sizing of low temp refrigeration cabinets

[DALO]

Can anyone out there give me a clear definite answer on sizing of refrigeration cabinets/coolrooms without relying on the manufacturer/ software.
Im looking for a rule of thumb calc. As i understand it the 1HP to 1 Tonne rule decreases rapidly to around 2kw at -10 and 500w at -40 approxiamately depending on refrigerant used.
Also what load should we allow for cabinet dimensions. One guy i worked with told me 70w/m3 with 4 inch walls.

[Peter_1]

There's no clear definite answer if you're looking for a rule of thumb.
Then the software is much more accurate.
Heatload or a rule has nothing to see with the refrigerant used. (500W = 500 W whatever gas you may use)
What load should you use regardig the room size: it all depends on what you want to store in it, how fast it must be cooled, temperature...

We once installed a freezer of 60 x 60 x 30 ft and they store it with vegetables just at 3 ft from the ceiling an 1 ft from the walls. The compressors are running from Friday evening till Monday morning. So, this is an extreme situation where rules of thumb doesn't work any longer. A precise calculation has then to be made.

In my opinion, rules of thumb are only valid for rooms where small hermetic compressors are used.
And even then...

[DALO]

Peter i grasp what your saying about the 500w is 500w etc but surely you wouldnt use a r134 application for any lower than -20. A few years ago i had numerous problems with a little -20 and it was running on 134. The customer and my boss swore blind it had worked from day one but i couldnt get it lower than -17. After installing a new drop in at 404A we never had a problem.
Guess what Heatcraft asked me the cabinet dimensions and that was it. It wasnt very technical investigation on their part!!!!!!

[rpbuenaflor]

Hi Dalo, I was with you, using a rule of thumb very proven when I am in the middle east. Try these; 160 BTU/Ft3
1 Ft3 = 160 BTU
Aplicable for refrigerators and freezers.

rudi

[US Iceman]

In my opinion, rules of thumb are only valid for rooms where small hermetic compressors are used. And even then...

I completely agree with Peters comment.

Rules of thumb are only valid when the exact same conditions apply to the new system. The rules of thumb are based on specific application parameters. When one of these parameters is changed, the rule of thumb is no longer of valid use.

A rule of thumb can be sufficient to hold a conversation, but should never be used for design purposes.

This is the same thing as guessing, if you do not know or understand what the rule of thumb was based on.