NBS

A1110D TfitEMfl PUBLICATIONS

NBSIR 79-1799

Performance of a Packaged

Solar Space- Heating System

Used With a Mobile Home

Dennis E. Jones

James E. Hill

NAT'L INST. OF STAND & TECH R.I.C.

A111D4 T 3 T b T

Building Thermal and Service Systems Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

August 1 979

Issued September 1979

Prepared for Division of Energy, Building Technology, and Standards

Department of Housing and Urban Development

Washington, D.C. . 20410

100

1)56

79-1799

1979

C.2

RsUonat Bures® FEB 1 1980

cvcc -6u/c

NBSIR 79-1799

PERFORMANCE OF A PACKAGED

SOLAR SPACE-HEATING SYSTEM

USED WITH A MOBILE HOME

Dennis E. Jones

James E. Hill

Building Thermal and Service Systems Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

August 1979

Issued September 1979

Prepared for Division of Energy, Building Technology, and Standards

Department of Housing and Urban Development

Washington, D.C. 20410

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Luther H. Hodges, Jr., Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director

PERFORMANCE OF A PACKAGED SOLAR SPACE-HEATING SYSTEM

USED WITH A MOBILE HOME

by

Dennis E. Jones

James E. Hill

ABSTRACT

As part of a continuing program to develop test methods for solar heating

equipment, NBS is now developing a standard test procedure for packaged

solar space-heating systems similar to test procedures now used for solar

collectors and thermal storage devices, and now under development for packaged solar water-heating systems. As a first step, a mobile home, which

was previously tested for thermal performance in an environmental chamber,

was equipped with a packaged solar space-heating system using air-heating

collectors and pebble-bed storage. The system was fully instrumented and

data were collected over the 1977-78 heating season at the NBS site in

Gaithersburg, Maryland. The performance of the system was determined and

various methods of correlating performance were explored.

Key Words: Mobile home; packaged solar space-heating system; rating;

standards; testing.

iii
TABLE OF CONTENTS

Page

ABSTRACT.... iii

1. INTRODUCTION AND BACKGROUND 1

2. TESTING AND RATING PROCEDURES 2

3. DESCRIPTION OF MOBILE HOME 4

4. DESCRIPTION OF SOLAR SYSTEM.. 4

5. DESCRIPTION OF INSTRUMENTATION AND TESTS 10

6. DATA REDUCTION AND PERFORMANCE ANALYSIS 20

7. TEST RESULTS 26

8. CORRELATION OF SYSTEM PERFORMANCE 31

9. SUMMARY AND CONCLUSIONS 36

10. REFERENCES 38

iv
PERFORMANCE OF A PACKAGED SOLAR SPACE-HEATING SYSTEM

USED WITH A MOBILE HOME

by

Dennis E. Jones

Janes E. Hill

I. INTRODUCTION AND BACKGROUND

The National Bureau of Standards (NBS), began in 1974 a program of developing test procedures for solar heating and cooling equipment, with support from the National Science Foundation (NSF), Energy Research and

Development Administration (ERDA), and later the Department of Energy

(DoE). The objective of the program is to encourage the adoption of consensus standards in the solar heating and cooling industry. The first

test procedures developed at NBS were for solar collectors and thermal

storage devices [1-5]. They were first published in early 1975 [1,2]

and made available to the American Society of Heating, Refrigerating and

Air-Conditioning Engineers (ASHRAE). As a direct result of this effort,

ASHRAE was able to adopt standards for both components in early 1977

[6,7].

Based on the current trend of solar energy use in this country, the next

logical step is to develop a standard test procedure for solar domestic

water-heating systems. ASHRAE has formed a committee to develop such

a standard and NBS is actively participating in its work. There are some packaged solar space-heating systems on the market. A packaged system

is defined as one in which all major components (collectors, storage,

controls, etc.) are contained within a single integral unit. It was

felt appropriate to begin the development of a testing standard for such

systems. This report describes the first steps at NBS toward the development of such a document.

During 1975 and 1976, the staff of NBS did extensive testing of a mobile

home in the Bureau’s large environmental chamber to completely determine

its thermal characteristics. The heating demand and part load characteristics of the gas-fired, forced-air, sealed-combustion furnace system

were determined for a complete range of outdoor conditions. Air leakage

measurements were performed on the home using two different experimental

techniques, and thermographic equipment was used to locate defects in

the installation of the wall insulation. Reports are available on the

complete test series [8,9].

Following the completion of that test program, it was decided to locate

the mobile home outside on the Bureau grounds and retrofit it with a packaged solar space-heating system. In this way, the Bureau could begin

examining the characteristics of such systems in anticipation of the

development of an applicable test standard. In January, 1977, the Bureau

purchased the only packaged system known to be widely available. It was shipped to Gaithersburg in February, 1977, installed next to the mobile

1
home, instrumented, and began operating in mid-March, 1977. Initial

instrumentation and testing were designed to provide only preliminary

data over the last few weeks of the 1976-1977 heating season. These

data were forwarded to the Department of Housing and Urban Development

(HUD) in a preliminary report [10]. During the summer of 1977, the

collector was isolated from the rest of the system and tested separately.

More detailed instrumentation was installed over the summer and the

system was operated over the entire 1977-78 heating season. The purpose

of this report is to describe these latter tests, present test results,

and discuss various techniques that could be used to describe the performance of such systems.

2. TESTING AND RATING PROCEDURES

Remmers and Kier have proposed a test procedure for rating residential

solar space-heating systems [11]. The proposed test is intended to be

implemented in the field after installation of a complete system onto a building and with a minimum of instrumentation. The test lasts six days

and begins with the thermal storage subsystem fully discharged on the

morning of the first day. For the first two days, the collector is

allowed to operate in its normal mode and no energy is withdrawn from

storage during this period. For the following three days, the collector

is not allowed to operate and no energy is withdrawn from the storage

device. On the sixth day, energy is withdrawn from the storage device

but the collector is still not allowed to operate. By making appropriate

measurements of incident solar radiation during the first two days and

of temperatures around and flow rate through the various subsystems for

all six days, the data are reduced and analyzed to give:

2 a. collection capability in Btu/ (ft day) for the first two days

and

b. storage capability in percentage of collected energy delivered

after three days of operation under stagnation conditions.

This test has been conducted on at least one solar space-heating system

[12]. The basic drawback to this testing procedure is that the value

of the collection capability is a unique function of the value of the

variables controlling the system performance that occurred during the

test, such as incident radiation, ambient temperature, and to a lesser

extent the wind velocity. In addition, the collection is begun under

the ideal situation of a fully discharged storage device. The numerical

values of such a rating would only be applicable under the conditions

that existed during the test.

Wolff [13] has proposed a very similar test procedure but with some notable modifications:

a. the collector is run during the night between the first and

second test days in order to gather heat loss data,

2
b. the storage device is fully charged through the use of an auxiliary energy source, if necessary, at both the beginning

and end of the three day stagnation period, and

c. considerably more detailed data are obtained than in [11] and

all data are reduced to relate the efficiency of the collector

array as a function of incident solar radiation and the difference in temperature between the collector outlet and

ambient air, and the performance of the storage device and

space-heating and air conditioning energy delivery devices

as a function of the appropriate temperatures and temperature

differences

.

This type of testing overcomes the basic disadvantage of that recommended

in [11] in that the performance of the device can now be predicted for

other operating conditions. The rating for the device is obtained by

using the basic equations in a computer model in conjunction with hourby-hour weather data for a complete year and location of interest to

predict the yearly energy delivered by the system. The main disadvantage of this procedure is the significant amount of modeling required

once the testing is complete. In addition, it is felt that specific

requirements would have to be added concerning the environmental conditions that exist during the test and/or additional test days will be

necessary in order to establish relations for the performance of the

subsystems which are accurate under all types of conditions.

A third possible procedure for testing and rating solar space-heating

systems is to gather data on the assembled system and establish a "correlation" of the primary performance factor of interest such as the

fraction of the load met by solar energy (solar fraction) as a function

of operating and environmental variables. If such a correlation were

successful, yearly or at least monthly average values of the operating

and environmental variables could be selected and yearly or monthly solar

fractions could be obtained directly from the correlation with relatively

simple calculations. Klein, Beckman, and Duffie [14, 15, 16] have shown

through a large number of computer simulations using TRNSYS [17, 18]

that for space-heating and water-heating systems, monthly solar fraction

correlates very well with two variables. One includes the monthly incident solar radiation, optical efficiency of the collector, and the

monthly load. The second variable includes the monthly heat loss from

the collector (with respect to a reference temperature) and the monthly

load. Liu and Hill [19] investigated how a very similar correlation

could be used as the basis for a standard test procedure for solar

domestic water-heating systems. Balcomb and Hedstrom [20, 21] have shown

through hour-by-hour simulations that solar fraction for a space-heating

system correlates very well on a month-by-month basis as a function of

"solar load ratio," the ratio of the monthly total solar radiation falling on the collectors to the monthly load. Because of the potentially

simpler form of this correlation compared to that of Klein, Beckman and

Duffie, it has been used in Section 8 of this report to analyze the

data for the space-heating system which was tested.

3
3. DESCRIPTION OF MOBILE HOME

The mobile home was a factory-produced two-bedroom model having nominal

dimensions of 15.2 m (50 ft) by 3.7 m (12 ft) with a 2.1 m (7 ft) interior

height. Nominal dimensions include a 1.2 m (4 ft) hitch, making the

actual length 14 m (46 ft). Floor construction was R-4 insulation over

0.16 cm (1/16 in.) asphalt-impregnated underlayment , 5. 1 x 15.2 cm (2x6 in.) floor joists with heating ducts running the entire length,

and with carpet and vinyl floor covering on top. Exterior wall sections

were R-7 insulation friction-fitted between 5.1 x 10.2 cm (2 x 4 in.)

framing with corrugated aluminum outside siding. The roof section consisted of R-14 insulation between framing members and over a 6-mil

polyethylene film with a 1.9 cm (3/4 in.) fiberboard ceiling material

and a sheet metal roof covering the top.

The mobile home was manufactured in Ephrata, Pennsylvania, and transported

by tractor to NBS. When it was originally placed in the NBS environmental

chamber, all utilities —electricity, water, natural gas and drainage

were connected. At its location outside, only electricity was connected.

After movement to the outdoor test site, supports were placed under the

chassis to take weight off of the tires, for leveling, and to reduce

vibration. Sheet metal skirting was also installed at the outer periphery between the bottom of the mobile home and the ground, and storm

windows were installed, as was done in the environmental chamber. The

home was factory-furnished with refrigerator, stove, two beds, dining

room table and four chairs, couch and divan, and curtains and draperies

for the windows. Figure 1 shows the home as it was installed in the

environmental chamber. Figure 2 shows it equipped with the solar system

at the outdoor test location.

The home came supplied with a warm-air, gas-fired, sealed-combustion

furnace which was rated at 16,500 W (56,500 Btu/h) input and 13,200 W

(45,200 Btu/h) output at the bonnet. For determining the efficiency of

the gas furnace during the indoor test program, the plenum was modified

to contain electric resistance heating elements. These electric heaters

were used as the auxiliary energy source in the present study. The voltage supplied to the elements was controlled by a variable transformer.

The thermostat was located in the hallway between the doors to the bedroom and furnace room.

4. DESCRIPTION OF SOLAR SYSTEM

The solar system used in the present study was purchased and shipped

from the factory in New York and delivered to NBS by truck. The unit

was a self-contained package with collector, two fans, dampers, controller, and controller sensors housed within one A-frame container.

The collector was covered with a hinged reflecting surface during transport. After placement at the site, this cover was opened and laid flat on the ground in front of the collector to reflect additional solar

energy onto the collector surface. The dimensions of the unit were

4.0 x 2.4 m (13 x 8 ft) at the base with a height of 2.4 m (8 ft) at the

4
Figure 1. Mobile home in the environmental chamber.

Figure 2. Mobile home equipped with the solar system at its outdoor test site.

5
apex. It weighed approximately 680 kg (1500 lb) as delivered from the

the factory.

The only steps necessary to put the unit into operation at the site were filling the storage bin with rock, connecting the unit to the mobile

home distribution system with insulated duct, and interfacing the controls with the mobile home thermostat. All these operations were performed for NBS by the manufacturer's local contractor.

A schematic drawing of the unit is shown in Figure 3 with a cross-section

looking down from above in Figure 4. It had basically four modes of

operation, one for charging the pebble-bed and three for supplying heat

to the house. In the charging mode, when the temperature sensor mounted

on the collector absorber surface indicated a temperature 5.6°C (10°F)

greater than the temperature in the "hot" side of the storage bin, the

collector fan turned on and circulated air from the storage bin through

the collector and back to the rocks. This continued until the temperature difference dropped below 2.8°C (5°F). In the first of the three

supply modes, when the mobile home thermostat called for heat, the

distribution blower in the solar unit turned on to deliver hot air

from the storage bin to the home. If after 15 minutes the home thermostat was not satisfied, the auxiliary electric heater in the home turned on and space-heating was accomplished by a combination of the solar

system and auxiliary energy sources. The second supply mode was designed

to deliver hot air directly from the collector to the home when the

pebble-bed charging mode occurred simultaneously with having to supply

heat to the home. The third mode occurred when the "hot" side storage

temperature dropped below 24°C (75°F). In this case, the solar system

delivery blower turned off altogether and space-heating was accomplished

solely by the auxiliary electric heaters and blower.

The solar collector used is shown schematically in Figure 5. It was basically a double-glazed air-heater in which the air passed over the

absorber and under the inner glazing. The absorber was a finned metal

plate coated with a non-selective flat-black paint. A horizontal aluminum reflector was located in front of the unit, as already mentioned, so as to reflect additional solar radiation onto the collector. The solar

collector had a nominal area of 8.9 nr (92 ft 2

) and an aperture area

of 8.2 m

2 (88 ft 2

). The reflector had an area of 8.9 m (96 ft ).

The pebble-bed contained approximately 11,300 kg (12.5 tons) of crushed

stone with a nominal diameter of 5 cm (2 in.). The stone was crushed

bluestone obtained at a local quarry and installed by the manufacturer's

local distributor. The stone was not washed prior to installation in

the unit. The duct work connecting the solar system to the mobile home

consisted of two straight runs of approximately 3.1 m (10 ft) each of

urethane foam square ducting with aluminum foil on the inside. The duct

cross-sectional dimensions were 33 x 33 cm o.d. (13 x 13 in.) and

20 x 20 cm i.d. (8x8 in.).

6
7

Figure

3.

Schematic

drawing

of

the

packaged

solar

system.
South

Figure 4. Schematic top view of the packaged solar system.

8
Frame

Insulation

2 Glass

Covers

Vertical

Vanes

Inlet and

Outlet Ducts

Figure 5. Schematic cross-section of the solar collector in the solar system.

9
5. DESCRIPTION OF INSTRUMENTATION AND TESTS

An energy flow diagram for the solar system and mobile home is shown in

Figure 6. The testing of the system involved determining the energy

flows across the control volume indicated, in addition to determining

some of the internal energy flows. The system was instrumented

using two different levels of sophistication. On one hand, a bare minimum of instrumentation necessary to determine the fraction of the load

supplied by solar energy was installed and used throughout the period

March, 1977 to April, 1978. In addition, detailed instrumentation was installed to determine as many important system parameters as possible

so that the performance of the system could be examined in detail. The

detailed level of instrumentation was used for the period December, 1977

to April, 1978. T

Simplified Instrumentation

The heat loss characteristics of the mobile home were determined in previous tests in the large NBS environmental chamber over a complete

range of outdoor conditions [8]. Based on these tests, equations were developed relating heating load to indoor-outdoor temperature difference.

Figure 7 is a plot of total energy input under steady-state conditions

as a function of inside-outside temperature difference. The heating

requirements of the home were found to be approximately 9.5 MJ/(°C*day)

(5000 Btu/ ( °F* day) ) at zero wind speed and 11.4 MJ/°C*day (6000

Btu/°F*day)) at 5.8 m/s (13 mi/h) which existed on the average for the

time period covered by this test.

The original furnace in the mobile home was a gas-fired, forced-air,

sealed-combustion unit. As already mentioned, the plenum was modified

during the tests in the environmental chamber to house electric resist- ance heaters in order to simplify energy measurements. These resistance

heaters continued to be used as the auxiliary heaters during this solar

test program, and calibrated watt-hour meters provided accurate and reliable measurements of auxiliary energy used.

The three fans in the solar system were each connected to a calibrated

watt-hour meter to obtain fan operating energy requirements. Total electric energy to the home and solar system was also measured by another

calibrated watt-hour meter. The internal heat generated from lights,

relays, and test equipment was determined by difference.

Air temperatures were measured using laboratory-fabricated type-T thermocouples. The incident solar radiation on the 60° tilted surface (collector tilt) was measured using a precision spectral pyranometer which was located several meters from the solar system to avoid measuring reflected

radiation from the collector reflector.

Through use of the watt-hour meters, monitoring of indoor and outdoor

air temperature, and measurement of the incident solar radiation on the

tilted surface (plus the previously-determined correlation relating

10
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x

UJ

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Figure

6.

Schematic

representation

of

the

energy

balance

occurring

on

the

mobile

home

equipped

with

the

solar

system.
WITHOUT

STORM

WINDOWS

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TEMPERATURE

DIFFERENCE

INSIDE

TO

OUTSIDE,

°C
heating load to indoor-outdoor temperature difference), it was possible

to determine the solar fraction.

Detailed Instrumentation

Table 1 is a summary of the detailed instrumentation used, and the asso- ciated sensor locations can be seen in Figure 8.

Prior to beginning testing using the detailed instrumentation, the collector thermal characteristics were determined by isolating the collector

from the rest of the system and performing collector efficiency tests

similar to those described in ASHRAE Standard 93-77 [6]. The reflector

in front of the collector complicated the determination of collector performance characteristics, since it produced a non-uniform radiation field

on the collector surface which was very difficult to measure. To eliminate this complication, the reflector was covered with a flat black material during the collector tests.

The collector test loop configuration was similar to that shown in the

schematic diagram of Figure 9. Type-T thermocouples were used to measure

temperatures at the collector inlet and exit. A six-junction type-T

thermopile was used for measuring differential temperature across the

collector. The static pressure drop across the collector was measured

using a slant-gage manometer. The fan was located so that it "pulled"

air through the collector array, creating a slight negative gage pressure

on the collector. Electric resistance heaters were used to heat ambient

air to the desired collector inlet temperature. The primary flow measuring device was downstream of the collector array and consisted of a receiving chamber, discharge chamber, and a 7.6 cm (3 in.) A.S.M.E.

nozzle. A commercial diaphragm type pressure transducer continuously

monitored pressure difference across the nozzle and a slant-gage mano- meter was used to measure gage pressure at the nozzle throat. The

resulting collector performance curve is shown in Figure 10.

One of the major problems in testing solar systems which use air as the

working fluid is measuring air flow accurately within the system without

disturbing system performance. Accurate air flow measurement with stateof-the-art methods requires either flow elements which result in high

pressure drops in the system or "hot-wire" equipment which requires

frequent calibration and careful installation. Neither of these methods

is satisfactory for system testing over a long period of time. An alternative, used in this study, was to calibrate the collector as a flowmeasuring element. The collector on the system being studied at NBS had

a pressure drop of approximately .19 kPa (0.75 in. of water) under normal

operation which allowed use of reliable, inexpensive electronic pressuredifference measuring devices. The high pressure drop also minimized

the effects of local variations in atmospheric pressure on the measurements.

Following the collector tests, the collector was "calibrated" using the

A.S.M.E. nozzle in series with the collector. A plot of air flow versus

13
Table 1. Detailed Instrumentation for the Solar-Heated Mobile Home

Measurement

Barometric pressure

Watt-hour meter reading for collector fan

Watt-hour meter reading for pebble-bed fan

Watt-hour meter reading for mobile home fan

Watt-hour meter reading for mobile home

excluding electric auxiliary heaters

Watt-hour meter reading for adjustable electric

heat

Watt-hour meter reading for fixed electric heat

Collector fan on/off

Delivery fan on/off

Auxiliary heat on/off

Irradiance on collector tilt w/o reflector

Collector temperature difference

Duct temperature difference

Collector fluid inlet temperature

Collector fluid exit temperature

Duct fluid temperature - hot side in mobile home

Duct fluid temperature - cold side in mobile home

Living room air temperature

Instrument room air temperature

Irradiance on horizontal surface

Pebble-bed centerline temperatures

Duct fluid temperature - cold side at solar

system

Duct fluid temperature - hot side at solar system

Effective sky temperature

Wind velocity

Wind direction

Ambient temperature

Relative humidity in mobile home

Beam irradiance

Irradiance on collector tilt w/o reflector,

second measurement

Pressure difference across collector

Symbol Instrument Frequency of

Measurement

Pb barometer daily

E

c watt-hour meter daily

ed watt-hour meter daily

% watt-hour meter daily

et watt-hour meter daily

exa watt-hour meter daily

exf watt-hour meter daily

relay 2 minutes

relay 2 minutes

relay 2 minutes

Giji pyranometer 2 minutes

At

c thermopile 2 minutes

At D the rmopile 2 minutes

C f > i thermocouple 2 minutes

C f,e thermocouple 2 minutes

t thermocouple 2 minutes

t the nnocouple 2 minutes

c r thermocouple 2 minutes

thermocouple 2 minutes

g

h pyranometer 2 minutes

f s thermocouple 2 minutes

t thermocouple 2 minutes

t thermocouple 2 minutes

t sky pyrgeometer 2 minutes

V

w anemometer 2 minutes

resistance pot 2 minutes

fc a thermocouple 2 minutes

rh transducer 2 minutes

g

b NIP 2 minutes

GT2 pyranometer 2 minutes

> O transducer 2 minutes

14
Figure 8. Instrumentation schematic of the solar system.

15
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Figure

10.

Solar

collector

efficiency

curve

with

the

reflector

covered.
the square root of the pressure drop across the collector divided by air

density resulted in a straight line with little scatter, as shown in

Figure 11. The resulting equation for flow is therefore:

V = 120.5 ~\J A pc /d - 9.6 (1)

* 3 where V = flow rate, ft /min

Ap

c = static pressure drop across the collector,

inches of water

d = air density in the collector, Ib/ft (computed using

the average of the inlet and exit temperatures and the

barometric pressure).

Thus it was possible to continuously measure collector flow rate by

monitoring pressure drop across the collector and collector inlet and

outlet temperatures.

Another major problem in determining the performance of solar heating

systems using air is air leakage through the various components. The

collector air flow rate which was measured and used in the performance

calculations was the air flow rate exiting the collector. When the collector was "calibrated" as a flow-measuring element using the nozzle,

all pressures and the flow rate were the same as those during actual

operating conditions. During the 1977-78 winter heating season, the

collector developed air leaks which progressively increased in magnitude.

The leakage undoubtly resulted in decreased collector performance and

also an underestimation of this decreased performance caused by the flow

measuring method.

Air flow rate in the supply duct was measured using a commercial laminar

flow element which consisted of a honeycomb air straightener upstream of

a pitot tube arrangement. This flow element was calibrated using an A.S.M.E. nozzle and was found to give good results once a "discharge"

correction factor was established. The correction factor, similar to

the discharge coefficient in a nozzle, was a constant multiplier which

corrected the indicated flow rate to actual flow rate. The correction

factor for this particular element was 0.93. The low pressure differentials in the flow element (11.3 to 13.8 Pa (0.045 to 0.055 in. I^O))

necessitated the use of a hook-gage manometer for accurate pressure

measurements.

After monitoring flow measuring pressures for a period of time with the

system in normal operation, equations and curves were developed relating

air flow rates in both the supply duct and the collector to the respective air densities, the blowers having constant speed motors. Thus

after some initial testing, it was possible to determine air flow rates

knowing only duct air temperatures and the barometric pressure.

18
uip ' o

19

Figure

11.

Solar

collector

air

flow

calibration

results
The incident solar radiation on a 60-degree tilted surface was measured

as with the simplified level of instrumentation, using a pyranometer

which was located several meters from the solar system.

Data were collected using a standard commercial data logger in conjunction with a reel-to-reel magnetic tape recorder. The scan rate was set

at two minutes, the short auxiliary heating cycle being the critical

controlling variable. The data logger had a capacity of 80 channels and

handled millivolt signals (0 to 400 mv) and type-T thermocouple inputs

with an internal reference junction. The data were reduced on a largescale digital computer at NBS.

Temperatures were measured using laboratory-fabricated type-T thermocouples. In addition to the thermocouples listed in Table 1, an additional 40 thermocouples were located in the pebble-bed.

Temperature differences across the collector and across the supply-toreturn ducts were measured using laboratory-fabricated six-junction

type-T thermopiles. To ensure a well-mixed air stream at the measuring

stations

1) the thermopiles were located far enough downstream from a right

angle turn to ensure proper mixing. Calculations showed that

flow conditions were in the turbulent regime, and

2) individual thermocouples were arranged across the various

cross-sections in order to detect any uneven temperature

distribution.

6. DATA REDUCTION AND PERFORMANCE ANALYSIS

Data Analysis Using Simplified Instrumentation

Data resulting from using the simplified level of instrumentation con- sisted of watt-hour meter readings, average ambient and indoor air temperatures, incident solar radiation, and average wind speed from nearby Washington National Airport.* These data combined with the known

thermal characteristics of the mobile home determined in previous tests

allowed calculation of the solar fraction.

Electric power consumption of the three fans, auxiliary heaters, and the

total electricity supplied to the mobile home was determined from the

watt-hour meter readings.

The daily space-heating load was calculated as follows:

L = UA* (21°C - tTa

) - E

g

(2)

* In a separate project at NBS conducted during the same time period

[22], good agreement was found between wind speeds at the NBS site

averaged over several hours and that recorded at the Airport.

20
where L = daily space-heating load, kJ

UA = building heat loss factor determined from the indoor

tests, kJ/°C

t a

= daily average ambient temperature, °C

E

g

= internal heat generated in the building from lights and

instruments, kJ

After reduction of the data obtained using the detailed instrumentation,

it was found that on some days the electric energy into the house far

exceeded the calculated heat loss. Since the heat loss factor on which

the calculated heat loss was based was determined indoors, it was assumed

that outdoor wind effects caused increased air infiltration and thus

additional heat loss. A correction factor was developed to take wind

effects into account, as will be explained in the next section

L* = L + correction factor (3)

where L* = corrected space-heating load, kJ

The solar fraction, f, was computed as follows, assuming that the solar

contribution was the difference between the space-heating load and auxiliary energy consumed.

f _ t (EAUX + E

C

+ ED + EH> (4)

L*

where EAUX daily energy consumed by the auxiliary electric heaters

in the mobile home, kJ

E

c = daily energy consumed by the collector fan in the

solar system, kJ

Ep = daily energy consumed by the load delivery fan in the

solar system, kJ

daily energy consumed by the distribution fan in the

mobile home, kJ

Data Analysis Using Detailed Instrumentation

Data from the detailed level of instrumentation were recorded on the

magnetic tape. Table 1 lists data items recorded. After collection of

the data, a data reduction program was used to produce both hourly and

daily summaries of the input data and selected performance factors. A

second program was used to calculate the performance of the system over

the winter heating season and to analyze the measured performance in

various ways.

21
The irradiation on the solar collector came from three sources: direct

radiation from the sun, diffuse radiation from the sky, and reflected

radiation from the reflector. As mentioned previously, the reflected

radiation was difficult to characterize accurately. Thus it was not

possible to measure the efficiency of the collector as an isolated unit

during the heating season, although the useful solar energy collected,

Qu , was measured. A collector efficiency based on the non-ref lected

irradiation onto the collector aperture was calculated during this test

period.

The amount of energy in thermal storage was calculated by taking the

average of the pebble-bed temperatures and multiplying by the pebblebed heat capacity. Heat losses from storage and ducts were calculated

by using an energy balance around the pebble-bed. This method was not

accurate, due to damper leakage that was found to occur in the system.

The energy provided by the solar system to the mobile home, Q^, was measured only when the delivery fan was operating. It was found during

operation, however, that a substantial amount of hot air leaked through

the dampers into the mobile home when the collector fan was operating, even though the load delivery fan was off. This leakage through the

dampers also prevented any direct measurement of heating load during

days of solar collection.

The heating load determination was based on the previous indoor thermal

loss tests. Wind effects significantly affected the load and a wind

correction factor was established using data taken during periods of no solar collection as will be explained below. Internally generated

heat was considered part of the load. Auxiliary heat to the load

included heat from both the furnace fan and the electric resistance

heaters.

Two major correction terms, based on the data over the winter heating

season, were derived and used to correct the data. The two factors were

a space-heating load correction factor due to wind and a heat leakage

correction factor due to air leakage through the dampers to the mobile

home.

To correct the space-heating load for air infiltration due to wind, the

amount of air leaking through the mobile home was assumed to be directly

proportional to the average wind velocity at nearby Washington National

Airport. Furthermore, it was assumed that the space-heating load correction factor was proportional to the infiltration multiplied by the insideto-outside temperature difference. Figure 12 is a plot of the difference

between measured and predicted space-heating load versus the product of

average wind speed and inside-to-outside temperature difference. The

following equation was developed from the curve:

L* - L + 0.144*Vw

’(t

r - t a

)

where Vw

= daily average wind velocity, mi/h

t r = reference temperature = 70°F

22

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Q31Vin01V3 QNV Q31MSV3MI N33M138 33N3H333IQ

23

WIND

SPEED

*

(INSIDE-OUTSIDE

TEMPERATURE

DIFFERENCE).

MPH
The air infiltration rate was characterized previously from tests in the

environmental chamber [9]. The difference in infiltration rate between

still air conditions and a simulated 3.6 m/s (8 mi/h) wind at an insideto-outside temperature difference of 22°C (72°F) was 0.15 air changes

per hour. The difference in infiltration rate due to a 3.6 m/s (8 mi/h)

wind using equation (5) is 0.39 air changes per hour. The difference

is due to the different conditions outside compared to inside the environmental chamber.

To correct for air leakage through the dampers from the solar system to

the mobile home, it was assumed that the leakage was directly proportional to the energy imbalance around the solar system. An energy

balance on the solar system indicated that the energy into the solar

system from the collector array and fans exceeded energy delivered to

the load plus the energy stored in the pebble-bed. The difference was assumed to be either leakage past the damper to the mobile home or heat

loss to the outside. The ratio of damper leakage to heat loss was assumed to be constant. The difference between the estimated and measured space-heating load plotted against the solar system imbalance is

shown in Figure 13. The resulting equation for correcting the energy

delivered from the solar system to the mobile home is:

Qd

* = Qd + 0.786 • AE (6)

where

Qp* = corrected daily energy provided to the mobile home

from the solar system, kJ

Qp - daily energy provided to the mobile home from the

solar system, kJ

AE = solar system energy imbalance, kJ

Several performance factors were calculated for the system. The solar

fraction, f, was calculated using equation (4). A solar system fraction,

f', which is defined as the fraction of the spaceheating load supplied

by the solar heating system, was calculated as follows:

f

' _ L* -(EAUX + %) (7)

L*

The solar system fraction represents the fraction of the load supplied

by the combination of solar energy plus the energy from the fans in the

solar system. The solar fraction defined by equation (4) accounts for

the energy from the sun only.

A coefficient of performance, COP, which is defined as delivered solar

heat divided by system solar fan energy requirements, was calculated as follows

COP Qd*

E„ + E„

24

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25
7. TEST RESULTS

Collector Performance

Results from the collector thermal performance tests conducted during

the summer of 1977 yielded an optical efficiency (y-intercept) of 0.62

and a heat loss factor (curve slope) of 7.38 W/ (m *°C) (1.3 Btu/

(h*ft^*F)) when the collector efficiency was plotted according to

ASHRAE Standard 93-77, as shown in Figure 10. These results were obtained with the reflector covered with a flat black material, as explained previously, and collector efficiency calculations based on the

aperture area of 8.13 m^ (88 ft^). The collector was tested with a flow

rate of approximately 0.19 mVs (400 ft'Vmin) with a corresponding pressure drop of 0.19 kPa (0.75 in. f^O). Flow rates through the collector

during system operation normally ranged from 0.18 to 0.21 m

J /s (390 to

450 ft'Vmin) depending on which mode the system was operating in.

It was difficult to predict the collector performance analytically due

to inadequate knowledge of the heat transfer coefficient off the absorber

fins. However, analytical methods outlined in reference [23] were used

to calculate theoretical values of 0.58 for the optical efficiency and

4.94 W/(m^*°C) (0.870 Btu/(h*f t^* °F)) for the heat loss factor. The

values were calculated using a ( T0Oe estimate of 0.72, a top loss coefficient of 6.6 W/(nV°C) (1.2 Btu/(h*rt^‘ °F)), a radiative exchange coefficient of 7.69 W/(nV°C) (1.35 Btu/ (h* f t^* °F) ) , and the performance

equations in Figure 7.12.1(d) of [23]. The convective heat transfer

coefficient off the fins was assumed to be between 5.0 and 44.7 W/(nV°C)

(0.88 and 7.87 Btu/(fTf t^* °F)) which are calculated coefficients for a stagnant air layer and for turbulent flow conditions based on the air

flow area, respectively. The flow was in the turbulent range through

the collector, although there may have been stagnant pockets between

fins. Calculating collector efficiency factors, F', for the two extreme

cases yielded values ranging from 0.88 to 0.90. Therefore, the heat

transfer coefficient for the fins has little effect on the collector

efficiency factor, the major heat loss path being from the air flow

stream to the inner glazing. The large discrepancy between actual and

theoretical values of collector heat loss coefficient was probably due

to air leakage in the collector. Air leaks around the perimeter of the

collector were observed during the test program.

The solar collector performance determined during the winter space-heating tests could not be directly compared to the performance curve of

Figure 10 due to the presence of the reflector during actual system

operation. The collector performance appeared to be substantially

enhanced by the reflector. Figure 14 is a plot of clear-day hourly collector efficiency values taken during the winter heating season with the

collector-only test curve included for comparison purposes. A reflector

enhancement factor was calculated for each set of clear-day data points.

The factor was based on the assumption that the difference in performance

was due entirely to additional reflected irradiation from the reflector.

26
% A0N3I3I333 U0133H03

27

Figure

14.

Solar

collector

performance

with

reflector.
Calculated clear—day enhancement factors ranged from 1.24 to 1.60 for

the data shown in Figure 14. The horseshoe shape of the collector performance curves in Figure 14 is characteristic of collectors such as air-heating collectors which have large time constants.

Early in the test program during a warm sunny day in which the collector

fan was not operating due to a temperature sensor failure, a dark brown

liquid condensed on the inside of the inner glazing. It is suspected

that this substance was driven off from the wood in the collector due

to the high temperatures created. Towards the end of the test program,

a dirty film slowly developed on the inner glazing, probably due to

outgassing of some material within the collector housing. The film was

not removed and its effect was not evaluated.

Pebble-Bed Storage Performance

The pebble-bed in this space-heating system was oversized. The ratio of

storage volume to collector area commonly used in solar air-heating

systems is o 0.15 m^/m^ (0.5 ft'Vft^). The rat:

t'Vft^). Temperature me.

3 2 J (0.5 The ratio in this particular system

was 0.87 nr/m^ (2.8 ft^/ft^). Temperature measurements within the pebblebed indicated that approximately half the storage capacity of the device

was never utilized for energy storage during the tests.

The pressure losses in the air stream passing through the pebble-bed were excessive due to a relatively tortuous path through the unit. The pressure drop across the pebble-bed was 1.25 kPa (5.0 in. 1^0) under typical

operating conditions as compared to a value of 0.062 kPa (0.25 in. 1^0)

typical in other systems. This pressure drop required a large amount

of fan power to move air through the pebble-bed, which adversely affected

the performance of the entire system. After the unit was dismantled, it was noted that a great deal of dust and finely crushed stone was present

in the pebble bed. The pebble-bed container and access panels appeared

to remain air tight during the test period.

Auxiliary Equipment Performance

The controller functioned correctly during the entire test, except for a brief period when the collector temperature sensor failed. The cause of

the failure was a broken wire on the resistance temperature element.

The two blowers within the solar system and the one in the mobile home

operated without any problems.

The two dampers on the inlets of the two blowers within the solar system

(magnetically latched back-draft dampers) performed poorly. When the

system was installed, the damper on the load fan would open whenever the

collector fan came on. Hot air from the collector would enter the

mobile home during the solar collection period, causing overheating of

the mobile home. This problem was solved by placing weights on the

damper.

28
There was a great deal of leakage through the dampers and/or partitions

within the solar system. Air leakage from the solar system to the mobile

home during collector operation continued to be a problem even after

modification of the damper as noted above; however, living space temperatures rarely exceeded 24°C (75°F). A second problem caused by leaky

dampers was flow through the collector at night when the load fan was operating. The high pressure drop across the pebble-bed caused this

leakage problem to be more serious than it might otherwise have been.

Daily System Performance

In order to describe the daily performance of the solar system, a typical day's in performance is shown here in detail. The day chosen

was February 4, 1978, which was clear and cold.

Beginning at midnight on this day, the storage was completely discharged

and the entire load was being supplied by the auxiliary electric heaters.

Room temperature was approximately 20°C (68°F) and ambient temperature

was approximately -10°C (14°F) at this time.

Shortly after 9:00 am, the collector fan came on, after which the delivery or load fan started operating. The average temperature of the air

supplied to the mobile home by the solar system during the first hour

was 17.5°C (63.5°F), which was too cool for heating. The auxiliary

heaters continued to supply energy during the first hour. A time lag in

supplying heat directly from the collectors to the mobile home was caused

by a section of the pebble-bed being in the flow path between the collector exit and the load supply duct.

The collector fan continued to run until approximately 4:30 pm and the

load fan continued to run intermittently throughout the day. Inside

room temperature reached a high of 23.3°C (74°F) at 4 pm, which was above the set point temperature in the home of 21°C (70°F). This effect

was caused by leakage through the load fan damper when the collector

fan was operating as already mentioned.

After sundown, the load was met by energy from storage with an occasional small boost from the electric auxiliary heaters. There was a substantial amount of flow through the collector at night, induced by

the load fan. In the late evening, there was a 15.5°C (28.0°F) temperature drop across the collector. Using the collector heat loss factor,

and this temperature drop, the flow rate through the collectors was calculated to be 0.062 kg/s (8.2 lb/min), or approximately 30% of the normal

flow rate when the collector fan was operating.

An energy audit over the 24-hour period starting at 6 am on February 4

and continuing to 6 am on the 5th yielded the results shown in Table 2.

This period was chosen since there was negligible change in internal

energy of the storage device between the beginning and end of this

period.

29
Table 2. Daily Energy Balance for the Solar Space-Heating System for February 4, 1978

Measurement Symbol Value

Internally generated ^GEN

heat

Heating load L

Additional infiltration L*-L

due to wind3

Corrected heating load L*

Solar energy incident on 60° G-j. tilt away from reflector

Solar energy collected Qu Energy delivered by Qp solar system

Heat leakage to mobile home3

Corrected energy delivered Q^*

by solar system

Collector fan energy E^ consumption

Load fan energy consumption E^

Mobile home fan energy E^ consumption

Auxiliary heaters eaux

Nighttime collector

losses3

Change in stored energy fiU

Storage and supply duct losses3

Solar fraction f

Coefficient of performance COP

Solar system fraction f'

Storage and delivery

efficiency 0

Collector efficiency0

Electric energy saved, fossil convent ional 3

Fossil energy saved, fossil convent ional^ ,e

Electric energy saved, conventional,

electric

28.0 MJ

28.4 MJ

24.8 MJ

273.2 MJ

209.6 MJ

140.9 MJ

75.6 MJ

59.7 MJ

135.3 MJ

16.5 MJ

22.3 MJ

16.9 MJ

127.9 MJ

22.5 MJ

0 MJ

23.2 MJ

32.8%

3.5

47.0%

74.8%

67.2%

-38.8 MJ

223.5 MJ

145.3 MJ

estimated value

Q* + Nightime Collector + Storage and Supply

' Losses Duct Losses

assuming the mobile home would be heated conventionally with a fossil energy source

e assumed fossil fuel conversion efficiency of 65%.

E assuming the mobile home would be heated conventionally with an electric energy source

& assumed electric conversion efficiency of 100%

30
Seasonal Performance

Monthly performance of the system was derived from use of the simplified

instrumentation. Results are presented in Table 3 for the last half of

the 1977-78 winter heating season.

The monthly solar fraction ranged from 12% to 60% with an overall solar

fraction of 24% for the five months. If it is assumed that the mobile

home would be heated conventionally by a fossil energy source, the total

electrical energy consumption for the home and system, including an average household consumption of 300 W, increased approximately 70% by

the addition of the solar system. The coefficient of performance, which

is defined as the useful solar energy delivered by the system divided by

the operating energy, was 1.9. Fossil fuel usage was reduced 42% by the

addition of the solar system. If the mobile home were heated conventionally with a total electric system, a net energy savings of 7971 MJ (7.5

MBtu) or 28% at the building boundary would have resulted for the five

month period.

8. CORRELATION OF SYSTEM PERFORMANCE

The detailed instrumentation was subject to frequent interruptions so

that continuous test data were not produced for the five month period.

Therefore instead of presenting test data on a monthly basis, data are presented here on either a daily basis or on a multi-day basis (3 to 7 days depending on data available).

Figure 15 is a plot of multi-day solar fractions (horizontal bars) versus

the day of the year. Monthly values obtained through the use of the

simplified instrumentation are also shown (cross-hatched rectangles).

Note a general trend toward higher solar fractions as the winter came to an end. The multi-day solar fractions ranged from approximately 7 to 75

percent. The upper limit on the solar fraction resulted from the low

COP of the solar system. In other words, if the system were operating

in mild weather and no auxiliary heating was required, the solar fraction would still be limited to approximately 75 percent due to the fan

operating energy requirements (included in the calculation of solar

f ract ion)

.

Figure 16 is a plot of the useful energy collected by the collector

divided by the heating load as a function of the solar load ratio (SLR).

A similar plot can be drawn for the energy delivered to the load. However, since the thermal storage subsystem is between the collector and

the mobile home, a term for the net change in stored energy must be

included. Figure 17 is a plot of the energy delivered to the load plus

the net change in stored energy divided by the load plotted as a function of the solar load ratio. It is evident from Figures 16 and 17 that

using the solar load ratio is a good correlation technique for the present system.

31
Table 3. Monthly Performance of the Solar Space-Heating System

Energy to Mobile Energy to Average Energy to Energy to Home Excluding Electric Average

Ambient Solar System Mobile Home Electric Auxiliary Auxiliary Wind

Days in Temperature Fans Fans Heaters Heaters Speed

Month Month (°C) (MJ) (MJ) (MJ) (MJ) (mi/h)

12 21 -.5 425 261 322 2844 9.8

1 31 -2.9 627 428 759 5508 11.0

2 28 -3.5 829 413 741 4392 10.0

3 31 3.7 778 340 778 2574 11.2

4 30 11.

675 193 407 295 11.7 3334 1635 3007 15613

Envelope

Corrected

Space Solar

Mobile Home Heating System

Electrical Energy

Consumption with

Solar System

Installed and

Mobile Home Heating System

Electrical Energy

Consumption with

Conventional

Total Electric

Energy Saved . Electric

Heat Loss Heating Solar System Electrical Auxiliary Electric Heat Conventional30

(MJ) Load(MJ) Fraction Fraction (MJ) (MJ) (MJ)

4289 4604 .233 .326 3530 4865 1335 7039 7453 .119 .204 6563 7881 1318 6517 6764 .167 .290 5634 7177 1543 5095 5182 .288 .438 3692 5522 1830 2822 2915 .601 .833 1163 3108 1945 25762 26918 .235 .359 20582 28553 28553

Mobile Home Heating System Mobile Home Fossil Consumption Heating System Total Total Electric

with Solar System Fossil Consumption Fossil Energy Saved,

Installed and with Conventional Saved, Fossil Fossil

Fossil Auxiliary0 Fossil Heatc Conventional0 Conventional0 (MJ) (MJ) (MJ) (MJ)

4375 7083 2708 -425

8474 11466 2992 -627

6757 10406 3649 -829

3960 7972 4012 -778

454 4485 4031 -675

24020 41412 17392 -3334

a assuming the mobile home would be heated conventionally with an electric energy source

k assumed electric conversion efficiency of 100%

c assumed fossil fuel conversion efficiency of 65%

^ assuming the mobile home would be conventionally heated with a fossil energy source

32
33

Figure

15.

Variation

of

solar

system

fraction

over

the

test

period.
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35
Figure 18 is a plot of solar fraction (f) (adjusted for the net change

in stored energy) versus the solar load ratio. Daily and multi-day data

points are shown as well as a cumulative data point for the full five

month test period based on data obtained using the simplified instrumentation. The following performance equation was derived from the plot:

f = 0.741* SLR - 0.146 - Au/L* (9)

where

SLR = solar load ratio, dimensionless

AU = net change in stored energy over the time period, kJ

The above result is significant since it shows that a single calculation

of the five-month value of the solar load ratio enables one to evaluate

the five-month solar fraction using equation (9).

9. SUMMARY AND CONCLUSIONS

Through tests on a complete solar space-heating system installed on a mobile home, it has been shown that the fraction of the load supplied

by solar energy correlates very well with the ratio of the total solar

radiation falling on the collector to the load imposed on the system.

Such a correlation should be location independent and could serve as

a basis for rating the system. For example, the solar fraction for

a specific value of solar load ratio could be used as the rating value

for the system. It is recommended that a detailed simulation study be

undertaken now, as was done in [19], to determine the smallest number

of days plus the kind of control required on the environmental and

operating conditions in order to produce a meaningful and accurate

correlation. In addition, the extent to which the correlation is

location independent should be determined.

36
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IRRADIANCE

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COLLECTOR

SURFACE
10 . REFERENCES

1. Hill, J. E. , and T. Kusuda, "Method of Testing for Rating Solar

Collectors Based on Thermal Performance," NBS Report NBSIR 74-635,

December, 1974.

2. Kelly, C. E. , and J. E. Hill, "Method of Testing for Rating Thermal

Storage Devices Based on Thermal Performance," NBS Report NBSIR74-634, April, 1975.

3. Hill, J. E. , Streed, E. R. , Kelly, G. E. , Geist, J. C. , and

T. Kusuda, "Development of Proposed Standards for Testing Solar

Collectors and Thermal Storage Devices," NBS Technical Note 899,

February, 1976.

4. Hill, J. E. , and E. R. Streed, "A Method of Testing for Rating

Solar Collectors Based on Thermal Performance,” Solar Energy,

Vol. 18, pp. 421-429, 1976.

5. Hill, J. E. , Kelly, G. E. , and B. A. Peavy, "A Method of Testing

for Rating Thermal Storage Devices Based on Thermal Performance,"

Solar Energy , Vol. 19, pp. 721-732, 1977.

6. "Methods of Testing to Determine the Thermal Performance of Solar

Collectors," ASHRAE Standard 93-77, ASHRAE, 345 East 47th Street,

New York, New York 10017, 1977.

7. "Method of Testing Thermal Storage Devices Based on Thermal Performance," ASHRAE Standard 94-77, ASHRAE, 345 East 47th Street, New

York, New York 10017, 1977.

8. Teitsma, G. J. , and B. A. Peavy, "The Thermal Performance of a TwoBedroom Mobile Home," NBS Report NBSIR 76-1182, January, 1977.

9. Hunt, C. M. , Treado, S. J. , and B. A. Peavy, "Air Leakage Measurements in a Mobile Home," NBS Report NBSIR 76-1063, August, 1976.

10. Hill, J. E. , and D. E. Jones, "Retrofitting a Mobile Horae for Solar

Space-Heating Preliminary Test Data," Letter Report to HUD,

April 15, 1977.

11. Remmers, H. E. , and H. W. Kier, "Field Test Procedure for Rating

Residential Solar Heating Systems Based on Useful Heat Delivery,"

International Solar Thermics Corporation Report No. ISC-01-23,

May, 1975.

12. "Report on Field Test of Champion Solar Furnace," Detroit Testing

Laboratory Report No. 605145-D, August 26, 1976.

38
13. Wolff, C. M. , "Measurement Technique and Instrumentation for

Rating Integrated Solar Heating and Cooling Systems," submitted

to the American Society of Testing and Materials, Committee

E21. 10.40, July 13, 1977.

14. Klein, S. A., Beckman, W. A., and J. A. Duffie, "A Design Procedure for Solar Heating Systems," Solar Energy, Vol. 18, pp. 113-127,

1976.

15. Klein, S. A., Beckman, W. A., and J. A. Duffie, "A Design Procedure for Solar Heating Systems," Solar Energy, Vol. 19,

pp. 509-512, 1977.

16. Beckman, W. A., Klein, S. A., and J. A. Duffie, Solar Heating

Design by the f-Chart Method , John Wiley and Sons, New York, 1977.

17. Klein, S. A., Cooper, P. I., Freeman, T. L. , Beekman, D. M. , Beckman,

W. A., and J. A. Duffie, "A Method of Simulation of Solar Processes

and Its Application," Solar Energy , Vol. 17, pp. 29-37, 1975.

18. "TRYSYS, A Transient Simulation Program," Report 38, Solar Energy

Laboratory, Engineering Experiment Station, University of Wisconsin,

October, 1977.

19. Liu, S. T. , and J. E. Hill, "A Proposed Technique for Correlating

the Performance of Solar Domestic Water Heating Systems," ASHRAE

Transactions , Vol. 85, Part I, 1979.

20. Balcomb, J. D. and J. C. Hedstrom, "A Simplified Method for Calculating Required Solar Collector Array Size for Space Heating,"

presented at the 1976 meeting of the International Solar Energy

Society, "Sharing the Sun," Winnipeg, Canada, August 15-20, 1976.

21. Balcomb, J. D. and J. C. Hedstrom, "Sizing Collectors for Space

Heating," Sun World , No. 1, pp. 25-27, July, 1976.

22. Private communication with C. M. Hunt, Thermal Analysis Group,

National Bureau of Standards, July, 1979.

23. Duffie, J. A., and W. A. Beckman, Solar Energy Thermal Processes , John Wiley and Sons, New York, 1974.

39
NBS-114A (REV. 0-78)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 79-1799

2.Gov't Accession No. V

'

. ''

3. Rooiptsht’s Accession No,

4. TITLE AND SUBTITLE

Performance of a Packaged Solar Space-Heating System Used

With a Mobile Home

5. Publication Date August 1979

7. AUTHOR(S) 8. Performing Organ. Report No. Dennis E. Jones, James E. Hill

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, city, state. ZIP)

Division of Energy, Building Technology, and Standards

Department of Housing and Urban Development

Washington, D.C. 20410

14 Project/Task/Work Unit No. 744 6500, Task C

11. Contract/Grant No.

13. Type of Report & Period Covered

M. growing Agency Code

. " I 15. SUPPLEMENTARY NOTES

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

16. ABSTRACT (A 200-word or leas factual summary of moat si gni ficant information. If document includes a significant bibliography or

literature survey, mention it here.)

As part of a continuing program to develop test methods for solar heating equipment,

NBS is new developing a standard test procedure for packaged solar space-heating

systems similar to test procedures now used for solar collectors and thermal storage

devices, and now under development for packaged solar water-heating systems. As a first step, a mobile home, which was previously tested for thermal performance in an environmental chamber, was equipped with a packaged solar space-heating system using

air-heating collectors and pebble-bed storage. The system was fully instrumented

and data were collected over the 1977-78 heating season at the NBS site in

Gaithersburg, Maryland. The performance of the system was determined and various

methods of correlating performance were explored.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Mobile home; packaged solar space-heating system; rating; standards; testing.

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