The Oracle at TED: HVAC
I’m reading a historical mystery novel based in ancient Rome, and I’m surprised by the parallels between that society and ours. Aside from the madness of power hungry politicians (some things truly never change) I was intrigued by the description of Roman Augurs, a class of priests who interpreted the the will of the gods by observing the fligths of birds or strokes of lightening.
Like an ancient Augur “taking the auspices,” I faithfully watch the spikes and deflections on my TED 5000 energy monitor and attempt to interpret their hidden secrets.
Every day, I learn something new, and the patterns and trends take on meaning as I begin to dig deeper into my home energy use. Over the next few weeks, months, or years, I hope to share what I learn and how it’s changing my energy consumption.
First up is a look at my HVAC system. I already talked about how heating and cooling affect my monthly energy bill, but now TED allows me to delve even deeper, understanding at the second time scale how my heat pump works. Take a look:
You’ll see my baseline at the time was running around 400 watts. At 11:37, the first stage of the heat pump turned on (that “click” you hear at the thermostat). There’s an initial 1.5 kW and then a slow climb to its full capacity of 2 kW.
All of this was well and good until I saw a spike to almost 13 kW and my jaw dropped open. It turns out that when the heat pump can’t reach temperature quickly, it turns on some electric “strip” heaters, akin to the coils in your toaster oven, that warm up fast but are horribly inefficient.
Calculating the area under that curve would give you kilowatt minutes and could give you a sense of how much it costs to heat the house. At 13 kW, it costs me a dollar an hour, but electric rates in other areas of the country can be twice that high. As you can imagine, I’d like to keep those strip heaters off as much as possible.
The reason that insulating and air sealing are such money savers is because of the graph above – heating and cooling represent a large portion of home energy use. And using Google PowerMeter gave me another idea:
The boxed areas represent the time that my HVAC system was programmed to run. It sets back during the day while I’m at work, and starts again in the evening when I arrive home. I had it set to turn on at 6 AM and off at 8:30 AM, which I thought was reasonable, until I noticed in Google PowerMeter that it was on while I was away from home for at least 30 minutes.
I’ve since adjusted the settings to come on at 6 AM to keep me warm when I get out of bed, an then to turn off at 7:30. I’m still at home then, but I don’t need the heat pump to run because the house is already toasty and I’m dressed for work. I let it coast for the next 30 minutes as I make my way out the door, and save a full hour of heating!
That could save me a couple of dollars every month (more in the cold of winter) and it cost me nothing to change. Nice.
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