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19-05-2015, 08:50 PM #1
Ammonia pump system and frequency regulator
Hi everyone,
I have simple question. Why frequency regulator for ammonia pump is not used? We are using solution for pressure regulation (for example Danfoss OFV or ICS (CVPP)) but not frequency regulator. I can't see how this will produce cavitation so I don't understand why this is not widely in use for new system's. I saw that in CO2 system this solution is applied to pumps.
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19-05-2015, 09:02 PM #2
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19-05-2015, 09:16 PM #3
Re: Ammonia pump system and frequency regulator
If it cavitate, You are right, regulator will try to speed it up if pressure switch isn't installed. Maybe the answer is in installation cost/benefit relation.
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20-05-2015, 11:06 AM #4
Re: Ammonia pump system and frequency regulator
So, the refrigeration plant uses 1000+ Amps, the liquid pump uses 6 Amps - the cost of the VSD would hardly be recovered in its lifetime..
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20-05-2015, 11:12 AM #5
Re: Ammonia pump system and frequency regulator
You always can limit the speed as the maximum speed (50 Hz example) so the cavitation danger will be the same as no use the VSD.
The pump power absorbed for each kW refrigerant is also very small for ammonia and maybe almost no one wants to improve a proven system that works well at many many years.
However carefull we must have since de liquid head (H) decrease a lot with the the decrease of the speed (square dependency). As will be a minimum pressure required defined by the pressure loss and manual flow regulating valve of the aircooler the operating point will be shifted to the left of the Q-H pump curve as the speed reduces so my opinion is that an automatic bypass valve or a Qmin orifice will be always needed to prevent the damage of the pump.To make progress is never good enough, I want to do better and better and better
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25-05-2015, 05:58 AM #6
Re: Ammonia pump system and frequency regulator
Since pressure is important for pump feed to multiple evaporators, speed control will not help here as Sandro said. The over low is always controlled by the orfices provided. I think there is no advantage from performance point of view by using variable speed drive for Ammonia pump.
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25-05-2015, 12:42 PM #7
Re: Ammonia pump system and frequency regulator
To make progress is never good enough, I want to do better and better and better
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26-05-2015, 08:32 AM #8
Re: Ammonia pump system and frequency regulator
Of course, possibility of using VSD is not at all denied. One more point needs to be considered -
All the metering valves are set considering certain upstream pressure. with speed reduction if the differential head is reduced the metering valves need to be adjusted accordingly. Else automatic control valve which will sense upstream pressure and control the flow accordingly.