Exergetic and energy-economic analysis of a building integrated photovoltaic and thermal system

This paper presents a detailed exergetic and energy-economic analysis of a Building Integrated PhotoVoltaic Thermal (BIPVT) system. For an optimal use of building envelope, BIPVT systems, consisting of flat-plate PVT solar collectors, are integrated in the south facing facade of a non-residential high-rise building. The BIPVT collectors produce: i) thermal energy for space heating purposes, by a radiant floor system, and Domestic Hot Water (DHW) production, and ii) electricity to satisfy the building energy demand. Electric air-to-water heat pumps/chillers and water-to water heat pump are used as auxiliary systems for space heating / cooling and DHW preparation, respectively. In addition, with the aim to mitigate the effects of solar energy intermittency and obtain a virtually grid-independent system, an electricity energy storage system coupled to the BIPVTs system is modeled. In order to compare the proposed BIPVT system to a traditional building, a reference building model, i.e. without BIPVTs, energy storage and radiant floor, is considered. Here, the space heating and cooling is obtained by air-to-water heat pumps (one for each floor), DHW is produced by a condensing boiler and electricity is supplied by the national grid. The comparison is performed for three thermal zones, well representative of the thermal behavior of the whole building. In this paper, a detailed simulation model implemented in TRNSYS environment, is developed in order to predict the dynamic behaviour of the BIPVT system. Energy and exergy balances are taken into account to determine, for the 1-year operation, the exergy destructions and exergetic efficiencies of each of the investigated components and of the whole system. The magnitude of the irreversibilities in the system are calculated with the aim to propose possible enhancements. In addition, the energy analysis of the proposed BIPVT system located in several European weather zones are also carried out. Such analysis aims to also assess the useful / undesired effects due to the building integration of PVTs and to the electricity storage on the building energy demands (e.g. heating / cooling and electricity). Finally, the economic viability of the proposed system is also discussed.