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  1. #1

    Expected amp draw for this fan (variable speed?)

    Had the REMC guy come out and do an energy audit. One thing he suggested was that we stop running the HVAC fan all of the time to lower our monthly power usage. I commented that we have a variable speed blower; so it should have a pretty minimal amp draw for just continuous cycling. When he tested the unit with just the fan running, the amp draw @ continuous fan speed was 3.3A... which was way higher than I expected. I went over and checked my parents' fan at continuous cycling speed and it was only .6A. They have the "same" furnace, just a smaller model. Theirs has a 1/2HP blower while ours has a 1HP... but 3.3 vs .6 still seems like too much of a difference. The REMC guy said there's no way we have a variable speed fan with that kind of amp draw at low speed; and that it must be 2 stage fan. The info I found on Carrier's website indicates it IS a 1hp variable speed fan, no other options listed for that model; but the only amperage information I can find is that the max draw is 12.8A. Can any of you experts confirm that the below-listed furnace is in fact only available with a variable speed fan... and, more importantly, do you know what the expected amp draw should be during the continuous cycling fan speed.


    Carrier Infinity 59TN6A100 V211120

    Thanks in advance for any help you can provide!

  2. #2
    Join Date
    Mar 2013
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    nh seacoast
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    variable speed blower motors are ECM motors, identified by the large control module on the back end and 2 wiring harnesses - one for power, the other for control signals. these require a true RMS clamp meter to read amps. the common averaging meter will read high, i think. plugged filters and coils, blocked/small returns will cause an ecm to draw more power as it tries to make programmed rpm against the restriction... support your local tradesman, get a full pm/cleaning! also depends on how the unit was set up - usually some way to select blower speeds for heat and cool with constant fan defaulting to a small percentage of either heat or cool speed.

  3. #3
    Join Date
    Aug 2010
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    West Monroe, LA
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    1,529
    Something else to consider/ look into is if you have a variable speed motor is the ductwork sized properly?

    While variable speed units when sized properly can previde lower amp draw, remove more humdity etc. if they are installed on undersided duct system they will do just like a standard motor and ramp up to try to overcome the bad system.

    I would have a pro out to review over the system and do a cleaning on the system. Have them look at your ductwork both supply and return and ensure it is sized properly for not only size but how much cfm needing to supply and return the rated the cfm it is set for.

    While variable speed systems are a great way to go and offer many Benfits the truth is they are only going to work right if duct system and unit are sized properly. Also if the coils indoor or outdoor are dirty can also cause the system to
    Ramp up to try to overcome this.

  4. #4
    Join Date
    Jan 2004
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    Lancaster PA
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    What type of air filter do you use. What is size air filter. Post full model number of the furnace. Post some pics of the duct work attached to the furnace.
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  5. #5
    Sorry I haven't gotten back with the info/pics you guys requested: we have a family member in poor health and that has been the priority lately. I'll tell you what I know for sure; and try to get some pictures up when I can.

    The filter is a Filtrete 1550 20x25x4". I change them every 6 months; and had just changed one the week before the REMC guy came out.

    The unit was installed January 2012. It's actually a 4 ton 2 stage WaterFurnace split unit (Envision?) with the Carrier Infinity furnace listed above as our stage 3 back up heat. I chose this over the typical electric heat strips because we live out in the county where the electric service can be sketchy during winter storms. I can run a propane furnace off of a standard 7kw generator during a power outage.

    The duct work in the "old" part of the house is very inadequate. There's a plenum (I'd guess 10"x18"), off of which run about 6-7 6" ducts... some of which are 50'+ long. the old part of the house doesn't have a traditional crawl space: just a very small crawl space big enough to put the plenum and attach the 6" ducts. The rest of the "old" house after that just has a few inches below the floor joists. No cost-effective way improve it. There is one ~12" x 18" return in the center of the old part of the house. The duct work in the new part of the house a lot "better", with a large plenum running end-end in a real crawl space with short runs of round duct going to each register and a few different returns in different rooms.

    At this point I'll chalk it up to the bad duct layout in the old part of the house. When they were designing the new system, the guy commented they needed to go to the 1hp fan to better push air through the restrictive ductwork. But he is also the one who recommended keeping the fan running 24/7 and said it would only add $6/month to our electric bill.

  6. #6
    Join Date
    Jan 2009
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    Keokuk, IA
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    That size unit has a the 5 ton (1 HP) ECM blwoer motor, while the smaller unit furnaces have a 3.5 ton (1/2" HP) version. The pwoer consumpiton depends on how muc hresistance you have in your ductwork and what speed it runs at. The low/med/hi blwoer speed on continous fan are based on the maximum speed for either heating or cooling, not nessesarily on the size of the motor. That 1 HP ECM at 1" static and max RPM could be comsuming as much as I think around 800Watts. At minimum RPM and maybe 500CFM, it might only consume around 50-70 Watts. With extremely low static, a 1/2 HP ECM near minimum RPM to deliver 300CFM could be as low as about 20 Watts.

    Lets say you're somewhere in the middle at 100 Watts on low speed. $6 would be about right at $0.10/kwhr. If you have ideal ductwork, it might be 1/2 that.


    BTW - I heard that Infinity didn't play nice with split geo systems because it wanted to use 50% airflow on 1st stage heating or cooling, not 80%. THe only "work around" is to tell the Furnace that the unit is a little larger and use higher airlfow on high stage of the compressor. So in your case, you may need to tell the Infinity controller that you have a 5 ton unit, not a 4 ton, otherwise you'll may be short on airflow in low stage. Just something to be careful about. Otherwise I think it defalts to only 800 CFM on low with the 4 ton unit, when you actually need at least 1000CFM and ideally closer to 1200. 5 tons and airflows set to "comfort" might work well.

  7. #7
    Quote Originally Posted by motoguy128 View Post
    At minimum RPM and maybe 500CFM, it might only consume around 50-70 Watts. With extremely low static, a 1/2 HP ECM near minimum RPM to deliver 300CFM could be as low as about 20 Watts.

    Lets say you're somewhere in the middle at 100 Watts on low speed. $6 would be about right at $0.10/kwhr. If you have ideal ductwork, it might be 1/2 that.

    If it's pulling 3.3A continuous, wouldn't that be ~726watts? (3.3A x 220V) When the REMC guy was out and crunched the numbers, he estimated it was adding ~$35/month to our bill having the fan run all of the time. Our power is $0.10/kwhr.

  8. #8
    Join Date
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    Quote Originally Posted by strawmyers View Post
    If it's pulling 3.3A continuous, wouldn't that be ~726watts? (3.3A x 220V) When the REMC guy was out and crunched the numbers, he estimated it was adding ~$35/month to our bill having the fan run all of the time. Our power is $0.10/kwhr.
    Your gas furnace is only a 120 volt appliance.
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  9. #9
    Quote Originally Posted by beenthere View Post
    Your gas furnace is only a 120 volt appliance.
    That's still 363 watts.

  10. #10
    Join Date
    Jan 2009
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    If it's actually using 323 Amps on low speed (50% of high heat) you have some fairly undersized ductwork. That would have to be close to 0.5" of static. Ideally it would be under 0.2".

    Whatever EER/SEER you think you are supposed to be getting on the system, knock at least 0.5 off for hte high static your seeing. I bet on high stage cooling it's close to maximum RPM and drawing at least 700 Watts.

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