22 May 2002
Carbon dioxide (CO2) is one of the very few non-toxic and non-flammable working fluids that neither contri¬butes to ozone depletion nor global warming, and CO2 is therefore regarded a promi¬sing long-term alternative to the CFCs, HCFCs and HFCs in many heat pumping appli-cations. CO2 has unique thermo¬¬¬physical properties, and by utilising these proper¬ties by means of optimised com¬po¬¬¬nent and system design, high energy efficiency may be achieved.
Preliminary investigations have demonstrated that a residential CO2 heat pump system is able to achieve the same COP as brine-to-water heat pumps using conventional working fluids. In order to demonstrate the potential of the technology, a project has been initiated at NTNU-SINTEF in Norway. In addition to modelling of the main components and system simulation, a full scale prototype brine-to-water CO2 heat pump system will be designed and tested. The prototype will deliver heat to a low temperature floor heating system, and will cover the entire hot water demand in the house. The gas cooler will be divided into separate sections for preheating of city water, space heating and reheating of hot water, and the optimum supercritical pressure is estimated to be around 80 to 85 bar.