Annual Performance of Sensible and Total Heat Recovery in Ventilation Systems: Humidity Control Constraints for European Climates
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Ensuring a comfortable indoor air quality requires a minimum fresh air supply by ventilation. Moreover, the improvement of the air tightness in new and refurbished high performance buildings enhances the role of mechanical ventilation and its importance in further increasing the energy efficiency. Indeed, a reduction of the ventilation load can be achieved by installing air-to-air heat recovery devices, whose potential energy savings can be easily assessed by means of their nominal effectiveness. However, this estimation does not consider the impact on the overall performance of the system, in particular when humidity control is needed. Proper control strategies can be defined on the basis of the indoor latent load to prevent preheating or avoid moisture recovery when dehumidification by cooling is then required. In this work, the energy saving potential of heat recovery systems has been analyzed, considering the impact of different control strategies on both energy and cost savings. The calculations have been generalized using the specific latent load, which allows for the analysis of strategies and savings based on typical utilization categories, without considering in detail all the building characteristics. Representative hourly weather data for 66 European cities have been used to evaluate sensible and total heat recovery devices. The energy and the cost saving results have been mapped per each European Köppen-Geiger climate class and each country, respectively. The proposed strategies based on humidity control can strongly reduce the attractiveness of total heat recovery with respect to sensible heat recovery in terms of energy and cost savings, especially when high specific latent loads are considered.