A comparative analysis of a heat pump application with grey wastewater source for domestic hot water preparation in hotels

System for domestic hot water (DHW) preparation generally represents a considerable portion of the energy and water consumption in hotels worldwide. As a consequence, a vast amount of heat is wasted through the drainage system from rooms and kitchens. Also, for hotel-type buildings, demand for DHW can vary according to their occupancy. Researchers and practitioners have a very challenging task to select the optimal and most sustainable solution. This paper analyses a DHW heating system with a heat pump system that uses grey wastewater (GWW) and rainwater as an energy source. The application is developed in combination with experimental site measurements (real system operation) and required standards. The research deals with the subject system in bivalent operation (basic and advanced configuration of heat pump system assisted with gas boiler). In order to evaluate the application of the advanced heat pump DHW heating system with GWW source, a comprehensive assessment is done with a gas boiler system only (base case) and solar plate collector system. For the advanced heat pump system, the study has determined the two key operation elements: hotel occupancy rate and system regulation. The financial assessment showed very promising economic metrics (PBP = 6.54 years, POP = 7.9 years IRR = 9.40%, MIRR = 17.00%) compared to the base case. The study provided results of a sensitive cost-effective system assessment for periods with lower than average hotel occupancy rates. Also, when the total operation and investment costs are compared with the data calculated on an average annual hotel occupancy rate of 68%, the final conclusion is that the investment in the advanced heat pump system is justified only if its gas consumption share is less than 14.27%. The analysis confirmed the main advantages of this heat pump system which are lowered energy consumption and reduced total operating costs.