Carbon, Costs and Coefficient of Performance – New Metrics for Heat Pumps

The coefficient of performance (COP) is traditionally used as an indication of the
efficiency of refrigeration, air-conditioning and heat pump (RACHP) systems, being used to derive its energy consumption and running costs, with higher COP indicating higher efficiency. As the electricity grid decarbonises, there are significant variations in the carbon intensity and cost of electricity, which is due to the fluctuating nature of renewable energy. This leads to periods when carbon emission factors and prices for electricity are considerably reduced. At these times, it could be useful to run heat pumps and air-conditioners, irrespective of their COPs, as operating costs and carbon emissions would be at their lowest. This paper investigates the impacts of time of use by analysing the carbon content and generation costs for heat, based on a combination of COP with historical data on average grid carbon intensity and dynamic electricity prices in the UK. Based upon a case study of a heat pump, the investigation shows how the proposed metrics can act as indicators of the carbon efficiency and
operating expenditure of air-conditioners and heat pumps, building upon the traditional COP concept to better express the benefits of RACHP technologies.