Screw compressors for this freezer application?

[georgedvf]

Hello everybody!

I have two identical very large freezer rooms (6,600m3) at -20ºC, the heat load is very variable due to product load, I will use a Parallel Compressors Rack but here I get two different opinions from the fellows:

1. To use Screw compressors since there's a very large heat load and just two rooms, there will be like (2) compressors.

2.To use Reciprocant compressors because the heat load is very variable and compressors will have to work at partial loads, so Screw compressors are not efficient at partial loads, in this case I will have to use (5) compressors.

What would you recommend????

Thanks!

[NoNickName]

5 reciprocating is better than 2 screws in cases of high load variability.

[georgedvf]

Thanks for the reply NoNickName.

Is this because of the low efficiency of screw on partial load???

Do you have some grafics or tables where this is indicated?

[NoNickName]

No, it's just that more compressors give better split capacity. Screw compressors are not that bad at part load, afterall. But surely 1/5 at full compressor load is better than 1/2 at part load.

[charlie n]

Two screws for two large rooms is not a good selection. It might look cheaper but the extra energy cost will pass the 4 or 5 compressor option in a very few years. You will also have no standby during service or i you have a problem with one machine. 4 economized screws would be a more efficient option than 2 and almost as efficient as the reciprocating option. If ammonia (I don't know why anybody would use anything else) The recips. would be two stage. These are not terrible but 4 screws would be a little less complex and probably give a lower maintenance cost.