DESIGN OF HOT WATER USER PROFILES FOR SWEDISH HOUSEHOLDS BASED ON TIME DIARIES Magdalena Lundh 1 , Ewa Wäckelgård 2 , Kajsa Ellegård 3 1,2 Dep. of Engineering Sciences, Uppsala University P.O. Box 534, SE-751 21 Uppsala, Sweden 1 Magdalena.Lundh@angstrom.uu.se 2 Ewa.Wackelgard@angstrom.uu.se 3 Technology and Social Change, Linköping University SE-581 83 Linköping, Sweden kajel@tema.liu.se ABSTRACT Energy demand from hot tap water usage on individual level has been modelled from data in time use diaries of 179 Swedish households living in detached houses and apartments. Data of activities that involve hot tap water was extracted and converted into energy – time diagrams (user profiles). The report describes the procedure to first convert each type of activity to an amount of hot water and secondly into energy. It was found that the energy use profiles for hot water consumption vary considerably between individual households. The average user profile of all households was compared to models of hot water use in two of the more frequently used simulation tools for solar thermal systems. It is shown that the profiles in the simulation tools are significantly different from the profiles modelled in this study. In a following study it will be investigated how these differences influence an optimal use of solar energy in a solar thermal system. INTRODUCTION A solar thermal system should, when functioning optimally, load the hot water storage with as much solar energy from the solar collectors as possible and minimize the use of auxiliary heating. In order to achieve a maximal solar energy usage the heat storage must be designed to keep temperature stratification in the tank. It is also important to charge the tank when the solar collectors are running. This implies the importance of the time for discharging the tank, i.e. when hot water is used in the household. It has to our knowledge not been studied in real cases how different unload strategies influence the solar fraction of the system. Jordan et al however performed system simulations with hot water profiles built on probabilities for different activities and water usage based on studies from Germany and Switzerland. It was shown that the fractional energy savings are reduced by more than three percentage units by introducing a probability based user profile instead of the more simple hot water profiles usually applied in simulation of solar thermal systems. The reason for reduced fractional savings is foremost the much larger number of draw-offs compared to the simplified profiles with only three draw-offs during the day. Furthermore, the main difference to the simplified model is during summer, when the solar energy gain is less with the realistic hot water profile. The importance of taking holidays with no hot water consumption into account is stressed. The probability for different activities to take place on different weekdays, on the other hand, only causes negligible reductions in energy gain. (Jordan et al., 2000) Creating realistic profiles without separating different weekdays, but only weekdays from weekend days, therefore seem reasonable. Models for predicting domestic hot water use have previously been developed for Swedish conditions as well. For example, Wollerstrand (1997) describes a statistical model based on the empirical work and probabilistic model developed in Holmberg (1987). The models are developed to enable simulation of hot water loads in different types of residential buildings, where the stochastic variables were derived based on measurements. Those models however focus on peak hot water load to enable sizing of components for district heating and do not take the actual hot water consuming activities in a household into account. In this study we have used data from time use diaries, presenting household activities, to construct profiles for hot water usage on single household level. Such profiles are “true stories” of how the activities follow each other in sequences that makes sense in how a household organises its everyday life. An approach based on probabilities for activities do not contain this dimension of organisation. This dimension is further highly valuable when working out strategies for hot water usage with optimal use of solar energy. This paper presents the results from construction of hot water profiles for 179 Swedish households living in detached houses and apartments. The time use study on which the hot water profiles are based will first be introduced. The method to convert the data on activities to energy use will then be described and important assumptions presented. The results, in form of the generated hot water profiles for detached houses and apartments as well as profiles used in two simulation tools, are then shown and compared. Finally, the future use of and possibilities with the results are discussed.