selecction compressor

[luissandoval]

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
please help me!!!!!!

best regar

Luis Sandoval.

[NoNickName]

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.

[US Iceman]

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.

[luissandoval]

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.

[Vytux123]

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;

[US Iceman]

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?

[nh3 sweden]

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.