Mixed Air Temperature Calculator

Calculate the resulting temperature and humidity when mixing two air masses.

Determine the equilibrium temperature and humidity ratio when combining air streams with different temperatures and moisture content using thermodynamic principles.

Examples

Click on any example to load it into the calculator.

HVAC Air Mixing

HVAC Air Mixing

Typical HVAC system mixing outdoor air with return air for energy efficiency.

Temp 1: 30 °C

Hum 1: 0.018 kg/kg

Flow 1: 3.0 kg/s

Temp 2: 22 °C

Hum 2: 0.010 kg/kg

Flow 2: 7.0 kg/s

Comfort Zone Mixing

Comfort Zone Mixing

Mixing warm humid air with cool dry air to achieve comfortable conditions.

Temp 1: 28 °C

Hum 1: 0.020 kg/kg

Flow 1: 2.0 kg/s

Temp 2: 18 °C

Hum 2: 0.008 kg/kg

Flow 2: 3.0 kg/s

Industrial Process Air

Industrial Process Air

Industrial application mixing hot process air with ambient air for cooling.

Temp 1: 45 °C

Hum 1: 0.025 kg/kg

Flow 1: 5.0 kg/s

Temp 2: 15 °C

Hum 2: 0.006 kg/kg

Flow 2: 10.0 kg/s

Laboratory Air Control

Laboratory Air Control

Precise mixing for laboratory environmental control systems.

Temp 1: 25 °C

Hum 1: 0.012 kg/kg

Flow 1: 1.5 kg/s

Temp 2: 20 °C

Hum 2: 0.009 kg/kg

Flow 2: 2.5 kg/s

Other Titles
Understanding Mixed Air Temperature Calculator: A Comprehensive Guide
Master the principles of air mixing thermodynamics and learn how to calculate the resulting temperature and humidity when combining different air streams. Essential knowledge for HVAC engineers, meteorologists, and environmental scientists.

What is Mixed Air Temperature Calculation?

  • Core Concepts
  • Thermodynamic Principles
  • Real-World Applications
Mixed air temperature calculation is a fundamental thermodynamic process that determines the resulting temperature and humidity when two or more air streams with different properties are combined. This process is governed by the conservation of mass and energy principles, where the total mass, energy, and moisture content of the mixture equals the sum of the individual streams. The calculation is essential in HVAC systems, meteorology, industrial processes, and environmental engineering where air mixing occurs naturally or is intentionally designed.
The Science Behind Air Mixing
When air streams mix, they exchange heat and moisture until they reach thermal and moisture equilibrium. The final temperature is determined by the mass-weighted average of the individual temperatures, while the humidity ratio follows a similar mass-weighted averaging process. This process is adiabatic (no heat transfer to the surroundings) and occurs rapidly in most practical applications. Understanding this process allows engineers to predict the performance of air handling systems and design efficient HVAC solutions.
Key Parameters in Air Mixing
Temperature (°C): The thermal energy content of each air stream, measured in degrees Celsius. This is the primary parameter affecting the final mixture temperature. Humidity Ratio (kg/kg): The mass of water vapor per unit mass of dry air, typically expressed in kg of water per kg of dry air. This parameter determines the moisture content of the mixture. Mass Flow Rate (kg/s): The rate at which air mass flows through each stream, determining the proportion of each stream in the final mixture. The ratio of flow rates directly affects the mixing proportions.
Applications in Modern Engineering
HVAC Systems: Air mixing is fundamental to heating, ventilation, and air conditioning systems where outdoor air is mixed with return air to maintain indoor air quality while optimizing energy efficiency. Industrial Processes: Many industrial processes require precise control of air temperature and humidity through mixing of different air streams. Environmental Control: Laboratories, clean rooms, and specialized environments rely on air mixing to maintain specific conditions. Meteorology: Understanding air mass mixing helps predict weather patterns and atmospheric conditions.

Common Air Mixing Scenarios:

  • Outdoor air (30°C, 60% RH) mixed with return air (22°C, 50% RH) in an HVAC system
  • Hot process air (45°C, 80% RH) mixed with ambient air (20°C, 40% RH) for cooling
  • Warm humid air (28°C, 70% RH) mixed with cool dry air (15°C, 30% RH) for comfort
  • Laboratory supply air (23°C, 45% RH) mixed with exhaust air (25°C, 55% RH) for energy recovery

Step-by-Step Guide to Using the Calculator

  • Data Collection
  • Input Preparation
  • Result Interpretation
Using the mixed air temperature calculator requires accurate measurement and understanding of the air properties involved. Follow these steps to ensure reliable results and proper application of the calculations.
1. Measure Air Stream Properties Accurately
Temperature measurement should be done using calibrated thermometers or temperature sensors with appropriate accuracy (±0.5°C or better). Humidity ratio can be calculated from relative humidity and temperature measurements using psychrometric relationships, or measured directly using specialized humidity sensors. Mass flow rates can be determined using flow meters, or calculated from volumetric flow rates and air density measurements.
2. Convert Measurements to Required Units
Ensure all temperatures are in degrees Celsius. If you have relative humidity measurements, convert them to humidity ratio using psychrometric charts or equations. Mass flow rates should be in kg/s - convert from other units if necessary. Verify that all values are within the valid ranges for the calculation to ensure accurate results.
3. Enter Data and Calculate Results
Input the measured values into the calculator, paying attention to the units and decimal precision. The calculator will perform the mass and energy balance calculations automatically. Review the results to ensure they are physically reasonable - the mixed temperature should fall between the input temperatures, and the humidity ratio should be within the range of the input values.
4. Apply Results to Your Application
Use the calculated mixed air temperature and humidity to design HVAC systems, optimize energy efficiency, or predict system performance. Consider the heat transfer rate to understand the energy implications of the mixing process. Apply these results to make informed decisions about air handling system design and operation.

Typical Air Properties Reference:

  • Outdoor air in summer: 30-35°C, humidity ratio 0.015-0.025 kg/kg
  • Indoor comfort air: 20-25°C, humidity ratio 0.008-0.012 kg/kg
  • Cooling coil discharge: 10-15°C, humidity ratio 0.006-0.010 kg/kg
  • Heating coil discharge: 35-45°C, humidity ratio 0.005-0.008 kg/kg

Real-World Applications and System Design

  • HVAC Engineering
  • Energy Efficiency
  • Process Optimization
Mixed air temperature calculations are essential in numerous real-world applications where air streams are combined for various purposes. Understanding these applications helps engineers design more efficient and effective systems.
HVAC System Design and Operation
In HVAC systems, air mixing is used to combine outdoor air (for ventilation) with return air (for energy efficiency). The mixed air temperature calculation helps determine the optimal mixing ratio to minimize energy consumption while maintaining indoor air quality. This calculation is crucial for sizing heating and cooling equipment, as the mixed air temperature determines the load on the heating and cooling coils.
Energy Recovery and Efficiency
Air mixing calculations are fundamental to energy recovery systems where exhaust air is mixed with fresh air to preheat or precool the incoming air stream. This reduces the energy required for heating or cooling, leading to significant energy savings. The calculation helps optimize the energy recovery efficiency and determine the economic feasibility of such systems.
Industrial Process Applications
Many industrial processes require specific air conditions that are achieved through mixing different air streams. For example, in drying processes, hot dry air might be mixed with cooler humid air to achieve the optimal drying conditions. In clean room applications, filtered air at specific temperature and humidity levels is mixed to maintain the required environmental conditions.

Common Misconceptions and Calculation Errors

  • Temperature vs. Energy
  • Humidity Considerations
  • Flow Rate Effects
Several misconceptions and common errors can lead to incorrect mixed air temperature calculations. Understanding these pitfalls helps ensure accurate results and proper system design.
Misconception: Simple Temperature Averaging
A common mistake is to simply average the temperatures of the mixing air streams. This approach ignores the mass flow rates and can lead to significant errors. The correct calculation uses mass-weighted averaging, where each temperature is weighted by its corresponding mass flow rate. This ensures that the energy balance is properly maintained in the mixing process.
Error: Ignoring Humidity Effects
While temperature is often the primary concern, humidity ratio also affects the energy content of the air and should not be ignored. The latent heat associated with water vapor can significantly impact the energy balance, especially when mixing air streams with very different humidity levels. Proper calculation includes both sensible and latent heat effects.
Pitfall: Incorrect Flow Rate Measurements
Accurate mass flow rate measurement is crucial for correct calculations. Volumetric flow rates must be converted to mass flow rates using the appropriate air density, which varies with temperature and pressure. Using incorrect flow rates can lead to significant errors in the calculated mixed air properties.

Calculation Accuracy Tips:

  • Always use mass flow rates, not volumetric flow rates, for accurate calculations
  • Consider the effect of altitude and pressure on air density and properties
  • Account for any heat gains or losses in the mixing process if significant
  • Validate results by ensuring the mixed temperature falls between input temperatures

Mathematical Derivation and Advanced Concepts

  • Energy Balance Equations
  • Mass Balance Principles
  • Psychrometric Relationships
The mathematical foundation of mixed air temperature calculation is based on fundamental thermodynamic principles. Understanding these equations provides insight into the physical processes involved and enables more sophisticated analysis.
Mass Balance Equations
The total mass flow rate of the mixture equals the sum of the individual stream flow rates: mtotal = m1 + m2. The mass balance for water vapor (humidity) is: mtotal × ωmixed = m1 × ω1 + m2 × ω_2, where ω represents the humidity ratio. This equation ensures that the total moisture content is conserved in the mixing process.
Energy Balance Equations
The energy balance equation accounts for both sensible and latent heat: mtotal × hmixed = m1 × h1 + m2 × h2, where h represents the specific enthalpy of the air. The specific enthalpy includes both the sensible heat (related to temperature) and latent heat (related to moisture content). This equation ensures energy conservation in the adiabatic mixing process.
Psychrometric Relationships
The relationship between temperature, humidity ratio, and enthalpy is described by psychrometric equations. For air at atmospheric pressure, the specific enthalpy can be approximated as: h = 1.006 × T + ω × (2501 + 1.86 × T), where T is temperature in °C and ω is humidity ratio in kg/kg. This relationship is essential for accurate energy balance calculations.
Practical Calculation Methods
For most practical applications, the mixed air temperature can be calculated using the mass-weighted average: Tmixed = (m1 × T1 + m2 × T2) / (m1 + m2). Similarly, the mixed humidity ratio is: ωmixed = (m1 × ω1 + m2 × ω2) / (m1 + m2). These simplified equations provide accurate results for most engineering applications while being easy to implement and understand.

Advanced Calculation Example:

  • For air stream 1: 30°C, ω=0.018 kg/kg, m=3 kg/s → h₁ = 1.006×30 + 0.018×(2501+1.86×30) = 75.8 kJ/kg
  • For air stream 2: 20°C, ω=0.010 kg/kg, m=2 kg/s → h₂ = 1.006×20 + 0.010×(2501+1.86×20) = 45.4 kJ/kg
  • Mixed enthalpy: h_mixed = (3×75.8 + 2×45.4)/(3+2) = 63.6 kJ/kg
  • Solving for mixed temperature: T_mixed = (63.6 - 0.015×2501)/(1.006 + 0.015×1.86) = 26.2°C