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  1. #1
    Join Date
    Jul 2008
    Location
    Huntsville AL
    Posts
    4

    Filter Size and Pressure Drop Question

    Just got a new Trane Package Heat Pump. I had read a discussion of air filters here a few weeks ago, and requested a 4 inch media filter. The contractor at first said I needed a bigger filter grill because my present one is 20 x 25. Once he saw that he'd have to cut into wall joists his story changed to me not needing a bigger size. Manual says 4 sq feet with a w.c. between .05 and .08 (it was contradictory) at a 300 fpm flow rate. I checked and the honeywell 4 inch Merv 10 filter has a w.c. of .21. So I'm in a pickle. Even with a bigger grill (which I'll have to demand), I'm way over the recommended w.c. rating for my unit. I don't see how any efficient filter is going to meet spec. Any advice?

    Thanks,

    Jim

  2. #2
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Quote Originally Posted by eldrijt View Post
    Just got a new Trane Package Heat Pump. I had read a discussion of air filters here a few weeks ago, and requested a 4 inch media filter. The contractor at first said I needed a bigger filter grill because my present one is 20 x 25. Once he saw that he'd have to cut into wall joists his story changed to me not needing a bigger size. Manual says 4 sq feet with a w.c. between .05 and .08 (it was contradictory) at a 300 fpm flow rate. I checked and the honeywell 4 inch Merv 10 filter has a w.c. of .21. So I'm in a pickle. Even with a bigger grill (which I'll have to demand), I'm way over the recommended w.c. rating for my unit. I don't see how any efficient filter is going to meet spec. Any advice?

    Thanks,

    Jim
    I believe it would be useful info to know the CFM you plan to flow through the filter. As a fellow homeowner, I would ask if there would be any opportunity to add a 2nd return as an alternative to enlarging the original one. That is what I had done. There's a lot of things I don't know but one thing I have learned is: the pressure drop goes way down based on the feet/min air speed at filter face going down, which in turn is dictated by your CFM airflow.

    Even 0.21 might be within the specified capabilites of your air handler. My Trane mfg VS (variable speed) air handler is spec'ed to deliver nearly constant airflow up to 0.90 total ESP, it just would use some extra electricity to do that.

    Best of luck -- Pstu

  3. #3
    Join Date
    Apr 2008
    Location
    Princeton, NJ
    Posts
    581
    I have a Trane XV95/XL15i 100Kbtu/4-ton system with a reccomendation of a 20x25 filter (Eventhough my side-return installation is only sized for a 17x25 max). Go figure

    Anyway, I had a new return drop installed with a cabinet that can handle 20x25 filters from 1 to 5 inch (primarily due to the horizontal installation).

    In an effort to get my static pressure down, several low cost filters were tested for pressure drop and here is the data.

    The blower is set on 400CFM/ton (1600 CFM) but is likely delivering only 1400 CFM at my static high pressure according to the servicts facts section in the installation manual.

    1. The blue cheapo see-thru filter was 1 inch thick and had a pressure drop of 0.05.
    2. The 5" Merv-10 media filter that came with the GeneralAire cabinet had a PD of 0.14.
    3. The 1" Merv-7 pleated filter (Ace Hardware brand) that looked identical to a Merve-8 Natralaire pleated filter, had a very high PD of 0.27
    4. A 1" thick Merv-4 Naturalaire washable Fiber filter had a PD of 0.07 .

    I decided to stay with the merv-4 since it it is better than the basic blue cheapo filter and a rating of merv-4 is not to bad if no smokers or pets in the house. In pollen season I will likely switch to the 5" GeneralAire Merv 10 filter.

    Key1

  4. #4
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by pstu View Post
    I believe it would be useful info to know the CFM you plan to flow through the filter. As a fellow homeowner, I would ask if there would be any opportunity to add a 2nd return as an alternative to enlarging the original one. That is what I had done. There's a lot of things I don't know but one thing I have learned is: the pressure drop goes way down based on the feet/min air speed at filter face going down, which in turn is dictated by your CFM airflow.

    Even 0.21 might be within the specified capabilites of your air handler. My Trane mfg VS (variable speed) air handler is spec'ed to deliver nearly constant airflow up to 0.90 total ESP, it just would use some extra electricity to do that.

    Best of luck -- Pstu
    Ditto!

    Tell us more abot the system,tons,model numbers,pics,etc..

  5. #5
    Join Date
    Apr 2008
    Location
    Princeton, NJ
    Posts
    581
    oh...all data was generated at the 100% blower speed (not the 80%).
    Key1

  6. #6
    Join Date
    Jul 2008
    Location
    Huntsville AL
    Posts
    4
    My Trane is a 3 ton package unit heat pump, XL16C, 16 Seer, 2 stage

    Extra return would be a major pain in my house. Good info on the P drops of diff filters. Was really hoping to attack the allergies with a high efficiency filter.

    Thanks,

    Jim

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    What the static pressure,supply and return??

    Duct system will need rework if static is too high,this can usually be done,space available,chage out high static elbows,fittings ,etc..

  8. #8
    Join Date
    Apr 2008
    Location
    Princeton, NJ
    Posts
    581
    Quote Originally Posted by eldrijt View Post
    Good info on the P drops of diff filters. Was really hoping to attack the allergies with a high efficiency filter.

    Thanks,

    Jim
    That should not be a problem if the static pressure is not too high.....and if it is too high there are ways to address it....

    Key1

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