losses caused by frosting and defrosting, and.losses because of transient conditions in the heating system during operation,.losses of the heat pump unit itself, realizing the real process and not the ideal Carnot process, with non-isentropic compression, electrical losses, temperature drops at the condenser and the evaporator, pressure drops, etc.,.The reasons for this poor efficiency factor are: This means that the efficiency factor of the actual system is 0.27. If one models this system, using a heat pump with the same heating capacity, but assuming ideal capacity control and operation with Carnot efficiency, the SPF will become 8.35. Taking a monovalent air/water heat pump integrated directly into the return line of a low-temperature distribution system, the SPF which can be achieved will be in the range of 2.2 to 2.4.
The seasonal performance factors of heat pump systems are usually poor compared to the steady state COP.
However, caused by the better thermal insulation of the building shell cooling becomes more and more common, like in Japan and in the US. In Europe the term heat pump has used for heating-only units with the heat sources outside air or exhaust air from the ventilation system, ground and ground water, combined with hydronic heat distribution systems (Gilli, Halozan 2001). The general term heat pumping technologies is used for processes in which the natural heat flow from a higher to a lower temperature level is reversed by adding high value energy, i.e. Heat pumps are one of the key technologies for energy conservation, increasing the share of renewable energy used and reducing CO2 emissions. With highly efficient systems the advantages of thermodynamic heating and cooling can be demonstrated and used for reducing the energy demand significantly. The choice of the refrigerant is most commonly a compromise between efficiency and cost, smaller equipment using a high-pressure working fluid can reduce the cost, a working fluid with low discharge temperatures can avoid a two-stage system. This COP depends on the refrigerant selected and on the components used like the compressor, the size and the design of condenser and evaporator, the flow sheet – single stage, two stage, economiser or cascade – and the internal cycle control. The efficiency of the unit commonly expressed by the COP, the coefficient of performance. Taking different applications of heat pumping technologies several items have to be taken into consideration like drive energy, design of the unit, integration into a system and the control strategy.
Heat pumps offer the possibility of reducing energy consumption significantly, mainly in the building sector. It is therefore generally accepted that: increasing the uptake of renewable energy systems and improving the thermal performance of both new and existing homes is critical if Europe is to achieve ambitious emission targets. INTRODUCTIONĮuropean governments have committed to significantly reduce the carbon footprint of new and existing homes. Inffeldgasse 25 / B, A-8010 Graz, Austria 1. Institute of Thermal Engineering, Graz University of Technology, Heat Pumps Reducing Losses – Increasing Efficiency Heat Pumps Reducing Losses – Increasing Efficiency