ENHANCING ENERGY UTILISATION IN BUILDING WITH COMBINING BUILDING INTEGARTED PV AND AIR SOURCE HEAT PUMP FOR UNDERFLOOR HEATING USING PHASE CHANGE MATERIALS

Installation of renewable energy to building heating systems with cost-effective and affordable ways is becoming an ever-growing factor. Heat Pump (HP) is a high energy efficient renewable energy device which can be a renewable-based alternative to fossil fuel boilers in buildings. Air source heat pumps (ASHPs) as a promising solution achieves the carbon reduction target in the domestic sector, but the limitation of electricity consumption and low supply flow temperatures (for most of the standard ASHPs the supplied heat temperature is around 55°C) will hinder the implementation of ASHP for domestic applications and replace the existing fossil boiler. With 20% of households using heat pumps, the peak grid demand increases by 7.5 GW (14%) making extra burden to the grid. However, the low temperature water supply by ASHP can benefit to the underfloor heating in the building, which provides the most indoor thermal comfort environment. The building integration of photovoltaics (BIPV) is another type of renewable energy, where the PV elements actually become an integral part of the building: by simultaneously serving as building envelope material and it acts as power generator. There is a growing consensus that the generated electricity by photovoltaic should provide electricity at the point of use, therefore the BIPV power can be used to drive ASHP. However, the on-site production of solar electricity is an intermittent source, typically the greatest may not be at or near the time of a building's peak loads for residential demanding. A thermal store is necessary for storing the heat produced by ASHP during the day time and discharge the heat for later usage. In addition, the high temperature in BIPV need to be regulated in order to avoid the reduction of the solar power conversion efficiency. Phase change materials (PCMs) absorb a large amount of energy as latent heat at a relative constant phase transition temperature and are thus used for passive heat storage and temperature control. PCMs incorporated into BIPV and underfloor heating system in buildings may be suitable for regulating the PV temperature rising and storing the heat from ASHP for underfloor heating.

A two dimensional temperature based finite volume numerical simulation model has been developed and experimentally validated for PCM energy store and temperature regulation. Using electricity generated by BIPV to drive the ASHP and store the thermal energy to thermal mass of PCM in underfloor heating system has been studied considerably in this paper. It has been found that the effect of using cooling coil of ASHP (evaporator) to augment the temperature regulation in BIPV keeps PV electricity efficiency at a high level. This paper summarizes the results of a detailed theoretical investigation and analysis of solar energy production and storage control in buildings. An optimised combination of using solar power to drive ASHP and store the heat in PCM for underfloor heating could improve the energy efficiency of PV through temperature regulation and may achieve a cost-effective and affordable heating system the building.