Last fall the PM columnists were all challenged to write about their “secret life” for their January columns. The idea was to write about something they do or enjoy that's a bit outside their normal monthly specialty.

Like my fellow PM columnists, there's seldom a waking hour when I don't think, to some degree, about my specialty or how it relates to other aspects of life. Even my secret life is influenced by the basic principals underlying hydronics. So this column is a story of how hydronic heating relates to - of all things - cycling.

Pedal Power

When I was in high school, my primary mode of transportation was a bicycle. Back then it was called a 10-speed. I used it to go places where I mowed lawns, pulled weeds and painted houses for summer employment.

By the time I got to college, cycle touring was popular. In 1976, three of my friends and I decided to ride our bikes from upstate New York to Bar Harbor, Maine. We made it in six days, in some cases logging 100+ miles per day.

After college came employment, marriage, house building and kids, pretty much in that order. My trusty steel steed got hung up in the garage of our new home, where I'm ashamed to say it remained, collecting dust and slowly deteriorating, for about 20 years.

When my oldest son Dale was 15, he got the same cycling bug that I had at his age. However, he set his sights a bit higher and really put his mind and body to it. Three years later, he won the New York State junior time-trial championship and managed to break the local bike club's time-trial course record.

In case you've never heard of time trials, it's pretty simple: You, on a bicycle, against the stop watch for a 10-mile course, no drafting, and lowest time wins.

Dale occasionally convinced me to leave the computer desk and all those piping schematics for a short ride with him. I vividly remember one of my first “comeback” rides after being off the pedals for more than 20 years. I doubt we road over five miles, but I could barely make it up the stairs when I got home. I came very close to concluding that my cycling days were over, but Dale persisted. Eventually he got me to ride the Tuesday nighttime trials with him.

My biggest concern was being dead last at the finish. My first times were nothing to write home about, but at least I did finish the race, and that in itself felt good.

Slowly but surely I improved. Dale coaxed me along on mutual rides much like an F-16 can fly in formation with a C-130 when necessary. I think he knew I was starting to get back into the speed, the sweat and even the pain of competitive cycling. I kept asking him his secret for great times. His profound advice: “Go as fast as you can and don't stop for 10 miles.”

To date, I've been back on road bikes around eight years. Every summer I do the weekly time-trial races with the local bike club. To my surprise, my times are actually getting better as I'm getting older. I hate to admit it, but next year I can ride in the men's senior category at race events. Although you may think this is for old geezers who can barely keep the bike upright, I've found it includes some of the fastest cyclists in our club. Guys in their 60s that even track-star teenagers can't stay with for 10 miles.

So what does all this have to do with hydronics?

Actually, there are quite a few parallels between cycling and hydronics. One has to do with something called the pump affinity laws. One of these laws states that the pumping power required to move a fluid through a piping system goes up with the cube of the flow velocity. Here's what the math looks like:

P = c x v3

Formula 1

P = pumping power required (watts)
c = a number based on the resistance of the piping system
v = fluid velocity in piping (ft./sec)

This relationship has a profound effect in both types of systems. In the case of hydronics, it implies that doubling the speed of a liquid through a piping system requires eight times more pumping power (e.g., 23 = 8).

When it comes to cycling, this relationship also has far-reaching consequences. For example, peddling a bicycle at 25 mph requires 95 percent more power from the rider than pedaling at 20 mph. Doesn't seem possible, does it? But it's all based on the same fundamental and inescapable physics.

This relationship really helps me respect the power output of someone that beats me by a mere 60 seconds in a time trial. Lets say they do the 10 miles in 24 minutes and I do it in 25 minutes. All other conditions being assumed equal (same bike, same aerodynamic drag factor, etc.), they put out 13 percent more power, on average, throughout the race.

I calculated that Lance Armstrong can ride at sustained power levels at least double what I can. Oh well, I wasn't really expecting to catch him anyway.

Most of you would be surprised at the physical exertion required to keep five small zone circulators running if you have to produce that power using a pedal-driven generator. I have a wattmeter on the indoor training bike, and holding the needle at 400 watts for 15 minutes straight leaves me panting pretty hard. It does help you put the indiscriminate use of wattage in perspective.

Lose The Drag

In time-trial cycling, some people use extreme measures to reduce aerodynamic drag. This lets them move incrementally faster for a given level of power output. Techniques include:

  • Using solid-disk rear wheels made of carbon fiber composites. If you have to ask how much these wheels cost, you can't afford them.
  • 19mm wide, hand-sown tubular tires pressurized to almost 200 psi.
  • Airfoil-shaped tubing on bicycle frames, as well as aero helmets and aero handlebars.
  • Stretch “booties” to cover latches on cycling shoes.
  • Fully shaved arms and legs - something that I just can't bring myself to do!

At high levels of competition, cyclists even train in wind tunnels where their riding position as well as the aerodynamic profile of their bicycle is tuned to perfection. Figure 1 shows a specially designed time-trial bicycle. It looks a bit different than your old Schwinn, because it's built for one purpose only - the fastest ride for a given level of rider power. This is the kind of bicycle that world-class riders push along at average speeds of 32+ mph, mile after mile.

Hydrodynamic drag is also very important in hydronic systems, although it's often overlooked or “trumped” by first cost considerations. Generously sized piping, cleaning reamed tubing, and bent tubing rather than soldered or threaded elbows, all reduce flow resistance and allow a given circulator to provide higher flows. The other way to look at this is that systems with reduced drag allow a smaller, less powerful circulator to provide the necessary flow rates, saving not only on first cost, but the life-cycle operating cost of the system.

The concept of using less and less power to properly distribute heat through a hydronic system is, in my opinion, one of the biggest challenges facing our industry in the years ahead. We simply can't afford careless hydraulic design and then overpower our sloppiness using bigger circulators.

Corrosion Is A Bummer

Nobody wants a corroded bicycle or a corroded heating system.

I once saw a steel bike frame shatter in a minor collision because the frame was internally corroded from being left in high-moisture environments. The rider probably had no idea of the silent internal oxidation taking place until it was too late.

Similarly, none of us likes the idea of our modern hydronic systems being slowly eaten up from the inside out. The lesson here is to learn what it takes to control corrosion in your systems, and make sure you do it. How many of you are currently “washing” your systems internally to remove flux, oils, etc., as part of the start-up process? What about going back to check the pH and reserve alkalinity of systems with glycol antifreeze? You probably think it's stupid to leave a $2,000 dollar bicycle out in the rain, but it's not much different than letting a $25,000 heating system slowly destroy itself from avoidable corrosion.


Here are a few more ways that cycling and hydronic heating parallel each other.

  • A helmet is a lot like a pressure relief valve; you spend money on it and always install it, but hope it never has to do its job.

  • Keeping the drive train of a high-performance road bike clean is important for good performance and long life. The same is true with a boiler and piping system.

  • A good bicycle wheel is like a good hydronic distribution system; both run best when well-balanced.

Tune-Up Time

For me, the best part of getting back into cycling was being able to drop a few pounds, lower my cholesterol levels, improve my cardiovascular endurance, and better manage the inevitable effects of aging.

As you probably expect, I spend a lot of time these days sitting in front of a computer or sitting on airplanes. A few years ago, while the bike was still hanging in the garage collecting dust, this was starting to take its toll on me. I finally realized that I had reached the point in life were I either had to “tune up the engine” or things would surely get worse.

Three or four hours a week of “serious” (elevated heart rate) cycling has really helped me improve my fitness. I urge those of you who have migrated to more sedentary work environments to find a way to get a few hours of elevated heart rate cardiovascular exercise every week. It really does make a big difference in how you feel, how you sleep and even how well you work.

If you're not sure how to do this, my suggestion is to get a decent used road bike and go for a five-mile ride at a reasonable pace a couple times a week for starters. Don't get discouraged because your legs hurt when you get back for those first few rides. Stay with it and you'll see good things happening. Chances are you'll learn to like it almost as much as drawing those hydronic piping schematics.

Happy New Year!


Thanks to Walt Putnam of ATPC/Heat Zone for spotting the fact that the schematic in Figure 4 of the November Hydronics Workshop column doesn't contain an expansion tank. Good eyes Walt, and thanks for studying the details. Yes indeed, this system is no exception, it does require a properly sized expansion tank connected near the inlet side of the circulators.