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Two (or maybe 4) stage chiller control
I've been working on building a couple chillers for a year to replace a manufactured unit and i'm close to starting it up but realize i need a water temperature control strategy. The one i'm replace was a trane two stage reciprocating R-22 15 ton unit which was low on sophistication for managing lower load which is what resulted in losing one compressor and then there was a refrigerant leak in the piping inside the chiller barrel on that same side so we're giving up and going our own way.
I've built this up using two 5 ton two stage condensor units so that actually gives me 4 stages theoretically. The Trane was controlled by an analog two stage aquastat. The theory is sound but I could actually use logic that could manage up to 4 stages and I would like to modestly vary the water temperature targets vs. outdoor temp although that is not essential. I used to just manually adjust the targets during 'shoulder' season as I was doing with hydronics before various affordable reset controls hit the market.
So looking for recommendations. I could do something as simple as use two two stage controllers and create an effective multiple lead lag circumstance by setting one for more aggressive temp range, e.g. 38 degrees on the lead with 6 degree diffential and then set the lag for 44 or thereabouts and spend some time calibrating the probes and calls although it would be nice if a I had a single control that responded to a single temperature probe to keep the stages on the same page without a lot of field calibration. Just looking to see if anyone has made up any solutions or found a ready made control that might have the logic for this.