HYDRONICS e Continued from p 36
heat demand. “But no doubt, one of the key
factors in attaining optimal system efficiency today is the advent of condensing boiler technology,” added Mishou. “Condensing boilers, like our Rheos+ or NeoTherm boilers, are built to extract latent heat from the moisture that forms in the condensing heat exchanger, dramatically enhancing combustion efficiency.” The use of a condensing boiler can play an even more important role.
Condensing boilers, like the Rheos+ or NeoTherm boilers, are built to extract latent heat from the moisture that forms in the condensing heat exchanger, dramatically en- hancing combustion efficiency.”
38
water temperature, the less condensate that’s produced within a condensing boiler, and its efficiency decreases toward that of a substantially less expensive, non- condensing boiler. “So the idea is to shift load to
conventional boilers as the water temperature goes up, since they will have efficiencies comparable to the condensing boiler operating in a non- condensing mode,” said Foley. “This is likely to make sense in larger systems using relatively high design load temperatures, such as those using fan- coils, air handlers, baseboard convectors or radiators.” There are also regional differences
to consider. “If the boiler system will be used as a backup for air-sourced heat pumps, geothermal heat pumps, or solar, these factors will play into the question importantly,” said Paul Pollets, president of Seattle, Wash.- based Advanced Radiant Technology.
“Typically, these systems provide lower return water temperature, keeping the condensing boilers in their ‘sweet spot’ most of the time.” In areas where these systems are
most popular, winter seasons are tempered somewhat, so high water temperatures are not routinely needed to heat interior space. These areas are likely to have broad outdoor temperature swings as well. Systems that can change the temperature of water used for heating tend to accommodate these outdoor temperature swings most efficiently.
System efficiency: the sum of many parts Though the boiler(s) may be the
most important single piece of a hydronic system, overall system efficiency depends on the
interrelationship of several key parts, all of which are changing and evolving as new ideas and technology influence their role in the mix.
1. Boiler efficiency Boiler efficiency is determined by
two key factors: combustion efficiency and thermal efficiency.
“How effectively the boiler interacts with the hydronic system is determined by its ability to deliver heat either quickly, or slowly, depending chiefly on the needs of the system and the ability of the boiler to adjust to changes in the system’s demand for heat,” explained Joan Mishou, manager of applications engineering at Laars Heating Systems
“Their tough resistance to thermal shock and the ability to accept low return water temperatures puts them in a category of their own and opens up many new possibilities for hi- volume, cold-start systems. One example is a commercial snow melt system,” said Watts Radiant’s John Sweaney. “A condensing boiler takes very low inlet temperatures in stride; in fact, the lower temperature of incoming water (or a water/glycol mix, as is usually the case), the higher the combustion efficiency of the boiler.”
2. System performance = efficiency “Other important factors in
determining system efficiency include modulation, or staged firing, as opposed to On-Off,” added Abularrage. “This demonstrates the giant strides the industry has made during the past several years. Modulating and staged fired boilers reduce fuel consumption by ‘sizing to the load’ so that the amount of heat
Variable speed circulators are used in conjunction with zone valves.
Company. The common term is “to size to the load.” System efficiency is at its best when
the equipment works at peak performance, with fuel consumption happening at the highest levels of combustion efficiency, at all levels of
produced by the system precisely matches the need.” According to Mishou, another key
facet is that more sophisticated controls are now capable of sampling changes over time and “learn” the
e Continued on p 40
phc august 2011
www.phcnews.com
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