Financial and energetic evaluation of solar-assisted heat pump underfloor heating systems with phase change materials

The objective of this work is the investigation of various underfloor solar heat pump heating systems with and without phase change materials (PCMs) in the floor layer. More specifically, a building of 100 m(2) floor area in Athens (Greece) is simulated and evaluated during the winter. The analysis is conducted with TRNSYS software and the results are presented in energy and financial terms. Solar collectors such as flat-plate, photovoltaic and thermal-photovoltaic are coupled to a tank which feeds a heat pump for space-heating purposes. In order to increase the storage capacity, a PCM-layer is placed on the underfloor heating system and different cases are examined by changing the thickness of the insulation in the floor and the area of the collectors. Moreover, this study presents the capital, variable and total cost, the electricity consumption, the coefficient of performance, the solar cover and the indoor temperature of the building for all the systems. The results prove that the use of the PCM-layer on the underfloor heating system reduces the heating load about 40% and the variable costs up to 20% because the electricity consumption can be reduced between 42% and 67%. Moreover, a multi-objective procedure was performed in order to evaluate all the scenarios and it is found that the thermal-photovoltaics seem to be the most appropriate cases due to the extremely low grid electricity consumption. The simple payback period of the system with flat plate collectors without PCM has been found 10.2 years and with PCM 18.3 years.