Significant changes to demand controlled ventilation in the 2021 International Mechanical Code

A modification to Section 403.3.1.3 (Demand Controlled Ventilation) of the 2021 International Mechanical Code states that the change clarifies that demand control ventilation schemes cannot eliminate all ventilation in a space while that space is expected to be occupied.

Section 403.3.1.3 allows for demand control ventilation, which means that the ventilation rate can be adjusted up or down as the number of occupants in a space increases or decreases. The section might be misinterpreted that the ventilation rate could reduce to zero if the number of occupants was zero. However, it was never intended that the outdoor airflow rate per square foot (Ra) prescribed by Table 403.3.1.1 could be overlooked when the occupant load in a space is zero. When the occupant load is zero, the minimum required ventilation rate is determined by the rate per square foot of floor area (Ra) in the next to last column of Table 403.3.1.1 times the net occupiable floor area of the space. Assuming the table has a prescribed airflow rate based on floor area (Ra) for the space in question in the table, there will always be some ventilation being provided, even when the space has no occupants.

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The 2021 Significant Changes guides are available for the International Building, Fire, Residential, Energy Conservation, Plumbing, Mechanical and Fuel Gas Codes. This valuable series can help any code user save time by zeroing in on the most critical changes in the 2021 International Codes. The Code Council’s technical experts provide summaries, analysis and graphics for these changes making them clear and easy to understand. Each edition provides a comprehensive analysis of significant changes since the 2018 edition, offering key insights into its contents and implications. Each change analysis features the affected code sections and identifies the change with strikethroughs and underlines to show modifications to the existing language. Each change is accompanied by a quick summary, detailed illustrations, and a discussion of its significance, which brings the technical jargon of the code to life in a real-world setting.

Significant Changes to the IPC, IMC, and IFGC, 2021 Edition is available in the ICC Store or through Digital Codes Premium for the International Plumbing Code, International Mechanical Code and International Fuel Gas Code.