When you are in a cold room, your sensation of chill is due more to the loss of your body heat to the surrounding surfaces than to the temperature of the air. To compensate for this condition, a radiant-heating (or panel-heating) system warms the surrounding surfaces so that you are more comfortable at a lower air temperature. This type of heating system consists of hot-air pipes, hot-water pipes, or electric coils that are embedded in walls, floors, or ceilings.

Most ventilating systems take advantage of the natural environment. The ventilating system is designed to use the natural forces of wind and interior-exterior temperature differences to cause circulation and maintain a continuous freshening of the internal air. In general, air is permitted to enter through openings at or near floor level and allowed to escape through openings high on the walls or in ceilings and roof. In mechanical ventilation, air circulation is induced by mechanical means-usually by fans-that may be combined with supply and exhaust duct systems.

Providing complete "comfort conditioning" for a building involves more than simply controlling temperature. It also includes providing balanced humidity; fresh and clean air that is free of odors, dirt, dust, and lint particles; and controlled air motion. Air conditioning is the process that provides and controls all of those conditions.

The cooling and warming of the air is usually referred to as winter and summer air conditioning. Winter and summer air conditioning is done by installing both cooling and heating equipment in the air-conditioning system. Of course, single units for heating and cooling may be used separately.

Heating equipment for winter air conditioning is most often automatic. Heating coils, usually built into the air-conditioning unit, give up heat from the water or steam that passes through them from a heating unit. Heat may also be generated within an air-conditioning unit directly by a gas-heating unit or by an electric heater. No matter what type of heat is used, the goal is to heat the air.

Figure 4-10.-FIoor-mounted air-conditioning unit (shown with cover panels removed).

Cooling equipment for air conditioning must be of a type that will satisfactorily cool the air for a particular space that is being air conditioned. One method used to cool air in air-conditioning units is to evaporate water. A discussion of this method, called evaporative cooling, can be found in chapter 10 of the UT3 TRAMAN. Another method, and one of the most important, is mechanical refrigeration. In this method, the air that is to be conditioned and cooled is blown through cooling coils having a temperature of about 50F. This not only cools, but dehumidifies the air. A discussion of this method can also be found in chapter 10 of the UT3 TRAMAN.

There are various types of air-conditioning units and systems. A few of the common types are discussed below.