The Nest learning thermostat has attracted much interest since its launch in 2011 – firstly because of its tenuous connection to Apple (being launched by ex-Apple employees) and secondly with its uniqueness in being a “learning” thermostat that learns from users’ behaviours. And not least its takeover in early 2014 by Google. [Engerati-The Google Smart Home Play]
Programmable thermostats are generally regarded as offering users around 20% energy savings, but according to Nest, in real homes the numbers just didn’t add up. In a new white paper Nest has published the results of three studies indicating savings of up to 17.5%. One is an internal study and the other two are independent.
The internal study was undertaken combining energy usage data collected through the MyEnergy service (a company acquired by Nest in May 2013).
Based on data from 624 homes for the electric analysis and 735 homes for the gas usage analysis across a total 41 US states, the average annual electricity savings were 585kWh, equivalent to 17.5% of air conditioner usage, compared to pre-Nest HVAC usage. The average annual natural gas savings were 56 therms, equivalent to 9.6% of heating usage.
Based on these figures, the average dollar savings are estimated in the range US$130 to US$145 per annum – translating into the two-year or less payback for the US$249 device.
The study also found that average Nest users who don’t sign up for MyEnergy may have up to about 2% more savings potential than the MyEnergy customers, as the latter, being interested in tracking their energy use, tend to be more energy conscious and efficient anyway.
Oregon heat pump pilot
In the fall of 2013, the non-profit Energy Trust of Oregon had Nest learning thermostats installed in 185 homes heated by heat pumps. Programmable thermostats are generally not recommended in this application, according to the US Department of Energy. However, those customers experienced an average annual reduction in electric heating use of 781kWh, equivalent to 12%, relative to their pre-Nest usage.
The majority also expressed satisfaction with the device and reported feeling more comfortable after its installation. Interestingly more than a third also thought the Nest thermostat was worth the full retail price even if it had provided no energy savings at all!
Indiana utility pilot
The third study was from a pilot undertaken by Vectren Energy in Indiana and involved a comparison of the Nest learning thermostat with standard programmable thermostats installed in 300 homes each. Homes that received a Nest thermostat recorded average annual electricity savings of 429kWh, equal to 13.9% of cooling use, and average annual natural gas savings of 69 therms, equal to 12.5% of the heating use. The respective savings at homes with the standard programmable thermostats were 332kWh (13.1%) and 30 therms (5%). Particularly notable is the more than double heating energy saving with the Nest device.
Real world savings
Nest says the results of the study indicate average savings of 10-12% on heating bills and 15% on cooling bills.
However, savings can be expected to vary significantly between homes, in particular due to variations in how temperatures are set prior to thermostat installation, as well as due to occupancy patterns, house characteristics and climate.