Stop bolting green kit on without controls

We bolted a 500 kW air source heat pump onto our compressor hall to reclaim waste heat and preheat process water. Looked great on paper: COP>3, gas boiler idle, finance smiling.

Then January hit. Defrost cycles and low ambient turned that COP into a rumor. The preheat loop starved, operators flipped it to hand, and the HMI lit up like a pinball machine. Well, there's your problem: no buffer storage, no setpoint authority, and no interlock to shed noncritical loads when the heat pump fell off. Bonus points for a fouled plate HX because someone saved a strainer and we had no DP alarm.

We fixed it with a 2 m3 buffer tank, bag filters with DP switches tied to a timed alarm and an auto bypass, staged control with the boiler on warm standby, and real alarm rationalization. Also froze setpoint ownership: process > energy > comfort. Now it rides through defrost without drama.

Lesson learned: renewables aren't fragile, lazy controls are. Design for failure modes, maintainability, and handoff to night shift. If you can't maintain it, you don't own it. And yes, just interlock it. What's on your must-have checklist to make these installs survive a Montreal cold snap?