Abstract
Solar assisted heat pump systems have been widely applied in domestic hot water productions due to their sustainability and stability in operations. However, their performance efficiency requires further improvement using advanced technologies such as energy storage with phase change materials (PCM) and optimal system controls. Accordingly, a test rig of a new indirect solar assisted heat pump (IDX-SAHP) system has been designed, built and instrumented. The IDX-SAHP system consists of three operational loops: solar thermal, solar assisted heat pump and load profile. A PCM heat exchanger tank was purposely designed and installed in the system solar thermal loop to store solar energy, when applicable, and release heat when required by the heat pump. In addition, an air cooling heat exchanger was also installed in the solar thermal loop to absorb heat from the ambient air for the heat pump. A detailed control strategy has been designed and implemented for the system for efficient operation in different modes and maintain constant load supply water temperature during an operational day. In different weather conditions of sunny and overcast, comprehensive measurements were carried out on the test rig and system structures with and without the PCM tank. Test results showed that the system could efficiently meet the daily domestic hot water demand and the PCM heat exchanger integration exerted a significant effect on system stability and performance efficiency. Quantitatively, the average COP of the IDX-SHAP system with a PCM tank could increase 6.1% and 14.0% on sunny and cloudy days respectively compared to systems without PCM tank integration.
Highlights
In the UK, up to 50% of national energy is consumed for heating purposes by direct burning of fossil fuels, in particular natural gas (IEA, 2007)
The test results can demonstrate that the system performance can be significantly improved on various weather conditions if the phase change material (PCM) tank could be integrated
The PCM tank was more compact and efficient comparing to conventional water storage tanks used in IDX-Solar Assisted Heat Pump (SAHP) systems
Summary
In the UK, up to 50% of national energy is consumed for heating purposes by direct burning of fossil fuels, in particular natural gas (IEA, 2007). For a series IDX-SAHP system, the solar energy is collected by a solar collector and stored in a water storage tank which is used as the only heat source for the heat pump. The study was effective in identifying the modes of operation and further numerical validation with focus on thermal storage stratification (Banister et al, 2014a, 2014b) Of these IDX-SAHP systems, the parallel and dual source are preferable in terms of system operational stability. A PCM storage heat exchanger tank and an air-source heat exchanger were purposely built and installed in the system solar thermal loop and connected to the heat pump evaporator. The research outcomes can lead to the optimisation of future system designs and controls
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