HYDRONICS
36
Finely-tuned Hydronic Systems: Sum of Many Parts
what it is that makes the “perfect boiler system.” Well, I did it for you, and one thing’s for sure: It’s more than just shopping for boilers. Today, with stratospheric energy
G
rates, homeowners and building managers alike are pushing the need for high efficiency systems. In response, installers must consider overall specifications, budget, boiler options, controls and heat distribution because, after all, high efficiency systems are the sum of many parts. Condensing boilers, deftly
extracting heat from condensate, have now pushed combustion efficiency into the 95 to 99 percent range. System components play a key role too: Variable speed circulators are attuned to precise Delta T and sleek, Btu-spitting zone valves do their part in maximizing overall system efficiency. That’s smart use of energy. This also
becomes a key system advantage when long-term operational cost of systems is scrutinized. When trade professionals can calculate a three- to four-year payback for new equipment, there’s real incentive to move ahead with the project. So, if the spec dictates high
efficiency, the next question may be, “How high?” Non-condensing boiler
o ahead: Ask the hydronic gurus, say Dan Foley, John Abularrage or Paul Pollets,
technology offers a lot, with broad capabilities and fuel efficiency into the mid-to-high 80s. If that's not enough, the conversation often turns to the latest, über-technology. But, as many of you know, other
facets influence the type of system that’s best suited for the job. A key factor in the selection of a boiler has to do with the anticipated temperature of the return water or glycol mix. If the temperatures are low (say, in the range of 60 to 130 F), a condensing boiler will operate most efficiently. If return water/glycol mix temperatures are high — above 130 F — then non-condensing equipment may make more sense. “Along with the need to consider
system temperature, stage-fired or modulating units should be considered,” said John Abularrage, president of Stone Ridge, N.Y.-based Advanced Radiant Design Inc. “These units supply less than full input when the full input of a boiler isn’t required. In many cases, a condensing boiler even gains efficiency when it’s running at a lower firing rate. Multiple boilers can be another way to increase system efficiency, again allowing for lower input to the system when full input isn’t needed.”
Condensing + non-con twist
One of the more interesting approaches to commercial boiler
By John Vastyan
system design is the deliberate joining of condensing and non-condensing boilers. Mixing condensing and “non- con” boilers in the same system is a concept that’s getting more attention these days. “By setting a condensing boiler to be
the lead boiler when the system temperature is at its lowest and/or outdoor reset controls are bringing water temperature down, the installer or system designer can better ensure that the investment made in a condensing boiler will be worth it, in terms of efficiency gain and fuel- savings,” added Dan Foley, president of Foley Mechanical Inc., based in Lorton, Va. “If more heat is needed in the
system, a non-condensing boiler can be the next in line,” he continued.
“The second non-con boiler — and additional downstream boilers, if called for — would then be an advantage, considering lower initial cost and suitability for efficient operation with higher return temperatures.” The basic concept is to operate the
condensing boiler when loads are low and, thus, so are supply water temperature needs. As the load increases, such as when weather gets colder, so does the supply temperature requirement with outdoor reset control. The higher the
e Continued on p 38
phc august 2011
www.phcnews.com
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