18 May 2017
The increases in efficiency of air/water heat pumps (A/W-HP) for building services through capacity control instead of on/off-control of compressor and fan have been proven theoretically and shown practically on the market. In the presented project, the potential for improvements of brine/water heat pumps (B/W-HP) through capacity control was quantified and an optimal control strategy was developed. Relevant interrelations for planning, designing and controlling efficient B/W-HPs for broad applications are described. The studies showed that for maximizing the efficiency of capacity-controlled B/W-HPs the compressor and the brine mass flow must be controlled whereupon the part-load efficiency of the compressor has a significant influence on the optimum control strategy. The seasonal performance factors (SPFs) of a B/W-HP with capacity control were theoretically and experimentally confirmed to be consistently higher than those of the on/off-controlled HP. The increase in efficiency remarkably depends on the operating conditions. For a heating water supply temperature of 46°C and a geothermal heat probe temperature of 6°C the examined capacity-controlled B/W-HP is 5% more efficient than the on/off-controlled B/W-HP. A heating water supply temperature of 30°C and a geothermal heat probe temperature of 13°C result in the capacity-controlled HP being 11% more efficient.