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  1. #14
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,981
    Quote Originally Posted by 54regcab View Post
    I'm a bit confused on how the location of the filter affects the total static pressure drop. If the filter has a drop of .2" @ 1400CFM and the return duct has a drop of .1" @ 1400CFM doesn't that equal .3" no matter if the return duct or filter comes first?
    For total SP, yes, but not for velocity across the face of the filter. We have to also account for filter grills having 40% of the open surface area blocked by louvers.

    Add in the ability for unfiltered air to infiltrate the return ducting between the filter grill and the blower assembly, and there are more reasons to put the filter close to the blower than there are reasons to have the convenience of a filter grill.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  2. #15
    Join Date
    Feb 2013
    Location
    New Jersey before and after Texas
    Posts
    67
    Nobody that I thumbed through has pointed out the fact of face velocity per area of the duct. Every installation is unique with their own idiosyncratic developments. Mastic the return air duct weather it's part of a municipal code or not, and if your using it in the return add up the free surface of the grille versus your cubic feet for the totatal equivalent length of duct. In many cases a higher M.E.R.V. Value is an option of cost but efficiency can be improved by capturing the correct velocity through engineering an oversized rack even with a one inch fiber constructed media..

  3. #16
    Join Date
    Feb 2013
    Location
    New Jersey before and after Texas
    Posts
    67
    Total not totatal... Forgive the typo.

  4. #17
    Join Date
    Feb 2013
    Location
    New Jersey before and after Texas
    Posts
    67
    Quote Originally Posted by RoBoTeq View Post
    For total SP, yes, but not for velocity across the face of the filter. We have to also account for filter grills having 40% of the open surface area blocked by louvers.

    Add in the ability for unfiltered air to infiltrate the return ducting between the filter grill and the blower assembly, and there are more reasons to put the filter close to the blower than there are reasons to have the convenience of a filter grill.
    Velocities suggested for a one inch media are considerably more tolerable to higher values than the four inch pleats. An EAC next to a furnace does not make sense when the F.P.M. is double if not tripple the recommended statistic derived from an UL standard. Slow it down for better filtration efficiency.

  5. #18
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    Quote Originally Posted by seanhoang View Post
    Also, I was thinking about adding a UV light behind the media filter. Is it really worth it?
    IF you decide to do a typical 1 or 2 bulb UVC system, have it irradiating the coil, otherwise it does little to no good.
    All of the materials within about 3 feet of it need to be rated for UVC exposure too.
    If more government is the answer, then it's a really stupid question.

  6. #19
    Join Date
    Jul 2005
    Posts
    5,576
    Quote Originally Posted by seanhoang View Post
    I've been looking into this option - replacing my 1" with a 4" media filter at the return grille.

    Would this option at the return grille gives the same performance as the one at the blower? If not, what is the differences?

    Also, I was thinking about adding a UV light behind the media filter. Is it really worth it?

    Thanks in advance pros.
    Filter(s) at the return air grille(s). The velocity will be lower there and dust won't accumulate in the return duct(s)/box/chase/whatever. Seal the return air path to prevent leakage or install a low resistance (cheap) secondary filter at the unit. Use your best judgment. Do some research on UV lights. They don't treat the air they treat the evaporator coil and can cause damage if not installed correctly.

  7. #20
    Join Date
    May 2006
    Location
    Austin, Texas
    Posts
    303
    Even pros have differing opinions. The main issue is keep the filter clean. I have seen both scenarios where the inside of the units were still clean after 10 years. I have also seen both scenarios where the units were dirty after just a few years.

  8. #21
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,981
    Quote Originally Posted by mark beiser View Post
    IF you decide to do a typical 1 or 2 bulb UVC system, have it irradiating the coil, otherwise it does little to no good.
    All of the materials within about 3 feet of it need to be rated for UVC exposure too.
    Ironically, though all materials within 3' need to be UV rated, UV light really only has a positive affect within 6-8" of the bulb and then only on substances that are exposed for a minimal amount of time. Air blowing across an UV light gets no positive results from that light.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


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