Analysis & Optimization of
Thermal Passenger Comfort in Aircraft Cabins

The main task of the environmental control system (ECS) of an aircraft is to provide air supply, thermal control and cabin pressurization for the crew and passagers. An amount of 0.55 lb/min of fresh air has to be supplied for each passenger within the following bounds:

• proper level of oxygen
• a moisture level of 7-15 %
• temperature in the range 21-25 °C
• a pressure level of approx. 750 hPa

The desired cabin pressure is regulated by controlled draining of stale air. Recirculation air and fresh air are mixed in roughly equal proportions.

For the normal flight operation, cabin temperature is regulated to 21-25 °C For cooling down an airplane while on the ground on a hot sunny day, one estimates the necessary cooling power to about 150-200 W per passenger. For a large capacity aircraft with 350 passengers this leads to a required cooling capacity of over 50 kW.

When putting the ECS system into operation, its efficiency is demonstrated with dynamic load cases

• typical summer load case: cooling down from 40 ° to 24 °C
• typical winter load case: heating up from -25 °C to 21 °C

The cabin target temperature has to be reached within 30 minutes. The process of heating up during the winter load case demands for up to 70°C fresh air temperature. The portion of needed fuel for the environmental control system compared to the total fuel consumption is approximately 5%.
For the summer load case while on the ground, about 25% of the ECS power is used for dehumidification of the air. Nowadays for that purpose high-pressure water separators are used. They utilize that fact that air at high pressure absorbs less water than at normal pressure levels.