Radiant Floor Heating
Benefits
Radiant-floor heating offers a number of significant benefits:
Comfort. By far, the biggest selling point for radiant-floor
heating is comfort. The large radiant surface means that most of the heat
will be delivered by radiation—heating occupants directly—rather than
by convection (the primary mechanism of heat delivery from conventional
hydronic baseboard “radiators”). Warmer surfaces in a living space
result in a higher mean radiant temperature, a measure of surface
temperatures in a space that influences the rate of radiant heat loss from
occupants). With higher mean radiant temperatures, most people are
comfortable even at lower air temperatures. Delivery of the heat at floor
level with a warm floor surface also allows occupants to walk around
barefoot even in winter—a very popular feature. Enhanced comfort should
be a big selling point in any green home, so a strong case can be made for
this heating approach.
“Until you’re lived with this form of heat,” says Radiant Panel
Association executive director Larry Drake (who got involved with radiant
heating after years of working with solar houses), “it’s hard to
understand how comfortable it is.” He argues that with green homes in
particular, after going to all the effort and expense to incorporate
healthy and sustainable materials, ensuring high levels of comfort with
radiant heat should be a top priority.
Energy savings. There is potential for saving energy with
radiant-floor heating through several mechanisms, including lower
thermostat settings, lower-temperature boiler settings, and reduced
infiltration. Homeowners with radiant-floor heating are likely to be
comfortable at lower air temperatures because of the elevated mean radiant
temperature in such homes, the lack of significant airflow (as occurs with
convective hydronic heating and forced-air heating systems), and the
delivery of heat at floor level. Proponents of radiant-floor heating argue
that someone normally comfortable at 72°F (22°C) will be comfortable in
a building with radiant-floor heating kept at 68°F (20°C). If this is
true, one would expect people with radiant-floor heating to keep their
thermostats lower and thus realize significant energy savings. (See page
13 for further discussion.)
The second opportunity for energy savings with radiant-floor heating is
through keeping the boiler temperature lower than is necessary with
conventional baseboard hot water distribution. The typical European
approach with radiant-floor heating is to circulate fairly low-temperature
water on an almost-continuous basis, varying the water temperature as
needed to satisfy the load. This practice might reduce heat loss into
unconditioned space if boiler and piping are located in an unheated
basement, but experts EBN spoke with suggest that the savings would be
very small at best—especially because of the additional electricity
consumption to operate pumps for long hours. Green building consultant
Marc Rosenbaum, P.E., of Meriden, New Hampshire, suggests using a low-mass
boiler that is fired on-demand, rather than a high-mass boiler operated
almost continuously.
The third opportunity for energy savings (over forced-air heat) is that
radiant-floor systems do not increase the rate of air infiltration.
Standard forced-air heating systems can significantly increase or decrease
air pressure in different parts of a building, which in turn can increase
air infiltration/exfiltration rates—at least in a conventional, leaky
building. With radiant-floor heating, as with baseboard hydronic heating,
this will not happen. (A well-designed, properly balanced forced-air
system should not increase infiltration.)
Potential for use of solar energy. The relatively low temperature required
for circulation water in a radiant-floor heating system provides an
opportunity to utilize solar hot water. This approach works best with
concrete-slab systems; higher-temperature water is generally required when
the tubing is attached to the underside of wooden floors. While such
systems are fairly complex and expensive, radiant slabs offer one of the
best ways to make use of solar energy for heating portions of a building
without direct access to sunlight. Most practical are systems in which
solar energy heats water in a storage tank that can then be circulated
through the slab. According to an EREN Consumer Energy Information Brief (www.eren.doe.gov)
titled “Solar Radiant Floor Heating,” such systems typically cost at
least $14,000. Backup heat is still required and can be provided with a
wood stove, through-the-wall-vented gas heater, electric resistance heat,
or backup heating element in the solar storage tank.
*From the Oregon Department of Energy - click
here to view the entire article
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