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  1. #1
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    Question Evaporator Selection


    Hello,

    I confuse with the calculation and selection for the blowers size. Some said refer to the coil surface, some said refer to the heat load (kW). Did that has a standard method? By the way, how select for the fin spacing?

    Thanks a lot

    chooipeng



  2. #2
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    Re: Evaporator Selection

    Are you confused with blower or Evaporator coil?

    Selection of fan blower depends on the following minimum data:

    > Total CFM/CMH of air to be delivered.
    > Total system pressure, which is the sum of system static pressure and velocity pressure in Pa.
    > Fan outlet velocity
    > Air/Gas Temperature/ density
    > Altitude

    pl note that fan size does not directly be evaluated from the TR loas of the system. For the same TR load the configuration of the fan may be different.

    Also note that term "TR" is not sufficient unless it is associated with Evaporating Temperature/Pressure in a refrigeration system.

  3. #3
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    Re: Evaporator Selection

    Quote Originally Posted by S.K.VARDE
    Are you confused with blower or Evaporator coil?

    Selection of fan blower depends on the following minimum data:

    > Total CFM/CMH of air to be delivered.
    > Total system pressure, which is the sum of system static pressure and velocity pressure in Pa.
    > Fan outlet velocity
    > Air/Gas Temperature/ density
    > Altitude

    pl note that fan size does not directly be evaluated from the TR loas of the system. For the same TR load the configuration of the fan may be different.

    Also note that term "TR" is not sufficient unless it is associated with Evaporating Temperature/Pressure in a refrigeration system.
    Quoting all.

  4. #4
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    Re: Evaporator Selection

    Quote Originally Posted by chooipeng
    By the way, how select for the fin spacing?
    The fin spacing selection is based on several factors:

    1. If the evaporator is used for an application that has evaporating temperatures below 32F (0C) the fin spacing may be selected for fewer fins. The wider fin spacing allows frost to build up on the fins without impeding airflow (blocking the air entering side of the coil, which will reduce the cooling capacity).
    2. Note: Some applications like blast freezing (very fast freezing rates) will accumulate a lot of frost on the evaporator fins. In these applications it is common to use a variable fin spacing. Typically the first two rows of tubes in the evaporator have wide fins spacing to collect frost and allow air flow for longer periods between defrost cycles. The remainder of the coil will have smaller fin spacing. The majority of the frost collection is on the first two rows of the coil (air entering side).
    3. For evaporators used with evaporating temperatures above 32F (0C), the fin spacing can be increased since no frost will form on the fins.
    4. Some evaporators operating with an evaporating temperature above 32F (0C) using more fins may require some type of air filtration device to prevent the dirt from collecting on the fins. (This would primarily be used for rooms where a high volume of dirt is possible.)
    5. If the evaporator is selected for smaller fin spacing (more fins on the coil), the overall heat transfer surface is increased, so the total capacity of the coil is slightly increased. Conversely, if the evaporator is selected for greater fin spacing (less fins on the coil), the heat transfer surface is decreased and the coil capacity is also decreased slightly.

  5. #5
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    Re: Evaporator Selection

    The evaporator coils for NH3 systems are usually selected on kW cooling load and temperature difference (or BTU per hour per degree TD).

    The temperature difference (TD) is based on the room temperature minus the evaporating temperature of the refrigerant in the coil.

    In effect, you are selecting the evaporator based on it's cooling capacity at a specific TD you will select.

    For a given coil capacity, a smaller TD will provide less capacity. A higher TD will provide more capacity for the same coil.

    The fan selections are done by the evaporator coil manufacturer. However, in some applications with high static pressure requirements you may have to increase the minimum coil capacity. The higher static pressure systems cause the fan air flow volume to be reduced (axial or propeller fans). The lower volume of air flow reduces the coil capacity.

    You should also be aware that some coil manufacturers list their coil capacity as only kW (or Tons). This usually indicates they have selected this rating on a specified TD of their choice. Be sure to check the small print in their catalogs.

    Does that help?
    Last edited by US Iceman; 12-07-2006 at 09:39 PM.

  6. #6
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    Re: Evaporator Selection

    Quote Originally Posted by chooipeng
    Hello,

    I confuse with the calculation and selection for the blowers size. Some said refer to the coil surface, some said refer to the heat load (kW). Did that has a standard method? By the way, how select for the fin spacing?

    Thanks a lot

    chooipeng
    Surface area and fin spacing is relative to the application

    High temperature units use smaler fin spacing

    Low temperature, especially Blast Freezing use more surface area for every kW compared to high temperature coils

    TD is usually a standard 8k in books, but normally good design dictates 6k

    DT accross the coil can also be important for some design requirements (humidity in high temperature)


    Hope this hepls.

    Kind Regards Andy
    If you can't fix it leave it that no one else will

  7. #7
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    Re: Evaporator Selection

    Chooiping, This may be of some use to you;


    http://www.cibse.org/pdfs/GPG280.pdf
    Last edited by wambat; 12-07-2006 at 11:46 PM.

  8. #8
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    Re: Evaporator Selection

    Hi wambat,

    Thanks for the posted link. In the PDF several other files are mentioned, but I could not find them on that website... Any ideas, or is this members only material?

    Thanks.

  9. #9
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    Re: Evaporator Selection

    Quote Originally Posted by US Iceman
    Hi wambat,

    Thanks for the posted link. In the PDF several other files are mentioned, but I could not find them on that website... Any ideas, or is this members only material?

    Thanks.
    Try this:http://www.cibse.org/pdfs/GPG280.pdf

  10. #10
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    Re: Evaporator Selection

    Hello, Thanks a lot. I need some time to look at the information and digest it.

    I work in refrigeration engineering dept. So, I learn to design, do calculation and select the suitable equipment for refrigeration system. Like cold room, ante room, blast freezer.....use for food product. Also, the piping system

    I'm engineering background (food and process engineering), but no fully know the whole refrigeration system as I study the basic in school. Any recomment for me to read? I found that too many information in www and hard for me to select the suitable sources.

    Thank you

  11. #11
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    Re: Evaporator Selection

    Hello,

    just wander which company u work with? since we are from same soil... i'm currently engage with few NH3 system providers, just wonder you are work with one of them... well i have the same problem with u too many resource on www, but here is definately great place to start with... cheers

  12. #12
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    Re: Evaporator Selection

    Hi chooipeng,

    Any recomment for me to read?
    Yes. Get some equipment literature from various manufacturers of different evaporators. They usually have some selection procedures you can use and follow.

    The same advice applies to condensers.

    For commercial refrigeration, you tend to find more information on selection procedures.

    For ammonia systems, not so much.

    Look in the Database section of the RE site. There you will find several recommendations for refrigeration books that can also help you.

  13. #13
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    Re: Evaporator Selection

    Dear US Iceman,

    Please visit the site www.actionenergy.org.uk which will automatically direct you to the new site carbontrust wherein you will have to register which will enable you to enter the download section. Select Refrigeration and you will find all the files therein.

    With best wishes and Happy reading,

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