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  1. #1
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    Standstiil unit cooler



    Hi folks,

    I am designing a cascade R134a/R744 system.
    R744 sideX system, working pressures -35C (evaporation) and -5C (condensation), The PS are 40barg and 27.5 barg for the high and low side respectively.
    The compressor has a standstill allowable pressure of 30barg and moves a mass flow of 360 kg/h.
    I want to install a condensing unit R404a for standstill to reduce pressure from -5C in liquid receiverf to say -15C (27.5 barg x 0.8 = 22barg @ -15C).
    The liquid receiver, located in the engine room, has a volume of 45 liters and Armaflex insulation 50mm.
    How to calculate the unit?

    thanks a lot.



  2. #2
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    Re: Standstiil unit cooler

    Dear Joslaz, you have to calculate the surface of the vessel, know the k-value of your insulation and dt. difference between the engine room (ambient temp.) and you calculated vessel temperatur.

    Q=A*k*dt

  3. #3
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    Re: Standstiil unit cooler

    Hi ATH,

    Vertical liquid receiver: 323 x 698 mm, Asurf=0,87m2
    Isolation: k=0,034 W/mk, so U=0,034/0,050=0,68 W/m2k
    Max. machine room temperature = 35C (supposed)
    Receiver temp, at standstill = -15C
    Q = UAdT = 0,68 x 0,87 x (35-(-15)) = 29,58W???

    What i do with this?

    Thanks.

  4. #4
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    Re: Standstiil unit cooler

    Hi Joslaz, with this small capacities I do not have any ideas to give you, unless you have an other unit in the engine room where you can connect it upto.

  5. #5
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    Re: Standstiil unit cooler

    Hi Joslaz, install the vessel in a home freezer.

  6. #6
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    Re: Standstiil unit cooler

    Hi ATH,

    This is not a typical solution. What about if receiver is quite bug and there is not a cold room?

  7. #7
    dblissett's Avatar
    dblissett Guest

    Re: Standstiil unit cooler

    Hi Guys,

    I have two questions;

    Does the R744 vessel isolate from the system during off cycle?

    What is the total system capacity?

    Also, when you are sizing a system it is prudent to build in some redundancy, perhaps allow for a 60% on cycle of your R404a system.

    Thanks.

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