Dynamic simulation of a heat pump serving a historical building: seasonal performance and economic evaluation

The effectiveness of a retrofit action on the heat generation system of a historical building of the University of Pisa was evaluated by means of a full dynamic energy simulation and subsequent cost-benefit analysis. The building is mainly used for offices and is located in the center of the city. It can be considered as a benchmark for many Italian Public Administration buildings. The analysis is split into two phases, namely: i) dynamic simulation of the building during the heating season, implementing actual daily and weekly schedules of presence, use of artificial lighting and other electrical equipment, management of fan coil units, and activation of the existing boiler; the calculated seasonal energy use is validated with past billings of natural gas; ii) evaluation of energy and economic savings obtainable by replacing the boiler with an air-to-water electrically-driven modulating heat pump; its performance is obtained by simulating thermodynamic cycles under real load conditions (working fluid: R134a). The success of the proposed retrofit measure was proven by economic investment metrics, viz.: discounted payback period, internal rate of return, net present value and profitability index at the expected end of life of the heat pump. The developed procedure can be readily applied to increase the accuracy of energy audit calculations involving a complex system as a heat pump, whose performance in tailored rating can be largely underestimated by current technical standards.