Thermal performance analysis of a solar water heating system with heat pipe evacuated tube collector using data from a field trial

This paper presents an analysis of the thermal performance of a solar water heating system with heat pipe evacuated tube collector using data obtained from a field trial installation over a year in Dublin, Ireland. An automated sub-system was developed and incorporated to control the hot water draw-offs and electric immersion heater to mimic the operation of solar water heating systems in domestic dwellings. The maximum recorded collector outlet fluid temperature was 70.3 degrees C while the water temperature at the bottom of the hot water tank was 59.5 degrees C. The annual average daily energy collected was 20.4 MJ d(-1), energy delivered by the solar coil was 16.8 MJ d(-1), supply pipe loss was 3.6 MJ d(-1), solar fraction was 33.8%, collector efficiency was 63.2% and system efficiency was 52.0%. Reducing the supply pipe losses which represented 17.7% of energy collected and 21.5% of energy delivered to the hot water tank, and developing a better pump control strategy for heavily overcast and intermittent cloud covered days could result in system improvement. (C) 2013 Elsevier Ltd. All rights reserved.