Investigation of a combined air source heat pump and solar thermal heating system within a low energy research home

Abstract

Over 75 % of the energy consumption of an average UK home can be attributed to space heating and hot water production (Department of Energy and Climate Change 2009). As such, it is important to develop and install efficient low carbon systems, integrated into buildings with high thermal performance, in order to reduce overall energy demand. To date, testing of Air Source Heat Pump (ASHP) technology in the UK climate has been limited. This study investigates the performance of a combined Panasonic Aquarea 9 KW ASHP and Hoval SolKit® solar thermal collector (STC) within a thermally efficient inhabited research home, in order to assess the ability of the system to deliver heating and hot water requirements. The testing period extends from 4th July 2011 to 29th February 2012. Initial results indicate that the ASHP and STC combined system is able to deliver the required levels of heating and hot water in order to meet the requirements of the occupants, with reduced bills as compared to traditional heating systems. Indoor temperatures have been maintained at a stable comfortable level, alongside minimal or no reliance on an auxiliary immersion heater for hot water. An average coefficient of performance (COP) of 3.99 has been calculated for the dataset, exceeding the desired industry target COP of 3 but falling slightly below the manufacturer expected efficiency of 4.1. The COP fell below both values for a significant number of individual days, leading to questions over the consistency of the system efficiency. It should also be noted that the test period coincided with an unseasonable mild winter in the UK. Whilst a single renewable technology source is unlikely to provide the energy levels required to heat an average UK home throughout an entire year, the combined system installed in the test house performs favourably when compared to conventional non-renewable heating and hot water systems. In the context of previous research, this study does show positive results and demonstrates that an ASHP/STC combined system may be a suitable installation in a UK home.