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Fundamental Series Item :HVAC Systems: How They Work file:/!/c ~/windows/TEMP/0,2637,14506,( 13 HVAC System ,Components The basic components in a common central HVAC system as illustrated in Figure 1 1: Fan(s) to circulate the supply air (5A) and return air (RA). 2. Supply air ductwork in which the air flows from the supply fan to the conditioned sl 3. Air devices such as supply air outlets and return air inlets. 4. Return air path or ductwork in which the air flows back from the conditioned spacE mixed air chamber (plenum). 5. Outside air (OA) device such as an opening, louver or duct to allow for the entrant outside air into the mixed air chamber. 6. Mixed air chamber to receive the return air and mix it with outside air. 7. Filter section(s) to remove dirt and dust particles from the mixed air. 8. Heat exchanger(s) such as hot water coil(s), steam coil(s), refrigerant evaporator( chilled water coil(s) to add heat to or remove heat from the circulated air. 9. Auxiliary heating devices such as natural gas furnace(s) or electric heating elemer 10. Compressor(s) to compress the refrigerant vapor and pump the refrigerant arour system. . 11. Condenser(s) to remove heat from the refrigerant vapor and condense it to a liq~ 12. Fan(s) to circulate outside air across air-cooled condenser(s) 13. Pump(s) to circulate water through water-cooled condenser(s); condenser water (CWP); and condenser water supply (CWS) and return (CWR). 14. Pump(s) to circulate hot water from the boiler(s) through the hot water coil(s) ant circulate chilled water from the chillers) through the chilled water coil(s) and back to chiller(s). 15. For central systems, water or steam boiler(s) as a central heating source. 16. For central systems, water chillers) as a central cooling source. 17. For central systems, cooling tower(s) with water~ooled condenser(s). 18. Controls to start, stop, or regulate the flow of air, water, steam, refrigerant and el HVAC System Example Airflow: The volume of air required to heat, cool and provide good indoor air quality is based on the heating, cooling and ventilation loads. The air volumes are in units of c per minute (cfm). Constant volume fans (supply and return) ciroulate the conditioned For the example system (Figure 1), the total volume of air supplied to the conditioner 6,000 cfm. Of this 6,000 cfm circulated through the conditioned space and back to tl' handling unit (AHU), 1,000 cfm is exhausted in the return air plenum through.the exf -(EA) damper. The remaining 5,000 cfm goes into the mixed air chamber. At the same time, 1,000 cfm is exhausted another 1,000 cfm is brought in through to air (OA) dampers in the mixed air plenum. This 1,000 cfm of outside air mixes with tl remaining 5,000 cfm of return air. The 6,000 cfm of mixed air then travels through th the coil sections.