10 hydronic lessons learned
July 2016 marks my 20th anniversary of writing the Hydronics Workshop for Plumbing & Mechanical magazine.
July 2016 marks my 20th anniversary of writing the Hydronics Workshop for Plumbing & Mechanical magazine.
I’ve really enjoyed bringing you this column. It has been especially gratifying to hear from readers on how the information in these columns has been used. Thank-you for reading and for your feedback.
The hydronics industry has changed a lot over two decades, most of it for the better. Higher-efficiency heat sources and variable-speed, ECM-based circulators are two definite improvements over what was available 20 years ago. Other advances include press fittings, better methods of dirt and magnetic particle separation, and web-accessible controls.
There also have been a fair share of problems with hydronic system design over this period. Morphed piping layouts, improperly configured controls, fluid quality issues and overly complex designs, to name a few.
We’ve all been there
During my years of writing this column, I’ve had the pleasure of meeting many individuals who I regard as true professionals. Many have shared stories of their experiences and their “experiments” with me. I can’t think of a single one who wouldn’t admit they’ve learned lessons along the way that led to significant changes in how they design or install hydronic systems.
Like them, I’ve spent many hours watching hydronic heating systems go through their paces. Each time I do, I like to compare what I see, feel and hear to what theory says I should see, feel and hear. The inevitable discrepancies between the theoretical and the observed usually lead to new understanding. Although they usually confound us for a while, many of these quirks are blessings in disguise. Finding their root cause, as well as how to correct them, inevitably helps us improve what we do on future projects.
Here are 10 lessons I’ve learned over the last 20 years. All have influenced the way I design systems, deal with clients and even choose the topics for this column.
1. Always protect conventional boilers against sustained flue gas condensation.Although I’ve written about the need to protect nearly all cast-iron, steel or copper-tube boilers in many columns, it wasn’t something I always understood or even cared about.
During my hydronics adolescence, I was so concerned about delivering the proper supply temperature to a low-temperature distribution system that I didn’t even think about what went back to the boiler.
However, after seeing first-hand what sustained flue gas condensation can do to boilers and vent connectors, I now wouldn’t think of letting a system design involving a conventional boiler and low-temperature distribution system leave the office without proper detailing to prevent this problem.
My experiences aside, boiler protection is still not fully understood in our industry. Myths abound about what does and doesn’t provide proper boiler protection. Boilers continue to be installed unprotected in both residential and large “engineered” systems.
Here’s one example. A few years ago I visited a building heated and cooled by a multiple water-source heat-pump system. Each of the 32 heat pumps connected to a constantly circulating piping loop. That loop’s temperature was maintained below 90° F by a cooling tower (when necessary) and above 70° by a staged multiple-boiler system.
The copper-tube boilers were connected to the main loop using closely spaced tees — a classic primary/secondary system. There was no provision to boost the water temperature entering the boiler. As a result, these boilers never operated above the dewpoint of their exhaust gases.
All three of the original boilers had to be replaced within 10 years. Their replacements were piped the same way, and thus doomed to the same premature death-by-condensation as their predecessors. All because the designer wasn’t aware of the need for boiler protection.
The boiler inlet water temperature necessary to protect a conventional boiler from sustained flue gas condensation varies with the type of boiler, the fuel used and the air/fuel ratio. A minimum sustained inlet water temperature of 130° is usually adequate to protect most boilers burning gas, fuel oil or dry firewood.
To properly protect a boiler there must be a “clutch” (a mixing assembly) between the “engine” (the boiler) and the “drive train” (the distribution system). In a car, proper control of the clutch allows the available mechanical power produced by the engine to flow to the drive train without “lugging down” the engine. Likewise, a mixing assembly that senses and reacts to low return temperature allows the full heat output of the boiler to reach the distribution system without pulling the boiler temperature down to where sustained flue gas condensation occurs.
To properly protect the boiler, the mixing control must sense the return temperature and, when necessary, be able to totally disconnect the boiler loop from the load, just like a clutch pedal pressed all the way down totally disconnects the engine from the drive train. It’s not enough to simply blend supposedly hot water from the boiler outlet with cool water returning from the distribution system.
Figure 1illustrates a situation in which a variable-speed circulator, piped as a bypass and constantly monitoring the boiler’s inlet temperature, cannot protect the boiler from sustained flue gas condensation.
No matter how fast the bypass circulator runs, it can’t make 130°-water out of 90°-water coming from the boiler’s outlet.
One could argue that the large thermal storage tank might eventually reach a condition where the boiler inlet water temperature would be at or above 130°. Fine, but what happens during the multiple hours it might take for such a large thermal mass to reach this condition? Here’s a hint: drip, drip, drip …
2. Don’t allow customers to select hardware.When you purchased your last vehicle, did the salesperson offer you a choice between different types of spark plug wires? Of course not. Some design professional made an informed decision for you. To some extent, that decision influenced the price you paid for the vehicle. Even if you wanted to purchase the vehicle with different spark plug wires, chances are it simply wasn’t an option.
When it comes to heating systems, you’re the professional who should make the decisions regarding hardware. You know what the system needs to assure a long and reliable life. If your customers hear that Option B does “essentially the same thing” as Option A, but costs half as much, why would they ever choose Option A?
Why even bring such a possibility up for discussion? Why let people who are usually unfamiliar with the technical intricacies of hydronic heating influence (or even select) the hardware you will use? Always select what you feel provides a quality system and price the job accordingly. If that’s not acceptable to the potential customer, move on to the next job. You won’t regret it.
3. Always document the systems you install. Long after it’s built, there comes a time in the life of every building when plans for expansion or other renovations will be made. Chances are the design and routing of the heating system will factor into the decisions being made.
It’s impossible for designers or installers to remember every detail of every system they work with. Even if you’re blessed with a photographic memory, there’s no guarantee you’ll be available when its time to print out those neural images.
I always make piping schematics, electrical schematics and a detailed description of operation for the systems I design. I encourage you to do the same. Proper documentation is not only indispensable during installation, it offers lasting value over the life of a building. It’s also evidence of professionalism that, when properly dispensed, can be a tremendous marketing tool.
It has never been easier to document your systems using low-cost drawing software in combination with digital cameras. Make it a part of your professional routine and price it into the job.
4. Install isolation flanges (or valves) on every circulator.Did I ever tell you about the time I tried the “quick switch” procedure with a small, wet-rotor circulator? The circulator had succumbed after 20 years of service. The system’s designer — some guy who writes columns about hydronic heating and draws lots of schematics — had not seen the need to install isolation flanges during the original installation, even though there were 950 gal. of water behind and above the circulator.
The quick switch might have worked had those flange gaskets not have rolled over when I tried to shove the replacement circulator between a pair of immovable flanges. Let’s just say a good bath of water from a hydronic system teaches a valuable lesson.
5. Be discriminating with sidewall venting.Sidewall venting has its place and, when properly applied, can be a real time-saver. I like to use it for metal-roofed buildings in deep snow country, as opposed to searching for the upper portion of the chimney after a heavy roof snow slide.
However, don’t put a sidewall vent a few feet away from a backyard patio. Don’t install it on the street side of a house, under an elevated deck or near exterior steps. Neither the steam plume nor the resulting ice on nearby surfaces will be appreciated. If someone slips on an icy surface that can be traced to steam coming from a nearby sidewall vent, you’re likely to be sued.
6. Don’t rely on a single thermostat in a building that’s highly compartmentalized. This refers to situations where the doors to individual rooms in a larger building remain closed most of the time. The variations in heat gains and losses make it nearly impossible to ensure the proper comfort in each space, even when the distribution system uses room-by-room circuiting. Use thermostats or thermostatic radiator valves to provide room-by-room temperature control.
7. Don’t design as you solder. Over the years I’ve learned it’s better to make plans before reaching for tools. This sentiment is not shared by everyone in this industry, especially in regard to piping design.
Some hydronic piping systems seem to evolve fitting by fitting. They expand out from the boiler, meander around the mechanical room and through the building, eventually finding their way back to the boiler.
Along the way, the installer miraculously receives “inspiration” about how best to proceed for the next five minutes. Such installers are like artists who throw globs of paint at a canvas until some impulse tells them what they’ve created constitutes a masterpiece.
I continue to see the results of morphing proven piping concepts together the way biologists splice genes in hopes of retaining only the desirable traits. Judging by some of the “inspired” piping layouts that arrive in my email, this approach is more likely to produce a Frankenstein instead of an Ironman.
Piping aberrations continue to waste time, material and customer patience in our industry. Study the basic hydronic piping layouts. Learn where each is best applied. Plan your layout using paper and pencil, or computer drawing software, instead of tubing and torch.
8. Stay away from open-loop systems whenever possible.Closed-loop systems are cleaner, quieter and have less operating problems than open-loop systems. If you have to incorporate a nonpressurized component, such as a nonpressurized thermal storage tank, separate it from the balance of the system with a heat exchanger.
9. Design for long-term serviceability. As an industry, we promote the concept that hydronic-heating systems should have a long service life. We must do everything possible to ensure we deliver it.
Picture the hardware you select after it’s been installed for 20 years. Do you see it holding up in the environment you are about to place it in for that period of time? Is the continued service of the systems you install critically dependent on a single component? If so, will that component or an updated/compatible version of it be available 20 years from now? Can you replace it, if necessary, without performing major surgery on the rest of the system?
Reasonable customers accept the fact that mechanical components fail over time. They shouldn’t accept that when it happens, we can’t expeditiously correct the problem.
10. Never forget that you install premium heating systems. They are seldom going to be the lowest-priced option available to your customer, even if you foolishly compromise performance by leaving out necessary hardware — such as the actuating motor and controller for a mixing valve.
If, after explaining the benefits your systems offer, your potential customer still wants price over performance, walk away from the situation with a smile on your face. You’ve made the right decision. A new opportunity to practice your profession without compromise is right around the corner.
I expect my list of lessons learned will continue to grow, as it should. Your list should keep growing, too. It’s an inherent aspect of being professionally involved with any technology.
Embrace the learning curve.
This article was originally titled “10 lessons learned” in the July 2016 print edition of Plumbing & Mechanical.