3.6.5.5 Ventilation Rate Procedure

90.1-2019

Ventilation Standard
Applicability	All projects
Definition	The ventilation standard used for the calculation of minimum ventilation rate required. The ventilation rates are defined based on the ventilation standard selected. This should be specified at the project level.
Units	List. ASHRAE Standard 62.1, IMC-2012, Title-24-2013, ASHRAE 170, Other
Input Restrictions	No restrictions. Any of the defined standards can be selected.
Baseline Building	Same as proposed The baseline rules for determining the use of DCV are defined according to Standard 90.1-2019, for any specified standard, including ‘Other’.

Ventilation Specification Method

Applicability

All HVAC zones

Definition

The method used to calculate total ventilation rates to a zone. The input must be either “Sum,” “Maximum,” or “No Ventilation.”

Sum means that the flows calculated from the fields Outdoor Airflow per Person and Outdoor Airflow per Area will be added to obtain the zone outdoor airflow rate.
Maximum means that the maximum flow derived from Outdoor Airflow per Person, Outdoor Airflow per Area, and Air Changes per Hour (using the associated conversions to cfm for each field) will be used as the zone outdoor airflow rate.
No ventilation indicates that the zone doesn’t receive any outdoor air.

Units

List: Sum, Maximum, No Ventilation

Input Restrictions

As designed.

For ventilation standard specified as = “62.1” and “IMC-2012,” the only available specification method would be “Sum.” For “T₂₄-2013,” the only available specification method is “Maximum.” For ventilation standard specified as “Other,” the specification method can be specified as either Sum or Maximum, and includes all components.

Baseline Building

Same as proposed

Zone Air Distribution Effectiveness

Applicability

All HVAC zones and spaces

Definition

The zone air distribution effectiveness (Ez) shall be no greater than the default value determined using Table 40.

Table 40. Air Distribution Effectiveness (ASHRAE Standard 62.1-2010)

Air Distribution Configuration	Ez
Ceiling supply of cool air	1.0
Ceiling supply of warm air and floor return	1.0
Ceiling supply of warm air 15°F (8°C) or more above space temperature and ceiling return	0.8
Ceiling supply of warm air less than 15°F (8°C) above space temperature and ceiling return provided that the 150 fpm (0.8 m/s) supply air jet reaches to within 4.5 ft (1.4 m) of floor level. Note: For lower velocity supply air.	1.0
Floor supply of cool air and ceiling return provided that the 150 fpm (0.8 m/s) supply jet reaches 4.5 ft (1.4 m) or more above the floor. Note: Most underfloor air distribution systems (UFADs) comply with this provision.	1.0
Floor supply of cool air and ceiling return, provided low-velocity displacement ventilation (DV) achieves unidirectional flow and thermal stratification	1.2
Floor supply of warm air and floor return	1.0
Floor supply of warm air and ceiling return	0.7
Makeup supply drawn in on the opposite side of the room from the exhaust and/or return	0.8
Makeup supply drawn in near to the exhaust and/or return location	0.5

Units

None

Input Restrictions

As designed

Baseline Building

Same as proposed

Ventilation Multiplier
Applicability	All projects
Definition	The ventilation multiplier is defined at the project level. This multiplier is applied to the user’s design component ventilation rates (Ra and Rp) to uniformly increase the component ventilation rates entered. The principal purpose of the multiplier is to facilitate simulating a uniform increase in proposed design ventilation rates, such as for buildings pursuing the LEED credit for 30% increased ventilation.
Units	No units
Input Restrictions	As designed. The default value is 1.
Baseline Building	The ventilation multiplier is always 1 for the baseline building

Ventilation Rates
Applicability	All HVAC zones
Definition	The method used to calculate total ventilation rates to a zone. The input must be either flow/person, flow/area, flow/zone, air changes/hour, sum, or maximum. Flow/Person (Rp) means the program will use the input from the field Outdoor Airflow per Person and the actual zone occupancy to calculate a zone outdoor airflow rate. Flow/Area (Ra) means that the program will use the input from the field Outdoor Airflow per Zone Floor Area and the actual zone floor area as the zone outdoor airflow rate. Flow/Zone means that the program will use the input of the field Outdoor Airflow per Zone as the zone outdoor airflow rate. Air changes per hour (ACH) means that the program will use the input from the field Air Changes per Hour and the actual zone volume (divided by 3600 seconds per hour) as the zone outdoor airflow rate. For non-occupied spaces, the values for Ra, Rp and ACH can be zero for the proposed and baseline building. Software tools can allow a check-box for indicating spaces that would be non-occupied and hence are permitted to have a value for zero for Ra and Rp.
Units	List: Flow/Person, Flow/Area, Air Changes per Hour
Input Restrictions	As designed. If the user specifies ventilation standard as ‘Other’ and DCV is used, a non-zero value for Rp must be specified for the ventilation air flow to vary with occupancy.
Baseline Building	The ventilation rates for the baseline building are determined by the ventilation standard and the space function. For zones/spaces with ventilation standard specified as ‘Other’ The code minimum ventilation rates are required to be specified by the user. If DCV controls are not specified for the proposed but are required for the baseline, the ventilation rate for the area component is determined based on Standard 62.1 and the balance of the user’s total design air flow is allocated to the Rp component for the baseline.

Total Design Zone Ventilation Airflow

Applicability

All HVAC zones

Definition

The total design outdoor air supplied to a zone (V_z-design).

Minimum outdoor air supplied to a zone (V_bz-min) is calculated based on the user input values of the ventilation multiplier (V_m), Ez, Ra and Rp. The method used to calculate total minimum ventilation airflow to a zone is specified below-

$$V_{bz-min}=V_m\times [(R_p\times P_z + R_a \times A_z)/E_z]$$

(8)

Where,

V_bz-min= Total Breathing Zone Outdoor Airflow (CFM)

V_m = Ventilation Multiplier

R_p = Outdoor Airflow Rate per Person (CFM/person)

R_a = Outdoor Airflow Rate per unit Area (CFM/ft²)

P_z = Zone Population: The number of people in the zone during typical occupancy

A_z = Zone Floor Area (ft²): the net occupiable floor area of the zone.

Units

List: CFM

Input Restrictions

As designed. The total design ventilation airflows should also include the impact of Ez and the ventilation multiplier. The user entered value for space/zone design ventilation airflow is required to be within 3% of the value calculated from the user entered R_a, R_p, E_z and V_m values. The user is required to modify the values for R_a, R_p or E_z such that the total airflow calculated from the components and the user defined airflow is within the tolerance limit. Similarly, if DCV controls are used in the proposed building design, the user entered value for V_z-designshould be within 3% tolerance of the value calculated by the design area rate component (Ra) and Ez.

Exhaust airflows are checked at the building story level. If the sum of proposed total design ventilation airflows for all spaces on a building story level (excluding spaces with ventilation standard specified as ‘Other’) is not within 10% of the calculated total code minimum ventilation airflow. To proceed, either the ventilation airflows for spaces that are under-ventilated, need to be increased or alternatively, the ventilation standard should be specified as ‘Other’ for spaces that are under-ventilated. For zones/spaces with DCV controls, the minimum ventilation airflow is the airflow when the space is unoccupied, calculated using the area component and Ez.

Baseline Building

The baseline design ventilation airflow rates for all spaces/thermal zones equal the proposed with the exception of the following:

a. The zone distribution effectiveness for the proposed building (Ez) > 1. In this case, Ez = 1 for the baseline building.

b. The proposed design ventilation airflow, on a building story basis, exceeds the code minimum ventilation airflow for the building story. In this case, the baseline ventilation rates will be calculated by uniformly reducing the proposed rates such that the total ventilation airflow to spaces on the building story equals the code minimum flow. This maintains a proportional distribution of ventilation air to spaces/zones on the building story between the proposed and baseline designs. Spaces with ventilation standard specified as “Other” are excluded from adjustments, and the baseline design ventilation rate equals the proposed.

c. The proposed design ventilation multiplier is greater than 1. In this case, the baseline design ventilation airflow is not increased by the multiplier. Instead, the total baseline design ventilation airflow is adjusted, as described in exception b, to be equal to the code minimum ventilation airflow.

d. The total proposed design ventilation airflow (excluding spaces with ventilation standard specified as “Other”), on a building story basis, is greater than 110% of the total building story exhaust airflow. In this case, the baseline design ventilation airflows will be calculated by uniformly reducing the proposed inputs (excluding spaces with ventilation standard specified as “Other”) such that the total ventilation airflow on the building story equals 110% of the total building story exhaust airflow. This maintains a proportional distribution of ventilation air (at design conditions) to spaces on the building story, while allowing sufficient additional ventilation air for pressurization.

Total System Design Ventilation Airflow
Applicability	All HVAC systems.
Definition	The design outdoor air intake at the system level (V_s-design)
Units	CFM
Input Restrictions	As designed Software tools are required to verify the input value for V_s-design. For all the zones served by the system, software tools are required to sum the zone level ventilation (V_bz-min) to calculate the minimum ventilation at the system level (V_s-min). If the design outdoor air intake (V_s-design) is less than the minimum ventilation airflow (V_s-min), the input should be flagged and the user should be required to increase the value for V_s-designuntil it is equal to or greater than V_s-min.
Baseline Building	The total system ventilation airflow for the baseline building is the sum of the zone level ventilation for the baseline building

System Ventilation Efficiency

Applicability

All HVAC systems

Definition

The efficiency of the ventilation system (Ev). This is the ratio of the design ventilation airflow to the minimum system ventilation airflow.

E_v = V_s-min/ V_s-design

(9)

Units

Ratio (unitless)

Input Restrictions

Calculated by software tool

Software tools are required to calculate and verify the input value for Ev. The maximum value of Ev=1 (for single zone systems). If Ev is greater than 1, an error should be displayed to the user and the user is required to increase the value of V_s-designuntil the value of Ev is less than or equal to 1.

Baseline Building

Same as proposed for all zones served by the proposed system. In the scenario where the building has a multizone system in the proposed case, but single zone system in the baseline case, all the zones served by the Multizone system in the proposed case have Ev same as the proposed system.

Similarly, if the proposed system is single zone and the baseline building has multizone systems, then the corresponding zones would have Ev specified as 1, same as the proposed building.

This approach ensures that the ventilation rates are the same between the baseline and the proposed building.