Simple methodology to estimate the mean hourly and the daily profiles of domestic hot water demand from hourly total heating readings

During recent years, the research in reduction of energy use in buildings has focused primarily on decrease of space heating needs, energy for ventilation and recently cooling, whereas domestic hot water (DHW) has been overlooked. In 2013, the energy use for DHW was estimated at 16% of total heat requirement in EU28 households, but in new energy-efficient buildings this share is documented to be around 40–50%. Generally, however, there is limited knowledge of DHW. This paper presents a simple methodology, which enables calculation of the mean hourly and the daily profiles of DHW demand from hourly values of the building total heat demand, and thus contributes to gaining a better understanding of the DHW usage. The method is validated with data from single-family houses and apartments and afterwards applied to dataset consisting of hourly total heat consumption readings from 38 single-family houses delivered by district heating. The method gives satisfying results when the DHW usage during summer is at least at the same level as the space heating demand, which is the case in apartments and in the energy-efficient houses. The standard deviation was used as preliminary classification criterion for deciding if the method can or cannot be applied. Two limits were found σ > 240 for apartments and σ < 800 for single-family houses.