Washington Administrative Code › Title 51 - Enterprise Services, Department of (Building Code Council) › Chapter 51-11C - State Building Code adoption and amendment of the 2021 edition of the International Energy Conservation Code, Commercial › Section 51-11C-403610 - Section C403.6.10-High efficiency VAV systems

Current through Register Vol. 24-14, July 15, 2024
C403.6.10
High
			 efficiency variable air volume (VAV) systems.
For HVAC systems subject
			 to the requirements of Section C403.3.5 but utilizing Exception 2 of that
			 section, a high efficiency multiple-zone VAV system may be provided without a
			 separate parallel DOAS when the system is designed, installed, and configured
			 to comply with all of the following criteria (this exception shall not be used
			 as a substitution for a DOAS per Section C406.6):
1. Each VAV system must serve a minimum of
			 3,000 square feet (278.7 m2) and have a minimum of
			 five VAV zones.
2. The VAV systems
			 are provided with airside economizer per Section C403.5 without
			 exceptions.
3. A direct-digital
			 control (DDC) system is provided to control the VAV air handling units and
			 associated terminal units per Section C403.4.11 regardless of sizing thresholds
			 of Table C403.4.11.1.
4.
			 Multiple-zone VAV systems with a minimum outdoor air requirement of 2,500 cfm
			 (1180 L/s) or greater shall be equipped with a device capable of measuring
			 outdoor airflow intake under all load conditions. The system shall be capable
			 of increasing or reducing the outdoor airflow intake based on feedback from the
			 VAV terminal units as required by Section C403.6.5, without exceptions, and
			 Section C403.7.1 demand controlled ventilation.
5. Multiple-zone VAV systems with a minimum
			 outdoor air requirement of 2,500 cfm (1180 L/s) or greater shall be equipped
			 with a device capable of measuring supply airflow to the VAV terminal units
			 under all load conditions.
6. In
			 addition to meeting the zone isolation requirements of C403.2.1 a single VAV
			 air handling unit shall not serve more than 50,000 square feet (4645
			 m2) unless a single floor is greater than 50,000
			 square feet (4645 m2) in which case the air handler
			 is permitted to serve the entire floor.
7. The primary maximum cooling air for the
			 VAV terminal units serving interior cooling load driven zones shall be sized
			 for a supply air temperature that is a minimum of 5°F greater than the
			 supply air temperature for the exterior zones in cooling.
8. Air terminal units with a minimum primary
			 airflow setpoint of 50 percent or greater of the maximum primary airflow set
			 point shall be sized with an inlet velocity of no greater than 900 feet per
			 minute.
9. Allowable fan power
			 shall not exceed 90 percent of the allowable fan power budget as defined by
			 Section C403.8.1.1.
10. All fan
			 powered VAV terminal units (series or parallel) shall be provided with
			 electronically commutated motors. The DDC system shall be configured to vary
			 the speed of the motor as a function of the heating and cooling load in the
			 space. Minimum speed shall not be greater than 66 percent of design airflow
			 required for the greater of heating or cooling operation. Minimum speed shall
			 be used during periods of low heating and cooling operation and
			 ventilation-only operation.
EXCEPTION:
For series fan powered terminal units where the volume
						  of primary air required to deliver the ventilation requirements at minimum
						  speed exceeds the air that would be delivered at the speed defined above, the
						  minimum speed setpoint shall be configured to exceed the value required to
						  provide the required ventilation air.
11.
			 Fan-powered VAV terminal units shall only be permitted at perimeter zones with
			 an envelope heating load requirement. All other VAV terminal units shall be
			 single duct terminal units.
EXCEPTION:
Fan powered VAV terminal units are allowed at interior
						  spaces with an occupant load greater than or equal to 25 people per 1000 square
						  feet of floor area (as established in Table 403.3.1.1 of the
International Mechanical Code
) with demand control ventilation
						  in accordance with Section C403.7.1.
12.
			 When in occupied heating or in occupied deadband between heating and cooling
			 all fan powered VAV terminal units shall be configured to reset the primary air
			 supply setpoint, based on the VAV air handling unit outdoor air vent fraction,
			 to the minimum ventilation airflow required per
International
			 Mechanical Code
.
13.
			 Spaces that are larger than 150 square feet (14 m2)
			 and with an occupant load greater than or equal to 25 people per 1000 square
			 feet (93 m2) of floor area (as established in Table
			 403.3.1.1 of the
International Mechanical Code
) shall be
			 provided with all of the following features:
13.1. A dedicated VAV terminal unit capable
			 of controlling the space temperature and minimum ventilation shall be
			 provided.
13.2. Demand control
			 ventilation (DCV) shall be provided that utilizes a carbon dioxide sensor to
			 reset the ventilation setpoint of the VAV terminal unit from the design minimum
			 to design maximum ventilation rate as required by Chapter 4 of the
International Mechanical Code
.
13.3. Occupancy sensors shall be provided
			 that are configured to reduce the minimum ventilation rate to zero and setback
			 room temperature setpoints by a minimum of 5°F, for both cooling and
			 heating, when the space is unoccupied.
14. Dedicated data centers, computer rooms,
			 electronic equipment rooms, telecom rooms, or other similar spaces with cooling
			 loads greater than 5 watts/sf shall be provided with separate cooling systems
			 to allow the VAV air handlers to turn off during unoccupied hours in the office
			 space and to allow the supply air temperature reset to occur.
EXCEPTION:
The VAV air handling unit and VAV terminal units may be
						  used for secondary backup cooling when there is a failure of the primary HVAC
						  system.
Additionally, computer rooms, electronic equipment rooms,
				telecom rooms, or other similar spaces shall be provided with airside
				economizer in accordance with Section 403.5 without using the exceptions to
				Section C403.5.
EXCEPTION:
Heat recovery per Exception 9 of Section C403.5 may be
						  in lieu of airside economizer for the separate, independent HVAC system.
15.
			 HVAC system central heating or cooling plant will include a minimum of one of
			 the following options:
15.1. VAV terminal
			 units with hydronic heating coils connected to systems with hot water
			 generation equipment limited to the following types of equipment: Gas-fired
			 hydronic boilers with a thermal efficiency, Et, of not
			 less than 92 percent, air-to-water heat pumps or heat recovery chillers.
			 Hydronic heating coils shall be sized for a maximum entering hot water
			 temperature of 120°F (48.9°C) for peak anticipated heating load
			 conditions.
15.2. Chilled water VAV
			 air handing units connected to systems with chilled water generation equipment
			 with IPLV values more than 25 percent higher than the minimum part load
			 efficiencies listed in Table C403.3.2(3), in the appropriate size category,
			 using the same test procedures. Equipment shall be listed in the appropriate
			 certification program to qualify. The smallest chiller or compressor in the
			 central plant shall not exceed 20 percent of the total central plant cooling
			 capacity or the chilled water system shall include thermal storage sized for a
			 minimum of 20 percent of the total central cooling plant
			 capacity.
16. The DDC
			 system shall include a fault detection and diagnostics (FDD) system complying
			 with the following:
16.1. The following
			 temperature sensors shall be permanently installed to monitor system operation:
16.1.1. Outside air.
16.1.2. Supply air.
16.1.3. Return air.
16.2. Temperature sensors shall have an
			 accuracy of +-2°F (1.1°C) over the range of 40°F to 80°F
			 (4°C to 26.7°C).
16.3. The
			 VAV air handling unit controller shall be configured to provide system status
			 by indicating the following:
16.3.1. Free
			 cooling available.
16.3.2.
			 Economizer enabled.
16.3.3.
			 Compressor enabled.
16.3.4. Heating
			 enabled.
16.3.5. Mixed air low
			 limit cycle active.
16.3.6. The
			 current value of each sensor.
16.4. The VAV air handling unit controller
			 shall be capable of manually initiating each operating mode so that the
			 operation of compressors, economizers, fans and the heating system can be
			 independently tested and verified.
16.5. The VAV air handling unit shall be
			 configured to report faults to a fault management application able to be
			 accessed by day-to-day operating or service personnel or annunciated locally on
			 zone thermostats.
16.6. The VAV
			 terminal unit shall be configured to report if the VAV inlet valve has failed
			 by performing the following diagnostic check at a maximum interval of once a
			 month:
16.6.1. Command VAV terminal unit
			 primary air inlet valve closed and verify that primary airflow goes to
			 zero.
16.6.2. Command VAV terminal
			 unit primary air inlet valve to design airflow and verify that unit is
			 controlling to within 10 percent of design airflow.
16.7. The VAV terminal unit shall be
			 configured to report and trend when the zone is driving the following VAV air
			 handling unit reset sequences. The building operator shall have the capability
			 to exclude zones used in the reset sequences from the DDC control system
			 graphical user interface:
16.7.1. Supply air
			 temperature setpoint reset to lowest supply air temperature setpoint for
			 cooling operation.
16.7.2. Supply
			 air duct static pressure setpoint reset for the highest duct static pressure
			 setpoint allowable.
16.8. The FDD system shall be configured to
			 detect the following faults:
16.8.1. Air
			 temperature sensor failure/fault.
16.8.2. Not economizing when the unit should
			 be economizing.
16.8.3. Economizing
			 when the unit should not be economizing.
16.8.4. Outdoor air or return air damper not
			 modulating.
16.8.5. Excess outdoor
			 air.
16.8.6. VAV terminal unit
			 primary air valve failure.