ASHRAE 62.1

HVAKR implements ASHRAE Standard 62.1 - Ventilation for Acceptable Indoor Air Quality using the Ventilation Rate Procedure.

Standard Overview

Purpose

ASHRAE 62.1 establishes minimum ventilation rates to maintain acceptable indoor air quality:

Dilute contaminants
Provide oxygen
Control odors

Scope

Applies to:

Commercial buildings
Institutional buildings
High-rise residential (4+ stories)

Standard Edition

The edition is a project setting. Open Settings from the left sidebar footer and set Ventilation Standard under Ventilation:

ASHRAE 62.1 / 170 (2025) (default for new projects)
ASHRAE 62.1 / 170 (2022)

The 2025 edition adds an air density correction factor to the required outdoor airflow. See Air Density Correction Factor. The two editions are otherwise the same calculation, and the shipped rate library holds 62.1-2022 rates for both.

Ventilation Rate Procedure

Zone Level

For each breathing zone:

Vbz = Rp × Pz + Ra × Az

Where:

Vbz = Breathing zone outdoor airflow
Rp = Outdoor air per person
Pz = Zone population
Ra = Outdoor air per area
Az = Zone floor area

Zone Outdoor Air

Adjust for distribution effectiveness:

Voz = Vbz / Ez

Where:

Voz = Zone outdoor airflow
Ez = Zone air distribution effectiveness

Space Calculated Outdoor Air

Voz is not where the space calculation stops. HVAKR takes the larger of Voz and the space type’s air-change minimum. It then applies the air density correction factor. Call the result Vreq:

Vach = Outdoor Air Changes × space volume / 60
Vreq = max(Voz, Vach) × EQ

Where:

Vach = the Outdoor Air Changes minimum on the space type. HVAKR converts it to airflow across the space’s floor area and ceiling height. It is a floor, not an addition. It replaces Voz only when it is larger
EQ = the air density correction factor. It is 1 under the 2022 edition
Vreq = the space’s calculated (code) outdoor air requirement

Vreq is the code requirement, not always the design airflow. Set a space’s compliance path to Custom and the airflow you type replaces Vreq. HVAKR still calculates Vreq and warns when your custom value is below it.

Air Density Correction Factor (EQ)

Under ASHRAE 62.1 / 170 (2025), HVAKR multiplies max(Voz, Vach) by EQ. Under the 2022 edition EQ is always 1. The requirement is then max(Voz, Vach) unchanged.

EQ is a step lookup on the project’s elevation:

Elevation (up to)	EQ
515 ft	1.00
1,855 ft	1.05
3,120 ft	1.10
4,320 ft	1.15
5,460 ft	1.20
6,540 ft	1.25
7,575 ft	1.30
8,560 ft	1.35
9,505 ft	1.40
10,410 ft	1.45
11,275 ft	1.50

At or below 515 ft the factor is 1.00. The 2025 edition therefore changes nothing for most projects.

Above 11,275 ft HVAKR does not read the table. It computes EQ from the outdoor design state: pressure ratio, dry-bulb temperature, and humidity ratio. Cooling and heating use their own outdoor design states. Above that elevation the two conditions can carry slightly different factors.

System Level

Each system’s outdoor air requirement follows the central unit’s Outside Air method, set in System Design > Configuration:

Sum of Spaces — HVAKR sums each space’s calculated requirement Vreq across the spaces the system serves. The sum therefore carries the air-change floor and EQ that each space already applied:
```
Vot = Σ Vreq
```
The sum is diversified. HVAKR applies the system’s Occupancy Diversity (D) to the people component of each member space first, so Vreq = max((D × Rp × Pz + Ra × Az) / Ez, Vach) × EQ. The area rate does not scale, and Vach stays a floor applied after D. Zone totals use no diversity; system and project totals do. See Ventilation.
Multi-Zone — HVAKR applies the ASHRAE 62.1 multi-zone equation. It divides the uncorrected outdoor air intake Vou (which applies the occupancy diversity D to the people component) by a system ventilation efficiency Ev, so the corrected intake can exceed the simple sum:
```
Vou = D × Σ(Rp × Pz) + Σ(Ra × Az) + Σ Vach + Σ Vcust
Vot = Vou / Ev
```
Ev defaults to 0.75 and drops to 0.88 × D + 0.22 when occupancy diversity falls below 0.6. Each space is counted once — through its breathing-zone rate (Rp, Ra), an air-change minimum (Vach) where air changes govern, or a space-level custom requirement (Vcust) — so the three sums cover disjoint sets of spaces.

Where:

Vot = System outdoor airflow

See Ventilation for the full system-outdoor-air treatment, including the fixed-fraction Percent and Custom methods.

Ventilation Rates

Where the Rates Live

Rp, Ra, and the air-change minimum are fields on the space type, in the Ventilation Requirements section of the Space Types table:

Field	Symbol	Notes
People Outdoor Air	Rp	Outdoor air per person
Area Outdoor Air	Ra	Outdoor air per unit floor area
Outdoor Air Changes	Vach	Air-change minimum. Behind the Advanced Settings toggle
Ez	Ez	Zone air distribution effectiveness

Each rate field carries an Outdoor Air Rate library button that opens the shipped ASHRAE 62.1-2022 rate table, so you can pick a published rate instead of typing one. Common values:

Space Type	Rp (CFM/person)	Ra (CFM/ft²)
Office	5	0.06
Conference	5	0.06
Classroom (9+)	10	0.12
Retail	7.5	0.12
Restaurant	7.5	0.18
Gym	20	0.18

A rate you leave empty counts as zero — HVAKR does not substitute a published rate for a blank field.

Occupancy

HVAKR ships no default occupancy. A space’s population comes from the space type’s People Density, rounded up:

Imperial: Pz = ceil(space area [ft²] × People Density [people/1000 ft²] / 1000)
Metric:   Pz = ceil(space area [m²] × People Density [people/10 m²] / 10)

Type an Occupancy on the space to override that. When neither is set, Pz is zero and the people component drops out of Vbz, leaving the area component and the air-change minimum.

Zone Air Distribution Effectiveness

Ez Is a Space Type Field

HVAKR does not derive Ez from a supply-and-return configuration table. Each space type stores one Ez value on the Space Types table, in the Ventilation Requirements section. You set it directly.

Default: 0.8
Maximum: 1.5

Choosing a Value

Use Table 6.2.2.2 in ASHRAE 62.1 to find the Ez for your system’s supply and return configuration, then enter that value on the space type.

Exhaust Requirements

Table 6.5

Minimum exhaust for specific spaces:

Space	Exhaust Rate
Restroom	50 CFM/fixture
Locker room	0.5 CFM/ft²
Kitchen (commercial)	Per equipment

How HVAKR Applies Them

Set any combination of three fields in the Exhaust Requirements section of the space type, then HVAKR uses the largest of the three results as the space’s required exhaust:

Exhaust Air Changes — air changes per hour
Area Exhaust — rate per unit floor area
Fixture Exhaust — rate per fixture. The space’s Exhaust Units field sets the count. Leave it empty and HVAKR counts one fixture

Transfer Air

The required exhaust above is a space-type result — HVAKR never subtracts transfer air from it. Transfer air is separate design data: set Transfer In and Transfer Out per space in System Design > Air Balancing, where HVAKR uses them to balance supply against the air leaving the space.

HVAKR Implementation

Automatic Calculation

HVAKR automatically:

Applies the rates from the assigned space type
Calculates the space, zone, and system outdoor air requirements

HVAKR does not grade a project against ASHRAE 62.1. The project Check reports structural and calculation problems — a space with no space type, a zone with no spaces, an incomplete load run — not code compliance. The one code-vs-design comparison is per space: type an outdoor airflow lower than the calculated requirement and the space warns that the custom value is below the code-required value.