Evapco 20 ton cooler unit

[rvmitch9927]

We have two EVAPCO units in a process room, they aren't cooling the room enough. The engineering team has came up with some changes to improve the peformance, which I don't think make any sense, can someone enlighten me. These units are supplied with high pressure liquid now with TEV expansion. Change #1 is to supply with subcooled liquid and replace TEV with a motorized valve controlling the level. Currently the units are backpressure regulated at 29 psgi. They want to change the suction piping to our 39 psig side, but also regulate the prssure to 58 psig. The suction change we were told was for the mass energy balance and the regulated pressure change is so the units won't have to be defrosted so often. They say the changes will make these units perform as if they are 35 ton units. Does this make sense to anyone? I don't have any of the numbers for heat load room size or anything with me, but there is a constant heat load in the room. Anyone have any ideas?

[US Iceman]

Sounds like an interesting predicament.

I'm assuming these are gravity flooded units since you said the new valves are controlling liquid level. What were the TXV's being used for? Where they Sporlan Level-Masters?

If the back pressure regulators are set for 29 psig and they raise the regulated pressure to 58 psig how is that supposed to increase the coil capacity? When the evaporating pressure increases so does the saturation temperature, which decreases the TD for the coil. This would lower the capacity, not increase it.

This does not make any sense.

[RANGER1]

What is room temp supposed to be firstly ?

Maybe coils are icing up to much loosing performance .

You would also think back pressure regulator would be set just above 32F as well if icing is occuring .

Assume its on ammonia ?

[AmmoniaMike]

It sounds like they are converting the coils from dry expansion to flooded. The reason I say this is you don't use TXV on flooded system. Process areas are typically kept at 50F so setting the BPV to 59 psig would give you 10TD. There would also be an increase in coil capacity but I think believing they will gain 15TR is overly optimistic.