Small ammonia heat pumps for space and hot tap water heating

Abstract

In this study a small ammonia ground source heat pump with a capacity of 8,4 kW has been designed to provide space heating and hot water preparation with estimated max heat load of 7,5 kW for space heating and 2 kW for hot tap water preparation. The main components and materials have been chosen to avoid corrosion and to be compatible for work with ammonia. Calculations with engineering equation solver (EES) have been done to estimate heat pump performance and evaluate the necessary size of the water tank for the heating system. Heat transfer from the heat pump to the storage tank has been calculated considering seven different working regimes with variable heating demand from 1 to 7 kW. Usually the storage tank for heat pumps is designed to prevent very frequent on/off operation of the compressor due to variations in the heating load. In this case the optimal volume of the tank was found in order to cover heating demand during the peak hours of high electricity price according to the Nordic power market. Calculated COP = 4 (Tevap = -3°C, Tcond = 40°C) provides energy savings of up to 75% in comparison with the electrical heaters. In case of the variable price of the electricity it is possible to achieve more savings with the installation of the storage tank. Optimal volume of the tank is 1000 litres to cover 2-3 hour peaks of the high electricity price.