Truly “smart” thermostats and boiler controllers?
Well, my new boiler is in (a Lochinvar WHN-85, with a Lochinvar SIT 40 indirect water heater). As far as I can tell this early in the season it’s working fine. But, I’ve been thinking about my thermostats and how they communicate with the boiler, and wondering if there might be a better way.
My old boiler was a standard dumb boiler. Each circulator was on if its thermostat was calling for heat, and the boiler was on (full blast) if a circulator was on and the water temp wasn’t at the limit. True bang-bang control.
Originally, the Honeywell Round thermostat in each zone was the smart part: it had hysteresis (the mercury sloshing back and forth in the switch) and a heat anticipator (a little adjustable heater, on when the thermostat was on). But it only had a contact closure to talk to the furnace, so its message to the boiler could only be “ON” or “OFF”.
A while ago I bought programmable thermostats so I could set the temp back at night. They replicate the hysteresis and the anticipation of the Honeywell Round, but still only have a contact closure to tell the boiler what to do.
Now I have a smart boiler, with temperature curves, outdoor reset, and all sorts of adjustments, delays, and other algorithms that help it Do The Right Thing. However, it’s still only being guided by a single contact closure per zone. So, there’s no way for the boiler to know just how much heat is being called for (“ON” versus “ON DAMMIT THE KID LEFT THE FRONT DOOR OPEN FOR FIVE MINUTES”). Nor does it know the difference between “ON: THE TEMPERATURE DIPPED A BIT” and “ON: THE NIGHT TEMPERATURE SETBACK JUST ENDED”.
I could get even smarter thermostats (e.g. the Nest), but with the communications link still so primitive there’s not a lot more it could do (excepting the improved programmability).
It seems to me that a smart boiler could do a lot better if it had better guidance from the thermostats. Are there (home) systems out there which have true “smart” temperature reporting thermostats, reporting to boilers which use the extra information intelligently?
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