A retrofit solar water-heating system has been operating for the past two years in a three-story apartment building at Drexel University. The system employs two conventional collector banks (9 PPG collectors) mounted at the latitude angle for Philadelphia of 40 deg from the horizontal and two double-exposure collectors (DEC's) mounted vertically in mirrored enclosures. The relative performance of the conventional and double-exposure collectors has been monitored with an instrumentation system which was developed and installed in the basement of the apartment building. The DEC units have been found to provide from two to four times as much useful heat output ...
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Description
A retrofit solar water-heating system has been operating for the past two years in a three-story apartment building at Drexel University. The system employs two conventional collector banks (9 PPG collectors) mounted at the latitude angle for Philadelphia of 40 deg from the horizontal and two double-exposure collectors (DEC's) mounted vertically in mirrored enclosures. The relative performance of the conventional and double-exposure collectors has been monitored with an instrumentation system which was developed and installed in the basement of the apartment building. The DEC units have been found to provide from two to four times as much useful heat output per panel area than the PPG collectors. The higher relative performance values occur on clear winter days whereas lower relative performance values are found on clear summer days and generally overcast days. A cost analysis for a DEC unit relative to a conventional collector has also been performed. In the Philadelphia area the DEC units with their mirror enclosures would cost approximately 1.7 times as much per panel area as conventional collectors. Since the DEC units provide two to four times as much useful heat output, they are a cost-effective choice for flat or gently sloping roofs for which they are designed. The performance of the DEC units relative to conventional collectors has also been calculated for both fixed-mirror units and for adjustable-mirror units. These calculations have shown that a modified rear mirror enclosure design would result in better DEC performance and that in general adjustable-mirror units are better than fixed-mirror units. A single DEC design was found to be appropriate for latitudes 35 to 45 deg. These calculations have also been extended to single-exposure collectors with flat mirror boosters.
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Larson, D. C. & Savery, C. W.Double-exposure collector system. Final technical report,
report,
October 19, 1979;
Philadelphia, Pennsylvania.
(digital.library.unt.edu/ark:/67531/metadc1093587/:
accessed February 21, 2019),
University of North Texas Libraries, Digital Library, digital.library.unt.edu;
crediting UNT Libraries Government Documents Department.
