Thermostat Programming

(Michael Langkilde) #1

Has anyone or is there already out there to control the thermostat by the number of times it runs let us just say, limit it to only run 2 or once an hour no matter the temperature?

(Aaron) #2

@zuperman4ever - Just curious. . … why? Saving wear and tear on equipment in exchange for tolerating wider temperature swings? Seems like a reasonable strategy for control of an unoccupied property but not a good strategy if occupied (unless it’s occupied by someone you don’t like).

Seems like it should be possible to, once an hour, turn thermostatMode from ‘off’ to ‘auto’. Then, watch thermostatOperatingState and look for it to come on, then complete a cycle (go back to 'idle?), then switch thermostatMode back to 'off; until the start of the next hour.

I appologize . . . I am HVAC-literate but an ST noob so I can’t offer much more than this.

(Michael Langkilde) #3

I will try to explain my reasoning here. I guess I was thinking of just having my heater or ac to run longer times instead of start and stop so many times. Or have a debounce or a delay start or the temperature has to be at the certain level before it actually kicks on the heater/ac. I guess I rather have it on longer or off longer then it turning on and then off multiple times.

(Aaron) #4

@zuperman4ever - The thermostat already manages this by imposing a deadband in the control algorithm. On some thermostats, this is an adjustable parameter and is usually presented as a ‘differential’. It varies by model but, for example, you may have a setting for ‘heating stage 1 differential’. Let’s say it’s set for 1° and your set point is 72°. The thermostat will wait until the temperature falls to 71 before starting a heating cycle. Then, it will stay on until the temperature is raised to 72°. If you want longer cycles, you would change the setting to, let’s say, 2°. Then, it will wait until the temperature is 70° before starting a heat cycle (longer off time) and it will stay on until the temperature is raised to 72° which is 2° and will take longer than raising just 1°.

Most thermostats also implement anti-short-cycle logic. That is, after the completion of a cycle, the thermostat may impose a 5 minute lock-out before another cycle can start. This is pretty important for equipment with compressors (AC or heat pump) but not so much for furnaces.

You might be able to argue that there is some slight humidity control advantage with longer cycles in cooling but, in general, I don’t think there is any reason to force longer cycle unless you are trying to limit wear and tear on the equipment and aren’t concerned about maintaining a constant level of comfort. Just my $0.02.

If you still want to do it, I think the strategy I outlined in my last post should be do-able.

(Aaron) #5

oh, , , , forgot to mention. . . it is also common for equipment with compressors to have their own timers in their controls to prevent short-cycling. Usually, this is on the order of 5 minutes.