Friends tipped us off to a study recently featured by the Garrison Institute. Researchers from Fraunhofer’s Center for Sustainable Energy Systems found that user-friendliness and energy savings don’t necessarily go hand-in-hand with programmable thermostats. They called these results “both surprising, and suggestive.” (The presentation can be found here.)
Surprising? Not really. Anyone who has every tried to convince their family to try CFLs, or heard their friends discuss how they leave the AC on all day so their home will be cool when they return in the evening, knows that the ease of making a simple change often has little effect on getting people to do it. . Even when people care about and understand the importance of energy savings, they still forget to turn things off when they leave the room. It’s not at all surprising that they don’t set a programmable thermostat, no matter how intuitive it may be.
But suggestive, yes. The presentation covers the three basics of behavior change: motivation (the user wants to change something), ability (the user has the power to change it), and a trigger (they are reminded to actually do it). Programmable thermostats supply the ability, but not necessarily the motivation or the trigger.
In the end, the authors come to the correct conclusion themselves, in the very last bullet point of a 25-slide presentation: “Have technology replace motivation and triggers.” Automation. That’s right, humans, you’re being taken out of the loop and replaced with a computer. Nowadays, occupancy sensors can tell a smart thermostat when a room is empty, and the thermostat can use that information to control AC units, radiators, and lights.
While convincing occupants to manually program their thermostats is a long shot, using occupancy sensors successfully is a slam dunk; current technology can automatically set back heating and cooling temperatures when spaces are unoccupied. These devices originally came from the hotel industry, but are well suited to offices, dorm rooms, small apartments, and any space with single-room HVAC zones, making them a great fit for vast swathes of New York City real estate.
For wall- and window-mounted AC units and for radiators, these devices have been shown to have a 2-3 year payback in NYC. About half the savings is in the heating bill and half in the cooling bill – savings that can amount to up to 30% of the total in the first year after installation.
Using a passive infrared sensor to detect when the room is occupied, the devices don’t turn off accidentally when an occupant is sleeping or still. When a room is empty for a certain time, perhaps 15-30 minutes, they set back the temperature for energy savings. Good ones can also be programmed for an even deeper setback after 24 hours of vacancy, assuming the occupant is gone for the weekend or on vacation. Savings are guaranteed, regardless of occupant behavior or whether they care about energy use.
When the room is reoccupied, the control turns the heating or cooling on again to return the space to the desired setpoint. In summer, occupants may notice the temperature is not what it was when they left, but since the AC is already blowing cold air, they are generally satisfied. The AC may cycle on occasionally to prevent humidity from building up that could cause mold or other issues. In winter, the heat turns back on again as soon as a person comes into the room, and the unit maintains a specified minimum temperature even during long vacant periods.
Three things to look for when you’re shopping for occupancy-based HVAC controls:
1) Recovery-time based setbacks. Rather than set back a fixed amount (say, 10°F), a good system will let you set the amount of time it will take for the room to reach a setpoint after it’s reoccupied (say, 10 minutes). A microprocessor decides how much to let the temperature “drift” during vacancy periods, so that a shaded room on the north side of a building might be set back more deeply than a sunny south facing room. This allows for the greatest energy savings – and the least discomfort for the people in the space.
2) Networked controls. Modern units will “talk” to a central system, with a dashboard allowing analysis and control of units remotely. This allows management to troubleshoot problems before tenants complain, for even greater energy savings and fewer maintenance headaches. For example, AC units that run 100% of the time but can never bring the room to setpoint probably need maintenance. (Or, the window might be open. Luckily, these systems can be “interlocked,” so that the AC turns off automatically if the window is open).
3) Good smart thermostat design. Yes, the study shows that people don’t use their programmable thermostats, even if they are easy to use. But in occupancy-based systems, the automatic controls do the energy-saving heavy lifting. A clean interface and easy-to-understand controls make it easier for a tenant to turn the AC and heat on and off, and set their desired temperature. That saves everyone headaches.
This technology might be difficult to implement in single-family homes, large apartments, or anyplace with a central system serving the whole space. In that case, homeowners might use something like the Nest Learning Thermostat, and commercial owners might try a computer-based Building Management System (BMS) or Energy Management System (EMS).
But for simple spaces with simple heating and cooling systems, bring on the robots.
