Documentation of an integrated thermal energy system for a building complex.

In large buildings and building complexes, energy use can be reduced by efficient interaction between heating and cooling demands and thermal storage (short and long term storage). This work describes an integrated energy system in Norway which supplied several commercial and residential buildings with heating and cooling. The integrated thermal energy system consisted of heat pumps (~1 MW total cooling capacity), solar thermal collectors (290 m2), district heating connection as well as water tanks (15000 l) and boreholes (62 x 300 m) for thermal energy storage. The water tanks acted as buffer and balanced the mismatch of supply and demand during a day. The seasonal operation modes were chosen depending on the outdoor conditions. In summer, the condenser heat from the cooling systems and the solar collectors was sent to the boreholes. In winter, the heat pumps used the boreholes and the surplus heat from the cooling systems as heat source and delivered heat to the buildings for space heating and domestic hot water. In spring, certain cooling demands could be covered by free-cooling as long as the borehole temperature was low enough. District heating was utilized to lift the temperature for the domestic hot water and also served as backup system. In this work, the system is described in detail and operational data is presented. Improvement suggestions are made which could cut operational costs.