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  1. #1
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    part load in evaporator and condenser



    Hello,
    Please help me, I am confusing about the part-load performance of water cooled chiller.
    My situation like this : screw chiller/ heat pump in reserve water cycle.
    1/ Cause the Dt syndrome, return chilled water temperature often lowered than designed set-point. So to maintaining fixed supply water set point without change the chilled water flow, we need reduce the evaporator load. What component will be responsible in this job ( we dont want change any thing in water side) ? and what affect working condition other (compressor, condenser, EEV...) ?
    2/ What problem in part-load conditions while need maintenance a fixed condenser pressure/temperature conditions (cause the ambient temperature) ?
    Thanks .



  2. #2
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    Re: part load in evaporator and condenser

    What?!

    For the little I understand:

    1) The evaporator load is reducing by lowering the differential, what you need is capacity control on the refrigeration side. New IN name: VRV.

    There are different components involved depending on the way you will try to achieve this. The least expensive is “hot gas bypass”.

    You can search many posts on capacity control and gas bypass using screw compressors in the “insustrial” forum here.

    2) If you do capacity control you may need to control the high side pressure but it depends on the TYPE of capacity control you choose. With hot gas bypass this is seldom necessary. This control does depend on ambient temperature among other things like size and type of condenser.

  3. #3
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    Re: part load in evaporator and condenser

    WTA, what type of compressor do you have? Scroll, srew, recip, centrifugal?
    What is operating mode? heating or cooling? And never change evaporator water flow. It must be like designed flow for your cooling capacity. Q = G x C x (Tin - Tout)

  4. #4
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    Re: part load in evaporator and condenser

    Quote Originally Posted by AlexG View Post
    WTA, what type of compressor do you have? Scroll, srew, recip, centrifugal?
    What is operating mode? heating or cooling? And never change evaporator water flow. It must be like designed flow for your cooling capacity. Q = G x C x (Tin - Tout)
    AlexG - thanks for your emails. It's screw compressor like CIAT LWP series with condenser leaving water temperature 50oc. Now, i find information about unloading procedure and their consequences inside the refrigerant cycle to optimizing the operation of chiller plant operation.

  5. #5
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    Re: part load in evaporator and condenser

    Quote Originally Posted by aramis View Post
    What?!

    For the little I understand:

    1) The evaporator load is reducing by lowering the differential, what you need is capacity control on the refrigeration side. New IN name: VRV.

    There are different components involved depending on the way you will try to achieve this. The least expensive is “hot gas bypass”.

    You can search many posts on capacity control and gas bypass using screw compressors in the “insustrial” forum here.

    2) If you do capacity control you may need to control the high side pressure but it depends on the TYPE of capacity control you choose. With hot gas bypass this is seldom necessary. This control does depend on ambient temperature among other things like size and type of condenser.
    we use slide valve with screw compressor. My case is 50/45 o C water leaving/entering chiller so i'm confusing about the unloading when still need keep the high condensing pressure.

  6. #6
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    Re: part load in evaporator and condenser

    Of course by unloading compressor you reduce heating capacity (if you work in heating mode) but more important to prevent evaporator freezing.

  7. #7
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    Re: part load in evaporator and condenser

    I still don't fully understand because you neither describe your system correctly nor the problem.

    One method to keep a minimum condensing pressure is a Head Pressure Control that lets you flood the condenser with refrigerant and simultaneously (if necessary) pressurize the liquid receiver. For this array to work you also need a correctly sized liquid receiver.

    You can get information on these types of valves from the manufacturers and lots of help from posts here.

  8. #8
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    Re: part load in evaporator and condenser

    Quote Originally Posted by aramis View Post
    I still don't fully understand because you neither describe your system correctly nor the problem.

    One method to keep a minimum condensing pressure is a Head Pressure Control that lets you flood the condenser with refrigerant and simultaneously (if necessary) pressurize the liquid receiver. For this array to work you also need a correctly sized liquid receiver.

    You can get information on these types of valves from the manufacturers and lots of help from posts here.
    My schematic in left of photo
    _revers_vody.jpg
    . We use for water cooled screw chiller with dry cooler. evaporator water in/out 12/07oC, condenser water in/out 45/50oC. in cooling mode we use chilled water from evaporator (keep the leaving evaporator water temperature), condenser connect to dry cooler. In heating mode, use water from condenser and evaporator connect to dry cooler (keep the leaving condenser water temperature).
    My situation like this the entering evaporator water temperature often lower than designed at part load. So i want unloading (reducing capacity) chiller but the ambient temperature still high so the condensing pressure/temperature need be keep high enough. So how to unloading chiller in this case with the refrigerant cycle control ?
    Thanks

  9. #9
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    Re: part load in evaporator and condenser

    Still dont understend the situation. If u in heating mode, outside tempetature is high (T=?), u use drycooler to reject "cool", why inlet evaporator T goes down? Just turn on all fans of drycooler.
    good luck

  10. #10
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    Re: part load in evaporator and condenser

    That situation in cooling mode when outside temprature is high (T = 38oC so leaving condenser water temperature = 50).
    inlet evaporator T goes down cause we use d three way valve at coil and distribution chilled water.

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