Home automation: Phase 1

I'm cheap. Even if saving energy wasn't in vogue, I'd still be all about it. Excess energy use is just money out of my pocket. And since I'm one of those analytical types, I'm all about systematically reducing my monthly bills. And since we're all a bit strapped for cash & worried about our environmental impact, maybe I can help some other people save some green (money is green.. the planet is green.. GET IT?!?).

The ultimate goal is a completely wired house capable of making decisions for me. It should tell me, for instance, that weather is rolling in and I should close my windows. Or that I have my windows open and the a/c is on. But that's all a bit ambitious right now.

I like the kickstarter idea of well defined projects with end-goals. So my first goal is better a/c management. I hope to reduce my overall energy consumption (and utility bill) by making smarter decisions about my a/c usage without sacrificing comfort. And measure that change.

Programmable thermostats are good. And they're cheap. But they're not very smart. Wouldn't it be cool to know about how long it takes your house to cool off, based on past attempts? And wouldn't it be nice to tell your house what time you'll be coming home so that it can be at the right temperature right as you walk in the door? Programmable thermostats fall a bit short in those areas. Oh, and the programmable thermostats can't tell you the power consumption.

So how is this to be accomplished? A buddy of mine set up a computer-controlled thermostat. It's mostly there. It was basically a USB-controlled relay (using phidget boards). And that (or an arduino-controlled relay) is the first part. Fortunately, thermostat wiring is brain-dead easy. You basically connect a couple of leads and a 24 volt signal (on most systems) travels to a transformer, which controls the system. Now, it's a little more complicated than that, but since systems vary, that's about as specific as I'm getting.

The new hardware I'd like to incorporate is some means of measuring the power going to my a/c unit. I hate the idea that I 1) can't see a live power draw for my whole house and 2) I'm incapable of figuring out which circuits are responsible for most of my power consumption. Current transducers seem like the 2-birds-1-stone fix. Wrapping around current lines, they give a pretty good idea of how much AC current is flowing through a circuit at a given time WITHOUT having to cut the line & add a device. And because line voltages are pretty standard, calculating power is pretty easy. And while we're down there, I can probably throw a temperature/humidity sensor in the crawl space to make sure it'd proper for wine cellaring ;-)

So then there's the software. Which is really my thing. I see pretty much everything as data to be used. Logging power usage just seems natural to me when figuring out how to be cheap. And it'll let me finally settle that stupid "is it better to leave your a/c on all day or let it get really hot during the day" debate. I have my opinion, but I've never seen evidence either way. So by keeping that data, I can share it and put it to use.

My vision is to have a "my house" web application and android app. I'd even make an iOS app if somebody wants to give me a dev device and kit ;-). As a starting point, I'd like it to be able to turn on/off my a/c and heat. I'd like it to show current and historical power usage. And I'd like it to predict how long it will take to cool the house to a certain temperature (taking into consideration the outside temperature). I'd like to be able to say, "I'm coming home at 6; do what you need to so that the house is 78 degrees when I get home. Thanks." In the future, I'd like it to adjust according to weather predictions.

Sound cool? I think it's a good little project.


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