Experimental investigation of a Scroll unit used as a compressor and as an expander in a Heat Pump/ORC reversible unit

On one hand, the use of solar energy for heating and electricity production should increase in the future to reduce greenhouse emissions. On the other hand, the use of water to water heat pumps allows the production of heat effectively in many applications. In this context, it is appropriate to study the concept of a reversible HP/ORC unit. This innovative system includes a water to water heat pump connected to a solar roof and a geothermal heat exchanger. This heat pump is also capable of reversing its cycle and work as an Organic Rankine Cycle. This heat is used primarily to cover the annual heating needs and excess heat generated during the summer is used to produce electricity. The key feature to achieve this is the reversibility of the compressor unit, i.e. its ability to work as an expander. This paper presents the experimental investigation on a first prototype of this HP/ORC reversible unit with a scroll compressor and refrigerant R134a. A global efficiency of 5.7% is reached in ORC mode with temperature of evaporation and condensation respectively of 88°C and 25°C. In heat pump mode, a COP of 4.2 is obtained with temperature of evaporation and condensation respectively of 21°C and 61°C. The scroll unit presents encouraging performance with isentropic efficiencies of 63% in expander mode and 77% in compressor mode.