Home Tech: The European Approach to Radiant Heat
When it comes to radiant heat, Europe has a nearly two-decade jump on the U.S.. More experienced, and faced with exorbitant fuel-prices, Europeans have turned radiant heating into high technology.
What Europeans seem to get that Americans don't is what we refer to as the "3-to-1 rule" of hot water heating. The rule states that for every 3 degrees (F) you lower the heating system's average water-temperatures, fuel-consumption decreases one percent. So is born, the art of low-temperature hydronics.
How do we get a system to operate at lower water-temperatures?
The answer is 'mass' and weather-responsive control. The more water-mass that can be added to the system, by way of additional radiation, the higher the amount of heat-exchange into the rooms that occurs. This additional mass can come in the form of radiators (old fashioned cast-iron, or modern flat-panels), or additional radiant-heating -- in the floors, walls or even ceilings.
Weather-responsive controls give the heating system a brain. The control device senses outdoor temperatures, which talks to the boiler and/or mixing-valve to ratchet the system's water-temperatures up or down according to the weather. In conventional heating systems (not weather-responsively controlled), the boiler fires at about 180-degrees all winter long, whether it's 30-degrees (F) or 10-below. But because the way we size a home's boiler, you only need 180-degree water on the coldest day of the year.
In upstate New York, for example, 80 percent-plus of the heating season is spent in the 30's. Weather-responsive controls take this fact in account, and ratchet the boiler temperatures down to match the actual heat-loss of the home, thereby lowering the system's average water-temperatures.
Weather-responsive controls
typically reduce fuel-consumption by 15-20%. Combined with a high-mass radiant system, one can expect even greater savings.
Caution:
When operating at lower water-temperatures, one must make provisions to protect the boiler from "thermal shock," particularly 'low-mass' cast-iron boilers. Cold return temperatures can also produce condensation in the flue, damaging the boiler and chimney, and compromising the system's ability to draft correctly. Mixing-valves are one way to protect the boiler.
One can also employ a "low-temperature" boiler specifically engineered for the task. Condensing boilers are the ideal choice for low-temperature radiant heating when gas is used as a fuel-source. In the oil-fired realm (condensing oil-fired boilers don't exist in the U.S.), a high-mass boiler, such as the Viessmann Vitola (www.viessmann-us.com) is a high-performance option.
Whichever boiler one chooses, without the brains of weather-responsive control, and the ability tp operate at low temperatures, radiant systems are simply dumb!
For more information about in-floor radiant heating systems, visit www.enhancedliving.net.
About The Author
John Bishop is vice president of Enhanced Living, Inc. (www.enhancedliving.net), heating, cooling and indoor air quality specialists based in the Albany, NY-area. Extensive experience in the field of building science and residential energy-management, John was formerly the state marketing coordinator for New York's award-winning Home Performance with ENERGY STAR and New York ENERGY STAR Labeled Homes Program. Copyright by Enhanced Living, Inc.
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