3.7.4 Outdoor Air Controls and Economizers

Outside Air Controls

Maximum Outside Air Ratio
Applicability	All systems with modulating outside air dampers
Definition	The descriptor is used to limit the maximum amount of outside air that a system can provide as a percentage of the design supply air. It is used where the installation has a restricted intake capacity.
Units	Ratio
Input Restrictions	As designed
Baseline Rules	1.0

Design Outside Air Flow
Applicability	All systems with outside air dampers
Definition	The rate of outside air that needs to be delivered by the system at design conditions. This input may be derived from the sum of the design outside air flow for each of the zones served by the system.
Units	cfm
Input Restrictions	As designed
Baseline Rules	Same as proposed design. This input along with occupant density determines if the zones served by the system shall have demand control ventilation. See ventilation control method at the zone level.

Outdoor Air Control Method
Applicability	All HVAC systems that deliver outside air to zones
Definition	The method of determining the amount of outside air that needs to be delivered by the system. Each of the zones served by the system report their outside air requirements on an hourly basis. The options for determining the outside air at the zone level are discussed above. This control method addresses how the system responds to this information on an hourly basis. Options include: Average Flow. The outside air delivered by the system is the sum of the outside air requirement for each zone, without taking into account the position of the VAV damper in each zone. The assumption is that there is mixing between zones through the return air fan. Critical Zone. The critical zone is the zone with the highest ratio of outside air to supply air. The assumption is that there is no mixing between zones. This method will provide greater outside air than the average flow method because when the critical zone sets the outside air fraction at the system, the other zones are getting greater outside air than required. The quantity of outside air can be controlled in a number of ways, but a common method is to install a flow station at the outside air supply which modulates the position of the outside air and return dampers to maintain the desired outside air flow. With the average flow, a CO₂ sensor in the return air duct is another way to control the position of the outside air and return dampers.
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	Same as proposed design

Air Side Economizers

Economizer Control Type
Applicability	All systems with an air-side economizer
Definition	An air-side economizer increases outside air ventilation during periods when refrigeration loads can be reduced from increased outside air flow. The control types include: No economizer Fixed dry-bulb. The system shifts to 100% outside air and shuts off the cooling when the temperature of the outside air is equal to or lower than the supply air temperature. Differential dry-bulb. The system shifts to 100% outside air when the temperature of the outside air is lower than the return air temperature but continues to operate the cooling system until the outside air temperature reaches the supply air temperature. Fixed enthalpy. The system shifts to 100% outside air and shuts off the cooling when the enthalpy of the outside air is equal to or lower than the supply air enthalpy. Differential enthalpy. The system shifts to 100% outside air when the enthalpy of the outside air is lower than the return air enthalpy but continues to operate the cooling system until the outside air enthalpy reaches the supply air enthalpy.
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	The control should be no economizer when the baseline building cooling capacity $\leq$50 tons AND the baseline building system total cooling capacity $\leq$95,000 Btu/h. Otherwise, the control should be based on the prescribed system type as shown in [bookref id="baseline-economizer-control-type"].

[table title="Baseline Economizer Control Type" id="baseline-economizer-control-type"]

Baseline building System	Economizer Control
System 1 – PTAC	None
System 2 – PTHP	None
System 3 – PSZ-AC	Differential dry-bulb None in climate zones 1a-4a and 1b
System 4 – PSZ-HP	Differential dry-bulb None in climate zones 1a-4a and 1b
System 5 – Packaged VAV with Reheat	Differential dry-bulb None in climate zones 1a-4a and 1b
System 6 – Packaged VAV with PFP boxes	Differential dry-bulb None in climate zones 1a-4a and 1b
System 7 – VAV with Reheat	Differential dry-bulb None in climate zones 1a-4a and 1b
System 8 – VAV with PFP boxes	Differential dry-bulb None in climate zones 1a-4a and 1b

Economizer High Temperature Lockout
Applicability	Systems with fixed dry-bulb economizer
Definition	The outside air setpoint temperature above which the economizer will return to minimum position.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	Not applicable

Economizer Low Temperature Lockout
Applicability	Systems with air-side economizers
Definition	A feature that permits the lockout of economizer operation (return to minimum outside air position) when the outside air temperature is below the lockout setpoint.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	Not used

Economizer High Enthalpy Lockout
Applicability	Systems with fixed enthalpy or differential enthalpy economizers
Definition	The outside air enthalpy above which the economizer will return to minimum position
Units	Btu/lb
Input Restrictions	As designed. The default is 25 Btu/lb.
Baseline Rules	No lockout limit

Outside Air Controls

Maximum Outside Air Ratio
Applicability	All systems with modulating outside air dampers
Definition	The descriptor is used to limit the maximum amount of outside air that a system can provide as a percentage of the design supply air. It is used where the installation has a restricted intake capacity.
Units	Ratio
Input Restrictions	As designed
Baseline Rules	1.0

Design Outside Air Flow
Applicability	All systems with outside air dampers
Definition	The rate of outside air that needs to be delivered by the system at design conditions. This input may be derived from the sum of the design outside air flow for each of the zones served by the system.
Units	cfm
Input Restrictions	As designed
Baseline Rules	Same as proposed design. This input along with occupant density determines if the zones served by the system shall have demand control ventilation. See ventilation control method at the zone level.

Outdoor Air Control Method
Applicability	All HVAC systems that deliver outside air to zones
Definition	The method of determining the amount of outside air that needs to be delivered by the system. Each of the zones served by the system report their outside air requirements on an hourly basis. The options for determining the outside air at the zone level are discussed above. This control method addresses how the system responds to this information on an hourly basis. Options include: Average Flow. The outside air delivered by the system is the sum of the outside air requirement for each zone, without taking into account the position of the VAV damper in each zone. The assumption is that there is mixing between zones through the return air fan. Critical Zone. The critical zone is the zone with the highest ratio of outside air to supply air. The assumption is that there is no mixing between zones. This method will provide greater outside air than the average flow method because when the critical zone sets the outside air fraction at the system, the other zones are getting greater outside air than required. The quantity of outside air can be controlled in a number of ways, but a common method is to install a flow station at the outside air supply which modulates the position of the outside air and return dampers to maintain the desired outside air flow. With the average flow, a CO₂ sensor in the return air duct is another way to control the position of the outside air and return dampers.
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	Same as proposed design

Air Side Economizers

Economizer Control Type
Applicability	All systems with an air-side economizer
Definition	An air-side economizer increases outside air ventilation during periods when refrigeration loads can be reduced from increased outside air flow. The control types include: No economizer Fixed dry-bulb. The system shifts to 100% outside air and shuts off the cooling when the temperature of the outside air is equal to or lower than the supply air temperature. Differential dry-bulb. The system shifts to 100% outside air when the temperature of the outside air is lower than the return air temperature but continues to operate the cooling system until the outside air temperature reaches the supply air temperature. Fixed enthalpy. The system shifts to 100% outside air and shuts off the cooling when the enthalpy of the outside air is equal to or lower than the supply air enthalpy. Differential enthalpy. The system shifts to 100% outside air when the enthalpy of the outside air is lower than the return air enthalpy but continues to operate the cooling system until the outside air enthalpy reaches the supply air enthalpy.
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	The control should be no economizer when the baseline building cooling capacity $\leq$50 tons AND the baseline building system total cooling capacity $\leq$95,000 Btu/h. Otherwise, the control should be based on the prescribed system type as shown in Table 6.7.4-1 .

Table 6.7.4-1: Baseline Economizer Control Type

Baseline building System	Economizer Control
System 1 – PTAC	None
System 2 – PTHP	None
System 3 – PSZ-AC	Differential dry-bulb None in climate zones 1a-4a and 1b
System 4 – PSZ-HP	Differential dry-bulb None in climate zones 1a-4a and 1b
System 5 – Packaged VAV with Reheat	Differential dry-bulb None in climate zones 1a-4a and 1b
System 6 – Packaged VAV with PFP boxes	Differential dry-bulb None in climate zones 1a-4a and 1b
System 7 – VAV with Reheat	Differential dry-bulb None in climate zones 1a-4a and 1b
System 8 – VAV with PFP boxes	Differential dry-bulb None in climate zones 1a-4a and 1b
System 9 – Heating and Ventilation	None (no cooling)
System 10 – Heating and Ventilation	None (no cooling)

Economizer High Temperature Lockout
Applicability	Systems with fixed dry-bulb economizer
Definition	The outside air setpoint temperature above which the economizer will return to minimum position.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	Not applicable

Economizer Low Temperature Lockout
Applicability	Systems with air-side economizers
Definition	A feature that permits the lockout of economizer operation (return to minimum outside air position) when the outside air temperature is below the lockout setpoint.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	Not used

Economizer High Enthalpy Lockout
Applicability	Systems with fixed enthalpy or differential enthalpy economizers
Definition	The outside air enthalpy above which the economizer will return to minimum position
Units	Btu/lb
Input Restrictions	As designed. The default is 25 Btu/lb.
Baseline Rules	No lockout limit

Outside Air Controls

Maximum Outside Air Ratio
Applicability	All systems with modulating outside air dampers
Definition	The descriptor is used to limit the maximum amount of outside air that a system can provide as a percentage of the design supply air. It is used where the installation has a restricted intake capacity.
Units	Ratio
Input Restrictions	As designed
Baseline Rules	1.0 for systems 3-8 and 11-13.

Design Outside Air Flow
Applicability	All systems with outside air dampers
Definition	The rate of outside air that needs to be delivered by the system at design conditions. This input may be derived from the sum of the design outside air flow for each of the zones served by the system.
Units	cfm
Input Restrictions	As designed
Baseline Rules	Same as proposed design, except for the following cases: When demand control ventilation is modeled in the proposed design for systems less than or equal to 3,000 cfm with an occupant load of 100 people per 1,000 ft² or less. When the proposed design uses the Ventilation Rate Procedure of Standard 62.1, Section 6.2 and has a ventilation effectiveness greater than 1.0. When outside air ventilation is increased above the requirements of Standard 62.1 in order to get credit for recognition programs. When modeling laboratory spaces that are prevented from recirculating return air. See ventilation control method at the zone level.

Outdoor Air Control Method
Applicability	All HVAC systems that deliver outside air to multiple zones
Definition	The method of determining the amount of outside air that needs to be delivered by the system. Each of the zones served by the system report their outside air requirements on an hourly basis. The options for determining the outside air at the zone level are discussed above. This control method addresses how the system responds to this information on an hourly basis. Options include: Average Flow. The outside air delivered by the system is the sum of the outside air requirement for each zone, without taking into account the position of the VAV damper in each zone. The assumption is that there is mixing between zones through the return air fan. Critical Zone. The critical zone is the zone with the highest ratio of outside air to supply air. The assumption is that there is no mixing between zones. This method will provide greater outside air than the average flow method because when the critical zone sets the outside air fraction at the system, the other zones are getting greater outside air than required. The quantity of outside air can be controlled in a number of ways, but a common method is to install a flow station at the outside air supply which modulates the position of the outside air and return dampers to maintain the desired outside air flow. With the average flow, a CO2 sensor in the return air duct is another way to control the position of the outside air and return dampers.
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	Same as proposed design

Air Side Economizers

Table 3.7.4-1 – Economizer Requirements for Baseline Building Systems 3-8 and 11-13

Thermal Zone	Humid (A)	Dry (B)	Marine (C)
0	Economizer not required	Economizer not required	Fixed drybulb economizer with high-limit shutoff of 75 °F
1
2
3
4
5	Fixed drybulb economizer with high-limit shutoff of 70 °F
6
7
8

Economizers are not required in the baseline building for systems meeting one or more of the following exceptions:

Systems that include gas-phase air cleaning to meet the requirements of Section 6.1.2 in Standard 62.1. This exception shall be used only if the system in the proposed design does not match the building design.
Where the use of outdoor air for cooling will affect supermarket open refrigerated casework systems. This exception shall only be used if the system in the proposed design does not use an economizer. If the exception is used, an economizer shall not be included in the baseline building design.
System types 3 or 4 that that serve computer rooms. If system type 11 is used to serve a computer room, it shall be equipped with a water economizer.

Economizer Control Type
Applicability	All systems with an air-side economizer
Definition	An air-side economizer increases outside air ventilation during periods when refrigeration loads can be reduced from increased outside air flow. The control types include: No economizer Fixed dry-bulb. The system shifts to 100% outside air and shuts off the cooling when the temperature of the outside air is equal to or lower than the supply air temperature. Differential dry-bulb. The system shifts to 100% outside air when the temperature of the outside air is lower than the return air temperature but continues to operate the cooling system until the outside air temperature reaches the supply air temperature. Fixed enthalpy. The system shifts to 100% outside air and shuts off the cooling when the enthalpy of the outside air is equal to or lower than the supply air enthalpy. Differential enthalpy. The system shifts to 100% outside air when the enthalpy of the outside air is lower than the return air enthalpy but continues to operate the cooling system until the outside air enthalpy reaches the supply air enthalpy. Differential dry-bulb or enthalpy economizers are also known as integrated economizers.
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	Fixed dry-bulb economizers are required for baseline building systems 3-8 and 11-13 except for climates identified in Table 3.7.4-1

Economizer High Temperature Lockout
Applicability	Systems with fixed dry-bulb economizer
Definition	The outside air setpoint temperature above which the economizer will return to minimum position.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	75 °F in all climates that require an economizer, except 70 °F in climate zones 6a and 7a. See Table 3.7.4-1.

Economizer Low Temperature Lockout
Applicability	Systems with air-side economizers
Definition	A feature that permits the lockout of economizer operation (return to minimum outside air position) when the outside air temperature is below the lockout setpoint.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	Not used

Economizer High Enthalpy Lockout
Applicability	Systems with fixed enthalpy or differential enthalpy economizers
Definition	The outside air enthalpy above which the economizer will return to minimum position
Units	Btu/lb
Input Restrictions	As designed. The default is 25 Btu/lb.
Baseline Rules	Not applicable since no baseline building system has an enthalpy economizer

90.1-2019

Outside Air controls

Maximum Outside Air Control
Applicability	All systems with modulating outside air dampers
Definition	The descriptor is used to limit the maximum amount of outside air that a system can provide as a percentage of the design supply air. It is used where the installation has a restricted intake capacity.
Units	Ratio
Input Restrictions	As designed. Maximum of 1.0.
Baseline Building	1.0 for all systems with economizers. For others, equal to the ratio of required outdoor air to the peak supply airflow at design conditions.

Design Outside Airflow
Applicability	All systems with outside air dampers
Definition	The rate of outside air that needs to be delivered by the system at design conditions. This input may be derived from the sum of the design outside airflow for each of the zones served by the system.
Units	cfm
Input Restrictions	As designed
Baseline Building	Same as proposed. This input along with occupant density determines if the zones served by this system are required to have demand control ventilation. This value might also be different for buildings using the ASHRAE 62.1 Ventilation Rate Procedure as described in Section 3.5.5.5 of this document. See Section 3.5.5.4 of this document for ventilation control method at the zone level.

Outdoor Air Control Method
Applicability	All HVAC systems that deliver outside air to multiple zones. (These requirements don’t apply to systems supplying air to single zones.)
Definition	The method of determining the amount of outside air that needs to be delivered by the system. Each of the zones served by the system reports its outside air requirements hourly. The options for determining the outside air at the zone level are discussed above. This control method addresses how the system responds to this information hourly. Options include: · Average flow: The outside air delivered by the system is the sum of the outside air requirement for each zone, without taking into account the position of the VAV damper in each zone. The assumption is that there is mixing between zones through the return air stream. · Critical zone: The critical zone is the zone with the highest ratio of outside air to supply air. The assumption is that there is no mixing between zones. This method will provide greater outside air than the average flow method because when the critical zone sets the outside air fraction at the system, the other zones are getting more outside air than required. The quantity of outside air can be controlled in a number of ways, but a common method is to install a flow station at the outside air supply that modulates the position of the outside air and return dampers to maintain the desired outside airflow. With the average flow, a CO2 sensor in the return air duct is another way to control the position of the outside air and return dampers.
Units	List (see above)
Input Restrictions	As designed
Baseline Building	Same as proposed. See Section 3.5.5.5 for details.

Outdoor Air Minimum Flow Schedule
Applicability	All HVAC systems that deliver outside air
Definition	The schedule shall allow the system to provide the minimum system outdoor air requirements based on a time of day schedule. This input is specifically helpful when ventilation intake needs to be modified for fan cycling operation during unoccupied hours. This schedule would be an “on/off” schedule that determines when the design outside air is supplied by the system.
Units	List (see above)
Input Restrictions	As designed
Baseline Building	In the following cases minimum design ventilation will be provided based on the HVAC availability schedule and outside air dampers shall be closed during night cycle and morning warm-up: · All systems in buildings three stories or more in climate zones 4 through 8 · All systems required to have an economizer · Systems required to include demand controlled ventilation In all other cases outside air shall be provided anytime the system operates.

Air Side Economizers

Economizer Control Type
Applicability	All systems with an air-side economizer
Definition	An air-side economizer increases outside air ventilation during periods when cooling loads can be reduced from increased outside airflow. The control types include: · No economizer. · Fixed dry-bulb. The economizer is enabled when the temperature of the outside air is lower than a fixed setpoint. · Differential dry-bulb. The economizer is enabled when the temperature of the outside air is lower than the return air temperature. · Fixed enthalpy. The economizer is enabled when the enthalpy of the outside air is lower than a fixed setpoint · Differential enthalpy. The economizer is enabled when the enthalpy of the outside air is lower than the return air enthalpy. · Differential dry-bulb and enthalpy. The economizer is enabled when the outside air dry-bulb is less than the return air dry-bulb AND the outside air enthalpy is less than the return air enthalpy. · Fixed dewpoint and dry-bulb. The economizer is enabled when the dewpoint and dry-bulb temperature of the outside air are below the specified setpoints.
Units	List (see above)
Input Restrictions	As designed
Baseline Building	Outdoor air economizers shall not be included in baseline HVAC systems 1, 2, 9, and 10. Outside air economizers shall be included in baseline HVAC systems 3 through 8, 11, 12, and 13, in climate zones 2B, 3B, 3C, 4C, 5B, 5C, 6B, 7, and 8. Economizers are not required in other climate zones. Economizer control shall be fixed dry bulb with a temperature setpoint as indicated under Economizer High-Temperature Lockout below. Exceptions: Economizers shall not be included for systems meeting one or more of the exceptions listed below. a. Systems that include gas-phase air cleaning to meet the requirements of Section 6.1.2 in Standard 62.1. In the scenario, where there isn’t a one-to-one mapping between the systems in the proposed and baseline building, all systems serving the zones that qualify for the exception in the proposed building will not have economizers. b. Where the use of outdoor air for cooling will affect supermarket open refrigerated casework systems. This exception shall only be used if the system in the proposed design does not use an economizer. c. Systems serving computer rooms which are baseline systems 3-4 shall not have an economizer. Systems that server computer rooms that are baseline system 11 shall include an integrated fluid economizer meeting the requirements of Standard 90.1-2019 Section 6.5.1.2, also summarized below and in Section 3.7.4 of this manual. Fluid Economizers Fluid economizer systems shall be capable of providing up to 100% of the expected system cooling load at outdoor air temperatures of 50°F dry bulb/45°F wet bulb and below. Exceptions: · Systems primarily serving computer rooms in which 100% of the expected system cooling load at the dry-bulb and wet-bulb temperatures listed in Table 6.5.1.2.1 of Standard 90.1-2019 is met with water-cooled fluid economizers.. · Systems primarily serving computer rooms in which 100% of the expected system cooling load at the dry-bulb temperatures listed in Table 6.5.1.2.1 of Standard 90.1-2019 is met with air-cooled fluid economizers. · Systems where dehumidification requirements cannot be met using outdoor air temperatures of 50°F dry-bulb/45°F wet-bulb and where 100% of the expected system cooling load at 45°F dry-bulb/40°F wet-bulb is met with water-cooled fluid economizers.

Economizer Integration
Applicability	Airside economizers
Definition	This input specifies whether or not the economizer is integrated with mechanical cooling. It is up to the modeling software to translate this into software-specific inputs to model this feature. The input could take the following values: · Non-integrated: The system runs the economizer as the first stage of cooling. When the economizer is unable to meet the load, the economizer returns the outside air damper to the minimum position and the compressor turns on as the second stage of cooling. · Integrated: The system can operate with the economizer fully open to outside air and mechanical cooling active (compressor running) simultaneously, even on the lowest cooling stage.
Units	List: Non-integrated, Integrated
Input Restrictions	As designed
Baseline Building	Integrated

Economizer High-Temperature Lockout
Applicability	Systems with fixed dry-bulb economizer
Definition	The outside air setpoint temperature above which the economizer will return to minimum position
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	Economizer control shall be fixed dry bulb with a temperature setpoint of 70°F in climate zones 5A and 6A and 75°F in all other climate zones where economizers are required

Economizer Low-Temperature Lockout
Applicability	Systems with air-side economizers
Definition	A feature that permits the lockout of economizer operation (return to minimum outside air position) when the outside air temperature is below the lockout setpoint
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	None

Economizer High Enthalpy Lockout
Applicability	Systems with fixed enthalpy or differential enthalpy economizers
Definition	The outside air enthalpy above which the economizer will return to minimum position
Units	Btu/lb
Input Restrictions	As designed. The default is 28 Btu/lb. (High altitude locations may require different setpoints.) The software shall apply a fixed offset and add 2 Btu/lb to the user-entered value.
Baseline Building	Not applicable since no baseline building system has an enthalpy economizer

Outside Air Controls

Maximum Outside Air Ratio
Applicability	All systems with modulating outside air dampers
Definition	The descriptor is used to limit the maximum amount of outside air that a system can provide as a percentage of the design supply air. It is used where the installation has a restricted intake capacity.
Units	Ratio
Input Restrictions	As designed

Design Outside Air Flow
Applicability	All systems with outside air dampers
Definition	The rate of outside air that needs to be delivered by the system at design conditions. This input may be derived from the sum of the design outside air flow for each of the zones served by the system.
Units	cfm
Input Restrictions	As designed

Outdoor Air Control Method
Applicability	All HVAC systems that deliver outside air to zones
Definition	The method of determining the amount of outside air that needs to be delivered by the system. Each of the zones served by the system report their outside air requirements on an hourly basis. The options for determining the outside air at the zone level are discussed above. This control method addresses how the system responds to this information on an hourly basis. Options include: Average Flow. The outside air delivered by the system is the sum of the outside air requirement for each zone, without taking into account the position of the VAV damper in each zone. The assumption is that there is mixing between zones through the return air fan. Critical Zone. The critical zone is the zone with the highest ratio of outside air to supply air. The assumption is that there is no mixing between zones. This method will provide greater outside air than the average flow method because when the critical zone sets the outside air fraction at the system, the other zones are getting greater outside air than required. The quantity of outside air can be controlled in a number of ways, but a common method is to install a flow station at the outside air supply which modulates the position of the outside air and return dampers to maintain the desired outside air flow. With the average flow, a CO₂ sensor in the return air duct is another way to control the position of the outside air and return dampers.
Units	List (see above)
Input Restrictions	As designed

Air Side Economizers

Economizer Control Type
Applicability	All systems with an air-side economizer
Definition	An air-side economizer increases outside air ventilation during periods when refrigeration loads can be reduced from increased outside air flow. The control types include: No economizer Fixed dry-bulb. The system shifts to 100% outside air and shuts off the cooling when the temperature of the outside air is equal to or lower than the supply air temperature. Differential dry-bulb. The system shifts to 100% outside air when the temperature of the outside air is lower than the return air temperature but continues to operate the cooling system until the outside air temperature reaches the supply air temperature. Fixed enthalpy. The system shifts to 100% outside air and shuts off the cooling when the enthalpy of the outside air is equal to or lower than the supply air enthalpy. Differential enthalpy. The system shifts to 100% outside air when the enthalpy of the outside air is lower than the return air enthalpy but continues to operate the cooling system until the outside air enthalpy reaches the supply air enthalpy.
Units	List (see above)
Input Restrictions	As designed

Economizer High Temperature Lockout
Applicability	Systems with fixed dry-bulb economizer
Definition	The outside air setpoint temperature above which the economizer will return to minimum position.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed

Economizer Low Temperature Lockout
Applicability	Systems with air-side economizers
Definition	A feature that permits the lockout of economizer operation (return to minimum outside air position) when the outside air temperature is below the lockout setpoint.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed

Economizer High Enthalpy Lockout
Applicability	Systems with fixed enthalpy or differential enthalpy economizers
Definition	The outside air enthalpy above which the economizer will return to minimum position
Units	Btu/lb
Input Restrictions	As designed. The default is 25 Btu/lb.

Outside Air Controls

Maximum Outside Air Ratio
Applicability	All systems with modulating outside air dampers
Definition	The descriptor is used to limit the maximum amount of outside air that a system can provide as a percentage of the design supply air. It is used where the installation has a restricted intake capacity.
Units	Ratio
Input Restrictions	As designed

Design Outside Air Flow
Applicability	All systems with outside air dampers
Definition	The rate of outside air that needs to be delivered by the system at design conditions. This input may be derived from the sum of the design outside air flow for each of the zones served by the system.
Units	cfm
Input Restrictions	As designed

Outdoor Air Control Method
Applicability	All HVAC systems that deliver outside air to zones
Definition	The method of determining the amount of outside air that needs to be delivered by the system. Each of the zones served by the system report their outside air requirements on an hourly basis. The options for determining the outside air at the zone level are discussed above. This control method addresses how the system responds to this information on an hourly basis. Options include: Average Flow. The outside air delivered by the system is the sum of the outside air requirement for each zone, without taking into account the position of the VAV damper in each zone. The assumption is that there is mixing between zones through the return air fan. Critical Zone. The critical zone is the zone with the highest ratio of outside air to supply air. The assumption is that there is no mixing between zones. This method will provide greater outside air than the average flow method because when the critical zone sets the outside air fraction at the system, the other zones are getting greater outside air than required. The quantity of outside air can be controlled in a number of ways, but a common method is to install a flow station at the outside air supply which modulates the position of the outside air and return dampers to maintain the desired outside air flow. With the average flow, a CO₂ sensor in the return air duct is another way to control the position of the outside air and return dampers.
Units	List (see above)
Input Restrictions	As designed

Air Side Economizers

Economizer Control Type
Applicability	All systems with an air-side economizer
Definition	An air-side economizer increases outside air ventilation during periods when refrigeration loads can be reduced from increased outside air flow. The control types include: No economizer Fixed dry-bulb. The system shifts to 100% outside air and shuts off the cooling when the temperature of the outside air is equal to or lower than the supply air temperature. Differential dry-bulb. The system shifts to 100% outside air when the temperature of the outside air is lower than the return air temperature but continues to operate the cooling system until the outside air temperature reaches the supply air temperature. Fixed enthalpy. The system shifts to 100% outside air and shuts off the cooling when the enthalpy of the outside air is equal to or lower than the supply air enthalpy. Differential enthalpy. The system shifts to 100% outside air when the enthalpy of the outside air is lower than the return air enthalpy but continues to operate the cooling system until the outside air enthalpy reaches the supply air enthalpy.
Units	List (see above)
Input Restrictions	As designed

Economizer High Temperature Lockout
Applicability	Systems with fixed dry-bulb economizer
Definition	The outside air setpoint temperature above which the economizer will return to minimum position.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed

Economizer Low Temperature Lockout
Applicability	Systems with air-side economizers
Definition	A feature that permits the lockout of economizer operation (return to minimum outside air position) when the outside air temperature is below the lockout setpoint.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed

Economizer High Enthalpy Lockout
Applicability	Systems with fixed enthalpy or differential enthalpy economizers
Definition	The outside air enthalpy above which the economizer will return to minimum position
Units	Btu/lb
Input Restrictions	As designed. The default is 25 Btu/lb.