A basic, off-the-shelf, thermostat employs one wire to command each power, fan, heating and cooling operation in a HVAC system. It is an inexpensive, low-tech way to put comfort control on a customer’s wall.

 But the problem with a basic, direct-wired thermostat is that up to 18 separate wiring connections may be necessary in order to reap the full benefits of the heat pumps, furnaces and air handlers deployed in a home. Installers must spend a lot of time to make sure each connection is properly wired and the system is properly configured. And after making all those connections, the customer is still left with a thermostat that is only capable of turning components on and off. On-off cycling is an inefficient way to control HVAC equipment — even if done with a programmable thermostat that gives the customer numerous scheduling and setback options.

Today, many customers want a smarter thermostat that makes them feel more in control of their home environment. After all, almost 50 percent of the average home’s utility bill comes from heating and cooling costs. Every British thermal unit saved is good for consumers’ pocketbooks — and the planet.

That’s why tech-savvy customers easily see the value of going beyond basic programmable thermostats. They like a thermostat with Wi-Fi connectivity that lets them adjust temperature settings with their smartphones. And they can get notifications about filter changes, airflow obstructions and other conditions to alert their dealer to ensure the system is working efficiently. For homeowners in California, building energy efficiency standards require all thermostats to have the capability to respond to demand-response signals from utility companies over the internet. This feature allows automatic thermostat set point adjustment during high electrical demand periods to reduce electric consumption and the need for brownouts.

Given the benefits of more intelligence and connectivity, several third-party “smart” thermostats have entered the market with a big splash. Many of these thermostat manufacturers promise that the homeowner can unscrew the old thermostat and install their new one in about a half hour. Smart thermostats can also learn homeowners’ habits to create a customized schedule without needing to manually program. Energy-saving opportunities and reports make the customer feel good about the electricity and natural resources they saved. At the same time, these are only scratching the surface of efficient, reliable and comfort-improving control. 

smart thermostats

For homeowners in California, building energy efficiency standards require all thermostats to have the capability to respond to demand-response signals from utility companies over the internet.

Creating connections that communicate

Data is crucial to improving comfort, efficiency and reliability of equipment. While connectivity to the internet certainly improves accessibility to systems, the richness of the information being delivered drives value.

As helpful as connectivity and smart features are, concrete benefits are limited if the thermostat cannot communicate with system components to use their full means to condition the space efficiently.

Advanced HVAC equipment offers more energy-saving capabilities than ever before, such as:

  • Fans that can vary airflow across the coil to improve dehumidification
  • Compressors that can modulate capacity to match the cooling load
  • Heat pumps integrated with gas furnaces to provide an economical dual-fuel heat source
  • Dynamic component status and faults
  • Self-configuration
  • Maximum of four wires required for system connectivity (point-to-point)

But to tap these abilities, HVAC components must have the intelligence to talk to thermostats, and thermostats need to be able to communicate with the system.

Serial communication unlocks the full potential of a HVAC market system. It delivers two-way messages that allow each of the critical system components to react and adjust to the changing environment in complete harmony. Because communicating control is crucial to system performance, the Environmental Protection Agency requires its Energy Star program’s most efficiently rated products to include a thermostat, or an on-board controller, designed to coordinate operation of the entire HVAC system.

The indoor and outdoor units of a split system have a multitude of sensors and switches that ensure reliable operation. These sensors are invisible to third-party thermostats. While the components are critical to each of the individual parts that make up the system, the integration of these mechanisms offer new insights and control of the system that improve reliability, efficiency and comfort.

The Hx, a touch-screen thermostat from York, is one model that allows this information to flow beyond the isolated component and engage the system as a whole. The acute knowledge of system health and operation is what gives communicating controls a distinct advantage over third-party products. It also provides a platform to execute more intelligent operation for advanced systems.

With increased efficiency standards and an energized customer base demanding a higher level of comfort, communications becomes essential to system design. As technology requirements increase in order to deliver on these demands, complexity for installation, service and control must remain simple.

For example, with some Wi-Fi thermostats, the installation involves just four standard 18-gauge thermostat wires configured the same way in any system being installed. At startup, the thermostat will “discover” the system components and configure the attributes of the system based on equipment that was installed. The connections, information sharing and commands to each component are made logically, not physically.

smart thermostats

Wiring diagram for fully communicating system components. A+ and B- are used for serial communications. Diagram courtesy of Johnson Controls.

Contractors and customers are more comfortable

With full system communication, thermostats such as the Hx and others ensure optimum equipment performance. Moreover, it enables all communicating components to be automatically and properly configured and calibrated and faults are displayed with detailed readouts specific to the component. 

This information is generating new means of control, service and benefits that surpass the systems of yesterday. Thanks to communicating-capable HVAC equipment and control, homeowners enjoy more consistent temperature throughout their home and greater system reliability. Contractors enjoy more accurate and faster connections to communications-capable air conditioners, heat pumps and air handlers. Plus, HVAC construction contractors can give customers what they really want — the feeling of being in touch with a HVAC system that can deliver maximum comfort and energy savings.  

smart thermostats