A heating, air-conditioning, or refrigeration system in which heat is exchanged directly with a surrounding material or space.

Stress without bending or shear; only compressive or tensile stress.

The sound which travels directly from the source to the point of observation no reflection of sound is involved.

A solar water-heating system in which water passes directly from the potable water supply, through the collectors and storage, to

The selection of a contractor by the owner, based on the owners evaluation of the contractors availability, competence, and reputation,