Making a Learning Thermostat 192
OzPeter writes "As reported in WA Today, Tony Fadell of iPod fame has been using Nest Labs to design and build a thermostat that learns how you live in your house by following how you manually change the temperature. Once you have taught it how to behave, it then can schedule temperature changes that suit your lifestyle, and help you cut down on energy costs."
Well it turns out those actually DO exist (Score:5, Interesting)
Really, I was surprised, but I have one on my A/C. So my A/C is a dual stage unit. Basically it has a bypass so that when it doesn't need to put out so much cooling, it can work the compressor less, spin down the fans, and so on. When needed, it can use full capacity. It is a 4 ton unit that effectively has about a 2.5 ton mode. Good for saving energy. Most days all you need is the first stage, even in the desert.
Well the thing is, the stage use is determined by two degree bands, temperature deltas. The first you set between 1 and 6 degrees. This is how much the temperature can swing before the unit engages. So if the degree band is 3 and the thermostat is 75, the A/C will come on at 78 (or the heat at 72 if in heat mode). The second one is another two degrees fixed. When the temperature is more than the first band plus the second, the thermostat engages the second stage of the A/C. So if set at 75 with a 3 degree band, the second stage engages at 80 degrees.
Needless to say the thing cools a hell of a lot more when fully spun up. So you really can make it cool down faster by setting the temperature lower.
In fact, I have to when it is really hot. When it is very hot, like 105 or above out, the low stage is really only enough to maintain the temperature. It cools as fast as heat leaks in (that is the design idea more or less). So to actually get it to cool, I have to kick in the 2nd stage. Means if I want 75, I set the temperature lower, until it hits 75, then set it to 74 and the A/C will continually run until the outdoor temperature cools off enough.
And yes, it is more efficient to run continuously in the low stage than cycle on and off in the high stage.