What would be the total KWH poeer of my ammonia compressors?

[Zainu]

Our IBT (like chilled water tank) has capacity of 1 lakh liters of water, the forward chilled water flow rate is 73000ltrs/ hr, the forward and return temperatures of chilled water are 2dc and 20dc, the load time can be considered as 24 hrs and all compressors are ammonia operated having superheated ammonia temperature of 80dc. The condensors are forced draft type and condensed ammonia temperature is 25dc. Then what would be the total KWH of my compressors?
Should we consider the capacity of water cooled condensors while calculating the power rate required for the above?

 

[georgeverghese]

When you take into account the change in Nre when switching to PPG/water at 20% wt, "heat transfer effectiveness" drops down to 80% of what it would be with plain water. So all chilled water consumers would need to have an inherent 20% excess surface area to make this change work.
The Cp value of 20%wt PPG/water also is less by 5%, which will require a 5% increase in pumping capacity to compensate, which will in turn mean a 10% increase in pumping dp.
It is nigh on impossible to get the exit water down to 1-2degC without changing to PPG/water, even with the new pumped circuit with compact plate HX installed. With the new pumped circuit and plate HX installed (without 20%PPG/water), suspect you wont get any better than 5degC for exit chilled water.
You have to drag in the engineering company who did the refrigeration system concept design and get them to make the necessary mods to enable chilled water at 1-2degC, if this is possible at all. Downright reckless mob. Clear cut case for industrial arbitration.
As others have pointed out, your HP stage compressors are not just running this chilled water circuit. Its also providing cooling for LP stage compression discharge vapor, gets subcooled and provides cooling for users at -40degC, -25degC etc

 

[georgeverghese]

To get down to -40degC with NH3 at the "Rollo machine", NH3 vaporisation pressure < 0.5bar abs. This must be the suction pressure at the LP stage compressors also. There is a risk of air ingress into the LP stage machines if the compressor shaft seals are not in good working condition. So too if pipe flanges and screwed fittings / valve packing on the entire 0.5bar abs side, including the Rollo machine.
If air does get in, it will blanket the HP stage condensor, making it difficult to achieve full condensation duty. Additional symptom of this non condensibles blanketing of the HP condensor will be an abnormally high discharge pressure on the HP compressor, which may back up as high pressure on the LP stage machines also. This may explain why you are getting good operation of the condensor in winter but not in summer. When was the last time your mechanical maintenance folks cleaned up the shaft seals on the LP stage compressor, and what about all the valves and pipe fittings and the Rollo machine floating on the LP compressor suction which may be pulling in ambient air? If I remember correctly, special packing is used in valves when in vacuum service.
Presume other machines operating at > -30degC wired up to LP stage compressors are fitted with backpressure valves (each with its own setting to suit the required consumer's control temp)downstream of each machine, so these wont see partial vacuum - details not shown on process sketch.

 

[MortenA]

@OP, i think the message is:You wont learn much by calculating the theoretical duty because the problem seems to be elsewhere. Currently two main theories has been posted By GerogeV:

1) Ice forms on your coils and lowers HTF
2) Air gets into the NH3 and reduces the efficiency of the system by introducing no condensable that accumulated in the condensor

So unless its for your own personal education in cooling systems it might be a good move to focus on these two issues and see if yu can find a way to verify/dismiss the scenarios.

For 1) You could inspect and see if there indeed is ice on the coils
For 2) GeorgeV has pointed some symtoms out for you.

Best regards, Morten

--- Best regards, Morten Andersen