A Modelling Technique for Estimating Hot Tap Water Consumption in District Heating Systems

Abstract

This paper is concerned with estimating the hot tap water consumption in district heating systems when direct measurements of the hot tap water are not available. Instead, only measurements of the total mass flow, that is the mass flow for both heating and hot water are assumed available. Thus, a method is needed that may be applied in order to separate the mass flow into these two parts, or even more if the mass flow is assumed to be consisting of more than two factors. Here, the mass flow is divided into one part dependent upon climate variables and one part that is independent of the climate. By assuming that the hot tap water consumption is to a high degree independent of the weather, the latter part is an estimate of the hot tap water. The data are from the Reykjavik Municipal District Heating System in Iceland. The results show that the hot tap water consumption has a noon and an evening peak and is at its minimum around 4 a.m. The average consumption is about 10 per cent of the yearly average mass flow. Furthermore, the consumption is highest during the winter time and lowest during the summer time. It was found sufficient to use one tap water profile on working days and one for weekends. It is shown that the solar effect on the mass flow is quite moderate. During working days it is about 1.2 per cent of the yearly average mass flow and 1.6 per cent during weekends (based on 10 hours of sunshine per day).