Lead-lag code for a Chiller?


Hey all you OptoFans,

Might any of you have some code to handle lead/lag/failover logic on a (5 compressor in this case) chiller system?

Or have tips for someone who’s about to start building a strategy for such a system?

Do share!

Alternating between two digital output points?

I’ve lead/lagged redundant chillers, but they run on their own factory code - Opto just tells them to go and make cold water. For these systems, I just rotate the lead chiller based on the month - Chiller 1 gets odd months, chiller 2 gets even.

For individual compressors, I would be inclined to consider the number of starts rather than just run-time.

FWIW, the factory programming on the chillers I mentioned above are supposed to lead/lag the compressors - but I rarely see that happening - starts with compressor A1 like 95% of the time.


I agree with Philip on rotating sequence and # of starts, especially if all compressors are the same or of similar capacity. if you have varying capacities, I use a “first on, first off” and smallest to largest sequence. This helps select an efficient combination of compressors, reduces cycling of larger compressors and, to some extent, balances runtime hours. Don’t forget anti-recycle timers to prevent short cycling. We typically use start to start time delay.


StartOffPulse would work good here, if only you didn’t need to keep track of calling it in a separate variable as there is no way to get the status of a pulse from the IO unit.