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Lambo
19-05-2015, 08:50 PM
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.

RANGER1
19-05-2015, 09:02 PM
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.

I think it can & has been done.
Possibly it saves very little money with electricity bill & costs more to install as well as program.
Also what happens if/when it does cavitate, does it speed up to try & achieve pressure.

Lambo
19-05-2015, 09:16 PM
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.

HVACRsaurus
20-05-2015, 11:06 AM
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..

Sandro Baptista
20-05-2015, 11:12 AM
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.

sandybapat
25-05-2015, 05:58 AM
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.

Sandro Baptista
25-05-2015, 12:42 PM
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.

Despite non significant advantageous on my point of view the VSD is still possible however the speed shall be limited by the VSD to ensure Qmin and an Qmin orifice shall always be used in combination with the VSD system.

sandybapat
26-05-2015, 08:32 AM
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.