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ASHRAE 90.1 Exhaust Energy Recovery Requirement Calculator

Determine mandatory Energy Recovery Ventilation (ERV) requirements for your Baseline Building model based on Climate Zone, Supply Airflow, and Outdoor Air percentage (Table 6.5.6.1).

Prescriptive Requirement
Based on ASHRAE 90.1-2010 Section 6.5.6.1 and Table 6.5.6.1 (SI).
Baseline Modeling
Critical check for Appendix G compliance (AHVAC27-B). Essential for determining System Type requirements.
Exemptions Applied
Account for labs, kitchen hoods, and hazardous exhaust exemptions.
Parameter
System Name
Supply Airflow (L/s)
Outdoor Air (L/s)
% Outdoor Air33.3%100.0%
ASHRAE Threshold2.596 L/s> 0 L/s
Requirement Status REQUIRED REQUIRED
Exemption
Tip: Systems are added as columns.

Methodology & Compliance

The Exhaust Air Energy Recovery requirement in ASHRAE 90.1 is determined by comparing the system's Design Supply Fan Airflow Rate and the Percentage of Outdoor Air against specific thresholds defined for each Climate Zone.

Calculation Steps

  1. Calculate % Outdoor Air: (Design Min OA / Design Supply Airflow) × 100.
  2. Lookup Threshold: Using Table 6.5.6.1, identify the minimum Supply Airflow (L/s) that triggers the requirement for your Climate Zone and %OA bin.
  3. Compare: If your system's Supply Airflow ≥ Threshold, Energy Recovery is REQUIRED (unless an exemption applies).

Baseline Modeling Requirements

If determined to be required, the Baseline system must model an energy recovery device with at least 50% total effectiveness (enthalpy change). This often dictates whether your baseline system is modeled as, for example, System 5 (VAV) vs System 7 (VAV with Reheat), or simply adds the recovery loop to the prescriptive system.

Note on Exemptions: Even if the flow rate threshold is met, systems may be exempt if they serve laboratory spaces (meeting 6.5.7.2), commercial kitchens, or hazardous exhausts. Use the "Check Exemptions" feature in the tool to document these cases.