Performance evaluation of the senergy polycarbonate and asphalt carbon nanotube solar water heating collectors for building integration

Senergy building integrated solar thermal collectors aim to reduce costs of solar water heating systems by utilizing polymer materials and offsetting costs of conventional roofing construction components. Carbon nanotubes can be added to polymer materials to improve their thermal, optical and mechanical properties. Two working prototypes; one Polycarbonate Carbon Nano-Tube (PCNT) collector and one Asphalt Carbon Nano-Tube (ACNT) collector; have been tested using the solar simulator facility at Ulster University and their performances compared. The PCNT collector is single glazed and uses a twinwall sheet to act as both the solar absorptive surface and the heat transfer fluid channeling element. The ACNT collector is unglazed and has an asphalt based absorber with embedded serpentine copper tubing to channel the heat transfer fluid. Tests were conducted with 800 W m�2 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 m�2 K�1 respectively. The performance of the PCNT collector was similar to benchmark values for single glazed collectors with selective absorber surfaces. The ACNT collector responded very slowly andperformance 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.