Radiant Heat Transfer

Radiant Heat Transfer is a concept within the domain of thermal engineering that is concerned with the creation, usage, conversion and exchange of thermal energy. What we know as “heat” is thermal energy and this energy is classified into mechanisms of thermal convection, thermal radiation, thermal conduction, and phase changes.

Advection: This is the transport of a fluid from one place to another.

Conduction: This is the transfer of energy between objects that are in physical contact.

Convection: This is the transfer of energy between an object and its environment.

Radiation: This is the transfer of electromatic radiation created by charged particles in matter.

The goal of thermal energy transfer is to reach a state of equilibrium between two physical systems. If one item is at a different temperature than another item, the heat available will flow from the warmer object to the colder object. According to the second law of thermodynamics, higher temperatures will always flow from a higher temperature space to a lower temperature space.

Practical Application

In the field of HVAC, radiant heating systems may be seen as radiant floors or walls. Heat is supplied to the floor or walls through surface materials to the room. This type of heating is more efficient than forced air heating because it does not involve the use of ducts which can leak or reduce temperatures over long paths.

Radiant Floor Heat

Heat coming from under flooring can be categorized into three basic types. There are air floors that allow air to be the medium through which heat is transferred. Electric floors use cables that are built into the flooring. Hot water floors use hydronic heat transfer to heat a space.

Air-Heated Radiant Floors: This type of radiant heat is not the most efficient because air simply does not hold temperatures very well. Only the daytime rays of the sun can energize this process due to the needed use of solar energy to maintain temperatures.

Electric Radiant Floors: This type of radiant heat uses electricity for its energy source resulting in efficiency ratings being determined by the cost of local energy suppliers. This system relies heavily on a thick concrete floor that can block any transfer of cold from the ground.

Hydronic Radiant Floors: This type of heating system is the most often used. Boilers are used that send the heat to tubing that is laid down in a pattern under the floor. Zoning valves can control which areas of the room will receive the warm water and which will not.

In radiant floor installations, the type of installation is important along with the type of floor coverings used. Ceramic tile is the most commonly used product for this type of flooring due to its ability to conduct heat. Ceramic also has the capacity to store heat for a while, thus reducing energy costs. Other coverings include linoleum, vinyl, carpet, and wood. Any floor covering installed must be thin as it will reduce the transfer of heat from under the floor to the room.

Radiant Heat Panels

Panels used in this type of heating system are mounted in the wall or ceiling. They are made of aluminum and heated by electricity or hot water. Because of the use of aluminum, these types of panels have the quickest response time as they are excellent conductors of thermal energy. If installed in the wall, they can heat a room quickly and efficiently.