Correlations between Apartment Occupancy Levels and Use of Household Electricity and Domestic Hot Water (ST-16-C053)

Both the current and future buildings will have very well-insulated building envelopes heated mostly by internal heat gains from occupants and household electricity. The occupant related energy uses, household electricity and domestic hot water heating, will have a large impact on the energy performance. In low-energy buildings the heating of domestic hot water is in the same order of magnitude as the energy for space heating. Knowledge of occupancy levels is critical for prediction and verification as well as optimization of various demand controlled systems. This article presents how household electricity and domestic hot water use varies due to occupancy level. Occupancy level, household electricity and domestic hot water were measured in 79 apartments during 12 days per apartment. Occupancy level was measured by electronic diaries in which those living in and visiting the apartment marked their attendance by pressing buttons when entering and leaving the apartment. Household electricity and domestic hot water were measured hourly while the diaries recorded data every second. The result shows that there are relatively weak correlations between occupancy level and the studied energy uses demonstrated by a large variation in both household electricity and hot water use at the same occupancy level. Household electricity has a stronger correlation to the occupancy level during the day compared to the occupancy level during the night, where the level during the night is assumed to describe how many people are living in the apartment. The hot water has a stronger correlation to the occupancy level during the night compared to the occupancy level during the day. One possible explanation is that larger quantities of domestic hot water could be due to showering in the morning, which would depend on how many people spent the night in the apartment while household electricity could depend more on how much of the day there are people in the apartment. The result shows that the average occupancy level during the day or the number of people living in an apartment describes only a small part of the use of household electricity and domestic hot water. Probably there is considerable individual differences in how people use electricity and hot water, which leads to a need to describe the variation by statistical distributions.