Energetic impact of temperature gradients in heat recovery in ventilation in dwellings
The installation of air-to-air heat exchangers in ventilation systems can contribute to reducing the heating demand of the building by recovering the heat from the exhaust air. When there is an active heating demand, the recovered heat becomes useful to reduce that demand. Howev-er, as the heat exch...
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Zusammenfassung: | The installation of air-to-air heat exchangers in ventilation systems can contribute to reducing the heating demand of the building by recovering the heat from the exhaust air. When there is an active heating demand, the recovered heat becomes useful to reduce that demand. Howev-er, as the heat exchanger works independently of the heating needs of the dwelling, the recov-ered heat may not contribute to the reduction in the heating demand. Furthermore, the indoor temperature gradients in the various rooms/zones of the dwelling can influence the heat re-covered by the ventilation system and, consequently, the useful recovered heat. A suitable method to evaluate the effect is based on dynamic multi-zone building energy simulations. In this work, a residential building typology has been modelled with eleven ventilations systems. Some of them work with fixed airflows and others are commercial smart ventilation systems with variable flow rates controlled by CO2, VOC and humidity sensors. Various systems do not have a heat exchanger due to their ventilation type. Still, the study was extended to those, con-sidering that the unwasted heat as a consequence of using a smart control would be equivalent to the presence of a heat exchanger. The building was heated with two heating strategies: uni-form heating in all the zones except for the attic and non-uniform heating with a specific set-point for three different types of zones. To evaluate the impact of the heat recovery, the annu-al heating demand and the recovered heat are compared between scenarios with different ef-fectivenesses for the heat exchanger and, to evaluate the effect of the temperature gradients, the results are compared between the two different heating strategies: uniform and non-uniform. The results for the case presented in this study show that centralized heat recovery systems perform better in the scenarios with uniform heating, while distributed ventilation systems perform similarly in both heating scenarios. |
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