Complex Times Call For Basic Measures
August 2, 2014 | By STEVE GOLDIE
I love how Mother Nature every now and again gives us a good old fashioned smack down, just to remind us who is really boss. The ice storms eastern Canada experienced this past winter are a good example, leaving hundreds of thousands, including yours truly without heat or power. My situation was not as severe as that of many however, having a gas stove we were able to cook and make tea; our standing pilot gas fireplace took the chill off; and our good old fashioned chimney vented standing pilot hot water tank gave us hot showers. The situation definitely illustrated the advantages of older, simpler technology, and made me wish in the moment at least, that I had an old gravity radiator system in my house. Those old standing pilot millivolt boilers could operate without electricity, and the old radiator system could circulate without the aid of pumps simply by relying on the laws of physics, with the heated more buoyant water rising to the top of the system thereby causing the cooler water to return to the boiler creating the natural “gravity” circulation.
Now before you go pulling the circulators off your systems let me clarify, I have not become a Luddite and turned my back on technology. I am simply enjoying a moment of nostalgia. Losing power has its benefits and brought neighbours together to help one another out, perhaps rekindling a true sense of community. Many families likely pulled out board games that had been gathering dust for too long and rediscovered the joys of a family game night. I am sure many people have some happy memories of pulling together and coping during this and other blackouts, but I do not see many cancelling the utilities and making it a permanent lifestyle choice. Having an old technology boiler system that will still work when the power goes out is definitely desirable, but paying the higher utility bills that go alonag with it may not be. Unfortunately, I see far too many under performing systems out there, and usually not because the technology is lacking, but because it is improperly installed, misapplied, not understood and/or under utilized.
In order to understand what I mean, let’s look at some of the most common errors we see and how they negatively affect efficiency: oversizing, short cycling, over pumping and improper piping strategies.
Oversizing of boilers continues to be an issue in our industry, and in the case of a boiler, bigger is not better. Burner modulation, which is a feature on over 90 per cent of the boilers I sell these days, certainly helps but it does not solve this problem altogether. If a boiler could modulate infinitely, firing once at the beginning of the heating season and never turning off until the spring, this would approach optimal efficiency. Multiple boiler plants, operating and modulating together can most closely approximate this, but even so we must be careful not to oversize. I understand nobody wants to be caught short but in truth I have been in this business for almost 35 years and I can count on one hand the number of jobs I have seen where the boiler plant was undersized. An accurate heat loss and properly sized boiler plant is the first step to a truly efficient hydronic system.
The second most common problem I see is directly related to boiler over sizing and it is boiler short cycling. When a boiler, or boiler plant is too big it produces heat faster than the system can deliver it to the building, which causes the boiler to overheat and shut down until the system catches up, repeating this on/off cycling over and over again. Not only is this detrimental to efficiency, much like stop and start city driving in a car, but it also results in more wear and tear on many of the components. Short cycling is a far bigger issue than most people realize and has a dramatic impact on efficiency.
I had my eyes opened to just how much several years ago on a commercial retrofit project I was involved in. We had worked with the same company on several buildings, achieving on average gas savings over 35 per cent, but we were only seeing savings of about 10 per cent in one building. After many hours of monitoring and lots of pulling my hair out, we finally discovered a defective relay in one boiler which had resulted in that boiler continually cycling on and off. Once this relay was fixed and the short cycling issue corrected, the savings jumped up more than 20 per cent. Short cycling is a problem that needs to be addressed and it is not simply a matter of proper sizing. Oversized pumps can also contribute, which leads me to my next point.
Just as we like to over size boilers, we seem to have the same penchant for over sizing pumps. As with boilers, when it comes to pumps bigger is not better. While the boiler produces the btus required to heat a building, the pump is the device that moves these btus to where we want them to go. The universal heating equation (GPM = BTUH ÷ ΔT x 500) shows how this works; GPM is the gallons per minute flow rate the system requires at a given point in time.
BTUH is the heating load at a given point in time, Delta-T (ΔT) is the designed-for temperature drop of the fluid; and 500 is a constant representing 100 per cent water. When we oversize a pump and deliver more GPM, our delta T is proportionally reduced. How does this affect efficiency? It can result in overheating, short cycling, less than optimal comfort and poor performance. I am sure many of you have been in boiler rooms and seen the boiler inlet temperature only three or four degrees cooler than the supply temperature, this is a sure sign of over pumping.
Properly sized pumps need to work with the boiler to deliver the heat at the rate required and designed for, ideally we should be using the variable frequency drive (VFD) pumps that are available to optimize this and work in tandem with the modulating boilers. If we are modulating the firing rate of the boiler then does it not make sense to also modulate the flow rate to match the demand?
As you may have noticed, all of these things are related and one leads to the other. The goal is to match the size of the boiler plant to the actual demand of the project. Secondly, we need to deliver the correct amount of heat to the system components with properly sized pumps. The properly sized boilers and pumps can only do their jobs well if the piping is sized and installed correctly also. Sadly, I could fill this entire magazine with stories and examples of the piping nightmares I have seen. Following a piping diagram is a good start, but there really is no substitute for a good fundamental understanding of how and why it works. If you are installing systems you really need to take the time to understand the whys. I hate to say it, but far too many of the poor underperforming jobs I see on a regular basis are the result of poor or improper piping.
I know this sounds harsh but unfortunately it is all too often the sad truth. As a wholesaler I would love to be able to say “Here you go, just buy the boilers we sell and your installs will be problem free and save your customer 30 to 40 per cent on their bills.” Do we sell problem free systems? Absolutely.
Can properly sized and installed hydronic systems save upwards of 30 and 40 per cent fuel usage? Yes they can, I have seen savings over 50 per cent on rare occasions. Is it simply a matter of choosing the “right” brand? Absolutely not. The truth is every manufacturer and every wholesaler today offers high efficient, high quality equipment that is capable of doing the job. What is the magic bullet? Good old fashioned knowledge.
We really do need to read those installation and operation manuals nowadays. Even better, take advantage of the many training opportunities that are offered by manufacturers and wholesalers as well as trade organizations. The more education and knowledge you get, the better systems you can install and set yourself apart from the pack.
Designing and installing an efficient and reliable hydronic heating system is not simply
a matter of picking all the right pieces and including all the latest and greatest controls,
components and gadgets. Take the time to understand the fundamentals – the how and the why of things will never be out of date. <>
Steve Goldie is with NEXT Plumbing Hydronics where he is the hydronics specialist. He learned his trade from his father while working as a plumber in the family business. He joined the wholesale side of the business in 2002 after 21 years in the field. Steve is frequently called on to troubleshoot systems and advise contractors. He can be reached at firstname.lastname@example.org.