Closing the residential energy loop: Grey-water heat recovery system for domestic hot water production based on heat pumps

[EN] Passive houses linked to more efficient heating and cooling technologies have been one of the focus in last years. However, to close the loop of the building sector, there is still one open source: wasted heat from grey water. This paper addresses the potentiality of the wasted heat from grey water as a heat source to produce domestic hot water (DHW) based on a heat pump system (HP). A heat pump optimized for these applications, a heat recovery heat exchanger and two variable volume storage tanks compose the system. The main objective of this work is to determine the potential recovery of the wasted heat in order to minimize the building energy consumption. Design guidelines of the components and the analysis of an optimum operation algorithm of the system have been performed in order to minimize CO2 emissions. In addition, an evaluation of the potential heat recovery of the wasted heat is included. As an example, that methodology has been applied to 20 dwellings. Based on that case, the obtained results demonstrate that by recovering 80% of the available recovery heat, the total demand of DHW is satisfied with high levels of comfort and efficiency.
Part of the work presented was carried out by Estefania Hervas Blasco with the financial support of a PhD scholarship from the Spanish government SFPI1500 x074478XV0. The authors would like also to acknowledge the Spanish `Ministerio de Economia Y Competitividad', through the project "Maximizacion de la Eficiencia Y Minimizacion del Impacto Ambiental de Bombas de Calor Para la Descarbonizacion de la Calefaccion/ACS EN Los Edificios de Consumo Casi Nulo" with the reference ENE2017-83665-C2-1-P for the given support.