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  1. #1
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    Another Humidity Question

    I have been trying for some time to find out how the Lennox Prodigy controls humidity in their RTU'S. I have seen jobs where it works fine but other jobs where the water removal was insufficient.
    Without knowing the capability there is no way to know for sure the RTU speced will do the job.
    Lennox did the research and made Walmart happy but I'm talking about smaller RTU'S than that. From 5 to 20 tons mainly.
    No man can be both ignorant and free.
    Thomas Jefferson

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    its mainly by the indoor humidity sensor that controls it with a connection to the board..you make the adjustments at the rtu settings controller..

    products/indoor-air-quality/humidity-control/Humiditrol-RTU
    https://www.lennoxcommercial.com/pro...Humiditrol-RTU

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    what I usually find on the units that it dont work right, it is either a missing sensor or one that is bad, and I have had them bad right out of the box.

  4. #4
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    How cold does the supply air get? Does the unit subcool and then reheat and if so how? How can I determine how much water the unit can remove from the air?
    Those are the things that are needed to determine if the unit will do the job or if other methods have to be employed.
    I have noticed that the Prodigy field set up is often less than desirable.
    No man can be both ignorant and free.
    Thomas Jefferson

  5. #5
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    they have the reheat coil like trane...both manufacturers can tell you..

    this is an older thread ..about it
    https://www.hvac-talk.com/vbb/showth...9-Reheat-Coils

  6. #6
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    The problem I have had is none of the manufacturers will tell me how cold the evaporator will get. That has to be controlled and all I want to know is to what temperature? I have tried everything from begging to irritating and still don't know how to tell the amount of water that can be removed in every case. My gut feeling is the air temperature is probably cooled to no lower than 48 F and reheated to around 60 F. The engineers I have discussed this with don't know and so far all just have confidence the air will be dehumidified as desired.
    There has to be a limit so what is the limit? I'm looking for real numbers!!!
    No man can be both ignorant and free.
    Thomas Jefferson

  7. #7
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    Quote Originally Posted by WAYNE3298 View Post
    The problem I have had is none of the manufacturers will tell me how cold the evaporator will get. That has to be controlled and all I want to know is to what temperature? I have tried everything from begging to irritating and still don't know how to tell the amount of water that can be removed in every case. My gut feeling is the air temperature is probably cooled to no lower than 48 F and reheated to around 60 F. The engineers I have discussed this with don't know and so far all just have confidence the air will be dehumidified as desired.
    There has to be a limit so what is the limit? I'm looking for real numbers!!!
    The humidistat controls it depending on the settings, I would start there...

  8. #8
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    I don’t know for sure the temp. But I have seen a Trane horizon, with a lot of outside air, freeze when the lat was a little below 48. So I would think 50 or so would be how cold. In a commercial building with 72-74 deg temps, 50 should be fine.

  9. #9
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    The problem I have is knowing the capacity for removing water in the dehumidifying mode. They use more than one method of control and I can deal with that. What I need to know is the minimum coil temperature and design airflow at that temperature to be able to accurately predict the max amount of water that can be removed from the air. I'm not questioning whether or not it works but if it will work on specific jobs.
    I just finished TAB on a small job where the humidity was out of control. The building manager ask me if it could be made to control the humidity to 50% at 70 F. All I could tell him was I didn't know. I found a lot of problems and set the system up to run as designed at 75 F @ 50% RH just to find out if it would do that. It did and that confirms the unit is working as designed which I had to know before going any further. In a few days it will be set at 70 F and 50% RH and we will see if it can do that. If I knew the information I have requested I wouldn't have to run two tests and the building would be done.
    Design engineers today don't have balls. I would tell the rep if you want to sell your crap you will answer my questions because to reject your submittal all I have to do is x it rejected.
    No man can be both ignorant and free.
    Thomas Jefferson

  10. #10
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    Theoretically Scoobie 50 F air will control humidity to 50% at 70 F. The old 20 degree rule actually holds with the psychrometric chart. In a building where you are picking up unwanted moisture you may need the dehumid cycle or if the unit is like the one I still have to finish that is not going to be operated at or near design.
    During the demid cycle you get very little cooling which raises the question can this unit dehumidify in a timely enough manner that the temperature can be controlled at setpoint.
    No man can be both ignorant and free.
    Thomas Jefferson

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    Well, if the space temp starts going up, the reheat would stop. We have put some small Trane units in with the hg reheat coils and they worked great. Corrected 20 year old problems that a lot of money had been thrown at.

  12. #12
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    If the space temperature going up stops the reheat coil before it finishes its job (which it will) the space humidity will not reach setpoint. I want to know before that happens if it will or won't.
    As a TAB guy you are the one everyone looks to if the desired space conditions are not met. A lot of people don't trust TAB guys so if something don't do the job expected you need a valid provable answer as to why it doesn't.

    An example I posted here before should illustrate the point. I balanced a building that the office AHU design was so bad the discharge air temperature with zero outside temperature would be 45 F. I sent an email and got a call back that a value engineering study had been done and it was OK. When the ambient got to zero they called complaining that the air was 45 F. My defense was on record before the problem showed up.
    No man can be both ignorant and free.
    Thomas Jefferson

  13. #13
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    You can also lower the blower motor speed or adjust the blower motor pulley to pick up more humidity “the old school way”

    I have also found moisture in the concrete foundations and walls with a moisture meter..also open plumbing fixtures like toilets /sinks/ showers and urinals..will actually add humidity (as it evaporates)

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