Heating season performance of a full-scale heat pipe assisted solar wall

Previous computer simulations and bench-scale experiments showed that the heat pipe assisted solar wall had the potential for significantly improved performance relative to conventional passive space heating systems. To further test this potential, a full-scale prototype of the heat pipe system was designed, built and installed in a classroom on the University of Louisville campus in Louisville, KY. During the spring heating season of 2010 (January–April), maximum daily peak thermal efficiency was 83.7% and average daily peak thermal efficiency was 61.4%. The maximum hourly average room gain achieved during the season was 163 W/m2. On days with good solar insolation, the thermal storage was heated to temperatures sufficient to provide significant energy to the classroom – even during the coldest days of the season. During the longest period (4 days) of low insolation during the season, average hourly heat delivery to the room from storage remained positive, and was never less than 16.6 W/m2. During good insolation days following a period of consecutive low insolation days, thermal storage temperature was quickly restored to levels comparable to those obtained during consecutive good insolation days. Estimated heat removal factor * transmittance absorptance product FR(τα) and heat removal factor * overall loss coefficient FRUL values for the system were comparable to those for glazed liquid active collectors.

► Full-scale prototype achieved maximum daily peak thermal efficiency of 83.7%.
► Average daily peak thermal efficiency was 61.4%.
► Heat delivery to room varied from 163 W/m2 on a warm, sunny day to 16.6 W/m2 after four days of low insolation.
► FR(τα) and FRUL values for the system were comparable to those for glazed liquid active collectors.