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  1. #1
    Join Date
    Aug 2010
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    15

    Bryant-Evolution: Mystery Fan Speed

    Question relates to system with Bryant two-stage heat pump compressor (3-ton), the FE4ANF002 air handler, and Evolution thermostat. We also have an Aprilaire humidifier integrated into the system.

    We always set the fan to low and leave it there (both summer and winter). The compressor usually runs on the low stage, and we barely hear the air coming through the ducts….all good.

    But yesterday (which was a humid and mild 50 degree F weather day), with the heat pump running on the low stage, I noticed that the air handler fan was running at a high speed, pushing much more air than usual. I am aware that, when needed, the Evolution system will run the fan at a high speed even when the fan setting on the thermostat is set to low (e.g., a very hot day in the summer, or very cold in the winter), but why in the world was it running at a high speed when the heat pump was just barely needed (and running at the low stage)? Do I have an issue…..or is this normal? But why would it be normal????? If anyone can solve this mystery for me, I would be very appreciative!!!

    Thanks!

  2. #2
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
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    2,040
    Did you happen to check the thermostat/control to see what the system status was? IE: What stage was running?
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  3. #3
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    Do you have "comfort" airflow enabled? I think the system will lower airfkow nfor warmer air in cooler outdor conditions, but raises airflow when outside temps rise to avoid tripping on high pressure. Ibe notced similar behavior in cooling. In cpoler weathe rthe airflow settings are higher since theres more capacity and thefore the coil would be colder.


    Sent from my SGPT12 using Tapatalk 2

  4. #4
    Join Date
    Aug 2010
    Posts
    15
    Responding to previous 2 questions:
    1. I did check...and the compressor was running on the low stage (which seems right given that it was 50 degress F outside)...just barely needed heat at all.
    2. I do not see any setting on the Evolution thermostat called "comfort."
    I have the heating humidification set to "auto." The inside humidity was above the target. Is it possible that the system was actually trying to dry the air by running it more quickly through the heat exchanger? Or do I have a malfunction?

  5. #5
    Join Date
    Jul 2000
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    Northern Wisconsin
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    Is the fan running on a higher speed all the time or just once in awhile?
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  6. #6
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    The "Comfort" airlfow setting is set in the advanced isntaller screens. When it's colder outside, a heat pump has less capacity, so to maintain a warmer supply air temperature, the system will lower the airflow when it's colder outside. In cooling mode, the Evolution cotnroller will do the same thing to manage humidity levels and supply air temps. IF it's hot outside, the system will reduce airflow sicen system capacity is lower. OR the other way ot look at it, is the system raises airflow at cooler temps to avoid freezing the coil.

    So it's not so much that airflow is increasing at higher outdoor temps, it's that it's reducing airflow at warmer temps.

    IF you hold hte "advanced" button down, you can go to the air handler status or heat pump condenser status and see the current airflow, blower RPM and static pressure. Take a few screen photos when it's above 50F and when it's at a lower temperature.


    IF you unit is oversized for cooling, you may have simply never head higher airflows sinec it might be always dehumidifying and running at a lower airflow.


    Again, when it's warmer outside a heat pump has more capacity. When it's colder, less capacity. Efficiency also drops. For example, if the airflwo was 1200 CFM on a 3 ton heat pump, at 55F it might have 38000BTU's capacity, but lets say at 20F, it only has 25,000 BTU's (jsut grabbing numbers out of the air). So if you keep airflow constant, at return air temperature was 70F, you'd have 99F supply air at 55F, but only a 89F air at 25F. But if you reduce airflow, you will lose a little capacity, but the tmerpatuers will increase. So if you slow the blower to lets say 1000CFM you might get 93F air.

    Maike sense?

  7. #7
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
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    6,051
    Did the heat strips come on?

  8. #8
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    Aug 2009
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    Beatrice, NE
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    It didn't go through defrost did it?

  9. #9
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    Quote Originally Posted by kls-ccc View Post
    It didn't go through defrost did it?
    I'd hope that a new HE heat pump wouldn;t be defrosting at 50F outdoor temps. The temp drop on the outdoor coil should only be I think 8-10F, so even if it was fairly humid, it would just sweat.

  10. #10
    Join Date
    Apr 2011
    Location
    SE Washington
    Posts
    559
    no mystery, when you chose the low fan speed that is only in the off cycle, the algorithm thats built in takes control of the fan when the heat pump operates, it will adjust to inside conditions as needed, so you can never really know what kind of airflow your goiing to be having, but it sounds like its fine, just doing what the engineers designed it to do
    Total Energy Management, inc

  11. #11
    Join Date
    Aug 2010
    Posts
    15
    OK...I understand now that the "low" setting only applies when the compressor is off, and the system takes over for the given conditions (thanks isuredo for straightening me out on that).....but my question still holds: why would the engineers program the Evolution system to go to a high indoor fan speed when the outside heat pump is working at the low stage at a very high efficiency, given the moderate 50 degree F temperature outside? (By the way, the system rarely goes to the high indoor fan speed.)

  12. #12
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
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    By rarely you don't mean once a day do you? The system does a self calibration fan test once every day. Mine is every day at 1pm. During that test the blower will run at a high speed for a short amount of time. The other possibility is that the unit is going into defrost which it really shouldn't be doing at 50°....... that is only if it's set to auto defrost. If it's set to timed defrost that's a different story. That is also something you can check in the advanced setup that someone else explained how to look at. Check under the heat pump settings. I always set them to auto defrost.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  13. #13
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    Goign to the advanced screens and watching what the blwoer is doing would probably expalin a lot. You'll learn a lot by beign a nerd and observing it's operation in different conditions. I spent a LOT of time in the advanced screen the first month or tow I owned my Infinity system trying ot understand it's logic in different conditions.

    One you understand what it thinks it's supposed to be doing, then when it's doing something weird it should be more noticeable.

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