Performance Evaluation of the Senergy Polycarbonate and Asphalt Carbon Nano-Tube Solar Water Heating Collectors for Building Integration

European Directives 2009/28 and 2010/31 require member states to reduce CO2 emissions by 20%, increase the share of renewable energy to 20%, achieve energy savings of 20% and mandate that all new buildings must be “nearly zero energy”, by 2020. Solar water heating collectors are cost effective and well suited to integration into building envelopes (facades and roofs) to provide heat for direct use inside the building. Senergy building integrated solar collectors are designed to offset traditional roofing elements. Two working
prototypes; one Polycarbonate Carbon Nano-Tube (PCNT) collector and one Asphalt Carbon Nano-Tube (ACNT) collector; have been tested at the solar simulator facility at Ulster University and their performances compared. The PCNT collector uses innovative polycarbonate twin-wall sheeting which forms both the solar absorptive surface and the heat transfer fluid channeling elements. The ACNT collector has an asphalt based absorber with embedded serpentine copper tubing to act as the heat transfer fluid channeling element. Tests
were conducted with 800 W/m2 illumination intensity and for water inlet temperatures between from 23°C and 47°C. The PCNT collector achieved 62% maximum collection efficiency compared to 45% for the ACNT collector. The heat loss coefficients were 6.0 and 8.1 W/m2K respectively. The performance of the PCNT collector was similar to benchmark values for single glazed collectors with selective absorber surfaces. The ACNT collector performance was lower than a typical unglazed solar water heater with non-selective absorber due to the high thermal resistance between the absorber surface and the serpentine tubing.