Engineering Manual o.. - HVAC.Amickracing

CONTROL FUNDAMENTALSHVAC SYSTEM CHARACTERISTICSGENERALAn HVAC system is designed according to capacityrequirements, an acceptable combination of first cost and operatingcosts, system reliability, and available equipment space.Figure 2 shows how an HVAC system may be distributed ina small commercial building. The system control panel, boilers,motors, pumps, and chillers are often located on the lower level.The cooling tower is typically located on the roof. Throughoutthe building are ductwork, fans, dampers, coils, air filters,heating units, and variable air volume (VAV) units and diffusers.Larger buildings often have separate systems for groups of floorsor areas of the building.DUCTWORKDAMPERAIRFILTERCOOLINGCOILFANCOOLINGTOWERHEATINGUNITVAV BOXDIFFUSERCHILLERPUMPBOILERCONTROLPANELM10506Fig. 2. Typical HVAC System in a Small Building.The control system for a commercial building comprisesmany control loops and can be divided into central system andlocal- or zone-control loops. For maximum comfort andefficiency, all control loops should be tied together to shareinformation and system commands using a buildingmanagement system. Refer to the Building Management SystemFundamentals section of this manual.The basic control loops in a central air handling system canbe classified as shown in Table 1.Depending on the system, other controls may be requiredfor optimum performance. Local or zone controls depend onthe type of terminal units used.8ENGINEERING MANUAL OF AUTOMATIC CONTROL