Some Like It Radiant
Learning Objectives - After this course, you should be able to:
- Describe the basic characteristics and benefits of radiant heat transfer.
- List the various ways radiant technology can be installed today.
- Explain why certain types of radiant systems are better suited to certain spaces.
- Understand how to avoid condensation in buildings with radiant cooling.
On some primal level, we all understand the thermal characteristics of radiation. After all, who hasn't ventured out from the cool shade of a canopy tree into the sun's warmth? The immediate and often dramatic change in temperature seemingly occurs by magic-with no ducts, blowers, or other man-made devices between the heat source and us.
According to Richard Watson, a member of the American Society of Heating, Refrigerating and Air-Conditioning Engineers' technical committee on radiant and in-space convective heating and cooling, and president of SSHC, an electric radiant heating systems company in Old Saybrook, Conn., "direct source-to-object radiant heat transfer is probably the most important of the three forms of heat transfer in our lives . . . yet, it is almost totally overlooked by the design commÂunity." That may be starting to change, albeit very slowly and strategically.
Heat, or thermal energy, can be transÂferred in three ways: between particles that are in direct contact (conduction); via fluid motion (convection); and through electromagnetic waves (radiation). Unlike the first two, radiation requires no medium or physical contact: it can occur in a vacuum between objects separated by great distances. If the temperature difference between these objects is small, the thermal source must have a large surface area to noticeably affect the other entity. Radiation also requires a direct line of sight because electromagnetic waves cannot turn corners.
According to the second law of thermodynamics, thermal energy will always move from an object of higher temperature to one of lower temperature until the two reach equilibrium. So, while the cooler object becomes warmer, the warmer object becomes cooler. Thus, radiant systems can be designed not just for heating but also cooling.
Illustrations: Peter Grundy