Paper Conference

Proceedings of BSA Conference 2017: Third Conference of IBPSA-Italy


Mapping Savings in Energy Demand by Heat Recovery for European Countries Under Consideration of Humidity Control

Stefanie Tafelmeier, Giovanni Pernigotto, Andrea Gasparella

Abstract: Sensible (SHR) and total heat recovery (THR) can play a significant role in energy savings in mechanical ventilation usage. Apart from the technical characteristics of the heat exchangers, the savings on the ventilation load depend on the air conditions for the two airstreams, namely the conditions maintained for the indoor air and the actual outside conditions, and on the proper control strategies deployed to minimize the impact on the air processes required after the heat recovery device. In this respect, humidity control can conflict with heat recovery whenever excessive humidity requires dehumidification of the ventilation air. In particular, SHR in heating mode should be preferably by-passed if the outside humidity exceeds the supply conditions required to compensate internal latent loads. For THR, moreover, the control strategy has also to account for the device’s latent effectiveness, which may require an even earlier limitation of heat recovery or a by-pass if the system effectiveness cannot be controlled. Depending on the specific climate, the actual heat recovery can be much lower than the expected one and needs to be evaluated in order to avoid overestimating its energy and economic performance. The humidity supply limit required in the analysis of the actual recovery can be defined considering the target indoor humidity ratio (corresponding to the relative humidity setpoints of 50 %) reduced by the amount needed to compensate any indoor humidity source. This reduction can be expressed in terms of a specific latent load, SLL, calculated as the ratio between the mass rate of water vapor produced indoor, and the mass rate of the ventilation air, no matter whether some recirculation exists or not. Since both vapor production and ventilation air mass rate depend on sources and occupants’ density inside the conditioned space (0.8,2,6, 2.0 or 2.4 gv/kgda), SLL is largely independent of the remaining building characteristics. In this research, we studied the savings from ventilation heat recovery in different European climatic zones and countries by applying different control strategies to avoid excess humidity. Only the ventilation system had to be modelled through a simplified effectiveness model, considering different SLL as the only relevant building characteristic. Savings were expressed in terms of energy demand per flow rate, averaged over climatic Köppen-Geiger classes.
Pages: 487 - 496