Reference

NAT'L INST. OF STAND & TECH

AiiiQt oasan

NBSIR 84-2930

Short Duration Winter-Time

Performances of Different Passive

Solar Systems

Bal M. Mahajan

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Gaithersburg. MD 20899

August 1984

Prepared for:

-QC100

.U56

U.S. Department of Energy

.ice of Solar Heat Technologies

ssive and Hybrid Solar Energy Division

}erimental System Research Program

iShington, DC 20585

34-2d30

1984

V

NATIONAL BUREAU

OF STANDARDS

library

NBSIR 84-2930 /

SHORT DURATION WINTER-TIME , PERFORMANCES OF DIFFERENT PASSIVE , ^

SOLAR SYSTEMS

Bal M. Mahajan

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Gaithersburg, MD 20899

August 1984

Prepared for: U.S. Department of Energy

Office of Solar Heat Technologies

Passive and Hybrid Solar Energy Division

Experimental System Research Program

Washington, DC 20585

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

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Director

ABSTRACT

The thermal performance of three full-sized adjoining rooms, each with a different south-facing passive feature, were monitored for two short periods

during January-February and February-March, 1984. These rooms are a Trombe

wall cell, a control cell, and a direct gain cell in the NBS Passive Solar

Test facility. During the experiments data from 436 sensors were collected.

The data include: auxiliary energy supplied, continuous air infiltration,

temperatures, solar radiation, and wind speed and direction. This report

briefly describes the test facility, instrumentation, data acquisition system

and procedures and test conditions for the experiments. The report presents

representative data and results of a preliminary analysis of the data. It

compares the performance of the three test cells, and the values of average,

centroidal, maximum and minimum air temperatures in the direct gain and Trombe

wall cells. Results indicate that regardless of the magnitude of the stratification the temperature recorded by the sensor placed in the vicinity of the

centroid of the cell was nearly equal to the average value of the cell air temperature .

The report also compares measured data with the predicted values of (1) the

ratios of various solar radiation quantities; and (2) the auxiliary energy

required to maintain the fixed value of the lower bound temperature in the

test cells. The data and predicted values show good agreement suggesting that

the procedures outlined in the "Passive Solar Design Handbook Volume Three"

for predicting these quantities are valid.

iii
NOMENCLATURE

AUXM

AUXP

Cp

»h

Hv

Ht

«b

LC

m

ONET

OREO

SSF

Ta

TAVE

TCEN

TMAX

TMIN

UA

Measured value of auxiliary energy supplied (kWh)

Predicted value of auxiliary energy requirement (kWh)

Specific heat of air (J/kgK)

Total solar irradiation on a horizontal surface (W/m^)

r\ Total solar irradiation on a south vertical surface (W/m'^)

Total solar irradiation transmitted through a glazing on a south vertical

surface (W/m^)

Ground reflected irradiation on an inverted horizontal plane (W/m^)

Direct normal beam irradiation (W/m^)

Heat loss coefficient for a cell, not including the passive solar aperture

and air infiltration (W/K) [LC = UA - loss coefficient for the solar

aperture]

Air infiltration mass flow rate (kg/hr)

Calculated value of the net reference load or the energy required to

maintain the nonsolar portion of a cell at the set temperature (kWh)

[QNET = OREO ~ Energy loss from the solar aperture]

Calculated value of energy required to maintain a cell at the set temperature (kWh)

Solar saving fraction

Ambient (outside) air temperature (®C)

Average of all air temperatures measured in a cell ("C)

Air temperature at the centroid of the cell volume (°C)

Maximum measured air temperature in a cell (°C)

Minimum measured air temperature in a cell (°C)

Overall heat loss coefficient for a cell, not including air infiltration

(W/K)

iv
TABLE OF CONTENTS

Page

ABSTRACT Ill

NOMENCLATURE Iv

1. INTRODUCTION 1

1.1 BRIEF HISTORY OF THE PROJECT 1 1.2 SCOPE OF THIS REPORT 2

2. BRIEF DESCRIPTION OF THE TEST FACILITY 3

3. INSTRUMENTATION AND DATA ACOUISITION 5

3.1 SENSORS 3

3.2 DATA ACOUISITION SYSTEM 5

3.3 DATA ACQUISITION AND DESTRIBUTION 5

4. TEST CONDITIONS 7

5. DISCUSSION OF REPRESENTATIVE RESULTS 8

5.1 SOLAR RADIATION 8

5.2 WIND SPEED AND AIR INFILTRATION 8

5.3 AIR TEMPERATURE 19

5.4 FLOOR SURFACE TEMPERATURE 31

5.5 AUXILIARY ENERGY SUPPLIED 31

5.6 COMPARISON OF SOME OF THE DATA WITH PREDICTED VALUES 46

5.6.1 Solar Radiation 46

5.6.2 Energy 46

6. CONCLUSIONS 51

7. ACKNOWLEDGEMENTS 51

8. REFERENCES 52

V
W =!••* -*. ».- 4.-*»

. a* «. _ ..... ....

^ ^

-

.* • m. -, •.'«:.» > vt -» >*. tt •• *-* «1S ^..ifim - - '^'i‘0i5

^

^ * 'iif<v^* I i ' v>r—

^’*'*.ii?.'" * *«•• •»*•*»*»*•«*., i '.j63t^W «XEj'^T>IO*OQjA*

*-'P^

' ‘ * *'*

*; •»• iBIW » o 'fi3 .*»4ffl JI^SSSJ^ ' ''.^^
1 . INTRODUCTION

1.1 BRIEF HISTORY OF THE PROJECT

In 1980, the U.S. Department of Energy (DOE) established a Program Area Plan for

the systematic performance evaluation of passive/hybrid heating and cooling

systems [1], This program area plan defines three levels of performance monitoring procedures which, in decreasing order of sophistication, have been

designated as Class A, B, and C. Both class A and class B level monitoring

involves fixed instrumentation and data acquisition equipment, while class C

level monitoring involves simple hand-recorded measurements and surveys of

occupant reactions.

Class B level monitoring provides limited detailed data (about 20 sensors per

building) from occupied buildings for field testing and statistical evaluation

of passive systems and buildings. Class A level monitoring provides carefully

measured detailed data (at least 200 sensors per building) under controlled

conditions for use in (1) detailed building energy analysis and model/algorithm

validation; and (2) performance characterization of various passive subsystems.

The National Bureau of Standards (NBS) passive solar test facility, constructed

under the sponsorship of DOE, has four full size adjoining rooms. The first room (cell //I) houses the data acquisition system and the other three rooms

(cells #2, #3, and #4) are the test cells. The test facility contains several

types of generic passive solar features such as a direct gain system, a collector

storage wall (Trombe wall), and clerestory windows. The NBS test facility was constructed as a part of the DOE’s Experimental Systems Research Program and

is used for acquiring and distributing to paticipating researchers class A

level performance data for various passive subsystems under different experimental

conditions

.

The test facility was made operational in October of 1981, with the direct gain

cell completely instrumented and the other cells minimally instrumented. A

handbook describing the NBS test facility, thermophysical properties of

construction materials, and sensor locations was published and distributed [2].

During FY82 performance data from the direct gain cell, under three different

experimental conditions, were collected and distributed to the participating

researchers. A technical paper containing the representative results from

these data was presented at the ASME Passive Solar Division Sixth Annual

Technical Conference in April 1983 [3].

In FY83 instrumentation of the Trombe wall cell was completed. A new data

acquisition system (DAS) and a multichannel continuous air infiltration monitoring

system (CAIMS) were procured and installed at the test facility. During FY83 some experiments were conducted to monitor the performance of the direct gain

and Trombe wall cells, and to measure the thermocirculation characteristics of

the Trombe wall. A paper containing a brief description of the new DAS and

CAIMS, and some representative results from the FY83 experimental work was presented at the Passive and Itybrid Solar Energy Update meeting in September

1984 [4]. The data tape containing the hourly average data sets was distributed

to the participating researchers.

1
In FY84 some additional sensors were installed in the control cell (cell #3)

in order to measure the floor surface temperatures. A comprehensive instrumentation and site handbook describing the test building, data acquisition system

and procedures, and containing a directory of the sensors installed in and

around the building was published and distributed [5]. The thermal performance

of the three test cells (a control cell, a direct gain cell, and a Trombe wall

cell) were monitored for two short duration experiments, the first for the

period of January 16 to February 13, 1984; and the second for the period of

February 17 to March 12, 1984. The data tape containing the hourly average

data sets from these experiments and copies of the data documentation were distributed to various researchers. A preliminary analysis of these data were

performed in order to: (1) characterize the performance of the different

passive solar systems, (2) compare the values of the average and centroidal

tempertures in the trombe wall cell and the direct gain cell; and (3) compare

the measured data with the predicted values of the ratios of various solar

irradiation quantities and energy requirements.

1.2 SCOPE OF THIS REPORT

This report briefly describe the test building, instrumentation, data acquisition system and procedures, and test conditions for the two performance monitoring experiments. The report contains representative data from the two performance monitoring experiments and results from a preliminary analysis of the

data, and compares the performance of the three test cells. The data presented

include: solar radiation; wind speed and air infiltration; ambient and room air

temperatures; average, centroidal, maximum and minimum room air temperatures

in the direct gain and Trombe wall cells; cell floor surface temperatures;

and auxiliary energy supplied. The report also contains predicted values of

the ratios of various irradiation quantities and the auxiliary energy required

to maintain the cells at 20‘*C, and compares the predicted values with the

measured data.

2
2. BRIEF DESCRIPTION OF THE TEST FACILITY

The NBS Passive Solar Test Facility is located in Gaithersburg, Maryland

(latitude 39°N, longitude 77.3°W) on an open area with no shading from the

surroundings. The building is a rectangular one-story slab on grade, frame

structure, with the long axis running from east to west. The building is

especially designed to be reconfigurable so that passive solar features can be

installed with minimum cost and effort. The current configuration provides

four test cells of equal area. Each cell has a floor area of 30.1 m^ and

contains a different south-facing passive feature. Cell //I houses the data

acquisition system, continuous air infiltration monitoring system, and componenttesting calorimeter; cell #2 contains a south facing Trombe wall; cell #3 contains a normal-sized double-pane casement window; cell //4 contains a south

facing direct gain fenestration. Figure 1 shows the south elevation of the

building, and Figure 2 shows the floor plan. A complete description of the

test building, including wall cross sections, physical properties of the construction material used, and sensor locations is available in reference 5.

3
Photograph of NBS Passive Solar Test Building.

Figure 2. Floor Plan of the NBS Passive Solar Test

Building

.

4
3. INSTRUMENTATION AND DATA ACQUISITION

3.1 SENSORS

A total of 457 sensors are installed in and around the test building. Of these,

26 sensors are outside the building; and 6, 173, 26, and 226 respectively are

in cells //I, //2, //3, and #4, The sensors include flow meters, heat flux meters,

pyranometers , resistance thermometers, themocouples , watt-hour meters, and

weather sensors. The general location of these sensors is summarized in Table 1.

3.2 DATA ACQUISITION SYSTEM

The data acquisition system, used for monitoring the sensors, consists of a desktop computer with 575K bytes of memory, real-time clock, and a scanner with

an intergrated digital voltmeter having 1 microvolt resolution. The system has

two cassette drives and a magnetic tape drive for data and software storage.

A completely separate system is used to monitor the air infiltration continuously

in three test cells. The multi-zone automated air infiltration monitoring

system, which uses the tracer gas decay method, was designed by Dr. Richard Grot

of NBS. A brief description of this system is available in reference 5 and a detailed description of the system may be found in reference 6.

3.3

DATA ACQUISITION AND DISTRIBUTION

The solar radiation and weather data are taken at 1 minute intervals, auxiliary

energy data are taken at 1-hour intervals, and all other data are taken at 10-

minute intervals. The data are converted to engineering units and stored on magnetic tape. Air infiltration data are stored separately on a floppy disk.

These data are later numerically integrated and averaged to create hourly

average data sets. The hourly average data sets, including air infiltration

data, are recorded onto a magnetic tape. A documentation file containing the

test conditions and an index to the data records is also recorded on the data

tape. The data tape along with a print-out of the documentation is distributed

to the participating researchers. The hourly average data sets are also archived

at the National Bureau of Standards where they are available upon request to

interested parties.

A statement of measurement uncertainty is available in reference 5. The maximum

overall uncertainty: in temperature measurements using type-T thermocouples

is estimated to be + 0.5®C; in air infiltration measurements is estimated to

be about + 10 percent [7]; and in other measurements is estimated to be + 5 percent

.

5
TABLE 1

Various Sensors Installed at the KES Passive Solar Test Facility

Iter, # Sensor Type Outside Cell #1 Cell #2 Cell #3 Cell #4

1 Flow neters (chiller 1 1 1 3 fluid)*

2 Heat flux meters 11 11

3 Resistance thermometers 2 2 3 7

A Radiation Sensors

4.1 Direct normal beam 1 1 4.2 Ground reflected 1 1 4.3 Infrared sky radiation 1 1 4.4 Total Itorirontal 1 1 4.5 Total on a south 1 vertical surface 1 2

5 Type-T thermocouples

5.1 Air 4 23 3 25 55 5.2 Black globe 3 5 8 5.3 Ceiling surface 12 12 24 5.4 East wall surface 2 3 13 18 5.5 Floor surface 12 20 12 44

5.6 Foundation 18* 54 72 5.7 Ground 12 11 46 69 5.8 Neat flux meter Surface 11 11 5.9 Heater discharge 1 1 5.10 North wall 1 3 16 20

5.11 Pink globe 2 2 5.12 Trombe wall 82 82 5.13 West wall 3 13 16

6 Watt-hour meters 6 6

7 Weather sensors

7.1 Wind direction 1 1 7.2 Wind speed 1 1

TOTAL 26 6 173 26 226 457

•CURRENTLY NOT MONITORED

6
4. TEST CONDITIONS

Two short duration performance monitoring experiments were conducted; the

first for the period of January 16 to February 13, 1984; and the second for the

period of February 17 to March 12, 1984. During the first experiment clerestory

window shutters were closed in all test cells. During the second

experiment clerestory window shutters were open in cells #2 and #4 and closed

in cell //3.

During both of the experiments, the room air temperature in the cells was allowed to float upward without restriction since no auxiliary cooling was provided. The lower bound room air temperature in the cells was fixed at 20°C

by the thermostat, and auxiliary heat was supplied as needed. The actual lower

bound temperature in the cells fluctuated between 19.5 and 20.5®C due to

thermostat hysteresis.

During both of the experiments, the north wall window shutters and the doors

between the cells were closed. The Trombe wall in cell #2 is a vented Trombe

wall; however, for these experiments vents of the Trombe wall were blocked.

No night insulation was provided for the glazings on the lower level south

wall. The fan coil unit fans were kept on in the test cells for the duration

of the experiment. Two destratifying fans, placed near the center of the

floor, were used in the direct gain cell (i.e. cell #4). One fan took the

room air from the floor level and discharged it at the sloped ceiling level

near the clerestory window; the other fan did the reverse. The combined action

of the two fans mixed the room air to reduce thermal stratification. Air

infiltration for the three cells and all of the sensors listed in Table 1 were

monitored during the experiments.

7
5. DISCUSSION OF REPRESENTATIVE RESULTS

Representative results from the hourly average data sets for a period of 13

days (0.0 a.m., January 24 to 0,0 a.m. February 5, 1984) from the first experiment

and for a period of 24 days (3.0 p.m. February 17 to 3.0 p.m, March 12, 1984)

from the second experiment are presented below. These results show data for

solar radiation, wind speed and air infiltration, ambient and room air

temperatures, floor surface temperatures, and the auxiliary energy supplied.

The results also show comparison data with the predicted values of various

solar radiation quantities, and with the auxiliary energy required to maintain

the test cells at the 20°C lower bound temperature,

5.1 SOLAR RADIATION

Measured data on solar radiation include; total on a horizontal surface, total

on a south facing vertical surface; total transmitted through a glazing on a south facing vertical surface; ground reflected radiation on an inverted

horizontal plane; and direct normal beam radiation. Figures 3 and 4 show the

variation of the total horizontal irradiance for the first and second periods

respectively. The thirteen days in the first period included six completely

sunny, four partial sunny, and three cloudy days. The twenty four days in the

second period include twelve completely sunny, eight partial sunny, and four

cloudy days. The solar radiation data was summed over the duration of the

periods and the resulting irradiation values are shown in Table 2.

Table 2, Solar Irradiation Data for the Two Periods

Quantity

January 24 to

February 5, 1984

February 17 to

March 12, 1984

Hh (kWh/m^) 29.1 77.5

(kWh/m^) 42.1 78.3

Hf (kWh/m^) 26.3 46.5

Hg (kWh/m^) 8.2 18.5

Hb (kWh/m^) 35.3 65.3

5.2 WIND SPEED AND AIR INFILTRATION

Figures 5 and 6 show the wind speed measured at a distance of about 50 m

southwest of the test building for the two experiments. Figures 7 and 8 show,

for the two experiments, the net air infiltration rates computed from the

measured values of the tracer gas concentration in the test cells. Figures 7a

and 8a, 7b and 8b, and 7c and 8c are respectively for cells #2, #3, and #4,

Although the use of one tracer gas precludes determination of intercell infiltration rates, the effects of any such infiltration must be very small because

the cell temperatures and pressures were nearly the same. The data in Figures

5 to 8 indicates that the wind speed did have some effect on the infiltration

rate, this effect, however, cannot be quantified at this time.

8
Irridance

w/m

9
800

700

600

500

400

300

200

100

0

0

Figure

96 192 288 384 480 576

Houra after 0.00 am 2-17-1984

4. Total horizontal irradiance during 2/17 - 3/12/84.

10
Wind

speed

m/s

Hours after 0.00 a.m. 1-24-1984

Figure 5. Wind speed measured at a height of 5 ni and a distance

of 5 in southwest of the building during 1/24-2/5/84

11
Wind

speed

m/

s

5

4 J

0 96 193 388 384 480 576

Hours after 0.00 a.TT!. 2-17-1984

Figure 6. Wind speed measured at a height of 5 m and a distance of

50 m southwest of the building during 2/17 - 3/12/84

12
Volume

Changes

13
Volume

Changes

Figure 7b. Air infiltration rates in cell #3 during 1/24 - 2/5/84

14
Volume

Changes

Figure 7c. Air infiltration rates in cell #4 during 1/24 - 2/5/84

15
Volume

Changes

0 96 193 388 384 480 576

Hours after 0.00 am 3-17-1984

Figure 8a. Air infiltration rates in cells #2 during 2/17 - 3/12/84

16
Volume

Changes

Hours after 0.00 am S-17-1984

Figure 8b. Air infiltration rates in cells //3 during 2/17 - 3/12/84

17
Volume

Changes

18
5.3 AIR TEMPERATURES

The outside air temperature is measured by four mechanically aspirated and

shielded thermocouples. Two of these thermocouples are place about 22 mm

from each other, about 1.2 m above ground and about 2.5 m south of the test

building; the other two thermocouples are similarly situated on the north of

the building. The room air temperature in cells #2, and is monitored by

22 shielded, 3 unshielded, and 22 shielded thermocouples, respectively. Figure

9 schematically shows the location of the sensors in cells #2 and /M; the

locations of the 22 shielded thermocouples in cells //2 are identical to those

of the 22 sensors in cell #4. The sensors are situated on the south to north

centerline of the cell. Findings from a preliminary analysis of the air temperature data are given below.

Figures 10 and 11 show the variation of ambient air temperature and room air

temperature in cells //2, #3, and //4, for the two periods respectively. The

data shown in these figures represent the average of 4 sensors for the ambient

air temperature; and the average of 22, 3, and 22 sensors for the air temperature

in cells #2, //3, and //4, respectively. As expected, the air temperature during

the solar hours was higher in cell //4 than the air temperatures in cell //2 and

//3. Due to the thermal storage effects of the Trombe wall, the cell temperature fluctuations lagged those of cells J'/3 and //4.

Figure 12 shows the variations of the average value of cell air temperature,

TAVE, and the cell centroid temperature, TCEN (i.e. temperature recorded by

sensor number 21 in Figure 9 which is located in the vicinity of the centroid

of the cell), for cell #2 for the first period. Figure 13 shows data similar

to that shown in Figure 12 for the second period. Figure 14 shows the variations

of the average temperature, TAVE, the maximum temperature, TMAX, and the minimum

temperature, TMIN, for cell //2 for the first period. Figure 15 shows data

similar to that shown in Figure 14 for the second test period. Figures 16

through 19 show data similar to that described above, but for cell #4

The data presented in Figures 12 through 19 indicate the following. (1) Despite

the use of fans (see section on test conditions for details), as expected, the

room air in cells //2 and /M was stratified, and the stratification (i.e. TMAXTMIN) was higher during solar hours than it was during nonsolar hours. (2) Due

to additional solar gain from the clerestory aperture during solar hours, the air

stratification in cell //2 was higher (up to about 13°C) during the second test

period than it was (up to about 7®C) during the first period. (3) Because

of the two additional destratifying fans, the air stratification in cell /M was about the same (up to 7®C) for both of the test periods. (4) Regardless of the

magnitude of the air stratification TAVE and TCEN were almost identical to each

other suggesting that TCEN adequately represented the average temperature of

the cell air and may be sufficient for one-nodal energy analysis simulations.

However, further investigation is needed to determine if the observation //4 stated above is valid for other experimental conf igurtions

.

19
Figure

9.

Schematic

locations

of

air

temperature

sensors

in

cells

#2

and

//4
Temperature

0 24 48 72 96 120 144 168 192 216 240 264 288 312

Hours after 0.00 a.m. 1-24-1984

Figure 11. Ambient and room air temperature variations during

2/17 - 3/12/84.

21
Temperature

® 96 193 288 384 480 576

Hours after 0.00 a.m. 2-17-1984

Figure 11. Ambient and room air temperature variations during

2/17 - 3/12/84.

22
Temperature

Hours after 0.00 a.tn. 1-24-198A

Figure 12. Variations of average and centroidal air temperature

in cell #2 during 1/24-2/5/1984

23
Temperature

u

o

88

27

26 _

25 _

24 _

23 _

22 .

21 .

20 .

19 .

18

TAUE

0 96 192 288 384

Hours after 0.00 a.m. 2-17-1984

Figure 13. Variations of average and centroidal

in cell #2 during 2/17-3/12/1984

I

i

480 576

air temperature

24
Temperature

e B4 AS 72 96 1S0 lAA 168 198 816 840 864 888 318

Hours after 0.00 a.m. 1-24-1984

' Figure 14. Variations of average, maximum and minimum air

temperatures in cell //2 during 1/24-2/5/1984

25
Temperature

Hours after 0.00 a.m. 2-17-1984

Figure 15. Variations of average, maximum, and minimum air

temperature in cell #2 during 2/17 - 3/12/84.

26
30

Figure 16. Variations of average and centroidal air temperature

in cell #4 during 1/24-2/5/1984

27
Temperature

0 96 193 388 384 480 576

Hours after 0.00 a.m. 2-17-1984

Figure 17. Variations of average and centroidal air temperatures

in cell #4 during 2/17 - 3/12/1984

28
Temperature

Hours after 0.00 a.n. 1-24-1984

Figure 18. Variations of average, maximum, and minimum air

temperatures in cell #4 during 2/17 - 3/12/84.

29
Temperature

Hours after 0.00 a.m. 2-17-1984

Figure 19. Variations of average, maxirauni, and minimum air

temperatures in cell #4 during 2/17 - 3/12/84.

30
5.4 FLOOR SURFACE TEMPERATURE

Surface temperatures of the concrete floor at four identical locations along

the south to north centerline of the three cells are presented in Figures

21 through 26; and these four locations are shown schematically in Figure 20.

Figures 21 and 22 show the data for cell //2 for the two test periods respectively.

Figures 23, 24, 25, and 26 show the data for cell #4 and cell #3 respectively.

The data presented in these figures indicates that the floor surface temperature

In the three cells was not uniform. Due to the solar irradiation received by

the floor through the south glazing during the first test period, location D1

in cell #4 (Figure 23) and location D2 in cell #3 (Figure 25) experienced higher

temperatures than the other floor locations. During the second test period location D1 in cell #4 and #3 (Figures 24 and 26) experienced the higher temperatures

for the same reason. These observations suggest that the assumption of a uniform floor temperature is not justified for passive solar systems, particularly

if a portion of the floor receives direct sunlight.

A close examination of Figures 21 through 24 also indicates that during the

solar hours the floor surface temperatures in cells #2 and #4, in general and

at location D4 in particular, were somewhat higher during the second test period

than they were during the first test period. This occurred because during the

second test period a fraction of the solar irradiation which was reflected

from the sloped ceiling reached the floor. An examination of Figures 25 and

26 reveals that due to the location of the south window in cell //3 and the

changing solar declination, different parts of the floor surface received

direct sunlight during different days of the year. This effect of the solar

declination on the floor surface receiving direct sunlight is depicted schematically in Figure 27.

5.5 AUXILIARY ENERGY SUPPLIED

The auxiliary energy supplied to the test cells is shown in figures 28 and 29

for the two test periods respectively. Figures 28a and 29a, 28b and 29b, and

28c and 29c are respectively for cells J'/2, #3 and #4. These values of auxiliary

energy include the energy used by the heaters, fans, and other energy consuming

devices such as signal conditioning equipment in the cells. These devices

establish the lower bounds to the auxiliary energy supplied that are apparent

in Figures 28 and 29. As expected, cell #4 consumed the most auxiliary energy

of the three during nonsolar hours because it had the largest heat loss through

the direct gain aperture.

31
Figure 20. Schematic location of floor surface sensors in

cells #2, #3, and #A.

32
Temperature

Figure 21. Variations of floor surface temperatures in cell ^2

during 1/24-2/5/1984

33
Temperature

0 06 102 288 384 480 576

Hours of ter 0.00 om 2-17-84

Figure 22. Variations of floor surface temperature in cell #2

during 2/17-3/12/1984

34
Figure 23. Variations of floor surface temperature in cell //A during 1/24-2/5/1984

35
40

38

36

34

32

30

28

26

24

22

20

18

16

Figure 24. Variations of floor surface temperature in cell #4

during 2/17-3/12/1984

36
Temperature

Figure 25. Variations of floor surface temperature in cell //3 during 1/24-2/5/1984

37
Temperature

28

26

24

u

o 22

20

18

16

8 06 162 288 384 480 576

D1

- 02

T

1 1 1 1 r

Figure 26.

Hours offer 0.00 om 2-17-84

Variations of floor surface temperature in cell ^^3 during 2/17-3/12/1984

38
All dimensions in centimeters

Figure 27. Effects of the solar declination on the floor

surface in cell

39
Auxiliary

Energy

supplied

per

hour

(kWh)

40
Auxiliary

Energy

supplied

per

hour

(kWh)

0 24 48 72 96 120 144 168 192 216 240 264 288 312

Hours after 0.00 am 1-24-1984

Figure 28b. Auxiliary energy supplied to cell //3 during 1/24 - 2/5/84

41
Auxiliary

Energy

supplied

per

hour

(kWh)

42
Auxiliary

Energy

supplied

per

hour

(kWh)

Figure 29a. Auxiliary energy supplied to cell #2 during 2/17 - 3/12/84

43
Auxiliary

Energy

supplied

per

hour

(kWh)

Hours after 0.00 am 2-17-1984

Figure 29b. Auxiliary energy supplied to cell #3 during 2/17 - 3/12/84

44
Auxiliary

Energy

supplied

per

hour

(kWh)

a

0 96 198 888 384 480

Hours after 0.00 am 8-17-1984

Figure 29c. Auxiliary energy supplied to cell #4 during

576

2/17 - 3/12/84

45
5.6 COMPARISON OF SOME OF THE DATA WITH PREDICTED VALUES

5.6.1 Solar Radiation

For the purpose of comparison, the ratios of various solar irradiation quantities

were calculated from the measured data given in Table 2 and predicted by following

the procedure outlined in the Passive Solar Design Handbook Volume Three [8].

The results are presented in Table 3 and show very good agreement between the

measured and predicted ratios of various solar irradiation quantities.

Table 3. Ratio of Various Solar Irradiation Quantities

January 24 to

February 5, 1984

February 17 to

March 12, 1984

Ratio Measured Predicted Measured Predicted

1.447 1.410 1.010 1.041

I^/Ho 0.625 0.649 0.594 0.610

Ht/Hh 0.904 0.915 0.600 0.634

%/Hh 0.282 * 0.239 *

* Assumed in reference 8 to be 0.3.

5.6.2 Energy

For the purpose of comparison, the auxiliary energy required to maintain cell

temperature during the test periods was computed in two different ways. First,

the energy required to maintain the test cells at the 20°C lower bound temperature in the absence of the solar radiation was calculated as:

n OREO = I [(UA + m Cp)(20-Ta)]i (1)

i

where n = the duration of the test period in hours, and where other quantities

are defined in the nomenclature.

Second, the predicted auxiliary energy required, to maintain the test cells at

the 20°C lower bound temperature, was calculated as:

AUXP = ONET (1 - SSF) (2)

where, QNET, the net reference load or the energy required to maintain the

nonsolar portion of the test cells at the 20°C lower bound temperature is calculated as:

46
(3)

n ONET = I [(LC + M Cp)(20-Ta)]i

Note that the difference between ONET and OREO is the energy loss through the

solar aperture. Both the OREO and ONET are calculated by using the hourly averages

of the measured values of air infiltration (m) and ambient temperature (Ta).

The solar saving fraction, SSF, was estimated by following the procedures outlined

in Appendix C of reference 8. For this calculation the Trombe wall in

cell //2 of the NBS test facility was taken as reference design type G2 as defined

in reference 8 for both test periods. Cell #3 was taken to be of reference design

type A1 for both test periods and Cell //4 was taken to be of reference design

type Cl for the first test period (when the clerestory window shutters were

closed) and type A1 for the second test period when the clerestory window shutters

were open). Measured solar irradiation data, and degree days computed from

the measured values of ambient temperature (Ta) and the 20°C fixed base temperature were used in the calculation of SSF.

The auxiliary energy supplied (shown in Figures 28 and 29) has been summed

over the test periods and the resulting values of total auxiliary energy

supplied, AUXM, are shown in Tables 4 and 5 and Figures 30 and 31 along with the

values of AUXP, ONET, and OREQ. The values of SSF, LC, and UA are also shown

in Tables 4 and 5. The data presented in Tables 3 and 4 and Figures 30 and 31

show a good agreement between AUXM and AUXP.

Table 4. Energy Values and SSF for the Three Test Cells for a Period of 312

Hours During the January-February , 1984 Experiment

Quality Cell //2 Cell #3 Cell #4

AUXM (kWh) 89.3 129.9 225.3

AUXP (kWh) 95.9 130.0 229.3

ONET (kWh) 141.0 139.0 259.3

OREO (kWh) 244.9 195.0 422.6

LA (W/K) 18.2 18.2 37.9

UA (W/K) 32.6 27.8 66.0

SSF 0.32 0.03 0.116

47
Table 5. Energy Values and SSF for the Three Cells for a Period of 576

Hours During the February-March , 1984 Experiment

Quality Cell #2 Cell #3 Cell #4

AUXM (kWh) 186.8 260.0 454.5

AUXP (kWh) 188.8 247.7 459.0

QNET (kWh) 250.7 260.0 494.2

OREQ (kWh) 553.4 493.0 869.8

LA (W/K) 17.2 18.2 37.9

UA (W/K) 46.4 41.6 74.0

SSF 0.247 0.025 0.071

48
Energy

kWh

450

Figure 30. Total values of various energies for the 13-day

period during 1/24-2/5/84

49
Energy

kWh

Figure 31. Total values of various energies for a 24-day period

during 2/17-3/12/84

50
6. CONCLUSIONS

Although the primary purpose of these experiments was to acquire detailed

performance data for model validation, some characterization of the passive

subsystems is also possible. Based on the data of these short-duration wintertime performance monitoring experiments the following conclusions may be drawn,

1) The Trombe wall cell (i,e, cell #2) performed best of the three test cells

in terms of its solar saving fraction and energy consumption, 2) Regardless

of the magnitude of the air stratification, the temperature recorded by the sensor located in the vicinity of the centroid of the cell represents the average

temperature of the cell air in the direct gain and Trombe wall cells, 3) The

floor surface temperature in the test cells was not uniform. The assumption

of a uniform floor temperture is not justified for passive solar systems, particularly if a portion of the floor receives direct sunlight, 4) The direct

gain cell (i,e, cell //4) consumed the largest amount of auxiliary energy of

the three cells, and had the largest upward temperature (average values) fluctuations, 5) The good agreement between the data and predicted ratios of

various solar irradiation quantities and between measured and predicted values

of auxiliary energies suggests that the procedures for predicting these quantities

outlined in reference 8 are valid,

7 , ACKNOWLEDGEMENTS

This work is sponsored by the Passive and Ifybrid Solar Heat Technologies, U,S,

Department of Energy, Washington, DC 20585, as part of the experimental system

research program.

The author wishes to express his sincere gratitude to Dr, Kent A, Reed and Dr,

Stanley T, Liu for their many valuable suggestions, and Mr, Donn F, Ebberts for

his valuable contributions in instrument installation.

51
8 REFERENCES

1, "Program Area Plan: Performance Evaluation of Passive/ Itybr id Solar Heating

and Cooling Systems," Solar Energy Research Institute Report SERI/PR-721-788

,

October 1980, Golden, CO,

2. Lindler, Keith W., "National Bureau of Standards Passive Solar Test Building

Handbook," NBS-GCR-82-398 , August 1982, National Bureau of Standards Wasington,

D.C. 20234.

3, Mahajan, Bal M, and Liu, Stanley T., "Initial Results from the NBS Passive

Solar Test Facility," Proceedings of the ASME Solar Division Sixth Annual

Technical Conference, April 19-21, 1983,

4, Mahajan, Bal M, and Liu, Stanley T., "Results from the NBS Passive Test

Facility - A Status Report," Proceedings of the Passive and Itybrid Solar

Energy Update, September 26-28, 1983,

5, Mahajan, Bal M,, "National Bureau of Standards Passive Solar Test Facility - Instrumentation and Site Handbook," NBSIR 84-2911, Aug, 1984.

6. Grot, R, A,, Hunt, C. M,, and Harrje, D, T, , "Automatic Air Infiltration

Measurements in Large Buildings," Proceeding of the First AIC Conference

Infiltration and Measuring Techniques; Windsor, U, K, , October 8-10, 1980,

7. ASTM Standard E741.80, "Standard Practice for Measuring Air Leakage Rate

Using Tracer Dilution Method." ASTM, 1980.

8. Jones, R. W,, Balcomb, J. D., Kosiewick, C, E. , Lazarus, G. S., McFarland,

R, D, and Wray, W, 0., "Passive Solr Design Handbook Volume Three: Passive

Solar Design Analysis," DOE/CS-0127/3, July, 1982,

52
U.5. OEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET (See instructions) NBSIR 84-2930 ^eptewbey 1984

4. TITLE and subtitle

SHORT DURATION WINTER-TIME PERFORMANCES OF DIFFERENT PASSIVE SOLAR SYSTEMS

5. AUTHOR(S)

Bal M. Mahajan

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8 . Type of Report & Period Covered

WASHINGTON, D.C. 20234

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

U.S. Department of Energy

Office of Solar Heat Technologies

Forrestal Building

Washington, D.C. 20585

10. SUPPLEMENTARY NOTES

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)

The performances of three full-sized adjoining rooms, each with a different southfacing passive feature, were monitored for two short periods during January-February

and February-March, 1984. These rooms are a Trombe wall cell, a control cell, and a direct gain cell in the NBS Passive Solar Test facility. During the experiment data

from 436 sensors were collected. The data include: auxiliary energy supplied, con- tinuous air infiltration, temperatures, solar radiation, and wind speed and direction.

This report briefly describes the test facility, instrumentation, data acquisition

system and procedures and test conditions for the experiments. The report presents

representative data and results of a preliminary analysis of the data. It compares

the performances of three test cells, and the values of average, centroidal, maximum

and minimum air temperatures in the direct gain and Trombe wall cells. Results

indicate that regardless of the magnitude of the stratification the temperature

recorded by the sensor placed in the vicinity of the centroid of the cell was equal

to the average value of the cell air temperature.

The report also compares data with the predicted values of (1) the ratios of various

solar radiation quantities; and (2) the auxiliary energy required to maintain the

fixed value of the lower bound temperature in the test cells. The data and predicted

values show good agreement suggesting that the procedures outlined in the "Passive

Solar Design Handbook Volvime Three" for predicting these quantities are valid.

12. KEY WORDS (Six to twelve entries; aiphabetical order; capitalize only proper names; and separate key words by semicolon s- auxiliary; average; centroidal; comparison; data; energy; passive solar; performance;

predicted value; surface; systems; temperatures

13.

AVAILABILITY

[X_j Unlimited

I I For Official Distribution. Do Not Release to NTIS nn 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

58

15. Price

$ 10.00

U^COmm-O* *
;V-;

/y->.

(f ,|iA' ;• iiM ’ -j|(s#ii^i

*1,

fill -'i^lm-^jlK^j^i^^ Mt»it;\!ir^;4^

mi^'T.