VSD Pump control

[Harper]

Hey everyone!

Are there any recommentations about variable speed drive pumps in condenser or evaporater circle?

Once we installt a NH3 chillerpackage with an vsd evaporater pump. The speed regulation depands on the temperature difference between evaporater glycol in- and outlet. This system runs perfect without any troubles and is high efficency espacially in part loud times.

Has anyone experiences with vsd pumps and would it also be possible in dx systems?

Have a good time!

[RANGER1]

Harper,
Do you mean something like this, or something else?

http://m.hysave.com/liquid-pressure-amplification-refrigeration-energy-savings/

[Harper]

Hi Ranger1,
if never seen or heard about an "Liquid Pressure Amplification", is it the same as an refrigeration pump? I have to search more about this - thanks for your link.

But actually im searching for variable speed drive evaporater pumps (glycol or water) used with chiller and how to regulate them? Because I think in DX systems it is a great challenge to regulate the water volume and have at the same time a stable superheat.

[seanf]

Would you not leave the DX chiller to do its own thing, regulating itself to the load the chiller sees.
Then run the VSD pump on its own control, regulating itself to the load the pump sees.

[RANGER1]

Lots of possible set ups.

What type of TX or EEV would you use.
Also would you use HB products?

[Harper]

Most of the chiller i know have a carel or danfoss eev. This type of valve works properly, but what would be if you regulate the water flow?
@ seanf: When you mean the pump regulate itself - do you mean pressure control?

[seanf]

@ seanf: When you mean the pump regulate itself - do you mean pressure control?

Guess you need to consider what the water/glycol/brine is being used for. But yer it could be pressure. It could be that you look at what loads are on the chilled water circuit, and when flow is switched off to a room/bit of equipment/ect.. you reduce the pump speed to suit the actual circuit volume flow requirement. Probably eaiser/cheaper to regulate it on one parameter.


Most of the chiller i know have a carel or danfoss eev. This type of valve works properly, but what would be if you regulate the water flow?

Would it not be like reducing the load on the chiller/getting close to set point. If the chiller has capacity control, it would ramp down. Would need to consider your set point and what fluid your chilling incase of freezing it up. Also consider how an increase in cooling demand is recognised, if the flow has been reduced, will it ramp back up in time to deal with a room/bit of equipment warming up.

[RANGER1]

Larger systems can have 2 &/or 3 way valves, buffer tanks with hot/cold side to smooth things out.

If DX imagine slow changes to be able to adjust pump speeds, in some cases Back pressure or crankcase pressure regulators on suction to avoid freezing when compressor changes capacity.

VSD pump not always necassary.

[Harper]

Thank you guys for the helpful answers!

I know that a VSD pump is not always necassary, but it´s always interesting. Grundfos says there is a current reduction up to 65% possible by using VSD.

So, I will hang on.

[RANGER1]

Harper, do they suggest a certain Hz, do they have a curve to match for maximum efficiency.
Sometimes all sounds good until VSD drive dies, new pump twice price as standard.
Have to take all into consideration sometimes.
Pool pump standard $500, VSD $2000, maybe 10 year payback, sometimes 2 years.

[Harper]

...Sorry I was wrong about grundfos, here is the correct statement:

For example, if the flow is reduced by 20 %, the motor’s power consumption falls to 65 % compared to the original consumption.

https://www.grundfos.com/ch/fr/learn/research-and-insights/speed-controlled-operation

[RANGER1]

Harper,
Yes true for compressors, pumps, fans etc.
If at full speed all the time, less efficient due to losses.
Some glycol systems operate on differential pressure, say closed loop glycol system.
My point sort of is reliability of the VSD.
You pay a lot more, if it fails & not under warranty, was there any savings?
Bigger equipment, bigger saving, also huge replacement cost, if it is even available, or not outdated.
Sorry, I’m sceptical on some of this stuff.

[MrFreez717]

Yes true for compressors, pumps, fans etc.

Not true for compressors.

Centrifugal pumps and fans, yes.

Gear drive pumps, no.

For centrifugal pumps, flow varies linearly with pump speed. Pressure varies by the inverse square of the speed ratio (1/2 speed will yield 1/4 the original pressure). Power varies with the inverse cube of the speed ratio. So at half speed, your pump will (theoretically) use 1/8 as much power as it would at full speed.

Obviously there is tremendous potential for energy savings because of this, but there are 2 challenges to overcome: 1) significantly reduced pump pressure at lower speeds, which moves you to a different and possibly less efficient point on the pump curve. And 2) changing flow rate changes work done by the chiller, and it can be challenging for expansion valves to adapt and still maintain steady superheat. Electronic valves are your best bet if you try this. You would certainly want to consider appropriate protection against freeze-up as well.

With most fans, VFDs are close to a no-brainer. For pumps, it is not nearly as easy to determine if a VFD is a good idea.

In my part of the US, most power providers will provide incentives for installations of VFDs, particularly on fan motors.

Best regards,
MrFreez717

[RANGER1]

Not true for compressors.

Centrifugal pumps and fans, yes.

Gear drive pumps, no.

For centrifugal pumps, flow varies linearly with pump speed. Pressure varies by the inverse square of the speed ratio (1/2 speed will yield 1/4 the original pressure). Power varies with the inverse cube of the speed ratio. So at half speed, your pump will (theoretically) use 1/8 as much power as it would at full speed.

Obviously there is tremendous potential for energy savings because of this, but there are 2 challenges to overcome: 1) significantly reduced pump pressure at lower speeds, which moves you to a different and possibly less efficient point on the pump curve. And 2) changing flow rate changes work done by the chiller, and it can be challenging for expansion valves to adapt and still maintain steady superheat. Electronic valves are your best bet if you try this. You would certainly want to consider appropriate protection against freeze-up as well.

With most fans, VFDs are close to a no-brainer. For pumps, it is not nearly as easy to determine if a VFD is a good idea.

In my part of the US, most power providers will provide incentives for installations of VFDs, particularly on fan motors.

Best regards,
MrFreez717

MrFreeze717,
I ould have thought compressor on VSD would give power savings if slide valve at 100 & ramps up/down to suit load.
In Australia we have 50 Hz & w was under the impression 45 Hz was a magic number for maximum efficiency of VSD & motor.
USA would be different, but same idea.
Like running 60 Hz on a 50 Hz power supply not that efficient.
Correct me if I’m wrong.

Thanks

https://www.aceee.org/files/proceedings/1995/data/papers/SS95_Panel2_Paper26.pdf

Off track but good paper

https://www.ampc.com.au/getmedia/80d38c43-41d9-47f6-a6fe-b061f2ee7b40/GUIDEBOOK_Industrial_Ammonia_Systems_Part_4.pdf?ext=.pdf