Results 1 to 4 of 4
  1. #1
    Join Date
    May 2013
    Posts
    8

    Objections to adding VFD's to CV AHUs?

    I have several constant air volume units with no reheats. They each supply a single large space. The units supplying air all have VFD's that limit fan speeds to 30 Hz. My question is can this cause problems with heating or anything else for that matter? I have electric heating coils instead of a boiler and have had trouble meeting set points.

    Thanks in advance

  2. #2
    Join Date
    Mar 2012
    Location
    West Chester, PA
    Posts
    511
    You say they are constant volume but then you say they have VFDs? Usually the point of a VFD is to provide something other than constant volume. There are minimum airflow ratings for heating packages. You should make sure that your blower is capable of delivering the required CFM or, yes, you will burn out your elements. 30hz isn't a peed it's a limit on the drive frequency. You need to know the actual CFM being delivered. If you aren't meeting set point then: 1)your packages are too small 2)your packages aren't getting enough air and they may or may not be cycling on limit.

  3. #3
    Join Date
    May 2013
    Posts
    8
    Thanks, ADillon, The VFD's were added 12 years later. "There are minimum airflow ratings for heating packages. You should make sure that your blower is capable of delivering the required CFM or, yes, you will burn out your elements." Thats helpful, I will look into this.

  4. #4
    Join Date
    Oct 2011
    Location
    NJ
    Posts
    149
    VFD's can be used to balance CV units to run at reduced speeds to save energy, but no more than just properly re-sheaving the unit to the reduced speed needed.

    They can also be used to soft start the fan motors to limit startup torque and reduce inrush amp draw and allow the unit to slowly ramp up to their operating hz. This was believed to help reduce demand charges by reducing inrush current, but since the demand charge is averaged over a 15 min period, it really doesn't do much.

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