Air conditioning in airplanes: Environmental Control System Essay

Consistently there are more than one billion individuals traveling by airplanes throughout the world and this number is expected to be doubled in the next 20 years
Aircrafts operate in a physical environment that is not survivable by unprotected humans such as an altitude of 11 000 m, a temperature of 55 C, the atmospheric pressure is around onefifth of that at the sea level and the moisture content is near zero [3]. Environmental Control System (ECS) is needed to change the air conditions such as pressure, temperature and moisture content before entering the cabin to be suitable for the passengers
the air is taken from the compressor stage (bleed air) and passes through a precooler unit which reduces its temperature before entering the air conditioning packs. After entering the air conditioning packs, the air enters the mixer unit and gets mixed with the recirculated air and finally enters the cabin. The recirculated air is drawn by fans and passes through filters before entering the mixer unit. There are alternative bleed air supply source such as Auxiliary Power Units (APU) during ground operations which supply the air conditioning packs with pressurized and consequently hot bleed air. Approximately, 50% of air from the air distribution system in an aircraft cabin is recycled to save energy [5]. The air is filtered through a HighEfficiency Particulate Air filters (HEPA). These filters remove dust, allergens, viruses and bacteria with an efficiency greater than 99.9% from the air recirculated into the cabin and cockpit to provide a safer, healthier and comfortable environment for the passengers.
Aircraft cabin air quality is a serious concern so many studies should be done on this topic to keep the aircraft cabin air quality improving and to keep up with the new technologies demands
the cabin environment is affected by some factors which can be classified into two main factors 1) factors affecting the air quality 2) factors affecting the entertainment of passengers. The factors affecting the air quality are the temperature, pressure, humidity and percentages of the contaminants such as dust, CO, CO2 and many other contaminants. The factors affecting the entertainment or luxury of the passengers are the Inflight entertainment, food and seats. Complaints about cabin environment are common due to thermal and humidity discomfort and indoor air quality. The ASHRAE requirements for ventilation in aircraft cabins demand approximately 10 l/s of air for passenger [8]. The requirements for temperature and air movement in spaces prescribed in the present standards [9, 10]. The recommended values of temperature are 21̊ C to 23.5̊ C and the air velocity values are 0.15 m/s to 0.18 m/s. The air temperature and velocity values are based on average values for a large group of occupants. Occupants physiological and psychological responses to the indoor thermal environment differ due to the differences in clothing, activity and individual preferences for air temperature, air velocity, etc. The high occupancy densities in aircraft cabins may cause spreading of airborne contaminants through activities such as talking, sneezing, coughing and vomiting