Minimum indoor air quality performance | U.S. Green Building Council
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LEED O+M: Existing Buildings | v4 - LEED v4

Minimum indoor air quality performance


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EQ Prerequisite: Minimum Indoor Air Quality Performance

Case 1. System Able to Meet Required Outdoor Airflow Rates.
  • Case 2. System Unable to Meet Required Outdoor Airflow Rates
  • Combined Case 1 and 2
  • Case 1 and 2
    • Determine whether your project is located in a non-attainment area for ozone. If your project is located in a non-attainment area for ozone and does not meet any of the Exceptions listed under Section of ASHRAE 62.1-2010, ensure that an air-cleaning device for ozone is installed and that the device has a minimum volumetric ozone removal efficiency of 40%.
    • Determine whether your project is located in a non-attainment area for PM2.5. If your project is located in a non-attainment area for PM2.5, ensure that MERV 11 particulate filters have been installed.
    • Ensure that the ventilation system is set up to represent the worst-case condition (the condition that results in the least amount of outside air entering the building) during outside airflow measurement testing. A description of the outside airflow measurement method or protocol must be provided.
    • Ensure that all air-handling units (AHUs), rooftop units (RTUs), and ventilation fans that supply ventilation to occupiable spaces have been accounted for.
    • Ensure that all occupiable spaces have been accounted for. As indicated in the Definitions section of this prerequisite in the LEED O+M v4 Reference Guide, occupiable space includes enclosed spaces intended for human activities, excluding those spaces that are intended primarily for other purposes, such as storage rooms and equipment rooms, and that are occupied only occasionally and for short periods of time.
    • Ensure that the calculations account for the appropriate zone population value (Pz), which should equal the largest (peak) number of people expected to occupy the ventilation zone during typical usage. The calculations must also account for the appropriate system population value (Ps), which should equal the largest (peak) number of people expected to occupy all ventilation zones served by the ventilation system during typical usage.
    • Ensure that actual peak occupancy values are utilized in the calculations. Default occupancy values listed in table 6-1 of ASHRAE 62.1-2010 should only be used for completely vacant space.
    • Ensure that partially occupied and vacant spaces have been accounted for under this prerequisite, as they are not exempt from the prerequisite requirements. For more information, refer to the Getting Started section of the LEED O+M v4 Reference Guide, under Variable Occupancy.
    • Ensure that the project's ventilation systems have been categorized correctly as either single-zone systems, multiple-zone recirculating systems, or 100% outside air systems, and that the appropriate Ventilation Rate Procedure methodology has been followed. Note that the different calculation methodologies are incorporated into the Minimum IAQ Performance Calculator. The appropriate system type must be selected in the Calculator.
    • Ensure that potentially critical zones have been analyzed for each system when performing the Ventilation Rate Procedure Calculations.
    • Ensure that potentially critical zones have been identified correctly. Additionally, ensure that a sufficient number of potentially critical zones have been included in the calculations (to ensure that the critical zone is correctly identified). Refer to the Definition section of ASHRAE 62.1-2010 for additional information on what is considered a ventilation zone.
    • Ensure that potentially critical zones have been identified in the supporting Ventilation Rate Procedure (VRP) calculations for AHUs serving vacant space. Zone level data is used to calculate the required outdoor air at the system level; therefore, sufficient information must be provided to show that potentially critical occupiable zones have been accounted for in the calculations individually to determine the critical zone. For an AHU that serves only vacant space, assume a reasonable distribution of future space use to identify potentially critical zones for the VRP calculations.
    • Ensure that the Ventilation Rate Procedure Calculations are performed for the worst-case operating conditions. This typically occurs during heating mode when supply airflows are lowest or supply air temperature is highest.
    • Determine whether the ventilation systems are constant volume or variable air volume. If the systems are variable air volume (VAV) systems, ensure that the Ventilation Rate Procedure calculations account for the worst-case conditions (typically when supply airflow volumes are at their minimum setpoints). The outside airflow measurements must also be performed for the worst-case operating conditions.
    • Ensure that individual potentially critical zones (e.g., spaces with high occupant density such as conference rooms and meeting spaces, and spaces with low minimum flow per unit area or per person) are accounted for in the Ventilation Rate Procedure (VRP) calculations. If entering all ventilation zones into the calculator, the remaining ventilation zones listed may group a large number of spaces, as long as the space occupant category is the same (e.g., office), the space population density is similar, the value for Ez is the same, the Vpz value per unit floor area is similar, and the primary air fraction (Ep) is similar. The values for Az, Pz, Vdz, and Vpz should be entered as the sum of the values for all ventilation zones that are grouped into a single zone.
    • If the project utilizes a demand controlled ventilation system with CO2 sensors, ensure that CO2 sensors are not located in the return air duct, as this design does not meet the prerequisite requirements. In addition, ensure that the minimum ventilation required by ASHRAE 62.1-2010 is being provided under all operating conditions while the project building is occupied. For additional information, refer to Section 6.2.7 of ASHRAE 62.1-2010 and Further Explanation, Considerations for Variable Operating Conditions under IEQp Minimum Indoor Air Quality Performance in the LEED O+M v4 Reference Guide.
    • Ensure that the ventilation system is controlled to provide the required amount of outdoor air in each zone, based on current full occupancy. If the project includes demand controlled ventilation, ensure that the CO2 setpoint for each zone is appropriate for the current full zone occupancy expected during normal operations. (Typically, the CO2 setpoint is not the same for all zones.)
    • If the project's ventilation system is designed with local recirculation (e.g., fan-powered VAV boxes), ensure that the Ventilation Rate Procedure (VRP) calculations account for this design and that the Ep and Er variables have been adjusted accordingly.
    • For constant volume systems without local recirculation, the Vdz and Vpz values are expected to be equal, resulting in an Ep value of 1.0. Supplemental heating or cooling equipment, such as perimeter fan coil units, that operate independently of the ventilation system should not be considered when determining whether the ventilation system includes local recirculation, as this equipment does not provide any ventilation benefit.
    • Outside air flow rates must be measured at the system level for each individual ventilation system.
    • Ensure that outside airflow calculations and measurements are performed at the furthest point along the distribution system prior to outside air being mixed with return air. For example, for projects in which a dedicated outdoor air supply fan supplies outdoor air to multiple air-handling units, the VRP calculations and outdoor airflow measures must be performed at the individual air handling units rather than at the dedicated outdoor supply fan.
    • If using the temperature of outdoor air that enters the mixing plenum, the temperature of return air to the plenum, and the temperature of mixed outdoor and return air to determine the outdoor airflow rate, ensure that the temperature limitations of this methodology (as described in ASHRAE 111-2008) have been met.
    • Ensure that documentation demonstrating that the HVAC system maintenance program has been implemented and maintained has been provided. Additionally, an explanation of whether or not the program is based on ASHRAE 62.1-2010, Section 8 is also required.
    • Ensure that the ventilation systems provide the minimum ventilation rates required in the breathing zone whenever the zones served by the system are occupied, including all part-load conditions. If the ventilation system has been designed for varying operating conditions and short-term occupancy, refer to ASHRAE 62.1-2010 Section for additional information.
    • A new USGBC VRP calculator is available for LEED-O+M v4 projects (
    Case 2
    • Projects pursuing Case 2 must provide a narrative that clearly indicates why building AHUs are incapable of supplying the outdoor air flow required by ASHRAE 62.1-2010 and provide technical evidence that demonstrates that these limitations are true for all system operating conditions, even when functioning properly. If the project team is able to make minor adjustments, such as setpoint adjustments, damper positioning, etc., to meet the requirements of Case 1 they are required to do so for prerequisite achievement. It is not necessary make adjustments if it involves any amount of capital investment or equipment purchase.
    Natural Ventilation
    • Naturally ventilated spaces must meet the requirements of Section 6.4 of ASHRAE 62.1-2010.
    • Documentation demonstrating that natural ventilation is an effective strategy for the project, as determined through the flow diagram process in Figure 2.8 of the CIBSE Application Manual 10: 2005, must be provided for naturally ventilated spaces.