Mixed Air Calculator
Free calculate mixed air properties when combining two air streams. Get instant, accurate results with our easy-to-use calculator.
Input Parameters
Air Stream 1
Air Stream 2
Results
Enter parameters to calculate
What is Mixed Air?
Mixed air refers to the resulting air stream when two air streams with different temperatures and humidity levels are combined. This is common in HVAC systems where outdoor air and recirculated air are mixed.
When air streams mix, the resulting properties (temperature, humidity) are determined by mass-weighted averages. The mixed air temperature is calculated using energy balance, and humidity is calculated using mass balance of water vapor.
Mixed air calculations are essential in HVAC design for determining the conditions entering the cooling/heating coil, optimizing energy efficiency, and ensuring proper ventilation and comfort.
Mixed Air Formulas
Where:
- • T₃ = Mixed air temperature (°C or °F)
- • ω₃ = Mixed air specific humidity (kg/kg)
- • m₁, m₂ = Mass flow rates of streams 1 and 2 (kg/s)
- • T₁, T₂ = Temperatures of streams 1 and 2
- • ω₁, ω₂ = Specific humidities of streams 1 and 2
How to Calculate
-
1
Convert temperatures to same units
Ensure both temperatures are in °C or °F for calculation.
-
2
Calculate mixed temperature
T₃ = (m₁T₁ + m₂T₂) / (m₁ + m₂). Mass-weighted average of temperatures.
-
3
Calculate mixed humidity (if provided)
ω₃ = (m₁ω₁ + m₂ω₂) / (m₁ + m₂). Mass-weighted average of specific humidities.
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4
Calculate total mass flow
m₃ = m₁ + m₂. Total flow rate of mixed air stream.
Practical Examples
Example 1: HVAC Mixing
Outdoor: 4°C, 2 kg/s. Recirculated: 25°C, 6.25 kg/s.
Solution:
T₃ = (2×4 + 6.25×25) / (2 + 6.25)
T₃ = (8 + 156.25) / 8.25
T₃ ≈ 19.9°C
Applications
HVAC Systems
Designing air handling units, calculating mixed air conditions entering coils, and optimizing energy efficiency.
Building Design
Determining ventilation requirements, calculating fresh air intake, and ensuring proper indoor air quality.
Industrial
Mixing process air streams, controlling humidity in manufacturing, and optimizing air conditioning systems.
Education
Teaching psychrometrics, understanding air properties, and demonstrating mass and energy balance principles.
Frequently Asked Questions
Why use mass flow rate instead of volume?
Mass flow rate accounts for density differences. Air density varies with temperature and humidity, so mass-weighted mixing gives accurate results. Volume flow rates would require density corrections.
What if I only know volume flow rates?
Convert to mass flow: m = ρV, where ρ is air density at the given temperature and pressure. Use ideal gas law: ρ = P/(RT), or approximate: ρ ≈ 1.2 kg/m³ at 20°C, 101.3 kPa.
Does the mixing process affect humidity?
Yes! If both streams have different humidities, the mixed air humidity is the mass-weighted average. This affects relative humidity, which depends on both temperature and absolute humidity.
What about enthalpy?
Mixed air enthalpy is also mass-weighted: h₃ = (m₁h₁ + m₂h₂)/(m₁ + m₂). This is useful for energy calculations in HVAC systems and determining cooling/heating loads.
Can I mix more than two streams?
Yes! For multiple streams: T₃ = Σ(mᵢTᵢ) / Σmᵢ. Simply extend the formula to sum all mass flow rates and their weighted temperatures.