Development of a dynamic analytical model for estimating waste heat from domestic hot water systems

Domestic Hot Water (DHW) production accounts on average between fourteen and thirty percent of the residential energy consumption worldwide. In UK dewllings, a quarter of the energy is consumed to produce hot water and this proportion is likely to increase as the energy required for space heating reduces over time in order to achieve demand reduction targets. As the margins for improving the performance of heating system technologies increase, the need for improving modelling accuracy and precision increases as well. Although studies have considered DHW use in buildings, there is a lack of reflection on the energy loss and performance of systems in contemporary dwellings. Current simulation tools with simplified assumptions and limited capabilities (due to a lack of considered variables and details of calculation algorithms) might lead to unreliable results in terms of the estimated heat losses. In this research, an analytical dynamic model has been developed to estimate heat loss from a domestic hot water system based on high resolution monitored data for a set of dwellings in the UK. The model estimated heat losses during flowing and non-flowing (cooling down) conditions in the distribution system as well as heat losses from the storage tank. It was found that apart from the significant heat loss from the storage tank, short draw-offs are particularly influential in determining the amount of heat wasted. Considerable savings might be achieved ”avoiding” short draw-offs through a better control of the system and/or changes in the user behaviour. Insulating and reducing the effective length of the distribution pipe network through better design of the system similarly predict significant reductions in heat losses.