Thermostats control HVAC operations to ensure your comfort, and, when used correctly, they can cut energy costs. Although different types of thermostats have been popular in commercial and industrial facilities, the newest generation of cloud thermostats (also known as smart or internet-connected thermostats) will be the standard in HVAC controls going forward due to their improved convenience and features.

What are the options?

There are three main types of thermostats: electromechanical, digital (also referred to as electronic), and cloud. Electromechanical thermostats have almost no features beyond temperature regulation. However, digital and cloud thermostats are more advanced and offer features like improved scheduling, automated load management, and better humidity control.

Electromechanical

Electromechanical thermostats use bimetallic thermometers—a strip made up of two metals that bend in different directions at higher or lower temperatures—and mechanical switches (which are usually filled with mercury) to regulate temperatures (figure 1). Their programming features are limited, and the devices are difficult to maintain and secure. Electromechanical thermostats are outdated and rarely found in the commercial sector anymore.

Figure 1: Honeywell electromechanical thermostat

The round model shown here used to be the most popular electromechanical thermostat, but there were also many rectangular models. To change the temperature, you turn the dial.
Photograph of a round electromechanical termostat with dial that shows actual temperature and set temperature.

You can program some electromechanical thermostats to a few set temperatures for different times of day. Programmable thermostats operate with a physical clock and pins that indicate the desired times for temperature changes.

If you replace an electromechanical thermostat, give it to a recycling program or organization such as the Thermostat Recycling Corp. to make sure the mercury is disposed of properly.

Digital

The main differences between digital and electromechanical thermostats are that digital thermostats:

  • Use electronic temperature sensors and microprocessors
  • Have digital readouts for the temperature settings and programming features (figure 2)

Figure 2: Honeywell digital thermostat

Digital thermostats have a display screen and buttons instead of the physical dials that electromechanical thermostats have.
Photograph of a digital thermostat. It has a digital display, toggles to turn the fan on or off and the system to cool, off, or heat. It also has buttons to program the system.

Digital thermostats can effectively save energy and manage comfort if you properly program and support them. However, building managers often don’t know how to correctly program and maintain the thermostats, and building occupants change settings without permission.

Many digital thermostats offer features such as programmability, peak load management, and humidity control.

Programmability Not all digital thermostats are programmable, but those that are offer more programming options than electromechanical thermostats. Some devices have 5-2 programming, which allows users to set separate programs for the weekdays and weekends. Seven-day programmable thermostats can run a program for each day of the week.

As the Lawrence Berkeley National Laboratory report How People Actually Use Thermostats (PDF) describes, programmable thermostats failed in the residential sector because residents didn’t use them the way designers intended. Residents didn’t achieve the energy savings they expected, and, in some cases, their energy usage actually went up. Though there aren’t many similar studies of commercial programmable thermostats, the commercial sector likely had comparable experiences.

Utility peak load management Generating additional electric capacity is most expensive for utilities during peak load periods, so utilities will use programmable thermostats that communicate over a network to reduce power draw. During a peak load period, the utility sends out a signal that either adjusts thermostat setpoints or cycles the heating or cooling device on and off for a limited time. Utilities usually offer customers a bill credit to encourage them to participate in these load management programs.

Humidity control Some thermostats can sense and maintain humidity levels.

Intelligent recovery Some digital thermostats sense how long it takes HVAC systems to recover after a setback or setup period and activate early to achieve the temperature setpoint by the desired time.

Security Most digital thermostats are equipped with security features that protect them from unauthorized tampering. Some have two levels of security: The first requires the use of a PIN to access all options and settings; the second lets users change temperature setpoints without entering a PIN but locks all other options and settings.

Service reminders The most common reminder is a notice to change batteries, air filters, or air cleaners—based on either an HVAC run time or a set interval. Some thermostats also have alerts on the thermostat screen for humidifier maintenance.

Cloud

Cloud thermostats enable programming and multistage scheduling via the internet. They also have digital temperature sensors and can store your device’s temperature settings and history online. Cloud thermostats typically have large display screens and few or no buttons (figure 3).

Figure 3: Ecobee cloud thermostats

Though Ecobee is primarily a residential smart thermostat manufacturer, it also markets to business customers. Customers can choose from a handful of thermostat models, depending on their needs, and use Ecobee’s SmartBuildings solution to centrally manage devices, even across multiple buildings.
Photograph of three different Ecobee cloud thermostats.

Much like advanced digital thermostats, cloud models are password-protected, offer humidity-control options, and can help utilities manage peak loads. In addition, some cloud thermostats incorporate various features such as sophisticated programmability and auxiliary inputs so you can connect to a building automation system or other equipment and sensors. If you’re using all of the features a cloud thermostat offers, you could potentially save up to 50% of your HVAC energy consumption compared to using a standard digital thermostat.

Programmability The programming capabilities of cloud thermostats are more advanced than those of digital thermostats. They go beyond the 5-2 programming option, offering 365-day programming. You can even schedule special holiday settings for five years out.

Utility peak load management With your permission, utilities can connect to your thermostats and alter your setpoint temperature in heating or cooling events. You can easily access online the reports that include the demand offsets from such events.

Internet connectivity An internet connection gives you online access and data reporting and allows you to control and monitor settings remotely with any device that has internet access—including computers, tablets, and smartphones (figure 4).

Figure 4: How cloud thermostats work

This diagram illustrates how web-enabled devices connect to cloud thermostats. You can communicate with cloud thermostats, manage settings, and analyze history with a smartphone, tablet, or computer.
Illustration showing how cloud thermostats work. The internet connects to web-enabled devices, like tablets and smartphones, through an ethernet cable or Wi-Fi connection. The internet also connects to an internet-connected thermostat via an ethernet cable or Wi-Fi connection. The thermostat connects to the building's HVAC equipment via a copper wire.

History and analysis Unlike digital thermostats, cloud devices save the history of HVAC use online. You can access and analyze the stored data to identify use patterns and diagnose failures. In-depth and consistent data recording can help you troubleshoot problems such as imbalanced heating.

Auxiliary relays Some cloud thermostats come with two auxiliary relays that can control other devices such as humidifiers.

Intelligent recovery Cloud thermostats turn your HVAC equipment on to reach a set temperature by a certain time, and some even factor in the outside temperature when computing their appropriate start time.

Notifications You can set notifications to alert you about extreme building temperatures and parts requiring maintenance. Digital models display a limited number of reminders based on HVAC run time or set intervals, but cloud thermostats can send you email alerts based on the live performance and historical performance of the HVAC system.

How to make the best choice

Cloud thermostats not only offer many valuable features at a low incremental cost, they also save energy. The Bonneville Power Administration’s Measure Summary Report: Web-Enabled Programmable Thermostats illustrates cloud thermostats’ energy-saving potential. It noted one particular instance of 50% energy savings when a digital model was replaced with an internet-connected thermostat.

When replacing a thermostat, make sure the new thermostat is compatible with your existing HVAC equipment. Some equipment—such as line-voltage heating systems—may require specific technology in the thermostat.

What’s on the horizon?

The next frontier for thermostats is combined HVAC and lighting controls, where you can remotely control HVAC and lighting settings with a single application. As with cloud thermostats, cloud lighting controls already exist and have benefits such as energy savings and maintenance alerts. It seems likely that manufacturers of cloud lighting or cloud thermostats will eventually design a product that will combine the features of the two products into one user-friendly package.

Who are the manufacturers?

For those interested in upgrading, the following manufacturers produce cloud thermostats:

These companies make the software and apps that support cloud thermostats:

Neither this list nor any mention of a specific vendor or product constitutes an endorsement or recommendation by the authors, nor does any content in the Business Energy Advisor constitute an endorsement or recommendation, explicit or otherwise, of the technology-related programs mentioned herein.

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