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assadp
19-05-2008, 03:38 PM
Hi we all know what happens if we have insufficient water flow through an evaporator, the suction pressure will drop, the evaporator can freeze and liquid refrigerant can smash up the compressor.

What happens if we have too much water flow through an evaporator.
Obviously insufficient heat will be removed from the water and our suction and discharge pressures will go up

But what else

Regards Assad

Chillin'
19-05-2008, 04:44 PM
With low flow I have also found a problem with oil. The oil stays in the evap because of low velocity and the unit may trip on oil fail b4 low pressure. The tech may then add more oil to a point where the unit will have too much and oil slugging will occur. This is more likely the cause of a smashed compressor rather than liquid refrigerant.

The amount of heat removed in total BTU's or KW will remain the same regardless of flow speed (up to a limit). If your unit has an excessive amount of flow, the unit will still function as long as the total load has not changed. What will happen is that your evap will wear prematurely and one of the tubes will leak and cause refrigerant loss and then a wet system.

assadp
20-05-2008, 09:58 AM
The reason for the question is we have a site which over the last few years has suffered numerious compressor failures (Smash Ups) up to recently it has belived it was poor water flow through the evapourator.
Now they have found it is too much water flow through the evapourator. I don't believe that too much water flow through the evapourator would cause compressor failures and this is the debate we are having in the office at pressent.
Regards Assad

teacher
20-05-2008, 01:24 PM
Too much waterflow can make that the evaporationpressure or the sunctionpressure gets too high for the compressor.
Rob

chemi-cool
20-05-2008, 08:08 PM
Why not check the manual, there is a minimum and maximum water flow.
just follow it and you are safe.



Chemi

1torr
20-05-2008, 09:25 PM
What about compressors starting too many times per hour?

Lowrider
20-05-2008, 10:11 PM
If water flow is too high, the chiller usually will not reach it's setpoint, unless there is also a hydraulic issue in the building and the machine left running with lower loads then acceptable!

What machine are we talking about?

nike123
20-05-2008, 10:27 PM
If water flow is too high, the chiller usually will not reach it's setpoint, unless there is also a hydraulic issue in the building and the machine left running with lower loads then acceptable!



Could you describe this, because I don't see why chiller will not reach it's setpoint.

Lowrider
20-05-2008, 10:40 PM
Could you describe this, because I don't see why chiller will not reach it's setpoint.

Say you have a chiller of 1MW and building load is more than the capacity of the chiller. If flow through is constant, which it should be, the chiller will not reach it's setpoint because no mather what happens, if the flow is say double that of what it should be, the chiller if designed for 6K will only do 3K. If the load from the building stay's higher than the chiller capacity the chiller will keep running and never reaches it's setpoint.

On the other hand, if building load is less the chiller minimal capacity, having the higher flow will keep the chiller on longer! which in this case is a good thing!

It's all down to Q=m*c*dT

nike123
20-05-2008, 11:22 PM
On the other hand, if building load is less the chiller minimal capacity, having the higher flow will keep the chiller on longer! which in this case is a good thing!

It's all down to Q=m*c*dT
OK, my question was referring at this quoted situation!

Lowrider
20-05-2008, 11:28 PM
What situation? We only know he has a problem, not the type and size of the machine, hydraulic lay out, flow's, etc.

Generaly taken a chiller with too much flow will not reach it's setpoint untill the load drops!

nike123
20-05-2008, 11:38 PM
What situation? We only know he has a problem, not the type and size of the machine, hydraulic lay out, flow's, etc.

Generaly taken a chiller with too much flow will not reach it's setpoint untill the load drops!

Of course that chiller would not reach his set point when building load is higher then chiller capacity.
I questioned that chiller will not reach set point when his capacity is higher then load, but flow thru evaporator is higher then nominal.
At least, that is how I understood your post #7!

I am with chillin here:

The amount of heat removed in total BTU's or KW will remain the same regardless of flow speed (up to a limit). If your unit has an excessive amount of flow, the unit will still function as long as the total load has not changed.

I have capacity correction factors for chillers that I service (Galletti):
dT 3K =0,975
dT 4K =0,990
dT 5K=1
dT 6K=1,015
dT 7K=1,030
dT 8K=1,040


Flow variation with change from nominal dT of 5K to 3K is 63% more flow then nominal.
That mean, 63% more flow wil make drop in capacity of 2,5%.
I don't see at what you base your statemant:

If water flow is too high, the chiller usually will not reach it's setpoint, unless there is also a hydraulic issue in the building and the machine left running with lower loads then acceptable!

Lowrider
20-05-2008, 11:57 PM
Of course that chiller would not reach his set point when building load is higher then chiller capacity.
I questioned that chiller will not reach set point when his capacity is higher then load, but flow thru evaporator is higher then nominal.
At least, that is how I understood your post #7!

I am with chillin here:

that's more or less the same as I wrote!

nike123
21-05-2008, 12:45 AM
that's more or less the same as I wrote!

Maybe I used wrong word (it is not my native language) or we have some miscommunication problem here.
I ad some clarification in last post!

assadp
22-05-2008, 01:54 PM
The reason for the original post was we have had numerious compressor smash ups and what we have found is the flow rate is too high.
I don't believe that too much water flow could or would cause liquid refrigerant returning back to the compressor causing it to smash up this is the debate we are having between us in the office. I do however believe the pressures would go up the delta T would go down and strugle to maintain the desired temp BUT not slug liquid back to the compressor to cause a smash up
Regards Assad

nike123
22-05-2008, 06:41 PM
The reason for the original post was we have had numerious compressor smash ups and what we have found is the flow rate is too high.

How much to high?


I don't believe that too much water flow could or would cause liquid refrigerant returning back to the compressor causing it to smash up this is the debate we are having between us in the office. I do however believe the pressures would go up the delta T would go down and strugle to maintain the desired temp BUT not slug liquid back to the compressor to cause a smash up
Regards Assad

Delta T would go down depending on amount of raised flow. From my example above, it is obvious that this fall is not dramatic with some reasonable flow increase.

Evaporation pressure will increase for corresponding difference in delta T of water in evaporator. If we have water temperature of 10°C then with dT of 5K we have evaporation temperature of 0°C and if we have dT of 3K then we have evaporation temperature 2°C. Maximum evaporation temperature with 10°C water in temperature should not exceed 5°C.
That is not much rise in pressure, and chiller should not feel any consequence from that.

At least, that is how I see relation of high flow of water in evaporator and pressure rise in refrigerant circuit from that!

If I saying something wrong here, please someone, correct me.