Quote:
Originally Posted by Vlad
Yes your amps going down, but you don't remove more BTUs. You just shift temperature range. Usually water regulating valve is just cracked open it means that you use only small part of condenser.
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Not true at all. Your suction temperature drops because your compressor is not working as hard and therefore can flow more mass of refrigerant. Therefore you *DO* remove more BTU's. Refrigeration in BTU or Watts or whatever is precisely linked to the refrigerant mass flow. It is after all the phase change of the fluid that provides the effect. More fluid, more heat moved.
Quote:
Originally Posted by Vlad
When I was in refrigeration school we did this many times by opening wide water regulating valve on water cooled units. Our instructor knew what happened just by looking at ice at suction at compressor. He was giving us s... because of converting walk-in cooler into walk-in freezer.
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The above quote proves my point. A walk-in is a balance between the heat you are removing, vs the heat infiltration and product load. If you drop the temperature in the room, you *must* be moving more heat unless you have radically re-insulated.
To counter this you can do one of two things.
- Increase heat load on evaporator resulting in more refrigerant mass flow and therefore a higher suction pressure. In my case I can do this by speeding up the fan.
- Reduce compressor speed to reduce the mass flow. My in-build unit will do this with the VFD.
The closer your evaporation and condensing temperatures, the more efficient your unit.
As your compression ratio drops, your compressor can move more refrigerant mass per revolution. This is to do with dead space at the top of the chamber, the efficiency of the valves and other factors. The effect is less on scrolls, but on Recips you can lose up to 30% of your mass flow by pumping to a much higher pressure. Plus of course your current draw increases.
If you have controls to allow you to tweak the other variables in the refrigeration cycle then you can easily take advantage of the increased efficiency. In the case of the walk-in you describe, you can't and therefore you cause the refrigeration system to find equilibrium outside the parameters it was designed for.
This is precisely how VRV systems utilize the best available parameters to get as efficient as possible.
On VRV systems, my comment about radically oversized condensers vs evaporators causing an issue with refrigerant management? I saw one today that has a 4 circuit condenser. When the unit hits the reversing valve, it only uses 2 of the circuits as evaporators, so half the available liquid capacity. Clever!