Heating Info From Warmair.net
Radiant Floors
A visit to any plumbing and heating trade show will give evidence to the
rise in popularity of radiant heat. Not only can it warm the home,
it can melt ice off the sidewalk or driveway, or warm seedbeds
in a greenhouse. Many factors contribute to its application and
promotion. This series of articles will deal with hot water radiant.
Comfort is the prime factor. The human body uses the feet and head to dispose
of excess heat. Because of this, warming the floor is not only
physically pleasing, but the room will feel warmer than it actually
is, allowing for lower temperature settings and fuel conservation.
The downside to radiant for fuel conservation is slow recovery.
With lower water temperatures in the tubing, setting the thermostat
back at night or when the house is vacant for short periods is
not possible, unless one wants to live with the discomfort while
the temperature slowly rises. An alternative to this will be offered
under the heading of "combination radiant and ducted".
Radiant heat can be installed in the ceiling when no alternatives are available,
but the comfort factor and efficiency are compromised.
Aesthetics plays an important part in the installation. Baseboard radiators
around the perimeter of each room or free standing cast iron units
are eliminated. with the piping in the floor or ceiling, the decor
is not affected.
With hot water as the median for radiant heat, domestic hot water can be
produced by the boiler or water heater, allowing one appliance
to do double duty.
The advent of computerized boiler controls that sense indoor and outdoor
temperatures and adjust the operating temperature of the boiler
to meet demand instead of maintaining a constant high temperature
setting increases the overall efficiency of the system. During
warm weather, the boiler maintains just enough temperature to
satisfy domestic needs.
Radiant tubing comes in a variety of materials: Cpvc, polyethylene, pex
(cross-linked polyethylene, and there are many types of pex as
well), reinforced rubber, polybutylene, and the original one,
copper.
Pex-al-pex and poly-al-poly describe tubing that is layered. A core of pex
or polyethylene is wrapped with aluminum, then an outer layer
of pex or polyethylene covers the aluminum. The aluminum forms
an oxygen barrier to prevent deterioration of the plastic, and
helps retain the shape of the tubing during installation. When
bent into a curve to make return loops, the aluminum stops the
plastic from springing back.
Radiant in Slab
If copper tubing is to be installed in a slab, certain precautions
must be taken. If it is slab on grade, soil compaction is crucial.
Flexing or cracks in the concrete can result in split tubing and
leaks. The copper can be fixed in place with wire or tie straps
to the re-enforcing wire or rods, but the steel and the copper
must be grounded. The system must be a closed loop. Fresh water
(hot water from a domestic hot water heater) will cause an electrolytic
reaction between the chemicals in the concrete and the copper,
eventually corroding and pitting the copper, creating plenty of
leaks. If the slab is on top of wood joists, a double layer of
3/4" plywood is needed to keep the deck as rigid as possible.
Slab on Grade
After soil compaction, 2" of rigid insulation is recommended.The
concrete re-enforcing mesh becomes a grid to fasten the tubing
to with plastic tie straps or wire. At least 3/4' of concrete
should cover the tubing to prevent weak spots that could collapse
under heavy objects placed on the finished floor. If extremely
heavy objects are to roll or sit on the floor, the deeper and
more even the cover, the better.
Slab on Slab
When pouring a new slab over an old one, rigid insulation is recommended
even if the old slab has insulation under it. Efficiency and recovery
time will be improved. Tubing can be attached to the mesh or to
tracks designed to clip the tubing into. At least 3/4' of concrete
should cover the tubing for floor strength.
Slab over Wood
There are two ways to insulate the wood deck before pouring the
slab over the tubing. Foil faced fiberglass insulation can be
fitted into the floor joists directly under the deck, allowing
a 2" air space. The tubing is then stapled to the deck or
fitted in the tracks manufactured specifically for the tubing.
An alternate method is to lay rigid insulation on top of the deck.
The fastening devices must reach through the insulation and into
the wood to prevent the tubing from floating up as the concrete
is poured.
Wood over Slab
If a wood floor is to be placed over a slab, sleepers are used
to create a space between the wood and the slab deep enough to
fit the tubing on top of rigid insulation. At least 1" of
rigid is needed, and 2 is better. Wood has nearly the same R-value
as insulation, and if the tubing is sandwiched between two materials
of equal insulation values, it will lose heat equally in all directions,
including the slab and into the soil below it.
Radiant and Warm Air
There are times when it is impossible or next to impossible to
get enough tubing in the floor or baseboard along the walls. Alternatives
are floor mounted recessed units or free standing radiators. With
central air almost the norm in new construction, ductwork is inevitable.
Rather than push the hot water to its limits, using a hydro-air
air handler (an air handler with a hot water coil and an evaporator
coil for the A/C), the heating demand can be done with a radiant
loop and backed up with ducted heat. Hot water is required for
the radiant anyway, so adding another circulator and feeding the
air handler isn't a big deal. By using a two stage thermostat,
the radiant loop can be the first heat call, and the ducted the
second. This design keeps the radiant as the priority heat source,
and the warm air as an assist.
Air rotation creates the opportunity for a central humidifier
and improved air filtration by using a high performance air filter
or electronic air cleaner.
This combination gives the homeowner the ultimate comfort system:
radiant heat in the floor, central air conditioning, air cleaning
and humidification, and the ability to lower the room temperature
during absences and retain the ability for fast recovery, which
radiant cannot do.
Radiant Controls and Circulation
It is possible to treat a radiant loop the same as any other hydronic
system by circulating the hot water as the thermostat calls
for heat, but it is not recommended.
Constant circulation through the loops will keep the floor an
even temperature and prevent cold spots from forming when there
is no call for heat. It also helps keep air out of the system
as well as reducing the risk of freeze up in applications where
a domestic hot water is used as the heat source and anti-freeze
cannot be used.
Sophisticated control units on the market sense indoor and outdoor
temperatures and adjust the temperature of the water in the loops
to keep the floor warm enough for comfort with minimal cool down.
This type of control will also adjust the boiler temperature accordingly
for fuel conservation. Another function is injection or mixing
hot water into the return water to prevent shocking the boiler
with a surge of cold liquid.
Non-electronic controls use a thermostat for the primary heat
call that actuates a zone valve and/or circulator to feed hot
boiler water to a mechanical control that uses a sensing bulb
with a capillary tube to meter the hot water into the distribution
manifold.
Many brands of manifolds are available that can be customized
to any application. If individual valves for each loop are not
built into the manifold, ball valves should be added so that each
loop can be flow adjusted to balance the system.
Custom distribution manifolds can be made to order that include
the circulator, automatic zone valves, a control panel with indoor
and outdoor sensors, supply and return water sensors, and individual
adjusting valves, nicely packaged on a frame for ease of installation.
These appear expensive at first glance, but if one adds up all
the components and the time it takes to construct it from scratch,
the price is understandable.
Radiant with Wood Framing
Under Deck
Radiant tubing can be installed under an existing floor with staples,
by drilling holes across the floor joists, or by just about any
means the installer can design to place the tubing as close to
the bottom of the sub floor as possible. Foil faced fiberglass
insulation should be positioned with a 2" air gap between the
foil and the bottom of the sub floor.
On Top of Insulated Deck
The insulation under the deck must have a 2" air space between the
top of the insulation and the bottom of the sub floor. Wood spacers
the same thickness of the tubing should support the floor over the
tubing. The radiant works best if it is touching the bottom of the
floor that is over it.
On Top of Uninsulated Deck
If the existing floor is not insulated and no access exists
to do so, sleepers must be placed on top of the floor to create
a gap deep enough to place rigid insulation between them that will
carry the radiant tubing on top in such a fashion that it will touch
the underside of the upper floor.
Masonry Filler
When tubing is installed between sleepers, a masonry filler will
increase the thermal mass of the floor as well as act as a sound
dampener. Do not fill the space around the tubing with products
such as vermiculite or perlite, or any Styrofoam filler that can
act as an insulator.
Copyright © 1999 Warmair.com, Inc.
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