Environmental control systems for aircraft need to be robust, lightweight and high performance. Usually they are forgotten by travelers. But the ventilation of aircraft cabins during covid brought them to the forefront and the Center for Disease Control and National Institute of Health added comments about these aircraft systems on their websites. Now that travel is recovering, the focus is on innovation and efficiencies.
Environmental control systems are amongst the most energy demanding systems on aircraft. They typically rank at number one in terms of power draw from the engines over the aircraft life cycle. It is no surprise that much of the effort on the advances of these systems is concentrated on making them more energy efficient. Industry experts provide an update on the technological advances of environmental control systems.
Technological Advancements and the Pandemic
According to Laurent Hartenstein, expert fellow at Liebherr-Aerospace Toulouse’s engineering directorate, the technologies used in environmental control systems are highly dependent on the high-level aircraft and engine design choices. “Besides, thermal management of new power systems (batteries, fuel cells, high by-pass ratio engines, etc.), and the associated consuming systems have become a large contributor of potential optimization, with direct links to functions or technologies used in environmental control systems,” he says. “Technological advances in environmental control system are therefore requiring large panel technology advances to support various needs at equipment and system level and at system integration level. At equipment and system level, the needs are to support increased efficiency of products, for example by developing energy recovery modules in the turbomachine to recover the otherwise wasted thermal, or cabin pressure energy. At system integration level the need is to design optimum thermal management between heating and cooling power sources or means available on aircraft.”
Technological advancements have improved the robustness and the reliability of cabin environmental systems, according to Andreas Bezold, Cabin Air Quality & Ventilation Systems Expert at Airbus. “Reducing the fuel consumption of the ECS with more energy efficient system design is another essential design objective. This is reflected in our latest R&T projects focusing on this design parameter primarily. This also includes modifications in the frame of maintaining our cabin air quality standards, investigating the use of improved filtration devices,” he says. “The pandemic has led to increased R&T efforts focusing on air distribution patterns, infection risks in aircraft cabins etc. R&T efforts are continuing on sanitizing surfaces.”
The pandemic has put a lot of public focus on cabin air quality as a key topic for environmental control systems design, affirms Hartenstein. “Although airplanes already display ‘indoor’ environment superior to that available in our everyday life, several avenues are being investigated to further address this demand: with new architectures of systems using air supply directly taken from outside the cabin, and compressed, or with enhanced cabin air filtration systems, such as volatile organic compound (VOC) or high efficiency particulate air (HEPA) filters,” he says.
HEPA filters have been common for quite some time on commercial narrow body and wide body aircraft, observes Teledyne. “Plenty of existing information has been written describing the advantages of HEPA filters, particularly during the Coronavirus pandemic, but what has not been documented in detail is the airlines’ ability to monitor the effectiveness of their HEPA filters, i.e., are they blocked with particulates and require changing, and how the airlines are monitoring their effectiveness,” says Teledyne. “The only way to answer those questions is with a cabin air quality monitoring system – which is why we developed the ACES solution in order to aid airlines in answering these questions in addition to providing confidence for the traveling crew and passengers, that the environment they are in is safe.”
HEPA filters are standard on almost all commercial aircraft produced today, starting back in the 1990s, observes Teledyne. “Aircraft not equipped with HEPA tend to be older generation aircraft. The advantage of HEPA filters is their ability to capture or block very small particles. As it relates to COVID-19, with an approximate size of 100 nanometers, the typical HEPA filter easily captures particles with 99.9% efficiency, down to 10 nanometers (HEPA filters actually increase in efficiency while in use). Good practice when replacing a HEPA filter would include gloves and a N95 mask,” says Teledyne.
While the HEPA concept is still the most efficient and practical method for removing dust and pathogens from air since decades, some enhancements have been made regarding the materials used to improve their durability and performance, observes Bezold. “Furthermore, architectural improvements were implemented to increase the capacity of HEPA filters. Some recirculation filters are available with absorber stages to reduce the concentration of odorous substances in the recirculated air,” he says. “Airbus has always taken great care to enable a safe environment on board an aircraft — a commitment which remains unchanged and enhanced in a post-pandemic world. Our aircraft are designed and equipped by leveraging the latest technology for the most rigorous and absolute best in health, safety, and comfort. Strict compliance with the published maintenance procedures is key to maintain good air quality. This also applies to troubleshooting and decontamination in the case of a cabin air event.”
As to the maintenance that is needed on HEPA filters, Hartenstein affirms that such filters require periodic replacement on airplane for optimum performance, with adapted procedure for removals and disposal by the maintenance crew.
Environmental control systems are highly automated control systems, affirms Hartenstein. “The control algorithms are typically designed to adjust the energy drawn from the aircraft to the necessary levels to ensure safe and comfortable environment in the cabin, in terms on temperature, air changes in the occupied compartments, humidity, pressure, and rate of pressure variation in the cabin during the mission,” he says. “Human factors are clearly a key element in the design of the monitoring, indication, and crew/system interfaces. The system interfaces are inherently designed with human factors and crew operation specialists to prevent selection of inappropriate conditions for the cabin (e.g., temperature, pressure), and provide comprehensive reporting and indication of malfunctions should crew actions be required.”
A key objective of environmental control systems’ design is aiming at minimising crew workload while providing smooth controls and superior thermal comfort where automation is a key enabler, observes Bezold. “Human factors are an essential element in the design of environmental control systems because they need to be considered to design systems with low crew workload and to achieve a smooth and efficient operation of the ECS maintaining a comfortable environment for passengers and crew,” he says.
There is currently no information to pilots or cabin crew if there is something else that they need to worry about – e.g., chemical substance that has the potential to harm crew and passengers, or potential gradual lack of oxygen which could be hard to detect until it is too late, according to Teledyne. “We want to empower the crew and the airlines with enhanced cabin environmental systems that assist in making informed decisions sooner, through the use of rich data,” says Teledyne.
Reliability and Maintenance
The reliability figures of environmental control systems have improved over the years due to extensive analysis of in-service data and consequent improvements of affected equipment and system areas, according to Bezold. “Thanks to a huge aggregation of operational data Airbus gains a deeper insight into operational effects. Hence the design teams are in a position to permanently improve reliability and reduce maintenance efforts of the customer. This is based on smart algorithms for data analytics and predictive maintenance functions,” he says.
Environmental control systems are typically complex electromechanical systems, operating continuously, and submitted to very harsh environments- i.e., high temperature, pressure, and vibration levels, observes Hartenstein. “The reliability of the equipment, the ease of maintenance, and the operational reliability of the system are key and have been the subject of considerable design efforts for improvement over the years,” he says. “For example, the implementation of newer generation of systems with better controls, optimized architectures, and improved equipment, has demonstrated multiple in-service merits, and specifically an improvement of reliability of key equipment up to a factor two or three and a reduction by a factor two or three of aircraft operational interruption due to air systems, while at the same time offering optimized energy draw from the engine reducing by up to 20% fuel burn associated with environmental control systems.”