FPEb = 12%)

0 0 1719 1733 1717 1719 17 33 1717

12 1.11 1576 1617 1573 1639 1677 1636

30 2.79 1352 1433 1370 1480 1545 1467

60 5.57 1451 1620 1526 1709 1806 1688

90c 8.36 1450 1687 1551 1805 1938 1760

a Life-cycle costs include the present value costs of (1) purchase and installation

for the 10' x 12' exterior wall of the office, including the spandrel panel and window, mullions, and interior curtain wall; (2) annual cleaning costs over 25 years;

(3) annual insurance costs over 25 years, and (4) annual energy costs for heating,

cooling, and lighting the office module over 25 years, with (5) all costs adjusted

for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than

for 60 ft 2 (5.57 m

2

) of area, due to estimated lower framing costs for the larger

area

.

59
SAN

ANTONIO,

TEXAS,

COMMERCIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS —

1550

HEATING

DEGREE

DAYS

AND

2000

COOLING

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lighting costs, and related reductions in cooling costs — but reduce the

least-cost window size due to the higher costs of undesirable heat gains and

losses through larger windows.

3.4 LOS ANGELES, CALIFORNIA

For Los Angeles, with its modest heating and cooling loads (1350 heating degree

days and 550 cooling hours), table 3.7 shows small net savings for large

(90 ft^) single-glazed windows on the south, even if energy prices are assumed

to increase rapidly and if daylighting is not practiced. * Small net losses are estimated for other sizes of single-glazed windows, and somewhat larger losses

for double-glazed windows of all sizes and orientations if energy prices rise

rapidly. As in the Los Angeles residential case, climatic conditions cause

the energy requirement for the windowed module in Los Angeles to be less than

the requirement for the windowless module—apart from daylighting.

/ Part A of table 3.8 shows that with daylight utilization and constant real

energy prices, net savings result for almost all sizes and orientations of

single-glazed windows. Net losses are estimated for double-glazed windows.

Part B of table 3.8 shows that if energy prices rise at a real rate of 12

percent per year, single-glazed windows will reduce life-cycle building costs

substantially if they are used for daylighting. The double-glazed windows are estimated to save considerably less.

Part A of table 3.9 shows that the window system which minimizes life-cycle

costs if real energy prices are constant, is unmanaged, used for daylighting,

90 ft^ (8.36 m^), single glazed, and facing south. It is expected to save about $184 over the 25 year period, and, due to its lower initial investment

cost, is expected to have an immediate payback.

Part B of table 3.9 shows that the window which minimizes life-cycle costs in

the face of rapidly rising energy prices also is unmanaged, used for daylighting, 90 ft^ (8.36 m^), single glazed, and south facing. With a sharp rise in

energy prices, however, the potential savings attributable to windows increases

to an estimated $576, due to larger cost reductions in electric lighting and

cooling costs.

3.5 ATLANTA, GEORGIA

Atlanta has not only a substantial cooling load requirement, but also a moderate

heating load requirement. The balance betwen the two energy requirements is

similar to that for Los Angeles except that the magnitudes are significantly

increased.

1 Note, however, the dependency of this finding on the assumption of a lower

estimated first cost for the 90 ft^ (8.36 m^) window wall than for other

window sizes.

61
TABLE 3.7

LOS ANGELES, CALIFORNIA, COMMERICIAL CASE STUDY: LIFE-CYCLE COSTS FOR A

WINDOW SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTING3

Window

(FT2

)

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

Area

(m2

) S

Orientation

E/W N S Orientation

E/W N

Part A (FPEb = 0%)

0 0 1271 1276 1274 1271 1276 1274

12 1.11 1283 1293 1289 1371 1380 1376

30 2.79 1278 1295 1287 1457 1469 1459

60 5.57 1360 1384 1370 1705 1720 1700

90c 8.36 1184 1215 1202 1662 1681 1649

Part B (FPEb = 12%)

0 0 1825 1840 1833 1825 1840 1833

12 1.11 1837 1870 1856 1924 1955 1940

30 2.79 1836 1895 1867 2024 2066 2032

60 5.57 1942 2027 1976 2310 2362 2291

90c 8.36 1792 1902 1856 2303 2369 2259

a Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

mullions, and interior curtain wall; (2) annual cleaning costs over 25 years;

(3) annual insurance costs over 25 years; and (4) annual energy costs for heating,

cooling, and lighting the office module over 25 years, with (5) all costs adjusted

for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than for

60 ft 2 (5.57 m

2

) of area, due to estimated lower framing costs for the larger area.

62
TABLE 3.8

\

LOS ANGELES, CALIFORNIA, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A

WINDOW SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT BUT WITH DAYLIGHTINGa

Window

(FT2

)

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

Area

(m2

) S Orientation

E/W N S

Orientation

E/W N

Part A (FPEb = 0%)

0 0 1271 1276 1274 1271 1276 1274

12 1.11 1261 1270 1266 1349 1358 1353

30 2.79 1176 1192 1190 1354 1366 1356

60 5.57 1240 1271 1281 1585 1601 1585

90c 8.36 1087 1130 1143 1565 1584 1560

Part B (FPEb = 12%)

0 0 1825 1840 1833 1825 1840 1833

12 1.11 1658 1692 1677 1746 1777 1761

30 2.79 1378 1435 1428 1564 1606 1572

60 5.57 1386 1494 1528 1753 1806 1752

90c 8.36 1249 1400 1445 1759 1826 1744

a Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

mullions, and interior curtain wall; (2) annual cleaning costs over 25 years;

(3) annual insurance costs over 25 years; and (4) annual energy costs for heating,

cooling, and lighting the office module over 25 years, with (5) all costs adjusted

for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m2

) of window area than for

60 ft 2 (5.57 m

2

) of area, due to estimated lower framing costs for the larger area.

63
LOS

ANGELES,

CALIFORNIA,

COMMERCIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS

--

1350

HEATING

DEGREE

DAYS,

550

COOLING

HOURS

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64
Part A of table 3.10 shows net losses to result from all but large (90 ft^)

(8.36 m^) south-, east-, and west-facing single-glazed windows, if real energy

prices are assumed constant and daylighting is not used.^ Single glazing

appears more cost effective than double glazing for all window sizes and orientations. Net losses are slightly lower for southern exposures than for other

exposures, because heating load requirements in Atlanta are somewhat more important than cooling load requirements.

If energy prices escalate at a real rate of 12 percent per year, part B of

table 3.10 estimates small to moderate net losses for all windows. Single

glazing and a southerly exposure remain the cost-effective choices,

particularly for larger windows.

Part A of table 3.11 shows that with daylight utilization and constant real

energy prices, the single-glazed windows for the most part lower life-time

building costs. Single glazing and southerly orientations continue to be

cost effective.

Part B of table 3.11 shows higher net savings associated with higher energy

prices due to greater lighting cost savings. A large single-glazed window area

on the south is estimated to save nearly $500 in present value dollars. 2 Single

glazing is generally more cost effective than double glazing, although there

is only a small cost difference in large single- and double-glazed windows on

the north.

Table 3.12 shows the least-cost choice to be a 90 ft2 (8.36 m2) single-glazed

window on the south, unmanaged, and used for daylighting, whether the real rate

of energy price escalation is zero or 12 percent. 2 For other than southerly

orientations, a smaller window (30 ft2) (2.79 m2) is recommended as cost

effective if energy price escalation is rapid.

3.6 WASHINGTON , D.C.

Table 3.13 shows that the windows unmanaged and not used for daylighting

generally add to the life-cycle cost of the office module in Washington, D.C.,

with its 4,200 heating degree days and 1000 cooling hours. However, with constant real energy prices (part A of table 3.13), a large (90 ft2 or 8.36 m2)

single-glazed window can be added to the south side with little or no estimated

cost penalty, because estimated savings in framing costs for the large window

offset its somewhat higher energy costs. With constant energy prices, single

glazing is estimated to cost less than double glazing over the long run for

all of the window sizes and orientations.

1 Note the dependency of this finding on lower first cost for the largest

window size.

2 Ibid .

3 Ibid.

65
TABLE 3.10

ATLANTA, GEORGIA, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHT I NGa

Window

(FT2

)

Life--Cycle Costs in Dollars

Single Glazed Double Glazed

' Area

(m2

) S Orientation

E/W N S OrientationE/W N

Part A (FPEb = 0%)

0 0 1155 1159 1156 1155 1159 1156

12 1.11 1171 1180 1175 1238 1246 1241

30 2.79 1172 1189 1187 1297 1310 1302

60 5.57 1247 1283 1286 1479 1500 1486

90c 8.36 1097 1156 1162 1417 1442 1423

Part B (FPEb = 12%)

0 0 1746 1760 1751 1746 1760 1751

12 1.11 1776 1807 1791 1835 1863 1847

30 2.79 1801 1860 1853 1907 1954 1926

60 5.57 1916 2044 2055 2119 2192 2141

90° 8.36 1807 2015 2038 2095 2184 2116

a Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

raullions, and interior curtain wall; (2) annual cleaning costs over 25 years; (3) annual

insurance costs over 25 years; and (4) annual energy costs for heating, cooling, and

lighting the office module over 25 years, with (5) all costs adjusted for tax deductible

expe nses

.

b FPE abbreviates ’’fuel price escalation rate.”

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than for

60 ft 2 (5.57 m

2

) of area, due to estimated lower framing costs for the larger area.

66
TABLE 3.11

ATLANTA, GEORGIA, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT BUT WITH DAYLIGHTING3

Window

(FT2

) Area

(m2

)

Life -Cycle Costs in Dollars

Single Glazed Double Glazed

S

Orientation

E/W N S

Orientation

E/W N

Part A (FPEb = 0%)

0 0 1155 1159 1156 1155 1159 1156

12 1.11 1143 1152 1150 1210 1218 1213

30 2.79 1065 1092 1096 1188 1203 1201

60 5.57 1127 1179 1191 1349 1379 1378

90c 8.36 999 1073 1090 1307 1342 1338

Part B (FPEb = 12%)

0 0 1746 1760 1751 1746 1760 1751

12 1.11 1591 1622 1613 1650 1678 1662

30 2.79 1336 1433 1448 1439 1491 1485

60 5.57 1376 1560 1599 1544 1649 1644

90c 8.36 1287 1548 1606 1529 1653 1640

3 Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

mullions , and interior curtain wall; (2) annual cleaning costs over 25 years;

(3) annual insurance costs over 25 years; and (4) annual energy costs for heating,

cooling, and lighting the office module over 25 years, with (5) all costs adjusted

for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m2

) of window area than for

60 ft 2 (5.57 m

2

) of area, due to estimated lower framing costs for the larger area.

67
ATLANTA,

GEORGIA,

COMMERCIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS —

2950

HEATING

DEGREE

DAYS,

1000

COOLING

HOURS 03 u o e w ^ —

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4-1 4-1 4-1 4-1 4-1 CO CD CQ CO 00 cd >v X >s v to iH

CD 4-1 CD CO CO cd

CJ 3 4-1 3 3 3 CD o cd o o o <D "3 33 X) TO TO

(3 4-1 3 3 3 ai •H •H •H -H u 3 X 3 3 3 •H 3 p

<D cd CD CD at

a

X

X 33

X 4-1 •> 4-1 4-1 4-1 iH

co • CD

4-1 TO 4-1 4-1 4-1 >v 3

cd (3 cd cd cd 4-1 <4-1 33 t4 X X 33 •H 2

4-1 .H 4-1 4-1 4-1

O

X •H 09

CO CO 00 OO

p <D

CD 3 <D CD (D 4J 4-1

4-1 cd 4-1 4-1 4-1 CJ cd

Cd *H cd cd cd CD •H O 4-1 CJ o o iH >

•H a>H •H •H CD CD x) 3 TO TO TO P 3 CD e C 3 X 30

•H > •H •H *H 30

Xcd ; . ; : w a Q 3D z P-I : : s tH

CdX

TO

<vc0

cdX

<u

a)

COo

,3o

0)>

4-1 cP

<d

coo01

CO

cda)

0) X

4-1

coCD

4-1 cdU

XJc

*HO TO

68 I

indicates

an

immediate

payback

due

to

estimated

lower

initial

investment

costs
TABLE 3.13

WASHINGTON, D.C., COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTING3

Window

(FT 2

)

Life--Cycle Costs in Dollars

Single Glazed Double Glazed

Area

(m2

) S

Orientation

E/W N

Orientation

S E/W N

Part A (FPEb » 0%)

0 0 1248 1252 1249 1248 1252 1249

12 1.11 1270 1282 1282 1364 1371 1368

30 2.79 1284 1308 1313 1473 1486 1482

60 5.57 1392 1439 1452 1767 1789 1785

90° 8.36 1249 1320 1343 1769 1800 1795

Part B (FPEb = 12%)

0 0 1846 1857 1848 1846 1857 1848

12 1.11 1887 1927 1927 1970 1993 1983

30 2.79 1939 2024 2043 2093 2138 2126

60 5.57 2119 2283 2331 2415 2494 2478

90c 8.36 2049 2296 2377 2450 2560 2541

a Life-cycle costs include the present value costs of (1) purchase and installation

for the 10' x 12' exterior wall of the office, including the spandrel panel and

window, mullions, and interior curtain wall; (2) annual cleaning costs over 25

years; (3) annual insurance costs over 25 years; and (4) annual energy costs for

heating, cooling, and lighting the office module over 25 years, with (5) all costs

adjusted for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than

for 60 ft 2 (5.57 m

2 ), due to estimated lower framing costs for the larger area.

69
If real energy prices escalate rapidly (part B of table 3.13), the energy costs

become more important relative to window acquisition costs, and single-glazed

windows loose much of their cost advantage, particularly for north-facing windows. A sharp rise in energy prices also makes window placement on the south

side more important economically. If the windows are not to be used for daylighting, it appears advisable to keep them small, single glazed, and oriented

southward, from the standpoint of the costs included here.

Table 3.14 shows the opportunity for reducing long-run building costs through

the use of windows for daylighting. For all single-glazed windows, as well as for double-glazed windows, the following pattern of changing costs in relationship to window size is revealed based on a rapid rise in energy prices: lifecycle costs tend first to fall as the window size is increased from zero to

30 ft^ (2.79 m^); costs then rise as the window size is increased further to

60 ft^ (5.57 m^); costs again fall as size is increased to 90 ft2 (8.36 m2).

In the case of single glazing, the initial fall in window costs as window size

is increased reflects both the lower acquisition cost for the windowed wall as compared with windowless wall and falling net energy costs due to savings from

daylighting. In the case of double glazing, the initial fall in costs reflects

the excess of energy savings from day lighting over the increase in window acquisition costs. As the window is doubled in size from 30 ft2 to 60 ft2 (2.79 to

5.57 m2), the savings from daylighting are substantially less than doubled, and

the increase in savings is exceeded by the increase in acquisition costs of

both the single- and double-glazed windowed wall. Consequently, total lifecycle costs rise. Life-cycle costs fall slightly for single-glazed windows as the window is expanded from 60 ft2 to 90 ft2 (5.57 to 8.36 m2), because of

assumed savings in framing costs for the largest of the single-glazed windows

examined.

Table 3.15 highlights the finding that escalating real energy prices increase

the savings potential of the window, but reduce its least-cost size. The

single-glazed, 30 ft2 (2.79 m2) window, comprising 25 percent of the southfacing exterior wall of the office, is estimated to be the most cost effective

of the window options examined if energy prices rise sharply and if the window

is used for daylighting. Because construction costs of the building are assumed to be lower with this window than without it, the window yields an immediate payback.

3.7 SEATTLE, WASHINGTON

Seattle has a relatively large heating load (4400 heating degree days) and a very small cooling load (100 cooling hours). The dominant heating load is

reflected in table 3.16 by the desirability of a southerly orientation for windows and of double glazing for the larger north-facing windows in anticipation

of rapid increases in energy prices. If they are not used for daylighting and

if energy prices escalate, the windows are estimated to increase life-cycle

costs, though not by a large amount.

Table 3.17 shows the impact on life-cycle costs of daylight utilization:

Life-cycle costs can be lowered by using a window, particularly on the south.

70
TABLE 3.14

WASHINGTON, D.C., COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT BUT WITH DAYLIGHTINGa

Window

(FT 2

) Area

(m 2

)

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

S

Orientation

E/W N S

Orientation

E/W N

Part A (FPEb = 0%)

0 0 1248 1252 1249 1248 1252 1249

12 1.11 1215 1227 1229 1306 1315 1313

30 2.79 1160 1189 1200 1339 1360 1362

60 5.57 1247 1299 1320 1599 1638 1643

90c 8.36 1103 1177 1200 1593 1646 1651

Part B (FPEb = 12%)

0 0 1846 1857 1848 1846 1857 1848

12 1.11 1692 1735 1742 1765 1798 1791

30 2.79 1505 1607 1645 1620 1695 1702

60 5.57 1609 1792 1872 1825 1963 1981

90c 8.36 1535 1795 1915 1833 2017 2036

a Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12* exterior wall of the office, including the spandrel panel and window,

mullions, and interior curtain wall; (2) annual cleaning costs over 25 years;

(3) annual insurance costs over 25 years; and (4) annual energy costs for heating,

cooling, and lighting the office module over 25 years, with (5) all costs adjusted for

tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m2

) of window area than for

60 ft 2 (5.57 m

2

) due to estimated lower framing costs for the larger area.

71
WASHINGTON,

D.C.,

COMMERCIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS —

4200

HEATING

DEGREE

DAYS,

1000

COOLING

HOURS

B3 CJ

O S W

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(0 4-4 CO 3 3 •rl

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CO • 3

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co 3 cO 3 3 4-4 <4H .3 *H 4= 43 43 •H Z

4-4 rH 4-4 4-4 4-4

a

-3 •H 3

CO CO 3 3 Vh 3 3 t3 CO 3 3 4-1 4-1

4-4 CCJ 4-4 4-4 4-1

O 3

CCJ -H 3 3 3 3 •H O 4-4 u O O rH >

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•H f> •rl •rl •H 45 453 - - - - W S a p 2 Oh - t s t«H

TjS

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cOX33

coo

4-1o3>3

Ui3

4-1

4-1 coo01•u

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CO3

at 43

4-1

72 I

indicates

an

immediate

payback

due

to

estimated

lower

initial

investment

costs
TABLE 3.16

SEATTLE, WASHINGTON, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM - - EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTINGa

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

Window' Area Orientation Orientation

(FT2

) (m2) S E/W N S E/W N

Part A (FPEb = 0%)

0 0 1201 1202 1203 1201 1202 1203

12 1.11 1217 1224 1229 1287 1290 1292

30 2.79 1224 1242 1253 1347 1356 1359

60 5.57 1318 1355 1378 1540 1557 1562

90c 8.36 1172 1230 1266 1469 1495 1500

Part B (FPEb = 12%)

0 0 1755 1761 17 63 1755 1761 1763

12 1.11 1785 1811 1826 1840 1852 1858

30 2.79 1834 1897 1933 1902 1932 1944

60 5.57 2005 2133 2215 2108 2170 2188

90° 8.36 1938 2139 2265 2059 2150 2168

a Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

mullions , and interior curtain wall; (2) annual cleaning costs over 25 years;

(3) annual insurance costs over 25 years; and (4) annual energy costs for heating,

cooling, and lighting the office module over 25 years, with (5) all costs adjusted

for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than

for 60 ft 2 (5.57 m

2

) due to estimated lower framing costs for the larger area.

73
TABLE 3.17

SEATTLE, WASHINGTON, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM EVALUATED WITHOUT WINDOW MANAGEMENT BUT WITH DAYHGHTINGa

Life -Cycle Costs in Dollars

Single Glazed Double Glazed

Window Area Orientation Orientation

(FT2

) (m2

) S E/W N S E/W N

Part A (FPEb = 0%)

0 0 1201 1202 1203 1201 1202 1203

12 1.11 1210 1219 1224 1278 1282 1285

30 2.79 1162 1185 1204 1276 1290 1299

60 5.57 1246 1291 1328 1454 1480 1496

90° 8.36 1121 1186 1237 1402 1437 1455

Part B (FPEb = 12%)

0 0 1755 1761 1763 1755 1761 1763

12 1.11 1668 1701 1718 1717 1732 1740

30 2.79 1521 1601 1669 1560 1609 1640

60 5.57 1625 1783 1912 1679 1772 1827

90 8.36 1568 1798 1976 1632 1755 1820

a Life-cycle costs include the present value costs of (1) purchase and installation

for the 10’ x 12' exterior wall of the office, including the spandrel panel and

window, mullions, and interior curtain wall; (2) annual cleaning costs over 25

years; (3) annual insurance costs over 25 years; and (4) annual energy costs for

heating, cooling, and lighting the office module over 25 years, with (5) all costs

adjusted for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than

for 60 ft 2 (5.57 m

2

) due to estimated lower framing costs for the larger area.

74
Single glazing is more cost effective than double glazing for southerly exposures; double glazing is cost effective for east, west, and northern exposures.

Table 3.18 shows that the least-cost window is single glazed, located on the

south side, and used for daylighting. If energy prices were to remain about

constant in real terms, it would pay to choose the largest size (90 ff2)

(8.36 m^) window, due to its lower framing costs together with its daylighting

benefits. Rapid energy price escalation gives a slight cost advantage to the

more moderate window size (30 ff2 or 2.79 m2), due to higher heating costs.

This least-cost window is estimated to save $234 and to pay for itself in just over a year.

3.8 INDIANAPOLIS, INDIANA

Indianapolis has a relatively heavy heating load requirement (5700 degree days)

and a moderately heavy cooling load requirement (750 cooling hours).

Without daylight utilization, all of the window alternatives examined increase

life-cycle costs. If future energy prices are level in constant dollars,

part A of table 3.19 shows relatively small increases in costs, but if energy

prices rise at a real rate of 12 percent compounded annually, part B shows that

net losses may approach $700 for a large window area with a northern exposure.

Single glazing is estimated to be cost effective for all windows if energy

prices are constant, but double glazing is cost effective for large north-facing

windows if energy prices escalate sharply.

From table 3.20, we can see the positive effect that daylight utilization has on total life-cycle costs. If energy prices rise at a rate of 12 percent per

year, net savings result for all windows up to and including 30 ff2 (2.79 m2),

and for south-facing, single-glazed windows up to and including 90 ft

2

(8.36 m2). The larger windows facing east, west, or north may result in

significant losses.

The relatively heavy heating load in this city has the effect of restricting

the size of the least-cost window and of increasing the importance of double

glazing for windows that do not face south. As shown by table 3.21, the least

cost of the options is a single-glazed, 30 ft 2 (2.79 m2) window on the south

side, used for daylighting.

3.9 PORTLAND, MAINE

Portland, Maine has a heavy heating load requirement (7600 degree days), and

a very modest cooling load requirement (250 cooling hours). Because of the

heavy heating load, the use of triple glazing to minimize winter heat losses

is considered as one of the options.

Part A of table 3.22 shows that even with the heavy heating load, single

glazing is more cost effective than either double or triple glazing at constant

real energy prices. Net losses exceed $600 for large, north-facing tripleglazed windows, $400 for large, north-facing double-glazed windows, and $200

for large, north-facing single-glazed windows.

75
SEATTLE,

WASHINGTON,

COMMERCIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS

--

4400

HEATING

DEGREE

DAYS,

100

COOLING

HOURS

Ej2 o y B W ^ o O r-. vl Bn N o o o • 3 C*4 ^ •H

22

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V

V oh u

CO C0 o CM o o U X) M • • • •

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00 *“H CO no CM

4-4 3 CM --4 --4 S

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co

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X >N >-. >N iH 4-4 CO 4-4 CO 3 3 3 3 JxJ O 3 y 5 4-4 5 3 3 3 3 O 3 o O o 3 3 X

03X 03 03 03 4-4 >N 3 4-4 3 3 3 3 rH 3

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04 CO 04 3 3 Q. 3 4-4 X X X J= O 3

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J3 -H

X

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4-4 rH 4-4 4-4 4-4

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X •H 3 1—1

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04 3 04 3 3 4-1 4-4 3 3

4-4 CO 4-1 4-4 4-1 CJ 3 X

CO *rt 3 3 3 3 •H 4-4 3

CJ 4-4 CJO

U rH > 3

•H 04 •H •H •H 3 3 3 4-1 T3 3 03 03 03 4-4 3 3 3 04 3 3 3 >N -O 4-4 y

•H > •rt •H •H £> -O 3 •H 3 y 03

•H 3 z - s - W 03 •H

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p Z PH 3M t-H 3 x o

76
TABLE 3.19

INDIANAPOLIS, INDIANA, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTINGa

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

Window

(FT 2

) Area

(m2

) S Orientation

E/W N S

Orientation

E/W N

Part A (FPEb « 0%)

0 0 1230 1234 1233 1230 1234 1233

12 1.11 1258 1270 1273 1335 1343 1343

30 2.79 1278 1303 1312 1427 1443 1443

60 5.57 1395 1440 1459 1683 1710 1711

90c 8.36 1268 1333 1365 1659 1697 1700

Part B (FPEb = 12%)

0 0 1832 1846 1842 1832 1846 1842

12 1.11 1898 1939 1949 1945 1975 1973

30 2.79 1979 2066 2097 2051 2108 2108

60 5.57 2206 2366 2433 2338 2434 2438

90c 8.36 2193 2422 2536 2346 2481 2490

a Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

mullions, and interior curtain wall; (2) annual cleaning costs over 25 years;

(3) annual insurance costs over 25 years; and (4) annual energy costs for heating,

cooling, and lighting the office module over 25 years, with (5) all costs adjusted

for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than for

60 ft 2 (5.57 m

2

) due to estimated lower framing costs for the larger area.

77
I

TABLE 3.20

INDIANAPOLIS, INDIANA, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM EVALUATED WITHOUT WINDOW MANAGEMENT BUT WITH DAYLIGHTINGa

Life-Cycle Costs in Dollars

Single Glazed Double Glazed

Window' Area Orientation Orientation

(FT 2

) (m2

) S E/W N S E/W N

Part A (FPEb = 0%)

0 0 1230 1234 1233 1230 1234 1233

12 1.11 1245 1258 1262 1320 1330 1331

30 2.79 1205 1230 1244 1344 1365 1370

60 5.57 1311 1359 1386 1584 1619 1628

90c 8.36 1207 1275 1314 1580 1628 1640

Part B (FPEb = 12%)

0 0 1832 1846 1842 1832 1846 1842

12 1.11 1759 1805 1817 1800 1833 1838

30 2.79 1631 1718 1766 1668 1742 1759

60 5.57 1786 1955 2047 1865 1987 2020

90c 8.36 1788 2029 2165 1876 2044 2086

a Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

mullions, and interior curtain wall; (2) annual cleaning costs over 25 years;

(3) annual insurance costs over 25 years; and (4) annual energy costs for heating,

cooling, and lighting the office module over 25 years, with (5) all costs adjusted

for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than

for 60 ft 2 (5.57 m

2

) due to lower framing costs for the larger area.

78
INDIANAPOLIS,

INDIANA,

COMMERCIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS

--

5700

HEATING

DEGREE

DAYS,

750

COOLING

HOURS

r i 0 o CJ 3X1 — 0 W /-s o o o O rH

rl Pm

N • e fa V V V V o X *—H 2oH XO

CO CO OH

XX rH

O

Pm XI • • • • • CO fH

CD CO

*-H CM rH cm

P* Pl,

(D *H X > 0 X CO CO

m <r o • rH CO co

/—>

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TABLE 3.22

PORTLAND, MAINE, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHTING3

Life-Cycle Costs in Dollars

Single Glazed Double Glazed Triple Glazed

Window

(FT 2

) Area

(m2

) S Orientation

E/W N S

Orientation

E/W N S Orientation

E/W N

Part A (FPEb = 0%)

0 0 1127 1133 1136 1127 1133 1136 1127 1133 1136

12 1.11 1155 1173 1186 1217 1230 1238 1242 1254 1260

30 2.79 1176 1212 1241 1291 1315 1330 1348 1368 1378

60 5.57 1286 1353 1408 1506 1548 1573 1654 1682 1696

90c 8.36 1177 1275 1356 1474 1532 1568 1697 1731 1748

Part B (FPEb = 12%)

0 0 1725 1745 17 56 1725 1745 1756 1725 1745 1756

12 1.11 17 91 1855 1898 1811 1856 1886 1826 1866 1889

30 2.79 1875 1999 2104 1822 1967 2020 1916 1985 2020

60 5.57 2097 2333 2524 2099 2247 2334 2215 2314 2362

90c 8.36 2102 2447 2730 2075 2281 2404 2261 2379 2441

3 Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

mullions, and interior curtain wall; (2) annual cleaning costs over 25 years; (3) annual

insurance costs over 25 years; and (4) annual energy costs for heating, cooling, and

lighting the office module over 25 years, with (5) all costs adjusted for tax deductible

expenses

.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than for

60 ft 2 (5.57 m

2

) due to estimated lower framing costs for the larger area.

80
Part B of table 3.22 shows that if energy prices rise at a real rate of

12 percent per year, single glazing loses its cost advantage for all of the

large (90 ft^ or 8.36 m^) windows—even those facing south. With the higher

energy costs, double glazing tends to be the most cost-effective glazing type

for most of the windows. Regardless of the type of glazing and the orientation,

however, total life-cycle costs are estimated to be increased to some extent by

windows not used for daylighting. These costs can be kept small by choosing

small windows and placing them on the south side of the building.

Table 3.23 shows the life-cycle costs associated with the windows when daylight

utilization is practiced. With daylight utilization and fuel price escalation

small savings are estimated for some of the windows—primarily for small-tomoderate sized south-, east-, and west-facing windows, as well as for large,

double-glazed windows on the south. With a high real rate of energy price

escalation, double glazing appears to be the most cost-effective glazing type

for most of the window sizes and orientations examined.

Table 3.24 emphasizes that with rapidly rising real energy prices, the

economically efficient window is moderate in size, double glazed if south-,

east-, or west-facing, and triple glazed if north-facing. The least-cost window

is estimated to save $170 over the life cycle. Net savings of only $36 are estimated for the 30 ft^ (2.79 m^) triple-glazed window with a northern exposure. Thus even in a climate with a heavy heating load, moderately sized windows which are well designed thermally and utilized to take advantage of natural

lighting may produce small reductions in life-cycle costs.

3.10 BISMARCK, NORTH DAKOTA

The last city treated, Bismarck, North Dakota, has the highest heating load

requirement (8850 heating degree days, 450 cooling hours) of the cities examined. It may be contrasted with the first commercial location, Miami, where

the heating load is small, but the cooling load requirement is very high.

Table 3.25 shows that without management or daylight utilization, windows cause life-cycle costs to rise, regardless of the type of glazing, size, or orientation. Part B of the table shows that when energy prices rise at a rate of 12

percent per year, net losses can be reduced by using double glazing on southfacing window and triple glazing on north-facing windows. Double and triple

glazings have approximately equal effects on east- and west-facing windows.

Table 3.26 shows that with daylight utilization, most of the windows except

those facing south have higher life-cycle costs than the windowless wall. To

prevent costs from rising in the face of higher energy prices, it is necessary

that the windows be carefully designed, sized and located. With 12 percent

energy price escalations over and above inflation, triple glazing appears economically desirable for all window sizes and orientations, except for larger

windows on the south for which double glazing is cost effective. Windows

small-to-moderate in size are estimated to cost less than large windows for

most of the cases examined; however, for southerly orientations, size is

estimated to make little difference in costs, particularly if the windows are double or triple glazed.

81
TABLE 3.23

\

PORTLAND, MAINE, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITH DAYLIGHTI NGa

Life-Cycle Costs in Dollars

Window Area

(FT 2

) (m2)

Single Glazed Double Glazed Triple Glazed

Orientation

S E/W N

Orientation

S E/W N

Orientation

S E/W N

Part A (FPEb = 0%)

0 0 1127 1133 1136 1127 1133 1136 1127 1133 1136

12 1.11 1148 1166 1181 1206 1221 1231 1230 1244 1252

30 2.79 1117 1154 1190 1222 1251 1272 1275 1301 1317

60 5.57 1217 1287 1352 1420 1472 1508 1556 1598 1624

90° 8.36 1126 1228 1322 1401 1472 1522 1609 1664 1695

Part B (FPEb = 12%)

0 0 1725 1745 1756 1725 1745 1756 1725 1745 1756

12 1.11 1680 1744 1795 1688 1741 1776 1701 1749 1777

30 2.79 1582 1714 1838 1555 1656 1731 1575 1665 1720

60 5.57 1739 1987 2215 1681 1864 1991 1756 1907 1996

90c 8.36 1751 2110 2437 1649 1897 2071 1781 1971 2080

a Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

raullions, and interior curtain wall; (2) annual cleaning costs over 25 years; (3) annual

insurance costs over 25 years; and (4) annual energy costs for heating, cooling, and

lighting the office module over 25 years, with (5) all costs adjusted for tax deductible

expenses

.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than for

60 ft 2 (5.57 m

2

) due to estimated lower framing costs for the larger area.

82
PORTLAND,

MAINE,

COMMERCIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS —

7600

HEATING

DEGREE

DAYS,

250

COOLING

HOURS i a

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83

that

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and

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is

accomplished
TABLE 3.25

BISMARCK, NORTH DAKOTA, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT AND WITHOUT DAYLIGHT INGa

Window

(FT 2

)

Life-Cycle Costs in Dollars

Single Glazed Double Glazed Triple Glazed

Area

(m2

) S Orientation

E/W N

Orientation

S E/W N S

Orientation

E/W N

Part A (FPEb = 0%) [

0 0 1102 1111 1114 1102 1111 1114 1102 1111 1114

12 1.11 1133 1157 1171 1176 1196 1206 1192 1211 1219

30 2.79 1156 1205 1238 1227 1262 1281 1262 1292 1306

60 5.57 1263 1355 1418 1391 1450 1483 1488 1533 1553

90c 8.36 1162 1298 1392 1329 1409 1456 1480 1533 1560

Part B (FPEb = 12%)

|

0 0 1737 1769 1781 1737 1769 1781 1737 1769 1781

12 1.11 1818 1904 1952 1804 1876 1910 1807 1872 1900 i

30 2.79 1916 2088 2205 1852 1977 2041 1855 1961 2009

60 5.57 2152 2475 2697 2019 2227 2343 2067 2224 2296

90° 8.36 2183 2658 2988 1969 2249 2416 2064 2250 2344

f. a Life-cycle costs include the present value costs of (1) purchase and installation for the

10' x 12' exterior wall of the office, including the spandrel panel and window, mullions,

and interior curtain wall; (2) annual cleaning costs over 25 years; (3) annual insurance

costs over 25 years; and (4) annual energy costs for heating, cooling, and lighting the

office module over 25 years, with (5) all costs adjusted for tax deductible expenses.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than for

60 ft 2 (5.57 m

2

) due to estimated lower framing costs for the larger area.
TABLE 3.26

BISMARCK, NORTH DAKOTA, COMMERCIAL CASE STUDY: LIFE-CYCLE COSTS FOR A WINDOW

SYSTEM — EVALUATED WITHOUT WINDOW MANAGEMENT BUT WITH DAYLIGHTINGa

Life-Cycle Costs in Dollars

Single Glazed Double Glazed Triple Glazed

Window Area Orientation Orientation Orientation

(FT 2

) (m2) S E/W N S E/W N S E/W N

Part A (FPEb = 0%)

0 0 1102 1111 1114 1102 1111 1114 1102 1111 1114

12 1.11 1125 1150 1167 1167 1188 1198 1183 1203 1211

30 2.79 1095 1148 1187 1160 1199 1223 1193 1227 1246

60 5.57 1190 1288 1360 1305 1372 1417 1393 1450 1482

90c 8.36 1106 1248 1351 1254 1347 1407 1391 1464 1504

Part B (FPEb = 12%)

0 0 1737 1769 17 81 1737 1769 1781 1737 1769 1781

12 1.11 1709 1797 1856 1694 1767 1804 1694 1763 1792

30 2.79 1624 1810 1946 1538 1674 1760 1531 1653 1719

60 5.57 1788 2131 2385 1609 1844 2001 1625 1825 1935

90c 8.36 1822 2319 2682 1543 1868 2081 1587 1841 1982

a Life-cycle costs include the present value costs of (1) purchase and installation for

the 10' x 12' exterior wall of the office, including the spandrel panel and window,

mullions, and interior curtain wall; (2) annual cleaning costs over 25 years; (3) annual

insurance costs over 25 years; and (4) annual energy costs for heating, cooling, and

lighting the office module over 25 years, with (5) all costs adjusted for tax deductible

expenses

.

b FPE abbreviates "fuel price escalation rate."

c Life-cycle costs are in some cases lower for 90 ft 2 (8.36 m

2

) of window area than for

60 ft 2 (5.57 m

2

) due to estimated lower framing costs for the larger area.
BISMARCK,

NORTH

DAKOTA,

COMMERCIAL

CASE

STUDY:

LEAST-COST

WINDOW

SYSTEMS —

8850

HEATING

DEGREE

DAYS,

450

COOLING

HOURS 0333

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86
Table 3.27 shows that of the window choices examined for the office in Bismarck,

the economically optimal is estimated to be 30 ft^ (2.79 m^) in size, south

facing, and used for daylighting. For constant real energy prices, this window results in approximately a break-even condition if it is single glazed.

But with the greater savings in lighting costs brought about by rapidly rising

energy prices, this window results in present value savings of about $200 if it

is triple glazed.

87
4. SUMMARY AND GENERAL CONCLUSIONS

Using a case study approach, this report has assessed the economic performance

of conventional type windows under selected conditions in two typical spaces:

a kitchen/family room in a brick rambler and an office module in a multi-story

commercial building. Life-cycle costs (in present value dollars) over 25 years

have been calculated based on (1) window sizes ranging from 0 to 60 ft^ for the

house and 0 to 90 ft^ for the office; (2) orientations including south, east/

west and north; (3) single, double, and, for northern locations, triple glazing;

(4) a range of future energy prices, (5) locations in nine U.S. cities covering

five heating zones and four cooling zones, and (6) alternative modes of window

use, including (a) windows left bare (unmanaged) and not used for day lighting,

(b) windows equipped with thermal shutters and Venetian blinds, room thermostat

adjustment (managed), and day lighting, and (c) windows unmanaged but used for

daylighting.

Included in the costs are (1) purchase and installation costs of the windows

in excess of the costs of a solid wall, (2) the additional costs of cleaning,

recaulking, and repainting the windows on a regular basis, (3) energy costs

for heating, cooling and lighting the space, and, for the commercial building,

(4) tax effects. Not included in the life cycle costs are energy effects asso- ciated with natural ventilation, safety effects, psychological effects, and

aesthetic effects. Also not included are those passive solar energy benefits

and costs of the south-facing window that are dependent on special absorber

materials and storage mass; however, passive effects estimated for the

buildings as designed are included.

Changes in total life-cycle costs of the two building spaces attributable to

the selected window alternatives have been assessed, and the least-cost options

of those considered have been identified for each space, based on geographical

location, directional orientation, and future energy prices. For each case

study, conclusions have been drawn as to the least-cost window option. Further,

the life-cycle data have been provided for each of the window sizes, orientations, and glazing options examined to allow the reader to interpret the case study results in light of the particular circumstances of his or her own building space and window needs. The heating and cooling zones of each city

studied are indicated to assist the reader in extending the results to other

regional locations.

To serve as a reference and overview, the following summary of the case study

data and general conclusions are presented. It is important that the reader

interpreting these data and conclusions keep in mind that there are many window

designs, accessories, framing techniques, and alternative wall constructions

other than those examined here. These other alternatives will likely have

different costs and performances associated with them, and, hence, will differ

in their cost effectiveness. These case results, however, may provide insight

as to how window decisions may translate into long-term costs of owning and

operating a building.

88
4.1 RESIDENTIAL WINDOW SUMMARY

Key results for the selected residential window systems are summarized in two

tables 4.1 and 4.2. Table 4.1 shows the cost-effective window choices for

each city as a function of the future rate of change in energy prices and the

way the window is accessorized and used. Table 4.2 indicates the least-cost

glazing for different window sizes and orientations for each city.

Looking more closely at table 4.1, one finds in column (1) the city and, in

parenthesis, two numbers keyed to figure 1.1 giving the heating and cooling

zones, respectively, for that city. Column (2) indicates two alternative projected rates of increase in gas and electricity prices—a zero rate in constant

dollar terms, (i.e., a rate just equal to the rate of general price inflation),

and a 12 percent rate compounded annually (i.e., a rate 12 percent faster than

the rate of general price inflation). These two rates are intended to "bracket"

the possible increase in these energy prices over the long run. Columns (3)

through (7) indicate the least cost of those options examined for windows that are unmanaged and not used for daylighting. Columns (8) through (11) give the

counterpart results for windows that are managed and used for day lighting.

The least-cost options for the "unmanaged, not used for daylighting" case

(columns (3) through (7)) are given, even though they are in all cases inferior

to the "managed, used for daylighting" case, because there are many situations

in which windows cannot be successfully managed and for which effective daylighting opportunities are limited. The building owner or operator may find

the information in columns (3) through (7) useful in reducing losses in this

less-than-optimal case.-*-

Column (3) indicates the window size, given the type of window considered that

will result in the lowest life-cycle costs of the room assuming the window is

unmanaged and not used for daylighting. It may be seen that this least-cost

size is in every case zero, that is, costs are estimated to be lower without

the window than with it, given the assumptions of these case studies. Column

(4) gives the next best window size in terms of costs, which is in every case

12 ft2 (1.11 m2

), the smallest size examined.

Column (5) shows that the least-cost direction for orienting the windowed wall

is dependent on the geographical region. In moderate to cold climates, orienting windows to the south tends to lower energy costs by taking maximum advantage of the passive solar heat gain that can be captured through the windows on winter days. Thus, the least-cost orientation for the windowed wall is shown

to be south for Atlanta, Washinton, D.C., Seattle, Indianapolis, Portland, and

Bismarck. In warm climate zones where it is desirable to minimize passive solar

-*- Similarly, there often may be compelling reasons to locate windows with

orientations other than those designated here as least cost, such as reasons

of design, code requirements, or view. In that event, the reader may wish

to refer back to the relevant case study chapter and the results for the

desired orientation.

89
TABLE 4.1 Summary: Cost-Effective Choices for the Selected Residential Window Systems'

I

Unmanaged, Not Used for Daylighting Managed, Used for Daylighting

City

(Heating and Cooling Zones)*5 (1)

Real

Fuel Price Escalation

Rate (%)c (2)

Least-Cost Window

Size

(3)

Least-Cost Window Size Greater Than 0

(ft2

) (m2

) (4)

Least-Cost Orientation

(5)

Glazing for Least-Cost Window

Greater Than 0

(6)

Impact on

LCCd (?)

(7)

Least-Cost Window Size

(ft 2

) (m2) (8)

Least-Cost Orientation

(9)

Glazing for Least-Cost Window

(10)

Impact

on

LCCd

(?) (11)

Miami

,

0 0 12 1.11 North Singlee 115 12 1.11 North Single** - 149 Florida (1,1) 12 0 12 1.11 North Doublee 271 18 1.67 North Singled -1000

San Antonio, 0 0 12 1.11 North Singlee 88 12 1.11 North Singled - 145 Texas (1,1) 12 0 12 1.11 North Singlee 185 18 1.67 North Singled - 986

Los Angeles, 0 0 12 1.11 North Singlee 59h 12 1.11 North Single - 125 California

(1/2, 5) 12 0 12 1.11 North Singlee 35 30 2.79 North Single -1051

Atlanta

,

0 0 12 1.11 South Singlee 60 12 1.11 South Singled - 147 Georgia (2,3) 12 0 12 1.11 South Singlee 80 18 1.67 South Singled - 972

Washington, 0 0 12 1.11 South Singlee 89 12 1.11 South Singled - 89 D.C. (3,4) 12 0 12 1.11 South Doublee 130 18 1.67 South Singled - 733

Seattle , 0 0 12 1.11 South Single*5 97 12 1.11 South Singled - 39 Washington

(3,5)

12 0 12 1.11 South Doublee 146 18 1.67 South Doubled - 600

Indianapolis

,

0 0 12 1.11 South Single*5 104 12 1.11 South Singled - 62 Indiana (3,4) 12 0 12 1.11 South Doublee 159 18 1.67 South Doubled - 660

Portland, 0 0 12 1.11 South Doublee 103 12 1.11 South Single*5 - 29 Maine (4,5) 12 0 12 1.11 South Triples 136 18 1.67 South Triple*5 - 489

Bismarck, 0 0 12 1.11 South Double^ 108 12 1.11 South Singlee - 23 North Dakota

(5,5)

12 0 12 1.11 South Triple* 147 18 1.67 South Triple*5 - 492

Summarized from the tables in section 2, and dependent on the assumptions given in table 1.1

b Numbers in parenthesis refer to the heating and cooling zones, respectively, as given by the heating and

cooling zone map in figure 1.1.

c Escalation rates in excess of general price inflation.

d The difference in present value dollar costs with the designated windows as compared with the costs with the designated solid wall section, over a 25 year life cycle. Positive figures Indicate the amount that windows

add to life-cycle costs; negative figures, the amount that windows save.

e There is less than a 5 percent difference between the costs of single and double glazing; the least-cost

choice is listed first.

f There is less than a 5 percent difference between the costs of single, double, and triple glazing; the leastcost choice is listed first.

8 There is less than a 5 percent difference between the costs of double and triple glazing; the least-cost

choice is listed first.

h The results for Los Angeles are somewhat unique among those cities examined. In Los Angeles, climate conditions are such that the windowed room has lower energy costs than the windowless room due to beneficial conduction losses and gains through the window (not taking into account natural ventilation effects).

However, the lower energy costs are not sufficient in the case examined to overcome the higher acquisition

and maintenance costs of the window. With higher energy price escalation, the energy savings from the window are raised, thereby offsetting more of the window acquisition and maintenance coBts and reducing

the amount of increase in total life-cycle costs as shown in column (7).

90
TABLE 4.2 Summary: Cost-Effective Glazing for the Selected Residential Windows

Cities

Fuel Price Escalation

Rate (%)

South Orientation East/West Orientation North Orientation

12 ft2 (1.11 m

2

)

30 ft 2 (2.79 m

2

)

60 ft 2 (5.57 m

2

)

12 ft 2 (1.11 m

2

)

30 ft2 (2.79 m2 )

60 ft2 (5.57 m

2

)

12 ft2 (1.11 m

2

)

30 ft2 (2.79 m

2

)

60 ft2 (5.57 m

2

)

Unmanaged, Not Used for Daylighting

Miami

,

0 S/D S S S/D S/D S/D S/D S/D S Florida 12 D/S D/S D/S D/S D/S D/S D/S D/S D/S

San Antonio, 0 S/D S/D S S/D S/D S/D S/D S/D S/D Texas 12 S/D S/D D/S D/S D/S D/S S/D D/S D/S

Los Angeles, 0 S/D S S S/D S S S/D S S California 12 S/D S/D s S/D S/D s S/D S/D s

Atlanta, 0 S/D S/D S/D S/D S/D S/D S/D S S/D

Georgia 12 S/D D/S D/S D/S D/S D D/S S/D D

Washington, 0 S/D S/D 5/D S/D S/D S/D S,D D/S D/S

D.C. 12 D/S D/S D D/S D/S D D/S D/S D

Seattle

,

0 S/D S/D S/D S/D D/S D/S S/D D/S D/S

Washington 12 D/S D D D/S D D D/S D D

Indianapolis

,

0 S/D S/D D/S D/S D/S D/S D/S D/S D Indiana 12 D/S D D D/S D D D/S D D

Portland, 0 D/T/S D/T/S D,T D,T/S T/D T/D D,T/S T/D T/D Maine 12 T/D T/D T/D T/D T/D T T/D D/T T

Bismarck, 0 T,D/S T/D T/D T/D/S T/D T/D T/D T/D T/D North Dakota 12 T/D T/D T T/D T/D T T/D T/D T

Managed, Used for Daylighting

Miami

,

0 S/D S S S/D S S S/D S S Florida 12 S/D S/D S/D S/D D/S D/S S/D S/D S/D

San Antonio, 0 S/D S S S/D S S S/D S S Texas 12 S/D S/D S/D S/D S/D S/D S/D S/D S/D

Los Angeles, 0 S S S S S S S S S California 12 S/D s s S/D S S S/D S s

Atlanta, 0 S/D s s S/D S s S/D s s Georgia 12 S/D S/D S/D S/D S/D S/D S/D S/D S/D

Washington, 0 S/D s S S/D S/D S S/D S/D S/D

D.C. 12 S/D S/D S/D S/D D/S D/S D/S D/S D

Seattle

,

0 S/D S/D S/D S/D S/D S/D S/D D/S D/S

Washington 12 D/S D D D/S D D D/S D D

Indianapolis

,

0 S/D S S S/D S/D S/D S/D S/D S/D Indiana 12 D/S D/S T/D D/S D/S D D/S D D

Portland, 0 S/D/T S/D/T S/D S/D/T S/D/T D/S/T D/T/S D/T/S D/T Maine 12 T/D/S T/D/S T/D T/D/S T/D T/D T/D T/D T

Bismarck, 0 S/D/T S/D/T S/D D/S/T D/S/T D/T/S D/T/S D/T/S T/D

North Dakota 12 T/D/S T/D T/D T/D T/D T/D T/D T/D T

Key: S = Single-glazed windows are lower in life-cycle costs than multi-glazed windows.

D = Double-glazed windows are lower in life-cycle costs than single- or triple-glazed windows.

T = Triple-glazed windows are lower in life-cycle costs than single- or double-glazed windows.

D/S, S/D = First listed is slightly lower in cost, but the difference is less

D/T, T/D, than 5 percent.

S/D/T

S/D/T = No difference at all in life-cycle costs of alternatives separated

by commas.

91
heat gain through windows, it pays to orient windows to the north. Thus, the

least-cost orientation is shown to be north for Miami, San Antonio, and Los

Angeles. Easterly and westerly orientations tend not to be recommended for

regions with large heating loads because they allow less solar heat gain in

winter than southerly orientations. They tend not to be recommended for

regions with large cooling loads because they are difficult to shade against

the summer sun and, hence, result in larger heat gains in summer.

Column (6) gives the least-cost glazing for the windows of the size and

orientation designated in columns (4) and (5). The least-cost choice of glazing

is shown to be sensitive to the rate of fuel price escalation designated in

column (2). In Washington, D.C., for example, single glazing is slightly more economically efficient for the 12 ft^ south-facing, bare window if energy

prices remain about level in constant dollars; double glazing is slightly more efficient for this window if prices rise at a rate 12 percent faster than general price inflation. If energy prices do not escalate rapidly, single glazing

is recommended for the 12 ft^ (1.11 m^) window with the designated orientation

for all but the two coldest locations, Portland and Bismarck, where double

glazing is recommended. If energy prices do escalate rapidly, double glazing

is recommended for the designated window in Washington, D.C., Seattle, and

Indianapolis, due to their significant heating loads, and in Miami, due to its

sizeable cooling load. Triple glazing is estimated to be cost effective for

Portland and Bismarck.

Column (7) gives the amount, in present value dollars, which the designated

window system is estimated to add to the total life-cycle costs of the kitchen/

family room over the 25 years.

These dollar figures are the difference between the construction, maintenance,

repair, replacement, and energy costs of the room with the designated window

system as compared to the room without any windows. In every case where it is

unmanaged and not used for daylighting, the window system increases the lifecycle costs of the room. With the exception of Los Angeles, the costs associated with the window are greater the higher the escalation in energy prices.

This is not the case for Los Angeles because a small energy saving from the

window is realized there, which is enhanced by higher energy prices. The

energy saving, however, is insufficient to offset the higher nonenergy costs

of the window, and net losses remain.

Looking now at the estimated least-cost results for the designated managed

windows used for daylighting, given in columns (8) through (11) of table 4.1, one finds that in every city it is more economical to have the designated

window system than not to have a window. Column (8) shows that if real energy

1 Note that these are not necessarily the least-cost glazing options for

other window sizes and orientations. (See table 4.2 for least-cost glazings

for other window sizes and orientations.) Also note (as indicated by the

table footnotes) that in these particular cases there is little difference

in life-cycle costs among the glazing options.

92
prices remain constant, the least-cost window is 12 ft^ —the smallest of those

examined—for all of the cities. But if energy prices rise rapidly, a somewhat

larger window providing more benefits in daylighting is estimated to be warranted an economic grounds: 18 ft^ (1.67 m^) for all locations except Los

Angeles, and 30 ft^ (2.79 m^) for Los Angeles.

These windows are estimated to be cost effective when managed and used for

daylighting, because the estimated net energy savings outweigh the estimated

costs for purchase, installation, maintenance, and repair. The Venetian blinds

and thermal shutters reduce the undesirable heat gains and losses to low levels;

the designated orientation enhances passive solar gain where heating loads are dominant and reduces it where cooling loads are dominant; the savings in electric lighting costs and related reduced cooling costs more than offset remaining increased heating costs. The least-cost window size increases with higher

energy price escalation, because in the relevant size range, the savings in

electric lighting costs increase more with larger window size than the costs

of the negative heat gains and losses.

Column (9) shows no change in the least-cost orientation due to management and

daylighting. A southerly orientation continues to be recommended for regions

with significant heating loads, and a northerly orientation for regions where

cooling loads are dominant.

As shown by column (10) the use of window accessories influences the preferred

type of glazing. With thermal shutters, single glazing is more often recom- mended than it was for the bare windows. This is because the thermal shutters

provide a partial substitute for multi-glazing and reduce its impact on energy

costs. When thermal shutters are used, multi-glazing is cost effective for

the designated window systems only if energy price escalation is rapid and if

heating loads are large. ^ Thus, it pays to use double glazing on the 18 ft^

(1.67 m^) south-facing window in Seattle and Indianapolis, and triple glazing

in Portland and Bismarck—in addition to thermal shutters —if energy prices

escalate at a rate of 12 percent.

1 Note that the case examples assume electric lighting and electric cooling

priced at $0. 03/kWh in the base year and gas heating priced at $0.30/therm in

the base year, with both electricity and gas prices escalating thereafter

within the bounds of zero and 12 percent real rates compounded annually. The

assumption of different energy sources for lighting, cooling, and heating,

with different current and/or future price relationships would change the

economic tradeoffs and, hence, the least-cost window size.

2 Again, the reader is reminded that these results apply only to the window

size and orientation designated in table 4.1, multi-glazing tends to be

cost effective for larger sized windows and/or for those windows with less

favorable orientations.

3 The differences in the cost effectiveness of the alternative glazings is,

however, small in these particular cases.

93
Column (11) shows the estimated dollar savings (indicated by a minus sign as a reduction in life-cycle costs) attributable to the window systems over the 25

year life cycle. The savings range from small to large depending on the climatic region and the rate of escalation in energy prices. Potential savings

from the designated window systems are greatest in the warmer climate regions,

i.e., Los Angeles, Miami, San Antonio, and Atlanta, where the benefits of daylighting can be realized with less of a penalty in undesirable heat losses.

Estimated net present value savings from the optimal window system are close to

$1000 in each of these four cities when energy prices are assumed to escalate

at a real rate of 12 percent.

Table 4.2 summarizes the case study findings regarding the optimal type of

glazing. In this table, the recommended type of glazing—single (S), double

(D), or triple (T) —is indicated for three of the window sizes examined—12 ft^

(1.11 m^), 30 ft^ (2.79 m2) and 60 ft^ (5.57 m2) —for four orientations—south,

east/west, and north—and for the two real rates of energy price escalation

zero and 12 percent. In a number of cases, more than one type of glazing is

indicated for a given case, e.g., S/D. This is done whenever there is less

than a five percent difference between the alternatives, but the glazing type

with the lowest life-cycle cost is given first. For example, with constant

windows (D) perform almost as well.

Looking first at the upper part of table 4.2 at the results for unmanaged

windows not used for daylighting, we find that when energy prices escalate

rapidly in real terms, multi-glazing is about as cost effective or more cost

effective than single glazing in most cases. The only exception for which

single glazing is significantly more cost effective is for large windows in

Los Angeles. Where multi-glazing is recommended, double glazing is most cost

effective in all cases except Portland and Bismarck, where triple glazing

tends to be somewhat more cost effective over the life-cycle.

Even if energy prices were to remain about constant in real terms, multi-glazing

is estimated to be the most cost effective for all windows in Portland and

Bismarck, and about as cost effective as single glazing for many of the other

applications.

Looking now at the lower part of table 4.2 at the results for the designated

managed windows that are used for daylighting, we can see that multiple-glazing

appears less often the most cost-effective choice for managed than for unmanaged

windows due to the substitution effect of thermal shutters. However, if energy

prices rise rapidly in real terms, multi-glazing is estimated to be cost effective for all of the window sizes and orientations considered for the colder

regions as represented by Seattle (double glazing preferred), Indianapolis

(double glazing preferred), Portland (triple glazing preferred) and Bismarck

(triple glazing preferred). Multi-glazing is also indicated for certain window

sizes and orientations in several of the more moderate climate regions. For

example, with rapid energy price escalation, double glazing—in addition to

thermal shutters—is preferred for north-facing managed windows in Washington,

D.C. Furthermore, double glazing is estimated to be as cost effective as

prices, single glazing (S) is designated the least-cost choice for

(1.11 m^) south-facing windows in Indianapolis, but double-glazed

94
single glazing for the window applications in Miami, San Antonio, and Atlanta,

if energy prices rise rapidly. Note, however, that in most of the cases the

difference between the glazing alternatives is relatively small.

4.2 COMMERCIAL WINDOWS SUMMARY

Tables 4.3 and 4.4 summarize key findings of the nine case studies of selected

office window systems. Table 4.3, the comercial building counterpart to table

4.1, identifies the cost-effective window size, orientation, and glazing type

of the alternatives considered. It also gives the estimated change in total

life-cycle costs attributable to the identified window system. Columns 3-7

pertain to unmanaged windows not used for daylighting, and columns 8-11, to

unmanaged windows used for daylighting.

Column (1) of table 4.3 lists the nine cities and their heating and cooling

zones, keyed to Figure 1.1. Column (2) designates the assumed rate of escalation in the prices of natural gas and electricity upon which the results in the

corresponding rows are based. Because future energy prices are critical to the

long-run economic performance of windows, but highly uncertain in amount, the

results are shown based on two rates of energy price escalation: a constant

real rate and a 12 percent per annum real rate.

Looking first at the part of table 4.3 which applies to windows unmanaged and

not used for day lighting, we can see from column (3) that in 14 of the 18 cases considered, it is estimated to be cheaper not to have the specified windows

in the office. The exceptions are in Los Angeles, where the climate conditions

cause heating and cooling costs to be lower with a window than without it, and

in Atlanta and Seattle, only if energy prices remain constant in relative terms

and if the construction costs are lowered by using the largest window (see

Appendix B for commercial construction costs.)

Column (4) shows that if windows are nevertheless to be used, the least-cost

size—with the Los Angeles exception—is the smallest size (12 ft^) (1.11 m^),

if energy prices rise rapidly. In the cities with moderate climates, the

largest window walls, with their estimated lower framing costs, are shown to be

the least-cost size, but only if energy prices remain about constant relative

to other prices.

Column (5) shows that the least-cost orientations for windows in the commercial

building, like those in the residential building, depend on the climate. In

moderate-to-cold climates, orienting windows to the south tends to lower energy

costs by taking maximum advantage of the solar heat gain that can be captured

1 Note that the least-cost size is predicated on the orientation and glazing

choices designated in columns (5) and (6).

95
TABLE 4.3 Summary: Cost-Effective Choices for the Selected Commercial Window Systems 8

Unmanaged, Not Used for Daylighting Unmanaged, Used for Daylighting

City

(Heating and Cooling Zones) b (1)

Real Fuel Price Escalation

Rate (X) (2)

Least-Cost Window

Size

(ft 2

) (m2)

(3)

Least-Cost Window Size Greater Than 0 (ft2

) (m2) (A)

Least-Cost Orientation

(5)

Glazing for Least-Cost Window

Greater Than 0

(6)

Impact

on LCCd ($)

(7)

Least-Cost Window Size

(ft2

) (m2

) (8)

Least-Cost Orientation

(9)

Glazing for Least-Cost Window

(10)

Impact on LCCd ($) (11)

Miami

,

0 0 0 90 8.36 North Single 15 90 8.36 North Single - no

Florida (1,1) 12 0 0 12 1.11 North Single /Doublee 71 30 2.79 North Single - 396

San Antonio, 0 0 0 12 1.11 North Single 26 90 8.36 South Single - 85 Texas (1,1) 12 0 0 12 1.11 North Single/Doublee 60 30 2.79 South Single - 366

Los Angeles, 0 90 8.36 90 8.36 South Single -87 90 8.36 South Single - 184 California

(1/2, 5)

12 90 8.36 90 8.36 South Single -33 90 8.36 South Single - 575

Atlanta, 0 90 8.36 90 8.36 South Single -58 90 8.36 South Single - 156 Georgia (2,3) 12 0 0 12 1.11 South Single/Doublee 30 90 8.36 South Single - 458

Washington, 0 0 0 90 8.36 South Single 01 90 8.36 South Single - 145 D.C. (3,4) 12 0 0 12 1.11 South Single/Doublee 41 30 2.79 South Single - 341

Seattle, 0 90 8.36 90 8.36 South Single -29 90 8.36 South Single - 80 Washington

(3,5)

12 0 0 12 1.11 South Single/Doublee 30 30 2.79 South Single/ Doublee

- 234

Indianapolis

,

0 0 0 12 1.11 South Single 28 30 2.79 South Single - 25 Indiana (3,4) 12 0 0 12 1.11 South Single/Doublee 66 30 2.79 South Single/ Doublee

- 200

Portland, 0 0 0 12 1.11 South Single 28 30 2.79 South Single - 10 Maine (4,5) 12 0 0 12 1.11 South Single/Double/

Triplef 66 30 2.79 South Double/ Triple/

Single^

- 170

Bismarck, 0 0 0 12 1.11 South Single /Double® 31 30 2.79 South Single - 7 North Dakota

(5,5)

12 0 0 12 1.11 South Double/Triple/

Single^

67 30 2.79 South Triple/

Double^

- 206

8 Summarized from the tables in section 3, and based on the assumptions given in table 1.1.

b Numbers in parenthesis refer to the heating and cooling zones, respectively, as given by the heating and cooling zone map in figure 1.1.

c Escalation rates in excess of general price inflation.

d The difference between the total present value building costs when the designated window system is used as compared with the costs when the designated opaque curtain wall is used, taken over a 25 year life cycle. Positive figures indicate the amount that windows add to life-cycle costs; negative figures, the amount that windows save.

e There is less than a 5 percent difference between the costs of single and double glazing; the least-cost choice

is listed first.

1 There is less than a 5 percent difference between the costs of single, double, and triple glazing; the least-cost choice is listed first.

8 There Is less than a 5 percent difference between the costs of double and triple glazing; the least-cost choice

1 s listed first.
TABLE 4.

A

Summa ry

:

Cost-Effective Glazing for the Selected Commercial Windows

Unmanaged, But Used for Daylighting

Cities

Real

Fuel Price Escalation

Rate (%)

South East/West North

12 ft 2 30 ft2 60 ft 2 90 ft 2 12 ft 2 30 ft 2 60 ft 2 90 ft 2 12 ft 2 30 ft 2 60 ft 2 90 ft2

Miami, 0 S S S S S S S S S S S S Florida 12 S/D S s S S/D s s s S/D S S S

San Antonio, 0 S S s S S s s s S S s s Texas 12 S/D S s s S/D s s s S/D S s S

Los Angeles, 0 S S s s S s s s S S s s California 12 s S S s S/D s s s S/D S s s

Atlanta, 0 s S s s S s s s S S s s Georgia 12 S/D S s s S/D S/D s s S/D S/D S/D S/D

Washington, 0 s S s s s s s s S S s s D.C. 12 S/D s s s S/D s s s S/D S/D s s

Seattle, 0 S s s s S/D s S s S/D S s s Washington 12 S/D S/D S/D S/D S/D S/D D/S D/S S/D D/S D/S D

Indianapolis

,

0 S S s s S S s s S S s S Indiana 12 S/D S/D S/D S/D S/D S/D S/D S/D S/D D/S D/S D/S

Portland, 0 S/D S s S S/D S S s S/D S s S Maine 12 S/D/T D/T/S D/S/T D/S D/S/T D/T/S D/T D/T D/T/S T/D D/T D/T

Bismarck, 0 S/D/T S s S S/D/T S/D S s S/D/T S/D/T S/D S/D North Dakota 12 D,T/S T/D D/T D/T T/D/S T/D T/D T/D T/D/S T/D T/D T/D

Key: S

D

T

S/D, D/S

D/T, T/D

S/D/T

S,D,T

= Single-glazed windows are lower in life-cycle costs than multi-glazed windows.

= Double-glazed windows are lower in life-cycle costs than single- or triple-glazed windows.

= Triple-glazed windows are lower in life-cycle costs than single- or double-glazed windows.

= First listed is slightly lower in life-cycle cost, but the difference is less than 5 percent.

= No difference at all in life-cycle costs of alternatives separated by commas.

97
through the windows on winter days.l Hence, the least-cost orientation for the

windowed wall is south for Washington, D.C., Atlanta, Seattle, Indianapolis,

Portland, Bismarck, and Los Angeles. In the warmer climates it pays to orient

the windows to the north to avoid undesirable solar heat gain. Thus, the

least-cost orientation is shown to be north for Miami and San Antonio.

Easterly and westerly orientations tend to increase costs if heating loads are

large, because they allow less solar heat gain in winter. They tend to

increase costs if cooling loads are large, because they are difficult to shade

against the summer sun and often result in undesirable summer heat gains.

Column (6) presents the least-cost type of glazing for the window size

identified in column (4). The alternatives considered are single, double, and

triple glazing. With constant real energy prices, single glazing is estimated

to be the cost-effective choice for all of the cases considered, except for

Bismarck for which there is no significant life-cycle cost difference between

single and double glazing. With 12 percent real price escalation, single and

double glazing are estimated to be about equal in cost effectiveness for all

of the windows except those in Los Angeles. Additionally, triple glazing is

cost effective in Portland and Bismarck.

The dollar estimates presented in column (7) are the differences between the

total present value cost of construction, maintenance, repair, insurance,

replacement, and energy, adjusted for income tax effects, of the office module

with the designated window systems and the total cost without any window. In

all of the cities except Los Angeles, the windows when not used for daylighting

are estimated to add somewhat to the life-cycle costs of the module if energy

prices increase rapidly. The higher the escalation in energy prices, the

greater the increase in cost.

The second part of table 4.3 gives the results for unmanaged windows used for

daylighting. We can see from column (8) that when daylighting is effectively

used, it is more economical in all of the cities to have the designated window

system than to have a windowless module. If energy prices remain constant in

real terms, the estimated cost-effective window is the largest examined (90 ft^)

for Washington, D.C., Miami, San Antonio, Los Angeles, Atlanta, and Seattle.

In Indianapolis, Portland, and Bismarck, the estimated cost-effective size is

the moderately sized window (30 ft^) (2.79 m^). With rapidly rising real energy

prices, the moderately sized window is estimated to be the cost-effective

choice for all of the cities except Los Angeles and Atlanta, for which the

largest size is estimated to be cost effective.

1 Note the earlier caveat that this analysis does not address possible

problems in distributing the available solar heat gain within the office

module.

2 Note the earlier caveat that this finding is based on the assumption of a lower first cost for the 90 ft^ window wall than for other sizes.

98
Column (9), like column (5), indicates an advantage to locating windows on

the south side of the building if heating loads are signficant and on the

north size if cooling loads predominate.

Column (10), like column (6), shows single glazing to be the least-cost

glazing choice in most cases, with the primary exception of windows in Portland

and Bismarck under conditions of rapdily rising energy prices.

Column (11) shows that the reductions in total life cycle costs (i.e., net

savings) attributable to the windows when they are effectively used for daylighting range from small to large, depending on climate and the escalation

in energy prices. Potential net savings are greatest in the mild-to-moderate

climate regions, i.e., Los Angeles, Miami, San Antonio, and Atlanta. For

example, net present value savings attributable to the designated least-cost

window system are estimated at nearly $600 in Los Angeles if energy prices

escalate at a rate of 12 percent. In contrast, net savings are estimated to

be close to $200 in Portland and Bismarck.

Table 4.4 focuses on the least-cost choice of glazing for the selected office

windows. Because day lighting without management has little effect on the

choice of glazing, the results are given for only one of the two modes of

commercial window use considered: unmanaged, used for daylighting. Where

there is less than a 5 percent difference in the cost-effectiveness of glazing

alternatives, all alternatives are given in order of their cost effectiveness.

For most of the designated window systems in Miami, San Antonio, Los Angeles,

Atlanta, and Washington, single-glazing is estimated to be the cost-effective

choice, although double glazing appears about equally cost effective for some

of the smaller window sizes and for some of the north-facing windows. Double

or triple glazing tends to be cost effective for the colder locations if energy

prices escalate rapidly.

4.3 GENERAL CONCLUSIONS

The results of thse 18 case studies have a number of implications for

cost-effective window selection and use. In broad terms, the results have

demonstrated for representative window systems and buildings that long-term

costs can be dramatically increased or decreased, or left largely unaffected,

depending on the design, size, orientation, accessories, and use of windows

in houses and office buildings. More specifically, the following general

conclusions can be drawn:

(1) By providing daylighting to reduce electric lighting costs, windows can

be a source of long-run energy savings and dollar savings.

1 The reader is again reminded that these results apply only to the window of

designated size and orientation; multi-glazing tends to be cost effective

in many cases for larger windows and/or for windows with less favorable

orientations.

99
(2) The use of window accessories, such as thermal shutters and Venetian

blinds can significantly reduce undesirable heat gains and losses and may

greatly improve the economic performance of windows, depending on the

relative costs of purchasing and installing the accessories versus purchasing energy to condition the space. Based on the case studies, thermal

shutters appear more likely to be cost effective for residential use,

with a relatively low purchase cost and installation by the homeowner,

than for commerical use, for which costs may be higher.

(3) In moderate-to-cold climates where the heating load is of prime concern,

it pays to orient windows to the south, other things being equal.

(4) In warm climates where the cooling load is of prime concern, it pays to

orient windows tp the north, other things being equal.

(5) With energy prices rising substantially faster than the general rate of

price inflation, multiple glazing will tend to be cost-effective for

residential windows such as those in the illustrative brick rambler in

locations with more than about 4,400 heating degree days (see fig. 1.1),

regardless of their orientation and whether or not they are equipped

with shutters.

(6) With rapidly rising energy prices, double glazing may be cost effective

for many unmanaged residential windows like those considered here, as well as for managed residential windows facing north, in locations with

as few as 2,000 heating degree days (see fig. 1.1).

(7) Double glazing may also be cost effective for residential windows in

very warm climates, such as Florida, to reduce cooling loads.

(8) Multiple glazing tends to be more cost effective when used for windows

not equipped with thermal shutters, and vice versa, due to substitution

effects between the two.

(9) For many applications—particularly for managed windows—the higher first

cost of multiple glazing may more-or-less offset its energy savings,

resulting in a breakeven situation whereby the thermal performance of the

building can be upgraded with little or no increase in total long-run

costs

.

(10) Single glazing may be cost effective for many commercial building

applications, except those in very cold climates.

(11) Daylighting benefits tend to increase at a decreasing rate and may

eventually reach a "saturation point" as window size is expanded. The

declining incremental benefits from daylighting, together with a growing

1 This conclusion applies specifically to conventional windows without special

passive solar features for thermal storage.

100
energy penalty as the window area is increased ,1 tends to constrain the

size of the economically efficient window.

(12) If, due to the nature of the building, daylight utilization, window

management, natural ventilation, and/or passive solar design cannot be

effectively employed, it will tend to pay in both warm and cold locations

to keep windows small, or even to eliminate them, apart from other con- siderations such as view and code and safety regulations.

(13) In all climatic regions considered, the potential for saving energy and

dollars through the considered selection, management, and use of windows

appears as great or greater than the potential for losses through

inefficient decisions.

1 This conclusion applies specifically to conventional windows without special

passive solar features for thermal storage.

101
SELECTED REFERENCES

1. Ruegg, Rosalie T. and Chapman, Robert E. Economic Evaluation of Windows

in Buildings: Methodology , National Bureau of Standards, Building

Science Series 119, April 1979.

2. Kusuda, Tamami and Collins, Belinda L. Simplified Analysis of Thermal and

Lighting Characteristics of Windows: Two Case Studies , National Bureau of

Standards, Building Science Series 109, Feburary 1978.

3. Hastings, Robert and Crenshaw, Richard. Window Design Strategies to

Conserve Energy , National Bureau of Standards, Building Science Series

104, June 1977.

4. Collins, Belinda L.; Ruegg, Rosalie, T.; Chapman, Robert; and

Kusuda, Tamami. A New Look at Windows , National Bureau of Standards,

NBSIR 77-1388, January 1978.

5. Petersen, Stephen R. Retrofitting Existing Housing for Energy Conservation : An Economic Analysis, National Bureau of Standards, Building Science

Series 64, December 1974.

6. Treado, S. and Kusuda, T. Daylighting Window Management Systems, and

Lighting Controls , National Bureau of Standards, NBSIR 80-2147, December

1980.

7. Jacobs, Madeleine, and Petersen, Stephen. Making the Most of Your Energy

Dollars in Home Heating and Cooling , National Bureau of Standards,

Consumer Information Series 8, 1975.

8. National Association of Home Builders Research Foundation, Inc. Insulation

Manual - Homes /Apartments , 1971.

9. Hemphill, J. Marshall. "A Model for Selecting Energy Saving Lighting

Systems," (Parts I and II) Specifying Engineer , September 1979 and May 1980.

10. Selkowitz, Stephen and Johnson, Richard. "The Daylighting Solution,"

Solar Age , August 1980, pp. 14-20.

11. Griffith, James W. "Benefits of Day lighting - Cost and Energy Savings,"

ASHRAE Journal , January 1978, pp. 53-56.

12. Federal Register , "Federal Energy Management and Planning Programs;

Methodology and Procedures for Life Cycle Cost Analyses (Average Fuel

Costs)," In Press, July 1981.

13. Kusuda, Tamami and Ishii, K. Hourly Solar Radiation Data for Vertical

and Horizontal Surfaces on Average Days in the United States and Canada , National Bureau of Standards, Building Science Series 96, April 1977.

102
APPENDIX A

Estimated Costs of Purchase, Installation, Maintenance, and Repair

for the Selected Window Systems in the Single-Family Residence

Table A.l shows the estimated costs of purchasing and installing the

double-hung wooden windows. Table A. 2 shows the estimated costs of purchasing

Venetian blinds and wooden thermal shutters. Table A. 3 shows the estimated

costs of maintenance and repair both for the base year and over the lifecycle. All costs shown are for the Washington, D.C. area. For use in the

analysis of windows in the other eight cities the cost data were adjusted by

location modifiers to account for regional price differences.

103
Table A.

1

Acqusition Costs of a Window in Excess of the

Cost of a Non-Windowed Wall

Component

Dollar Costs, by Size of Area

12 ft2

(1.11 m

2

)

18 ft2

(1.67 m

2

) 30 ft2

(2.79 m2

) 60 ft2

(5.57 m2

)

Windows3

Single Glazed

Double Glazed

52.20

81.80

70.70

109.36

122.55

192.61

245.10

385.23

Wallb 33.72 50.58 84.30 168.60

Window Cost Less Wall Costc

Single Glazed

Double Glazed

18.48

48.08

20.12

58.78

38.25

108.31

76.50

216.63

a Purchase prices are beginning 1978 list retail prices, reduced 10 percent

to reflect a typical builder's discount, for good quality wood double-hung

windows, provided by a distributor in the Washington, D.C. area. Prices

are for single and multiple units of windows of available sizes which

approximate the designated percentages of the exterior wall to be glazed.

The 12 ft 2 (1.1 m^) area is provided by a 3' x 3' 11" window (0.9 m x 1.2 m);

the 18 ft 2 (1.7 m^) area, by a 3' x 6' (0.9 m x 1.8 m) window; the 30 ft2

(2.8 m2) area by two 3' x 5' (0.9 m x 1.5 m) windows; and the 60 ft2

(5.6 m2) area, by four 3' x 5' (0.9 m x 1.5 m) windows. An installation

cost of $5.00 per window or pair of windows is used, based on an estimate

given by a home builder in the Washington, D.C. area for beginning 1978.

The installation cost is added to the purchase cost to arrive at the window

acquisition cost.

b Cost of nonwindowed wall areas corresponding in size to the windowed areas are based on a price of $2.81/ft2 ($30.25/m2) as estimated by a home

builder in the Washington, D.C. area for beginning 1978. The wall section

is assumed to be face brick veneer over 8” (203 mm) cinder block with

building paper sheathing, 3 1/2" (89 mm) of insulation, and 1/2" (13 mm) of

painted interior drywall.

c The differential acqusition costs attributable to windows are estimated

by taking the difference between the costs of the windows and the costs

of the comparably sized wall area.

104
Table A. 2

Cost of Window Accessories

Dollar Cost by Size of Window

Type of Accessory

12 ft 2

(1.11 m

2

)

18 ft 2

(1.67 m

2

)

30 ft 2

(2.79 m

2

)

60 ft 2

(5.57 m

2

)

Ventian Blindsa 17 20 36 72

Wooden Thermal Shutters^ 42 51 96 192

a Prices shown are averages of beginning 1978 prices quoted by several

low-to-moderately priced department stores. Installation is assumed to be

done by the homeowner at negligible cost.

b Estimates are those of a Washington area building contractor for

constructing, installing, and finishing solid, tightly fitting wooden

shutters at the beginning of 1978. (Prices quoted by custom drapery shops

in the area were considerably higher.

105
Table A. 3

Window Maintenance and Repair Costs

Type of Maintenance and Repair Dollar Costs by Window Area

12 ft 2

(1.11 m

2 18 ft2

) (1.67 m

2

)

30 ft 2

(2.79 m2

) 60 ft2

(5.57 m

2

)

Cleaning Costs

Annual Cleaning Cost,

beginning 1978a 1.20 1.80 3.00 6.00

Present Value Dollar Cost over

25 years*5 13.00 19.00 32.00 64.00

Scraping, Recaulking, and Repainting Every 5th Year at 1 .50/ft 2 ($16. 15/m2

)

Recurring Cost Every 5th Year,

beginning 1978 Dollars0 18.00 27.00 45.00 90.00

Present Value Dollar Cost Over

25 Years^ 30.00 45.00 75.00 151.00

a Based on a rate of $0. 10/ft 2 ($1.08/m2 ).

b Based on annually recurring costs in constant dollars discounted with an

8 percent discount rate and rounded to the nearest dollar.

c Based on a rate of $1. 50/ft 2 ($16. 15/m2

) in beginning 1978 dollars.

d Based on recurring costs every 5th year in constant dollars discounted

with an 8 percent discount rate and rounded to the nearest dollar.

106
APPENDIX B

Estimated Costs of Purchase, Installation, Maintenance, and Repair

for the Selected Window Systems in the Commercial Office Building

Table B.l provides the acquisition costs of the exterior office wall (bay).

These costs include the purchase and installation prices for all glazing

(spandrel panel and window), mullions, and the interior curtain wall. A

25 percent markup for contractor overhead and profit is included.

Table B.2 gives the costs of Venetian blinds and insulated thermal shutters.

Table B.3 gives the estimated contract price at the beginning of 1978 for

annual washing of all' windows of a specified size in the office building. All

costs are shown for the Washington, D.C. area. For use in the analysis of

window in the other eight cities, the cost data were adjusted by location

modifiers to account for regional price differences. Table B.3 also shows

estimated annual insurance premiums as beginning 1978, as a proxy for repair

and replacement costs, for windows of different size.

107
Table B.l

Commercial Case Study: Acqusition Costs 3

Dollar Cost of Wall by Size of Windows

Glazing Type

0 ft2

(0 m

2

)

12 ft 2

(1.11 m

2

) 30 ft2

(2.79 m

2

) 60 ft 2 (5.57 m

2

) 90 ft2

(8.36 m

2

)

Single . 1238 1229 1204 1257 1009

Double 1238 1301 1323 1446 1255

a Cost figures are for the entire 10' x 12' (3.0 m x 3.7 m)

exterior wall (bay) and include the purchase and installation

costs for all glazing (spandrel panel and window), mullions, and

the interior curtain wall, plus a 25 percent markup cost for con- tractor overhead and profit. The cost differential associated

with a given window size/type is thus equal to the difference

between the cost of the bay with that window size/type and the

windowless bay. The area of the exterior wall is 120 ft 2 (11.1 m^). Varations in cost among window sizes are due both to

differences in framing costs and to the costs of glazing. Lower

framing costs are particularly evident in the case where the

window area is 90 ft2 (8.4 m

2

).

Source: A leading manufacturer and distributor of building materials

provided the cost estimates.

108
Table B.2

Commercial Case Study: Cost of Window Accessories

Dollar Cost by Size of Window

Type of Accessory

12 ft 2 (1.11 m

2

) 30 ft 2

(2.79 m

2

) 60 ft 2

(5.57 m

2

) 90 ft2

(8.36 m2

)

Venetian Blinds 47 47 64 95

Thermal Shutter 232 412 750 1050

a All costs are for beginning 1978, and reflect purchase,

installation, and contractor markup.

Source: A leading manufacturer and distributor of building

materials provided the cost estimates.

109
Table B.3

Commercial Case Study: Cleaning and Insurance Costs

Dollar Cost by Window Area

Type of Cost

12 ft2

(1.11 m2

) 30 ft2

(2.79 m

2

) 60 ft 2

(5.57 m

2

) 90 ft 2

(8.36 m

2

)

Annual Cleaning Cost for 1977 3.10 A. 10 5.80 7.50

Annual Insurance Cost for 1977a

Premium^5

Single 0.60 1.70 A. 10 5.90

Double 3.80 10. AO 2A.50 35.60

a Insurance costs are used as a proxy for repair and replacement costs.

b Premiums are unadjusted for regional rate differentials.

Source: Insurance costs were provided by a major insurance company, based

on company rate manuals.

110
NBS-114A (REV. 2-60) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS1R 81-2248

2. Performing Organ. Report No. 3. Publication Date

July 1981

4. TITLE AND SUBTITLE

A REGIONAL ECONOMIC ASSESSMENT OF SELECTED WINDOW SYSTEMS

5. AUTHOR(S)

Rosalie T. Ruegg and Robert E. Chapman

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions

)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

10. SUPPLEMENTARY NOTES

23 Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This study, the fifth in a series of reports from the National Bureau of Standards

interdisciplinary project on windows, provides guidance in selecting and using

windows in buildings for greater cost effectiveness. It presents the life-cycle

costs of selected window systems used in a room of a representative residence and

in an office module of a representative commercial office building for nine cities

in the United States, representing five heating zones and four cooling zones. The

cities covered are Miami, Florida; Atlanta, Georgia; Washington, D.C.; Portland,

Maine; Indianapolis, Indiana; San Antonio, Texas; Los Angeles, California; Bismarck,

North Dakota; and Seattle, Washington. The results of the regional analyses are

summarized, and the implications of these results are considered, both for selecting

windows in new buildings and for managing windows in existing buildings. The

emphasis of this report is on conveying the research findings to builders, designers,

and building owners and operators — those involved immediately with the building

process. The research method is described in an earlier companion report. Economic

Evaluation of Windows in Buildings; Methodology. NBS BSS 119.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Building economics; daylighting; energy conservation; engineering economics;

life-cycle costs; passive solar; regional analysis; thermal efficiency; windows.

13. AVAILABILITY

Unlimited

| 1 For Official Distribution. Do Not Release to NTIS

i ~) Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

123

15. Price

$ 11.00

USCOMM-DC 6043-P80
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