Energy and economic analysis of different heat pump systems for space heating

The consumption of natural gas as a primary energy source in Italy has increased during recent years, mainly due to more widespread use of modern natural gas-fired combined cycle power plants. It is generally accepted that such an increased use of natural gas is beneficial, particularly in summer, due to the “take-or-pay” contracts that often regulate the energy supply. Conversely, the use of electrical energy should be decreased, in order to limit the “peak demand” problem that has become prevalent in Italy. Therefore, besides electrically driven heat pumps that achieve good efficiencies, it is interesting to also consider the option of combustion engine driven heat pumps for space heating purposes. In the latter type of heat pump, losses attributed to the production and transport of electricity are eliminated and, in addition, there is the possibility to re-use the heat from the combustion engine. This paper presents an assessment of the annual economic and energy profiles of electric and internal combustion engine heat pumps for space heating purposes. Due to the dependency of the performance of such technology on the source and sink (heating circuit) temperature levels, a comparison is performed for air-to-water heat pump systems (the most widely used) in two cases of maximum flow temperatures. The calculations show that natural gas-driven heat pumps can achieve approximately the same efficiency as electrically driven heat pumps that are powered with electricity from modern natural gas-fired combined cycle power plants. Within this study, the efficiencies of such systems are also compared to those that utilise conventional boiler technologies.