Install Instructions

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IM-PR 566442 1114 (Design Manual)
3.6.2 Capacity
To determine the cooling capacity of a radiant
slab for your application, refer to the cooling
capacities provided in Table 3-8, which captures
both the radiation and convection heat transfer
from a surface in typical indoor applications (e.g.,
room temperature of 79°F and radiant panel
surface temperature of 66°F). For operating
temperatures other than these, you may calculate
the cooling capacity by multiplying the combined
radiative and convective heat transfer coefficient
by the temperature difference between the
room temperature and the radiant panel surface
temperature.
Radiant Cooling Panel
Combined Radiative
and Convective Heat
Transfer Coefficient
(Btu/hr/ft²/°F)
Floor 1.1
Wall 1.4
Ceiling 1.9
Table 3-8 Combined radiation and convection
sensible heat transfer coefficient for radiant cooling
applications. The coefficient may increase in the
case of direct solar gains. Cooling capacity is based
on a radiant panel surface temperature of 66°F and
a room temperature of 79°F.
While Table 3-8 can be used to derive a rough
estimate of the cooling capacity of a radiant
panel, other factors to consider in making a final
determination include:
• Surface emissivity: Radiant transfer of heat
is reduced by surfaces with a low emissivity
coating.
• Skylights: Floor areas that experience direct
solar radiation may have a cooling capacity
as high as 32 Btu/hr/ft².
21
Where the sensible cooling load exceeds the cooling
capacity of the radiant cooling device, a common
practice is to provide supplemental sensible cooling
and latent cooling (dehumidification) through
secondary systems, which are addressed in the
Cooling equipment section.
3.6.2.1 Floor coverings
To maximize cooling potential of radiant surfaces,
it is important to minimize the covering R-value.
Consider an unfinished or stained slab installation
for floor applications, or if a floor covering must be
installed, look for hard surfaces with low R-values.
R-values of floor coverings over 0.25 are not
recommended. Table 3-7 shows the effect of floor
covering R-value on cooling capacity.
3.6.2.2 Placement of tubing within the slab
Viega recommends that in-slab tubing be installed
anywhere from the bottom of the slab to the
midpoint of the slab. If specifying Climate Mat,
installation is easiest when done directly over a
sub-base (e.g., compacted sub-base, sub slab or
subfloor). Installation of tubing within the middle of
the slab will provide a slight improvement in cooling
capacity but generally has less of an effect on the
cooling capacity than selection of floor covering. In
all cases, ensure that you have at least ¾" concrete
coverage over the tubing for in-slab applications.
Table 3-7 shows the effect of tubing depth on
cooling capacity.
3.6.3 Cooling equipment
Primary and Secondary Sensible
Radiant cooling lends itself to the use of relatively
high system water temperatures, which increase
options for specifying high-efficiency or
renewable-energy equipment such as ground
and air source heat pumps, indirect evaporative
cooling and solar absorption cooling systems for
sensible cooling. Further, air source heat pumps,
indirect evaporative coolers and conventional
chillers all operate more efficiently when outdoor
temperatures are low, so off-peak cooling can be
pursued as a strategy to reduce energy use, utility
costs and peak load.
Where cooling loads exceed the capacity of radiant
cooling surfaces, secondary sensible cooling
may be provided by water to air heat exchangers
such as VAV or Dedicated Outdoor Air Systems
(DOAS). These systems can be used to supply
and precondition required ventilation air. Further,
if a design is able to decouple the radiant cooling
system’s cooling plant from the secondary sensible
system, the radiant cooling system’s cooling
21. Olesen, B.W. 2008. “Radiant floor cooling systems.” ASHRAE Journal 50(9):16 – 22.