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indamental Series Item :HVAC Systems: How They Work file:///cl/windows/TEMP/0,2637,14506,OO.h~ 14 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 (SA) and retum 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. Retum air path or ductwork in which the air flaws 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 entranr 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 elemei 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. 1=an(s) to circulate outside air across air-cooled condenser(s) 13. Pump(s) to circulate water throughwater-cooled condenser(s); condenser water (CWP); and condenser water supply (CWS) and retum (CWR). 14. Pump(s) to circulate hot water from the boiler(s) through the hot water coil(s) anc 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. 1 T. For central systems, cooling tower(s) with water-cooled condenser(s). 18. Contrels 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 i; based on the hea#ing, cooling and ventilation loads. The air volumes are in units of c per minute (cfm). Constant volume fans (supply and retum) circulate 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 tf• handling unit (AHU), 1,000 cfm is exhausted in the retum air plenum. through the exf -(F.A) 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 th air (DA) 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.