Chapter 5.2.4 - Framed Fast-Acting Radiant Ceiling Panels

Factory-made radiant heaters include visible wall or cove units that are not generally
preinsulated. Visible radiant ceiling panels are usually constructed with internal
insulation. Framed preinsulated electric radiant heating modules are constructed
with the surface-heating element affixed directly to an insulation substrate without
an interceding air space, metal encapsulation, or protective surface grill. An insulated
surface element is characterized by higher radiant output than integral concealed
heating elements, but lower watt density than metal-encapsulated or
grill-protected elements. Framing secures the fiberglass perimeter and provides the
structure for mounting (Fig. 2.6).

2.4.1 Impact of Preinsulation

The use of insulation as a substrate for a visible radiant panel increases the maximum
permissible watt density compared with concealed or uninsulated zero-clearance systems.
Concealed systems are limited in watt density by the characteristics of the

materials with which they are, or may potentially be, in contact. For a visible ceiling
panel, thermal bridging (i.e., the transfer of heat across beams, joists, and other contiguous
surfaces) is eliminated.The insulation substrate reduces transmission of heat
through the backside of the heater, thereby permitting zero-clearance mounting to
commonly encountered building surfaces.These are distinguishing features of preinsulated
visible radiant ceiling panels.

Insulated surface element panels also feature a very fast warm-up cycle, generally
reaching full output temperature in approximately 5 minutes. The resulting surface
temperature is a function of heat capacity, surrounding air temperature, and proximity
and magnitude of heat loss. The normal operating surface temperature range
is between 150°F and 210°F, yet is safe to touch due to the lightly textured surface.
The significance of fast warm-up is quick comfort restoration through MRT elevation
without increasing output sizing.

The feature of occupancy setback recovery without increased sizing results in significant
comparative capacity reduction for radiant panel systems. The ASHRAE
Handbook recommended a sizing increase of 40 percent for conventional forced-air
systems for both day and night setback. However, actual convective equipment size
is often defaulted by the available equipment capacity selection. In addition, contractors
often oversize equipment with the idea that more is better, and that oversizing
is likely to reduce callbacks. Finally, owner bias is toward having a safety factor
for additions, space conversions, and as insurance against being cold. Radiant panel
location and sizing is precise and important in order to assure that comfort requirements
are met under dynamic operating conditions. See Sec. 8 of this Handbook for
sizing information.

The significance of and the potential for backloss vary with the application. The
absence of additional backside insulation normally impacts energy cost and comfort
performance, necessitating incorporation of appropriate design factor compensation.
In many T-bar grid ceiling applications, additional insulation is absent, yet heat
loss to the space above may be sizable and of little benefit. At the other extreme,
installation direct to a superinsulated R-70 ceiling reduces backloss to the point
where it is almost nonexistent. Determination of the amount and impact of backside
heat loss is an important design factor for sizing and/or equipment specification.

Maximizing radiant output is the goal of radiant panel design. Minimizing backloss
is an important first step toward maximizing frontal radiant output.Another sig-
nificant factor is the impact of air movement, whether natural or mechanical, in
reducing the surface temperature of the radiant heat panel, thereby reducing the
radiant output. In the built environment, air movement is usually primarily a function
of the heating system design.This is especially significant design input for radiant
panel sizing and performance analysis (Fig. 2.7).

Radiant panel planar placement is the primary determinant of the split between
radiant and convection frontal heat output. Preinsulated heat panels placed upon
the ceiling have 95 percent radiant output. The same panel placed on the wall will
have from 60 to 70 percent radiant frontal outputs. Face-up floor placement further
increases convection, while reducing radiant output to between 50 and 60 percent.
These differences are important sizing determinants. Radiant output is a key factor
in reducing the energy that is required to provide conditions of equivalent human
thermal comfort with a radiant system.

Factory-made radiant heaters include visible wall or cove units that are not generally
preinsulated. Visible radiant ceiling panels are usually constructed with internal
insulation. Framed preinsulated electric radiant heating modules are constructed
with the surface-heating element affixed directly to an insulation substrate without
an interceding air space, metal encapsulation, or protective surface grill. An insulated
surface element is characterized by higher radiant output than integral concealed
heating elements, but lower watt density than metal-encapsulated or
grill-protected elements. Framing secures the fiberglass perimeter and provides the
structure for mounting (Fig. 2.6).

2.4.1 Impact of Preinsulation

The use of insulation as a substrate for a visible radiant panel increases the maximum
permissible watt density compared with concealed or uninsulated zero-clearance systems.
Concealed systems are limited in watt density by the characteristics of the

materials with which they are, or may potentially be, in contact. For a visible ceiling
panel, thermal bridging (i.e., the transfer of heat across beams, joists, and other contiguous
surfaces) is eliminated.The insulation substrate reduces transmission of heat
through the backside...