1150532 - Performance Evaluation Methods for Air Cleaners

In ANSI/AHAM AC-1-2020, Clean Air Delivery Rate (CADR) measures the appliance’s ability to reduce aerosol particles. Indoor air cleaners (IACs) are used as an adjunct to source control and ventilation. Following a tedious and time-consuming procedure, the CADR measurement must be carried out in an AHAM chamber. In contrast to IAC’s recirculating indoor air, fresh air cleaners (FACs) purify outdoor air before delivering into an indoor environment. There is still no officially accepted test method for FACs, although the FAC performance, can also be measured using the AHAM chamber to obtain the CADR value. An alternative approach is developed in this work, using the product of the flow rate and the filtration efficiency of the FAC. This product is named equivalent CADR or CADRE. The pros and cons of these two methods are then compared and analyzed.

A small chamber (15 L) was built to substitute the AHAM chamber to adapt to the small homemade air cleaners. Di-ethyl-hexyl-sebacate (DEHS) was used as a test agent. A constant output aerosol generator was used to generate DEHS particles. The aerosol output was neutralized using a radioactive source, then introduced into the test chamber. A mixing fan was used to uniformize the aerosol concentration in the room. The natural decay rate (kn) and the total decay rate (ke) were then measured using a condensation particle counter to determine the CADRC. The aerosol number concentration and size distribution upstream and downstream of the FAC were measured using a scanning mobility particle size to obtain the filtration efficiency as a function of particle size. The flow rate of FAC was measured using a gas meter with a unique design to offset and balance the air resistance of the gas meter.

The product of filtration efficiency and flow rate of FAC, i.e., CADRE, is influenced by filter properties and the fan characteristic P-Q curve. The filtration efficiency increases with decreasing velocity for a given filter because of a longer retention time with the filter media. Notice that the CADRE and CADRC should be identical if the test aerosol is monodisperse. The CADRE is always lower (58% in this work) than the CARDC if the MPPS is used. If the whole size distribution of the challenge is included, the CADRE is 14% higher than CADRC. This mismatch becomes more significant if the spread of the test aerosol increase, i.e., toward a higher geometric standard deviation (GSD). Through simulation, the longer the operation of the air cleaner, the particle distribution becomes more monodisperse. A higher geometric standard deviation would lead to a higher CADRC. Additionally, under the same GSD, the CADRC will be higher if CMD is far from MPPS.

Based on the experimental results, both performance testing methods correlate very well. The CADRE is a more conservative value because it is based on the MPPS. The CADRE is always lower than CADRC., if the filtration efficiency is based on the MPPS. Overall, the CADRE is more robust, conservative, and faster than the traditional chamber test method.