Sensitivity of the total heat loss coefficient determined by the energy signature approach to different time periods and gained energy

In order to identify buildings that have energy saving potential there is a need for further development of robust methods for evaluation of energy performance as well as reliable key energy indicators. To be able to evaluate a large database of buildings, the evaluation has to be founded on available data, since an in-depth analysis of each building would require large measurement efforts in terms of both parameters and time. In practice, data are usually available for consumed energy, water, and so on, namely consumption that the tenants or property holder has to pay for. In order to evaluate the energy saving potential and energy management, interesting key energy indicators are the total heat loss coefficient Ktot (W/K), the indoor temperature (Ti), and the utilisation of the available heat (solar radiation and electricity primarily used for purposes other than heating). The total heat loss coefficient, Ktot, is a measure of the heat lost through the building's envelope, whereas Ti and the gained energy reflect the user's behaviour and efficiency of the control system.In this study, a linear regression approach (energy signature) has been used to analyse data for 2003–2006 for nine fairly new multifamily buildings located in the Stockholm area, Sweden. The buildings are heated by district heating and the electricity used is for household equipment and the buildings’ technical systems. The data consist of monthly energy used for heating and outdoor temperature together with annual water use, and for some buildings data for household electricity are also available. For domestic hot water and electricity, monthly distributions have been assumed based on data from previous studies and energy companies. The impact on Ktot and Ti of the time period and assumed values for the utilised energy are investigated.The results show that the obtained value of Ktot is rather insensitive to the time period and utilised energy if the analysis is limited to October–March, the period of the year when the solar radiation in Sweden yields a minor contribution to heating. The results for the total heat loss coefficient were also compared to the calculations performed in the design stage; it was found that Ktot was on average 20% larger and that the contribution to heating from solar radiation was substantially lower than predicted. For the indoor temperature, however, the utilised energy had a large impact.With access to an estimate of Ktot and Ti, an improved evaluation of the energy performance may be achieved in the Swedish real estate market. At present the measure commonly used, despite the fact that monthly data is available, is the annual use of energy for space heating per square metre of area to let.