Staying Ahead Of The Game

There is a long history to radiant floor heating, dating back to at least the Roman Empire when subfloor fires where used to generate heat. It was not until the invention of cast iron boilers that water was used as a heat transfer medium. Mercury bulb thermostats controlled these early radiant systems. When mixing applications were required for hydronic floor heating, tempering valves were used as mixing options to lower the boiler supply temperature. 

Experience and theory eventually challenged the practice of a fixed boiler temperature and inspired further innovation. From that point on, electronic control of boiler operation, system pumps and mixing devices paved the way, first using analog electronics and more recently microprocessors.

Today’s radiant controls are easier to use, access more information and protect equipment in order to optimize system performance and increase comfort. As the radiant heat industry has responded to advances in technology, controls have evolved to meet or exceed the growing and diverse expectations of today’s HVAC applications. For any radiant configuration, you will likely find a control solution to make it work – or one to make it work better. 

When radiant controls were originally introduced the results seemed revolutionary. They accomplished what was expected at the time: to supply heat when needed, efficiently if possible, without manual intervention. Installers used dials to enter a few static parameters, erring on the safe side of design conditions. Boilers always ran hot and heat output was controlled by cycling the equipment on and off. Spaces experienced temperature swings, fluctuating from cold to hot as the thermal mass slowly cooled or warmed. These controls were designed for automation without consideration for efficiency or comfort, and it was not long before they were deemed unsatisfactory.

With the introduction of electronic controls came the first milestone – the introduction of outdoor temperature reset. This concept was based on the fact that a building’s heat loss is proportional to the outdoor temperature and efficiency can be gained by varying the supply temperature accordingly. Since outdoor temperatures do not typically experience sudden swings, the system delivered a stable, continuous heat supply; as such, outdoor temperature reset quickly gained favour. This control feature enhanced the performance of heating systems, but failed to consider internal gains and losses from less predictable variables such as people, equipment, and the sun. Although radiant systems became far more stable and efficient with outdoor temperature reset, they were blind to indoor reactions and thus still at risk of under and overheating.

New ideas for improving radiant control continued to generate change. With increasing demand for radiant floors, mixing methods were considered. Tempering valves were used to provide cooler water temperatures, unfortunately, these valves did not protect boilers from corrosion caused by low temperatures. To provide boiler protection, motorized three-way and four-way valves operated by outdoor temperature reset controls were introduced. Electronic controls also opened low cost opportunities for other methods for mixing, such as variable speed injection systems. Controls were designed to vary the speed of standard off-the-shelve circulators to provide mixing capabilities while protecting the boiler.

As the capability of radiant controls advanced, so did the complexity of residential designs. Modern homes were built with far more rooms than those in previous generations, and architectural features such as vaulted ceilings and large windows became common place. Now more than ever, creating a ‘perfect’ system with reduced energy costs requires the ability to continually react to varying outdoor and indoor environments. With microprocessor technology, new control features were possible to keep pace with growing design demands.

Using communication between control points became the new industry benchmark. This generation of radiant controls used indoor temperature feedback to share real-time measurements to determine the exact heat supply required for each room and coordinate heating cycles through zone synchronization. These features offered significant improvements in comfort and efficiency, especially in large residences with many purpose-specific rooms.

Hydronic designs were simplified by grouping rooms with similar construction, location and user frequency together in a single zone. To prevent the zones from making random boiler demands, communicating controls received thermostat demands, set the appropriate water temperature, and determined the on-times for each cycle length. Zones were satisfied with far fewer cycles on the mechanical equipment plus comfort and efficiency were increased through better control.

In addition to communication, microprocessors enabled the development of settings to protect equipment. The protection feature in early radiant controls was limited to a boiler minimum dial setting. Current controls not only featured boiler minimum settings, but also managed mixing and staging operations to maximize efficiency while protecting both the boiler and the floor installations.

Thermostats now maintain set floor temperatures with connections to auxiliary slab sensors. Floor maximum settings limit the surface temperature to prevent thermal damage; floor minimum settings enhance comfort by warming surfaces in zones like bathrooms. If more heat is needed during the colder months, the control will direct the operation of a second stage of heat to reach the target temperature. Installations are protected and comfort is maintained, because today’s customers demand both.

Radiant controls have certainly advanced in response to technology, but also in response to a society that has moved towards customized applications. Older radiant controls were stand alone units designed to manage individual requirements in an uncomplicated heating arrangement. Today there is an expectation to control any design, need or preference; controls must be diverse and expandable to remain viable solutions. By way of communication, a myriad of heat sources and outputs can now be networked through communication into a highly efficient, custom system. Solar collectors and heat pumps staged with backup boilers, snow melt operations, pool or hot tub set points, and multi-stage heat and cool operations are all possible in a single radiant design. Every operation must be cohesively directed and mindful of the overall system to achieve the expected performance. Contemporary radiant controls are designed to achieve a quality system by adapting to creative applications.

The hydronic control industry has come a long way from the days when clocks and dials were used to enter schedules and settings. Without viewing screens, users were prevented from observing their system data making troubleshooting much more difficult. As technology advanced, controls adopted user-friendly interfaces with enhanced options for added convenience. Dials were replaced with buttons, indicator lights, and eventually LCD viewing screens making programming and schedule changes simple and quick. 

With the emergence of mobile technology, some of today’s radiant controls are configured for web enabled remote access. With these accessories, homeowners and contractors can view real time data from their hydronic systems and make instant adjustments from any computer, smart phone, or tablet.

System management is also more convenient using home automation software whereby users can monitor and adjust temperatures at a centralized touch screen interface that controls lighting, audio, security and more. Controlling all aspects of energy usage at a single point is not only easier for the homeowner, but also conserves more energy by coordinating the system.

Radiant controls have changed significantly since early applications with common thermostats. The new generation of communicating
controls is designed to optimize efficiency, protect equipment, enhance comfort and conveniently manage diverse energy systems. Algorithms have grown more sophisticated, but the automatic intelligence is now hidden inside user-friendly interfaces.

With advancing technology and market responsive solutions, radiant controls continue to offer better solutions for today’s applications.

Elizabeth Brown, who is a customer support specialist with tekmar Control Systems, a Watts Water Technologies Company, holds degrees in mechanical engineering and education. With experience in both fields, Brown is focused on teaching contractors and designers how to get the best performance out of their systems. She can be reached at customerservice@tekmarControls.com.