Thermostats Are Getting Smarter, but It Is Still a Dumb Answer to the Problem of Saving Energy

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credit: Nest

In a previous post, In praise of the dumb home, I noted that Nest and other smart thermostats work best in lousy, poorly insulated and sealed houses, where a few degree change in thermostat settings makes a very big difference in energy savings. But as Megan noted recently in her post Nest thermostat now helps users avoid peak electricity rates, these thermostats are getting a lot smarter. Now they can dial up the AC when the power is cheaper and let it coast a bit when the power is more expensive. Nest writes on their blog:

So if your thermostat sees that you like to cool things down at noon, but that’s when electricity prices spike, it might start cooling the house at 11:30 when energy’s still cheap.

Megan concludes: “Right now Nest is launching the Time of Savings program with SolarCity customers while Southern California Edison and other major energy companies are coming soon.”

southern edison time of use

© Southern California Edison

California Edison’s summer time of use rates peak in summer from noon to six. That’s when it is hottest out and the air conditioning is running hardest. The cost of power is almost three times as high as at the off-peak times. So Nest’s scenario makes some sense.

duck curve
© If it looks like a duck ... California ISO

But what happens when SolarCity and other companies cover California roofs with solar panels? Every year more power is generated at peak solar times from 12 to 6 to the point where at some times of the year, more power is being generated than can be used.

So the thermostat will have to get even smarter, to know when the solar panels are delivering so much energy that it should be cooling more from 12 to 6 and dialling it back when the evening peak starts taking over, even though that’s when the family is home, generating heat and wanting the house cooler.

Then you read Nest’s white paper on HVAC control, and how it now deals with multi-stage heat pumps and new control technology, it gets really complex.

HVAC Control 2.0 uses the thermal model to optimize the control of the HVAC system. It simulates many different ways that it could control the HVAC system. It must choose when to turn the system on, which stage of the system to turn on, how long to run that stage of the system, when to switch to a different stage, and when to turn the system off. It makes these choices while considering the current state of the home, the outdoor weather, and the upcoming schedule.



California headlines/Screen capture

Turning down the thermostat a couple of degrees in today's southwestern US is inconsequential. The Nest thermostat is inconsequential. It is adding layers of complexity to a problem that has to be solved and that it never will. Instead, it is time to get serious and demand radical building efficiency. To turn our homes and buildings into a form of thermal battery; you don’t have to fire up the heat or the AC at peak times because the temperature in them doesn’t change that fast. So a really efficient building can trim the peaks and troughs of our energy production as effectively as any other kind of battery. A properly designed house would need so little cooling or heating that it can be maintained at any time without making a big difference in energy use, without all this complication.

headline screen shot

headlines/Screen capture

It can get people through times like this, when the entire electrical system might melt down at any time. As Dr. Stephen Fawkes noted as on of his 12 laws of energy efficiency:

An exciting energy or energy efficiency discovery in a lab somewhere is not the same as a viable technology, which is not the same as a commercial product, which is not the same as a successful product that has meaningful impact in the world.

The Passivhaus people have a term for it, but it can apply to any system: Fabric First. Oliver Wainwright of the Guardian described it in a look at the Passsivhaus standard:

It is a "fabric-first" approach to energy efficiency, meaning the building does the work, rather than relying on bolt-on renewable energy devices, like solar panels and ground-source heat-pumps. Based on the tenets of super-high insulation, absolute air-tightness, and harvesting the sun's energy through south-facing windows, passive houses aim to keep as much heat inside the home as possible.

The principle also works in hot climates; Insulation keeps heat out as well as in. Thermos bottles keep their contents both hot and cold. Smaller, shaded, solar controlled windows reduce solar gain. Cooling loads become negligible. Simple systems work. The smart thermostat is bored stupid.

The geniuses at Nest and their owners at Alphabet are applying all this brain power to save a few watts when it is really a very simple problem: fix the envelope instead of the technology. Whether it’s Passive or Net Zero or just a pretty good house: Fabric First.