ASTM E905-87(2001)
(Test Method)Standard Test Method for Determining Thermal Performance of Tracking Concentrating Solar Collectors
Standard Test Method for Determining Thermal Performance of Tracking Concentrating Solar Collectors
SCOPE
1.1 This test method covers the determination of thermal performance of tracking concentrating solar collectors that heat fluids for use in thermal systems.
1.2 This test method applies to one- or two-axis tracking reflecting concentrating collectors in which the fluid enters the collector through a single inlet and leaves the collector through a single outlet, and to those collectors where a single inlet and outlet can be effectively provided, such as into parallel inlets and outlets of multiple collector modules.
1.3 This test method is intended for those collectors whose design is such that the effects of diffuse irradiance on performance is negligible and whose performance can be characterized in terms of direct irradiance.
Note 1—For purposes of clarification, this method shall apply to collectors with a geometric concentration ratio of seven or greater.
1.4 The collector may be tested either as a thermal collection subsystem where the effects of tracking errors have been essentially removed from the thermal performance, or as a system with the manufacturer-supplied tracking mechanism.
1.4.1 The tests appear as follows: SectionLinear Single-Axis Tracking Collectors Tested as Thermal Collection Subsystems11-13System Testing of Linear Single-Axis Tracking Collectors14-16Linear Two-Axis Tracking and Point Focus Collectors Tested as Thermal Collection Subsystems17-19System Testing of Point Focus and Linear Two-Axis Tracking Collectors 20-22
1.5 This test method is not intended for and may not be applicable to phase-change or thermosyphon collectors, to any collector under operating conditions where phase-change occurs, to fixed mirror-tracking receiver collectors, or to central receivers.
1.6 This test method is for outdoor testing only, under clear sky, quasi-steady state conditions.
1.7 Selection and preparation of the collector (sampling method, preconditioning, mounting, alignment, etc.), calculation of efficiency, and manipulation of the data generated through use of this standard for rating purposes are beyond the scope of this test method, and are expected to be covered elsewhere.
1.8 This test method does not provide a means of determining the durability or the reliability of any collector or component.
1.9 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.10 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E905–87(Reapproved2001)
Standard Test Method for
Determining Thermal Performance of Tracking
Concentrating Solar Collectors
This standard is issued under the fixed designation E905; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope tion of efficiency, and manipulation of the data generated
through use of this standard for rating purposes are beyond the
1.1 This test method covers the determination of thermal
scope of this test method, and are expected to be covered
performanceoftrackingconcentratingsolarcollectorsthatheat
elsewhere.
fluids for use in thermal systems.
1.8 This test method does not provide a means of determin-
1.2 This test method applies to one- or two-axis tracking
ing the durability or the reliability of any collector or compo-
reflecting concentrating collectors in which the fluid enters the
nent.
collectorthroughasingleinletandleavesthecollectorthrough
1.9 The values stated in SI units are to be regarded as the
a single outlet, and to those collectors where a single inlet and
standard. The values given in parentheses are for information
outlet can be effectively provided, such as into parallel inlets
only.
and outlets of multiple collector modules.
1.10 This standard does not purport to address all of the
1.3 This test method is intended for those collectors whose
safety concerns, if any, associated with its use. It is the
design is such that the effects of diffuse irradiance on perfor-
responsibility of the user of this standard to establish appro-
mance is negligible and whose performance can be character-
priate safety and health practices and determine the applica-
ized in terms of direct irradiance.
bility of regulatory limitations prior to use.
NOTE 1—For purposes of clarification, this method shall apply to
collectors with a geometric concentration ratio of seven or greater.
2. Referenced Documents
1.4 The collector may be tested either as a thermal collec-
2.1 ASTM Standards:
tion subsystem where the effects of tracking errors have been
E772 Terminology Relating to Solar Energy Conversion
essentially removed from the thermal performance, or as a
2.2 Other Standard:
system with the manufacturer-supplied tracking mechanism.
ASHRAE 93-86, Methods of Testing to Determine the
1.4.1 The tests appear as follows:
Thermal Performance of Solar Collectors
Section
NOTE 2—Where conflicts exist between the content of these references
Linear Single-Axis Tracking Collectors Tested as
and this test method, this test method takes precedence.
Thermal Collection Subsystems 11–13
NOTE 3—The definitions and descriptions of terms below supersede
System Testing of Linear Single-Axis Tracking Collectors 14–16
Linear Two-Axis Tracking and Point Focus Collectors
any conflicting definitions included in Terminology E772.
Tested as Thermal Collection Subsystems 17–19
System Testing of Point Focus and Linear Two-Axis
3. Terminology
Tracking Collectors 20–22
3.1 Definitions:
1.5 This test method is not intended for and may not be
3.1.1 area, absorber, n—total uninsulated heat transfer
applicable to phase-change or thermosyphon collectors, to any
surfaceareaoftheabsorber,includingunilluminatedaswellas
collector under operating conditions where phase-change oc-
illuminated portions. (E772)
curs, to fixed mirror-tracking receiver collectors, or to central
3.1.2 collector, point focus, n—concentrating collector that
receivers.
concentrates the solar flux to a point. (E772)
1.6 This test method is for outdoor testing only, under clear
3.1.3 collector, tracking, n—solarcollectorthatmovessoas
sky, quasi-steady state conditions.
to follow the apparent motion of the sun during the day,
1.7 Selection and preparation of the collector (sampling
rotating about one axis or two orthogonal axes. (E772)
method, preconditioning, mounting, alignment, etc.), calcula-
3.1.4 concentration ratio, geometric, n—ratio of the collec-
tor aperture area to the absorber area. (E772)
This test method is under the jurisdiction of ASTM Committee E44 on Solar,
Geothermal, and otherAlternative Energy Sourcesand is the direct responsibility of
Subcommittee E44.05on Solar Heating and Cooling Subsystems and Systems. Annual Book of ASTM Standards, Vol 12.02.
Current edition approved Aug. 28, 1987. Published January 1988. Originally Available from the American Society of Heating, Refrigerating, and Air
published as E905 – 82. Last previous edition E905 – 82. Conditioning Engineers, Inc., 1791 Tullie Circle, N.E. Atlanta, GA 30329.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E905
3.1.5 quasi-steady state, n—solar collector test conditions 3.2.11 solar irradiance, direct, in the aperture plane,
when the flow rate, fluid inlet temperature, collector tempera- n—direct solar irradiance incident on a surface parallel to the
ture, solar irradiance, and the ambient environment have collector aperture plane.
stabilized to such an extent that these conditions may be 3.2.12 solar irradiance, total, n—total solar radiant energy
considered essentially constant (see Section 8).
incident upon a unit surface area (in this standard, the aperture
of the collector) per unit time, including the direct solar
3.1.6 Discussion—The exit fluid temperature will, under
irradiance, diffuse sky irradiance, and the solar radiant energy
these conditions, also be essentially constant (see ASHRAE
reflected from the foreground.
93-86).
3.2.13 thermal performance, n—rate of heat flow into the
3.2 Definitions of Terms Specific to This Standard:
absorber fluid relative to the incident solar power on the plane
3.2.1 altazimuthal tracking, n—continual automatic posi-
of the aperture for the specified test conditions.
tioningofthecollectornormaltothesun’sraysinbothaltitude
3.3 Symbols:
and azimuth.
2 2
A =collector aperture area, m (ft ).
a
3.2.2 area, aperture (of a concentrating collector),
2 2
A =absorber area, m (ft ).
n—maximum projected area of a solar collector module abs
2 2
A =ineffective aperture area, m (ft ).
through which the unconcentrated solar radiant energy is 1
C=geometric concentration ratio A /A , dimensionless.
admitted,includinganyareaofthereflectororrefractorshaded
a abs
−1 −1
C =specific heat of the heat transfer fluid,J·kg ·° C
by the receiver and its supports and including gaps between
p
−1 −1
(Btu · lb ·°F ).
reflector segments within a module. (E772)
E =diffuse solar irradiance incident on the collector aper-
3.2.3 clear-sky conditions, n—refer to a minimum level of
s,d
−2 −1 −2
−2 −2
ture, W · m (Btu · h ·ft ).
direct normal solar irradiance of 630 W · m (200 Btu · ft ·
−1
E =direct solar irradiance in the plane of the collector
h ) and a variation in both the direct and total irradiance of
s,D
−2 −1 −2
aperture, W · m (Btu · h ·ft ).
less than 64% during the specified times before and during
E =directsolarirradianceintheplanenormaltothesun,
each test.
s,DN
−2 −1 −2
W·m (Btu · h ·ft ).
3.2.4 end effects, n—in linear single-axis tracking collec-
E =globalsolarirradianceincidentonahorizontalplane,
tors, the loss of collected energy at the ends of the linear
s,2p
2 −1 −2
W·m (Btu · h ·ft ).
absorber when the direct solar rays incident on the collector
E =totalsolarirradianceincidentonthecollectoraperture,
make a non-zero angle with respect to a plane perpendicular to
s,t
−2 −1 −2
W·m (Btu · h ·ft ).
the axis of the collector.
f=focal length, m (ft).
3.2.5 fluid loop, n—assembly of piping, thermal control,
g=spacing between the effective absorbing surfaces of
pumping equipment and instrumentation used for conditioning
adjacent modules, m (ft).
the heat transfer fluid and circulating it through the collector
K=incident angle modifier, dimensionless.
during the thermal performance tests.
L=length of reflector segment, m (ft).
3.2.6 module, n—the smallest unit that would function as a
l =length of receiver that is unilluminated, m (ft).
solar energy collection device. r
−1
m =mass flow rate of the heat transfer fluid, kg · s (lbm ·
3.2.7 near-normal incidence, n—angular range from exact
−1
h ).
normal incidence within which the deviations in thermal
−1
˙
Q =net rate of energy gain in the absorber, W (Btu · h ).
performance measured at ambient temperature do not exceed
−1
˙
Q =rate of energy loss, W (Btu · h ).
62%, such that the errors caused by testing at angles other L
r=overhang of the receiver past the end of the reflectors, m
than exact normal incidence cannot be distinguished from
(ft).
errors caused by other inaccuracies (that is, instrumentation
R (u)=ratio of the rate of heat gain to the solar power
errors, etc.).
incident on the aperture, dimensionless.
3.2.8 rate of heat gain, n—the rate at which incident solar
s=angle which the collector aperture is tilted from the
energy is absorbed by the heat transfer fluid, defined math-
horizontal to the equator, and is measured in a vertical N-S
ematically by:
plane, degrees.
˙
Q 5 m˙C Dt (1)
p a
t =ambient air temperature, °C (°F).
amb
3.2.9 response time, n—time required for D t to decline to t =temperature difference across the absorber, inlet to
a
D a
10%ofitsinitialvalueafterthecollectoriscompletelyshaded
outlet, °C (°F).
from the sun’s rays; or the time required for Dt to increase to
t =temperature difference across the absorber inlet to
a
D a,i
90% of its value under quasi-steady state conditions after the
outlet at the time of initial quasi-steady state conditions, °C
shaded collector at equilibrium is exposed to irradiation.
(°F).
3.2.10 quasi-steady state, n—refers to that state of the t =temperature difference across the absorber inlet to
D a,f
collector when the flow rate and inlet fluid temperature are outlet at the time final quasi-steady state conditions are
constant but the exit temperature changes “gradually” due to reached, °C (°F).
the normal change in solar irradiance that occurs with time for t =temperature difference across the absorber inlet to
D a,T
clear sky conditions.
outlet at time T, °C (°F).
3.2.10.1 Discussion—Itisdefinedbyasetoftestconditions t =temperature of the heat transfer fluid at the inlet to the
f,i
described in 10.1. collector, °C (°F).
E905
w=width of reflector segment, m (ft). method therefore do not by themselves constitute a rating of
b=solar altitude angle, degrees. the collector under test. Furthermore, it is not the intent of this
G(u )=end effect factor, dimensionless.
test method to determine collector efficiency for comparison
||
d=solar declination, degrees.
purposes since efficiency should be determined for particular
u=angle of incidence between the direct solar rays and the
applications.
normal to the collector aperture, degrees.
5.2 This test method relates collector thermal performance
u , u =angles of incidence in planes parallel and perpen-
|| '
to the direct solar irradiance as measured with a pyrheliometer
dicular, respectively, to the longitudinal axis of the collector,
with an angular field of view between 5 and 6°. The prepon-
degrees.
derance of existing solar radiation data was collected with
u =maximum angle of incidence at which all rays incident
i
instruments of this type, and therefore is directly applicable to
on the aperture are redirected onto the receiver of the same
prediction of collector and system performance.
module, degrees.
5.3 This test method provides experimental procedures and
u8 =minimum angle of incidence at which radiation re-
c
calculation procedures to determine the following clear sky,
flected from one module’s aperture is intercepted by the
quasi-steady state values for the solar collector:
receiver of an adjacent module, degrees.
5.3.1 Response time,
f=solar azimuth angle measured from the south, degrees.
5.3.2 Incident angle modifiers,
4. Summary of Test Method
5.3.3 Near-normal incidence angular range, and
4.1 Thermal performance is the rate of heat gain of a
5.3.4 Rate of heat gain at near-normal incidence angles.
collectorrelativetothesolarpowerincidentontheplaneofthe
collector aperture. This test method contains procedures to
NOTE 4—Notallofthesevaluesaredeterminedforallcollectors.Table
measure the thermal performance of a collector for certain 1 outlines the tests required for each collector type and tracking arrange-
well-defined test conditions. The procedures determine the ment.
opticalresponseofthecollectorforvariousanglesofincidence
5.4 This test method may be used to evaluate the thermal
ofsolarradiation,andthethermalperformanceofthecollector
performance of either (1) a complete system, including the
at various operating temperatures for the condition of maxi-
tracking subsystems and the thermal collection subsystem, or
mum optical response. The test method requires quasi-steady
(2) the thermal collection subsystem.
state conditions, measurement of environmental parameters,
5.4.1 Whenthistestmethodisusedtoevaluatethecomplete
and determination of the fluid mass flow rate-specific heat
system, the test shall be performed with the manufacturer’s
product and temperature difference, Dt , of the heat transfer
a
tracker and associated controls, and thus the effects of tracking
fluid between the inlet and outlet of the collector. These
error on thermal performance will be included in the results.
quantitiesdeterminetherateofheatgain, m˙C Dt ,forthesolar
p a
Linear single-axis tracking systems may be supplemented with
irradiance condition encountered. The solar power incident on
the test laboratory’s tracking equipment to effect a two-axis
the collector is determined by the collector area, its angle
tracking arrangement.
relative to the sun, and the irradiance measured during the test.
4.2 Two types of optical effects are significant in determin-
5.4.2 When evaluating a thermal collection subsystem, the
ing the thermal performance: (1) misalignment of the focal
accuracyofthetrackingequipmentshallbemaintainedaccord-
zone with respect to the receiver due to tracking errors and
ing to the restrictions in 10.3.
errors in the redirection of the irradiance intercepted by the
5.5 This test method is to be completed at a single appro-
collector, and (2) changes in the solar power incident on the
priate flowrate. For collectors designed to operate at variable
collector aperture due to decreased projected area (cosine
flowrates to achieve controlled outlet temperatures, the collec-
response) and other optical losses. The first effect is accounted
tor performance shall be characterized by repeating this test
for primarily in terms of the data generated for near-n
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