A thermostat that knows when you’re away (review of Verdant V8-BB-7S with occupancy sensor)


Resources used by housing and transportation dwarf those associated by other parts of our “lifestyle.” If you want to be green in deed as well as attitude, you’ve got to take on the way you get around, and the energy used by your house.

In the house, technology can obviate the impulse to nobly suffer to save energy (remember President Carter in his sweater?). Probably the first thing I installed in my family’s house when I moved in was a programmable thermostat.  It saves energy by lowering the thermostat when I’m not likely to be home or wanting heat, and raise it when I know I want it to come on. No more running across a freezing floor at 5:30 AM to turn the heat on.

Now comes a thermostat that takes this idea one step further – incorporating motion and thermal sensors to detect when someone is using the room. If the room hasn’t been occupied for a few minutes, it can lower the programmed thermostat temperature (“setpoint”) by a few degrees.  If the room hasn’t been occupied for hours, it can lower the setpoint even more.  When someone returns to the room, it returns to the programmed setpoint.

It’s a truly simple and promising idea that in some dwellings could save huge amounts of energy.  It comes from Verdant, a company with a Montreal address and a still-incomplete website. There you’ll find a study from a hotel setting where this technology saved 40% of energy consumption.  Of course people act differently in hotels. (I, for one, tend to crank up the heat and luxuriate.)  But you can see the promise.

I’ve been testing a consumer model of their thermostat (the Verdant V8-BB-7S) for about a week and can report that it pretty much works.  This model controls heat for 120-240 volt systems, so it’s a good match for a radiant floor or baseboard heater setup — ideally one powered by green electricity.  (I can’t find any model available for lower-voltage wiring typically used to control household furnaces.) However at least one of the claims on the box is a bit overblown.

The test environment was a newly renovated attic room not served by my house’s main furnace.  It is well insulated with solid panel insulation faced with radiant foil, and has fairly good air sealing.  The room contains a 750 watt hydronic baseboard heater.  I used the thermostat to control this heater.

I was curious about several claims made in marketing the thermostat.  The box says the product can “save at least 30%” on energy consumption, and features “100% reliable occupancy detection.” The prothermostats.com web site adds the claim that it will detect you “even when you sleep.”

I found the thermostat reliably detected my presence or absence on the basis of motion, and prevented the heater from coming on many needless times. I can believe a 30% reduction in consumption could be achieved. If I had been gone a few minutes, it lowered the setpoint 4 degrees.  If I had been gone an hour, it lowered the setpoint all the way to 40 degrees F. These parameters are adjustable by the user.

However, the “100% reliable occupancy detection” was a stretch.  The thermostat did NOT detect occupancy when the room was used for a nap by a small boy. That meant the heat turned off when it should have been on. He was sleeping in a bay of the room out of direct line of sight from the thermostat, but still only about 10 feet away. Not a big problem, IMHO, but a bit of a disappointment for a sensor system that claims to be “100% reliable.”

That little failure raises some interesting questions. Can or should a thermostat be able to distinguish between humans and other living things, such as pets (or extremely bad children, who nominally qualify as living 🙂 ) ? Are there any sources of motion or heat (for example clocks, appliances) that might fool the thermostat into thinking the room is occupied?  Perhaps Verdant needs to add some sort of sensitivity control rather than, in effect, claiming its product has ESP.

(Journalistic note: I sent an email to Verdant asking for clarification of these details, but as yet have received no response.)

I think this is a really useful and promising product that in its present form could save a lot of energy and money. But it’d be helpful if the manufacturer could clarify the capabilities and limitations of what it’s selling.

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The geeky background: According to a comprehensive study sponsored by the Union of Concerned Scientists and published partly in The Consumer’s Guide To Effective Environmental Choices, housing and transportation combined represent 65% of the typical American’s contributions to greenhouse gas emissions, while personal items and services (yup, all of them except food) represent a twiddly 6%.

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