Filter Flow Rates

[SideArm66]

Hi all,

I am very interested in methods to reduce AC system energy consumed. I believe that one of the easiest ways of reducing energy consumed in AC systems is by reducing fan pumping losses. A particular culprit here is excessive pressure drops across air filters. The cumulative power consumption over a few years can be greatly reduced if a lower flow velocity through filters is used. Obviously this will mean larger duct and higher initial cost. But the running costs will be reduced.

If anyone has any experience with lowering flow velocity through filters and can advise a flow velocity for primary, secondary, MERV and HEPA filters your expertise will be greatly appreciated.

Does any ASHRAE documents address filter flow rates and pressure drops specifically?

Thanks in advance
SA66

[breathe easy]

SA66
I am not sure I understand your question. But here is some information that might be helpful.

In the ASHRAE 52.2 Standard there are 7 acceptable flow rates at which tests can be run. They are 118fpm, 246fpm, 295fpm, 374fpm, 492fpm, 630fpm and 748fpm. The filter company requesting the test specifies the flow rate. Most commercial filters are tested at 492fpm.

Pressure drop of the filter is one of the things determined by the test. Obviously, the pressure drop will vary depending on the airflow rate chosen ie. the higher the velocity - the higher the pressure drop.

You can decrease pressure drop by increasing the media area of the filter. That is why a 4" pleated filter will have the same pressure drop as a cheap 1" throw away filter.

Hope this helps.

[George2]

Hi all,

I am very interested in methods to reduce AC system energy consumed. I believe that one of the easiest ways of reducing energy consumed in AC systems is by reducing fan pumping losses. A particular culprit here is excessive pressure drops across air filters. The cumulative power consumption over a few years can be greatly reduced if a lower flow velocity through filters is used. Obviously this will mean larger duct and higher initial cost. But the running costs will be reduced.

If anyone has any experience with lowering flow velocity through filters and can advise a flow velocity for primary, secondary, MERV and HEPA filters your expertise will be greatly appreciated.

Does any ASHRAE documents address filter flow rates and pressure drops specifically?

Thanks in advance
SA66

You mentioned enlarging the ductwork, i.e, higher costs. Well, as mentioned, a 4" hi.-eff. filter is a great route to take.

If there is enough "throat" in the boot, then the cost to install the new filter/rack is very reasonable.

A good investment on many levels.