Issue: 1/02

I recently saw an advertisement showing the Wright brothers' aircraft having just lifted off on its maiden flight. The photo in the ad was covered with scribble lines suggesting it was a "vision" conceived in someone's mind that, with additional contemplation, seemed unattainable and therefore should be abandoned in favor of more realistic pursuits.

The ad's obvious implication was not to give up on such future concepts, even when the path to attaining them is not immediately apparent. So many advances in all areas of technology have come about as a result of relentless, and at times discouraging, pursuit of such visions.

The North American hydronic heating industry has certainly seen some significant technical advances over the last couple of decades. PEX tubing, super-high-efficiency heat sources and microprocessor-based control systems are but a few examples. But where do we go from here?

Every once and awhile, it's inspiring to speculate about where our industry is headed beyond the range of our current day planners. What kind of products we'll be working with five years from now? How "outdated" will some of the hardware we have yet to install be at that point? Will we as an industry be better or worse than we are today?

This article makes some predictions on the technology that will be used for hydronic heating in the years ahead. The predictions are based on observed trends, published technical research, software concepts used in other industries, and what several people on the cutting edge of this industry have shared with me.

After reading them, you may consider some to be "pie in the sky" ideas, unattainable in decades, much less five years. Time will tell. However, even if you don't agree with my prognostications, be sure to develop some of your own. Complacency with the present is simply unacceptable in any area of technology.

As Good As It Gets?

If there's one area of hydronics technology where we've barely scratched the surface, it's controls.

If you've been designing hydronic heating systems for the last couple of decades, go look through some of your old catalogs and job files from the 1980s. Compare the control concepts and the hardware used back then to what you work with today.

A couple of decades ago, bimetal thermostats wired to circulators or zone valves were about as complicated as controls got in residential and light commercial systems. Airplanes had auto-pilot, cars had cruise control, the microprocessor was rapidly being integrated into other consumer appliances, but hydronic heating systems were mostly controlled by electromechanical switches, the designs for which date back to the 1950s.

Today, many new residential hydronic heating systems sport at least one microprocessor-based controller. Larger systems often use several such controls wired together to form an overall control system.

Is this as good as it gets? I certainly hope not! Although current control strategies have much to offer, they also have shortcomings begging for improvement.

One vulnerability of our present approach is that the designer of a "custom" hydronic heating system is often the only person who fully understands how the overall control strategy and hardware is supposed to work. The moment something zigs when it should have zagged, the owner better hope that one person is still available and reasonably priced. Otherwise, the hydronics industry acquires a dissatisfied customer who undoubtedly will spread his or her justified frustration to many others whenever the opportunity arises. This scenario played itself out repeatedly as the rage for solar energy systems swept through the U.S. in the late '70s and early '80s.

Toward this end, designers must be diligent in documenting the hardware settings and operating sequences of the systems they create. Beyond proper installation and start-up, such documentation helps assure each system remains serviceable by any reasonably competent technician over its foreseeable lifetime. I can still find plenty of local mechanics to service my 1981 Ford tractor. Shouldn't my clients be confident that local heating technicians could service their new heating systems for at least the next 20 years?

Other areas for improvement include the fact that current controllers can still require a technician to drive 50 miles to turn a dial or push some programming buttons if the initial settings are a tad off. Many reset controls cannot prevent a high thermal mass heat emitter (such as a radiant floor slab) from causing significant overshoots in room temperature when a cold night is followed by a warm day. Most still deal with only the real-time information they sense within the system and outside, and cannot "think" beyond the present. Finally, many current controllers, even those produced by the same manufacturer, cannot communicate common information between them. A current state-of-the-art system with multiple boilers and three variable speed injection pumps operated on outdoor reset control requires four outdoor temperature sensors. All four sense the same information, but each sends that information to a small, isolated part of the system. The redundancy resulting from the inability to share such information is obvious.


Most controls we'll be using two or three years from now will be capable of Internet connection. Soon you'll be able to sit at your computer and dial up the Web page of a hydronic system miles away, or on the other side of the world for that matter. The Web page will give you the current operating status of the system, as well as a playback of how the system has performed during a previous period. The control system may even contact you when a critical parameter is out of bounds. With the proper authorization, a technician could change the operating settings without leaving the office.

Even the need for a technician to adjust control settings will steadily decrease in the near future. Instead, controls will learn and adapt as they operate. They will remember how the system reacts when the boiler is fired; when zones 2, 3 and 11 all operate at the same time; or what happened to indoor temperature the last time a cold night was followed by a sunny day. Using this information, they'll self-adjust, constantly tuning themselves to optimize system performance.

An Internet link also opens the possibility that controls could automatically access an online weather forecasting system to download the probable local weather conditions for, say, the next 24 hours. They would then base their operation on these anticipated conditions, as well as real time sensor readings.

We're also going to see a move away from control systems consisting of several dedicated-purpose boxes wired together. Instead of a reset controller that ties to a multiple boiler controller that ties to a multiple zone controller, we'll soon be working with much more flexible "single box" system management controls. Different requirements from one job to the next will be handled by changing the software executed by the box, rather than the box itself. Need a control system to handle 13 thermostats, two boilers, and four independent variable speed pumps? No problem, just select a template of that particular system from a menu of hundreds of possible configurations, make a few mouse clicks to adjust the details, and download the program to the box. Turn it on and walk away.

Heating Up the Future

Imagine driving your car by repeatedly executing the following procedure: Floor the gas pedal, "pop" the clutch, accelerate for say 10 seconds, and then push the clutch in and coast for the next 20 seconds.

As ridiculous as this seems to any reasonable driver, it's not a bad analogy to describe how energy flows from the heat source to the load in many current hydronic systems. Wouldn't it make sense to "throttle" the fuel input to our boilers as we've done for years with our cars?

Modulating boilers that match heat output to ever-changing loads are already being installed by progressive hydronic heating professionals, even in smaller residential and light commercial systems. In many cases, they minimize or eliminate the need for other types of operating controls such as outdoor reset. Look for continued refinements with modulating gas and oil burner technology.

In the area of non-modulating boilers, I think we'll see a trend toward ultra-low-mass combustion chamber/heat exchangers, used in combination with well-insulated storage vessels. The concept is to leave as little heat as possible in the combustion chamber/heat exchanger at the end of each firing cycle. The highly insulated storage vessel would store the surplus heat until needed by a load. Each time the burner fires, it remains on for several minutes to maximize cycle efficiency and minimize emissions. The surplus heat is "parked" in the insulated storage vessel until needed by the load. Think of the concept as an instant-start blowtorch married to a Thermos bottle.

A current trend that seems likely to continue is the use of sealed-combustion boilers that don't require inside air for combustion. As energy costs increase, uncontrolled building air leakage will decrease both voluntarily and through code mandates. Tighter buildings can serve as a battleground for various appliances all competing for airflow. Why risk backdrafting carbon monoxide when the entire air supply venting process can be isolated from variations in building pressure?

Another technology that will work its way into the hydronic heating industry over the next 5 years is cogeneration. We'll soon be installing devices that produce both heat and electricity. They've already been involved in experiments in both Europe and North America. An internal combustion engine running on natural gas, propane or fuel oil turns the shaft of a generator to produce electricity. The waste heat of the engine and generator is captured by a coolant flowing through and around these components. Water is the perfect coolant, and hydronics is the perfect way to distribute that heat to our buildings.

We may even see boilers harvesting the energy in the light given off by the flames within the combustion chamber. The key component--photovoltaic cells--have been around since the '60s. The wattage generated won't be enough to power an entire house, but may operate the burner, circulator, or other small electrical devices in the system. A small battery charged by the photovoltaic cells could allow the heat source and circulator to operate during a power failure. Think about that during the next big ice storm!

Those of you in fuel oil territory can expect to see burners with significantly lower firing rates. Modulating burners with oil input rates as low as 0.2 gallons per hour (28,000 Btu/hr) will allow boilers to be better matched to the heating loads of modern well-insulated homes and apartments.

Forward Flow

Another area where things are bound to change is pumping. Specifically, the use of variable speed circulators in all parts of a hydronic system. When a zone valve closes, such circulators will instantly adjust their speed to match the new flow requirement. Aside from the favorable flow dynamics, variable speed pumping also lowers electrical consumption. As the cost of the latter increases, designers will increasingly focus on reducing wasteful "overpumping" in both large and small systems. Anticipating this trend, several pump manufacturers already offer variable speed circulators ready to be interfaced with standard control outputs, such as 0-10 volts DC or 4-20 milliamps.

Pipe Dreams

My bet in this area is on new types of composite pipe. Most will likely be a mix of metal and polymers, perhaps the successors to our present generation of PEX-AL-PEX pipes. These new pipes will exploit the chemical resistance of polymers, as well as the physical strength of thin layer(s) of metal. Such tubing will steadily replace the use of all-metal pipe (copper, steel and black iron) for distribution piping. Copper tubing will still be used where high rates of heat transfer are needed, but less as a general purpose piping material.

Beyond CAD

Could any of you use software capable of importing architectural CAD files and automatically performing heat loss calculations? Using the results along with minimal user queries, the same software may then develop a tubing layout plan for the floor heating system. After performing much of the design and documentation chores, this software would even provide a detailed bill of materials and the associated pricing.

The algorithms for performing such automated design already lie beneath the surface of other types of industrial software. As the hydronics market grows, so will the incentive for enterprising software developers to "repurpose" these powerful algorithms. The complex computer code presently used for printed circuit board layout and CNC machining may soon assist you in rapidly designing and documenting hydronic heating systems.

Imagine software that lets you graphically assemble the major components of a proposed heating system on your monitor, then completely simulate how that system would operate. Wouldn't it be nice to know how to set all those balancing valves so you don't have to return to the building two or three times to tweak them? It's certainly less expensive and embarrassing to correct errors on a "virtual" hydronic system, one that exists only in your computer's memory, than it is to replace expensive hardware that's already screwed, soldered and wired into your client's building. Such simulation tools are already extensively used in the design of electronics, aircraft, automobiles and even artificial hearts. What remains is to adapt the simulation engines used in these other applications to the components used in hydronic systems.

Those Who Learn Will Earn

As more and more people experience the comfort only a quality hydronic system can deliver, there's little doubt this industry will continue to gain market share. The new technology we've discussed will only further improve the comfort, energy efficiency and long term reliability of hydronics. Those professionals who stay abreast of this new technology, and learn to apply it well, will find no shortage of clients desiring what it has to offer.