hVac controls guide for Plans examiners and Building inspectors

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c) VAV fan pressure reset strategyIf direct digital control of individual zone boxes reports to central control panel, then a static pressurereset strategy must be included in the controls. Reset must to be based on the zone requiring thehighest supply pressure.Code SectionsIECCASHRAE2009: 503.4.2 2007: 6.5.3.2.32012: 403.4.2.2 2010: 6.5.3.2.3Humidity ControlWhere humidifiers or dehumidifiers are provided, the system must control their operation to preventsimultaneous humidification and dehumidification and to shut off the components when they are not required.Plan ReviewSuggested Compliance Check(s):• If the system has a humidifier with a preheat jacket, then confirm on the mechanical floorplan that a valve is shown on the hot water supply line feeding the preheat jacket.• Verify that control of the preheat valve is described as a note oneither the mechanical schedule or mechanical plans.*• Verify that the control sequence specifies a means to preventsimultaneous humidification and dehumidification.** 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.Building InspectionSuggested Compliance Check(s):• Where applicable, verify that an automatic valve has been installed on humidifier preheat jackets.• Verify that simultaneous humidification and dehumidification has been prevented inaccordance with the approach defined in the approved mechanical design.Additional Detail:a) Humidifier shutoffHumidifiers with preheating jackets mounted in the airstream shall be provided with an automatic valve toshut off preheat when humidification is not required.32 Control Requirements for Complex Systems
Code SectionsIECCASHRAE2009: NA 2007: 6.4.3.62010: 6.4.3.6 2012: NAb) Simultaneous humidification/dehumidificationLimit switches, mechanical stops, or other means of control, such as a sequence of operations, must beincluded that are capable of preventing simultaneous humidification and dehumidification.Code SectionsIECCASHRAE2009: NA 2007: 6.4.3.72012: NA 2010: 6.4.3.7Hydronic SystemsHVAC systems often operate at peak capacity for only a small portion of the heating and cooling season.Energy codes require that hydronic systems be provided with controls to reduce the system’s energyconsumption when operating at less than peak capacity. This is achieved through equipment sequencing,reducing the pumping of fluid through the system, and by resetting the temperature of the hot water andchilled water supply.Plan ReviewSuggested Compliance Check(s):• Review the boiler specifications in the mechanical schedule to verify that largeboilers are required to have multistaged or modulating burners.• If multiple boilers are specified, check the control specifications to confirmthat they will be linked to a common control system (figure 24).*• For large systems (see additional details below), check mechanical schedules to verify thatVSDs or multi-staged pumps are provided for the pumps. Differential pressure sensorsshould also be specified, to provide the necessary feedback to the controls (figure 25).• Review control sequences to ensure that a supply water temperature reset is included (figure 26).*• For heated and chilled water systems with one shared distribution network (a 2-pipesystem), review control sequences to verify that the system does not switch betweenheating and cooling without an outside air temperature change of at least 15 degreesand that controls can prevent such a switch without a 4 hour interval (figure 27).*• Verify that language is included in control sequences for boilers and chillers toreduce flow through the plant when capacity is reduced (figure 28).*Control Requirements for Complex Systems 33
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 and 28: 4) The supply of outside air is red
Page 29 and 30: must be positioned well down the du
Page 31: Figure 23: BAS screen shot indicati
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.

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