Air Mixing Calculator

Psychrometric analysis of mixed air conditions from two airstreams. Fresh air ratio optimization.

What is the Air Mixing Calculator?

The air mixing calculator analyzes the psychrometric mixing conditions of two different airstreams. It accurately computes the mixed-point temperature, relative humidity, absolute humidity and enthalpy that occur in fresh (outdoor) + return (recirculation) blending, economizer cycles, post-recovery bypass calculations, or make-up air integration.

The mixing calculation is based on mass balance: T_mix = (ṁ₁ × T₁ + ṁ₂ × T₂) / (ṁ₁ + ṁ₂) and W_mix = (ṁ₁ × W₁ + ṁ₂ × W₂) / (ṁ₁ + ṁ₂). Temperature and humidity weights are scaled by mass flow; mass flow corrected by air density is used instead of volumetric flow (m³/h). The mixing point is plotted on the psychrometric chart along a straight line between the two inlet points.

The tool is a critical input for fresh-air ratio optimization, winter-summer economizer cycle analysis, energy recovery exchanger bypass calculation, and mixing-point control in variable air volume (VAV) systems. ASHRAE 90.1 and EN 16798-3 define economizer control strategies based on mixing-point enthalpy.

NKT engineering uses this calculation in AHU fresh-air sizing, lithium-ion dry room make-up air blending, hospital operative-block 100% outdoor air analysis, and office building seasonal energy optimization projects. If the mixed air has a high moisture load, a downstream desiccant dehumidification stage is planned; if low, a steam or adiabatic humidifier is added.

Applications

• AHU fresh-air ratio optimization
• Economizer cycle analysis (ASHRAE 90.1, EN 16798-3)
• Energy recovery exchanger bypass
• VAV mixing point control
• Lithium-ion dry room make-up air blending
• Hospital 100% outdoor air analysis
• Data center free-cooling feasibility
• Office building seasonal energy optimization

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Technical terms used in this tool

Access concise ASHRAE-referenced definitions of technical concepts you encounter in the calculation.

Frequently Asked Questions

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