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16-03-2014, 12:58 PM #1
How to calculate total cooling capacity of the whole plant?
I work in a large industrial refrigeration plant. We have a 125,000 lb ammonia charge here, it is a two stage system that operates a suction of 5" hg, an intermediate of 38 psig, and an average condensing pressure of 135 psig. The plant was built sometime in the sixties and has been added on to and taken away from over the years. There is very little in the way of OEM literature on the really old stuff but on most of the things acquired in the last 20 yrs there has been good record keeping. What I am trying to say is that it isn't possible to calculate cooling capacity from equipment manuals alone.
I do however know the horsepower of each compressor and the total horsepower in the engine room is 8700 hp. I understand that this along with the operating pressures in the plant can be put into a formula that will give me the tons of refrigeration per HP.
I came across the following diagram online during my search:
ROT for ammonia refrigeration that I found in the literature:
For "air" condensation at about 120oF:HP/TR = 2.1444 - 0.02668x + 0.000152x2For "water" condensation at, say, 106oF:HP/TR = 1.6952 - 0.02657x + 0.0001373x2where x : evaporation temperature, oF.
Can someone please tell me where all of those numbers came from? Thanks in advance.
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16-03-2014, 03:56 PM #2
Re: How to calculate total cooling capacity of the whole plant?
There are some items you can gather and then plot on a diagram to determine the capacity of your two stage system. First is subcooling, if you have an intercooler the refrigerant is being sub cooled by latent heat transfer from an internal liquid ammonia heat exchanger or maybe a flash type intercooler you will have a significant amount of subcooling that will reduce the flash gas that is entering your low pressure vessel. This is important as it will change the latent heat of boiling and add to your refrigeration effect. The next item is going to be the suction superheat to your booster compressor. The superheat is important because it will ADD to the latent heat of boiling and reduce the refrigerating effect, also be sure to calculate the pressure drop between your low stage evaporator/surge drum as this will add to the superheat reading.
Next item is total heat of compression for your booster, total discharge superheat, theoretical discharge temperature/actual temperature. This will let you know how many BTU/H are being removed by your oil cooler. The booster discharges it's gas into the intercooler. Determine pressure and temperature of the high stage compressor suction. Heat of compression for the high stage compressor, total discharge superheat, theoretical discharge temperature/actual temperature.
At this point you can determine total heat rejected by the condenser. The evaporative condenser should have a condenser drain temperature at or very close to saturation.
All this data can be plotted on a mollier diagram to determine the refrigeration effect of one lb of R-717.
BHP= volt x amps x power factor x motor efficiency x 1.73 / 746
KWH= volts x amps x power factor x 1.73 / 1000
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16-03-2014, 09:11 PM #3
Re: How to calculate total cooling capacity of the whole plant?
Last edited by RANGER1; 16-03-2014 at 09:30 PM.
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17-03-2014, 11:10 AM #4
Re: How to calculate total cooling capacity of the whole plant?
Ok I have got ton rating off of the compressors.
Boosters- 3222
High Stage- 4500
These are the tonnage ratings from the manufacturer, does this mean that at peak performance and design pressure the plant is capable of 7722 tons of refrigeration?
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17-03-2014, 11:10 AM #5
Re: How to calculate total cooling capacity of the whole plant?
All of the compressors have thermosyphon oil cooling.
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17-03-2014, 08:16 PM #6
Re: How to calculate total cooling capacity of the whole plant?
It's impossible to make anything foolproof because fools are so ingenious...
Don't ever underestimate the power of stupid people when they are in large groups.
Please, don't teach me how to be stupid....
No job is as important as to jeopardize the safety of you or those that you work with.
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17-03-2014, 09:02 PM #7
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17-03-2014, 09:14 PM #8
Re: How to calculate total cooling capacity of the whole plant?
A mix and match of different ones most of them being Mycom of which there are 14, three Howdens, and one D and B. All screws.
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18-03-2014, 10:03 AM #9
Re: How to calculate total cooling capacity of the whole plant?