The paper presents the results of the heat pump operation cooperating with a buffer bin with a variable volume included in the heating system of the greenhouse facility. The research results cover the analysis of physical parameters of the heat pump in varied conditions of the power demand. The research was carried out during operation of the pump, which cooperated with three selected volumes of the buffer bin. The obtained results allow statement that application of buffer bins is justified in the heating systems of greenhouse facilities supplied with the heat pump. A higher volume of the bin allows obtaining a higher index of efficiency and higher endurance of the spring aggregate operation. Increasing the buffer bin volume allows elimination of energy peaks and considerably improves internal microclimat conditions. Increasing the bin volume from 120 to 350 litres we obtain the increase of COP index by 80% and we eliminate approx. 30% of turn ons of the compressor operation within one day.