Danfoss SC255 - Dynamic Suction Float

[georgedvf]

Hello everyone.
I'm new using the Danfoss AK2-SC255 controller and I need to set the Dynamic Suction Float for a Distribution Center with 13 circuits. I read the manual and I got that I have to set ON the circuits to be taken into acount when floating, but it doesn't explain how it will determine when to float and how many psi.

Is it based on temperature?
If I have 4 different temperatures among the 13 circuits, and I set all of them ON to suction float, how will the AK2-SC255 determine how many PSI to float on each case? or is it always the Maximum value I set on config no matter which temperatures are reached?

Thanks!

[Brian_UK]

I don't know anything about these controls but doing some reading below may help you..

Page 32 of this manual explains some of it
http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/AK255E_UserGuide.pdf

Other docs here may be of help
http://www.danfoss.com/North_America/BusinessAreas/Refrigeration+and+Air+Conditioning/Literature/RA_Documentation.htm?CatalogKey=RA-6aa56192-f7e6-4793-b7f9-4c2fa908cc23-en-US:RA-6aa56192-f7e6-4793-b7f9-4c2fa908cc23-en-US&DocumentType=All&Language=en-US&FreeText=AK-SC255

[georgedvf]

Thank you Brian_UK, that's interesting reading, my controller doesn't have the "Pack Configuration" menu, I think there are two (or more) versions, the manual says version E and I think mine is R.

Anyway, this manual does say that the controller uses temperatures of the rooms to determine which is the most loaded (the one that has to work the hardest to mantain temperature).
But once it finds the most loaded case then what???? If it is the lowest temperature room it does nothing but if it is the highest temperature room it floats or what's the logic for this???

Also it mentions a Max pressure to float, but doesn't say if there are "steps" to float if several cases and several temperatures are present. Does anyone has used this???

Thanks!

[Brian_UK]

Use the second link to download an 'R' version.

[taffy-boy]

nice links thankyou

[750 Valve]

The float works like this.

- Select the circuits to be included in the float
- The temp setpoints in the circuit settings will be the ones the dynamic float looks at to make a decision if the rack can float up or down
- If the temps are within setpoint +/- deadband then the controller will consider that circuit is satisfied
- If all circuits selected in the float are within desired temps (excluding defrost pulldown) then the rack will be allowed to float up
- If there are circuits are not achieving temps then rack will be allowed to float down
- Under rack settings you can set the maximum float value +/- setpoint
- Under evaporator status the controller will graphically display which circuit has been the furthest away from setpoint and has affected the float

I suggest the rack be set to NOT float below setpoint and only float above setpoint, only include rooms in the float that work at the lowest design SST, let the float take care of raising the suction pressure as the rooms reach a desired temp.

[mrfix]

Can anyone explain the aka65.ini file used by Danfoss or tell me where to get the information please?

[georgedvf]

The float works like this.

- Select the circuits to be included in the float
- The temp setpoints in the circuit settings will be the ones the dynamic float looks at to make a decision if the rack can float up or down
- If the temps are within setpoint +/- deadband then the controller will consider that circuit is satisfied
- If all circuits selected in the float are within desired temps (excluding defrost pulldown) then the rack will be allowed to float up
- If there are circuits are not achieving temps then rack will be allowed to float down
- Under rack settings you can set the maximum float value +/- setpoint
- Under evaporator status the controller will graphically display which circuit has been the furthest away from setpoint and has affected the float

I suggest the rack be set to NOT float below setpoint and only float above setpoint, only include rooms in the float that work at the lowest design SST, let the float take care of raising the suction pressure as the rooms reach a desired temp.
Thanks 750 Valve, somehow I lost the track of this post since now that there was another answer. That's quite explicit to understand. I have one more doubt, we have been told that when using EPR the best practice is to set the objective temperature on the controller few degrees below, so the EPR can work better to keep the room at more constant temperature, do you agree with that?

[750 Valve]

Yes I agree, that is the best way to setup the rooms