Chapter 5.2.4.4. - Heating Applications and Sizing

Hybrid, or combination radiant and convection, systems are the subject of Sec. 7 of this Handbook. Commercial variable air volume (VAV) systems utilize perimeter radiant heat panels in place of in-duct convection electric resistance heating coils. Perimeter radiant panels are used in combination with heat pumps without central resistance backup coil heaters in order to reduce the potential usage peak in areas with demandbased electric rates. The same potential for installed capacity reduction is possible with all heat pump installations that have resistance backup (Fig. 2.10). Sizing capacity is significantly lower for framed fast-acting radiant heat panels than for conventional convective systems and other radiative systems. Delivery of almost all heat output in the form

of comfort-producing radiant energy within the occupied space is one characteristic
among many that are explained in Secs. 4 and 8 of this Handbook.

For purposes of preliminary planning, radiant ceiling panels can be likened to lighting
due to their diffuse radiant output. The flat panel configuration of heat delivery
usually requires from 10 to 15 percent of ceiling coverage for common watt densities
in residential building rooms or commercial building perimeter rooms. Although the
panels are generally positioned in relation to heat loss requirements in each room, an
exterior wall perimeter offset of 1.5 ft is normally recommended.Where the design
falls in the 10 to 15 percent range of ceiling coverage depends upon insulation, ceiling
height, glazing, doors, and other sources of heat loss, as well as geographic location.For
size estimating purposes, the range for the footprint of the common commercial office
is from 4 to 7 W/ft². The use of 4 W is appropriate for supplemental heating; 7 W is
appropriate for perimeter corner rooms and bathrooms; the average remaining office
types fall somewhere in between. Refer to Sec. 8 of this Handbook for design information
and system sizing.

Framed fast-acting radiant panels are used as primary and supplemental heating
in all types of buildings. Their use in multifloor buildings eliminates the increase in
stack effect that can be caused by a convection heating system. In buildings where
the stack effect causes discomfort, comfort can be restored through the use of radiant
heating, which may be the only cost-effective solution. Concrete floors that are
in contact with the earth will tend to take on the temperature of the substrate that in
most heating climates approximates 50°F. Radiant ceiling panels are an easy retrofit
solution to warm the surface of cold floors.

Use in housing for the elderly and nursing homes allows the provision of required
comfort through increased MRTs and equal or lower air temperatures (Fig. 2.11).
Ceiling location permits architect, owner, or occupant determination of floor space
requirement, utilization, and unobstructed floor maintenance. Elimination of air distribution
for heat delivery reduces filtration and blower costs, permitting optimum
air distribution design in conformance with code. Ease and simplicity of control, lack
of mechanical maintenance, and long heater life may reduce or eliminate building
engineering support, often required with mechanical heating, ventilating, and air-

conditioning (HVAC) systems.These are a few of the many reasons why inclusion of
radiant heating in the overall analysis process arms the designer with an important
addition to the pool of HVAC selection options.