A comparison between the hot topics of the past and those of the present.

I began writing the Hydronics Workshop column forPlumbing & Mechanicalalmost 15 years ago. Back then, each column was typed up on a boxy little Macintosh computer with a 9-inch monochrome screen, printed on a dot matrix printer and saved on a 3.5-inch floppy disc. Each month, a printed copy of the column, along with the floppy disc, were mailed to then-editor Steve Smith. Steve would do his editing and mail me a copy of the completed layout. We then discussed any final changes over the phone.

At the time, hydronic heating was enjoying a resurgence of interest, driven by the red-hot topic of radiant floor heating. In the years that followed, radiant floor heating continued to be the tail wagging the hydronics dog. During the late ’90s, many of us became accustomed to radiant heating market growth rates of 25+ percent per year. Many newbies were drawn into hydronics through a growing interest in radiant heating.

Other hydronic-related topics that generated strong interest back then included:
  • Mixing strategies and devices.
  • Protecting boilers against flue gas condensation.
  • Primary/secondary piping.
  • Differential-pressure bypass valves.
  • Outdoor reset control.
  • Radiant-specific thermostats.
  • Customized controls using ladder dia-grams and programmable logic controllers.
  • Oxygen barrier tubing vs. nonbarrier tubing.
  • The energy savings of radiantly heated buildings vs. those heated by other means.
  • How comfort was attained at lower air temperatures in radiantly heated buildings.
  • High-capacity domestic water heating.
  • Snow melting - steps, patios, walk-ways, driveways and entire parking lots.

Conventional fuel was relatively cheap and the American economy was growing at a healthy rate. These circumstances, in combination with advancing building technology, set the stage for a boom in what many of us now call “McMansion” homes of more than 10,000 square feet.

The hydronics industry benefited from this trend. A growing number of hydronic “artisans” acquired the skills needed to assemble complex hydronic systems that often contained thousands of dollars worth of electronic controls, walls full of circulators and miles of PEX tubing. Many of these residential systems were arguably more complex than systems in much larger commercial buildings. The market was awash with devices that allowed these hydronic artisans to sculpt increasingly complex and intricate designs. I know, because I was one of those aspiring artisans.

Most of these high-end systems worked, but many required several hours of “tweaking” to weed out unexpected control, pumping or balancing issues. I even remember one installer telling me how he would “camp out” overnight in mechanical rooms trying to tame the beasts he had created.

Some of this is still happening today. McMansions are still being constructed, although in lower numbers due to eroding investment portfolios. Those that are being built often aspire to be “green” by including renewable energy heat sources (i.e., eight heat pumps instead of four boilers) along with thousands of other components assembled on site by those accomplished artisans who live and breathe hydronics.

Forced change

The entire HVAC market got a slap in the face when the bottom fell out of the real estate market in 2007. Double-digit growth gave way to limiting losses. Marketing terms such as green, sustainable, renewable and LEED became the industry’s new vocabulary. Today, the topics consistently generating strong interest in the hydronics industry include:
  • Solar thermal combisystems.
  • Ground-source heat pump systems.
  • Use of intelligent ECM-based circulators.
  • Using methods other than primary/secondary piping to achieve hydraulic separation in multiple circulator systems.
  • Dealing with short cycling of mod/con boilers.
  • Post-PVC boiler venting systems.
  • Chilled water cooling - radiant and convective.

Interest in both solar thermal systems and ground-source heat pump systems is currently very strong. It’s the result of saturation-level eco-marketing along with government subsidies that generously reward those who use these heat sources. I would venture to say most of those reading this column, including myself, have seen their businesses affected - in a positive sense, I hope - by this trend.

Appropriate use of renewable energy heat sources is something I strongly support. The fact that hydronics enables the operation of nearly all thermally based renewable energy technologies could be a tremendous “stimulus” for the North American hydronics industry. However, building a business model based on the currently available government subsidies really worries me. I lived through the early 1980s when the feds first pulled the plug on renewable energy. One of the lessons I learned was renewable energy systems will only gain mainstream acceptance when deployed in configurations that are reliable, have a long life, are easily repeatable and can create immediate monthly savings without government subsidies.

Those who have read my columns over the last few years have surely figured out I’m a big proponent of ECM-based intelligent circulators. I think they represent the single biggest advancement in hydronics technology over the last two decades. I encourage people to think of these circulators as the compact fluorescent light bulbs of our industry. When eventually implemented by the millions, they will have a profound positive effect on the industry, further widening the gap between what’s possible using water-based rather than air-based distribution systems.

Primary/secondary piping remains a viable design technique. However, more and more designers are learning how to use the broader concept of hydraulic separation to provide the benefits of primary/secondary piping without the need for constructing primary loops, or incurring the installation and operating cost of primary loop circulators. Retaining all the benefits using simpler and less-expensive approaches is value engineering at its best. Look for this trend to continue.

Zoning has been, and will continue to be, a major benefit of using hydronic heating and cooling. However, zoning is slowly shifting from the extensive use of small, wet-rotor circulators in previous decades to valve-based techniques (e.g., either zone valves or thermostatic radiator valves). There are strong economic arguments for this metamorphosis. This trend also will continue as energy costs increase and more heating professionals learn to market the advantages of these devices.

The use of PVC venting for mod/con boilers seems to be at a crossroads. While PVC remains acceptable to some boiler manufacturers, other manufacturers have specifically banned it from use with their products. The issues in question include long-term integrity of the pipe and its joining methods at higher-than-expected flue gas temperatures, leaching of potentially corrosive chlorides from the pipe, and the lack of specific approvals from some PVC pipe manufacturers regarding use of their pipe for venting heat sources.

I think it’s inevitable that AL29-4C stainless steel and polypropylene will take over as the preferred venting materials for all condensing heat sources.

Snow melting continues to be an option the hydronics industry offers. However, increasing energy prices, growing altruism about reducing energy use, and increasingly restrictive energy codes are reducing when and where snow melting is deployed. And just in case you’re wondering, solar-powered snow-melting systems are not a good idea.

The issue of short cycling has become an Achilles’ heel to those who work with low-mass mod/con boilers. I often ask contractors at seminars about this issue and find it to be a pervasive problem. It all stems from the fact that it’s easy to “microzone” hydronic systems. The ability to create a six- or 12-zone system, in combination with low thermal mass boilers that can only reduce their stable operation to about 20 percent of full firing rate, is the cause of short cycling.

This situation wasn’t very common when residential boilers contained 400+ pounds of cast-iron, 10 or more gallons of water and served one to three zone distribution systems. We didn’t appreciate the self-buffering characteristics of these older systems, at least not until we began using low-mass boilers with ever-increasing numbers of zones. I think the solution lies in restoring thermal mass to the heat source, preferably as site-added water rather than manufacturer-added metal. I predict future combustion-based hydronic heat sources will rely on increased water mass as their stabilizing element.

Chilled-water cooling has been used in commercial buildings for decades. It’s now poised for increased use in residential buildings for several reasons. One is that radiant cooling systems can shift the sensible portion of the cooling load from air-based distribution to hydronic distribution. The electrical energy used in the latter is often a small fraction of that used in the former.

The ability to easily zone hydronic-based cooling vs. air-based cooling is another draw. So is the fact that ground-source heat pumps, air-to-water heat pumps and gas-fired absorption heat pumps can all efficiently produce chilled water for cooling, as well as warm water for hydronic heating. Look for increased interest and application of small-scale chilled-water cooling.

The watch list

There are several developing situations that could significantly impact the future growth of our industry,ifwe recognize the need and respond with appropriate solutions. These include:
  • Ultra-low-energy-use buildings that need “drop-in” heating and cooling solutions.
  • Homes requiring heat generation capacities no higher than 40,000 Btuh, along with heat sources that can remain in stable operation while delivering 5 percent or less of this capacity.
  • Appropriate integration of renewable energy heat sources where they can deliver positive monthly cash flows from when they are first turned on.
  • Increased demand for ultra-low-mass heat emitters that can quickly respond to changing loads due to internal and solar heat gains.
  • The advantages of central heat generation along with heat metering in multiple-occupancy buildings (condos, apartments and leased office space).
  • Increasing awareness that the distribution system, and not just the heat source, plays a significant role in determining system operating cost.
  • Smart grid technology and time-of-use electrical rates that need on-site thermal energy storage. Water is the best stuff on earth for storing sensible heat.
  • Net-zero building with solar photovoltaic arrays, and therefore a strong preference for electrically driven high-efficiency heat sources (e.g., heat pumps), along with low-energy-use distribution systems (e.g., hydronics).
  • Micro CHP (combined heat and power) generators needing a means for continuous collection and distribution of the heat produced by their engines. Hydronics is ideally suited to this task.

  • Gas-fired absorption heat pumps that can supply heating water at temperatures up to 140 degrees F, equivalent combustion efficiencies up to 140 percent and chilled water for cooling.

Hydronics 2.0

In the months ahead, I’ll use this column to focus on these and other topics in more detail. I’ll write those columns on an iMac with a 27-inch color LED display, e-mail them to the editors atPlumbing & Mechanicaland very seldom print anything on paper.

The computer I used to write the first Hydronics Workshop column has long since evolved into a device that is now indispensable to my business and has undoubtedly improved the quality of my life. This happened because a certain computer manufacturer recognized the need to provide solutions rather than boxes classified by megahertz and gigabytes.

Hydronics technology, working behind the scenes and without the glory of eco-aggrandized headlines, holds the potential to improve the quality of our lives and reduce our national energy needs. This potential teeters on the ability of our industry to deliver solutions rather than hardware. I think it can be done.