Suction group pressures

[zapatasblood2]

On rack systems, I notice they all have suction pressure set points to maintain. Just wondering what saturation temps we typically try to keep them set for. Im guessing 10 degrees SST below case temps? Thanks guys

[lovetowork]

That's a good rule of thumb, but also depends on what type of cases and how new the cases are. You are really trying to keep them 2 degrees below evaporator temp. A lot of the newer cases, especially medium temp glass doors have a much tighter difference between suction set point and discharge air, resulting in a higher SST. Other ways they do this is with more fins per inch and tighter coil passes.

[icemeister]

The best way to think of this is you only need to set the rack suction low enough to offset the pressure drop between the rack and the lowest temperature case. Most rack controllers will have a suction float feature which adjusts the rack suction to satisfy the temperature of the lowest temperature case.