Mixed Air Temperature Calculator

You can use the mixed air temperature calculator to find the total temperature of two gases with different temperatures and concentrations. The mixed air temperature equation can also be applied to HVAC systems — so you could also use this calculator as a HVAC mixed air temperature calculator.

Do you know how to find the thermal equilibrium temperature of two gases, or how to calculate mixed air temperature? Keep reading to find out!

The mixed air temperature calculator computes the total temperature of two gases in thermal equilibrium with different concentrations. The mixed air temperature equation is given by:

where:

• $T$ — The mixed air temperature;
• $T_1$ — Temperature of gas 1;
• $P_1$ — Percentage of gas 1 in the reservoir;
• $T_2$ — Temperature of gas 2; and
• $P_2$ — Percentage of gas 2 in the reservoir.

Remember — because these two gases are the only ones in the reservoir, the percentages $P_1$ and $P_2$ must add up to 100%.

So, the mixed air temperature formula can deliver the final temperature inside the reservoir after the gases reach thermal equilibrium.

The mixed air temperature formula can be changed to determine the supply air temperature of a HVAC (heating, ventilation, and air conditioning) system. HVAC refers to a system that is responsible for maintaining comfortable and healthy indoor air quality.

The supply air temperature in an HVAC system is defined as the temperature of the air being delivered or supplied to the conditioned space. It is the temperature at which the air exits the HVAC system and enters the room or building.

This temperature can be determined considering the mixture of the outside air with the return air in a HVAC system. Thus, the HVAC mixed air temperature calculator is based on the following equation:

where:

• $T_{\rm{oa}}$ — Temperature of outside air;
• $\text{cfm}_{\rm{oa}}$ — Flow rate of outside air in cubic feet per minute ($\text{cu ft / min}$);
• $T_{\rm{ra}}$ — Temperature of return air;
• $\text{cfm}_{\rm{ra}}$ — Flow rate of return air in cubic feet per minute; and
• $T_{\rm{s}}$ — Supply air temperature, or alternatively, HVAC mixed air temperature equation result.

Let's consider that the outside air temperature is about $30\text{°C}$ and that the typical flow rate of outside air to cool a three-bedroom house is $60 \rm{\ (cu\ ft/min)}$. Moreover, we can assume that the total flow rate ($\text{cfm}_{\rm{oa}}+\text{cfm}_{\rm{ra}}$) supplied by the HVAC system is $1,\!400 \rm{\ (cu\ ft/min)}$.

Therefore, the flow rate of return air is $1,\!340 \rm{\ (cu\ ft/min)}$. If the return air temperature is about $23\text{°C}$, then the supply air temperature to cool a house is $T_s = 23.3\text{°C}$.

The temperature of a gas is a measure of its thermal energy, reflecting the average kinetic energy of the gas molecules. It is a fundamental property used in various scientific and engineering calculations.

Different measurement techniques, such as thermocouples, thermometers, or thermistors, are employed to determine the temperature of gases in practical applications.

If we are considering an ideal gas, its temperature can be measured by using the ideal gas law, which is given by

where:

• $P$ — Pressure of the gas;
• $V$ — Volume of the gas;
• $n$ — Number of moles of the gas;
• $R$ — Ideal gas constant, whose value is $8.31446\rm{\,J/ (K\cdot mol)}$; and
• $T$ — Temperature of the gas.

The concept of thermal equilibrium refers to a state where two or more systems are at the same temperature, and there is no net transfer of heat between them. This means that the heat transfer rates from one system to another are equal, resulting in a state of thermal balance.

Therefore, the Zeroth law allows us to define the concept of temperature — since if two or more bodies are in thermal equilibrium, their particles have the same average kinetic energy, and then they are at the same temperature. So, if there is a temperature difference between two or more systems, heat will flow from the hotter systems to the colder ones until thermal equilibrium is reached.

The temperature can be measured using different thermodynamic scales, such as the Celsius and Kelvin scales. The Celsius scale sets the freezing point of water at 0°C and the boiling point at 100°C (at standard atmospheric pressure). On the other hand, the Kelvin scale sets absolute zero (the lowest possible temperature) at 0 Kelvin, with temperature increments equal to those on the Celsius scale.