Effective Outdoor Air Dilution, Continuous Infiltration Credit, and Multi-Zone Mass-Balance Modeling under ASHRAE 62.2

HVACLogic Research Group; Miad S.

doi:10.6084/m9.figshare.172310811

HL-TR-2026-IAQ04DOI: 10.6084/m9.figshare.172310811Published: 2026-02-24

Effective Outdoor Air Dilution, Continuous Infiltration Credit, and Multi-Zone Mass-Balance Modeling under ASHRAE 62.2

A mass-balance analysis of residential mechanical ventilation rates, dwelling volume air changes, and continuous versus intermittent exhaust fan duty cycles.

By HVACLogic Research Group • Miad S.

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Abstract

Evaluates indoor air quality (IAQ) mechanical ventilation compliance under ASHRAE Standard 62.2-2022 and ASHRAE Standard 62.1. Examines total required ventilation rate equations ($Q_{\text{tot}}$), continuous natural infiltration credits ($Q_{\text{inf}}$), dwelling area square footage factors, bedroom occupancy allowances, and fan runtime efficacy adjustments for balanced ERV/HRV energy recovery ventilators.

Key Technical Findings & Code Impacts

In tight modern enclosures ($<3.0\text{ ACH}_{50}$), mechanical ventilation must deliver at least $45\text{ to }75\text{ CFM}$ of continuous fresh outdoor air to maintain steady-state indoor $\text{CO}_2$ concentrations below $1,000\text{ PPM}$.
Energy Recovery Ventilators (ERVs) with sensible recovery effectiveness $\ge 72\%$ reduce winter ventilation thermal conditioning penalties by up to $65\%$ while managing indoor winter relative humidity.
Intermittent mechanical ventilation strategies operating at fractional duty cycles ($<100\%$) require non-linear airflow rate multipliers ($ge 1.33\times$) under ASHRAE 62.2 Section 4.5 to maintain equivalent air exchange effectiveness.
Combustion air makeup requirements for non-direct vent fossil-fuel appliances must be decoupled from general dilution ventilation to prevent hazardous backdrafting under negative building depressurization.

Governing Industry Standards & Codes

🏛️ASHRAE Standard 62.2-2022 (Ventilation for Acceptable Indoor Air Quality in Low-Rise Residential)

🏛️ASHRAE Standard 62.1-2022 (Ventilation for Acceptable IAQ in Commercial Buildings)

🏛️EPA Clean Air Act & Indoor airPLUS Specification

🏛️NFPA 54 / ANSI Z223.1 National Fuel Gas Code

Mathematical Formulations & Governing Equations

ASHRAE 62.2 Total Ventilation Rate Equation

governing_model_eq_1.math
PEER-REFERENCED
Q_{\text{tot}} = 0.03 \times A_{\text{floor}} + 7.5 \times (N_{\text{bedrooms}} + 1)

💡 Governing standard equation defining minimum continuous volumetric outdoor airflow based on conditioned floor area and default occupant density.

Continuous Mechanical Fan Sizing with Infiltration Credit

governing_model_eq_2.math
PEER-REFERENCED
Q_{\text{fan}} = Q_{\text{tot}} - Q_{\text{inf}} = \left[ 0.03 A_{\text{floor}} + 7.5(N_{\text{br}} + 1) \right] - \left( \frac{\text{NL} \times wsf \times A_{\text{floor}}}{1000} \right)

💡 Determines net required mechanical ventilation fan rate after applying natural infiltration credits derived from blower door envelope leakage tests.

Steady-State Indoor CO2 Dilution Mass-Balance

governing_model_eq_3.math
PEER-REFERENCED
C_{\text{indoor}} = C_{\text{outdoor}} + \frac{G_{\text{CO2}}}{Q_{\text{ventilation}}}

💡 Predicts indoor steady-state contaminant concentration from outdoor ambient baseline, occupant generation rate, and effective outdoor air exchange rate.

Companion Calculation Engines & Simulation Models

CFM Airflow & Duct Velocity Calculator

Calculate air changes per hour (ACH), velocity in FPM, and required room CFM.

Launch Live Simulator →

Combustion Air Ventilation Calculator

Size indoor and outdoor combustion air openings per NFPA 54 / IFGC.

Launch Live Simulator →

Kitchen Exhaust Hood CFM Calculator

Size range hood exhaust and makeup air requirements.

Launch Live Simulator →

Academic Citations & BibTeX

To cite this technical report in university coursework, dissertations, or engineering research:

APA Format:

HVACLogic Research Group, & S., M. (2026). Effective Outdoor Air Dilution, Continuous Infiltration Credit, and Multi-Zone Mass-Balance Modeling under ASHRAE 62.2 (Technical Report No. HL-TR-2026-IAQ04). HVACLogic Open-Access Building Science. https://doi.org/10.6084/m9.figshare.172310811

BibTeX Entry:

@techreport{hvaclogic_2026_iaq_ventilation,
  author = {{HVACLogic Research Group} and S., Miad},
  title = {Effective Outdoor Air Dilution, Continuous Infiltration Credit, and Multi-Zone Mass-Balance Modeling under ASHRAE 62.2},
  institution = {HVACLogic Open-Access Building Science Monograph Series},
  year = {2026},
  number = {HL-TR-2026-IAQ04},
  doi = {10.6084/m9.figshare.172310811},
  url = {https://hvaclogic.com/research/effective-dilution-iaq-ventilation-mass-balance}
}