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Evaporator Selection at 17F Design TD

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BigRob
BigRob Member Posts: 322
Ok. I'm trying to understand how to select an evaporator. The industry uses a 10F TD as the nominal rating condition for evaporator units I see. I would like to run 17F TD (for wine) with a 1800btu/hr wine room load at 38F SST, so the wine room ambient is 55F.

So, it would it be:

Effective 17F TD coil rating = (evap 10F rated TD/target 17F TD) * (10F TD coil rating).

So 0.588 * 1800btu/hr is 1059btu/hr. So I would select a 10F TD rated coil of capacity around 1058btu/hr to run with my 1800btu/hr, 38F SST @ 90F ambient condenser.

Does this sound right?

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,829
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    Most mechanical engineers don't even try to make the selection. Give the specs you want to hit to the equipment supplier and let them make the selection
  • BigRob
    BigRob Member Posts: 322
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    Thanks, but I am trying to learn this stuff, so I want to work through a design.
  • BigRob
    BigRob Member Posts: 322
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    The Heatcraft Engineering Manual number H-ENGM0408 states:

    "The unit cooler to be selected should have a minimum base capacity (BTU/deg T.D.) of 12696/10deg T.D. or 1270 BTU/deg T.D./hr. to be sure that the unit cooler is large enough to balance properly with the condensing unit.

    Low relative humidity requirements permit higher T.D. which in turn will allow selection of unit coolers with small base ratings (BTU/hr./deg T.D.)"

    I take this to mean you divide the calculated required box heat load by the required TD you need for the specific product, then multiply that result by the standard 10deg TD to select the correct evaporator size from a list of evaporators who's ratings are based on the 10deg convention.

    In my case, it would be 1800/17 = 106 btu/TD/hr

    106 btu/TD/hr * 10 TD = 1060 btu/hr

    So I need a 1060 btu/hr evaporator rated at 10F TD to run at 17F TD to balance my 1800 btu/hr condenser. I will set a pressure regulator on the suction line for 38F SST and have a TXV to manage the refrigerent volume to control super heat. I will use an ICM fan control on the condenser for winter months.

    Can anybody confirm my reasoning, above?

  • BigRob
    BigRob Member Posts: 322
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    bump
  • ChrisJ
    ChrisJ Member Posts: 15,913
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    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • ChrisJ
    ChrisJ Member Posts: 15,913
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    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • KC_Jones
    KC_Jones Member Posts: 5,749
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    @ChrisJ That's a side of things I do not get into. We have selection software and our engineers will make selections for customers as well. We are an industrial manufacturer, not sure what kind of support is offered by the residential/commercial side.

    I think on residential there are a lot more companies that are certified, on the industrial side it's only us, the rest "cheat" on the ratings. So I would suggest even calling the manufacturer (in some cases) can be risky on an Evaporator.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • ratio
    ratio Member Posts: 3,696
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    Hmmm. It's a little outside my experience, but if I were trying to size the evaporator, I'd match the capacity of the condenser & play with the airflow & refrigerant flow to get the sensible vs latent I wanted.

    My only experience with refrigeration is a few service calls and an old wine cooler we relocated. (I got it nearly working before they stopped paying for it—apparently they were trying to 'save money' on their 2 million dollar addition by reusing it. <sigh>)