Mixed Air Temperature Calculator
Free calculate mixed air temperature 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 Temperature?
Mixed air temperature is the resulting temperature when two air streams with different temperatures are combined. It's calculated using a mass-weighted average based on energy conservation.
When air streams mix adiabatically (no heat exchange with surroundings), the mixed temperature is determined by the mass flow rates and temperatures of the individual streams. The stream with higher mass flow rate has more influence on the final temperature.
This calculation is fundamental in HVAC systems where outdoor air and recirculated air are mixed before entering the cooling or heating coil. It helps determine the required cooling/heating capacity and optimize energy efficiency.
Mixed Air Temperature Formula
Where:
- • T₃ = Mixed air temperature (°C or °F)
- • m₁, m₂ = Mass flow rates of streams 1 and 2 (kg/s)
- • T₁, T₂ = Temperatures of streams 1 and 2 (°C or °F)
Note: This assumes adiabatic mixing (no heat loss) and constant specific heat capacity.
How to Calculate
-
1
Convert temperatures to same units
Ensure both temperatures are in the same units (°C or °F) for calculation.
-
2
Calculate weighted sum
Multiply each temperature by its mass flow rate: m₁T₁ + m₂T₂.
-
3
Calculate total mass flow
Sum the mass flow rates: m₁ + m₂.
-
4
Calculate mixed temperature
Divide the weighted sum by total mass flow: T₃ = (m₁T₁ + m₂T₂) / (m₁ + m₂).
Practical Examples
Example 1: HVAC System
Outdoor air: 4°C, 2 kg/s. Recirculated air: 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
Example 2: Equal Flow Rates
Stream 1: 30°C, 5 kg/s. Stream 2: 10°C, 5 kg/s.
Solution:
T₃ = (5 × 30 + 5 × 10) / (5 + 5) = 200 / 10
T₃ = 20°C (simple average when flows equal)
Applications
HVAC Design
Calculating mixed air conditions entering cooling/heating coils, determining required capacity, and optimizing energy use.
Ventilation
Designing ventilation systems, calculating fresh air requirements, and ensuring proper indoor air quality through air mixing.
Process Control
Mixing process air streams in industrial applications, controlling temperature in manufacturing, and optimizing air handling.
Education
Teaching energy balance, understanding mass-weighted averages, and demonstrating mixing principles in thermodynamics.
Frequently Asked Questions
Why use mass flow rate instead of volume?
Mass flow accounts for density differences. Air density varies with temperature, so mass-weighted mixing gives accurate results. Volume flow would require density corrections at each temperature.
What if flows are equal?
When m₁ = m₂, the formula simplifies to T₃ = (T₁ + T₂)/2 - a simple arithmetic average. This is because both streams contribute equally to the mix.
Does this assume adiabatic mixing?
Yes, the formula assumes no heat exchange with surroundings. If there's heat loss/gain during mixing, you'd need to account for it using energy balance: m₁h₁ + m₂h₂ = m₃h₃ + Q_loss.
What about specific heat capacity?
The formula assumes constant specific heat. For air, this is reasonable over typical temperature ranges. For large temperature differences, you might need to account for temperature-dependent cp.
Can I use this for more than two streams?
Yes! For multiple streams: T₃ = Σ(mᵢTᵢ) / Σmᵢ. Simply sum all (mass × temperature) products and divide by total mass flow rate.