Smart Thermostat for Residential HVAC Control
Residential Thermostat: Smart vs. Conventional Programmable
A smart thermostat provides advanced energy management features. Capabilities include occupancy sensing, remote monitoring, data analysis, automation, system optimization, and reporting to optimize control of home space conditioning enabled by advanced technology for sensing, computing, and communicating. Some smart thermostats use current weather conditions, forecasts, HVAC equipment type, and a home's historical run-times and performance to create a unique thermal model to minimize heating and cooling costs while maintaining comfort levels.
Item ID: 240
HVAC--Sensors & Controls
Technical Advisory Group: 2012 Smart Thermostat TAG (#6)
Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
Average TAG Rating: 2.6 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:
- I have not been convinced about the value of these for a commercial space. Most commercial spaces can be served well with a simple programmable thermostat (as long as it gets programmed correctly and someone checks it annually).
- Residential smart thermostats do not meet commercial ventilation requirements, and are not a commercial HVAC measure.
- This technology has seemingly captured and inspired an aspect of the marketplace - residential consumers - in a way almost all other technologies fail to do.
- A perfect house would not need it: great envelopes lead to very stable indoor temperatures that may not benefit as much from setbacks, etc. That emphasizes the role of great new construction programs. For retrofits, I'm cynical enough to see more sex appeal than rationale - but see Consumer Reports lab tests recently. I think savings potential is likely to be over-rated, particularly for those who are not strongly motivated to save money by any means possible.
- This seems more like an opportunity for energy efficiency to get into big data - which is why I support it. I'm not sure it saves that much energy per home.
- I think that there is potential for savings or for demand response. We have yet to reliably measure savings.
- These are great for the interactive control and easy interface, but the savings are impacted by the HVAC system in many other ways so the system needs attention to get the savings
- Holds promise for delivering efficiency but needs much more testing in commercial buildings
Programmable thermostats are the baseline technology for residential temperature control. They are required for new construction by most energy codes for homes with forced air heating and cooling systems. Programmable thermostats allow users to schedule heating and cooling temperature setpoints, often for sleep, home/awake, and away periods, each day of the week.
The U.S. Department of Energy (USDOE) estimates that the average homeowner can save between 5% and 15% of their heating and cooling costs by programming a set point schedule for sleep, home/awake, and away periods, compared to maintaining a constant temperature. However, some surveys show that programmable thermostats are successfully used by 70% or less of home occupants. Barriers to energy savings occur when programmable thermostats are not used as intended due to programming difficulties, small buttons and fonts, and hard-to-understand abbreviations. Smart thermostats eliminate these barriers.
Internet-connected thermostats facilitate ease of use by allowing program setup and modification at a web portal accessible by PC, smart phone or tablet. Users can adjust setback periods or temperature setpoints or set vacation schedules remotely. A smart thermostat with machine learning, occupancy sensing, and/or optimization capability should improve efficiency beyond simple set point scheduling.
Smart thermostats cost between $100 and $250. They can be installed by the homeowner or a contractor in homes with Wi-Fi connectivity. ACEEE reviewed national demonstration programs and estimates a 12% annual electrical energy savings (heating and cooling loads) from smart thermostats. Their high estimate is 15% with a low estimate of 8% (ACEEE, 2015). Avista conducted a demonstration using the ecobee smart thermostat at 57 households in Pullman, Washington that produced a whole house annual energy savings of 9.5% (Melton, 2015). The Energy Trust of Oregon installed Nest smart thermostats at 174 homes with heat pumps. Weather-normalized energy savings amounted to 781 kWh/year or 4.7% of household annual electricity consumption (Apex Analytics, 2014) (Apex & ETO, 2015).
Smart connected devices offer the potential to utilities to determine an accurate energy use baseline, identify homes with high heat loss rates, target information and efficiency measure incentives to appropriate households, and provide real time measurement of performance while conducting remote verification of energy savings. Utilities can also obtain demand reductions through making changes in temperature setpoints during periods of peak demand.
Baseline Description: Typical central electrically heated residential HVAC system in the Northwest, with a 7-day programmable thermostat
Baseline Energy Use: 4.2 kWh per year per square foot
Only the technical potential of those homes currently heated by electrical appliances is considered. With new options for multiple indoor units in many styles, it is assumed this technology could be used in conjunction with virtually all residential electric heating systems in the Northwest.
Values for annual electric usage for heating single-family and manufactured homes in the Northwest are taken from the 2011 Residential Building Stock Assessment. Heating usage for multifamily homes is estimated based on the fact that heating energy usage in a multifamily home should be significantly less per square foot than in a single-family home because a multifamily home has significantly less envelope exposure to the outside. The weighted average is calculated by taking the heating Energy Use Intensity (EUI) for each category of home and multiplying it by the total square footage that is electrically heated for that category, summing all of them, then dividing by the total electrically heated square footage in the region. While these thermostats are only applicable to homes with central heating systems, this data will provide adequate rough estimates of energy use (Baylon, 2012).
| Electric Heat || Homes || % Electric Heat || Electrically Heated Homes || kWh/Home for Heat || Avg. sf per home of class || EUI (kWh/sf/yr) || Total sf |
| Single Fam || 4,023,937 || 34.2 || 1,376,186 || 8,116 || 2,006 || 4.0 || 2,760,630,027 |
| Mfr'd. Home || 543,730 || 70.1 || 381,155 || 8,848 || 1,280 || 6.9 || 487,878,054 |
| Multifamily || 863,104 || 84.1 || 702,567 || 2,000 || 766 || 2.6 || 538,166,058 |
| Total || 5,430,771 || || 2,459,908 || || || || 3,786,674,140 |
Weighted Average: 4.21 kWh/sf/yr.
Note: If small commercial applications are added, this prorated value would be higher.
Manufacturer's Energy Savings Claims:
Generally manufacturers claim 20% to 30% savings on heating and cooling costs. Ecobee claims homeowners save an average of 23% of heating and cooling loads annually with their ecobee3. Nest claims that their product can save homeowners 20% to 30% (based on both space heating and cooling energy use). A simulation study by Nest indicates that for uses in Spokane, Washington that utilized the Auto-Away feature for absences and the 1-degree "carving" feature results in heating savings of 10% to 30% when compared to operation with a "hold" baseline. Note that for this simulation, the "hold" temperatures are established at 70 deg F for heating and 76 deg F for cooling (i.e. no scheduled setbacks are employed) and would be characteristic of those who do not program their programmable thermostat.
Best Estimate of Energy Savings:
"Typical" Savings: 12%
Low and High Energy Savings: 8% to 15%
Energy Savings Reliability: 4 - Extensive Assessment
The USDOE estimates 5% to 15% heating savings from a programmable thermostat setback for 8 hours at night (DOE, 2014). Additional smart thermostat energy savings will result from setback during other occupied periods and from cooling setups. ACEEE reviewed national demonstration programs and estimates a 12% annual electrical energy savings (heating and cooling loads) from using smart thermostats. Their high estimate is 15% with a low estimate of 8% (ACEEE, 2015). Energy savings from smart thermostats vary considerably due to:
Weather zones, including year-to-year variations that necessitate heating and cooling degree-day corrections
Use of backup space heating systems, such as wood or pellet stoves
The system management algorithm of the thermostat, such as if the thermostat has strip heat lockout or management for heat pumps
The features available with the thermostat
Household size, number of occupants, and heating system type (heat pump, central forced air)
Home characteristics, such as insulation package.
Puget Sound Energy conducted a demonstration project that included 1,000 test homes and a 1,000 home control group. Provisional savings due to installation of Honeywell VisionPro smart thermostats were found to be 8% of the heating load. Avista conducted a field trial using the ecobee smart thermostat at 57 households in Pullman, Washington that produced a whole house annual energy savings of 9.5% (Melton, 2015). ETO conducted a field demonstration project in which Nest smart thermostats were installed at 174 homes with heat pumps. Weather-normalized energy savings amounted to 781 kWh/year, equivalent to 4.7% of household annual electricity consumption or 12% of space heating energy use. Cooling savings were not considered. Seventy-five percent of participants had a programmable thermostat while 25% used a manual thermostat (75% of manual thermostat users claimed to adjust temperatures at least daily). The ETO sample group and comparison homes were populated by older, highly educated, and relatively affluent homeowners. Interestingly, 20% of participants turned the Nest Auto-Away feature off because it was triggered when people were at home (Apex Analytics, 2014) (Apex & ETO, 2015).
A “standard” programmable thermostat is expected to save approximately $180 per year, according to Energy Star. A Smart Thermostat which is replacing an analog thermostat would be expected to achieve a level of savings at least as high as a programmable thermostat, with the potential for higher savings due to increased user engagement and the more refined management capabilities of the smart thermostat.
The availability of a programmable thermostat does not guarantee energy savings; savings depend on how the device is programmed and used in each household. Barriers to energy savings occur when programmable thermostats are not used as designed due to programming and design issues, such as small buttons and fonts, abbreviations that are hard to understand, and difficulty and details involved in programming. Studies indicate that only about 69% of homeowners in the region use manual control or programmable thermostats to enter a heating setback.
Smart thermostats are designed to engage the user’s behavior to increase efficiency of HVAC system operation. Nest promotes conservation by displaying a green leaf icon when an economical setpoint is selected. Ecobee provides a programming interface that is similar to that of a smartphone application.
Energy Use of Emerging Technology:
3.7 kWh per square foot per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
For purposes of Northwest electric utility programs, technical potential is limited to residential electrical heating systems that are controlled by central thermostat. This eliminates those households with baseboard electric heaters as they utilize zone control. Smart thermostats are also appropriate for small commercial enterprises; however, programmable thermostats already serve 33% of the conditioned floor space in these applications and energy management systems control an additional 37% of this conditioned floor space (CADMUS, 2009).
Single-family homes: 54.1% have forced-air systems, and 9.8% of these are electric: (4,023,937 households x 0.541 x 0.098 x 2,006 sf/house) = 427.9 million square feet
Manufactured homes: 11.5% have electric forced-air systems: 80 million square feet
Multifamily homes: 79% are forced-air, and 84% of these are electric: 439 million square feet
If small commercial square footage is included in this estimate, the technical potential would increase, but the average savings per sf would be reduced due to lower occupancy rates in the commercial facilities.
Total: 946 million square feet
Regional Technical Potential:
Source: (Baylon, et. al., 2012)
0.48 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: square foot
Emerging Technology Unit Cost (Equipment Only): $0.12
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.04
Baseline Technology Unit Cost (Equipment Only): $0.05
Smart thermostats are available at prices ranging from $100 to about $300, depending on product features. Professional installation will add to the cost, but most claim to be user-installable. Avista operates a smart thermostat rebate program and reports that about 30% of their participants are “do-it-yourselfers.” Typical contractor thermostat installation costs are about $100. Many of the contractor installed units occur in conjunction with a furnace upgrade.
Assume a first cost of $250 divided by 2,006 square feet (or $0.12/sf). Existing programmable thermostats can range from approximately $25 to over $100. Assume a baseline technology cost of $100 (or $0.05/sf). Installation costs are taken as 0.7 x $100 or ($0.035/sf).
Users may pay a monthly fee to their internet service provider or thermostat web hosting site, which partially offsets their energy cost savings.
Note: This is a deemed measure under the October 1, 2014 BPA "Energy Efficiency Implementation Manual." The deemed amount ranges from $105-$160 per unit.
Simple payback, new construction (years): 1.5
Simple payback, retrofit (years): 3.5
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
Cost-effectiveness is still to be determined. If the additional features of smart thermostats that are not provided by programmable thermostats prove to be effective in saving energy, then cost-effectiveness can be calculated more accurately.
Smart thermostats have two specific capabilities. First, they must be fully programmable and equipped to run programs for each day of the week using daily occupancy schedules and temperature setpoints, and allow for the use of setback or setup temperatures during unoccupied periods. Second, they must provide external communications and remote programming capability via Internet connectivity to a personal computer, smartphone, or tablet.
Many of the thermostats that monitor local weather and forecasts also use the information to operate the system more efficiently. For instance, the Nest thermostat checks the forecast before implementing a setback called for by the user. If setting the temperature back will cause the heat pump to use auxiliary heat in the morning, but it can use the compressor heat to keep it warm in the evening, it will keep the house up to temperature to minimize the use of auxiliary heat.
To eliminate programming obstacles, the Nest features self-learning capability—meaning that it learns the occupants’ behaviors and preferences on a weekly basis. The occupants train the thermostat by using it as if it was a manual thermostat, simply turning it to the setting they want when they get up in the morning, leave the house, come back or go to bed. After a week or so, the thermostat will begin building a model for user preference, and will set the temperature according to predictions of that model.
Additional Nest’s features include an "Airwave" feature turns the air conditioner off a few minutes early but keeps the fan on to circulate residual cool air from the coils to get some extra "free" cooling. The manufacturer claims the compressor can run as much as 30% less. Manufacturers have web access to each thermostat and can update software for an individual thermostat, for all thermostats, or can make custom changes to a group of thermostats, such as in a specific geographic region.
nest, nest thermostat
Filtrete, Model 3M-50
Intwine, IETC 220
Bayweb, Internet Connected Thermostats
Insteon, Remote Thermostats
Schneider Electric , Wiser
Bryant , HouseWise
Programmable thermostats or manual operation represent the baseline practice for setting home comfort levels. Programmable thermostats typically allow users to enter a heating or cooling temperature setpoint and a night setback or setup temperature for each day of the week. Most devices contain an override and allow the user to specify a vacation or away setting. Programmable thermostats typically include a warm-up or intelligent recovery feature that starts the HVAC system in advance so the zone is at the desired temperature at the prescribed time. For residential and commercial applications, the Washington State Energy Code requires seven-day comfort control with four control slots per day, a minimum 5°F deadband, vacation setback mode, auto-start/intelligent recovery, and heat pump strip heat lockout capabilities. Some energy codes now require that the thermostats in new homes be pre-programmed with appropriate heating and cooling temperature setpoints, setbacks, and setups.
Standard residential programmable thermostats display information about room temperatures and thermostat setpoints, but do not allow access to or reprogramming through a web portal or with a personal computer, smartphone, or tablet.
Smart residential thermostats are readily available and are offered by many manufacturers. However, the products are relatively new and are in constant development, and updates often occur more than once a year. Several of the companies update the software in the thermostats already installed in the field via the Internet when they offer a software upgrade, so all installed thermostats have the latest software. Smart thermostats vary by the technologies used for sensing indoor conditions such as occupancy, and in the software used for responding to data and controlling indoor environments (ACEEE, 2015).
Most smart thermostats are programmable through a touchscreen or by turning a spinning ring, and allow programming and modification through external communications such as wireless internet connectivity and/or access through mobile applications. The Ecobee supports remote sensors (temperature and occupancy) in other rooms of the house and also displays local weather forecasts. The Honeywell Lyric has a “geofencing” feature that can monitor your location and go into power savings mode when you are away and turn on your heater or cooling system when it detects you are returning home. Another Honeywell product has voice command capabilities so one can shout across the room to make it cooler. Quirky’s Norm opts for full Smartphone control of their thermostat. A Smartphone App is available for various products to walk users through the installation process.
Smart thermostats come with a variety of features to make them more user-friendly and effective than standard programmable thermostats. These features range from home energy use displays, interview-based programming, remote access for comfort control, adaptive learning, and full home energy automation with connection to the smart grid. Smart thermostats use current weather conditions, forecasts, HVAC equipment type and a home's historical run-time information to create a unique thermal model that makes optimal decisions to minimize heating and cooling costs while maintaining comfort levels.
A self- or machine-learning thermostat resolves problems related to occupant difficulties with thermostat programming or cloud computing. Simplicity of operation, pleasing aesthetics, flexibility and accessibility should entice people to use the smart thermostats currently available on the market. Other smart thermostat manufacturers have adopted different approaches to facilitate thermostat programming. Honeywell's Prestige 2.0 offers voice activated programming. Recent development efforts provide services for utilities, such as peak load management and equipment audits and maintenance alerts.
Products are available that are compatible with the following systems :
- Forced air, radiant, heat pump, ductless heat pump, oil, gas and electric
- One- or two-stage conventional heating
- One-stage conventional cooling
- One-stage heat pumps with auxiliary heat or two-stage heat pumps without auxiliary heat
- 24 volt systems
- Zoned systems (systems with multiple thermostats).
The Venstar ColorTouch Wi-Fi smart thermostat allows users to display family photos and text messages. Their advertising states that, with customizable screensavers and wallpapers, this smart thermostat serves as a digital picture frame. If installed in a hallway, it also serves as a night light.
Some Wi-Fi thermostats can access local weather stations and provide a weather forecast, and display outdoor and indoor temperatures (such as the ecobee Si). Some thermostat models also provide humidity sensing. Other smart thermostats provide an alert or service reminder when a maintenance action should be taken.
Some equipment manufacturers attempt to eliminate thermostat programming difficulties by offering voice-controlled thermostats. This simplifies thermostat interactions involving initial setup and out-of-schedule requests. One example is the interview-based programming provided by the Honeywell Prestige 2.0 Comfort System. The thermostat asks questions of the homeowner and then programs itself based on responses received. Many homeowners may prefer this “set and forget” approach to home energy management. This feature and the ability to remotely program the smart thermostats are also desirable for elderly or motion-challenged people.
Familiar, easy, and intuitive drop-and-drag techniques are generally available for establishing setpoints and setbacks; this ease in programming should prompt more users to take advantage of the thermostat's programmable features. Some thermostats allow group programming when more than one thermostat is installed in a home or business.
There are some devices that are part of more comprehensive home management systems which can incorporate home security elements, including remote video monitoring.
Smart thermostats offer may benefits to utilities that operate energy efficiency and demand response programs. The available of customer analytics can assist utilities to target their marketing and customer engagement programs. Energy consumption and an accurate heating and cooling energy use baseline can be obtained without intervention with kW and kWh data available in real time by geographical area or customer segment. Home heat loss rates can be determined through examining ramping rates and interior and ambient temperatures, and HVAC system capacity can be ascertained. Smart thermostats can also be used in utility measurement and verification (M&V) efforts and allow for changing temperature setpoints that produce reductions in power for demand response programs. Work is underway to establish standards for data collection, analysis (on-site or in the cloud) and communication.
End User Drawbacks:
The first cost is relatively high, and payback on an energy-savings basis alone may be difficult to justify. A smart thermostat may decrease efficiency of HVAC system operation, if the homeowner had previously used a manual or programmable thermostat effectively.
Some users are concerned about reduced security and external control of home systems due to hackers. See "Hacking and attacking automated homes" (Smith, 2013) and "Breaking and Entering: Hackers Say “Smart” Homes are Easy Targets" (Roberts, 2013).
Operations and Maintenance Costs:
Some manufacturers of smart thermostats require that a homeowner pay a monthly fee to access their thermostat via the manufacturer's web portal. Others require an additional payment to enable remote access. It is assumed that most purchasers of smart thermostats already have access to wireless service.
Anticipated Lifespan of Emerging Technology: 15 years
The effective life should be about the same as other electronic equipment - about 15 years. The manufacturer expects that even existing thermostats will get software updates as they become available, which will help alleviate the concerns of existing thermostats becoming obsolete, which may a big concern about a brand new "smart" product.
The Northwest Power and Conservation Council Regional Technical Forum uses a 15-year measure life for electronic thermostats. Some electronic devices (such as cell phones) may have a shorter life due to obsolescence with respect to functionality rather than components wearing out. Smart thermostats are capable of being updated by their manufacturer while in the field (similar to computers).
Many of the smart thermostats are poised to take on additional home energy management tasks. When coupled with an AMI meter, smart thermostats are already capable of displaying real time energy consumption, the premise’s electrical energy use over the last hour, and total electrical energy use and costs on an hourly, daily, or weekly basis. Perhaps the issue is not which technologies compete with smart thermostats, but how much smart thermostats may begin competing with each other and other devices, such as home energy monitoring and management systems.
Reference and Citations:
Embracing a Bottom-up Approach to Load Control Programs
Electric Light & Power
Nest unleashes the power of its smart thermostat with data-driven services
Meier, et. al.,
Thermostat Interface and Usability: A Survey
Lawrence Berkeley National Laboratory
Peffer, et. al.,
How People Use Thermostats in Homes: A Review
Building and Environment
Meier, et. al.,
How People Actually Use Thermostats
American Council for an Energy-Efficient Economy
Baylon, et. al.,
2011 Residential Building Stock Assessment: Single-Family Characteristics and Energy Use
Northwest Energy Efficiency Alliance & Ecotope
Field Evaluation of Programmable Thermostats: Does Usability Matter?
Fraunhofer Center for Sustainable Energy Systems
FPL Residential Thermostat Load Control Pilot Project Evaluation
Applied Energy Group, Inc.
Can Smart Thermostats Rise from the Ashes of Their Programmable Predecessors?
Nest Learning Thermostat Efficiency Simulation: Update Using Data from First Three Months
Thermostat cycling vs. temperature offset: customer comfort and load reduction analysis
The Nest Learning Thermostat - Good or Not So Much?
Home Energy Pros
Interesting forum discussion on the Nest thermostat
Home Energy Management Standing Technical Committee Presentation
Energy Efficiency and Renewable Energy
Reinventing the Wheel
Tech Beat: What's So Hot About Smart Thermostats
Alliance to Save Energy
A thermostat that learns? Three months with the Nest
New features save energy & make money. Automatically.
What is Rush Hour Rewards?
Nest Labs, Inc.
Demand Response Enabled Appliances/Home Energy Management System
Upgradeable Setback Thermostats
California Energy Commission
Smart Grid Thermostat Project
Iowa Association of Municipal Utilities
Move over Siri. Introducing Iris, Lowe's smart home hub
Comcast enters smart thermostat game
The Smart Grid: An Estimation of the Energy and CO2 Benefits
Pacific Northwest National Laboratory
4 smart thermostats that save money and energy
Is a Smart Thermostat Right for You?”
Consumer Demand Up for Home Energy Management Systems
Smart Grid Insights
The 50 Best Inventions of 2009
The State of IP (Web-Based) Enabled Thermostats
Baylon, et. al.,
Residential Building Stock Assessment Reports
Northwest Energy Efficiency Alliance & Ecotope
Northwest Commercial Building Stock Assessment (CBSA): Final Report
Prepared by the CADMUS Group for the Northwest Energy Efficiency Alliance
Energy Saver: Thermostats
U.S. Department of Energy
Energy Trust of Oregon: Nest Thermostat Heat Pump Control Pilot Evaluation
Prepared by Apex Analytics LLC for the Energy Trust of Oregon
Evaluating Smart Thermostats' Impact on Energy Efficiency and Demand Response
Electric Power Research Institute
Hacking and Attacking Automated Homes
Breaking and Entering: Hackers Say “Smart” Homes Are Easy Targets
New Horizons for Energy Efficiency: Major Opportunities to Reach Higher Electricity Savings by 2030
American Council for an Energy Efficient Economy
An Approach to M&V for Smart Thermostats Using Daily Average Temperature and Run Time
Bonneville Power Administration, presented at ENERGY STAR Climate Controls Stakeholder Workshop, San Francisco
Burmester, and others,
Big Data, Cloud Computing, and Real-Time Control: New Options for Integrated Demand Side Management and Customer Engagement
Energy Solutions, presented at the 2014 ACEEE Summer Study on Energy Efficiency in Buildings
Apex & ETO,
Nest Thermostat Heat Pump Control Pilot: Evaluation Findings
Apex Analytics and Energy Trust of Oregon Presentation at AESP-NW, May, 2015, Conduit NW
Pacific Northwest Smart Grid Demonstration (PNSGD) Project Overview & Transactive Energy
Pacific Northwest National Laboratory, Presented to PNWER Summit – Energy and Environment Working Group Session