hVac controls guide for Plans examiners and Building inspectors
hVac controls guide for Plans examiners and Building inspectors hVac controls guide for Plans examiners and Building inspectors
Additional Detail:a) Range of operationEconomizers shall be capable of operating at 100 percent outside air, even if additional mechanical cooling isrequired to meet the cooling load of the building. This strategy is known as integrated economizer control.Code SectionsIECCASHRAE2009: 503.4.1 2007: 6.5.1.32012: 403.4.1.1 2010: 6.5.1.3b) System integrationEconomizers should be used for cooling, even if supplemental mechanical cooling is required.Code SectionsIECCASHRAE2009: NA 2007: 6.5.1.32012: 403.4.1.3 2010: 6.5.1.3c) High limit shutoffWhen increase in outdoor air will no longer reduce cooling energy use, economizers must be able toreduce outdoor air to the design minimum.Code SectionsIECCASHRAE2009: NA 2007: 6.5.1.1.32012: NA 2010: 6.5.1.1.3d) Heating impactUse of the economizer must not result in an increased use of building heat.Code SectionsIECCASHRAE2009: NA 2007: 6.5.1.42012: 403.4.1.4 2010: 6.5.1.4Variable Air Volume (VAV) FansVAV fans with motors larger than 10 hp (7.5 hp under IECC 2012), must be driven by variable speed drives,use vane-axial fans with variable-pitch blades, or incorporate controls such that motors use at most 30%of the design fan power when the system delivers 50% of the design air volume. The most common meansof meeting this provision is with a variable speed drive controlled by a static pressure sensor located in thesupply air duct. The pressure measured by the sensor is used to set the speed of the drive, and the sensor28 Control Requirements for Complex Systems
must be positioned well down the duct from the fan to provide good feedback. As heating or cooling demanddecreases in the zones served, the dampers that control the supply of conditioned air to those zones willbegin to close. As they close, the pressure in the duct increases. The sensor measures this increase and signalsthe drive to slow until the static pressure setpoint is achieved.When the zone dampers are controlled by digital controls, the system efficiency should be further increasedby resetting the static pressure setpoint pressure lower, until the damper serving the zone with the greatestdemand is almost fully open. The control of VAV fans through this method is an important and somewhatcomplicated part of the HVAC control design strategy. However, verifying compliance with the coderequirements requires only a few steps.Plan ReviewSuggested Compliance Check(s):• Check the mechanical floor plan and mechanical schedule to see that large VAV fans arespecified with VSDs or are vane-axial fans with variable-pitch blades (figure 20).• If a direct digital control (DDC) system is specified on the plans, then locate controlsequences and verify that the design engineer has defined a pressure reset strategy.In the strategy, the speed of the drive, often stated as a percentage, should be relatedto the operation of a remotely located zone box or “terminal unit” (figure 21).*• Check the mechanical and electrical floor plans to verify that a pressure sensor is specifiedto be located in the supply air duct, well away from the supply fan (figure 22).* If the building is equipped with a building automation system (BAS), then these capabilities will most likely beprovided by the BAS. The BAS specifications or manual should indicate that the required capabilities are present.Figure 20: VSD specified on mechanical scheduleRemarks• Split system HVAC unit, suspended air handler, max height 48”• Hot water heating coil with 2-way control valve sized for coil performance• Variable frequency drive supply fan with variable air volume pressure control• 100% outdoor air integrated economizer with differential dry bulb control• Air flow meter• Factory installed DDC controls with selectable protocol• Remote controls interface• Premium efficiency motors• Low leakage dampersControl Requirements for Complex Systems 29
- Page 2 and 3: ContentsIntroduction ..............
- Page 5 and 6: Commercial buildingControl requirem
- Page 7 and 8: Prescriptive requirementsfor Comple
- Page 9 and 10: Code Requirements andCompliance Che
- Page 11 and 12: Control Requirements for All System
- Page 13 and 14: Figure 4: Sample control sequence s
- Page 15 and 16: d) Automatic setback and shutdown c
- Page 17 and 18: Figure 9: VSD installed on a supply
- Page 19 and 20: Figure 13: Motorized damperFigure 1
- Page 21 and 22: Building InspectionSuggested Compli
- Page 23 and 24: 4) The supply of outside air is red
- Page 25 and 26: ) Control strategyEconomizers must
- Page 27: 4) The supply of outside air is red
- Page 31 and 32: Figure 23: BAS screen shot indicati
- Page 33 and 34: Code SectionsIECCASHRAE2009: NA 200
- Page 35 and 36: Figure 27: Illustrated control sequ
- Page 37 and 38: Code SectionsIECCASHRAE2009: 503.4.
- Page 39: Building InspectionSuggested Compli
- Page 42 and 43: Building InspectionSuggested Compli
- Page 44 and 45: Figure 38: Sample control sequence
- Page 46: Building Technology ProgramThe U.S.
must be positioned well down the duct from the fan to provide good feedback. As heating or cooling dem<strong>and</strong>decreases in the zones served, the dampers that control the supply of conditioned air to those zones willbegin to close. As they close, the pressure in the duct increases. The sensor measures this increase <strong>and</strong> signalsthe drive to slow until the static pressure setpoint is achieved.When the zone dampers are controlled by digital <strong>controls</strong>, the system efficiency should be further increasedby resetting the static pressure setpoint pressure lower, until the damper serving the zone with the greatestdem<strong>and</strong> is almost fully open. The control of VAV fans through this method is an important <strong>and</strong> somewhatcomplicated part of the HVAC control design strategy. However, verifying compliance with the coderequirements requires only a few steps.Plan ReviewSuggested Compliance Check(s):• Check the mechanical floor plan <strong>and</strong> mechanical schedule to see that large VAV fans arespecified with VSDs or are vane-axial fans with variable-pitch blades (figure 20).• If a direct digital control (DDC) system is specified on the plans, then locate <strong>controls</strong>equences <strong>and</strong> verify that the design engineer has defined a pressure reset strategy.In the strategy, the speed of the drive, often stated as a percentage, should be relatedto the operation of a remotely located zone box or “terminal unit” (figure 21).*• Check the mechanical <strong>and</strong> electrical floor plans to verify that a pressure sensor is specifiedto be located in the supply air duct, well away from the supply fan (figure 22).* If the building is equipped with a building automation system (BAS), then these capabilities will most likely beprovided by the BAS. The BAS specifications or manual should indicate that the required capabilities are present.Figure 20: VSD specified on mechanical scheduleRemarks• Split system HVAC unit, suspended air h<strong>and</strong>ler, max height 48”• Hot water heating coil with 2-way control valve sized <strong>for</strong> coil per<strong>for</strong>mance• Variable frequency drive supply fan with variable air volume pressure control• 100% outdoor air integrated economizer with differential dry bulb control• Air flow meter• Factory installed DDC <strong>controls</strong> with selectable protocol• Remote <strong>controls</strong> interface• Premium efficiency motors• Low leakage dampersControl Requirements <strong>for</strong> Complex Systems 29
Change language