Calculation of Annual Energy Consumption of a Heat Pump by the Bin-method

Heat pumps are electrical devices that transfer thermal energy from the environment into a heated space. Thanks to their ability, compared to electric resistance heaters, to deliver three to six times more thermal energy to the conditioned space, heat pumps represent an unrivaled solution in heating technology in terms of efficiency. When the thermal energy source is outdoor air — as in the case of air-to-air heat pumps — their efficiency directly depends on the temperature of the outdoor air. Therefore, the assessment of the total energy consumption of a heat pump must be based on a methodology that takes into account the variation of this temperature. According to Standard EN 15316, two methods are defined for determining the total energy consumption of a heat pump: the degree-day method and the temperature-bin method. In domestic practice, only the simpler and less accurate degree-day method is used. The temperature-bin method, although more reliable, has remained almost unknown, probably due to the need for hourly outdoor air temperature data. To present and bring this method closer to engineering practice, the paper describes the theoretical background and outlines the main steps of the method, while its application is demonstrated through a case study of the EPS AD office building in Bajina Bašta. By grouping actual hourly outdoor air temperature data into temperature bins and linking them with the operating points of the heat pump, while including the operation of auxiliary equipment and backup heaters, the total annual electricity consumption was determined. The obtained consumption of 56,150 kWh of electricity — of which 86% occurs in the heating and 14% in the cooling mode — clearly indicates the dominant influence of winter hours on total energy use.