ASTM E905-87(1995)

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.

General Information

• Status: Historical
• Publication Date: 27-Aug-1987
• Technical Committee: E44 - Solar, Geothermal and Other Alternative Energy Sources

Relations

• Replaced By: ASTM E905-87(2001) - Standard Test Method for Determining Thermal Performance of Tracking Concentrating Solar Collectors
• Effective Date: 28-Aug-1987

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or
withdrawn. Contact ASTM International (www.astm.org) for the latest information.
Designation: E 905 – 87 (Reapproved 1995) An American National Standard
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Determining Thermal Performance of Tracking
Concentrating Solar Collectors
This standard is issued under the fixed designation E 905; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope through use of this standard for rating purposes are beyond the
scope of this test method, and are expected to be covered
1.1 This test method covers the determination of thermal
elsewhere.
performance of tracking concentrating solar collectors that heat
1.8 This test method does not provide a means of determin-
fluids for use in thermal systems.
ing the durability or the reliability of any collector or compo-
1.2 This test method applies to one- or two-axis tracking
nent.
reflecting concentrating collectors in which the fluid enters the
1.9 The values stated in SI units are to be regarded as the
collector through a single inlet and leaves the collector through
standard. The values given in parentheses are for information
a single outlet, and to those collectors where a single inlet and
only.
outlet can be effectively provided, such as into parallel inlets
1.10 This standard does not purport to address all of the
and outlets of multiple collector modules.
safety concerns, if any, associated with its use. It is the
1.3 This test method is intended for those collectors whose
responsibility of the user of this standard to establish appro-
design is such that the effects of diffuse irradiance on perfor-
priate safety and health practices and determine the applica-
mance is negligible and whose performance can be character-
bility of regulatory limitations prior to use.
ized in terms of direct irradiance.
NOTE 1—For purposes of clarification, this method shall apply to 2. Referenced Documents
collectors with a geometric concentration ratio of seven or greater.
2.1 ASTM Standards:
1.4 The collector may be tested either as a thermal collec-
E 772 Terminology Relating to Solar Energy Conversion
tion subsystem where the effects of tracking errors have been
2.2 Other Standard:
essentially removed from the thermal performance, or as a
ASHRAE 93-86, Methods of Testing to Determine the
system with the manufacturer-supplied tracking mechanism.
Thermal Performance of Solar Collectors
1.4.1 The tests appear as follows:
NOTE 2—Where conflicts exist between the content of these references
Section
and this test method, this test method takes precedence.
Linear Single-Axis Tracking Collectors Tested as
NOTE 3—The definitions and descriptions of terms below supersede
Thermal Collection Subsystems 11–13
any conflicting definitions included in Terminology E 772.
System Testing of Linear Single-Axis Tracking Collectors 14–16
Linear Two-Axis Tracking and Point Focus Collectors
Tested as Thermal Collection Subsystems 17–19 3. Terminology
System Testing of Point Focus and Linear Two-Axis
3.1 Definitions:
Tracking Collectors 20–22
3.1.1 area, absorber, n—total uninsulated heat transfer
1.5 This test method is not intended for and may not be
surface area of the absorber, including unilluminated as well as
applicable to phase-change or thermosyphon collectors, to any
illuminated portions. (E 772)
collector under operating conditions where phase-change oc-
3.1.2 collector, point focus, n—concentrating collector that
curs, to fixed mirror-tracking receiver collectors, or to central
concentrates the solar flux to a point. (E 772)
receivers.
3.1.3 collector, tracking, n—solar collector that moves so as
1.6 This test method is for outdoor testing only, under clear
to follow the apparent motion of the sun during the day,
sky, quasi-steady state conditions.
rotating about one axis or two orthogonal axes. (E 772)
1.7 Selection and preparation of the collector (sampling
3.1.4 concentration ratio, geometric, n—ratio of the collec-
method, preconditioning, mounting, alignment, etc.), calcula-
tor aperture area to the absorber area. (E 772)
tion of efficiency, and manipulation of the data generated
3.1.5 quasi-steady state, n—solar collector test conditions
when the flow rate, fluid inlet temperature, collector tempera-
ture, solar irradiance, and the ambient environment have
This test method is under the jurisdiction of ASTM Committee E-44 on Solar,
Geothermal, and other Alternative 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 E 905 – 82. Last previous edition E 905 – 82. Conditioning Engineers, Inc., 1791 Tullie Circle, N.E. Atlanta, GA 30329.
E 905
stabilized to such an extent that these conditions may be incident upon a unit surface area (in this standard, the aperture
considered essentially constant (see Section 8). 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.
tioning of the collector normal to the sun’s rays in both altitude 3.3 Symbols:
2 2
and azimuth.
A 5 collector aperture area, m (ft ).
a
2 2
3.2.2 area, aperture (of a concentrating collector),
A 5 absorber area, m (ft ).
abs
2 2
n—maximum projected area of a solar collector module
A 5 ineffective aperture area, m (ft ).
through which the unconcentrated solar radiant energy is
C 5 geometric concentration ratio A /A , dimensionless.
a abs
−1 −1
admitted, including any area of the reflector or refractor shaded
C 5 specific heat of the heat transfer fluid,J·kg ·° C
p
−1 −1
by the receiver and its supports and including gaps between
(Btu · lb ·°F ).
reflector segments within a module. (E 772)
E 5 diffuse solar irradiance incident on the collector
s,d
−2 −1 −2
3.2.3 clear-sky conditions, n—refer to a minimum level of
aperture, W · m (Btu · h ·ft ).
−2 −2
direct normal solar irradiance of 630 W · m (200 Btu · ft ·
E 5 direct solar irradiance in the plane of the collector
s,D
−1
−2 −1 −2
h ) and a variation in both the direct and total irradiance of
aperture, W · m (Btu · h ·ft ).
less than 64 % during the specified times before and during
E 5 direct solar irradiance in the plane normal to the
s,DN
−2 −1 −2
each test.
sun, W · m (Btu · h ·ft ).
3.2.4 end effects, n—in linear single-axis tracking collec-
E 5 global solar irradiance incident on a horizontal
s,2p
2 −1 −2
tors, the loss of collected energy at the ends of the linear
plane, W · m (Btu · h ·ft ).
absorber when the direct solar rays incident on the collector
E 5 total solar irradiance incident on the collector aper-
s,t
−2 −1 −2
make a non-zero angle with respect to a plane perpendicular to
ture, W · m (Btu · h ·ft ).
the axis of the collector.
f 5 focal length, m (ft).
3.2.5 fluid loop, n—assembly of piping, thermal control,
g 5 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 5 incident angle modifier, dimensionless.
during the thermal performance tests.
L 5 length of reflector segment, m (ft).
3.2.6 module, n—the smallest unit that would function as a
l 5 length of receiver that is unilluminated, m (ft).
r
solar energy collection device.
−1
m 5 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 5 net rate of energy gain in the absorber, W (Btu · h ).
performance measured at ambient temperature do not exceed
−1
˙
Q 5 rate of energy loss, W (Btu · h ).
L
62 %, such that the errors caused by testing at angles other
r 5 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) 5 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 5 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)
t 5 ambient air temperature, °C (°F).
p a
amb
t 5 temperature difference across the absorber, inlet to
3.2.9 response time, n—time required for D t to decline to D a
a
outlet, °C (°F).
10 % of its initial value after the collector is completely shaded
t 5 temperature difference across the absorber inlet to
from the sun’s rays; or the time required for Dt to increase to D a,i
a
outlet at the time of initial quasi-steady state conditions, °C
90 % of its value under quasi-steady state conditions after the
(°F).
shaded collector at equilibrium is exposed to irradiation.
t 5 temperature difference across the absorber inlet to
3.2.10 quasi-steady state, n—refers to that state of the
D a,f
outlet at the time final quasi-steady state conditions are
collector when the flow rate and inlet fluid temperature are
reached, °C (°F).
constant but the exit temperature changes “gradually” due to
t 5 temperature difference across the absorber inlet to
the normal change in solar irradiance that occurs with time for
D a,T
outlet at time T, °C (°F).
clear sky conditions.
t 5 temperature of the heat transfer fluid at the inlet to the
3.2.10.1 Discussion—It is defined by a set of test conditions
f,i
collector, °C (°F).
described in 10.1.
w 5 width of reflector segment, m (ft).
3.2.11 solar irradiance, direct, in the aperture plane,
n—direct solar irradiance incident on a surface parallel to the b5 solar altitude angle, degrees.
G(u ) 5 end effect factor, dimensionless.
collector aperture plane.
||
3.2.12 solar irradiance, total, n—total solar radiant energy d5 solar declination, degrees.
E 905
u5 angle of incidence between the direct solar rays and the purposes since efficiency should be determined for particular
normal to the collector aperture, degrees. applications.
u , u 5 angles of incidence in planes parallel and perpen- 5.2 This test method relates collector thermal performance
|| ’
dicular, respectively, to the longitudinal axis of the collector, to the direct solar irradiance as measured with a pyrheliometer
degrees. with an angular field of view between 5 and 6°. The prepon-
derance of existing solar radiation data was collected with
u 5 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 5 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,
f5 solar azimuth angle measured from the south, degrees.
5.3.2 Incident angle modifiers,
5.3.3 Near-normal incidence angular range, and
4. Summary of Test Method
5.3.4 Rate of heat gain at near-normal incidence angles.
4.1 Thermal performance is the rate of heat gain of a
collector relative to the solar power incident on the plane of the
NOTE 4—Not all of these values are determined for all collectors. Table
1 outlines the tests required for each collector type and tracking arrange-
collector aperture. This test method contains procedures to
ment.
measure the thermal performance of a collector for certain
well-defined test conditions. The procedures determine the
5.4 This test method may be used to evaluate the thermal
optical response of the collector for various angles of incidence
performance of either (1) a complete system, including the
of solar radiation, and the thermal performance of the collector
tracking subsystems and the thermal collection subsystem, or
at various operating temperatures for the condition of maxi-
(2) the thermal collection subsystem.
mum optical response. The test method requires quasi-steady
5.4.1 When this test method is used to evaluate the complete
state conditions, measurement of environmental parameters,
system, the test shall be performed with the manufacturer’s
and determination of the fluid mass flow rate-specific heat
tracker and associated controls, and thus the effects of tracking
product and temperature difference, Dt , of the heat transfer
a
error on thermal performance will be included in the results.
fluid between the inlet and outlet of the collector. These
Linear single-axis tracking systems may be supplemented with
quantities determine the rate of heat gain, m˙C Dt , for the solar
p a
the test laboratory’s tracking equipment to effect a two-axis
irradiance condition encountered. The solar power incident on
tracking arrangement.
the collector is determined by the collector area, its angle
5.4.2 When evaluating a thermal collection subsystem, the
relative to the sun, and the irradiance measured during the test.
accuracy of the tracking equipment shall be maintained accord-
4.2 Two types of optical effects are significant in determin-
ing to the restrictions in 10.3.
ing the thermal performance: (1) misalignment of the focal
5.5 This test method is to be completed at a single appro-
zone with respect to the receiver due to tracking errors and
priate flowrate. For collectors designed to operate at variable
errors in the redirection of the irradiance intercepted by the
flowrates to achieve controlled outlet temperatures, the collec-
collector, and (2) changes in the solar power incident on the
tor performance shall be characterized by repeating this test
collector aperture due to decreased projected area (cosine
meth
...