Hybrid system, heat pump, boiler, simulation
The contribution of residential buildings primary energy consumption in the U.S. accounts for more than 20% of the total. In this context, improving the efficiency of heating systems represents a key point for keeping up with the carbon reduction goals. Air-to-water heat pumps are a promising technology that has been deeply studied in recent years. Their main advantage is to improve the share of renewables. Nevertheless, they have some drawbacks, such as the poor efficiency at low ambient temperatures and at high supply water temperatures, necessary e.g. for domestic hot water production and in high temperature heating systems. The latter can be found in a high percentage of the building stock. Hybrid systems combining heat pumps and boilers (HHPS) can represent a viable solution to overcome these issues. The sizing of the generators and the control logic according to which they are operated play an important role in the performance of the system. For this purpose, comprehensive studies analyzing different types of buildings in different climates and considering both space heating (SH) and domestic hot water (DHW) production are still missing in the literature. The aim of this work is to identify the best configuration of system, in terms of primary energy consumption, for different heating loads. To do so, a model of the hybrid system is firstly developed by means of a technical computing language (TCL) software. It includes the control logic, that manages the switching of the devices according to the operating conditions. The TCL model has been combined with a dynamic building simulation (DBS). Two different configurations of HHPS were analyzed varying different parameters, such as building thermal insulation, type of heating emission system, DHW demand profile and climate, with a corresponding demand of SH and DHW. The hybrid configurations are compared to a heat pump only solution. The paper presents the results of the simulations with the aim of identifying the most efficient system configuration for each set of parameters considered, in terms of primary energy consumption.