Figure 4-6.—One-pipe water-heating system.Figure 4-7.—Two-pipe water-heating system: A. direct return;B. reverse return.A two-pipe system is shown in figure 4-7. In thissystem, the supply main carries hot water, and thecooled water is returned through a separate return pipe.For a more thorough discussion of hot-waterheating systems and equipment, you should read chapter10 of Utilitiesman 2, NAVEDTRA 10662.Unit HeatersUnit heaters are either gas-fired units or they consistof coils of tubing that circulate hot water or steam. Abuilt-in fan behind the unit or coils blows the heated airthroughout the area it is heating. When used, unit heatersare usually suspended from ceilings or are mounted highon walls in large, open areas of garages, shops, andsimilar facilities.Radiant-Heating SystemsWhen you are in a cold room, your sensation of chillis due more to the loss of your body heat to thesurrounding surfaces than to the temperature of the air.To compensate for this condition, a radiant-heating (orpanel-heating) system warms the surrounding surfacesso that you are more comfortable at a lower airtemperature. This type of heating system consists ofhot-air pipes, hot-water pipes, or electric coils that areembedded in walls, floors, or ceilings.VENTILATING SYSTEMSMost ventilating systems take advantage of thenatural environment. The ventilating system is designedto use the natural forces of wind and interior-exteriortemperature differences to cause circulation andmaintain a continuous freshening of the internal air. Ingeneral, air is permitted to enter through openings at ornear floor level and allowed to escape through openingshigh on the walls or in ceilings and roof.In mechanical ventilation, air circulation is inducedby mechanical means-usually by fans-that may becombined with supply and exhaust duct systems.AIR-CONDITIONING SYSTEMSProviding complete “comfort conditioning” for abuilding involves more than simply controllingtemperature. It also includes providing balancedhumidity; fresh and clean air that is free of odors, dirt,dust, and lint particles; and controlled air motion. Airconditioning is the process that provides and controlsall of those conditions.The cooling and warming of the air is usuallyreferred to as winter and summer air conditioning.Winter and summer air conditioning is done byinstalling both cooling and heating equipment in theair-conditioning system. Of course, single units forheating and cooling may be used separately.Heating equipment for winter air conditioning ismost often automatic. Heating coils, usually built intothe air-conditioning unit, give up heat from the water orsteam that passes through them from a heating unit. Heatmay also be generated within an air-conditioning unitdirectly by a gas-heating unit or by an electric heater.No matter what type of heat is used, the goal is to heatthe air.4-7
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