Results 1 to 11 of 11
  1. #1
    Join Date
    Jun 2006
    Posts
    7

    Confused

    I keep seeing literature on the electric savings of variable speed vs multispeed motors. But was just wondering if I ran the multi speed in low 24/7 wouldn't this give me a comparable savings to an variable and also save me in initial cost in buying an variable speed?

    Your opinions greatly appreciated!

    Thanks

  2. #2
    Join Date
    Dec 2005
    Posts
    3,931
    No.

    The variable speed compensates for different load conditions.

    In a multi speed fan, it has to be set to the proper speed by the installing contractor.

  3. #3
    Join Date
    Jun 2006
    Posts
    7

    Unhappy

    What I remember them saying was using an external relay to put the motor into low speed while in fan only mode. How much more are we talking about for getting a 2 stage, variable speed furnace w/T-STAT? Is it worth it I live in N. CA where the temp is fairly moderate. I would probably use the AC 6 days a year and the heater maybe 4 months out of the year. I want a 10 SEER and 80% furnace with I guess vairable speed, 2 stage if I can get it that way from Frigidaire. How does this sound what would be the best config for someone like me without costing too much?
    Thanks

  4. #4
    Join Date
    Jun 2006
    Posts
    13
    Below is taken from GE info about ECM motors which are the variable speed motors used. A multi speed motor is considered an induction motor.

    Ultra-high efficiency
    ECM 2.3 efficiencies are as high as 82%. At full load the ECM 2.3 is 20% more efficient than a standard induction motor. At low speed the ECM is over 30% more efficient than a standard induction motor. On constant fan speed, the ECM consumes 60-80 Watts as compared to 400 watts for the induction motor. What's more, its permanent magnet, DC design allows it to maintain its efficiency over its wide speed range.

    http://www.geindustrial.com/cwc/products?pnlid=4&id=ecm

    [Edited by advent on 06-18-2006 at 01:19 AM]

  5. #5
    Join Date
    Jun 2006
    Posts
    628
    I'm just another consumer. Variable speed motors do have a hefty pricetag, that even very heavy AC users may take many years to break even on, but to me even in a mild climate I see the increased comfort as worth the cost. In your situation with very little AC, fair amount of heating, I think I would just look for the best value multispeed.

  6. #6
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    Variable speed is all about comfort and not energy savings. Variable speed is also much better for setting the correct cfm for a system with minor ductwork problems. Motor will ramp up to achieve the desired cfm per ton of heating or cooling required. Multispeed is just what it says, multiple fixed speed, motor speed will not change to compensate for slightly plugged filter or other restrictions in the system.
    "Go big or Go Home"

  7. #7
    An AC sized properly with duct work, would give you the comfort you need, at the right price tag - even with a multispeed blower.

    Why not couple with multispeed compressor for better energy savings?

    However, you'll be better off with a unit that will give you the comfort, at the lowest ownership cost. The choice is yours.

    http://www.air-conditioner-selection...ing-guide.html

  8. #8
    Join Date
    Jan 2003
    Location
    CA
    Posts
    8
    Be aware that the words "low" in a variable speed and "low" in a multi-speed mean different things in the context of continuous fan.

    In variable speed the airflow for continuous fan is often 50% or less of the corresponding operating selection.

    Variable speed fans are inherently efficient at all power ranges. Multi-speed motors achieve their lower speeds by a crude de-optimization of the magnetic induction angles by selecting different phasing. Usually the slowest tap is 25% less efficient than full power.

    Thus we have 3 savings; the fundamental efficiency of operating at 50% or less airflow; the difference in efficiency of the two types of motor if used at full power; and by avoiding a crude multi-tap design in multi-speed motors if used in anything but full blast.

    Note that you will find some of this information in the “Service Facts” or similar documents labeled “customer property” that the installers typically never leave.

    The theory is consistent with practice and with my tests using complex power-factor corrected power meters accurate on electronically commutated loads (variable speed motors). In my case the continuous fan on my Variable speed unit took 26% of the AC power of the previous similarly sized multi-speed unit.



  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,748
    Originally posted by mjk_na
    An AC sized properly with duct work, would give you the comfort you need, at the right price tag - even with a multispeed blower.

    Why not couple with multispeed compressor for better energy savings?

    However, you'll be better off with a unit that will give you the comfort, at the lowest ownership cost. The choice is yours.

    http://www.air-conditioner-selection...ing-guide.html
    Although you can use 2 stage condensers with multi speed motors, you won't get the same benifits as a VS blower.

    The multi speed won't lower the air flow as much, nor does it have the ability to ramp up slowly giving the coil time to get colder like a VS.
    Contractor locator map

    How-to-apply-for-Professional

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

  10. #10
    Originally posted by beenthere
    Although you can use 2 stage condensers with multi speed motors, you won't get the same benifits as a VS blower.

    The multi speed won't lower the air flow as much, nor does it have the ability to ramp up slowly giving the coil time to get colder like a VS.
    Indeed.

  11. #11
    Join Date
    Jun 2006
    Posts
    7

    Talking

    wow you guys are awesome. Thanks for the info all of you!!! Really appreciate it.

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