Note:

Mixed Air Temperature Calculation determines the resulting temperature when combining outdoor and recirculated air. This fundamental HVAC calculation helps optimize ventilation and energy use while maintaining indoor air quality.

Why Mixed Air Temperature Matters for the Environment?

Proper air mixing reduces HVAC energy consumption by minimizing the temperature difference the system must handle. Optimized mixing strategies can cut building energy use by 10-20%, significantly reducing carbon emissions.

Key Parameters:

• Outdoor Air Temperature - Current external air temperature (°F)
• Return Air Temperature - Temperature of air returning from conditioned spaces (°F)
• Outdoor Air Percentage - Fraction of total air coming from outdoors (0-100%)
• Return Air Percentage - Fraction of total air being recirculated (0-100%)

Real-Life Applications:

• HVAC System Design - Sizing air handling units and cooling coils
• Energy Management - Optimizing economizer operation
• Indoor Air Quality - Meeting ASHRAE 62.1 ventilation requirements
• Retrocommissioning - Verifying proper air mixing in existing systems

Lessons from History:

• 1976 Legionnaires' Outbreak - Highlighted importance of proper air mixing for IAQ
• 2003 SARS Outbreak - Demonstrated need for minimum outdoor air percentages

Industry Standards & Guidelines:

ASHRAE Standard 62.1 specifies minimum outdoor air percentages (typically 15-30%). Energy codes often require economizer controls when outdoor temperatures are below return air temperature. Proper mixing is critical for achieving design delta-T across cooling coils.

Conclusion:

Mixed air temperature calculation is essential for designing efficient, code-compliant HVAC systems. By understanding this fundamental relationship, engineers can optimize energy use while maintaining healthy indoor environments. This simple calculation has outsized impacts on both operational costs and environmental performance.