Modelling of decentral DHW preparation in large multi-family buildings

The works contributes to the need to design more efficient heating and domestic hot water preparation systems. Dynamic building and simulation plays an important role in the development of domestic hot water (DHW) preparation systems for residential buildings, in order to evaluate and optimize the final energy and the DHW comfort. The case study of this work is a big multi-family building composed of 96 flats. District heating (DH) is used to heat up the water in the storage tank located in the technical room. A distribution system connects the storage to all the fresh water stations (FWS) located in each flat. The chosen approach is to simulate the building-level DHW preparation with a single heat exchanger (HX) which approximates the behaviour of all the HXs of the building. For this purpose, the simultaneity factor (fs) should be considered. First, a representative model of the FWS for each flat is implemented in Matlab/Simulink and tested with two different control strategies of the circulation pump and two different DHW profiles, derived either from standard EN16147 or created as a stochastic profile. From the flat-level model, a building-level model is derived. Four different building-level DHW profiles are used to evaluate the simultaneity factor, and so the peak load of the building, in order to size the HX for the whole building. The DHW profiles (and so the simultaneity factor) and the parametrization of the HX influence the results. Final energy and DHW comfort (i.e. the DHW temperature and the “waiting time” to reach this temperature) are compared in each case. The return temperature of the fluid sent back to the storage is also analysed. The development of the return temperature to the storage is influenced by the DHW profiles and the thermal capacity of the pipe.