Modelling Approaches for Decentral Domestic Hot Water Heat Exchangers in Hydronic Simulations

To assess the building hydronic system performance, dynamic simulations are necessary to examine factors such as return temperature and controls. Extensive simulation effort might be required, especially with complex distribution systems and multiple apartment heat exchangers (HXs). This study investigates modelling approaches to simplify the simulation models by implementing lumped HXs. The first part of the paper suggests approaches to lump hydronic systems with one and two rising pipes. The second part involves developing and optimizing lumped models and comparing them against detailed physical models. Results indicate that the modelling of the HX bypass has a great influence on the lumped HX optimization. The HX heat loss coefficient (UA) and the HX capacity influence the return temperature and the energy consumption between lumped and detailed models, suggesting the adoption of low values both for the heat loss coefficient and the capacity. The runtime-saving benefits of lumped models become evident when dealing with more than four HXs; for example, with 10 HXs, the simulation time is about one-tenth of that necessary for detailed models. Additionally, the modelling effort is significantly reduced and is independent from the number of considered (lumped) HXs. The lumped models offer a promising way to evaluate building energy performance efficiently, which is crucial for projects with multiple-apartment buildings.