3.6.5.4 Outdoor Air Ventilation

Ventilation Source
Applicability	All HVAC zones
Definition	The source of ventilation for an HVAC system. The choices are: Natural (by operable openings) Mechanical (by fan)
Units	List: natural or mechanical
Input Restrictions	As designed.
Baseline Rules	For residential units, set to natural, for all other occupancies, set equal to mechanical.

Ventilation Control Method
Applicability	All HVAC zones
Definition	The method used to determine outside air ventilation needed for each hour in the simulation. This information is reported to the system serving the zone. The method of controlling outside air at the system level in response to this information is discussed under secondary systems. Options at the zone level are: Demand control ventilation: Occupant sensors: When the space is occupied, the outside air requirement is equal to the design ventilation rate, otherwise, the outside air requirement is the minimum ventilation rate. CO₂ sensors in the space: The outside air is varied to maintain a maximum CO₂ concentration in the space. This shall be approximated by multiplying the ventilation rate per occupant times the number of occupants for that hour. Turnstiles to determine the number of occupants in the space (appropriate for theatres, etc.): The outside air requirement is modulated based on the number of occupants in the space, based on the turnstile counts. Fixed ventilation rate. Outside air is delivered to the zone at a constant rate and is equal to the design ventilation rate (see above).
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	The baseline building shall use the same ventilation control method as the proposed design except for the following: When the proposed design in systems with outdoor air capacity less than or equal to 3000 cfm serving areas with an average design capacity of 100 people per 1000 ft² or less use demand control ventilation, the baseline building shall be modeled as fixed ventilation (G3.1.2.5 exception 1).

Design Ventilation Rate
Applicability	All HVAC zones
Definition	The quantity of ventilation air that is provided to the space for the specified thermal block at maximum occupancy.
Units	cfm or cfm/occupant
Input Restrictions	As designed. Appendix B provides default values.
Baseline Rules	Same as the proposed design except in the following cases: When designing systems in accordance with ASHRAE Standard 62, where the proposed design has a zone air distribution effectiveness greater than 1.0, the baseline ventilation shall be calculated using the proposed design ventilation rate procedure calculation with the zone air distribution effectiveness changed to 1.0 (G3.1.2.5 exception 2). If the proposed design ventilation rate exceeds that required by the rating authority or building official, then the baseline design ventilation rate shall be only what is required by the rating authority or building official, whichever is greater (G3.1.2.5 exception 3). For baseline systems serving only laboratory spaces that are prohibited from recirculating return air by code or accreditation standards, the baseline system shall be modeled as 100% outdoor air (G3.1.2.5 exception 4). For systems serving kitchens, the minimum outside air ventilation rate is the exhaust air ventilation rate minus available transfer air. Refer to building description ‘Kitchen Exhaust’.

Minimum Ventilation Rate
Applicability	All HVAC zones
Definition	The minimum quantity of ventilation air that must provided to the space when the HVAC system is operating. This ventilation rate must be provided whether or not the space is occupied.
Units	cfm or cfm/ft²
Input Restrictions	As designed
Baseline Rules	Same as the proposed design

Exhaust Fan Schedule
Applicability	All HVAC zones
Definition	Demand control ventilation (DCV) is required for spaces larger than 500 ft2 and with a design occupancy for ventilation of greater than 40 people per 1000 ft2 of floor area and served by systems with one or more of the following: a.an air-side economizer, b.automatic modulating control of the outdoor air damper, c.a design outdoor airflow greater than 3000 cfm. Exceptions: a.Systems with the exhaust air energy recovery complying with Standard 90.1 2010 Section 6.5.6.1. b.Multiple-zone systems without DDC of individual zones communicating with a central control panel. c.Systems with a design outdoor airflow less than 1200 cfm. Spaces where the supply airflow rate minus any makeup or outgoing transfer air requirement is less than 1200 cfm.
Units	CFM or CFM/occupant
Input Restrictions	As designed. DCV is a mandatory requirement for spaces larger than 500 sq.ft, with a design occupancy of more than 40 people per 1000 sq.ft unless any of the exceptions specified above apply.
Baseline Rules	Same as proposed for spaces or systems where DCV is required as described above. For other spaces and systems DCV is not modeled.

Outdoor Air Ventilation Source
Applicability	All HVAC zones
Definition	The source of outdoor air ventilation for an HVAC system. The choices are: Natural (by operable openings) Mechanical (by fan)
Units	List: Natural or mechanical
Input Restrictions	As designed
Baseline Building	Ventilation is set to mechanical for the baseline building

Minimum Outdoor Air Ventilation Rate
Applicability	All HVAC zones
Definition	The minimum quantity of outdoor ventilation air that must be provided to the space when it is occupied
Units	cfm or cfm/ft²
Input Restrictions	As designed
Baseline Building	Minimum ventilation system outdoor air intake flow shall be the same for the proposed and baseline building designs. Except in the following conditions: Demand control ventilation shall not be modeled in zones served by systems with outdoor air less than 3000 cfm and occupant density of 100 people per 1000 ft2 or less. If the minimum outdoor air intake flow in the proposed design is provided in excess of the amount required by the rating authority or building official, then the baseline building design shall be modeled to reflect the greater of that required by the rating authority or building official and will be less than the proposed design. For systems serving kitchens, the minimum outside air ventilation rate is the exhaust air ventilation rate minus available transfer air. Refer to building descriptor Kitchen Exhaust. For systems serving laboratories, refer to building descriptor Laboratory Exhaust, Section 3.6.5.3. When designing systems in accordance to Standard 62.1, Section 6.2, “Ventilation Rate Procedure”. Refer to Section 3.6.5.5 of this document for requirements.
Example	Example 1: Should DCV be required in the following case? Can a savings credit be taken? Proposed Design: Every other floor DOAS air handlers with 8,000cfm of OSA controlled by demand controlled ventilation. Baseline: System 7 VAV, floor by floor with 4,000cfm of OSA Answer: No the design does not meet the exceptions listed above, therefor both designs should be modeled with DCV. If the design airflow of the system in question was less than 3000 CFM then DCV would only be modeled in the proposed case and credit could be taken.

Design Outdoor Air Ventilation Rate and Schedule
Applicability	All HVAC zones
Definition	The quantity of outdoor air ventilation that is provided to the space for the specified thermal zone at maximum occupancy
Units	cfm or cfm/occupant
Input Restrictions	The outdoor air ventilation rate would be as designed. Outdoor air ventilation schedule for proposed building can be either of the two: a. As designed b. The outdoor air ventilation schedule follows the HVAC availability schedule. In this case outdoor air isn’t supplied during unoccupied times or during night cycling operation. Some proposed building designs might bring in ventilation air during unoccupied hours for night flush or economizer operation. Due to these reasons, an option for user input of schedule for outdoor air availability is provided.
Baseline Building	Same as proposed, except: When designing systems in accordance with ASHRAE Standard 62.1, Section 6.2, Ventilation Rate Procedure, where the proposed design has a zone air distribution effectiveness greater than 1.0, the baseline ventilation shall be calculated using the proposed design ventilation rate procedure calculation with the zone air distribution effectiveness changed to 1.0. Refer to Section 3.6.5.5 for details on the ventilation rate procedure. If the proposed design ventilation rate exceeds that required by the rating authority or building official, then the baseline design ventilation rate shall be only what is required by the rating authority or building official, whichever is greater.

Ventilation Control Method
Applicability	All HVAC zones
Definition	The method used to determine outside air ventilation needed for each hour in the simulation. This information is reported to the system serving the zone. The method of controlling outside air at the system level in response to this information is discussed under secondary systems. Options at the zone level are: Occupant sensors: When the space is occupied, the outside air requirement is equal to the design ventilation rate; otherwise, the outside air requirement is the minimum ventilation rate. CO₂ sensors in the space: The outside air is varied to maintain a maximum CO₂ concentration in the space. This shall be approximated by multiplying the ventilation rate per occupant by the number of occupants for that hour. (When turnstile counts are used to automatically adjust ventilation levels based on occupancy, this method may also be used.) Fixed ventilation rate: Outside air is delivered to the zone at a constant rate and is equal to the design ventilation rate (see above).
Units	List (see above)
Input Restrictions	As designed
Baseline Building	Baseline building shall be modeled with a fixed ventilation rate which would be equal to the design ventilation rate (see above). No ventilation control methods shall be modeled for the baseline building design except for the following: Demand control ventilation shall be modeled in zones served by systems with outdoor air greater than or equal to 3000 cfm and occupant density of 100 people per 1000 ft2 or less.

Design Ventilation Rate: Demand Control Ventilation
Applicability	All HVAC zones
Definition	Demand control ventilation is required for spaces larger than 500 ft² and with a design occupancy for ventilation of greater than or equal to 25 people per 1000 ft² of floor area and served by systems with one or more of the following: a. An air-side economizer b. Automatic modulating control of the outdoor air damper c. A design outdoor airflow greater than 3000 cfm Exceptions: a. Systems with the exhaust air energy recovery complying with Standard 90.1-2019, Section 6.5.6.1 b. Multiple-zone systems without dynamic demand control (DDC) of individual zones communicating with a central control panel c. Systems with a design outdoor airflow less than 750 cfm a. Spaces where >75% of the space design outdoor airflow is required for makeup air that is exhausted from the space or transfer air that is required for makeup air that is exhausted from other spaces. b. Spaces with one of the following occupancy categories as defined in ASHRAE Standard 62.1: correctional cells, daycare sickrooms, science labs, barbers, beauty and nail salons, and bowling alley seating.
Units	cfm or cfm/occupant
Input Restrictions	As designed. DCV is a mandatory requirement for spaces larger than 500 ft², with design occupancy of more than 25 people per 1000 ft² unless any of the exceptions specified above apply.
Baseline Building	DCV is not modeled for the baseline building except for zones served by systems with outdoor air greater than or equal to 3000 cfm and occupant density of 100 people per 1000 ft² or less

Outdoor Air Ventilation Source
Applicability	All HVAC zones
Definition	The source of outdoor air ventilation for an HVAC system. The choices are: Natural (by operable openings) Mechanical (by fan)
Units	List: Natural or mechanical
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations Ventilation is set to mechanical for the baseline building G3.3 Minor Alterations Same as proposed design except if modeling credit for natural ventilation according to Standard 90.1 Table G3.1 #4 Baseline Building Performance column exceptions 1-3.

Minimum Outdoor Air Ventilation Rate
Applicability	All HVAC zones
Definition	The minimum quantity of outdoor ventilation air that must be provided to the space when it is occupied
Units	cfm or cfm/ft²
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations Minimum ventilation system outdoor air intake flow shall be the same for the proposed and baseline building designs. Except in the following conditions: Demand control ventilation shall not be modeled in zones served by systems with outdoor air less than 3000 cfm and occupant density of 100 people per 1000 ft2 or less. If the minimum outdoor air intake flow in the proposed design is provided in excess of the amount required by the rating authority or building official, then the baseline building design shall be modeled to reflect the greater of that required by the rating authority or building official and will be less than the proposed design. For systems serving kitchens, the minimum outside air ventilation rate is the exhaust air ventilation rate minus available transfer air. Refer to building descriptor Kitchen Exhaust. For systems serving laboratories, refer to building descriptor Laboratory Exhaust, Section 3.6.5.3. When designing systems in accordance with Standard 62.1, Section 6.2, “Ventilation Rate Procedure”. Refer to Section 3.6.5.5 of this document for requirements. G3.3 Minor Alterations The baseline shall be modeled as minimally compliant with Standard 90.1-2022 Section 6.5.3.8 with the same feature as the proposed design. Where the proposed design does not include one of these features it is recommended that the baseline be modeled according to Standard 90.1-2022 Section 6.5.3.8 option a with no more than 135% of the required minimum outdoor air rate modeled in the baseline. Standard 90.1-2022 Section 6.5.3.8 states that the required minimum outdoor air rate is the larger of the minimum outdoor air rate or the minimum exhaust air rate required by Standard 62.1, Standard 62.2, Standard 170, or applicable codes or accreditation standards. The section also requires that outdoor air ventilation systems comply with one of the following: a. Design minimum system outdoor air provided shall not exceed 135% of the required minimum outdoor air rate. b. Dampers, ductwork, and controls shall be provided that allow the system to supply no more than the required minimum outdoor air rate with a single set-point adjustment. c. The system includes exhaust air energy recovery complying with Section 6.5.6.1. Exception: the minimum outdoor air ventilation rate should be modeled the same in the baseline and proposed if, based on the requirements of 90.1-2022 Section 6.1.4 and the scope of the alteration, the 90.1-2022 Section 6.5.3.8 requirements are inapplicable. If the following conditions are met, DCV is specified in the proposed design, Standard 90.1-2022 Section 6.4.3.8 is applicable based on the scope of the alteration and the requirements of 90.1-2022 Section 6.1.4, and DCV is not required to be modeled in the baseline according to 90.1 Section 6.4.3.8 then ventilation air flow may differ between the baseline and proposed due to DCV. See the Design Ventilation Rate: Demand Control Ventilation descriptor for the requirements of 6.4.3.8.
Example	Standard 90.1 G3.2 Example 1: Should DCV be required in the following case? Can a savings credit be taken? Proposed Design: Every other floor DOAS air handlers with 8,000 cfm of OSA controlled by demand-controlled ventilation, average design occupant density is 110 people per 1000 ft2. Baseline: System 7 VAV, floor by floor with 4,000 cfm of OSA Answer: No, the design does not meet the exceptions listed above, therefore both designs should be modeled with DCV. If the design airflow of the system in question was less than 3000 CFM or the average design occupant density was 100 people per 1000 ft² or less, then DCV would only be modeled in the proposed case and credit could be taken.

Design Outdoor Air Ventilation Rate and Schedule
Applicability	All HVAC zones
Definition	The quantity of outdoor air ventilation that is provided to the space for the specified thermal zone at maximum occupancy
Units	cfm or cfm/occupant
Input Restrictions	The outdoor air ventilation rate would be as designed. Outdoor air ventilation schedule for proposed building can be either of the two: a. As designed b. The outdoor air ventilation schedule follows the HVAC availability schedule. In this case outdoor air isn’t supplied during unoccupied times or during night cycling operation. Some proposed building designs might bring in ventilation air during unoccupied hours for night flush or economizer operation. Due to these reasons, an option for user input of schedule for outdoor air availability is provided.
Baseline Building	G3.2 New Construction/Major Alterations Same as proposed, except: When designing systems in accordance with ASHRAE Standard 62.1, Section 6.2, Ventilation Rate Procedure, where the proposed design has a zone air distribution effectiveness greater than 1.0, the baseline ventilation shall be calculated using the proposed design ventilation rate procedure calculation with the zone air distribution effectiveness changed to 1.0. Refer to Section 3.6.5.5 for details on the ventilation rate procedure. If the proposed design ventilation rate exceeds that required by the rating authority or building official, then the baseline design ventilation rate shall be only what is required by the rating authority or building official, whichever is greater. G3.3 Minor Alterations The baseline shall be modeled as minimally compliant with Standard 90.1-2022 Section 6.5.3.8 with the same feature as the proposed design. Where the proposed design does not include one of these features it is recommended that the baseline be modeled according to Standard 90.1-2022 Section 6.5.3.8 option a with no more than 135% of the required minimum outdoor air rate modeled in the baseline. Standard 90.1-2022 Section 6.5.3.8 states that the required minimum outdoor air rate is the larger of the minimum outdoor air rate or the minimum exhaust air rate required by Standard 62.1, Standard 62.2, Standard 170, or applicable codes or accreditation standards. The section also requires that outdoor air ventilation systems comply with one of the following: a. Design minimum system outdoor air provided shall not exceed 135% of the required minimum outdoor air rate. b. Dampers, ductwork, and controls shall be provided that allow the system to supply no more than the required minimum outdoor air rate with a single set-point adjustment. c. The system includes exhaust air energy recovery complying with Section 6.5.6.1. Exception: the minimum outdoor air ventilation rate should be modeled the same in the baseline and proposed if, based on the requirements of 90.1-2022 Section 6.1.4 and the scope of the alteration, the 90.1-2022 Section 6.5.3.8 requirements are inapplicable. If the following conditions are met, DCV is specified in the proposed design, Standard 90.1-2022 Section 6.4.3.8 is applicable based on the scope of the alteration and the requirements of 90.1-2022 Section 6.1.4, and DCV is not required to be modeled in the baseline according to 90.1 Section 6.4.3.8 then ventilation air flow may differ between the baseline and proposed due to DCV. See the Design Ventilation Rate: Demand Control Ventilation descriptor for the requirements of 6.4.3.8.

Ventilation Control Method
Applicability	All HVAC zones
Definition	The method used to determine outside air ventilation needed for each hour in the simulation. This information is reported to the system serving the zone. The method of controlling outside air at the system level in response to this information is discussed under secondary systems. Options at the zone level are: Occupant sensors: When the space is occupied, the outside air requirement is equal to the design ventilation rate; otherwise, the outside air requirement is the minimum ventilation rate. CO2 sensors in the space: The outside air is varied to maintain a maximum CO2 concentration in the space. This shall be approximated by multiplying the ventilation rate per occupant by the number of occupants for that hour. (When turnstile counts are used to automatically adjust ventilation levels based on occupancy, this method may also be used.) Fixed ventilation rate: Outside air is delivered to the zone at a constant rate and is equal to the design ventilation rate (see above).
Units	List (see above)
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations Baseline building shall be modeled with a fixed ventilation rate which would be equal to the design ventilation rate (see above). No ventilation control methods shall be modeled for the baseline building design except for the following: Demand control ventilation shall be modeled in zones served by systems with outdoor air greater than 3000 cfm and occupant density of greater than 100 people per 1000 ft2. G3.3 Minor Alterations Baseline building shall be modeled with a fixed ventilation rate which would be equal to the design ventilation rate unless demand control ventilation is required by Standard 90.1-2022 Section 6.1.4, based on the scope of the alteration, according to Standard 90.1-2022 Section 6.4.3.8. See the Design Ventilation Rate: Demand Control Ventilation descriptor for the requirements of 6.4.3.8.

Design Ventilation Rate: Demand Control Ventilation

Applicability

All HVAC zones

Definition

Demand control ventilation is a mandatory requirement for spaces larger than the floor area in Table 43 based on an occupant outdoor airflow component in cfm per 1000 ft² and served by systems with one or more of the following:

a. An air-side economizer

b. Automatic modulating control of the outdoor air damper

c. A design outdoor airflow greater than 3000 cfm

The occupant outdoor airflow component in cfm per 1000 ft² in Table 43 is required to be calculated as the product of the default occupant density and outdoor airflow rate per occupant(Rp) as shown in ASHRAE Standard 62.1, Table 6.2.2.1.

Exceptions:

a. Multiple-zone systems without dynamic demand control (DDC) of individual zones communicating with a central control panel

b. Spaces where >75% of the space design outdoor airflow is required for makeup air that is exhausted from the space or transfer air that is required for makeup air that is exhausted from other spaces.

c. Spaces with one of the following occupancy categories as defined in ASHRAE Standard 62.1: correctional cells, daycare sickrooms, science labs, barbers, beauty and nail salons, and bowling alley seating.

d. Spaces where the requirements of ASHRAE Standard 170, applicable codes, or applicable accreditation standards do not allow the reduction of outdoor airflow.

Table 43. Demand Control Ventilation Floor Area Thresholds

Climate Zone	Occupant Outdoor Airflow Component (cfm/1000 ft²)
	100 to 199	200 to 399	³400	100 to 199	200 to 399	³400
	Minimum Space Floor Area in ft²where DCV Is Required
	Areas without Exhaust Air Energy Recovery			Areas with Exhaust Air Energy Recovery (where required by Section 6.5.6.1)
7, 8	400	200	150	800	400	250
5A, 6A, 6B	600	250	150	1400	900	400
0A, 0B, 1B, 3A, 4A, 5B, 5C	800	400	250	2000	1000	500
2A, 2B, 4C	1100	600	300	2300	1100	600
3B, 4B	1500	700	400	5200	2350	1250
1A	2400	1100	600	5800	2600	1400
3C	7000	3000	1700	12,000	6000	3000

Units

cfm or cfm/occupant

Input Restrictions

As designed.

Baseline Building

G3.2 New Construction/Major Alterations

DCV is not modeled for the baseline building except for zones served by systems with outdoor air greater than or equal to 3000 cfm and occupant density of 100 people per 1000 ft² or less.

G3.3 Minor Alterations

Demand control ventilation shall be modeled for spaces as required by Standard 90.1-2022 Section 6.4.3.8 if applicable based on the scope of the alteration and the language in Standard 90.1-2022 Section 6.1.4. See the Definition for this descriptor for the requirements of 6.4.3.8. Where Standard 90.1-2022 Section 6.4.3.8 is not applicable based on the scope of the alteration and the language in Standard 90.1-2022 Section 6.1.4 DCV should be modeled identically in the baseline and proposed.