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-40353 - Section C403.5.3-Air economizers

Current through Register Vol. 24-14, July 15, 2024
C403.5.3
Air economizers.
Air
			 economizers shall comply with Sections C403.5.3.1 through C403.5.3.5.
C403.5.3.1
Design capacity.
Air
			 economizer systems shall be configured to modulate
outdoor air
and return air dampers to provide up to 100 percent of the design
			 supply air quantity as
outdoor air
for cooling.
C403.5.3.2
Control signal.
Economizer controls and dampers shall be configured to sequence the dampers
			 with the mechanical cooling equipment and shall not be controlled by only mixed
			 air temperature. Air economizers on systems with cooling capacity greater than
			 65,000 Btu/h shall be configured to provide partial cooling even when
			 additional mechanical cooling is required to meet the remainder of the cooling
			 load.
EXCEPTION
:
The use of mixed air temperature limit control shall be
						  permitted for systems that are both controlled from space temperature (such as
						  single
zone
systems) and having cooling capacity less than
						  65,000 Btu/h.
C403.5.3.3
High-limit shutoff.
Air economizers shall be configured to automatically reduce
outdoor air
intake to the design minimum
outdoor air
quantity
			 when
outdoor air
intake will no longer reduce cooling energy
			 usage. High-limit shutoff control types shall be chosen from Table C403.5.3.3.
			 High-limit shutoff control settings for these control types shall be those
			 specified in Table C403.5.3.3.
Table C403.5.3.3 High-Limit Shutoff Control Setting for
				Air Economizersb
Device Type
Required High Limit (Economizer off
						when):
Required High Limit For Cycling
						Fansc (Economizer off when):
Equation
Description
Equation
Description
Description
Fixed dry-bulb
TOA
75°F
Outdoor air temperature exceeds 75°F
TOA
70°F
Outdoor air temperature exceeds 70°F
Differential dry-bulb
Toa
[GREATER THAN]
Tra
Outdoor air temperature exceeds return air temperature
TOA
[GREATER THAN]
						(
TRA
- 5)
Outdoor air temperature exceeds return air temperature - 5
Fixed enthalpy with fixed dry-bulb temperatures
hOA
[GREATER THAN]
						28 Btu/lba or
TOA
[GREATER THAN] 75°F
Outdoor air enthalpy exceeds 28 Btu/lb of dry
						aira or outdoor air temperature exceeds 75°F
hOA
[GREATER THAN]
						26 Btu/lba or
TOA
[GREATER THAN] 70°F
Outdoor air enthalpy exceeds 26 Btu/lb of dry
						aird or outdoor air temperature exceeds 70°F
Differential enthalpy with fixed dry-bulb temperature
hOA
[GREATER THAN]
hRA
or
TOA
[GREATER THAN] 75°F
Outdoor air enthalpy exceeds return air enthalpy or
						outdoor air temperature exceeds 75°F
hOA
[GREATER THAN]
						(
hRA
- 2) or
TOA
[GREATER THAN] 70°F
Outdoor air enthalpy exceeds return air enthalpy or
						outdoor air temperature exceeds 70°F
For SI: °C = (°F - 32) × 5/9, 1 Btu/lb = 2.33
				kJ/kg.
aAt altitudes substantially
				different than sea level, the fixed enthalpy limit shall be set to the enthalpy
				value at 75°F and 50 percent relative humidity. As an example, at
				approximately 6,000 feet elevation the fixed enthalpy limit is approximately
				30.7 Btu/lb.
bDevices with selectable setpoints
				shall be capable of being set to within 2°F and 2 Btu/lb of the setpoint
				listed.
cWhere fans cycle on only to provide
				heating and cooling, limits are adjusted lower to compensate for fan energy use
				in economizer mode.
dFor cycling fans at altitudes
				substantially different than sea level, the fixed enthalpy limit shall be set
				to the enthalpy value at 70°F and 50 percent relative humidity.
C403.5.3.4
Relief of excess
			 outdoor air.
Systems shall be capable of relieving excess
outdoor air
during air economizer operation to prevent
			 over-pressurizing the building. The relief air outlet shall be located to avoid
			 recirculation into the building.
C403.5.3.5
Economizer dampers.
Return, exhaust/relief and outdoor air dampers used in economizers shall comply
			 with Section C403.7.8.