Formulation of final resistance of the air filters / Yit Jing Ee

Yit, Jing Ee (2023) Formulation of final resistance of the air filters / Yit Jing Ee. PhD thesis, Universiti Malaya.

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Abstract

Air filters play an indispensable role in maintaining a good indoor air quality (IAQ) for the occupants in a building. However, a significant drawback of the air filter applications is the high pressure drop across it, causing a high energy consumption of the HVAC system. The dust cake formation on the filter media after a certain period of usage can even further increase the high energy consumption. Therefore, an accurate setpoint of the final resistance can ensure energy-saving of the system while the indoor air quality is not compromised. In the industrial practice, the final resistance is set twice the initial resistance according to ASHRAE 52.2-2020 recommendation or set using Rule of Thumbs as there is a lack of final resistance study in the literature. In this research, a pleated fibreglass air filter is studied to identify the factors affecting filtration performance and formulate the final resistance relationship. The filtration performance parameters, including the initial pressure drop, filtration efficiency, pressure drop across dust cake and the dust holding capacity of the filter, are studied experimentally and via CFD. A triangular pleat is found to have the lowest initial pressure drop, and it is found that the fibre diameter, filtration velocity, pleat density and pleat depth are the contributing factors affecting filtration performance. The empirical models of filtration performance parameters are expressed in terms of the contributing factors. The models are validated that the predicted models are acceptable as the difference between predicted and validated R2 values are only less than 1.5 %. The validated empirical models are used for the prediction in the final resistance model in consideration of the filter lifespan and the energy cost. The findings of this study can effectively provide a guideline to the filter manufacturers in the filter design stage or the filter selection stage. The filtration performance can be easily predicted by inserting the design parameters into the empirical models. The final resistance can also be determined analytically with the proposed model in consideration of the predicted filter lifespan and energy cost. The proposed filtration performance parameter models and final resistance model can provide a better filter selection for the end-users, giving a better solution in maintaining the building’s IAQ and, at the same time, minimizing the operation cost.

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