In my ongoing quest for more electricity savings, I signed up for SmartAC with PG&E. On the whole this is a great deal. You call up PG&E and they come in and replace your dumb old analog thermostat with a fancy new digital one and then send you a rebate check for your trouble. The digital thermostat enables you to program complex schedules, and does things you can’t do with an analog thermostat, such as run the fan for 15 minutes on the half hour which delivers a surprising amount of cooling for relatively little energy. You can also control the thermostat via the SmartAC website, except that the web interface curiously lacks some of the functionality on the thermostat itself. So this is definitely a cool thing, and since they pay you to do it, it’s hard to argue against it. Wait, you ask, why would they do this? Well there is a catch. On peak power days PG&E can use the internet link to force your AC into fan mode at regular intervals. If you absolutely can’t stand that, you can login on the website and say no on that day. So the benefit for PG&E is to protect against blackouts/brownouts on peak days, and generally reduce the amount of peak power used, which in general is by a large margin the most expensive and therefore unprofitable power for PG&E. Additionally PG&E has another program whereby they actually give you a discount on most of your power in exchange for charging you a lot more on those peak days – encouraging you to conserve on those days.
So with all this, how can one argue against it ? Having had it for a while now, I’m beginning to realize it has a flaw from an energy conservation standpoint. (I’m setting aside for a moment the contribution to peak power days, which is indisputable.) The advantage of the digital thermostat over the analog thermostat is that by setting complex schedules it remembers to turn the AC or heating OFF or DOWN in cases where you on your own would be too lazy or distracted to do it yourself. That it does real well. However, it also has the attribute that it turns it ON on days when you might not. This seems to be its downfall. Before, we only occasionally turned on the AC. Now it’s running quite a bit more. Admittedly the upstairs is very, very pleasant, and this cooling level is accomplished with a minimum of power. But it’s definitely doing more cooling than when we did it manually. The typical heating pattern in our house is that the house gradually warms up during the day, and that by night, when it’s already cooling off outside is when the maximum temperature is reached inside. Before we’d wait till the house was very hot, and then air condition like crazy. Now it runs more often, but sporadically, throughout the afternoon, early evening. It’s clearly working less hard, yet it’s also cooling the upstairs when we’re not there.
Obviously the system is too simple. What’s needed is to couple the smartac to an occupancy sensor. The other issue is the need to remember to close the windows when the a/c runs, or more specifically, when it’s hotter outside than the target temperature. Having just listened to an account of how to automate the whole house (see my previous blog entry), I’m now intrigued. I’m thinking my house is a lot like the way my audio/visual setup was before I automated it – a mass of separate parts not talking to one another. The one difference is that the stereo became so complex my family couldn’t operate it, and when I started having trouble too I had to act. The house on the other hand is certainly easy to operate, it’s just wastes energy. I could probably knock ~$30 off the monthly electricity bill with better tooling. The fancy house automation claims to have an ROI period of 8 years, which is unrealistic because the computers will be out of date in three years. I tend to believe three years is a realistic lifespan for digital toys. So in three years, I could save $1080. This means I could spend $1000 on home automation and at least amuse myself and break even. Somehow I think this will cost more than $1000. This requires more design. To be continued.
