Optimal IP

[RANGER1]

Does the site manual explain function of valves , or just settings .
Sometimes someone has a bright idea in design but no one can understand it without explanation .
Where was system designed , NZ ?

[Superfridge]

For me, it is not clear about BPV and BPRV. At slide valve position below 75% , port will be connected to the suction and efficiency will be lost. Unless, other compressors can handle IP load, the gas at IP pressure will go to the suction(again) through BPV.
What are you going to achieve? Do you have solenoids and hand expansion valves for LP and IP receivers?

I need to re-read my post before posting
I missed the R out of the BPV. I will ammend that too.
Yes, hand expansion + soleniod valves for both receivers and you are right, at less than 75% the econ flash gas goes to suction.

Does the site manual explain function of valves , or just settings .
Sometimes someone has a bright idea in design but no one can understand it without explanation .
Where was system designed , NZ ?

The site manual states the BPRV between economiser and suction is there to provide a pressure difference at all times ie: when low load and compressor unloads and economiser to compressor BPRV is de-energised. The only settings in the manual is this 190kpa economiser pressure. I think the econ to suction BPRV was put in later as it's not on the drawings.
It's a NZ company installation but the design?

[Segei]

Pressure regulator can be wide open manually. Your minimum IP pressure is 200 kpa. If solenoid to IP vessel open, high pressure liquid will go to IP vessel and a lot of flash gas will be produced. This flash gas is the load to the port. Pressure in the port will increased to (assume) 400 kpa or to the pressure when bypass PR will open. Some plants have BPR to keep certain pressure in IP vessel, because this is requirement for additional refrigeration load. Dock cooling can be connected to IP vessel and pressure in IP should be 300 kpa. Lowering set point of BPR slightly increase capacity of the plant, but it will not improve efficiency. What are you going to achieve by lowering BPR setting?
You mentioned about design pressures. Do you operate plant at 1065 kpa condensing pressure?

[Superfridge]

Thanks for your replies and interest

What are you going to achieve by lowering BPR setting?

Thats the reason for the post, i'm not sure. Less LP flash gas but will the associated valves work with roughly 90kpa deltaP? I will have to check supplier.

As stated above, the manual lists LP=100kpa, IP=190kpa and HP=1065kpa but I think the IP is too low. I have set the IP to comp BPRV to 390kpa and should the comp go below 75%, the IP to comp BPRV de-energises and the IP to LP BPRV will then keep IP to 420kpa (this valve has no soleniod control so that is why it is set higher) and will see how the plant runs.

You mentioned about design pressures. Do you operate plant at 1065 kpa condensing pressure?

Plant keeps to above conditions well.

[Segei]

Thanks for your replies and interest



Thats the reason for the post, i'm not sure. Less LP flash gas but will the associated valves work with roughly 90kpa deltaP? I will have to check supplier.

As stated above, the manual lists LP=100kpa, IP=190kpa and HP=1065kpa but I think the IP is too low. I have set the IP to comp BPRV to 390kpa and should the comp go below 75%, the IP to comp BPRV de-energises and the IP to LP BPRV will then keep IP to 420kpa (this valve has no soleniod control so that is why it is set higher) and will see how the plant runs.




Plant keeps to above conditions well.

Probably, you provide required cooling. However, a lot of energy is wasted.
I looked at current weather in Welligton(I don't know where is your plant located). Temp. 6 degC, humidity 81%. I assume that your plant has evaporative condensers. Current optimum(the best) condensing pressure is in the range of 600 kpa. This is huge energy savings by changing condensing pressure from 1000 kpa to 600 kpa.

[Superfridge]

Probably, you provide required cooling. However, a lot of energy is wasted.
I looked at current weather in Welligton(I don't know where is your plant located). Temp. 6 degC, humidity 81%. I assume that your plant has evaporative condensers. Current optimum(the best) condensing pressure is in the range of 600 kpa. This is huge energy savings by changing condensing pressure from 1000 kpa to 600 kpa.

Thats an interesting point, every industrial plant I have ever worked on has had a fixed condensing pressure in the range of 1000kpa and yes it wastes energy.

It is best practice in this neck of the woods to keep condensing pressure up when ambient is down.

Would the hand expansion valves from HP to IP need to be opened if the condensing pressure was lowered from 1000kpa to 600kpa to compensate the lower deltaP and lower liquid flow? As the IP pressure is fixed, the liquid flow rate to LP would stay the same.

[Segei]

Thats an interesting point, every industrial plant I have ever worked on has had a fixed condensing pressure in the range of 1000kpa and yes it wastes energy.

It is best practice in this neck of the woods to keep condensing pressure up when ambient is down.

Would the hand expansion valves from HP to IP need to be opened if the condensing pressure was lowered from 1000kpa to 600kpa to compensate the lower deltaP and lower liquid flow? As the IP pressure is fixed, the liquid flow rate to LP would stay the same.

Condensing pressure should "float" based on wet bulb temperature. Hand expansion valve setting is one of many issues that should be solved. Recently, I've posted several newsletters related to floating condensing pressure and energy savings. You can read them.