Hot Economizer Lines

[Casimirblue]

We have a new warehouse installation with the following.

Frick RWFII 222
-22F Suction
93F Condensing Designed
Economized / Side Port to +20F Suction
Compressor is on Variable speed.
(This has been the only compressor running)

This unit is experiencing a severly hot economizer line between the compressor (160F) and the control valve (A4AS). I have seen this before in fixed speed compressors but not this severe. Is this recompression??? a fuction of the variable speed? Has anyone experienced this?


Thanks
James

[Segei]

I assume that refrigerant is NH3. What is the condensing pressure?

[RANGER1]

We have a new warehouse installation with the following.

Frick RWFII 222
-22F Suction
93F Condensing Designed
Economized / Side Port to +20F Suction
Compressor is on Variable speed.
(This has been the only compressor running)

This unit is experiencing a severly hot economizer line between the compressor (160F) and the control valve (A4AS). I have seen this before in fixed speed compressors but not this severe. Is this recompression??? a fuction of the variable speed? Has anyone experienced this?


Thanks
James

James ,
Would expect its worse on minimum speed as port is not as efficient .
If small or no load from economizer would agree with you that its recompression.
We sometimes use economizer connection on mycoms for oil seperator oil return & these lines also get very hot at times .

[Casimirblue]

I apologize:

It is ammonia. Design Condensing is 93F but for winter will run down in the 65F Condensing range.

James

[Casimirblue]

Ranger 1

I haven't personally been to the sight but I'm just looking at pictures. It may just be a set up problem (new installation) with the regulator only flowing very little. The economizer check and regulator are above the compressor, so approximately 6-8' pipe to the check. I don't know if this pipe volume / length exaggerates the problem.


James

[Segei]

It seems like something wrong with compressor.
Usually, screw compressor with VFD have 2 modes.
1. VFD modulated speed of the motor from 100% to 50%(20%). Slide valve is in fully loaded position.
2. When required capacity is below 50%, slide valve will modulate to handle the load.
Set VFD to 100% and let slide valve to handle the load fluctuation. This action will eliminate VFD as a reason of this issue.
I'm surprised by 93F design condensing temperature. It looks like a bit high. What is the wet bulb design temperature for this plant?

[CanadianIce]

I have seen this before when there wasn't any flow from the economiser and the valve group was more than a couple feet away. It could be as simple as the A4AS is set above the economiser port pressure.

[RANGER1]

Sergei,
93F = 34 deg C Whats wrong with that?

Also if compressor is on min speed as well as low load , economizer will be also on very low or no load situation.

[Segei]

Sergei,
93F = 34 deg C Whats wrong with that?

Also if compressor is on min speed as well as low load , economizer will be also on very low or no load situation.
20-30 years ago designers were focused on minimizing capital investments and design condensing temperature was 95F. Today many company are focused on energy savings and design condensing temperature is in the range of 85-90F. This plant has compressor VFD which improve plant efficiency. However, they have relatively small condensers and this factor will reduce plant efficiency.

[TXiceman]

Is the compressor runing on VFD for turn down or slide valve when this occurs? The slide valve will uncover the side port around 80% Slide valve and let the port pressure go to suction pressure. You could be backing up into the line ig the regulator and check valve are not mounted at the compressor.

Also, is this a parallel compressor operation? One machine will lead and take all of the side port flow and the other one will back up in the economiser port.

Ken

[RANGER1]

20-30 years ago designers were focused on minimizing capital investments and design condensing temperature was 95F. Today many company are focused on energy savings and design condensing temperature is in the range of 85-90F. This plant has compressor VFD which improve plant efficiency. However, they have relatively small condensers and this factor will reduce plant efficiency.


Sergei ,
This is certainly lagging in Australia as power was cheap but now increasing dramatically.
Of course we are utilizing VFD but only some major players would instal it for power savingsas well as have extra condensing capacity.
I think a lot of engineers instal it for plant versatility with turn down & only usually installed on 1 machine in plant room.

[Segei]

Sergei ,
This is certainly lagging in Australia as power was cheap but now increasing dramatically.
Of course we are utilizing VFD but only some major players would instal it for power savingsas well as have extra condensing capacity.
I think a lot of engineers instal it for plant versatility with turn down & only usually installed on 1 machine in plant room.
Many people use VFDs for energy savings, because they don't know another way to achieve this savings. However, I think that optimization of refrigeration plant operation is the best way to save energy. Can you elaborate about plant versatility?

[RANGER1]

Sergei ,
What I was trying to say was the VFD is used as top up machine with base load machines at full load.

The VFD can allow the compressor to cover a lot more load situations.
I know I'm not telling you anything new & agree its only one part of plant optimization.

[Segei]

Sergei ,
What I was trying to say was the VFD is used as top up machine with base load machines at full load.

The VFD can allow the compressor to cover a lot more load situations.
I know I'm not telling you anything new & agree its only one part of plant optimization.
Usually, plant is designed to have one trimming VFD compressor per every suction temperature. It is expensive to have VFD for every compressor and it is not efficient.:eek: VFD itself takes additional 3-3.5% of energy. However, I know one cold storage that have 3 compressors and every compressor has VFD. This is waste of money and energy.

[sterl]

Move the Check Valve and if equipped, Strainer as close to the machine connection as possible.

Make sure there is oil injection upstream of the side port at all operating conditions; some of the lower speed versions of VFD-equipped machines (those that will drop to say 25% motor speed) re-route or re-balance oil flows at low RPM. Also if the machine has considerable wear, the speed setting may be too low and the oil seal is not effective; though that should show up as high discharge temps and oil temp as well.

Ensure that your Slide Valve Position sensor is calibrated right: It may be reading 75% and the controls close the Eco regulator; but you are really at a Higher SV and there is compression (and re-compression) occurring at the Port. The Eco should be flowing but its not cause the controls are keeping it out of action.

Make sure that you have the correct setting on the Regulator and that the Output to the solenoid coil on the A4AS is actually firing, voltage good, etc.