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  1. #1
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    Supermarket with humidity problems

    Hi. I am currently working on a supermarket with humidity problems. Humidity cant get lower than 70%rh. I put a data logger and sometimes RH% gets to 90!!!! There is even starting to grow mold on the ceiling. The problem is mainly in the freezers and refrigeration area that is close to the entrance of the supermarket. They installed a motored air curtain in the entrance to keep the outside air outside. The a/c for that area is a 25 ton York split system. Some people recomended me that they should install a reheat coil in the supply duct to reduce humidity. Is it true that reheat coils remove humidity and need a drain? I have no experience with reheat coils. I wanted to know what you guys recomend. Thanks!

  2. #2
    jpsmith1cm's Avatar
    jpsmith1cm is offline Global Moderator/AOP Committee
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    I will assume that you are a technician.

    First advice that I will give you is to get your post count up and apply for free Professional Membership. We can discuss humidity control in much more depth in the Pro Technical forums here.

    Is all of the AC in the building working correctly? Charged right, airflows right, filters cleaned, etc?

    What controls the AC? Are the settings correct?

    I'd also stop using %RH as a metric for humidity and instead start using Dewpoint temperature for two reasons.
    1. Dewpoint is what really matters in a supermarket. We're concerned with keeping the equipment happy.
    2. Dewpoint is a better measure of the absolute quantity of moisture in the air.

    Reheat coils are for keeping the space comfortable while the AC runs almost continuously.

  3. #3
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    I dont do markets but if a building needs an air curtain to try an contain infiltration when doors open I think the issue lies elsewhere . . .

  4. #4
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    Quote Originally Posted by hvac wiz 79 View Post
    I dont do markets but if a building needs an air curtain to try an contain infiltration when doors open I think the issue lies elsewhere . . .
    Leaning that way myself. Kinda sounds like not enough outside air being pulled in. May need outside air dampers installed on unit or units.

  5. #5
    jpsmith1cm's Avatar
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    Air curtains are very common on grocery stores.

    They help keep the conditioned air contained within the building as the doors open and close. They also help with keeping bugs out of the building.
    \

  6. #6
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    Yes. I am a tech. The units are working good. The units are controled by individual termostats for each unit. The dew point in the area that has the problem is between 57 and 67.

  7. #7
    jpsmith1cm's Avatar
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    Maximum conditions for a grocery store is 74 degrees DB with a 55 Dewpoint.

    You have problems with the HVAC equipment that you haven't located, yet.

    Possibly bringing in too much outside air as was mentioned. Maybe a lot of other things.

  8. #8
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    I am checking the logger readings and temperature in the area is too cold. Its between 70 to 66 degrees db.

  9. #9
    jpsmith1cm's Avatar
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  10. #10
    jpsmith1cm's Avatar
    jpsmith1cm is offline Global Moderator/AOP Committee
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    Another question.

    Is the AC cycling on the thermostats?

    If so, then you really have no control over humidity, only temperature.

    Using a humidistat will enable you to do a better job of dehumidifying, but then you ARE going to need reheat.

  11. #11
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    I have to check the wet bulb in this week because the logger dont measure wet bulb.

  12. #12
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    Yes. The ac are just controling temperature. I guess i should start by installing a humidistat with a reheat coil. Do you recommend that the humidistat controls the reheat coil? ( sorry if my english is not good. I am from puerto rico and my main language is spanish lol!)

  13. #13
    jpsmith1cm's Avatar
    jpsmith1cm is offline Global Moderator/AOP Committee
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    Actually, your English is better than many native speakers. You are very clear and easy to understand. Thank you.


    Do you have multiple RTUs?

    Puerto Rico I guess has its own set of design considerations that a snow belt guy like myself hasn't considered.

    I still think you have an HVAC issue.

    Start at the beginning. Airflow correct, charge correct, unit operation correct before you go spending a bunch of time and money installing a reheat coil that may not have the desired effect.

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