Design and simulation of a heat pump for simultaneous heating and cooling using HFC or CO2 as a working fluid: Fid-Bau Portal

Design and simulation of a heat pump for simultaneous heating and cooling using HFC or CO2 as a working fluid

Byrne, Paul / Miriel, Jacques / Lenat, Yves

A Heat Pump for Simultaneous heating and cooling has been designed in the aim of heating and cooling luxury dwellings, hotels and smaller office buildings and also producing domestic hot water. Running costs and greenhouse gas emissions can be diminished by using the same electric energy to produce hot and cold water simultaneously. This machine also proposes an answer to reduce the performance loss of air-to-water heat pumps under low ambient temperatures and especially during defrosting sequences by alternation between an air evaporator and a water evaporator. The HPS has been designed for HFCs and CO2. The results are obtained for highly efficient compressors and perfect heat exchangers and are closely linked to these assumptions. Today, HFCs are the most efficient and 'secure' fluids on the market but they are greenhouse gases. Carbon dioxide is environmentally friendly but it is less efficient and its technology needs more development to be really competitive in space heating applications. Nevertheless its thermodynamic properties enable domestic hot water production. The alternated winter sequence offers a new solution for defrosting. Especially, it increases the average performance in heating, and increases further with a high subcooling capacity available with CO2. The CO2 HPS outperforms the HFC standard heat pump in terms of first law COP and annual electricity consumption and this opens the door to carbon dioxide as a working fluid for space heating applications. The properties of the carbon dioxide transcritical cycle enhance the operation of the HPS in the dual mode as shown through the Carnot COP and second law efficiency annual values. TEWI calculations conclude to a reduction of greenhouse gas emissions by the use of carbon dioxide instead of R407C as a working fluid for this concept of HPS. Also, the environmental analysis could be extended to the life cycle cost (LCC) which could advantage more carbon dioxide because of the difference between the synthesis of R407C and the capture of CO2 and because of smaller (thus probably cheaper in terms of CO2 emissions) components for CO2. In conclusion, transcritical CO2 technology is improving day after day and offers a slightly lower impact on global warming. However, HFC heat pumps for space heating and cooling still remain more efficient and less costly in terms of energy consumption.