Heat Pump control comparison of a conventional superheat system over a subcooling control system for Domestic Hot Water production

Abstract

[EN] The water heating consumption of the average European dwelling accounts at this moment for 14.5 %, according to the European Commission, whereas heating and cooling percentage account for 64.7 %. The European Union, with the introduction of the Nearly Zero Energy Buildings (NZEB) concept, intends to decrease in a great amount the total energy consumption of the residential sector acting over the percentage associated to heating. This will have an effect on the water heating consumption, increasing its consumption percentage. Therefore, in order to reduce the residential sector consumption and more concretely the percentage associated to water heating consumption, it will be key the use of highly energy efficient technologies since it is not possible to reduce the water heating energy consumption by acting on the demand without the risk of not satisfying the user comfort. In that sense, heat pumps are a technology of increasing interest. It is considered as renewable when its SPF is above 2.5, its production does not depend on external factors (as sunlight) and will play a key role in the cities of the future since it has the capability of acting as a booster from heat distribution networks. At this moment, the heat pumps available in the market for domestic hot water production using subcritical cycles are cost-effective but its design does not differ significantly from the used for heating applications. In the frame of the European project NEXTHPG, a heat pump system specifically designed for domestic hot water production with a variable subcooling control was developed. In this work, a comparison between the energy consumption at the system level of this prototype with a commercial water-to-water heat pump for domestic hot water production is performed. The results show a big difference in terms of energy efficiency between both cases. The variable subcooling case results in a 26.68 % positive energy efficiency difference regarding the conventional case when compared in their maximum efficiency point. The sizing of the heat pump-storage tank duality plays an important role since it could lead to an energy efficiency loss of almost 17 %. These results show clearly the advantages of the innovative heat pump model in front of the conventional heat pumps used for domestic hot water production.