CH-24-C081 - Ceiling Fan Filtration System: Fluid Dynamics Factors for Filters on Ceiling Fan Blades

Ceiling fans are an integral part of most residential dwellings, and the new generation of ceiling fans are highly efficient when considering airflow-to-electrical-power ratio. Adding filtration capacity to ceiling fans can improve indoor air quality while supporting energy efficiency and building decarbonization efforts. The clean air delivery rate (CADR) of a ceiling fan filtration system depends on the filter media and the fluid dynamics of the airflow in the filter media. This study investigates gas removal media integrated into the fan blade structure for various prototype configurations and provides CADR values for ozone and toluene based on test chamber experiments. In this study a new metric for integration of filters with ceiling fans is introduced. This metric is named filter fluid dynamics factor (FFDF), and it is defined as the ratio of the CADR of a filtered fan configuration to the maximum possible clean air delivery rate – defined as the product of filter efficiency and total fan airflow rate. This metric aims to allow performance predictions of a ceiling fan filtration system configuration based on fan manufacturer data (nominal fan flow) and filter manufacturer data (nominal filter media efficiency). Preliminary results for one filtered ceiling fan configuration with gaseous pollutants show that the FFDF is significantly different for two different filter media with ozone, and significantly different for one filter media with two different gases, ozone and toluene. In the first case, the difference is likely attributed to the difference in pressure drop curves for the two materials resulting in less airflow through the higher-efficiency filter material. In the second case, the FFDF for non-reactive toluene is much lower than the FFDF for reactive ozone with the same filter media in the same configuration. This difference is likely attributed to the different removal mechanisms of adsorption and reaction. The FFDF metric is not predictive for removal by different filter media for one gas or for removal of different types of gases (reactive versus non-reactive) by one type of media. It may still have predictive power for removal of different non-reactive gases, but that has not been tested. Increasing the blade pitch to get higher airflow through the filter for toluene testing increased CADR up to a point but then leveled off around a maximum CADR. Further investigation revealed that the steep blade pitches caused the fan motor to hit its peak power, resulting in lower fan speed with further increases in pitch. This highlights the need to consider motor power and to monitor fan speed when comparing configurations. Power measurements with and without the filters in place show that the impact of filters on energy use is minimal. Overall, our experiments demonstrated that the filtered ceiling fan concept for supplemental ozone and toluene filtration is feasible, but it will require careful design.