Development of a heat pump running cost comparison tool

A tool was developed for Marstair Ltd, a leading HVAC systems manufacturer, to allow comparisons of the economic and environmental performance of an air source heat pump with other technologies and fuels. The basis of the tool is an empirical spreadsheet based model of the heat pump incorporating building performance data that was derived using dynamic thermal simulation of three Scottish house types, under conditions of continuous and intermittent occupancy. The tool allows the effects of equipment efficiencies, fuel tariffs, and CO₂ emission assumptions on the comparisons to be easily assessed.

The empirical model was constructed in the form of an Excel spreadsheet. This carries out a series of calculations at each hourly time step using demand data derived from the dynamic simulation for a complete year, for each combination of house type and heating schedule. A two-dimensional frequency distribution was derived to analyse the hourly data, and allowed a considerable reduction in the size of the spreadsheet, with no significant loss of calculation accuracy.

The performance of the heat pump in meeting the heat demand is compared to that of four alternative heat sources: a gas condensing boiler, an oil fired boiler, a coal fired boiler, and direct electric heating. The fuel consumption, fuel cost and CO₂ emissions for each of the four alternative technologies for the six house type and occupancy scenarios were calculated.

The figure shows the annual costs associated with meeting the heating requirement for each technology type and for each housing scenario. The tool demonstrates that deployment of air source heat pump technology in these housing types would yield energy costs comparable with modern (condensing) gas or oil fired boilers, and considerably lower than direct electric or coal fired heating systems. CO₂ emissions for the heat pump were 40% to 70% less than those for the other fuel fuel types.

Commenting on these results, John Lightfoot, Sales Director of Marstair said “Thank you for the excellent work carried out on our behalf. The project was executed with total professionalism, on time and to budget. Without your assistance we would not have been able to demonstrate so clearly to our prospective client base, the benefits our product could offer to them in terms of helping to reduce fuel poverty, whilst at the same time reducing carbon emissions by up to 3 tonnes per dwelling per annum. I look forward to working with you again in the near future.”