We’ve all learned a few things in our time; there’s a good chance we’ve learned them the hard way. I always told new hires that the lessons we learn and never forget are usually because it cost a lot of money to fix or made you look like a complete nincompoop.
Lucky for those of you reading, you may be able to skip the blow to your pride and the expense! So, here are a few things that I’ve learned:
Potable connections to systems using glycol
Glycol is common in applications such as snow melting, vacation homes and even areas with extremely low temperatures. Glycol does have a purpose, but I always remind contractors to use it only when needed. A colleague once noted that the only good thing about glycol is that it doesn’t freeze — meaning it has pitfalls. Glycol is costly, harder to move around, and not as good at transferring energy.
When you get to the point where you know you need it, glycol should be very closely guarded. Once you’ve created that perfect cocktail for your system, you need to keep tabs on it at every maintenance trip.
In one case, using a refractometer, I found that a system had lost almost all its freeze protection! Unbeknownst to the building owner, there was a leak. Leaks are always a bad thing, but having a fill valve connected to potable water for this system made it even worse.
As the leak allowed fluid to escape and reduce system pressure, the boiler fill valve did its job by introducing fresh water to bring that pressure back up. Slowly but surely, the glycol concentration dropped. Luckily, the building owner didn’t find this out the hard way. Usually, nobody knows about this problem until power is lost or some other failure allows the system to freeze.
So, instead of connecting to potable water, use a feeder (bought or built) with a limited amount of fluid (Figure 1). And always make sure to incorporate a low-water cut-off to protect equipment.
Excessive velocity
It’s a regular occurrence to find systems with oversized circulators or undersized piping. This is usually a result of poor design or someone desperately trying to get flow to areas lacking without having to go to the trouble of balancing.
The first thing building occupants will notice is the velocity noise from piping or heat emitters. Most systems are designed around 2 to 4 feet/second (fps) velocities, but if you start approaching or exceeding 5 fps, that’s when the trouble starts. Not only will your system be noisy, but it will also have the potential for premature pipe failure. On top of that, your system will be more expensive to operate.
What we’re looking for with 2 to 4 fps is that just-right velocity, like Goldilocks and her porridge. Too low and you won’t be able to keep air bubbles moving so they can get to the air separator. You will also limit heat transfer due to laminar flow in heat emitters. Too high and you’ll get noise, failed piping and an expensive operation. Sizing circulators and piping can be quite the balancing act!
Pumping into mixing valves
Three-way mixing valves are often used in hydronic systems to control temperature to a zone or heat emitter requiring a lower fluid temperature than the rest of the system. Think of that house with fin-tube baseboard at 180 degrees and the remodeled kitchen with the added radiant in-floor heat at 120 degrees. A mixing valve is used to blend fluid from your heat source with the return fluid from the zone it is serving.
If I had a nickel for every time I found a mixing valve that was piped incorrectly, I could probably buy a gas station hot dog (or two!) that I would later regret. The first rule of three-way mixing valves is that you always pump away from them (Figure 2). This allows the mixing valve to choose what side to pull from to get the desired outlet temperature to supply to the heat emitter.
Pumping into a mixing valve happens when the outlet side of the circulator is pointed toward the hot inlet of the valve (Figure 3). When this happens, you have the potential to short-circuit right through the valve and back into the return, providing no flow where you need it.
Another possibility is that the mixing valve will be force-fed from the hot side and close off the hot inlet in an attempt to control the temperature. This could either greatly reduce flow (that isn’t going where you need it anyway) or even deadhead your circulator. Always pump away.
Using (untreated) site water to fill systems
Water is probably the most common fluid used in hydronic systems. Luckily, most hydronic systems are in homes or buildings with fresh water piped all through them from your local water utility or private well. However, this is where your luck can run out. Just because you can drink the water doesn’t mean you can put it in your hydronic system!
Every manufacturer of a hydronic heat source has water quality requirements in its literature. Highlighting the importance, some are even putting them on the second page, right after the cover, which only shows a picture of the boiler!
These requirements usually dictate limits for total dissolved solids (TDS), pH, chlorides, iron and even copper. This will immediately rule out on-site water from almost every home in my area, as we have very hard water. While the use of a water softener will take care of the hardness, it will do nothing to help with TDS, as it will replace the magnesium and calcium with sodium.
This leaves you with a silly sounding option like purchasing your boiler water or treating the on-site water using demineralization. Demineralization is a similar process to water softening, except it replaces all dissolved solids with hydrogen (H+) and hydroxide (OH-), which conveniently come together to make H2O!
Water is a fantastic heat transfer fluid, but it’s also a fantastic solvent that picks up other materials along the way. Making sure to use water in your hydronic systems and not all the extra stuff that comes with it will go a long way when it comes to longevity, reliability and efficiency.
As an industry, we need to start worrying about the whole system as much as we worry about AFUE or COP. Without good heat transfer fluid, properly designed/applied piping and appropriate controls, your hydronic system may as well be a racecar with no tires! l
Cody Mack has nearly 20 years’ experience as an installation contractor, service technician, application engineer and, most recently, as training manager for Caleffi North America. He’s a family man, gear-head, and motorcycle enthusiast with a common-sense approach to hydronics. Cody can be reached at [email protected].
