Optimal design and operation of a central domestic hot water heat pump system for a group of dwellings employing low temperature waste heat as a source

In this work, a study of an energy recovery system from a low-grade temperature source based on heat pumps for domestic hot water is done. The main components of the system are a pre-heating heat exchanger, an optimized heat pump for domestic hot water production, and a variable-volume storage tank. A model has been developed in TRNSYS to analyse the best configuration and control strategy of the system in order to satisfy the profile demands of 10, 20, and 30 multifamily houses, which are considered as a representative target market for this type of application. From this analysis, the influence of the design/sizing parameters on the system CO2 emissions has been obtained and a design criterium for their minimization has been supplied. Finally, a sensitivity analysis based on different net and heat source temperatures has been done in order to estimate the generalizability of the proposed solution. The obtained results show that this kind of system, with the proper design, sizing, and operation, offers potential CO2 emissions reductions by a factor of almost five compared to a conventional gas boiler system but a bad system selection could reduce this potential benefit up to 25%. •Subcooled heat pump maximizes the efficiency in energy recovery applications.•Introduction of a variable volume storage tank to maximize the efficiency.•Development of topology and sizing criteria of the presented system.•The proper system size is bounded to the selected control strategy.•A bad system design could increase energy consumption up to 25%.