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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
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.
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
Too much waterflow can make that the evaporationpressure or the sunctionpressure gets too high for the compressor.
Rob
Why not check the manual, there is a minimum and maximum water flow.
just follow it and you are safe.
Chemi
What about compressors starting too many times per hour?
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?
Could you describe this, because I don't see why chiller will not reach it's setpoint.Quote:
Originally Posted by Lowrider
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.Quote:
Originally Posted by nike123
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!Quote:
Originally Posted by Lowrider
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.Quote:
Originally Posted by Lowrider
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:
I have capacity correction factors for chillers that I service (Galletti):Quote:
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.
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:
Quote:
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!
that's more or less the same as I wrote!Quote:
Originally Posted by nike123
Maybe I used wrong word (it is not my native language) or we have some miscommunication problem here.Quote:
Originally Posted by Lowrider
I ad some clarification in last post!
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
How much to high?Quote:
Originally Posted by assadp
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.Quote:
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
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.