Method of Choice of Low TEWI Refrigerant Blends

The TEWI analysis of residential heat pumps shows that it is sensitive to refrigerant emissions and mainly dependent on the seasonal coefficient of performance of the heating unit. Otherwise for countries where electricity is mainly produced by a combination of nuclear-power and hydro-power, the direct emissions become not negligible compared to the indirect emissions. Both direct and indirect emissions must then be considered. The selection of new refrigerant candidates will depend on climatic conditions, the refrigerant global warming potential, the refrigerant safety and many other criteria such as the COP, the volumetric capacity and system operating pressures and temperatures. This paper presents a new method for the selection of refrigerant blends based on a series of selection criteria. The flammability analysis is based on experimental data of flammability limits and theoretical heat of combustion calculations. The chemical reactions are also introduced. The RF-number introduced by Kondo as an index for flammability classification is used. This method is applied to retrofit applications of air-to-water heat pumps installed for moderate temperatures hydronic heating systems (55°C-45°C). Alternative blends are compared to R-407C. A first general evaluation shows a few number of refrigerant blends with flammable and non flammable refrigerants. A second more restricted evaluation shows some other blends with slightly flammable candidates.