Liquid Pumps High Delivery Pressure

[Superfridge]

Hi all,

Can high pumped liquid pressure have a detrimental effect on coil performance and if so how?

At what differental pressure is pumped liquid too high? I find it varies so much from site to site i'm guessing that all cannot be ideal?

Cheers

[RANGER1]

Hi all,

Can high pumped liquid pressure have a detrimental effect on coil performance and if so how?

At what differental pressure is pumped liquid too high? I find it varies so much from site to site i'm guessing that all cannot be ideal?

Cheers

Superfridge, each plant is different because liquid pumps are selected to suit each plant.
Pump Head you will notice on pump nameplates is different at each plant.
Metres of head changes pump pressures as required on different plants so pump works in it's design curve, so to avoid cavitation & can overcome pipework lift & pressure drops of valves/pipework.

Pressure may be high at pump, but a lot less when at higher level like in roof space.
It could effect plant performance if to high as some units may have to much liquid flowing through hand expansion with no pressure drop across HEV causing brining, see links.
https://www.globalpumps.com.au/head
https://www.parker.com/literature/Refrigerating%20Specialties%20Division/HRP%20Manual.pdf see page 9
http://www.nhtres.com/Mechanically-Pumped-Liquid_Overfeed-Evaporators.pdf

http://www.nhtres.com/download.shtml

[mbc]

Hi
As you know
with too much head pressure on liquid pump
we have to close inlet REG valve to evaporator and adjust it (1/3 of evaporator coil should be fill with Ref.)
Becouse we have changing phase from liquid to gas in there and boiling refregirant in evaporator
if we charge too liqild with high pressure . our eparatores pressure rise up and boiling pressure rise up and temperature of evaporator goes up and our efficency (delta T) comes down .
also our suction valves and contro valves ( PM ) can not operate corectly

[Segei]

Maximum heat transfer for ammonia bottom feed overfed coil can be achieve when overfeeding is 3-4:1. To provide this feeding hand expansion valve should be adjusted properly. Typically, coil manufacturer can give the pressure difference between liquid after HEV and suction pressure. Usually, it is 5-7 psig.

[Superfridge]

Ok, it would appear that more liquid is often less duty.

Thanks RANGER1, great links, will take a bit of time to get through, still got a bit to learn eh.
mcb, 1/3 of coil filled with refrigerant, whats the rest filled with? liquid and vapour mix? Suction PM valves cannot deal with too much liquid?
Segei, this 3-4:1 ratio is invisable to the service engineer, how do you know the state of the refrigerant leaving the coil? Only by manufacturer data? Do bottom feed coils have orrifices?

How do you folks set up HEV? I have always used temperature difference between air on and air off, never had coil data at my fingertips. With liquid pump pressure fluctuations due to load changes are we looking for a happy medium?

[mbc]

Hi
In All wet evaporator we have mix liquid and vapor and refrigerant is boiling . on bottom more liquid and at top more vapor and if can not adjust it well some time returning liquid to separator .

[RANGER1]

Ok, it would appear that more liquid is often less duty.

Thanks RANGER1, great links, will take a bit of time to get through, still got a bit to learn eh.
mcb, 1/3 of coil filled with refrigerant, whats the rest filled with? liquid and vapour mix? Suction PM valves cannot deal with too much liquid?
Segei, this 3-4:1 ratio is invisable to the service engineer, how do you know the state of the refrigerant leaving the coil? Only by manufacturer data? Do bottom feed coils have orrifices?

How do you folks set up HEV? I have always used temperature difference between air on and air off, never had coil data at my fingertips. With liquid pump pressure fluctuations due to load changes are we looking for a happy medium?


Air on/off is most common, but can take time.
In links I think it also mentions frosting on return bends with fan off.
On a new job if you have coil design data, depending on brand of valve, a pretty close setting can be achieved.
Last year I was involved with blast chiller with 8 Danfoss HEV to set, looked up Danfoss Coolware 2, told me 7 turns open on each valve for evaporator kw, valve size & pump pressure, see you later. To find 7 turns opens could have taken a few days to work out otherwise.
As far as excess pump pressure as MBC indicates on back pressure valve, can force open as evaporator pressure/pump pressure higher than setting.
You mention pump pressure changes due to load changes, is a little unusual unless pump is oversized & bypass line back to accumulator is just a valve cracked open.
Obviously best to set up under full load first if possible.
Normally pump pressure follows suction pressure.
Some have differential pressure regulator on bypass to cover that situation.

It makes me wonder why gauge access point not installed before/after HEV to set pressure drop , as Segei suggests, $$$ I guess!

https://www.irc.wisc.edu/export.php?ID=279

[mbc]

Hi
this file might help

[mbc]

Hi
I have one pdf file.
it is about 800 k and I could not uploaded to here
(Mechanically-Pumped-Liquid_Overfeed-Evaporators .pdf )
it is good to see drawing of pipes for pumps
send you mail I will mail it to you.

[Segei]

Bottom feed overfed coil. Liquid goes through HEV than goes to the header and each circuit fed through small orifices. Pressure between HEV and orifices is feeding pressure usually 5-8 psig above suction pressure. During defrosting defrost BPR release pressure from the header. It means during cooling mode BPR gauge shows liquid feeding pressure. Usually, I look at this pressure when adjust liquid supply to the coil.

[Superfridge]

Got those files mbc thank you, haven't had a chance to read it all yet.
Segei, at the pressures i'm working at there is about 3degC over 5psi difference therfore I sould see this pressure drop using a contact thermometer. I'll check it out next time on site, worth a crack.
The system i am concerned about has about 5-6 bar pumped liquid difference at the coil depending on load. Ranger1, I will check the bypass/minimum flow line too thanks.

[mbc]

hi
where do you live in Auckland?

[RANGER1]

Got those files mbc thank you, haven't had a chance to read it all yet.
Segei, at the pressures i'm working at there is about 3degC over 5psi difference therfore I sould see this pressure drop using a contact thermometer. I'll check it out next time on site, worth a crack.
The system i am concerned about has about 5-6 bar pumped liquid difference at the coil depending on load. Ranger1, I will check the bypass/minimum flow line too thanks.

Also can you advise of type of pump & details on nameplate, assume ammonia.
6 bar seems very high, is that above suction pressure?
Do transducers/gauges read correctly?

[mbc]

hi Ranger
it should not be above suction pressure
I think(from my memory) maximum head of NH3 pump is 5 bar
Normally it is 2 up 3.5 bars
minimum about 1 bar
all of them above suction pressure

[Superfridge]

Yes above suction, all pressures checked with a service gauge.
I wont be back to this site for a few weeks. Thanks for all the input.

[mbc]

Hi
these files for head of NH3 pump

[Superfridge]

Hi all, finally got back to site for a short time to confirm some details.

Ammonia, Suction pressure in the pot is 160kPa, pumped liquid pressure at the evaporators is 550 to 650 kPa variable with rooms on/off. The pumping head is about 12 meters. The Q min valves are open. The pump is a Hermetic CAM 3/3, Q(m3/h)=16.3, Density=655.00, H(m)=81.0.

The coil frost patton was poor, I closed down the HEV and opened 1/2 turn, the coils came to life. TD better, room temperature started to come down, all return end bends nicely frosted.


I did take photos just got to figure out how to get them on here.

Cheers

[Brian_UK]

Sounds good, thanks for the update.