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simplygold
16-03-2014, 12:58 PM
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 + 0.000152x2
For "water" condensation at, say, 106oF:
HP/TR = 1.6952 - 0.02657x + 0.0001373x2
where x : evaporation temperature, oF.

Can someone please tell me where all of those numbers came from? Thanks in advance.

TF12
16-03-2014, 03:56 PM
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

RANGER1
16-03-2014, 09:11 PM
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 + 0.000152x2
For "water" condensation at, say, 106oF:
HP/TR = 1.6952 - 0.02657x + 0.0001373x2
where x : evaporation temperature, oF.

Can someone please tell me where all of those numbers came from? Thanks in advance.

Simply gold can you tell me what compressors you have (model number)on low & high side anyway.
Also what is maximum amount of machines run & % loaded on each stage.
Are they on liquid injection or what type of oil cooling

simplygold
17-03-2014, 11:10 AM
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?

simplygold
17-03-2014, 11:10 AM
All of the compressors have thermosyphon oil cooling.

Josip
17-03-2014, 08:16 PM
Hi, simplygold :)


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?

4500 TR only ... all boosters i.e. 3222TR + 1278TR

seems a good designed plant ... you have quite good condensing pressure ...

Best regards, Josip :)

RANGER1
17-03-2014, 09:02 PM
All of the compressors have thermosyphon oil cooling.

Simplygold, can you give us a hint on type of compressors.Fuller rotaries, Dunham Bush screws or other???

simplygold
17-03-2014, 09:14 PM
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.

RANGER1
18-03-2014, 10:03 AM
Simplygold, can you give us a hint on type of compressors.Fuller rotaries, Dunham Bush screws or other???

If you PM me or post here I could give you pretty accurate capacities.
if you are interested I would need model number plus duty, booster or high side etc.
example Mycom 250LUD-L or 250VLD
Howden as well example WRV25516526