Solar hot water and space heating systems constructed of commodity polymers have the potential to reduce the initial cost of solar thermal systems. However, a polymer absorber must be prevented from exceeding its maximum service temperature during stagnation. Here, the addition of a thermotropic material to the surface of the absorber is considered. The thermotropic layer provides passive overheat protection by switching from high transmittance during normal operation to high reflectance if the temperature of the absorber becomes too high. A one dimensional model of a glazed, flat-plate collector with a polymer absorber and thermotropic material is used to determine the effects of the optical properties of the thermotropic material on the optical efficiency and the stagnation temperature of a collector. A key result is identification of the reflectance in the translucent state required to provide overheat protection for potential polymer absorber materials. For example, a thermotropic material in its translucent state should have a solar-weighted reflectance greater than or equal to 52% to protect a polypropylene absorber which has a maximum service temperature of 115 °C.

References

References
1.
Hudon
,
K.
,
Merrigan
,
T.
, and
Burch
,
J.
,
2012
, “
Low-Cost Solar Water Heating Research and Development Roadmap
,” National Renewable Energy Laboratory (NREL), Technical Report No. NREL/TP-550054793.
2.
Merrigan
,
T
.,
2007
, “
Solar Heating & Lighting: Solar Water Heating R&D
,”
DOE Solar Energy Technologies Program
, Denver, CO, Apr. 17–19.
3.
IEA Task 39,
2014
, “
Polymeric Materials for Solar Thermal Applications, Solar Heating & Cooling Program
,” International Energy Agency (IEA), accessed Feb. 2, 2014. Available at: http://task39.iea-shc.org/
4.
Kohl
,
M.
,
Meir
,
M. G.
,
Papillon
,
P.
,
Wallner
,
G. M.
, and
Saile
,
S.
,
2012
,
Polymeric Materials for Solar Thermal Applications
,
Wiley-VCH Verlag & Co.
,
Weinheim, Germany
, p.
393
.
5.
Burch
,
J. D.
,
2006
, “
Polymer-Based Solar Thermal Systems: Past, Present and Potential Products
,”
Proceedings of the 64th Annual Technical Conference & Exhibition
,
Society of Plastic Engineers
, Charlotte, NC, May 7–11, pp.
7
11
.
6.
Martinopoulos
,
G.
,
Missirlis
,
D.
,
Tsilingiridis
,
G.
,
Yakinthos
,
K.
, and
Kyriakis
,
N.
,
2010
, “
CFD Modeling of a Polymer Solar Collector
,”
Renewable Energy
,
35
(
7
), pp.
1499
1508
.10.1016/j.renene.2010.01.004
7.
Tsilingiris
,
P
.,
2002
, “
Back Absorbing Parallel Plate Polymer Absorbers in Solar Collector Design
,”
Energy Convers. Manage.
,
43
(
1
), pp.
135
150
.10.1016/S0196-8904(01)00015-2
8.
Mintsa Do Ango
,
A.
,
Medale
,
M.
, and
Abid
,
C.
,
2013
, “
Optimization of the Design of a Polymer Flat Plate Solar Collector
,”
Sol. Energy
,
87
, pp.
64
75
.10.1016/j.solener.2012.10.006
9.
Cristofari
,
C.
,
Notton
,
G.
,
Poggi
,
P.
, and
Louche
,
A.
,
2002
, “
Modelling and Performance of a Copolymer Solar Water Heating Collector
,”
Sol. Energy
,
72
(
2
), pp.
99
112
.10.1016/S0038-092X(01)00092-5
10.
Siqueira
,
D. A.
,
Vieira
,
L. G. M.
, and
Damasceno
,
J. J. R.
,
2011
, “
Analysis and Performance of a Low-Cost Solar Heater
,”
Renewable Energy
,
36
(
9
), pp.
2538
2546
.10.1016/j.renene.2011.02.019
11.
Meir
,
M.
, and
Rekstad
,
J.
,
2003
, “
Der Solarnor Kunststoffkollektor–The Development of a Polymer Collector With Glazing
,”
Proceedings of the Leobner Symposium Polymeric Solar Materials
, Leoben, Austria Nov. 6–7, pp.
II-1
II-8
.
12.
Resch
,
K.
, and
Wallner
,
G. M.
,
2012
, “
Polymeric Materials for Solar Thermal Applications
,”
Polymeric Materials for Solar Thermal Applications
,
M.
Kohl
,
M. G.
Meir
,
P.
Papillon
,
G. M.
Wallner
, and
S.
Saile
, eds.,
Wiley-VCH Verlag & Co.
,
Weinheim, Germany
, pp.
129
134
.
13.
Rhodes
,
R. O.
,
2010
, “
Polymer Thin-Film Design Reduces Installed Cost of Solar Water Heater
,”
Proceedings of the 39th ASES national Solar Conference
, May 17–22,
Phoenix
, AZ, pp.
1580
1588
.
14.
Russell
,
L.
, and
Guven
,
H.
,
1982
, “
Modeling and Analysis of an All-Plastic Flat-Plate Solar Collector
,”
ASME J. Sol. Energy Eng.
,
104
(
4
), pp.
333
339
.10.1115/1.3266326
15.
Baer
,
S. C.
,
1985
, “
Thermal Control System for Solar Collector
,” U.S. Patent No. 4,528,976.
16.
Harrison
,
S.
, and
Cruickshank
,
C. A.
,
2012
, “
A Review of Strategies for the Control of High Temperature Stagnation in Solar Collectors and Systems
,”
Energy Procedia
,
30
, pp.
793
804
.10.1016/j.egypro.2012.11.090
17.
Thür
,
A. V.
,
Hintringer
,
C.
, and
Richtfeld
,
A.
,
2013
, “
Status Quo Der Entwicklungen Eines Überhitzungsgeschützten Kunststoffkollektors
,” Erneuerbare Energie, accessed June
16
,
2014
, http://www.aee.at/aee/index.php?option=com_content&view=article&id=749&Itemid=113
18.
Buckley
,
B. S.
, and
Guldman
,
T. A.
,
1983
, “
Method and Apparatus for Overtemperature Control of Solar Water Heating System
,” U.S. Patent No. 4,399,807.
19.
Kusyy
,
O.
, and
Vajen
,
K.
,
2011
, “
Theoretical Investigation on a Control-Based Approach to Avoid Stagnation of Solar Heating Systems
,”
Proceedings of ISES Solar World Congress
,
Kassel
,
Germany
, Aug. 28–Sept. 2, pp.
3323
3330
.
20.
Kearney
,
M.
,
Davidson
,
J.
, and
Mantell
,
S.
,
2005
, “
Polymeric Absorbers for Flat-Plate Collectors: Can Venting Provide Adequate Overheat Protection?
,”
ASME J. Sol. Energy Eng.
,
127
(
3
), pp.
421
424
.10.1115/1.1979518
21.
Mahdjuri
,
F
.,
1999
, “
Solar Collector With Temperature Limitation Using Shape Memory Metal
,”
Renewable Energy
,
16
(
1
), pp.
611
617
.10.1016/S0960-1481(98)00236-5
22.
Roberts
,
J.
,
Brandemuehl
,
M.
, and
Burch
,
J.
,
2000
, “
Overheat Protection for Solar Water Heating Systems Using Natural Convection Loops
,”
Proceedings of the Solar Conference
,
American Solar Energy Society
,
American Institute of Architects
, Madison, WI, pp.
273
278
.
23.
Rich
,
A. C.
,
1995
, “
Solar Collector Venting System
,” U.S. Patent No. 5,404,867.
24.
Slaman
,
M.
, and
Griessen
,
R.
,
2009
, “
Solar Collector Overheating Protection
,”
Sol. Energy
,
83
(
7
), pp.
982
987
.10.1016/j.solener.2009.01.001
25.
Wallner
,
G. M.
,
Resch
,
K.
, and
Hausner
,
R.
,
2008
, “
Property and Performance Requirements for Thermotropic Layers to Prevent Overheating in an All Polymeric Flat-Plate Collector
,”
Sol. Energy Mater. Sol. Cells
,
92
(
6
), pp.
614
620
.10.1016/j.solmat.2007.12.005
26.
Muehling
,
O.
,
Seeboth
,
A.
, and
Haeusler
,
T.
,
2009
, “
Variable Solar Control Using Thermotropic Core/Shell Particles
,”
Sol. Energy Mater. Sol. Cells
,
93
(
9
), pp.
1510
1517
.10.1016/j.solmat.2009.03.029
27.
Gladen
,
A. C.
,
Davidson
,
J. H.
, and
Mantell
,
S. C.
,
2013
, “
Selection of Thermotropic Materials for Overheat Protection of Polymer Absorbers
,”
Sol. Energy
,
104
, pp.
42
51
.10.1016/j.solener.2013.10.026
28.
Gladen
,
A. C.
,
Mantell
,
S. C.
, and
Davidson
,
J. H.
,
2013
, “
A Parametric Numerical Study of Radiative Transfer in Thermotropic Materials
,”
ASME
Paper No. HT2013-17183.10.1115/HT2013-17183
29.
Resch
,
K.
,
Hausner
,
R.
, and
Wallner
,
G. M.
,
2009
, “
All Polymeric Flat-Plate Collector—Potential of Thermotropic Layers to Prevent Overheating
,”
Proceedings of ISES World Congress 2007
, Beijing, China, Sept. 18–21,
D. Y.
Goswami
and
Y.
Zhao
, eds.,
Springer
,
Berlin, Heidelberg, Germany
, Vol.
I–V
, pp.
561
565
.
30.
Weber
,
A.
, and
Resch
,
K.
,
2014
, “
Thermotropic Glazings for Overheating Protection. I. Material Preselection, Formulation, and Light-Shielding Efficiency
,”
J. Appl. Polymer Sci.
,
131
(
4
), p. 39950.10.1002/app.39950
31.
Weber
,
A.
,
Schmid
,
A.
, and
Resch
,
K.
,
2014
, “
Thermotropic Glazings for Overheating Protection. II. Morphology and Structure–Property Relationships
,”
J. Appl. Polym. Sci.
,
131
(
4
), p. 39910.10.1002/app.39910
32.
Weber
,
A.
,
Schlögl
,
S.
, and
Resch
,
K.
,
2013
, “
Effect of Formulation and Processing Conditions on Light Shielding Efficiency of Thermotropic Systems With Fixed Domains Based on UV Curing Acrylate Resins
,”
J. Appl. Polym. Sci.
,
130
(
5
), pp.
3299
3310
.10.1002/app.39571
33.
Weber
,
A.
, and
Resch
,
K.
,
2012
, “
Thermotropic Glazings for Overheating Protection
,”
Energy Procedia
,
30
, pp.
471
477
.10.1016/j.egypro.2012.11.056
34.
Resch
,
K.
, and
Wallner
,
G. M.
,
2009
, “
Thermotropic Layers for Flat-Plate Collectors—A Review of Various Concepts for Overheating Protection With Polymeric Materials
,”
Sol. Energy Mater. Sol. Cells
,
93
(
1
), pp.
119
128
.10.1016/j.solmat.2008.09.004
35.
Gladen
,
A. C.
,
Mantell
,
S. C.
, and
Davidson
,
J. H.
,
2014
, “
A Parametric Numerical Study of Optical Behavior of Thermotropic Materials for Solar Thermal Collectors
,”
ASME J. Heat Transfer
,
136
(
7
), p.
072703
.10.1115/1.4027153
36.
Seeboth
,
A.
,
Ruhmann
,
R.
, and
Muehling
,
O.
,
2010
, “
Thermotropic and Thermochromic Polymer Based Materials for Adaptive Solar Control
,”
Materials
,
3
(
12
), pp.
5143
5168
.10.3390/ma3125143
37.
Nitz
,
P.
, and
Hartwig
,
H.
,
2005
, “
Solar Control With Thermotropic Layers
,”
Sol. Energy
,
79
(
6
), pp.
573
582
.10.1016/j.solener.2004.12.009
38.
Weber
,
A.
, and
Resch
,
K.
,
2014
, “
Thermotropic Systems With Fixed Domains Exhibiting Enhanced Overheating Protection Performance
,”
J. Appl. Poly. Sci.
,
131
(
12
), p. 40417.10.1002/app.40417
39.
Brunold
,
S.
,
Ruesch
,
F.
, and
Kunic
,
R.
,
2012
, “
Polymeric Materials for Solar Thermal Applications
,”
Polymeric Materials for Solar Thermal Applications
,
M.
Kohl
,
M. G.
Meir
,
P.
Papillon
,
G. M.
Wallner
, and
S.
Saile
, eds.,
Wiley-VCH Verlag & Co.
,
Weinheim, Germany
, pp.
319
349
.
40.
Lenel
,
U. R.
, and
Mudd
,
P. R.
,
1984
, “
A Review of Materials for Solar Heating Systems for Domestic Hot Water
,”
Sol. Energy
,
32
(
1
), pp.
109
120
.10.1016/0038-092X(84)90054-9
41.
Duffie
,
J.
, and
Beckman
,
W.
,
2006
,
Solar Engineering of Thermal Processes
,
3rd ed.
,
Wiley-Interscience
,
Hoboken
, NJ, pp.
204
237
.
42.
Papillon
,
P.
, and
Wilhelms
,
C.
,
2012
, “
Polymeric Materials for Solar Thermal Applications
,”
Polymeric Materials for Solar Thermal Applications
,
M.
Kohl
,
M. G.
Meir
,
P.
Papillon
,
G. M.
Wallner
, and
S.
Saile
, eds.,
Wiley-VCH Verlag & Co.
,
Weinheim, Germany
, pp.
29
70
.
43.
Solar Ratings & Certification Corporation (SRCC), OG-100 Certification, accessed June 17,
2014
, http://www.solar-rating.org/ratings/index.html
44.
Fischer
,
S.
,
Druck
,
H.
,
Bachmann
,
S.
,
Streicher
,
E.
,
Ullmann
,
J.
, and
Traub
,
B.
,
2012
, “
Conventional Collectors, Heat Stores, and Coatings
,”
Polymeric Materials for Solar Thermal Applications
,
Kohl
,
M.
,
Meir
,
M. G.
,
Papillon
,
P.
,
Wallner
,
G. M.
, and
Saile
,
S.
, eds.,
Wiley-VCH Verlag & Co.
,
Weinheim, Germany
, pp.
73
106
.
45.
Duffie
,
J.
, and
Beckman
,
W.
,
2006
,
Solar Engineering of Thermal Processes
,
3rd ed.
,
Wiley-Interscience
,
Hoboken
, NJ, p.
908
.
46.
Hollands
,
K.
,
Unny
,
T.
, and
Raithby
,
G.
,
1976
, “
Free Convective Heat Transfer Across Inclined Air Layers
,”
ASME J. Heat Transfer
,
98
(
2
), pp.
189
193
.10.1115/1.3450517
47.
McAdams
,
W. H.
,
1954
,
Heat Transmission
,
McGraw-Hill
,
New York
.
48.
Duffie
,
J.
, and
Beckman
,
W.
,
2006
,
Solar Engineering of Thermal Processes
,
3rd ed.
,
Wiley-Interscience
,
Hoboken
, NJ, pp.
139
173
.
49.
ASTM Standard G173,
2012
, Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37 Deg Tilted Surface, Vol. 14.04, Annual Book of ASTM Standards, West Conshohocken, PA.
50.
Mantell
,
S. C.
, and
Davidson
,
J. H.
,
2012
, “
Polymer Durability for Solar Thermal Applications
,”
Polymeric Materials for Solar Thermal Applications
,
M.
Kohl
,
M. G.
Meir
,
P.
Papillon
,
G. M.
Wallner
, and
S.
Saile
, eds.,
Wiley-VCH Verlag & Co.
,
Weinheim, Germany
, pp.
187
210
.
51.
Raman
,
R.
,
Mantell
,
S.
, and
Davidson
,
J.
,
2000
, “
A Review of Polymer Materials for Solar Water Heating Systems
,”
ASME Trans.-Am. Soc. Mech. Eng. J. Sol. Energy Eng.
,
122
(
2
), pp.
92
100
.10.1115/1.1288214
52.
UL746B,
1998
,
Polymeric Materials—Long Term Property Evaluations
,
Underwriters Laboratories, Inc.
,
Northbrook
, IL.
53.
ASTM Standard D648,
2007
,
Test Method for Deflection Temperature of Plastics Under Flexural Load
, Vol.
08.01
,
Annual Book of ASTM Standards
, West Conshohocken, PA.
You do not currently have access to this content.