Radiant Heating Theory and Fundamentals

There are three basic types of heat transfer: conduction, convection and radiation.

Radiant energy is the transmission of electromagnetic waves that travel in straight lines and are absorbed thus heating objects that they strike. These objects reradiate to other colder surfaces.

Radiant ceiling panels having elevated surface temperatures cause radiant energy to be transmitted to colder surfaces. Radiant energy travels in straight lines heating solid objects such as walls, floors, furniture, people etc. In turn, all these surfaces within the space reradiate to one another until equilibrium is attained. Heated radiant ceiling panels transmit energy in the infrared portion of the electromagnetic spectrum. Glass is opaque to infrared long wave length energy. Inside glass surface temperatures increase and the glass also reflects radiant energy.

Perimeter walls with significant amounts of glass will have much lower surface temperatures than the air temperature of the space. Forced convective air reheat systems are not able to effectively counteract discomfort due to large radiant losses of occupants to the outside wall.

In conclusion, the principal benefits of perimeter radiant heating in providing superior occupant comfort are:

• Increased surface temperatures of perimeter walls reducing radiant heat loss from the body
• Downdrafts from cold outside walls are reduced especially from walls with large amounts of glass.
• The side of the human body adjacent to the outside wall receives direct radiant energy offsetting heat loss to the exterior wall.