Geocooling potential of borehole heat exchangers in low energy office buildings analysed with dynamic system simulations

A reference office building has been defined in order to simulate its thermal behaviour and comfort conditions and for assessing potentiality of geocooling with borehole heat exchangers. The building has low heating and cooling demands, a condition that makes it possible to use active concrete plates for heating and cooling. Starting from the reference case, a list of buildings has been defined varying the glazing ratio, internal or external solar protections, windows typologies and the heat distribution systems. A borehole heat exchanger field is coupled to a heat pump in winter and to the heat distribution system in summer through a flat plate heat exchanger. The cooling requirement satisfied by a direct heat transfer into the ground through the borehole heat exchangers is so called geocooling. A dynamic system model has been developed to simulate the building, the emission of thermal energy, the technical installations including the borehole heat exchanger field and the interconnected thermal interactions. Building design, system technical feasibility and limits of the ground coupled system are discussed and result from the analysis of the numerous system simulations. Geocooling potential depends on the quality of the building design and its heat emission. The importance of the ground thermal conductivity and the ground recharge ratio on the system design are highlighted.