Abstract
Air to air heat exchangers play a crucial role in mechanical ventilation equipment, due to the potential primary energy savings both in case of refurbishment of existing buildings or in case of new ones. In particular, interest in heat wheels is increasing due to their low pressure drop and high effectiveness. In this paper a detailed optimization of design parameters of heat wheels is performed in order to maximize sensible effectiveness and to minimize pressure drop. The analysis is carried out through a one dimensional lumped parameters heat wheel model, which solves heat and mass transfer equations, and through appropriate correlations to estimate pressure drop. Simulation results have been compared with experimental data of a heat wheel tested in specific facilities, and good agreement is attained. The device optimization is performed through the variation of main design parameters, such as heat wheel length, channel base, height and thickness and for different operating conditions, namely the air face velocity and the revolution speed. It is shown that the best configurations are achieved with small channel thickness and, depending on the required sensible effectiveness, with appropriate values of wheel length and channel base and height.
Highlights
It is well known that buildings are responsible for around 40% of primary energy consumption in developed countries and for 20%–40% in developing countries [1]
The heat wheel design is optimized in order to maximize effectiveness and minimize pressure drop, which is directly related to ventilation power consumption
Results are reported in Figure 7: It is possible to state that for each air face velocity there is a clear boundary along which sensible effectiveness is maximised as a function of pressure drop
Summary
It is well known that buildings are responsible for around 40% of primary energy consumption in developed countries and for 20%–40% in developing countries [1]. In case of refurbishment of existing buildings or in new ones, the introduction of a heat exchanger between exhaust and fresh air streams play a crucial role due to relevant achievable energy savings [2,3,4,5,6,7,8]. Two air streams pass through the cross sectional area of the device: The supply one, which is the fresh air stream, and the exhaust one, which is the return air flow from the building. A purge sector between exhaust and supply air streams is often used in order to reduce contamination of the fresh air flow. Heat is transferred from one air stream to the wheel matrix and from the matrix to the other stream. If one of the two flows reaches the dew point, water is transferred between the two streams
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