I thanks the chaps that responded to my thread last week on changing oil filters on this beast - that seems to have alleviated some problems, but others have surfaced.
I know that low load scenarios are the BANE of chiller operators - oil return problems, short cycling etc., but I will give it to you quickly - BTW , I have good water flow with 10 - 11 deg. F @ 100% load.
The chiller in question cools the rather large MCC ( 24 / 7 ) in the Recovery boiler building at a Pulp and Paper company. I am the sole HVAC guy, with 30 years under my belt, but my exposure to the new generation of screw compressor with all the associated electronics is very limited - I used to work on D/B vertical screws - maybe that cursed me ??
Anyway, I quickly have a couple of questions - BTW, I changed internal and external oil filters on both A and B compressors on this machine last week, and while running, oil pressures seem OK ( less than 10 psi on the PD reading etc. ) There are two oil sight glasses on each system - I suspect the level should be at least between them, as the brass oil level float is centered between them. A compressor has the bottom glass full, sometimes the top glass has something in it, B compressor always has both glasses full. Is there a preferred level?
Compressor A will start to unload as you get near the setpoint ( 44 F, chilled water, no glycol ) and cycle @ 10% ( at which time the hot gas valve opens ), back up to 24%, then up to 37%, even when I have a leaving water temp of 45-46F, entering about 2-3 F higher.
Compressor B, running by itself @ the same conditions, runs @ 46%, with a 4-5 degree inlet ( higher ) temp. - The 46% is total unit capacity, and that is what it seems amperage wise - so it is basically running flat out - I have not seen it get to a point where the hot gas valve opens.
Is there a specific control setting strategy that will help me on low load scenarios? Without some guidance, I don't want to be screwing around too much.
I am sceptical to go changing parameters as the Carrier guy set it up back in May; the unit ran trouble free in the fall when we had similar ambient temps. - all in the 40 - 50 F range. It even ran trouble free when we were at the 20 - 35 F ambient for a couple weeks in December.
I will also add that the condenser is Mill water that is metered thru the condenser via a Carrier supplied butterfly valve that gets a 4 - 20 signal from the board - the condensing temp. is set @ 90 F and even though the entering mill water is 44F, it does a good job of maintaining head pressure/temperature.
Sorry about rambling on - I want to try to resolve this on my own, but we will call in Carrier if need be; we are a ferry ride from Vancouver and it isn't a simple chore to get here.
I wish I had had more time to play with this unit, but as the only guy looking after 250 pieces of HVAC equipment that is 20 plus years old, well, you get the picture.
Dave Beauchesne CM
aka : Freonguy