Abstract
In this study, the influence of variables defining indoor temperature is studied, focusing on operational data and visual and technical inspections rather than the temperature control setpoints and occupancy schedule. This is incorrect because infiltration and insolation are highly variable. This results in lowering the temperature difference between the supply and return lines, overheating some spaces, lowering the indoor temperature in others, and poor hydronic balancing. The novelty lies in studying the actual operating condition of real district heating (DH) systems. The research hypothesis is that internal heat gains along with the infiltration of and variations in outdoor temperature cause daily changes in indoor temperature. These factors seem to be the primary reasons for the variations in supply and return temperature, if the rate of energy loss is not large in new office buildings constructed according to tightened contemporary energy conservation regulations. The saving effect is achieved by allowing the energy to be dumped into building envelopes; thus, the flow rate or supply temperature are varied in a narrower range. Dumping heat by using the storage capacity of building envelopes is suggested. The corrected design approach minimizes energy consumption and increases annual performance (e.g., by 14.1% here). Advantages are achieved by tuning a controller at a DH substation.