I want to quit lying to my programmable thermostat

I’m lying to my programmable thermostat, a Honeywell Home wifi-enabled smart programmable model. I want to quit, but I have to do it to get what I want. Am I wrong?

Here is what I mean. I buy electric power from my local electric monopoly on a time-of-use rate. From 3 PM to 6 PM on weekdays during July and August the price I pay is about 4X the offpeak rate. (May, June, Sept, and Oct the peak is about 3X the offpeak rate.)

It makes sense to shift power consumption, particularly for the largest energy consuming device in most Arizona homes: the air conditioner. After the thermostat was installed the first order of business was setting the schedule. This is when the lying started.

You see, my thermostat has a handy programming interface that aims to make it simple for consumers to use. You tell it what temperatures you want when you wake up, while you are away during the day, when you return in the evening, and while you sleep. It does the rest!

Which would be great except there is no way to tell it to shift load away from my TOU peak rate period. So, as the image shows, I am telling the thermostat I wake at midnight, leave the house at 2:45 PM, return at 3:00 PM, and go to sleep at 7:30 PM. None of those things are true, but I trick the thermostat into saving me money.

Do I really leave at 2:45 PM and return home at 3:00 PM? No I do not.

I’m estimating that I save about a $1 every weekday by pre-cooling the house before 3 PM and then letting the temperature rise (to about my limit at 83F). Actually I save a bit more than $1/weekday in July and August and a bit less in the other months from May to October. By the end of October I expect to have saved enough to cover the price of the thermostat.

The chart below shows my average July energy use per hour during weekdays, but excluding July 11. On July 11 the local utility called an “energy conservation event,” and I’m enrolled in a program that lets them temporarily reprogram my thermostat to save energy when the grid is stressed. Turns out that they do what I am trying to do, though maybe they are a little better at it than I am.

I’d like to do even better. The red line in the chart represents my July average. Notice the V-shape indicating that energy use bounces back steadily. The blue line is the performance on July 11 when the local utility was in control. They achieved more of a U-shape, delaying most of the recovery until after the peak rate ended.

Either I need to tell better and more elaborate lies to my thermostat, or it and me learn how to communicate better together and I can finally tell it the truth.

The truth might not set me free, but it might allow me to boost my energy savings another 20 or 30 percent. I’d like that.