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We have a cascade system with a 15 hp low stage compressor and a 30 hp high stage compressor. Is there an easy way to figure the tons of refrigeration this system is putting out? The high stage has a tower water cooled condenser. Low stage is 508B and high stage is 22.
Hi Hank,
It depend on evaporating and condensing temp of the compressor.
Wouldn't it be easy to to look in the compressor manufacturer catalogue and choos it from there?
Chemi :)
Actually we were wondering what affect the cascade aspect has on the tonage rating? An older similar unit at this site has 4 30 hp compressors, and another has 2 50hp compressors, while our cascade systems do the same with a 15hp and a 30 hp, it appears that the cascade exponentially increases the capacity. It is hard to grasp how this can be possible, but it is, it works.
Our evap temp is -80C and our cond. temp is -10C for the low stage and the high stage is -10C for evap and +20 to +35C condensing temp.
I do not know of any way to convert input power (HP) into tons of capacity. There are too many variables, such as evaporating temps, condensing temps, stages of economizing, type of refrigerant used and so on.
Like suggested above, use the compressor manufacturers data and your actual operating conditions.
The 30 HP compressors may not be drawing 30 HP, but may actually be drawing 23 or 24 HP. The 50 HP compressors may be drawing 45 HP. So you can not compare motor size to get an accurate comparison.
Ken
can i use r134 compressor in r12 system ?
Well if the Condensing for the low temp cmp is the same as the evap for the high stage, its not cascading; or it has an infinitely large interstage heat exchanger.
Nominally: in the absence of closed cycle injection or other enhancers to the low side circuit or direct heat rejection from the low stage compressor, the heat absorbed (the refrigeration effect) plus the heat input of the low stage compressor (thermal equivalent of the BHP draw, not the nameplate HP) will represent the high stage load. Identify the numbers for the High Stage compressor at the specific evaporating and condensing temperature; measure the current input to the Low Stage compressor; deduct one from the other and you should end up with the low stage capacity.
Measure the process flow and temperature change. If you can find the specific heat of the process fluid it's easy to calculate the refrigeration effect (capacity). Measure the motor amps to calculate the power input. Divide one by the other & you have COP
Dear all the formula is
1.34hp = 3412 Btu/hr
with regards:
Hank,
Glad to see that you are still around. Some time ago you had issues with oil return in a R-508B system but you never let us know if you solved it and if so how. Please let us know.