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  1. #1
    Join Date
    Aug 2007
    Location
    Dallas, TX
    Posts
    43

    single unit/dual zone setup

    All-

    We've got a single unit dampered for dual zones. That is the supply side is dampered, the return side pulls from the whole house regardless. Is this correct, or should the return side be switched as well? I ask as all our bedrooms and two baths are on one (slightly smaller) zone, rest of the house on the other. At night, we turn the unoccupied side way up so as to not waste any AC, but when the bedroom side cycles on, it's like a jet engine. Since it's pulling from the entire house, I'm assuming the supply side has to balance out and so we're pushing a full house worth of air through less than half of it. Or, should the system know it's only supplying to half of the house, and adjust accordingly? 3,000 sqft, 5ton Trane XL19i (so it's a dual compressor, variable speed fan). Installed 4 years ago, just never spent anytime thinknig about it until I started educating myself with all of your help

    Thanks!

  2. #2
    Join Date
    Jul 2008
    Location
    Alabama
    Posts
    658
    Sounds like you need your a/c man to check the bypass damper. If its got one. You can adjust the bypass to quieten the smallest zone.

    One common return is okay if it is big enough.

  3. #3
    Join Date
    Jan 2008
    Posts
    78
    i've had a similar problem going on for about 3 months with a new install...if you get it figured out, let me know....seems like rather than slowing the fan down, the industry solution seems to be to just divert air using a bypass damper which seems like a total waste.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,876
    Could be a bypass damper problem. Or miswired that its running in second stage when it shouldn't.
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  5. #5
    Join Date
    Jul 2008
    Posts
    7
    You should probably be utilizing a zone control with a discharge air sensor since you have a variable speed blower. saves alot of hassle as the board cycles the compressor to maintain air temp. and reduces blower speed when only one zone or a small zone is calling.(at least on lennox and trane) Same for heat as well.

  6. #6
    Join Date
    Jan 2008
    Posts
    78

    Dallen

    can you please elaborate on the discharge sensor? How does a temp discharge sensor reduce blower speed? I've had zoning problem for 3 months and getting desperate..controlling fan speed seems to be a the problem that can't be solved

  7. #7
    Join Date
    Jul 2008
    Location
    Alabama
    Posts
    658
    Quote Originally Posted by DAllen View Post
    You should probably be utilizing a zone control with a discharge air sensor since you have a variable speed blower. saves alot of hassle as the board cycles the compressor to maintain air temp. and reduces blower speed when only one zone or a small zone is calling.(at least on lennox and trane) Same for heat as well.

    If it is a Honeywell zone board it came with a DAS(discharge air sensor).

    It may not be on the unit though.

    BTW....the zone control can't slow the blower. Heres why. When the VS air handler gets a "G" call it ramps according to time...if you lose "G" call the fan ramps down to the "OFF" position.

    Carrier infinity and Bryant Evolution are the only units i've seen that don't have a bypass.

    Homeowner, have your company check the bypass, wiring of the a/h, and the dip switches of the VS blower.

  8. #8
    Join Date
    Jan 2008
    Posts
    78
    the name Variable speed is incredibly misleading...in my mind, when i bought a varialbe speed a/h i assumed it would vary the fan speed as needed..being able to change the max fan speed with jumper helps the installer, not the homeowner. The fact it ramps up then down doesn't mean jack to me. in hindisght, getting a single zone system or 2 separate compressors is the way to go

  9. #9
    Join Date
    May 2002
    Location
    Houston Texas
    Posts
    6,321
    Answer to the OP's first question, no, the returns should not be controlled by the control panel. When setting up a zoned system you can control the return side but I personally don't see the benefit in most application. More to the point on your question it will not reduce air noise.

    Next a zoned system with a variable speed motor should not have a bypass damper; if it does it can cause the motor to hunt continually due to fluctuating static pressures. I say should not because there are always exceptions to any rule.

    Lennox, Carrier and Trane all have zone control panels that modulate the airflow depending on the requirements of the zones calling for air. That doesn't mean that you have such a board you need to post model numbers of the zone components.

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,876
    Quote Originally Posted by superd77 View Post

    BTW....the zone control can't slow the blower. Heres why. When the VS air handler gets a "G" call it ramps according to time...if you lose "G" call the fan ramps down to the "OFF" position.
    A signal on the G terminal doesn't ramp according to time.
    Usually just runs at 50% of high cooling speed. A signal to Y1or Y2 is required to activate the timing sequences.
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  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,876
    Quote Originally Posted by njhusky View Post
    the name Variable speed is incredibly misleading...in my mind, when i bought a variable speed a/h i assumed it would vary the fan speed as needed..being able to change the max fan speed with jumper helps the installer, not the homeowner. The fact it ramps up then down doesn't mean jack to me. in hindsight, getting a single zone system or 2 separate compressors is the way to go
    Yes, the name is misleading.
    It does vary its speed as needed. There are limitations though.
    Your install/setup wasn't done right, or you would be happy with your VS blower and set up.
    Don't blame the equipment, for the contractors short comings.
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  12. #12
    Join Date
    Jan 2008
    Posts
    78
    Beenthere...thanks for all your sage counsel during this process.

    I've decided to buy an extech datalogging anemometer (about $300), so I can really figure out what is happening with the fan speed. Is this decent equip?

    also--is there a way to tell if the system is on 1st stage or second stage? want to track how long it stays on stage 1 before switching over to stage 2.

    I think Trane should take some lessons from Honda on VS a/h. in my car, when it comes to temp, the fan speed slows down, when it gets hot, the fan speeds up..If I don't agree with the car's choice, I simply change the fan speed. How simple is that. They make this stuff way more complicated than it needs to be.

    The biggest hassle is the time I've spent on this rather than running my own business...at least you guys are teaching me something..

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,876
    I have no background on that anometer.

    No easy way to tell if its in first or second. Ususally the change in air flow from the registers tells most people.

    Unfortunately, too many people would be adjusting their fan spped all the time, and calling that its not cooling good enough, if they had complete control over fan speed.
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