Evaluation of the Vuilleumier heat pump for heating applications

A general evaluation of the performance of a Vuilleumier heat pump for residential heating is given. The basic considerations were devoted to the choice of hot, intermediate and cold operating volumes and temperatures, to the phase angle of the two displacers, to the dead volumes and to the choice of the working gas. Specific attention was then paid to the heat transfer problems at each of the three temperatures. The main difficulty was identified with the solid-gas heat transfer at both low and intermediate temperatures. For a machine of gas volume 5,2 dm3, pressure 150 bar, operating frequency 1/s and heat rejecting capacity 10 kW, the temperature drops were evaluated to be 105 K over the hot end heat exchanger, 40 K over the intermediate temperature heat exchanger, and 47 K over the cold end heat exchanger. This limits the coefficient of performance defined as the ratio of the heat rejected at the intermediate temperature to the heat supplied at the high temperature to 1,9. This figure is lower still when other loss factors are taken into account. Moreover, the pressure level should necessarily be dropped in order to comply with the regulations for unauthorized users. Another sample calculation for 16 bar gas pressure, 3,3 dm3 gas volume, and 16 1/s operating frequency yielded only 1,3 for the coefficient of performance.