hVac controls guide for Plans examiners and Building inspectors

Figure 21: Pressure reset strategy shown in control sequenceSupply Fan Control via Static Pressure Control: Controller shall modulate supply fan VFD speed to maintainstatic pressure setpoint.• Initial static pressure setpoint shall be 0.75in H 2O.• AHU controllers shall be networked with their associated terminal units.• The static pressure setpoint shall be reset lower, until all airflow requests are satisfied and the damper onone terminal unit is wide open.• The DDC controller shall modulate fan speed to maintain the duct static pressure setpoint. As duct pressuredecreases, fan speed will increase. As duct pressure increases, fan speed will decrease.Figure 22: Illustration of VSD (here VFD) control based on static pressure sensor and zone dampersBuilding InspectionSuggested Compliance Check(s):• Verify that VSDs (or variable pitch vane-axial fans) have beeninstalled as shown in the approved mechanical design.• Confirm that static pressure sensor(s) have been installed as shown in the approved mechanical design.• If the control sequence in the approved submittal included static pressurereset, check that the corresponding control system (most likely a buildingautomation system) is installed and operational (figure 23).30 Control Requirements for Complex Systems