An outdoor facility constructed to evaluate solar collector performance for conditions that would be encountered by collectors if they were incorporated in a solar heating/cooling system is described. Preliminary performance data is presented

Vernon, R. W.

English

NASA Technical Reports Server

NASA TECHNICAL NASA TM X-71689
MEMORANDUM
00
(NASA-TM-X-71689) SOLAR COLLECTOR N75-21794
X PERFORMANCE EVALUATED OUTDOORS AT NASA-LEWIS
RESEARCH CENTER (NASA)
Unclas
G3/44 18648
PRICES SUBJECT TO CHANGE
SOLAR COLLECTOR PERFORMANCE EVALUATED
OUTDOORS AT NASA-LEWIS RESEARCH CENTER
by R. W. Vernon
Lewis Research Center
Cleveland, Ohio 44135
TECHNICAL PAPER presented at
Workshop on Solar Collectors for Heating and Cooling of Buildings
sponsored by the National Science Foundation
New York, New York, November 21-23, 1974
Reproduced by
NATIONAL TECHNICAL
INFORMATION SERVICE
US Department of Commerce
Sprinegield, VA. 22151
https://ntrs.nasa.gov/search.jsp?R=19750013722 2020-03-22T21:23:54+00:00Z
SOLAR COLLECTOR PERFORMANCE EVALUATED OUTDOORS
AT NASA-LEWIS RESEARCH CENTER
By
R. W. Vernon
Lewis Research Center
National Aeronautics and Space Administration
Cleveland, Ohio
INTRODUCTION
A facility was constructed at Lewis Research Center to evaluate
solar collector performance for conditions that would be encountered
by collectors if they were incorporated in a solar heating/cooling
system. NASA-Lewis has the responsibility to select and provide
solar collectors that will be incorporated in a solar heated and
cooled office building at NASA's Langley Research Center in Hampton,
Virginia (ref. 1). The solar project at Langley will provide a test
bed for determining actual field performance of components that com-
prise a solar heating/cooling system. Test results obtained from
the outdoor test facility at Lewis will provide one of the inputs to
the selection process for the collectors to be used on the solar
project at Langley.
In addition to providing initial collector performance data, the
outdoor facility will enable collector durability and early degra-
dation rates to be evaluated for operating periods of several months.
Also, the data obtained from the outdoor tests will be correlated
with data obtained using a solar simulator.* This will allow a
determination of.the extent to which collector performance can be
predicted by using data obtained in the simulator facility. This
paper describes the outdoor test facility and presents some prelimin-
ary performance data.
DESCRIPTION OF FACILITY
A simplified schematic of the flow loop is shown in figure 1. The
liquid in the flow loop .is a mixture of 50 percent ethylene-glycol
and 50 percent water by weight. A conventional home hot-water heater,
80 gallon capacity, is used for storage. The electric heating elements
in the storage tank are controlled by a thermostat. The storage tank
heaters provide a ready means to raise the temperature of the entire
liquid inventory when desired. A centrifugal pump, driven by a 1/4
horsepower electric motor, circulates the liquid. A filter provides
*The solar simulator facility at the Lewis Research Center is described
in companion paper authored by Fred Simon elsewhere in this document.
2continuous filtration of the liquid. A conventional air-liquid
heat exchanger, with an on-off fan control, is used to reject energy
when desired. A by-pass around the heat exchanger and the associated
proportional control valves permit modulation of the liquid tempera-
ture at the outlet of the heat exchanger.
A flow through each collector is manually adjusted with a remotely
operated valve. The flow rate through the collector by-pass line is
controlled to maintain a constant pressure in the collector inlet
manifold. Thus, when the flow rate through one collector is varied,
the flow through the remaining collectors remains constant with no
adjustment of the flow-control valves. The flow rate through each
collector is determined with a calibrated turbine-type flowmeter.
Auxiliary heaters with electric immersion elements are located at the
inlet of each collector. These heaters provide a controlled variation
of inlet temperature from collector to collector. The liquid discharge
from the collectors is returned to the storage tank. An expansion
tank accommodates volume changes of the liquid inventory.
When completed the outdoor collector facility will include two
identical flow loops with a capability of testing ten collectors
simultaneously. One of the flow loops is presently completed and
is shown in figure 2. The range of possible test conditions is
presented in figure 3.
The instrumentation is summarized in figure 4. In addition to the
collector performance and solar insolation data, the following
weather data are recorded: air temperature, wind speed and direction,
and relative humidity. At the present time all temperatures are
measured with chromel-constantan thermocouples, ISA type E. The
temperature measurement method is being reviewed and may be modified
in the future. Presently only a single pyranometer, mounted in the
plane of the collectors, is used to measure solar flux. The remain-
ing pyranometers and the pyrheliometer, for direct or beam radiation,
will be installed when available. The solar flux will also be inte-
grated continuously in the future.
PRELIMINARY RESULTS
Preliminary results are presented in figure 5 for a collector fabri-
cated at the Lewis Research Center from two copper heat-transfer
panels (Thermon Manufacturing Co.). The panels were sprayed with a
nonselective black paint (a = 0.97). Two glass covers were placed
over the panels and four inches of fiberglass insulation beneath.
The panels, plumbed in parallel, each measured 22 inches by 45 inches.
The outside dimensions of the collector frame are 48 inches by 49
inches. In figure 5, the instantaneous collector efficiency,
mC (T -T. )
p out in
qsolar Aabsorber
3is plotted as a funmtion of the ratio
Tin 
- Tamb air
qsolar
This format is particularly useful when employing the collector
design factors presented in references 2 and 3. A general equation
developed therein expresses the collector efficiency as
71 = F [- UL (Tin-Tamb air
- R qsolar I
By plotting the data as shown in figure 5, the values FR and UL
are readily obtained. Knowing the effective at product, FR can
be determined knowing the vertical intercept. Then, knowing FR
and the slope of the curve, UL can be determined. These early
data are presented primarily to demonstrate the approach to be
taken for presenting data. No correction was incorporated for the
effects of wind, incident angle, sky temperature, etc. In thefuture, using the integrated values of solar flux, the collector
efficiency will be determined on both an hourly and daily basis.
The collector performance determined outdoors will be correlated
with data obtained using a solar simulator (ref. 4 and 5) to con-
firm the simulator approach to acquiring performance data.
CONCLUDING REMARKS
A facility to determine solar collector performance outdoors has
been constructed. Preliminary performance data have been obtained.
Performance data obtained from the outdoor tests will be employed
as one of the bases for selecting collectors for installation on
the solar project at NASA-Langley. The solar simulator approach
to obtaining collector performance will hopefully by confirmed by
correlation of data acquired outdoors with data previously measured
in a solar simulator facility.
REFERENCES
1. Ragsdale, R.G. and Namkoong, D., Jr., "The NASA Langley
Building Solar Project and the Supporting Lewis Solar Technology
Program", paper presented at International Solar Energy Society,
Annual Meeting, Aug. 19-23, 1974, Fort Collins, Colorado.
2. Hottel, H.C. and Whillier, A., "Evaluation of Flat-Plate
Solar Collector Performance", in Trans. Conf. on the Use of
Solar Energy - The Scientific Basis, Vol. 2, Oct. 31 - Nov. 1,
1955, p. 74, Tucson, Arizona.
3. Bliss, R.W., Jr., Solar Energy, 3, 55 (1959).
44. Simon, F.F. and Harlamert, P., "Flat-Plate Collector
Performance Evaluation", paper presented at International Solar
Energy Society, Annual Meeting, Oct. 3-4, 1973, Cleveland, Ohio.
5. Vernon, R.W. and Simon, F.F., "Flat-Plate Collector Per-
formance Determined Experimental with a Solar Simulator", paper
presented at International Solar Energy Society, Annual Meeting,
Aug. 19-23, 1974, Fort Collins, Colorado.
SYMBOLS
Aaborber Area of absorber, ft
Cp Specific heat of fluid, Btu/lbOF
FR  Overall collector plate heat removal efficiency,
dimensionless
qsolar Total flux in plane of collector, Btu/hr ft2
m Fluid mass flow rate, lb/hr
Tamb air Ambient air temperature, OF
T. Fluid temperature at collector inlet, aF
an
out  Fluid temperature at collector outlet, OF
UL Overall heat loss coefficient, Btu/hr 
ft 2F
a Absorptivity of collector absorber, dimensionless
SCollector efficiency, dimensionless
T Transmittance of collector cover system, dimensionless
EXPANSION
TANK
COLLECTOR COLLBYPASS
80 GAL ELECTRIC
AUX HEATER STORAGEAGE HEATERS
BYPASS
- /
TURBINE
FLOW METER
FLOW
CONTROL
VALVE
IHEAT
INLET MANIFOLDCHR PUMP
PRESSURE SENSOR' -------------
AIR
Figure 1. - Schematic of outdoor collector facility.
C COLLECTOR TILT ANGLE, 450
INLET TEMPERATURE, 900 TO 1400 F
0o FLOW RATE, 10 LB/HRIFT2 ABSORBER
60 SOLAR FLUX, 190 TO 320 BTIJIHR FT2
>: 40 -
m 20
0 10 20 30 40 50 60
Tin - Tamb air 02OF HR FT
2
qsolar x BJ
Figure 2. - Performance of Lewis collector, preliminary data.
* FLOW --------------------------------------- TO 3 GAL/MIN
* INLET FLUID TEMPERATURE ------------------------ AMBIENT TO 2000F
* TILT ANGLE ---------------------------------------- 20 TO 60 DEGREES
* COLLECTOR SIZE ----------------------------------- UP TO 4 X 8 FT
FIGURE 3.- RANGE OF OUTDOOR TEST CONDITIONS
.53
* COLLECTOR
FLOW RATE
TEMPERATURE PRESSURE
IN IN
OUT DELTA P
PLATE
GLASS
* SOLAR FLUX
TOTAL IN PLANE OF COLLECTOR (PRESENT)
TOTAL HORIZONTAL
DIFFUSE HORIZONTAL (FUTURE)
DIRECT
FIGURE 4.- INSTRUMENTATION FOR OUTDOOR COLLECTOR
TESTS
C-74-3265
Figure 5. - Outdoor collector facility.
NASA-Lewis


Solar collector performance evaluated outdoors at NASA-Lewis Research Center

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server