On the optimal mix between lead-acid battery and thermal storage tank for PV and heat pump systems in high performance buildings

The coming into force of the European Directive 2009/28/CE [1] increases the role of renewable energy sources to satisfy the energy consumptions of new buildings and major renovations. In this respect, the vapor-compression heat pump coupled with PV panels is a promising solution and, consequently, it is increasingly used for residential heating applications. This HVAC solution is especially advantageous in high performance building when low temperature hydronic systems are adopted. However, in these buildings some issues arise in the HVAC control and the building might be easily subject to poor comfort conditions when approaching the nZEB target while maintaining economical convenience. Besides, the seasonal performance of the heating system is strongly dependent on the HVAC design. Hence, the optimal size of the storage components is a key aspect in order to maximize the renewable coverage factor, overcoming the shift in time between PV production and energy demand. For this reason, different strategies may be adopted such as the thermal storage tank or the electricity storage in lead-acid battery. This paper analyses the mix among the thermal storage tank, the lead-acid battery and the thermal capacitance of the building envelope for the optimal design solutions in three Italian climates. The complex interactions among building, occupants, weather conditions and HVAC systems are considered by means of a dynamic simulation tool. The optimal design solutions were studied, according to the cost optimal approach of the EPBD context, by means of a genetic algorithm developed in Matlab®. The energy performance for heating (EPh) and the net present value (NPV) are considered as competitive goals.