hVac controls guide for Plans examiners and Building inspectors

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