Chapter 5.4.10 - Radiant Hydronic Floor Panels

The most common form of radiant hydronic heating involves use of the entire
floor mass as the radiant floor heat transfer panel. The encapsulation of steel or
copper pipe in concrete has been superseded by the use of cross-linked polyethylene
(PEX) tubing. PEX is available in several formulations that exhibit varying
characteristics of rigidity, flexibility, temperature tolerance, pressure strength,
chemical stability and resistance, and heat transfer efficiency. Conduit diameters
commonly used for radiant floor heating are 3⁄4, 1⁄2, and 5⁄8 in for residential and up to
1 in or more in large-scale commercial applications. Conduit characteristics must
accommodate heat distribution pattern design, heat delivery capacity, panel construction
requirements, and be accounted for in mass volume calculations. (See
Fig. 4.14.)

4.10.1 Concrete Slab Heating

For buildings that already incorporate a concrete slab construction design feature,
installation of radiant conduit may be a relatively inexpensive heating solution. Slab
conversion to a radiant panel requires design review to determine what additional
insulation, mass thickness, or other features may require modification to ensure that
radiant performance parameters are met. For buildings that do not incorporate a
convenient encapsulation medium, there may be alternative design options that are
also cost-competitive.

Radiant slabs are high-mass systems.The panels’ surface temperature change is a
function of the heat transfer characteristics of the composition, tubing, and system
heat delivery capability. For many reasons mass temperature change is gradual and
a significant design characteristic.Temperature setback strategies, if used at all, must
be tempered in relation to the performance characteristics of the application. Radiant
slab thermal control in relation to seasonal heating requirements is accomplished
through the use of outdoor reset controls and anticipation.Thermal stability
is a key feature around which design control is based. For additional information,
refer to Sec. 6 of this Handbook.

In a sense, the entire foundation for concrete slab radiant floor heating becomes
part of the radiant panel system and requires comprehensive design specification in
order to ensure optimum performance.This requires finite definition of the radiant
panel in order to minimize side and back heat loss. Depending on design, the underlayment
may function as insulation, mass thermal storage, or heat conduit.Attention
to insulating the perimeter of the slab is especially important for smaller slabs due to
the larger proportional relationship to overall slab heat loss and the influence on
thermal comfort within the small designed space.

For slabs that are brought up to temperature in the fall and allowed to discharge
at the end of the heating season, the energy expended to initially charge the mass
may be small in relation to total heating season energy usage. Side loss reduction
insulation, appropriate for the climate and frost depth, ensures that perimeter heat
loss is cost-effectively minimized.The ongoing loss through the backside may also be
relatively small if surrounding materials and soil are kept dry, are porous, and not
compacted, so that heat conduction is minimized. In most climates the ground temperature,
approximately 5 to 10 ft inside of the perimeter and 2 to 3 ft below the
heated slab, will remain at the stable year-round temperature indigenous to the
region, usually just above or below 50°F.

The most common form of radiant hydronic heating involves use of the entire
floor mass as the radiant floor heat transfer panel. The encapsulation of steel or
copper pipe in concrete has been superseded by the use of cross-linked polyethylene
(PEX) tubing. PEX is available in several formulations that exhibit varying
characteristics of rigidity, flexibility, temperature tolerance, pressure strength,
chemical stability and resistance, and heat transfer efficiency. Conduit diameters
commonly used for radiant floor heating are 3⁄4, 1⁄2, and 5⁄8 in for residential and up to
1 in or more in large-scale commercial applications. Conduit characteristics must
accommodate heat distribution pattern design, heat delivery capacity, panel construction
requirements, and be accounted for in mass volume calculations. (See
Fig. 4.14.)

4.10.1 Concrete Slab Heating

For buildings that already incorporate a concrete slab construction design feature,
installation of radiant conduit may be a relatively inexpensive heating solution. Slab
conversion to a radiant panel requires design review to determine what additional
insulation, mass thickness, or other features may require modification to ensure that
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