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  1. #1
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    close contol design

    Hi I have an area 14m long 8m wide 3m high which requires 23 c 50% rh on tight control
    I am going to use chilled water and thyristor heaters
    I have calculated at 20ACH that I need about 24kw cooling for the dehum based on 1.8 m3/s and off coil 12 degrees water 5 in 10 out with delta t of 5
    What i am struggling with is the reheat to keep the tight control on the temp.
    Need to calculate the size of heating required
    this will be +/- 1 degree and 4% rh control

    thanks

  2. #2
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    Re: close contol design

    Sensible capacity is the answer.

  3. #3
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    Re: close contol design

    Does the humidity of the air at the outlet need to be within the 4% control?

  4. #4
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    Re: close contol design

    Hi Sean,
    Yes as tight as we can within reason hence why we are on chilled water with motorised actuator and thryrister heating to pulse when on dehum but I need to know what capacity heating I will need to match the sensible cooling of 24kw
    The unit i am looking at currently has 15kw heating but i think this may need topping up which i can do but need to know how much ?

  5. #5
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    Re: close contol design

    Quote Originally Posted by AndyT539 View Post
    Hi Sean,
    Yes as tight as we can within reason hence why we are on chilled water with motorised actuator and thryrister heating to pulse when on dehum but I need to know what capacity heating I will need to match the sensible cooling of 24kw
    The unit i am looking at currently has 15kw heating but i think this may need topping up which i can do but need to know how much ?
    Considering a 24kW sensible cooling load, a 15kW heating capacity may require supplementation during dehumidification cycles. To optimize performance, consider a heating unit with additional capacity, ensuring it can effectively balance the cooling load. A thorough evaluation of your specific system dynamics and local conditions is advised. Adjustments can then be made based on real-world efficiency. It's always prudent to consult with a HVAC professional to tailor the solution precisely to your requirements, guaranteeing optimal performance and energy efficiency.

  6. #6
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    Re: close contol design

    Quote Originally Posted by AndyT539 View Post
    Hi Sean,
    Yes as tight as we can within reason hence why we are on chilled water with motorised actuator and thryrister heating to pulse when on dehum but I need to know what capacity heating I will need to match the sensible cooling of 24kw https://magic8balls.org/
    The unit i am looking at currently has 15kw heating but i think this may need topping up which i can do but need to know how much ?
    Hi,
    It sounds like you're aiming for optimal efficiency with your HVAC system. Given your current setup with chilled water and motorized actuators, along with thyristor heating for dehumidification, matching the 24kW sensible cooling capacity is crucial. While the unit you're considering has a 15kW heating capacity, topping up may be necessary to meet the required heating demand. Determining the additional heating capacity needed will ensure your system operates effectively in maintaining comfort conditions while managing humidity levels.
    Last edited by Aditi5897; 25-02-2024 at 01:59 PM.

  7. #7
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    Re: close contol design

    Hi Guys,
    What are the key principles to consider when designing a closed-loop control system for optimal performance and stability?

  8. #8
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    Re: close contol design

    Would plotting the points on a chart help?
    Something like https://www.flycarpet.net/en/psyonline or https://fenix.tecnico.ulisboa.pt/dow...ometrica_1.pdf
    Last edited by seanf; 23-11-2023 at 09:01 PM. Reason: mistake

  9. #9
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    Re: close contol design

    Using the Carrier psychrometric chart, maybe something like:

    Starting at 12C 100%RH, Enthalpy: 34.2 kJ/kg.

    Finish at 23C 50%RH, Enthalpy: 45.5 kJ/kg and Volume: 0.85 m3/kg dry air.

    Mass: 1.8m3/s / 0.85m3/kg = 2.1kg/s.

    (45.5 - 34.2) x 2.1 = 23.7 kJ/s

    Very roughly done and recommend checking over. Been a long time since doing any calcs.

  10. #10
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    Re: close contol design

    And not to forget the bypass factor of the coil which can only be found by practical test.
    You need anyhow a special controller for this , an enthapy controller
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  11. #11
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    Re: close contol design

    With consideration the size of the containment: Is this a draw down scenario or a steady state type of operation? If draw down you will have to prioritize temperature, then humidity and depending on the weight and nature of the contained product, you may quickly find 20 ACH is not nearly enough. It might be for flowers or nuts, definitely won't be for green crops (lettuce, celery) or ginseng, depending on how things are packaged.

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