A11102 15MM61

NATL INST OF STANDARDS & .'ii•,'*^

A11102154481 PUBLICATIONS

NBS BUILDING SCIENCE SERIES 137

An Evaluation of

Thermal Energy Conservation Schemes

4A—— n Experimental Masonry Building

HO, 157

1932

c. 2

\RTMENT OF COMMERCE • NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

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calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities^ — Radiation Research — Chemical Physics —

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THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

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Engineering — Building Technology — Fire Research — Chemical Engineering^

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

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The Institute consists of the following centers:

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'Headquarters and Laboratories at Gailhersburg, MD, unless otherwise noted; mailing address Washington, DC 20234. 'Some divisions within the center are located at Boulder, CO 80303.
MATIONAJL BURKAL

OF 3TANDARU8

LJHBAnv

SEP 1 5 1982

NBS BUILDING SCIENCE SERIES 137

An Evaluation of

Thermal Energy Conservation Schemes

for an Experimental Masonry Building

Parambir S. Gujral and Raymond J. Clark

Skidmore, Owings & Merrill

33 W. Monroe Street Chicago, IL 60603

Douglas M. Burch

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

Sponsored by: Skidmore, Owings & Merrill National Bureau of Standards and King Abdul Aziz University

Makkah Campus

Saudi Arabia

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued July 1982
Library of Congress Catalog Card Number: 81-600175

National Bureau of Standards Building Science Series 137

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 137,39 pages (July 1982)

CODEN: BSSNBVU.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1982

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402

Price $4.75 (Add 25 percent for other than U.S. mailing)
ABSTRACT

A one-room masonry building with exterior polystyrene rigid board insulation was built within a

large environmental chamber at the National Bureau

of Standards. Various climatic conditions were

simulated within the chamber, and the transient thermal response of the test building was monitored.

Three schemes (night cooling using a ceiling-mounted valance cooling coil, natural ventilation night cooling,

and passive solar heating) were investigated with

regard to energy conservation. The test results indicated that these operating practices resulted in a considerable reduction in energy consumption for space heating and cooling.

The measured performance of the test building

compared favorably with the corresponding

performance obtained with an analytic model.

Key words: building thermal mass; dynamic

performance of buildings; energy conservation; heat

transfer in buildings; night ventilation; night space

cooling; passive solar heating.
ACKNOWLEDGMENTS

The authors would Hke to thank Dr. Jafar Sabbagh,

Vice Chancellor of King Abdul Aziz University, for

his contribution to the project development, and Mr.

Robert Jones of the National Bureau of Standards for Project Administration. Also, appreciation is expressed to Mark LeMay for his technical assistance

in the installation of the instrumentation, to Dave

Ward and Doug Grant for operating the environmental chamber which simulated the weather

cycles, and to Mrs. Mary Reppert for editing this manuscript.

In addition, the authors would like to express special thanks to the National Concrete Masonry Association,

Brick Institute ofAmerica, Pella Rolscreen Company,

Dow Chemical U.S.A., Edwards Engineering

Corporation, Hale Engineering Company, Inc., Flexicore Company, Inc., for donating building materials used

for construction of the test building, and to Kettler

Brothers, Inc., for building the test building.
CONTENTS

Page

ABSTRACT Hi ACKNOWLEDGMENTS iv LIST OF FIGURES vi LIST OF TABLES vi

1. INTRODUCTION I 1. DESCRIPTION OF TEST BUILDING 3

3. INSTRUMENTATION AND MEASUREMENT TECHNIQUE 5

4. MATHEMATICAL MODEL 7

5. HEAT-TRANSFER PARAMETERS 10

6. EXPERIMENT PLAN 12

7. TEST RESULTS 15

7.1 NINE-HOUR NIGHT COOLING TEST 15 7.2 TWELVE-HOUR NIGHT COOLING TEST 17

7.3 NIGHT VENTILATION COOLING TEST 20

7.4 PASSIVE SOLAR HEATING TEST 2!

8. SUMMARY AND CONCLUSIONS 22 REFERENCES 23 APPENDIX A. THERMOGRAPHIC SURVEY 24 APPENDIX B. AIR INFILTRATION MEASUREMENTS 27 APPENDIX C. WALL MOISTURE CONTRIBUTION TO THE HUMIDITY

RESPONSE OF THE TEST BUILDING 29 APPENDIX D. EVALUATION OF THE EFFECT OF ENVIRONMENTAL

CHAMBER WALL TEMPERATURE ON THE PERFORMANCE OF

THE TEST BUILDING 31

V
Figures

Page

Fig. 1. Fig. 2. Fig. 3. Fig. 4.

Fig. 5.

Fig. 6. Fig. 7.

Fig. 8.

Fig. 9.

Fig. 10.

Fig. 11.

Fig. A.l

Fig. A.l

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

A.2

A.2

A.3

A.3

A.4

A.4

A.5

A. 5 B. l.

Fig. C.l

Photograph of the test building during construction , Photograph of the interior of the test building showing the valance cooling coil Isometric view of the test building showing the thermocouple locations , Comparison of measured and predicted indoor temperatures for the 9-hour night

cooling test Variation of indoor relative humidity over a 24-hour period for the 9-hour night

cooling test Measured indoor temperatures at various heights

Comparison of measured and predicted indoor temperatures for the 12-hour night

cooling test , Comparison of measured and predicted indoor temperatures after the valance

cooling was stopped following the 12-hour night cooling test Comparison of the measured and predicted indoor temperatures for the night

ventilation cooling test Response of the indoor temperature to a brief period of ventilation during the hot

part of the day

Comparison of measured and predicted indoor temperature response of the test building for the passive solar test (a) . Conventional photograph of the test house

(b). Infrared photograph of the test house

(a) . Conventional photograph of the upper inside corner

(b) . Infrared photograph of the upper inside corner

(a). Conventional photograph of the inside door surface

(b) . Infrared photograph of inside door surface

(a) . Conventional photograph of valance coil

(b) . Infrared photograph of valance coil

(a) . Conventional photograph of wall/ceiling edge

(b). Infrared photograph of wall/ceiling edge

Rate of air infiltration plotted as a function of the inside-to-outside temperature

difference Comparison of measured and predicted indoor relative humidity for the period

when the cooling coil is turned off

4

4

6

16

16

17

18

19

20

20

212424

25

25

25

2526

26

2626

28

30

Tables

Page

Table 1. Heat-transfer properties of building materials Table 2. Surface areas used for the analysis

Table 3. Hourly sol-air temperatures, °F (°C)

Table 4. Solar window heat gains

Table 5. Hourly sensible and latent cooling loads removed by the valance coil for 9-hour

night-cooling test, Btu/hr (W)

Table 6. The normal daily air temperature extremes and relative humidities for selected

cities for July

Table 7. Hourly sensible and latent cooling loads removed by valance coil for 12-hour

night-cooling test, Btu/hr (W)

Table B.l. Measured rates of air infiltration Table D.l. Measured temperatures and calculated values

II

II1314

17

19 2732

vi
1. INTRODUCTION

This study investigates the temperature response of a prototype dormitory building for a Saudi Arabian

university. The university buildings were designed to incorporate a number of energy-saving concepts, some

of which are reported herein. The campus is to be

built in Makkah, Saudi Arabia, where the climate is essentially a summer condition for the entire year and

an extreme summer condition for most of the year. The test building was built at the National Bureau of Standards within a high-bay environmental chamber in which various diurnal temperature cycles for Makkah

were simulated. The test building was a one-room

structure with massive masonry walls insulated from

the environment by polystyrene board insulation placed exterior to the masonry. This type of

construction creates a large amount of thermal storage

capacity at the interior of the building which may be

used to save substantial energy throughout the year. Three energy-savings schemes were investigated and

are described below.

The first scheme investigated was night cooling using

a ceiling-mounted valance cooling coil. This coil exchanged heat with the indoor air by means of

convection. For this scheme, the test building was

cooled during a nighttime period during which the

interior surfaces of the walls, floor, and ceiling were

cooled. During the day when the cooling system was

not operated, the interior mass absorbed heat and

thereby maintained a comfortable indoor condition. This study investigated the 24-hour indoor

temperature response of the test building when it was

cooled for 9- and 12-hour periods at night.

This scheme can be used in situations where a large group of buildings is served by a single central cooling

plant. In such a situation, different sets of buildings serviced by a plant may be cooled at different times during a 24-hour period, thereby distributing the cooling load more uniformly and substantially

reducing the peak load of the central plant. The

1
concept is particularly applicable to academic

campuses where the occupancy normally shifts between classrooms and dormitories at times coincident with the space cooling schedule. In this way, the buildings are unoccupied during system off periods and occupied during system on periods.

The second scheme investigated was the use of night

ventilation to cool the interior mass during the night

hours. Night ventilation was accomplished by opening

the windows and door and operating a ceiling fan to increase the rate of natural ventilation. During

daytime periods, the interior mass absorbs heat and

maintains comfortable conditions. During winter

months in Makkah, the high daytime temperatures

produce large cooling loads. However, the nighttime

air frequently falls below a room comfort condition of

80 °F (27 °C). It has been theoretically shown [1]* that

this cool night air may be used to cool the interior mass of a building and thereby provide "free" cooling.

This study investigated the 24-hour indoor

temperature response of the test building cooled in this fashion. It was shown that such a procedure has the

potential of essentially eliminating air conditioning energy consumption during certain times of the year

that ordinarily require substantial mechanical cooling.

A third energy-conservation scheme investigated was

passive solar heating of the test building. This

procedure is most applicable to the case of a passive

solar house. A test was carried out in which the test building was exposed to a simulated window solar gain (using infrared heat lamps) for a mid-western U.S.

climate, and the diurnal indoor temperature response was monitored.

* Numbers in brackets are references cited at the end of the

report. 2
2. DESCRIPTION OF TEST

BUILDING

A one-room test building was built within an environmental chamber at the National Bureau of

Standards. The external dimensions of the test building were 21-ft 4-in (6.50 m) long by 17-ft 4-in (5.28 m)

wide by 15-ft 2-in (4.62 m) high to the top of the

parapet. The- inside ceiling height was 13-ft 4-in (4.06 m).

The building contained a door and two windows

on one wall and three windows in the opposite wall. A photograph of the completed building is given

above. A photograph of the building under

construction is given in figure 1. The wall

construction, from outside to inside, consisted of nominal 4-in (10 cm) face brick, an air space, 3 1/2-in

(8.9 cm) rigid polystyrene insulation fastened to nominal 8-in (20 cm) solid concrete block with metal

ties and 3/4-in (2 cm) plaster applied to the interior surface of the concrete block (see fig. 1). The total wall thickness was 16 7/8 in (43 cm).

3
FIGURE 1. PHOTOGRAPH OF THE TEST

BUILDING DURING CONSTRUCTION

The roof consisted of concrete block pavers placed over 4-in (10 cm) polystyrene board insulation,

which in turn was placed on 8-in (20 cm) precast

hollow-core concrete panels spanning the short dimension of the building. A layer of 3/4-in (2 cm)

plaster was applied to the inside ceiling surface, giving

a total roof thickness of 14 3/8 in (37 cm).*

A 5 in (13 cm) thick concrete floor slab was poured

over 4-in (10 cm) polystyrene board insulation placed over a compacted gravel bed. Thin-set quarry tile was

mounted atop the concrete slab. The floor was

insulated from the ground in order to simulate the thermal performance of the top floor of a three-story

building.

* A roof membrane was not included on the test building. However, one is normally included on such a building constructed in the field.

The five windows were single-pane casement type. A

removable second pane of glass was located at the

interior side of the window. The windows contained

complete weatherstripping with latches. The solid wooden door was weatherstripped.

A valance chilled-water cooling coil was installed below the ceiling. This unit was 18 ft (5.5 m) long and

contained an eight-row coil. A drain pan under the

coil was used to collect moisture condensed from the room air. A photograph of the valance coil with drain pan removed is shown in figure 2. When in operation, the valance cooling coil creates cool natural convection air currents within the space. These currents are induced by buoyant forces caused

by temperature differences within the interior space of

the test building. Such a system does not require a fan or blower. A ceiling fan was installed within the

structure to increase air movement during periods

when the valance coil was not operated.

FIGURE 2. PHOTOGRAPH OF THE INTERIOR

OF THE TEST BUILDING SHOWING THE

VALANCE COOLING COIL , ^

4
3. INSTRUMENTATION AND

MEASUREMENT TECHNIQUE

Twenty-four-gage copper-constantan thermocouples were mounted at various locations throughout the test building to monitor the indoor temperature.

Thermocouples were placed at the inside and outside

surfaces of the roof and the four walls. These

thermocouples were centrally located and attached to the building surfaces with epoxy. For each surface thermocouple, there is a second thermocouple located approximately 1 ft (30 cm) from the surface to sense

the air temperature. The east wall contains two

additional thermocouples, one located between the

insulation and the concrete block, the other attached

to the inside surface of the face brick. Thermocouples were also centrally located on the top and bottom

sides of the rigid floor insulation to sense the one- dimensional heat transmission through the center

portion of the floor slab. The thermocouple locations are depicted in figure 3.

5
FIGURE 3. ISOMETRIC VIEW OF THE TEST

BUILDING SHOWING THE THERMOCOUPLE LOCATIONS

A vertical column extending from the floor to the ceihng was located at a point 4 ft (1.2 m) in from the center of the south-facing wall. Thermocouples were

located along this column at heights of 2, 5, 8, and 1

1

ft (0.6, 1.5, 2.4, and 3.4 m) above the floor to measure

the floor-to-ceiling temperature gradient. A Dunmoretype relative humidity transducer was also located on

the vertical column at a height of 4 ft (1.2 m) above

the floor. This transducer, with potentiometer and

power source, produced a millivolt signal proportional

to the indoor relative humidity.

These transducers were connected to a 100-channel

data acquisition system (DAS) located in the control

room of the environmental chamber. The DAS

contained an internal electronic ice-point reference. The channels of the DAS could be programed to output in millivolts, degrees Celsius, or degrees

Fahrenheit. Recordings were printed at 30-minute

intervals.

The rate of total heat removed (q) from the valance

cooling coil was determined from the relation:

q = m-c.. iT,-T,) (1)

where

-T,

mass flow rate of chilled water;

specific heat of water; and

temperature rise of chilled water across coil.

The temperature rise (Tg-T,) through the chilled water

cooling coil was measured with a thermopile. This

thermopile consisted of 10 thermocouple junctions.

Five of these junctions were installed in a thermocouple well protruding into the supply Une

approximately 1 ft (30 cm) from the test building. The

other five junctions were installed in a similar thermocouple well protruding into the return line. The

output of this thermopile was measured with a strip chart recorder and a digital voltmeter. A water flowmeter was installed in the supply line of

the cooling coil. This meter produced a contact

closure for each metered gallon of water. The output

of the meter was connected to a pulse counting system

which printed the number of hourly accumulated

contact closures. A condensate collection system was installed to determine the weight of condensate collected. This

system did not function as it was intended, because water drained from the fins of the cooling coil only

after it became saturated with water.

6
4. MATHEMATICAL MODEL

The theoretical performance of the test building was

predicted using a mathematical model which

performed a simultaneous heat balance at 15 building

surfaces and the indoor air of the test building. The

surfaces included the inside and outside wall for the four wall orientations, the inside and outside roof, the

inside floor, and the windows and door for the four

wall orientations. The resulting 16 simultaneous linear equations were solved by matrix inversion on a digital

computer.

The following heat-transfer assumptions were made in the mathematical analysis:

1. the heat flow through all building surfaces is one-dimensional;

2. heat transfer properties of building materials are

constant;

3. the indoor air is perfectly mixed (i.e., indoor air temperature is uniform);

4. infiltration rate is constant;

5. indoor air has negligible thermal storage

capacity; and

6. the thermal storage capacities of the windows

and door are negligible.

7
A single heat balance was used at each indoor and

outdoor surface assuming a uniform temperature

across the entire surface. A thermographic survey (see appendix A) of the inside surfaces of the test building

showed this assumption to be valid except for the narrow region where the walls joined the ceiling. The

time series heat conduction equation for the indoor

and outdoor opaque building surfaces was taken from

ref. [2] and is given below:

Indoor Surface N

j=0

N

- 2 Dj Q,,,_j

N

j=0

(2)

where

Q.,

To,l-j Q,.H

heat transferred through the indoor surface at time t; temperature of indoor surface at time t-j\ temperature of outdoor surface at time t-j; and

heat transferred through the indoor surface at time t-j.

The five windows and door were assumed to have

negligible thermal storage. The heat balance equation

used for these surfaces is given below:

(4)

where

T'9.' T

= heat transferred through the thermally quick*

surfaces at time /; = temperature of the environment chamber air = temperature of the quick surface at time /; and = temperature of the room air at time t.

The chamber and room thermal resistance values (R^

and R^) given in eq (4) are the summation of the conduction and the convection-radiation components.

R, = 1/A, + R,

Rr = \/K

(5)

(6)

where

hi combined convection-radiation coefficient

at the indoor surface; and

combined convection-radiation coefficient

at the outdoor surface.

sLirlacc-to-surface thermal resistance of quick

surface.

Outdoor Surface N N

j=0 7=0

The heat balance for the indoor air of the test building contains terms describing the heat transferred from the massive and quick indoor surfaces, the heat

contribution of infiltrating air, and the heat added by

the simulated occupancy load, or:

N

2 Dj Qo,-j

where

Qo,

Qo.,-j

(3)

heat transferred through the outdoor surface

at time t; and

heat transferred through the outdoor surface

at time t~j.

0=1 hj, . Sj . (T,,,-T,,)

where

(7)

P = the number of internal surfaces;

hji = combined convection-radiation coefficient

for the yth surface;

In eq. (2) and (3), Aj, Bj, Cj, and Dj, (for y= 0,1,2, . . . are the modified conduction transfer —

functions according to Mitalas and Arsenault [3].

* Here the term "quick" refers to surfaces with negligible thermal heat capacity.

8
Sj = area ofyth surface perpendicular to heat flow;

Tj, = temperature ofyth surface at time /; = mass flow rate of infiltrating air; = specific heat of air; = occupant sensible heat gain; and = sensible heat gain or loss from air conditioning

system.

The sensible total cooling load {Q^) served as an input

for the mathematical model. For each of the tests, the test building was exposed to a diurnal sol-air temperature cycle. This sol-air temperature cycle was determined by area-averaging

the sol-air temperature for each of the building

surfaces, or:

1 ' ^•^ St ^ ^^J-'^^ (8)

where

T, = area-averaged sol-air temperature at time t, and

Sj = area of j th surface. Sj = total area The sol-air temperature (T^ ,) for each of the surfaces

(i.e., four walls and the rooO was determined from the procedures given in ref [5].
5. HEAT-TRANSFER

PARAMETERS

The heat-transfer properties of the building materials used in the analysis are summarized in table 1. The

areas used to compute heat flows through the building

components were the exterior areas for each of the building components. These areas are summarized in table 2.

The coefficient of transmission for the solid wooden

door was taken to be 0.47 Btu/hr-ft^-°F (2.6 W/m^-K).

This value is based on data contained in ref. [5]. The

coefficient of transmission for the windows was taken

to be 0.44 Btu/hr-ft^-°F (2.5 W/m^-K). This value is based on data supplied by the window manufacturer.

10
Table 1. HEAT-TRANSFER PROPERTIES* OF BUILDING MATERIALS

Material Thickness Conductivity Density Specific Heat

in (cm) Btu/hr-ft-°F (W/m-K) ib/ft^ (kg/m^) Btu/lb-°F (J/Kg-K)

Face brick 3.5 (8.9) .75 (1.30) 130. (2080) .20 (840)

Polystyrene

insulation 3.5 (8.9) .018 (0.03) 2. (40) .20 (840) Concrete

block 7.6 (19.0) .50 (0.87) 130. (2080) .18 (750)

Plaster 0.7 (1.9) .42 (0.73) 116. (1860) .20 (840)

Roof panels 8.0 (20.0) .52 (0.90) 85. (1400) .20 (840)

Roof pavers 2.0 (5.1) .43 (0.74) 95. (1500) .20 (840)

Quarry tile 0.5 (1.3) .80 (1.40) 95. (1500) .20 (840) Concrete

floor 5.0 (13.0) .80 (1.40) 150. (2400) .20 (840)

* Values taken from refs. 4,5, and 8.

The tracer gas technique was used to determine the air infiltration rate for the test building. A complete

description of this technique is given in Appendix B. These measurements revealed that the test building

had an extremely low rate of air infiltration. This was

attributed to the tight construction and design of the

test building. It was shown that air infiltration during

winter could be correlated with respect to the inside- to-outside temperature difference. Under these simulated winter conditions, the rate of air infiltration varied from 0.017 to 0.052 volume changes per hour

over a range of inside-to-outside temperature

differences from 0 to 70 "F (0 to 39 °C). For the summer measurements, the infiltration rate remained

essentially constant at about 0.022 volume changes per

hour.

Table 2. SURFACE AREAS USED FOR

THE ANALYSIS

Surface Area

ft^ (m^)

North wall 260. (24.1) East wall 294. (27.3) South wall 260. (24.2) West wall 273. (25.4) Roof 370. (34.4) Floor 370. (34.4) Window 53. (4.9) Door 20. (1.9)

For the determination of sol-air temperatures, the surface absorptance of the exterior surface of the test building was taken to be 0.3, and the overall heat- transfer coefficient at the exterior surface was taken to be 1.46 Btu/hr-ft^-°F (8.24 W/m^-K). The surface areas used for this analysis were the values given in table 2.

II
6. EXPERIMENT PLAN

Four tests were carried out in the environmental

chamber (see above photograph) and are described in this section. For these tests, the test building was

exposed to a diurnal sol-air temperature cycle until a steady-periodic condition was attained. This condition was deemed to exist when the interior temperature

fluctuations at various locations repeated themselves at 24-hour intervals.

Nine-hour night cooling test (Test 1): For the 9-hour

night cooling test, the test building was repeatedly

exposed to a sol-air temperature cycle developed for a peak summer day in Saudi Arabia until the heat flows reached a steady-periodic condition. Hourly values for the sol-air temperature cycle are given in table 3. During this diurnal cycle, the test building was cooled

using the valance cooling coil for 9 hours at night,

12
Table 3. HOURLY SOL-AIR TEMPERATURES, 'F CC)

Time, h Tests 1 and 2 Test 3 Test 4

0100 79. (26.) 71. (22.) 20. (-6.7) 0200 78. (26.) 70. (21.) 19. (-7.2) 0300 77. (25.) 69. (21.) 18. (-7.8) 0400 76. (24.) 68. (20.) 18. (-7.8) 0500 75. (24.) 68. (20.) 18. (-7.8) OoOO 81. (27.) 69. (21.) 18. (-7.8) 0700 95. (35.) 75. (24.) 19. (-7.2) 0800 105. (41.) 91. (33.) 25. (-3.9) 0900 113. (45.) 100. (38.) 33. (-.6) 1000 120. (49.) 107. (42.) 38. (3.3)

1 100 125. (52.) 1 10. (43.) 40. /A A\ (4.4) 1200 129. (54.)

11/1

1 14. (46.) 42. (j.6) 1300 134. (57.) 119. (48.) 44. (6.7) 1400 136. (58.) 120. (49.) 45. (7.2) 1500 135. (57.) 118. (48.) 43. (6.1) 1600 129. (54.) 110. (43.) 37. (2.8) 1700 120. (49.) 95. (35.) 30. (-1.1) 1800 104. (40.) 88. (31.) 29. (-1.7) 1900 96. (36.) 85. (29.) 27. (-2.8) 2000 92. (33.) 81. (27.) 25. (-3.9) 2100 88. (31.) 78. (26.) 24. (-4.4) 2200 85. (29.) 76. (24.) 22. (-5.6) 2300 83. (28.) 74. (23.) 21. (-6.1) 2400 81. (27.) 73. (23.) 20. (-6.7)

Night ventilation cooling test (Test 3): For the night

ventilation cooling test, the test building was exposed

to a reduced diurnal sol-air temperature cycle and the

internal load schedule as for the previous two tests. Hourly values of the sol-air temperature cycle are given in table 3. It represents an average November

day in Saudi Arabia. Night sky radiation losses were

not taken into account in the derivation of this cycle, since they would reduce the night air temperature a few degrees, and thereby affect the ventilation response of the test building. During this cycle, the

test building was naturally ventilated during periods

when the outdoor air temperature fell below the indoor temperature (i.e., the windows and door were

opened and the ceiling fan was operated). The test building was closed in the morning when the simulated outdoor temperature rose above the indoor

temperature.

2100 to 0600. The thermostat was set at a low value so

that the valance coil operated continuously during the 9-hour period. An internal load was simulated using

incandescent light bulbs controlled by a 24-hour clock

timer. This internal load was set at 1000 Btu/hr

(290 W) from 1900 through midnight and at 500 Btu/hr (146 W) from 0100 until 0700. These loads were selected to simulate the sensible heat released from two dormitory occupants and associated lighting.

Twelve-hour night cooling test (Test 2): For the 12- hour night cooling test, the test building was

repeatedly exposed to the same hourly sol-air temperature cycle and internal load schedule as for the previous test. During this test, the valance coil was

operated during a 12-hour period from 1800 to 0600. The thermostat was set as 74 °F (23 °C), allowing the valance cooling system to cycle during the night

hours.

13
Passive solar test (Test 4): For the passive solar heating test, the test building was exposed to a sol-air temperature cycle representative of an average December day in a mid-western U.S. climate (see table

3). For this cycle, an hourly solar window heat gain

for a theoretical clear-sky 40° latitude location [5] in the month of December was simulated using infrared heat lamps. Solar window heat gains used for this test are summarized in table 4. This simulated solar heat

gain is equivalent to the theoretical solar heat gain that would enter the test building if all the double-pane

window systems were south-facing. The hourly heat

Table 4. SOLAR WINDOW HEAT

GAINS

Time, h Heat Gains

Btu/hr (W)

0800-0900 1,870. (548.) 0900-1000 4,550. (1,330.) 1000-1100 7,700. (2,260.) 1100-1200 10,200. (2,990.) 1200-1300 10,900. (2,990.) 1300-1400 11,000. (3,220.) 1400-1500 9,950. (2,920.) 1500-1600 7,250. (2,120.) 1600-1700 4,310. (1,260.) 1700-0800 0 (0)

output of the infrared heat lamps was adjusted using a

variable voltage transformer and measured using a watthour meter. The actual heat output deviated

slightly from the theoretical values due to changes in the lamp resistance and experimental error. For the

passive solar test, using data contained in ref. [7], a diurnal schedule of internal heat gains was devised to simulate the heat release for lighting, equipment, and

occupants for a residence. The test building was

assumed to be occupied by two persons during the night and by a single person during the day. The

occupancy heat input to the test building was not varied on an hourly basis; rather, the day was divided

into two periods and the simulated heat gain was

maintained constant during each period. During the daytime period from 0600 to 2100 hours, the simulated

occupancy load was maintained at 1470 Btu/hr

(430 W). At night from 2100 to 0600 hours, the simulated occupancy load was maintained at 550

Btu/hr (160 W).

As in the previous test, the test building was

repeatedly exposed to a series of sol-air temperature

cycles. The solar window and occupancy heat gains were simulated as described above. After a steadyperiodic condition was reached, the indoor

temperature response of the test building was

recorded.

14
7. TEST RESULTS

7.1 NINE-HOUR NIGHT COOLING TEST

For the 9-hour night cooling test, a steady-periodic condition was attained in four weeks. A comparison of

the predicted and measured indoor air temperatures is given in figure 4. The measured values are the average

of the four thermocouple temperatures located along

the vertical column. The predicted curve was

generated by inputting into the mathematical model

hourly measured values for the sensible heat removed

by the valance cooling coil. It can be seen that there is good agreement between the measured and

corresponding values predicted with the mathematical

model, supporting the validity of the model. It should be pointed out that previous studies [4] have shown

that inputting indoor temperatures and predicting

cooling loads result in much less agreement.

15
HOUR OF DAY FIGURE 4. COMPARISON OF MEASURED

AND PREDICTED INDOOR TEMPERATURES

FOR THE 9-HOUR NIGHT COOLING TEST

The hourly sensible loads for the cooling coil were

determined by subtracting the latent cooling load from

the total cooling load of the coil determined from eq(l).

During the operation of the cooling coil, it was

not possible to accurately measure the hourly latent load because water tended to accumulate on the fins of the coil until it became saturated and did not

readily drain into the condensate collection system.

During the first hour of operation of the valance coil, the indoor relative humidity dropped considerably

(see fig. 5). For the first hour (2100 to 2200 hours) the

latent load (^i) was estimated from the relation: q^= V-p-hj^g- Ao),. (9) where

V = volume of test building; p = density of air;

hj-g = latent heat of vaporization; and

Aw, = change in humidity ratio of indoor air.

40 I 1 1 1 1 1 1 I I I 1 I 2 4 6 8 10 12 14 16 18 20 22 24 HOUR OF DAY FIGURE 5. VARIATION OF INDOOR RELATIVE HUMIDITY OVER A 24-HOUR PERIOD

FOR THE 9-HOUR NIGHT COOLING TEST

For the remaining hours of operation of the valance

coil, the latent load (gi) was estimated from the

relation:

= (W-V.p.Ai^) . h^/(N-\) (10)

where

W — net condensate collected over a period of a day;

and

TV = number of hours of coil operation

The other symbols are as previously defined. Here the estimated water collected during the first hour is subtracted from net amount collected during a day.

This difference is assumed to condense equally during

the remaining operating period of the coil. This is a good assumption, since the indoor relative humidity

remained approximately constant during the remaining

operating period of the coil (see fig. 5).

For the 9-hour night cooling test, the total amount of condensate collected (W) during the diurnal cycle was

4.8 lb (2.2 kg). The resulting hourly sensible and latent cooling loads determined for the first test are given in table 5. Note that the latent loads are small in comparison with the sensible loads, except during the

first hour of coil operation.

When the flow of chilled water ceased, the valance

coil remained saturated with water during the period

when the cooling system was off, indicating that little water was evaporating from the coil. However, during

this same period the indoor relative humidity rose

rapidly, suggesting that an additional source of moisture was present. It was hypothesized that the source of this moisture was the wall surface (i.e., original water contained in the concrete mortar

holding the concrete blocks together). To verify this hypothesis, a polystyrene container, measuring

17x 17x23 in (43x43x58 cm), was sealed to the wall

surface. The relative humidity within this container

tended to track the rise in indoor relative humidity.

This would suggest that the source of moisture was

indeed the wall surface. A detailed analysis of wall moisture contribution to the humidity response of the

test building is given in Appendix C.

Figure 6 shows the temperatures measured at different heights within the test building. The vertical temperature gradient is observed to be greatest during

the system-on hours. However, the gradient is less than 2 °F (1 °C) at all hours of the diurnal cycle. It is interesting to note that during the daytime hours the

16
Table 5. HOURLY SENSIBLE AND LATENT COOLING LOADS REMOVED BY

THE VALANCE COIL FOR 9-HOUR NIGHT COOLING TEST,

BTU/HR (W)

Latent Time, h Sensible Latent Total fraction

Rtii/hr UlU/ 111 CW^ \^ TV f MJ I U/ III \yv

)

DIU/ HI ^ w ; /O

2100-2200 9300. (2700.) 2700. (790.) 12,000. (3,520.) 23. 2200-2300 8700. (2500.) 310. (91.) 9,010. (2,640.) 3. 2300-2400 8400. (2500.) 310. (91.) 8,710. (2,550.) 4. 2400-0100 8100. (2400.) 310. (91.) 8,410. (2,460.) 4. 0100-0200 8000. (2300.) 310. (91.) 8,310. (2,430.) 4. 0200-0300 7800. (2300.) 310. (91.) 8,100. (2,380.) 4. 0300-0400 7800. (2300.) 310. (91.) 8,110. (2,380.) 4. 0400-0500 7700. (2300.) 310. (91.) 8,010. (2,350.) 4. 0500-0600 7700. (2300.) 310. (91.) 8,010. (2,350.) 4. 0600-2100 0. (0) 0. (0) 0. (0)

FIGURE 6. MEASURED INDOOR TEMPERATURES AT VARIOUS HEIGHTS

floor-to-ceiling temperature gradient is less than 1 °F

(0.6 °C). These results support the validity of the assumption that the indoor air is perfectly mixed (see

sec. 4). The foregoing results indicated that the operation of

the valance cooling coil only during a 9-hour night

period to cool interior mass of the walls, ceiling, and

floor resulted in an adequate indoor temperature

during the day period. The observed daytime

temperature rise of 6 °F (3.3 °C) is acceptable,

although during this 15-hour period the relative humidity rose to 80 percent. The source of moisture was determined to be primarily from the masonry

surfaces of the test building. This condition was

attributed to the original water contained in the concrete mortar.

The sol-air diurnal temperature cycle used for the 9-hour night cooling test was derived from weather

data for a desert climate. It is based upon a daytime

high temperature of 1 10 °F (43.3 °C) and nighttime

low temperature of 79 °F (26 °C). This temperature

cycle is seen to be hotter than all the selected cities of

the the United States shown in table 6. It should be

noted that certain remote desert regions within the United States may exhibit temperature extremes which

exceed the simulated diurnal temperature cycle. It is therefore apparent that night mechanical cooling of a building of this type construction is a viable strategy

for all habitable locations of the United States.

7.2 TWELVE-HOUR NIGHT COOLING TEST

For the 12-hour night cooling test, the measured and

predicted indoor temperatures are compared in figure

7. The variation in indoor temperature was similar to

that found in the previous test. Good agreement was

again observed between predicted and measured

17
Table 6. THE NORMAL DAILY AIR TEMPERATURE EXTREMES AND

RELATIVE HUMIDITIES FOR SELECTED CITIES FOR JULY

High Low At

°F(°C) °FCC) RH% time

Albuquerque 91 (33) 66 (19) 36 1100

Atlanta 87 (31) 71 (22) 64 1300 Chicago 81 (27) 67 (19) 55 1200

Dallas 95 (35) 75 (24) 50 1200 Denver 88 (31) 57 (14) 36 1300 Houston 94 (34) 71 (22) 55 1200 Los Angeles 76 (24) 62 (17) 68 1000 Memphis 91 (33) 72 (22) 57 1200 Miami 89 (32) 75 (24) 64 1300 Minneapolis 84 (29) 61 (16) 56 1200

Nashville 91 (33) 70 (21) 58 1200 New York 85 (29) 68 (20) 55 1300 90 (32) 67 (19) 45 1 100 Pheonix 105 (41) 75 (24) 29 1100

Pittsburgh 85 (29) 65 (18) San Francisco 64(18) 53(12) 75 1000

Seattle 76 (24) 54(12) 66 1000

St. Louis 89 (32) 67 (19) 58 1200 Washington, DC 87 (31) 69 (21) 52 1300

necessary because the cyclic operation of the valance

coil produced fluctuations in indoor temperature.

As in the case for the previous test, the predicted

indoor temperature was obtained by inputting hourly

values of the sensible cooling load into the mathematical model (see table 7) during the night hours.

For the 12-hour night cooling test, 3.3 lb (1.5 kg) of water was collected each day, and a similar trend in relative humidity to that observed during the first test was observed for the 12-hour night cooling test. At the conclusion of this test, the sol-air cycle in the environmental chamber was continued, and the valance cooling was stopped. Unfortunately, a malfunction of the environmental chamber permitted

only 30 hours of data to be recorded. The recorded results along with corresponding values predicted with the mathematical model for 50-hours

are shown in figure 8. It is seen that the measured

indoor temperatures closely followed the predicted

values. It is interesting to note the slow rate at which

the indoor air temperature rose. After 30 hours, the indoor temperature rose only 10 °F (5.6 °C), including

the 6 °F (3 °C) rise which occurred during the first hour when the valance cooling system was shut off

indoor temperatures. For this test, the thermostat was

set at 74 °F (23 °C), and the indoor temperature rose

7 °F (4 °C) during the 12-hour daytime period when

the valance coil was not operated.

The measured values in figure 7 are the average of the

four sensors located on the vertical column time

averaged during each hour. The time averaging was

-r

SOL ftIB TEMPERATURE

PREDICTED INDOOR

O O O MEASURED INDOOR ''

3 10 12 14 16 18 20 22 24 HOUR OF DAY FIGURE 7. COMPARISON OF MEASURED

AND PREDICTED INDOOR TEMPERATURE

FOR THE 12-HOUR NIGHT-COOLING TEST

18
/ \

1 1 1

1 1 1 1 1 I I t I

/' \ / \

1 SOL AIH TEMPERATURE

/ PREDICTED INDOOR

1 0 0 o o MEASURED INDOOR

1 1

1—1

1 1 1

1—1 1 1 1 1 1 1 111' 1

1 1 1 1

z

30 UJ

ELAPSED TIME, HOURS FIGURE 8. COMPARISON OF MEASURED

AND PREDICTED INDOOR TEMPERATURES

AFTER THE VALANCE COOLING WAS

STOPPED FOLLOWING THE 12-HOUR

NIGHT-COOLING TEST

Table 7. HOURLY SENSIBLE AND LATENT COOLING LOADS REMOVED

BY VALANCE COIL FOR 12-HOUR NIGHT COOLING TEST,

BTU/HR (W)

Time, h Latent

Sensible Latent Total Fraction

Btu/hr (W) Btu/hr (W) Btu/hr (W) %

1800-1900 8,800. (2,600.) 2,700. (790.) 11,500. (3.370.) 23 1900-2000 6,000. (1,800.) 140. (41.) 6,140. (1,800.) 2 2000-2100 7,600. (2,200.) 140. (41.) 7,740. (2,270.) 2 2100-2200 6,900. (2,000.) 140. (41.) 7,040. (2,060.) 2 2200-2300 6,500. (1,900.) 140. (41.) 6,640. (1,950.) 2 2300-2400 6,200. (1,800.) 140. (41.) 6,340. (1,860.) 2 2400-0100 4,800. (1,400.) 140. (41.) 4,940. (1,450.) 3 0100-0200 4,400. (1,300.) 140. (41.) 4,540. (1,330.) 3 0200-0300 4,900. (1,400.) 140. (41.) 5,040. (1,470.) 3 0300-0400 4,400. (1,300.) 140. (41.) 4,540. (1,330.) 3 0400-0500 4,400. (1,300.) 140. (41.) 4,540. (1,330.) 3 0500-0600 4,300. (1,300.) 140. (41.) 4,440. (1,300.) 3

19
7.3 NIGHT VENTILATION COOLING TEST

For the night ventilation coohng test, the ventilation

rate during periods of night ventilation was

determined using the tracer-gas technique (see Appendix B), and found to be approximately 14 volume

changes per hour. The measured and predicted indoor

temperatures for this test are compared in figure 9. The mathematical model closely predicted the indoor

temperature during all parts of the diurnal cycle.

It is seen from figure 9 that the indoor temperature

remained below 79 °F (26 °C), even though the valance cooling system was not operated. The

mathematical model was used to predict the total cooling load that would be required to maintain the

test building at 79 °F (26 °C) if it were air conditioned

in a conventional manner. The predicted total cooling

load was 36,000 Btu (10,500 W-hr) for the sol-air cycle

shown in figure 9. This is the amount of energy that is saved by the night ventilation cooling.

The chamber dewpoint temperature for this test was

maintained at a constant value of 54 °F (12 °C). This

value is the average dewpoint temperature for Makkah

in November, as derived from site weather data. The

use of night ventilation alleviated the humidity

problem previously discussed. The night air was

observed to dry the wall surfaces sufficiently to maintain the relative humidity level below 50 percent

during daytime periods.

During this test, an investigation was made to determine the recovery time for the test building when

it was exposed to brief periods of infiltration during

the hot part of the day. This gave an indication of the

rate at which cool interior mass of the walls, roof, and

floor absorbs heat. During the hottest period of the day, the windows and doors of the test building were

opened and the ceiling fan was turned on, ventilating the test building with approximately 14 volume

changes per hour at an outdoor temperature of 120 °F

(49 °C). This ventilation rate was continued for approximately 8 minutes until the indoor temperature

tended to level off (see fig. 10). At this time, the rate of heat absorption by the walls is approximately

balanced by the energy added by infiltrating air. The

test building was subsequently closed off and the indoor temperature response was recorded. From

figure 10, it is seen that the indoor temperature of the

test building recovered within 10 minutes with cooling

being provided solely by the interior building mass.

For the night ventilation cooling test, the measured

indoor air temperature remained below 79 °F (26 °C)

without mechanical cooling. The sol-air temperature

cycle used for the night ventilation test was based on

an outdoor air temperature that ranged from a daytime high of 93 °F (34 °C) to a nighttime low of

68 °F (20 °C). Most regions of the United States exhibit

similar, or lower, temperature extremes for their peak summer months (see table 6). Therefore, it is apparent

that night ventilation is a viable cooling strategy for

this type of construction in most parts of the United

States.

1

1 1 r

SOL AIR TEMPERATURE

PREDICTED INDOOR ,'

DO MEASURED INDOOR /

HOUR OF DAY

FIGURE 9. COMPARISON OF MEASURED

AND PREDICTED INDOOR TEMPERATURES

FOR THE NIGHT VENTILATION COOLING

TEST

- SOL AIR TEMPERATURE

) MEASURED INDOOR

ELAPSED TIME, MINUTES

FIGURE 10. RESPONSE OF THE INDOOR

TEMPERATURE TO A BRIEF PERIOD OF

VENTILATION DURING THE HOT PART OF

THE DAY

20
7.4 PASSIVE SOLAR HEATING TEST

For the passive solar heating test, the measured and

predicted indoor temperature responses for the test building are compared in figure 1 1. It is seen that a near-comfort condition was maintained even with the small amount of simulated window solar heat gain

(i.e., 21 percent glass in south wall). The agreement

between the measured and predicted values is good.

SOL AIR TEMPERATURE

PREDICTED INDOOR

30 0 MEASURED INDOOR

HOUR OF DAY FIGURE 11. COMPARISON OF MEASURED

AND PREDICTED INDOOR TEMPERATURE

RESPONSE OF THE TEST BUILDING FOR

THE PASSIVE SOLAR TEST
8. SUMMARY AND

CONCLUSIONS

A well-insulated test building having high interior mass was constructed within a high-bay environmental

chamber at the National Bureau of Standards. This

test building was subjected to a series of diurnal sol-air temperature cycles, and the indoor temperature

response of this building was measured when the following three energy-conservation schemes were

implemented: night cooling using a ceiling-mounted

chilled-water valance coil; night ventilation cooling;

and passive solar heating. For a 9-hour night cooling

test, the valance cooling coil system of the test building was operated continuously during a 9-hour

night period. During the 15-hour day period, the indoor temperature was observed to rise only 6 °F

(3.3 °C). However, the indoor relative humidity rose

to 80 percent during the same period. The source of

this moisture was determined to be primarily from the masonry surfaces. This condition was attributed to the

original water contained in the concrete mortar during

its construction.

22
A similar test, using a 12-hour night cooling period, was carried out. During this test, the operation of the valance cooling coil system was thermostated and

maintained the indoor temperature at an average value of 74 °F (23 °C). For this test, the indoor temperature

rose 7 °F (4 °C) during the 12-hour daytime period

when the valance cooling coil was not operated.

The diurnal sol-air temperature cycle used for the night cooling tests was derived from weather data for a desert climate which is hotter than all habitable parts of the United States. It is therefore apparent that night

mechanical cooling of a building of this type

construction is a viable strategy for all habitable

locations of the United States. For the night ventilation cooling test, the test building was exposed to a sol-air temperature cycle having a daytime high of 93 °F (34 °C) and a nighttime low of

68 °F (20 °C). The test building was naturally

ventilated by opening the windows and operating a

ceiling fan during periods when the outdoor temperature fell below the indoor temperature. During the day period when the test building was closed, the indoor temperature remained below 79 °F (26 °C)

without mechanical cooling. Most regions of the United States are seen to exhibit similar temperature

extremes for their peak summer months. Therefore, it

is apparent that night ventilation is an energy saving

cooling strategy for buildings having this type

construction in most parts of the United States. For the passive solar heating test, the test building was

exposed to a diurnal sol-air temperature cycle

representative of an average December day in a mid- western climate. During this test, an hourly (clear day)

solar window heat gain for 21 percent glass in the south wall was simulated using infrared heat lamps. A

near comfort indoor condition was maintained even

with the small amount of simulated solar window gain.

REFERENCES

1. "Analytical Study for Building Construction Parameters on Dynamic Response for Intermittent System

Operation and Outdoor Ventilation." Technical Report No. SOM-ME-781, Skidmore, Owings and

Merrill, Chicago, January 1978.

2. "Procedure for Determining Heating and Cooling Loads

for Computerized Energy Calculations," Algorithms

for Building Heat Transfer Subroutines, ASHRAE

Task Group, 1976.

3. Mitalas, G. P. and Arsenault, J. G., "Fortran IV

Program to Calculate z transfer Functions for the Calculation of Transient Heat Transfer through Walls and Roofs," DBR Computer Program No. 33, Ottawa, Canada, June 1972.

4. Peavy, B. A., Powell, F. J., and Burch, D. M., "Dynamic

Thermal Performance of an Experimental Masonry

Building," National Bureau of Standards Building Science Series 45, July 1973.

5. ASHRAE Handbook of Fundamentals, American Society of Heating, Refrigerating and Air Conditioning

Engineers, 1977.

6. Peavy, B. A., Burch, D. M., Powell, F. J., and Hunt, C. M., "Comparison of Measured and ComputerPredicted Thermal Performance of a Four-Bedroom

Wood-Frame Townhouse," National Bureau of Standards Building Science Series 57, April 1975.

7. "Mixed Strategies for Energy Conservation and

Alternative Energy Utilization (Solar) in Buildings,"

Energy Resources Center, Honeywell, Inc., Minneapolis, Minn., 1978.

8. Kreith, F., Principles of Heat Transfer, Second Edition,

International Textbook Co., Scranton, Pa., 1965.

9. Burch, D. M. and Hunt, C. M., "Retrofitting an Existing

Wood-Frame Residence for Energy Conservation

An Experimental Study," National Bureau of Standards Building Science Series 105, July 1978.

10. Hunt, C. M. and Burch, D. M., "Air-Infiltration Measurements m a Four Bedroom Townhouse Using

Sulfur Hexafluoride as a Tracer Gas," ASHRAE

Transactions 81, Part 1, p. 186-201. 1975.

23
APPENDIX A ^ THERMOGRAPHIC SURVEY

S. J. Treado - , "

,:•

A method for investigating the thermal performance

of buildings and their components is infrared thermography. An infrared television system senses

the long-wave radiation emitted and reflected from a

surface. This radiation is received by an infra.red camera and converted into a video signal which is displayed on a color or black-and-white oscilloscope

monitor. For the color monitor, the surface temperatures are represented by 10 color-coded

i^9therm^.,jTliq temperature, difference .between

adjacent isotherm units is dependent on a sensitivity

setting of the equipment. A conventional camera is used to photograph the oscilloscope screen. A

photograph of the oscilloscope screen is called a thermogram. A more detailed description of thermographic equipment and measurement technique

is given in ref. [9]. The experiment procedure followed in carrying out

the thermographic survey was to expose the test building for several days to the diurnal cycle for tests

1 and 2. At the time of the survey, the indoor

temperature was approximately 75 °F (24 °C) and the outdoor temperature approximately 120 °F (49 °C). Each figure contains two photographs. The first shows a part of the building in the

visible spectrum; the second is a thermogram which is a thermal picture of the scene as viewed by the IR

camera. The sensitivity of the system was adjusted

such that the temperature range displayed in the ther- mal picture was 9 °F (5 °C). Therefore, each of the 10 colors displayed in the thermal picture represents

approximately a 0.9 °F (0.50 °C) temperature band. The temperature ascends from cold to hot, correspondingly left to right on the scale displayed at the bottom. The relative surface temperature between

different surfaces displayed in the thermal picture may

be determined by comparing the color of the locations with the color scale displayed at the bottom.

The first surface to be viewed was an external corner

of the test building (see fig. A.l). A vertical temperature gradient is shown along the wall surface from the floor to the ceiling. This is shown by the change from dark blue near the ground to the beginning of red-purple on the wall near the top edge

of the window. This corresponds to a change of five color isotherms on the scale, or a temperature change

of 4.5 °F (2.5 °C). The infrared picture was taken during the initial conditioning period before the test building reached a steady-periodic condition.

FIGURE A.l (a). CONVENTIONAL PHOTOGRAPH THE TEST HOUSE

FIGURE A.l (b). INFRARED PHOTOGRAPH

OF THE TEST HOUSE

Thermograms taken after a steady-periodic condition was reached showed that vertical temperature

gradients did not exist within the test building. The

relatively warm region at the corner is due to twodimensional heat transfer. Figure A. 2 shows an upper inside corner of the test building. A thermal bridge is observed in this region.

Inspection of the construction of the test building in the vicinity of the thermal bridge revealed a highconductance heat-flow path which by-passed the

insulation. The higher heat transmission through this

.24
FIGURE A.2 (a). CONVENTIONAL PHOTOGRAPH OF THE UPPER INSIDE CORNER

FIGURE A.3 (a). CONVENTIONAL PHOTOGRAPH OF THE INSIDE DOOR SURFACE

FIGURE A.2 (b). INFRARED PHOTOGRAPH

OF THE UPPER INSIDE CORNER

part is displayed in tan and red. This effect weakens

the validity of the assumption that the heat transfer is one-dimensional (see sec. 4.1). The impact of this defect and others on the overall performance of the

test building was assumed to be small. Therefore, these

defects were not corrected. Figure A.3 shows the

interior door surface of the test building. The door is observed to be warmer than the wall surfaces, indicating a relatively larger heat flow through this region. It is interesting to ftote that the doorknob

appears cooler. However, the doorknob has a lower"

FIGURE A.3 Cb). INFRARED PHOTOGRAPH

OF INSIDE DOOR SURFACE

emittance than other building surfaces displayed in the thermal picture, causing it to appear colder than other

surfaces. The C9pler spot in the center of the door is caused by the insulating effect of a small sign hanging on the exterior surface of the door. , , ,

The valance coil in operation is shown in figure A. 4. The coil is observed to create a low-temperature

region along the rear wall extending 3 to 4 feet below

the coil. This is caused by the cool valance discharge

air scrubbing the wall surface. Also seen in this

25
I it 11 Hi I

FIGURE A.4 (a). CONVENTIONAL PHOTOGRAPH OF VALANCE COIL

FIGURE A.4 (b). INFRARED PHOTOGRAPH

OF VALANCE COIL

r -tili I. . thermogram is a large temperature difference between

the wall and the window frame (blue to yellow on the isotherm scale). The thermographic system was also used to investigate the air leakage paths of the test building. For these measurements, a blower was utilized to depressurize the building, and the thermographic

system was used to detect warmer regions heated by

infiltrating air. The region of most pronounced air infil- tration was observed at the interface of the wall and

ceiling. This air leakage path can readily be seen in figure A. 5.

In summary, the bulk of the wall areas appeared to be

at a uniform temperature, except for a few areas, indicating that the test building was essentially free of thermal bridges.

FIGURE A.5 (a). CONVENTIONAL PHOTOGRAPH OF WALL/CEILING EDGE

FIGURE A.5 (b). INFRARED PHOTOGRAPH

OF WALL/CEILING EDGE

26
APPENDIX B B.2 MEASUREMENT TECHNIQUE

AIR INFILTRATION

MEASUREMENTS

Robert M. Caravello

B.l THEORY

A small amount of tracer gas, sulfur hexafluoride

(SFft), was released within the test building and the

tracer gas concentration was measured as a function of

time over a 10-hour period as it decayed. During these measurements, the indoor temperature was maintained

at 75 °F (24 °C). Mixing was achieved by using the overhead fan. The decay of tracer gas was caused by

air infiltration. For a first-order exponential decay process, the change in tracer concentration with respect to time is given by the relation:

Sulfur-hexafluoride (SF^) concentrations were

measured with a gas chromatograph equipped with an

electron-capture detector. Sampling and analysis were

performed semi-automatically. The logarithm of the

relative concentration (c/cj was was plotted as a function of time. A best-fit straight line was obtained

using a least-squares procedure. The negative slope of

this straight line was taken to be equal to the rate of

air infiltration. Further information on the SF^ tracer-gas technique

may be found in ref [10].

B.3 RESULTS

Table B.l gives the measured infiltration rates for the

test building when the indoor temperature was

maintained at a constant 75 °F (24 °C) and the outdoor

temperature was maintained constant at five different conditions.

dc V

dt ~V

(B-1)

where

c = concentration of tracer gas, ppb;

V = air infiltration rate, ftVhr (mVs);

V = volume of the test building, ft' (m'); and

t = time, hr (s).

For an initial concentration of c„, the solution to eq

(B- 1) is given by

Table B.l. MEASURED RATES OF AIR

INFILTRATION

Infiltration Rate, AT Condition

volume changes per hour °F °C

.033 40. 22 Winter

.052 70. 39 Winter

.017 0. 0 No temp.

diff

.022 -20. -11 Summer

.022 -40. -22 Summer

(B-2)

or The winter values given in table B.l were fitted to the following linear expression:

- ;

ln(c/cj I = A + B-{T,-T,) (B-3)

where

Here A and B are constants. A regression analysis gave the following correlation:

/ = air infiltration rate, volume change/hr; and

Cg = initial concentration at t=0, ppb.

The foregoing expression was used to determine the

air infiltration rate (I) from measured time decaying

values of the SF^ concentration.

/ = 0.0159 + 0.000495 • (r,-r„) (B-4)

A plot of the infiltration rate as a function of temperature difference is given in figure B.l. With a temperature difference (T, -T^) equal to 0 °F (0 °C), the

infiltration rate was 0.017 volume changes per hour.

27
TEMPERATURE DIFFERENCE, K

5 10 IS 20 25 30 35 06

I

1 1 \ 1 1 \ r- X

O 10 20 30 40 50 60 70 TEMPERATURE DIFFERENCE, °F

FIGURE B.l. RATE OF AIR INFILTRATION

PLOTTED AS A FUNCTION OF THE INSIDETO-OUTSIDE TEMPERATURE DIFFERENCE

At a temperature difference of 70 °F (39 °C), the rate of air infiltration was 0.052 volume changes per hour. These figures indicate that the test building has an extremely low rate of air infiltration due to its very

tight construction and the use of low-permeability

polystyrene insulation in the walls, ceiling, and fioor.

It should be noted that in deriving the curve given in figure B.l only winter values were used. Note that the

infiltration rate increased as the temperature difference

increased. The two summer measurements were

excluded because they did not show a correlation with

respect to temperature difference. Approximately eight door openings occurred during

each of the measurements. It is estimated that these door openings contributed approximately 0.0027 volume changes per hour,

B.4 CONCLUSIONS

Air infiltration measurements revealed that the test building possessed extremely tight construction. It was shown that air infiltration during winter could be

correlated with respect to the inside-to-outside temperature difference. Under these simulated winter

conditions, the rate of air infiltration varied from 0.017

to 0.052 volume changes per hour over a range of

inside-to-outside temperature differences from 0 to 70 °F (0 to 39 °C). For the summer measurements, the

infiltration rate was observed to remain essentially constant at about 0.022 volume changes per hour.

28
APPENDIX C

WALL MOISTURE CONTRIBUTION TO THE HUMIDITY RESPONSE OF THE TEST BUILDING

The purpose of this appendix is to present a mathematical model for predicting the indoor

humidity response of the test building. It has been

noted in the main body of the report that, when a polystyrene container, measuring 17x 17x23 in (43x43x58 cm), was sealed to the interior wall

surface, the relative humidity within the container tended to track the rise in indoor relative humidity.

This would suggest that the source of moisture that caused the indoor humidity to rise was the wall

surface (i.e., the original water contained in the mortar

holding the concrete blocks together). For the present

analysis, it is assumed that the source of moisture is indeed the wall surface. The analysis is presented

herein. The rate of change of the moisture content of the indoor air is equal to the rate of evaporation from the wall surface, or:

pV — = h A {oy,,,-oi) (C-l)

at

The quantity (pV/hA) is a time constant for a first- order exponential process. An average value for the water-vapor transfer coefficient (h) may be obtained by integrating the

right side of (C I) over the period (P) during which

the chilled-water coil is operated, or W

A I f(a),„-w)^/?

(C-3)

Here is the weight of condensate collected over the period P, and the other symbols are as previously

defined. For the first test (9-hour night cooling test), the weight of condensate collected was 4.8 lb (2.2 kg). The

temperature of the interstices of the wall was taken to be 75 °F. The saturation humidity ratio corresponding

to this temperature is 0.0188 lb water/lb dry air (or 0.0188 kg water/kg dry air). The interior surface area

(A) of the walls is 1087 ft^ (101 m^). Using measured

values for during the period P, the integral of eq (C-3) was found to be 0.0963 lb water-hr/lb-air.

Substituting these quantities into (C-3), the water- vapor transfer coefficient (h) was found to be 0.0459 lb air/hr-ft^ and the thermal time constant (pV/hA) was

found to be 7.3 hours. Therefore,

(C-4)

where

PV

density of indoor air, Ib/ft^ (kg/m^);

inside volume of test building, ft^ (m^); humidity ratio of indoor air, lb water/lb air (kg water/kg air); water-vapor transfer coefficient, lb water/hr-ft^

(kg water/s-m^);

saturation humidity ratio of interstices of wall surface, lb water/lb air (kg water/kg

air); time, hr(s); and

surface area of walls, ft^(m^);

For this analysis, it is assumed that the water-vapor

transfer coefficient (h) and the saturation humidity

ratio (Wja,) of the interstices of the wall surface are

constant. Separating the variables and applying the

initial condition:

0} = a)g at t = o we obtain the following solution to (C-l):

(C-2)

After the chilled water coil was turned off, the humidity ratio of the indoor air approached the

saturation humidity ratio of the interstices of the wall. Therefore, we can divide the numerator and

denominator of the left side by oj^^, and making use of

the approximate relation for relative humidity (<f)):

we obtain:

4> - w/oj,,

i-<i>o

(C-5)

(C-6)

Here 4>g is the initial relative humidity.

The predicted humidity response given by equation

(C-6) is compared to the measured response during the 15-hour period for test 1 when the chilled-water coil is turned off in figure C. 1. Note that the predicted

indoor relative humidity rises considerably more

slowly than the measured response. This suggests that either there is another source of moisture or that the wall is drying out more rapidly than predicted by the

29
T—I—I—I—T—I—I—I—I—I

I—I—I—

r

10 - -

I I I I I

I I I I 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ELAPSED TIME, HOURS

FIGURE C.l. COMPARISON OF MEASURED

AND PREDICTED INDOOR RELATIVE

HUMIDITY FOR THE PERIOD WHEN THE

COOLING COIL IS TURNED OFF

model. During the 15-hour off period, the temperature

of the interstices of the wall may increase above 75 °F, giving rise to an increased rate of evaporation of

water. The chilled water coil is another source of

moisture not accounted for in the model. In addition, the predicted response rises to a higher value than the measured response at the end of the 15-hour period.

This is probably because the mathematical model does

not account for loss of moisture from the space due to

air infiltration.
APPENDIX D

EVALUATION OF THE EFFECT

OF ENVIRONMENTAL CHAM

BER WALL TEMPERATURE ON

THE PERFORMANCE OF THE

TEST BUILDING

For the test carried out, the test building was exposed

to a sol-air temperature cycle. A sol-air temperature is an equivalent outdoor temperature which produces

the same overall rate of heat conduction through the opaque portions of the building envelope as would

exist if the test building were exposed to a combined

outdoor ambient air and solar load. The test building was located within an environmental chamber, and its exterior surfaces exchange heat not only by means of convection with the ambient air but also by means of

radiation with the walls of the environmental

chamber. When the temperature of the chamber walls

differs from that of the ambient air within the environ- mental chamber, the building senses an effective sol-air temperature which is different than the desired value. This causes the rate of heat conduction through the building envelope to be different than it would be if the ambient air and chamber walls were at the same

temperature.

In this appendix, the effect of radiation exchange

between a wall of the test building and the chamber

walls on the effective sol-air temperature is analyzed.

It is assumed that the results for the entire test building are very similar to the response of a single

wall. The analysis is presented herein. The heat transfer at an exterior surface of the test building is the sum of the convection and radiation exchange, or q/A = h, . (T,,-T,) + or . F„ . [(r,,+ 460/

-(r, + 460)^] (D-1)

where

q/A = heat transfer at an exterior surface of the

test building, Btu/hr-ft^ (W/ft^); = convection heat-transfer coefficient, Btu/hr-ft^-°F (W/m'-K); = sol-air temperature cycle, °F (°C);

Tj = surface temperature of test building, °F (°C);

or = Stefan-Boltzmann constant, Btu/hr-°F'' (W/K"*);

F,2 = configuration factor from surface 1 to 2 with consideration taken for the emittance

of the two surfaces; and = chamber wall temperature, °F (°C).

Treating the two surfaces as parallel flat plates, the gray-body configuration factor is given by the

relation:

F,2 = l/(l/e,+ 1). (D.2)

Here the emittance for the test building (ej was taken

to be 0.93 and emittance for the dull aluminum

chamber walls (e^J was taken to be 0.85 |8|. The heat transfer occurring at the exterior surface from combined radiation and convection is equated to the case where the chamber wall surface temperatures

are the same as the sol-air temperature. This is given by

the following relation:

q/A = {h, + h,) • (T,-T,) (D-3)

where

q/A — defined by eq (D-I); = radiation coefficient = 4 cr F,2 (/„, + 460)\

Btu/hr-ft^- °F, (W/m--K);

t„ = mean temperature between the exterior of

the test building and the chamber walls at the

sol-air temperature °F (°C); and = effective sol-air temperature, °F (°C).

The effective sol-air temperature (TJ in eq (D-3)

represents the equivalent chamber air temperature

which produces the same heat exchange that would

occur when the ambient and chamber walls are at a

different temperature.

The value of was calculated for test 4 from

recorded values of all other variables, i.e., T^^, T^, and

T^„. The ambient air and surface temperatures were

measured with thermocouples. The chamber

wall temperature was taken as the average value of

three surface-mounted thermocouples at the chamber

wall. The value of was estimated using the relation:

h, = 0.19(A7)'^^ (D-4)

where

A7' = temperature difference between surface and air, °F.

This expression is applicable to natural convection at a

vertical surface. The measured values and the calculated effective sol-air temperatures are given in columns 4 and 5 of table D.l. The effective sol-air temperature represents the temperature felt by the test building through the combined effects of radiation and

convection. Ideally, this temperature should equal the

sol-air cycle; however, this is not the case. The

maximum difference (column 6) between the sol-air

31
Table D.l. MEASURED TEMPERATURES AND CALCULATED VALUES

Chamber Building Sol-air Effective Time, h wall wall temp. sol air AT

°F(°C) °F(°C) "FfC) TfC) "FCO

0000 27.9 (-2.3) 31.1 (-0.5) 24.0 (-4.4) 25.9 (-3.4) -1.9 (-1.1) 0200 25.4 (-3.7) 28.7 (-1.8) 21.1 (-6.1) 23.2 (-4.9) -2.1 (-1.2) 0400 23.5 (-4.7) 26.7 (-2.9) 19.9 (-6.7) 21.7 (-5.7) -1.8 (-1.0) 0600 21.7 (-5.7) 24.7 (-4.1) 18.0 (-7.8) 19.8 (-6.8) -1.8 (-1.0) 0800 20.5 (-6.4) 23.9 (-4.5) 19.0 (-6.7) 19.8 (-6.8) -0.8 (0.4) 1000 27.9 (-2.3) 26.5 (-3.1) 29.5 (-1.4) 28.6 (-1.9) 0.9 (0.5) 1200 35.5 (1.9) 31.0 (-5.6) 37.4 (3.0) 36.4 (2.4) 1.0 (0.6) 1400 41.1 (5.1) 35.4 (1.9) 43.4 (6.3) 42.2 (5.7) 1.2 (0.7) 1600 43.4 (6.3) 38.5 (3.6) 43.6 (6.4) 43.5 (6.4) 0.1 (0.1) 1800 37.9 (3.3) 37.4 (3.0) 33.5 (0.8) 35.9 (2.2) -2.4 (-1.3) 2000 33.3 (0.7) 35.3 (1.8) 29.0 (-1.7) 31.2 (-.4) -2.2 (-1.2) 2200 30.7 (-0.7) 33.3 (0.7) 27.0 (-2.8) 28.9 (-1.7) -1.9 (-1.1)

and effective sol-air temperature is seen to be 2.4 °F

(1.3 °C), indicating that the test building feels the

actual sol-air temperature to within 2.4 °F (1.3 °C)

throughout the diurnal cycle. This deviation is small compared with the temperature difference across the

envelope of the test building. Therefore, the effect of

radiation exchange between the test building and the chamber walls on the heat conduction through the envelope of the test building is small.

32
NBS-n4A (REV. 2-ec) U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO. SHEET (See instructions) NBS BSS 137 July 1982

4. TITLE AND SUBTITLE

All Evaluation of Thermal Energy Conservation Schemes

for an Experimental Masonry Building

5. AUTHOR(S)

Parambir S. Gujral, Raymond J. Clark, and Douglas M. Burch

6. PERFORMING ORGANIZATION (If joint or other thon NBS. see in struct/on sj * NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

Skidmore, Owings & Merrill

33 W. Monroe Street

Chicago, IL 60603

7. Contract/Grant No.

8. Type of Report & Period Covered Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

Skidmore, Owings & Merrill National Bureau of Standards King Abdul Aziz University

33 W. Monroe Street Washington, DC 20234 Makkah Campus

Chicago, IL 60603 Saudi Arabia

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 81-600175

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a significant

bibliography or literature survey, mention it here)

A one-room masonry building with exterior polystyrene rigid board insulation was built within a large environmental chamber at the National Bureau of Standards.

Various climatic conditions were simulated within the chamber, and the transient

thermal response of the test building was monitored. Three schemes (night cooling

using a ceiling-mounted valance cooling coil, natural ventilation night cooling,

and passive solar heating) were investigated with regard to energy conservation.

The test results indicated that these operating practices resulted in a considerable reduction in energy consumption for space heating and cooling.

The measured performance of the test building compared favorably with the corre- sponding performance obtained with an analytic model.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

building thermal mass; dynamic performance of buildings; energy conservation;

heat transfer in buildings; night ventilation; night space cooling; passive solar

heating.

13. AVAILABILITY

Unlimited

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|""X| Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

[^31 Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

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