Thermostats: Good, Better, Best, and Good Enough (Part 2)

By Bradford E. White, CEM

Today’s technology has given us thermostats that know when you are home, when you leave, or can receive remote communication from you to warm up the house ahead of schedule. This new crop of devices includes the Nest, Lyric, and Ecobee—similar, but different. All use Wi-Fi and either can be, or must be, used with a mobile device, at least to set them up, or to take advantage of certain features. There are more Wi-Fi enabled thermostats than those mentioned here and which are also, to a degree, “intelligent.” But key to these three are the advanced features that monitor your habits, sleeker design, dynamic adaptation versus preset schedules, and, perhaps to an extent, better marketing.

Overview of Wi-Fi Thermostats

The Nest was developed by former Apple engineers and shares the simplicity of operation and design for which Apple is renowned. The Nest looks like a conventional round thermostat, but senses motion; it learns your living patterns: when you are home or away, asleep and awake. Internally, it has a motion detector with a time delay and a grid. A person passing through the viewing range of the sensor will register, but a pet or toddler below view and smaller would not. The Nest sensor system assumes you are not there for just two minutes, but that you are around for some duration. It also responds to your direct adjustment, same as any thermostat. The two functions, coupled together, form a learning pattern for typical days. After a week or so, the pattern is set for the duration: higher temperature during occupancy and lower during away times.

Photo by Grant Sewell via Flickr Creative Commons

The experiences of several user blogs sprouting from the Nest community show that, for families with sporadic schedules, the benefits of the occupancy feature are diminished; the Nest is more often in learning mode than using what it has learned. Homes with regular schedules benefit most. The developers are working on this, according to Nest, with software generation upgrades. One suggestion being considered is to use Bluetooth or other cell-phone-related applications so that proximity versus direct line of sight would be taken into account.

The Nest features an energy conservation notification when you are in a savings mode, known as “the leaf.” Over time, it creates a calendar of energy use by hours of heating or cooling and how many days you earned leaf status for energy savings.

One downside is that, if the thermostat location is not in a regular traffic path, your presence may be requested, but not taken into account. This can be a problem, so the location should be verified as both ideal for a thermostat (away from heat sources, light sources including daylight, and not on an outside wall) and in view of normal daily activities.

Another downside is that the drift (the allowable departure from set-point) is plus or minus three degrees F. This may be too much for some people’s comfort and is not, as of this writing, adjustable. It may be corrected with a software update, and I understand that this is in the works. Both the Lyric and the Ecobee, by comparison, are plus or minus one degree F.

The Lyric is Honeywell’s market entry to compete with the Nest and it learns your living habits. But, instead of a motion detector, it uses your smartphone location with what is known as a “geofence” application to determine not just if you are home, but how far away and in what general direction you are traveling to or from home. One need not be in sight of the Lyric to make oneself known.

One current downside of this feature is that the Lyric cannot tell you how far your fence is from home. If you stay within the fence (your work is nearby), it may think you are still at home and keep the house at temperature even though you prefer to be saving energy. If you stray outside the unknown fence zone for an hour’s errand, it may shut down your heating system prematurely. Honeywell is committed to working out the bugs, but the Lyric is still considered “beta” by many reviewers—promising, but not mature technology. There is also no current data retention for energy use.

Another downside is that you need a three-wire cable, which is the standard two wires plus a common or “C” wire to deliver power to the unit. Absent this, you need to rely on batteries. Current reports have the battery life being about two months, compared to a year or more with today’s standard thermostats. The Lyric is also priced higher than the other thermostats discussed here.

The Ecobee is a more recent Canadian import with many of the same features of the Nest and Lyric, but also has a higher number of features, including additional remote sensors—more than a dozen that can be spread around your home. Ecobee has a more graphic-based user interface and a more refined energy tracking application. The remote sensors in different rooms average the space conditions for a more even temperature and no initial learning period to get the system to start optimizing energy and comfort.

Conclusions

No programmable thermostat by itself will save money, except to the extent that it remembers to turn the temperature set-point down and back up again in accordance with your schedule. A manual thermostat can do that, with your help each time, so think of programmable thermostats as convenience devices.

The clear advantage of the family of Nest, Lyric, and Ecobee is their dynamic approach to your schedule and convenience, especially when you are away from home and decide to return home earlier than planned, as one example. The enhanced convenience is in allowing your remote adjustment.

All Wi-Fi enabled thermostats consume appreciably more power than conventional programmable thermostats. If you only have a two-wire cable, you must rely on batteries alone for thermostat power; if you go that way, buy batteries in bulk.

Were I to install one of these three, it would be the Ecobee. But for now and the foreseeable future, I am keeping my Honeywell seven-day programmable two-wire thermostat with smart recovery. It gives me individual schedules each day, up to four on/off periods per day, and costs a third to half of what the dynamic Wi-Fi enabled thermostats cost. I cannot place a cost savings difference between my Honeywell and the Wi-Fi enabled devices that would justify the additional $150 to $200 premium, nice as they are.

Bradford E. White is an HVAC engineer in Boston with more than 30 years of experience in the design of HVAC systems. Brad is a LEED Accredited Professional (BD+C), a Certified Energy Manager and Certified Energy Auditor (CEM and CEA) with the Association of Energy Engineers, and has been a valued BBR workshop teacher for many years.

© 2015 by Bradford E. White, CEM. Published with permission by Boston Building Resources.