HVAC Control in the New Millennium.pdf - HVAC.Amickracing

Energy and Power Management, Distributed Control TrendsTable 2-2. Variable Air Volume Air Handler Operations————————————————————————————————Priority Control• PID closed-loop control of temperature and pressure (includesoccupancy and optimization)• AlarmingSecondary Control• Morning warm-up• Reset• Return fan control• Space pressurization• After hours override—tenant billing• Trending• Safeties and diagnostics• Preventive maintenanceIntegrated Control• Indoor air quality• Fire/smoke evacuation• Demand limit control• System data————————————————————————————————Control of Temperature and PressureVAV equipment must provide discharge air temperature control bysensing temperature and modulating an outside air damper for ventilation.Free cooling, along with heating and cooling equipment may alsobe involved.The controlled parameters are supply air temperature and ductstatic pressure. Another control component is alarming. The temperaturecontrol sequence may use several loops for the overall sequence of operations.One loop or control might be used to make control decisions onthe mode of operation, heat or cool. Two additional control loops, onefor heating and one for cooling, then determine the amount of heatingor cooling to provide. This amount is based on staging or the modulatingof independent capacities, but it may also include an outdoor air©2001 by The Fairmont Press, Inc. All rights reserved.