Conference Year

2016

Keywords

Propane, heat pumps, natural refrigerants, hot water, subcooling

Abstract

In the last decades the use of heat pumps are in increased due to its potential for high efficiency. They are considered an environmentally friendly technology, where a portion of the energy captured by a heat pump having an estimated average seasonal performance factor (SPF) higher than a reference value is considered as if it were obtained from renewable energy sources. For the specific case of domestic hot water production, where the water temperature lift is considerably high, e.g. 50K, transcritical cycles working with CO2 have focus most of the attention from the scientific community due to its high performance when working with high water temperature lift. The reason of this high performance, is the heat rejection process at gas cooler, which entails a high temperature glide in the refrigerant side, hence the temperature profile between the refrigerant and water side fits better for the transcritical CO2 than the cases where a two phase process takes place. The temperature profile of the refrigerant in a subcritical system can be modified by adding subcooling in order to obtain a similar effect that the CO2 transcritical cycles. In this way, the refrigerant temperature profile can be adapted to water temperature profile by means of subcooling, which will be higher for higher water temperature lift. Hence subcooling is a way to enhance the effectiveness of the condenser in a subcritical cycle. This paper presents the experimental results of a water to water heat pump for sanitary hot water production specially designed to work with large amount of subcooling, where the working fluid, is the natural refrigerant, propane. The results have shown a performance improvement up to 31% in heating COP, when working with subcooling compared with the same heat pump without subcooling.Â

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