Experimental Evaluation Of NightCool Nocturnal Radiation Cooling Concept: Performance Assessment In Scale Test Buildings

An experimental test evaluation has been conducted of a night sky cooling system designed to substantially reduce space cooling needs in homes in North American climates. The system uses a sealed attic covered by a highly conductive metal roof (a roof integrated radiator) which is selectively linked by air flow to the main zone with the attic zone to provide cooling- largely during nighttime hours. Available house mass is used to store sensible cooling. Additional dehumidification is done during the evening hours as warranted by interior conditions. A previous report describes a detailed simulation model of the relevant night cooling phenomenon, examining potential performance. Here, we summarize an experimental evaluation of concept performance using two highly instrumented test sheds. Data is presented on the comparative passive performance of the building thermal performance under static conditions (NightCool not operating), and also in a circumstance where NightCool is operating via natural convection alone between the interior of the test building and the sealed attic. Further tests show the performance of the full implementation of the concept with circulating fans when attic conditions are favorable for nocturnal cooling and with conventional air conditioning at other times. Achieved performance is in the expected range from the previous simulation analysis. Cooling rates were in the range of 2-6 Btu/ft2 of conditioned floor area under roof - from one third to a full ton of sensible cooling. Substituting for nighttime air conditioning, cooling energy reductions of 17-53% were demonstrated with energy efficiency ratios (EERs) ranging from 27 - 54 Btu/Wh