With more stylish and elegant form factors than their predecessors, a digitalized user interface, and mobile application control that allows for more sophisticated scheduling, smart thermostats appear to give homeowners complete control over their home climates. But have they actually improved outcomes when it comes to accuracy, consistency, and efficiency? Have they actually made homes more comfortable? Surprisingly, the answer to that question is often no. The cause? Incompatibility between smart thermostats and HVAC systems resulting in set temperature variance, noisy and inefficient system operation, and the dreaded “thermostat deadband.” Let’s dive into the nature of this communication breakdown and the problems it creates for professionals servicing this space and their customers.

Rapid Growth in Both Smart Thermostat and Inverter Markets

Several contributing factors, such as the adoption of hybrid work models and the exacerbation of heat waves in specific regions of the U.S., have resulted in an emerging trend characterized by individuals spending greater amounts of time at home than ever before. With this increased time inside comes heightened demand for interior climate control and greater usage of heating and cooling resources. This use of energy is expensive, as “using air conditioners and electric fans to stay cool accounts for nearly 20% of the total electricity used in buildings around the world today,” according to a report from the International Energy Agency. Motivated both by rising energy costs and sustainability concerns related to climate change, consumers have grown more desirous of energy-efficient living. One result of the confluence of these trends is the growth in popularity of smart thermostats, the best of which can save homeowners up to 8% on energy bills according to U.S. Environmental Protection Agency (EPA) data used for Energy Star certification. The smart thermostat market has expanded steadily in recent years, with that growth projected to continue through the 2020s.

These trends have also influenced the growth of the market for inverter/VRF HVAC control systems, which offer more sophisticated and efficient control than traditional, single-speed electromechanical units. Unlike their single-speed system counterparts, which operate on an on/off or all-or-nothing dichotomy, inverter/VRF HVAC systems are capable of adjusting fan speed and airflow to provide full heating/cooling when called for but then automatically adjust to keep an environment at a precisely set temperature. It is estimated the global inverter/VRF market will grow from $17.6 billion (2020) to $31.9 billion (2025) at a compound annual growth rate (CAGR) of 12.7%, with the U.S. identified as the fastest-growing inverter/VRF market.

Given the rapidly expanding markets, it would be logical to think the easy interface of today’s smartest thermostats and operational efficiency of the best inverter/VRF HVAC controllers could combine to create an exceptionally comfortable and cost-efficient experience for homeowners and an easily interoperable install for HVAC pros. However, that is strictly not the case.

The Incompatibility Problem Between these Increasingly Popular Products

While smart thermostats come with many user-friendly features, they have not been developed to control inverter/VRF equipment intelligently. In fact, when coupled with a smart thermostat, most features and benefits of inverter/VRF equipment are lost due to lack of adequate two-way communication. These industries have grown in a relatively siloed fashion in the U.S., so even though smart thermostats and inverter/VRF equipment may both be compatible with select protocols, they aren’t able to communicate nuanced commands completely. Put simply, when today’s smart thermostats are connected to connected and energy efficient inverter/VRF HVAC solutions, those systems effectively lose all the features and functionality that make the unit intelligent and default back to operating like a single-speed HVAC system would.

What’s the Result of Thermostat-VRF/Inverter Incompatibility?

Imagine being in your living room, wanting to set the temperature to 68°F. You use a smartphone app to adjust your smart thermostat. The thermostat sends the command to your HVAC system controller, which turns on the system until it reaches about 67°, then off until it rises to 69°/70° before turning on again. This cycle creates the "Thermostat Deadband," resulting in homeowners rarely experiencing their desired temperature consistently. The operation is also noisy, as the HVAC system runs at full capacity each time it restarts. This "all-or-nothing" approach is less energy efficient, similar to stop-and-start city driving versus smooth highway cruising. These drawbacks disappoint homeowners expecting benefits from their purchases and burden installers who must either explain this complex issue or spend time attempting to resolve it.

What Can Be Done to Address the Incompatibility?

Today’s most sophisticated smart thermostats and most efficient VRF/inverter HVAC control units have excellent functionality — they just need to send and receive commands for that functionality more fluently. The growing divide between smart thermostats and HVAC systems has led to issues with temperature accuracy, consistency, and efficiency, resulting in homeowner dissatisfaction and increased challenges for the professionals integrating these systems. However, there are innovative solutions specifically designed to address these compatibility issues. As the demand for energy-efficient living continues to rise, it's essential for consumers and industry professionals alike to explore and adopt these solutions, bridging the communication gap between smart thermostats and inverter/VRF systems. By doing so, we can unlock the full potential of these technologies, creating comfortable and cost-effective home environments while minimizing the negative impacts on our planet.