18 May 2017

O.1.4.5 High efficiency heat pumps for low temperature lift applications

Today heat pump and chiller units are widespread and sophisticated technologies for heating and cooling applications in buildings. Their efficiency as measured by the coefficient of performance (COP) is closely related to the inner temperature lift. In applications with a low external temperature lift, these units have a large potential for saving primary energy and reducing the CO2 emissions of buildings. Unfortunately, this potential is not fully exploited because standard systems are designed for lifts of 30-60 K. The following paper presents practical guidelines for the planning and designing of systems for low temperature lift applications. In order to demonstrate the potential for efficiency improvements, two systems for low temperature lifts were developed, one with a reciprocating compressor and the other with a small-scale turbo compressor. Based on these two systems, detailed experiments were carried out to quantify and confirm the potential of low temperature lift application. Over a relevant temperature lift range of 10 K to 30 K, the low temperature lift heat pump with a turbo compressor achieves an unprecedented high and relatively constant Carnot efficiency of around 60%. By using geothermal heat probes in combination with efficient heat delivery and supply systems, a COP of about 9 for heating mode can be achieved for a temperature lift of 20 K. The use of high temperature space cooling systems in combination with optimized recooling systems leads to a temperature lift of approximately 10 K and a COP of about 15 for cooling mode.