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  1. #1
    Join Date
    Oct 2010
    Location
    Minnesota
    Posts
    15

    Less restrictive filter?

    System:
    <1 yr old a/c and furnace
    Furnace: Carrier Infinity 58MVCO8O
    A/C:Carrier Performance 24APA53OA003
    Infinity Control
    Carrier Media Filter Box 16x25
    Filter: 4 inch MERV 8 Carrier FILXXCAR0020 (first one said FILXXCAR0016)

    -I get the warning to change or clean filter after only about 2 months of use.
    -When cooling when I set the fan to high, the airflow does not seem to move all that fast.
    -The A/C does not quite keep up (maintain cool enough temp) on 90 degree days

    I checked the A/C status with the Infinity controler, here are my results:
    Fan set to auto, thermostat temp set to 71, outdoor temp 81, indoor temp 74.

    Airflow CFM 875
    Coil Temp 81
    Outdoor temp 81
    Blower RPM 720
    Static Pressure .40

    If I remove the filter from the cabinet:
    Blower RPM drops to 657 and static press drops to .30

    I tried setting the fan to high, it didn't change the #s

    Correct me if I am wrong, but I think my static press is limiting my airflow, so in order to protect the system the blower never kicks in high RPMs...always under 876 when cooling.

    I have already added a return when I had the system installed. Everyone of the installers (some from this forum) said my ductwork was OK.

    I can (not so happily) live with the way the system works now (although it does not keep pace like my old oversized system).

    2 questions;
    1. Do my #s look OK?
    2. Would using an even less restrictive filter help (only MERV 8 now)...any suggestions on a filter that would work?
    Last edited by MiniSoCold; 09-02-2011 at 01:15 AM. Reason: sp

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,248
    Seems like Reasonable operation to me ( unless the unit is running > 14 hours a day).

    You can not do Any better with filter selection.
    Warning to clean filter Frequently is a bit troublesome.
    I do not understand - my expectation would be to clean maximum of 4 times a year and change once a year.

    Expectation of < 72'F is a bit extreme when it's > 90'F.
    However, 71'F should be achieved a little after sunset.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,778
    Your static pressure at 875CFM is fine. By calcs, it should only rise to .45" when the blower goes to 1000 CFM.
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  4. #4
    Join Date
    Oct 2010
    Location
    SW Michigan, near Battle Creek
    Posts
    921
    if the system was unhappy about the static pressure ithink it would tell you. you do not say the airflow increases with no filter. it sounds like the blower slowes to maintain cfm.

  5. #5
    Join Date
    Oct 2010
    Location
    Minnesota
    Posts
    15
    I don't think the Infinity controler ever lets the static pressure go higher than .41 thus the blower never goes to 1000 RPMs, and never over 875 CFM to reach .45 static pressure when cooling. Thank you!

  6. #6
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    I thought Infinity would allow static pressure of closer to 1.0". I think 0.50" is considered "nominal" for most any system near nominal rated cooling CFM. I'm guessing yours is 1200CFM. So it would be just a little high, but not too bad.

    Beenthere, what's the max RPM for that motor? I'm guessing at least 1500RPM.

  7. #7
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,058
    Quote Originally Posted by MiniSoCold View Post
    System:
    <1 yr old a/c and furnace
    Furnace: Carrier Infinity 58MVCO8O
    A/C:Carrier Performance 24APA53OA003
    Infinity Control
    Carrier Media Filter Box 16x25
    Filter: 4 inch MERV 8 Carrier FILXXCAR0020 (first one said FILXXCAR0016)

    -I get the warning to change or clean filter after only about 2 months of use.
    -When cooling when I set the fan to high, the airflow does not seem to move all that fast.
    -The A/C does not quite keep up (maintain cool enough temp) on 90 degree days

    I checked the A/C status with the Infinity controler, here are my results:
    Fan set to auto, thermostat temp set to 71, outdoor temp 81, indoor temp 74.

    Airflow CFM 875
    Coil Temp 81
    Outdoor temp 81
    Blower RPM 720
    Static Pressure .40

    If I remove the filter from the cabinet:
    Blower RPM drops to 657 and static press drops to .30

    I tried setting the fan to high, it didn't change the #s

    Correct me if I am wrong, but I think my static press is limiting my airflow, so in order to protect the system the blower never kicks in high RPMs...always under 876 when cooling.

    I have already added a return when I had the system installed. Everyone of the installers (some from this forum) said my ductwork was OK.

    I can (not so happily) live with the way the system works now (although it does not keep pace like my old oversized system).

    2 questions;
    1. Do my #s look OK?
    2. Would using an even less restrictive filter help (only MERV 8 now)...any suggestions on a filter that would work?
    Your filter choice is fine, your static at this point is fine your cfm is at 350 default. Have your dealer set it up for 400 cfm and that wil increase your sensible capacity

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,778
    Quote Originally Posted by motoguy128 View Post
    I thought Infinity would allow static pressure of closer to 1.0". I think 0.50" is considered "nominal" for most any system near nominal rated cooling CFM. I'm guessing yours is 1200CFM. So it would be just a little high, but not too bad.

    Beenthere, what's the max RPM for that motor? I'm guessing at least 1500RPM.
    1200 or 1300 RPM. After that it won't report a static pressure as I recall.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #9
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,908
    -I get the warning to change or clean filter after only about 2 months of use.
    Pleated filters are face loading verses media filters that load through the depth of the media; therefore they may load faster even though they have a lot more sf of physical area.

    -When cooling when I set the fan to high, the airflow does not seem to move all that fast.

    -The A/C does not quite keep up (maintain cool enough temp) on 90 degree days
    A setting of 71F on high heatload days is too low a setting, try 75F. On hot days, what temp does it achieve?

    I checked the A/C status with the Infinity controler, here are my results:
    Fan set to auto, thermostat temp set to 71, outdoor temp 81, indoor temp 74.
    In MN do you have medium heatloads with high humidity control problems?
    If so, that could be why they set it at 350-cfm per ton.

    I don't have specific figures on your particular filter.
    A 16X25X4 Merv8 figures at 1400-cfm & 492-fpm velocity, pd is 0.21", physical square feet is 18.8-sf'. Therefore, even at 1000-cfm if the rest of the duct system meets Manual D standards the static might well be within tolerances.

    Merv8 filter specs - download the pdf:
    http://www.google.com/url?sa=t&sourc...KP0L0IY5mN3PZw

  10. #10
    Join Date
    Feb 2011
    Location
    oregon
    Posts
    139
    What size unit is it in ton for us non HVAC guys please?

  11. #11
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,248

    Thumbs up FILTER IS FINE ! !!

    Quote Originally Posted by udarrell View Post


    I don't have specific figures on your particular filter.

    A 16X25X4 Merv8 figures at 1400-cfm & 492-fpm velocity, pd is 0.21", physical square feet is 18.8-sf'. Therefore, even at 1000-cfm if the rest of the duct system meets Manual D standards the static might well be within tolerances.

    Merv8 filter specs - download the pdf:
    http://www.google.com/url?sa=t&sourc...KP0L0IY5mN3PZw
    Translating ...
    at 900 CFM the rated filter dP is only 0.087" ( not 0.21" @ 1400 CFM)
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  12. #12
    Join Date
    Feb 2011
    Location
    oregon
    Posts
    139
    What size unit is it in ton for us non HVAC guys please?

  13. #13
    Join Date
    Feb 2011
    Location
    oregon
    Posts
    139
    Sorry double post.

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