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Earth-to-air heat exchangers are energy-efficient systems that use the ground for cooling in summer and heating in winter. Design, simulation and planning tools are available in the market, and earth-to-air heat exchangers are well-accepted in the built environment. Furthermore, there is a wide knowledge on their performance in operation. Based on long experiences in the design and operation of earth-to-air heat exchangers, pre-defined operation strategies are applied in ventilation concepts. In ventilation concepts with highly efficient heat recovery systems, optimized operation strategy should optimized rather in a combined optimization of airhandling unit and earth-to-air heat exchanger than a single optimization of the earth-to-air heat exchanger.
The study is based on monitoring data from a sports hall which was built in Passivhaus style. The heating and cooling concept is based on thermo-active building systems which are supplied by a ground-coupled absorption heat pump. The supply air is heated in winter and cooled in summer by an earth-to-air heat exchanger. The air-handling unit is directly coupled to the earth-to-air heat exchanger without bypass option and doesn’t contain any additional heating or cooling.
A coupled plant-and-building simulation model is set up for the design and development of an optimized operation strategy. The model is developed in the R program.
A monitoring campaign in summer is used for the model validation. The simulation models is based on the simple-hourly-method building model according to ISO 13790, a simplified heating and cooling system, a characteristic-line model for the heat recovery system, and a detailed earth-to-air heat exchanger model. The building is controlled by a building-energy-management-system (BEMS) which is modeled according to the current operation (for model validation) and is used for the optimization of the operation strategy.
The improved control strategy takes the indoor temperature and the outdoor temperature into account. The outlet temperature is not suitable as input for the control strategy since the monitoring value is only indirectly available in operation.