Results 1 to 5 of 5
  1. #1

    static pressure and motor speed

    I've just had a new 2 and 1/2 ton Rheem Heatpump, model RPNL, with RHLL air handler installed in my attic using existing ductwork to replace a 24 year old Weathertron of same tonnage. When I asked the installers about the static pressure, they informed me that they never do this, don't know how. According to the info I have read, the x-13 GE blower motor should be set to switch 2 or 3 depending on the static pressure. I figured that it's better to assume I have a lot and connect to switch 3 to insure maximum airflow over the coils, so I had them set it on this switch. What negative effect (other than wasting electricity to turn the motor) will it have on my system if I have lower static pressure and am pushing too much air across the coils? Also, is there any way to ballpark figure static pressures based on duct size, configuration and materials?

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,074
    If the velocity is too high it could pull the water off the coil. It may not dehumidify as good as it should.
    Contractor locator map

    How-to-apply-for-Professional

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

  3. #3
    Thanks Beenthere. Any idea how high that would have to be? The air handler I'm using can be used with a 2 1/2 or 3 ton heatpump and the three ton unit requires a lot more CFM and runs on switch 4 or 5, so I figured running the extra air wouldn't be a problem for the handler or coil. For my heatpump, nominal flow is 1000 cfm, with minimum and maximum around 935 to 1130 (or there abouts). With the 3 ton I think nominal was 1200, didn't pay as much attention to those numbers. Hard to tell at this point what the humidity is going to do. My HP has been out since winter, and the humidity was about 90% in the house when the unit started up, so I know it's going to take a few days to pull some of that moisture out. It dropped pretty quickly to about 90% but crept back up to 85 or so overnight with no AC required. Right now, I've set my thermonstat on the continuous fan position, which runs the fan at a very low speed until it calls for AC, then it ramps up.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,074
    If you duct system is sized for 2.5 tons, you'll have high velocity air using the higher setting.
    If you want humidity removal, slow is better.
    Running the fan continuos will increase your indoor humidity.
    Slow the blower and set the fan to auto.
    Contractor locator map

    How-to-apply-for-Professional

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

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,074
    If you duct system is sized for 2.5 tons, you'll have high velocity air using the higher setting.
    If you want humidity removal, slow is better.
    Running the fan continuos will increase your indoor humidity.
    Slow the blower and set the fan to auto.
    Contractor locator map

    How-to-apply-for-Professional

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

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event