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  1. #14
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    to answer the controls questions, ramp the compressors by space temp demand.

    I think its a bad idea honestly.

  2. #15
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    Even though you cannot use a drive on your compressors, you can still be the hero. Tell them to get the mechanical guy retrofit the thing with one of these:

    https://rawal.com/products/apr-control-hot-gas-bypass

    It has been a while, but on packaged systems they used to say they could unload down to 15-25% of total capacity. Then you can run your fan as low as you want. The system just mechanically unloads - nothing to control. Super easy. I installed one a long time ago, and it worked well. It was tough to braze though... not your problem I guess.

    I also wanna know why you go through evaps so fast though....
    Quote Originally Posted by MaxBurn View Post
    Why are you having coils fail inside of 5 years?!
    Hmmmm....smells like numbatwo to me.

  3. #16
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    it sounds like you have a Carrier unit with the evap description. I have never used it. but carrier makes a kit to replace the orifice header on the evap with a txv. kit includes a txv, distributor and cap tubes. if you want to go all mad scientist, you could put that in but split the coils with it, and do the same to the suction header. PITA I know.

    why dont you look into making the refrigerant circuits a common circuit.

  4. #17
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    Thread Starter
    Thank you for the link. It's very interesting. Just curious, how the by-pass method can save kwh, which is a major benefit to VFD the compressor. If the compresser runs at the full speed, the kwh usage should be about the same. Please correct me if wrong.

    to answer @MaxBurn the question, the units are located where there are lots of lint. Those lint enter inside the condenser coil and make the system fail. We all know those coil can not be economically replaced. It cost more than half of the unit price. I cant hardly understand though.
    I asked the question in another thread.
    https://hvac-talk.com/vbb/showthread...8#post25759118



    Quote Originally Posted by numbawunfela View Post
    Even though you cannot use a drive on your compressors, you can still be the hero. Tell them to get the mechanical guy retrofit the thing with one of these:

    https://rawal.com/products/apr-control-hot-gas-bypass

    It has been a while, but on packaged systems they used to say they could unload down to 15-25% of total capacity. Then you can run your fan as low as you want. The system just mechanically unloads - nothing to control. Super easy. I installed one a long time ago, and it worked well. It was tough to braze though... not your problem I guess.

    I also wanna know why you go through evaps so fast though....

  5. #18
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    Quote Originally Posted by Spitz View Post
    What type of compressor? A discus may be slowed to around 25hz. A basic scroll 45-50hz.

    Sent from my SM-G960U using Tapatalk
    2 5 ton compressor from carrier packaged unit. I guess they are scrolls. If I can unload it to 45hz, I will be very happy.

  6. #19
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    Quote Originally Posted by windpoint View Post
    Thank you for the link. It's very interesting. Just curious, how the by-pass method can save kwh, which is a major benefit to VFD the compressor. If the compresser runs at the full speed, the kwh usage should be about the same. Please correct me if wrong.
    Work = amps. When you slow a motor using a VFD, it does less work, so it draws less amps. However, when you bypass from the discharge back into the suction side of a compressor (called hot gas bypass), you also do less work, and therefore draw less amps. There is no real work done, so your amps drop off, and therefore your power draw is less. It's like running a blower motor with no blower wheel, the amp draw is negligible, because no work is being done.

    The problem is that it is possible to hot gas bypass a compressor to death. They are not made to suck hot gas, so when you get above a certain % of bypass, the oil breaks down, windings get hot, things go boom. So the APR does the HGBP into a chamber, and places a TXV on the other side of said chamber. The txv adds enough cooling capacity to cut the superheated gas down to a reasonable temp to save the compressor, making more unloading possible to do safely. This is a very simplified explaination, as I got work to do and you have a link. But it should be clear enough.

    As a side note, I am a firm believer that if one cannot be nice they should be quiet.... but be careful what mechanical advice you take. If you decide to take some of the mechanical suggestions on this thread, run them through the pro's forum on commercial service first. Just be sure the poster has a firm grip on what he is talking about before you lay your reputation or a customer relationship on the line.
    Hmmmm....smells like numbatwo to me.

  7. #20
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    Quote Originally Posted by windpoint View Post
    I asked the question in another thread.
    https://hvac-talk.com/vbb/showthread...8#post25759118
    Just a heads up, your thread link above discusses Condenser coil failures. In this thread you mentioned Evaporaror coil failures. Maybe it was a slip of the keyboard?

    Anyhow, I posted in your other thread.
    Hmmmm....smells like numbatwo to me.

  8. #21
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    .

    Sent from my SM-G960U using Tapatalk

  9. #22
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    You told us previously that you had some electrical background.

    There is more than electrical that you'll need to think of.

    Your main concern as the system as not been designed for variable speed will be oil return.
    Some compressor wouldn't last long with a vfd.
    Replacement cost of the compressor will offset
    energy saving by a lot.

    Unit are small tonnage I see no gain in doing that.

    Personnaly I wouldn't recommend it.

  10. #23
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    Quote Originally Posted by patpinet View Post
    You told us previously that you had some electrical background.

    There is more than electrical that you'll need to think of.

    Your main concern as the system as not been designed for variable speed will be oil return.
    Some compressor wouldn't last long with a vfd.
    Replacement cost of the compressor will offset
    energy saving by a lot.

    Unit are small tonnage I see no gain in doing that.

    Personnaly I wouldn't recommend it.
    Thank you for reply.

    Running full speed every say 30 minutes will help solve oil problems. Learned this online. I cant prove it.

    This main purpose of this approach is to test and learn. Like it or not, VFD will play big part in AC world. If I can learn something ahead of time, will benefit from it later on.

  11. #24
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    That is a great idea.
    Maybe you can ask Emerson for guidance or check there bulletin.
    If it's a scrool be advised that the one for vfd have been modified to help the lubrification for both bearing.
    You might find a kit from Emerson if you want to replace compressor.
    You might want to install a EEV instead of a TXV.

  12. #25
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    I git my info from a bulletin from Emerson I will post the number later. Also be aware they do make a retrofit digital scroll kit. Something to look at if you have a dead compressor.

    Sent from my SM-G960U using Tapatalk

  13. #26
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    Is it me or does it sound like doing all these modifications to the system it might be better to do nothing, wait for the next replacement and get a unit that is capable of all this with warranty? Maybe save the money on mods and do the replacement a bit early?

    DigiRTU is fairly non invasive, they put the whole unit on VFD from what I understand, no modifications to the refrigerant system. As an owner that might be the furthest I'd be willing to go.

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