Domestic Retrofit Assessment of the Heat Pump System Considering the Impact of Heat Supply Temperature and Operating Mode of Control—A Case Study

Abstract

In this study, performance assessment of the variable speed compressor-based air source heat pump (ASHP) system as a domestic retrofit technology instead of fossil fuel-based heating technologies for the 1900s Mid terraced house is investigated. The assessment was conducted considering operating mode of control and heat supply temperature impact of the system. In the literature, ASHP system experimental development with variable speed mode (VSM) of control in comparison to fixed speed mode (FSM) of control at low to medium and high heat supply temperature in the context of UK was found with very limited number of studies, but without considering retrofit application. The focus of the earlier studies was on the individual components and performance improvement. The designed heat pump (HP), developed, and tested at constant heat load, simulating the real domestic heat demand under the controlled laboratory conditions and numerical modeling is utilized for the analysis purposes. The HP performance, energy demand, carbon emissions, and cost varies significantly due to changing heat supply temperature (35 °C, 45 °C, and 55 °C), control mode and accordingly the carbon emission and cost savings are achieved. The oil and gas boilers ranges from conventional to highly efficient type and evaluated in terms of annual running cost, energy consumptions, and carbon emissions in comparison with the HP system. Additionally, a comparative study with the existing retrofitted very high temperature ASHP inside the house is conducted. The developed HP at 55 °C could not defeat the very high heat supply temperature HP system (75 °C supply temperature) in performance and cost savings but become attractive at low supply temperature (35 °C). The HP system in VSM at low heat supply temperature instead of gas boiler (90% efficiency) could cut the annual carbon emissions by 59% but with additional 6% running cost for the Mid terraced test house in Belfast climatic conditions.