Result
Preliminary calculation: This tool is for quick sizing and information. In real projects, load calculation, selection and commissioning require engineering calculations and a site survey. Results are approximate values.
Calculation method
w_m = (ṁ_f·w_f + ṁ_r·w_r) / (ṁ_f + ṁ_r)h_m = (ṁ_f·h_f + ṁ_r·h_r) / (ṁ_f + ṁ_r)T_m = (h_m − 2501·w_m) / (1.006 + 1.86·w_m)Since fresh and return airflows are given on a volume basis, they are converted to mass flows via specific volume. The temperature of the mixture is found not by taking a direct average but from the enthalpy and humidity balance.
- The fresh air quantity is determined by the number of occupants and the regulation
- With an economizer and free cooling, the ratio varies with outdoor air
- In cold climates, freeze protection is needed in the mixing chamber
Frequently asked questions
Why does the fresh air ratio matter?
Fresh air is generally warmer and more humid than room air; as the ratio increases, the cooling and dehumidification load rises, but air quality improves.
What happens if the mixture humidity exceeds 100%?
The mixture becomes saturated, and fog and condensation form. In this case the mixture conditions cannot physically occur; the line design and preheating should be reviewed.
Why are flow rates entered by volume?
Air handling unit catalogs give flow in m³/h. The tool sets up the mass balance itself.