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Thread: selecction compressor
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24-09-2008, 03:45 PM #1
selecction compressor
Hi everybody:
I have to select a compressor for a ammonia system, but i have a question what is the sucction temperature for the compressor if the evaporating temperature in the blast freezer is -42ºC. more characteristics are:
- Inside temperaure -35ºC
- Outside temperature +35ºC
- freezing time 10 h
- fish 12000 kg
- Load aproximate 138000 Kcal/h
best regar
Luis Sandoval.
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24-09-2008, 04:09 PM #2
Re: selecction compressor
It very much depends on the setup. I would tend to assume that the superheating is larger when the fresh food is loaded in the room, and suction temperature would progressively reduce as the temperature approaches the setpoint.
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24-09-2008, 07:09 PM #3
Re: selecction compressor
What type of evaporator are you using?
I hope it is not a DX coil at that evaporating temperature!
The superheat in the suction line of an ammonia system is usually minor if adequate insulation is used on the suction piping and vessels.If all else fails, ask for help.
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24-09-2008, 08:17 PM #4
Re: selecction compressor
i'm using pumpcirculated evaporator, what is the procedure for the correct selection of the compressor if i know the refrigeration load in the blast freezer.
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25-09-2008, 08:05 AM #5
Re: selecction compressor
If you have flooded system, you should calculate the pressure losts in suction line between compressor and recirculating receiver. Usually - normaly it is lower 0.6K. Then you get, that evap. temp. for compressor is -42.5ºC;
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25-09-2008, 03:04 PM #6
Re: selecction compressor
You need to determine the pressure loss in the suction line and discharge line. Then do this:
Evaporating pressure - suction line pressure loss = Suction pressure. now convert the suction pressure to temperature.
Now for the difficult part: you did not mention if this is a single stage compressor or a two-stage compressor, or of you are using a reciprocating compressor or a screw compressor.
What type of compressor do you want? And, what type of systems is it? single stage or two-stage?If all else fails, ask for help.
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25-09-2008, 07:36 PM #7
Re: selecction compressor
It sounds like you need a two-stage plant with pumpcirkulation. Reciprocating compressor is my favourite. Depending on if you are running 100% all the time or going down to 25% for longer periods. Other wise a screw compressor will do the jobb on the low stage with reciprocating compressor on the high stage.
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