Final Report Summary - ISPACE (innovative Systems for Personalised Aircraft Cabin Environment)
Executive summary:
ISPACE investigated unique concepts and technologies to reach a step-change in personalised passenger climate control. The overall objective of ISPACE was to provide aircraft manufacturers and the supplier industry with know-how and innovations to address the individualisation of passenger cabin environment. This ultimately provides a step-change in passenger comfort during flight.
The first steps achieved within ISPACE were to define the specific requirements and boundary conditions for individualisation of passenger cabin environment and comfort within aircraft cabins. Parameters and aspects which were considered and defined are environmental parameters (such as air temperature, surface temperatures, air humidity, airflow, air quality), human related aspects (e.g. perception of comfort, human physiology, well-being, ergonomics) and technical requirements (such as mass, volume, weight, safety, energy consumption, lifetime, maintenance). Based on these first steps, ISPACE developed concepts for individualisation of passenger cabin environment and comfort within aircraft cabins. The different concepts were evaluated against the requirements identified. For the most applicable concepts possible technology solutions were determined. Subsequently, detailed feasibility studies were carried out by taking evaluation criteria into consideration. Simulative parameter studies were carried out for selected technologies to achieve a preliminary qualitative basis for the judgement of feasibility and to reduce parameter variation for further integration in real scale of these technologies.
Within the second period of the ISPACE project an experimental proof of individualisation of cabin climate and comfort was performed. Experiments were carried out with 42 subjects on ground in a most realistic flight test environment (Flight Test Facility (FTF) at Fraunhofer IBP). Based on the results of the feasibility study a detailed test design was developed to achieve this experimental proof. Selected technologies were tested with the focus on passengers' well-being and their comfort increase due to individualised cabin environment. Dedicated environmental parameters were generated locally at the subjects' seat level to provide maximum flexibility for testing. The goal was to find out by environmental measurements and subject questionnaires which control parameters are the critical ones and how well the cabin climate can be individualised for a single passenger at seat level. In addition, the limiting factors for individualisation (e.g. geometrical, physical) were determined. Parallel with testing a computational fluid dynamic (CFD) simulation of the individual environment was validated with STAR-CCM+ and ICON FOAMpro. Testing showed that individualisation of personal environment lead to higher well-being and comfort level. Fully equipped seats with different personalised ventilation systems achieved the highest satisfaction. Additional seats equipped with seat heating/ventilation mats had a high comfort level.
Within the third period of the ISPACE project the investigated prototypes (individualised seats, humidifier, PCRA filter system and seat heating / ventilation) were exhibited at the Berlin AirShow ILA 2012 which resulted in high interest of the press and visitors. Detailed results were presented and discussed during the Final Stakeholders' Club Meeting (24 October 2012). Stakeholders from diverse aircraft industry branches, ranging from suppliers to airliners, attended the meeting. Besides the presentation of ISPACE and its results they got the possibility to experience the ISPACE prototypes and the testing environment of the FTF. A lively and fruitful discussion on further exploitation possibilities concluded this event and the ISPACE project.
Project context and objectives:
The scientific and technological objectives of ISPACE were the following:
(1) the development of concepts for individualisation of passenger cabin environment and the general prove of feasibility;
(2) the development of technologies for individualisation of passenger cabin environment and proof with subject testing;
(3) the provision of simulation tools for individualised cabin environment and the recommendations for existing and future commercial aircraft.
The project ISPACE was divided in six work packages (WPs). In the following the WPs and their work task (WT) described in detail with respect to objectives of ISPACE project.
Within WP1 'State-of-art of science and technology and their requirements' the objective was the construction of a systematically arranged collection of requirements, prepared on the basis of cross-section of influential factors related to the system: human, space / room, climate, structure / envelope, installations.
The WP was divided into four subtasks:
Within WT1.1 'Existing knowledge and expertise' knowledge and partners' information was collected and compiled as a sound basis for development, testing and final evaluation of the developed technologies.
The output of WT1.2 'Existing technologies and their principles' provided a summary of existing technologies for personalised climate control, their principles and applications with respect to aircraft application.
In WT1.3 'Requirements for individualised cabin environment' information on the requirements for an individualised cabin environment, comprising both general requirements for human comfort and well-being as well as requirements specific for the aircraft environment and the integration of technologies were provided.
In WT1.4 'Requirements and boundary conditions for simulation' knowledge and partners information towards a virtualisation of the problem was collected and compiled as a sound basis for the CFD model which was generated in the parametric study of WP2. WP1 served as a source of target information for the study of possible intervention measures which were treated first of all in the framework of WP2 and the feasibility studies on individualisation of passenger cabin climate.
WP2 'Concept development, selection and test design' had one main objective: to select step change technologies to be developed and their concepts of integration for WP3, which were tested and evaluated in WP4. In WT2.1 'Feasibility' the feasible integration of personal climate control systems into aircraft cabin environments was assessed.
In WT2.2 'Qualitative simulation and parameter study' the parametric study was performed to study the effect of personalised inlets in a first class (F/c) seat using CFD. For the computational study four F/c seats in a row located in a section of an exemplary A380 lining were used. The aim of the study was to find suitable positions of the personalised inlet in terms of fresh air delivery, efficiency of humidity local delivery to the passenger and at the same time maintain thermal comfort.
In WT2.3 'Selection of Concepts' performance and acceptability of the concepts, systems and technologies were assessed. For that purpose, many criteria were evaluated and considered. Generally, systems for personalised air conditioning are more complex systems, which cost more, use more space and have a higher mass than current or no such systems. However, it is expected to achieve higher customer satisfaction and comfort with these systems.
In WT2.4 'Test design' a test design was developed to prove the individualisation of passenger cabin climate in a highly realistic flight environment, focusing on the selected innovative technologies. The test design takes into account physical and chemical measurements, as well as human response parameters of psychological and to some extend physiological measurements.
In WP3 'Technology development and integration' two main objectives were realised:
(a) to develop technologies for the local generation and the control of air temperature, surface temperature, air humidity, air quality, airflow etc. ;
(b) to integrate these technologies into a most realistic test environment - separately as well as in combination.
These objectives were gathered within three work tasks. WT3.1 'Individual temperature zone' considered heating / cooling devices and concepts for distribution of air at seat level. Seat heating elements for backrest, seat cushion, leg rest and foot rest were prepared. Within WT3.2 'Personalised ventilation' a humidification system was developed and a filtration system based on the photocatalytically regenerated adsorber principle. Different concepts for ventilation in / outlets were tested and analysed. The developed technologies were integrated in WT3.3 'Integrated technologies' into first and business class (B/c) seats and installed in a most realistic flight test environment (FTF FTF at Fraunhofer IBP). The main objective of WP4 'Testing, analysis and evaluation of technological concepts' was to prove whether the local climate in an aircraft cabin can be individualised for each single passenger by the technologies developed and integrated in WP3. Within the following four work tasks this could be realised.
In WT4.1 'Detailed simulation of individualised cabin environment' the boundary conditions were finalised for the CFD simulations to match the actual boundary conditions of the seats in the FTF geometry based on the parametric study results and previous studies. The impact of seat integrated local ventilation arrangements was analysed in the context of cold, normal and hot climate environmental conditions.
In WT4.2 'Testing of technologies for individualised cabin environment' system and subject testing was achieved. During system testing the performance of all single in-/outlets was tested and measured. A subject test campaign was performed with 42 subjects under different thermal conditions using different setups of B/c and F/c seats with individualised systems developed in WP3.
In WT4.3 'Analysis of test data' the data of questionnaire ratings and physiological parameters from subject testing and physical measurement data were analysed. The data of the questionnaire ratings and physiological parameters revealed that subjects' well-being and comfort was differently perceived across seats and was also affected by ambient temperature and differed systematically between aisle and window seats.
In WT4.4 'Validation of simulation of individualised cabin environment' the results obtained from detailed simulation in WT4.1 were compared with results obtained during testing in WT4.2.
In WT4.5 'Evaluation of technologies for individualised cabin environment' certification aspects were considered as well as the performance of technology developments during testing and with simulation. The developed technologies were checked for applicability and if they are suited for integration as stand-alone or combined technologies with respect to their impact on passengers' health, well-being and comfort.
The objectives of WP5 'Dissemination and exploitation' were:
(a) to involve stakeholders views in the whole project to streamline technology development and to ensure applicableness of the new concepts;
(b) to guarantee consideration of intellectual property rights throughout the whole project;
(c) to generate an overview of the work accomplished in WT4.5 to emphasise the critical evaluations of the technologies studied in this project for individual passenger climate control. This permits to identify technologies for industrialisation and the key factors to account for industrialisation of these systems;
(d) to draw, from critical evaluations of the WP3 and WP4 results, some recommendations for both future aircraft and the current fleet;
(e) to disseminate these results and conclusions by both publications and demonstration within the consortium and to the outside world, especially to other European organisations working on commercial and business aviation.
WT5.1 'Stakeholders club' included a web-based questionnaire to gather opinions of stakeholders. Stakeholders were informed regularly about the status of ISPACE with newsletters. Stakeholders were invited to a project consortium meeting (September 2011) and took part at a test flight for individualised cabin environment at FTF (November 2011). In October 2012 a final stakeholder club meeting was achieved.
In WT5.2 'Exploitation and protection of results' arose intellectual property rights were considered, patents were reviewed and summarised and exploitation strategies were worked out. CFD tools FOAMpro and STAR-CCM+ were used. ISPACE prototypes were exhibited at the Berlin AirShow ILA in September 2012.
In WT5.3 'Publications and recommendations' several publications were achieved including press releases as well as scientific conference papers and posters.
In WP6 'Management' Fraunhofer IBP as the coordinator successfully set out the management strategy and achieved the proper coordination of the project.
Project results:
Four different personalised ventilation systems were tested with subject testing in the FTF at Fraunhofer IBP. The tested systems are:
(1) ventilation side;
(2) humidification;
(3) heating / ventilation mat;
(4) ventilation front.
These four systems were tested as single components at B/c seats. Additionally all four systems were combined in one B/c and one F/c seat. One B/c and one F/c seat had no personalised ventilation systems and were used as control seats.
Each subject tested each type of seat during one day of flight for at least 20 minutes and evaluated it with a questionnaire. This was repeated at three different temperature conditions of the cabin:
- low temperature (~19.5 degrees of Celsius),
- middle temperature (~23.5 degrees of Celsius),
- high temperature (~27.5 degrees of Celsius).
Each setting was achieved for one day of testing. All subjects participated on three sequent days. Other environmental parameters remained constant for all three temperature conditions:
- Relative humidity: 10 %
- Noise: 74 dB(A)
- Pressure: 7000 ft equivalent height
1.3.1 Analysis of Test Data
In general big differences for the overall temperature ratings can be seen depending on the temperature conditions, but the differences are relatively small for the 1A seat, also for the fully climatised (7F, 7G) and for the ventilated seats (4F, 4G). There are very big differences in the control conditions, so this gives a very clear picture that the climatisation of 1A, 3, and 7 is working, although there is no significant difference between the warm and the normal condition. There are very big differences at the seat 8, for the ventilation front, for both seats (window and aisle), but much more for the aisle seat.
The experienced temperature at feet level is generally perceived somewhat cooler than at the other levels, and shows a comparable pattern with less differences across seats than at the other levels, and most pronounced for the cool condition.
In particular for the cold condition overall draught was perceived as too much, although the difference to zero is not that big in general. However, in the ventilation conditions from the front, there are pronounced effects and relatively strong 'too much' in the cold condition. The ratings are very close to zero, meaning 'good', for the seats 4F and 4G.
Highest comfort ratings independent of temperature - were reported for seat 1A. Compared to the control seat 2A, there are general rather bad conditions. For the blue condition (cool) the window seat 7F had the highest comfort rating.
The main effect averaged over the temperature conditions shows clearly that the most comfortable ones are the seats 1A and 7F as well as 4G. The control seats are worse. To some extent the aisle seats 5G with ventilation side and seat 8G with ventilation front are somewhat bad wrt. sitting comfort.
Ratings on comfort are very close to the ratings of overall temperature, but there are not so much differences between the normal and the warm condition. This may be because there were some problems to reach all the planned ambient temperatures, there may be other reasons, but it is very clear: the more negative, the more uncomfortable, in particular for the cool temperature and it is more uncomfortable in the control than in the climatised seats.
1A reports were on the uncomfortable side for seats 8G/F for the cool condition. The analysis of the number of symptoms revealed a clear effect of temperature. For the cold conditions there are more symptoms in general and no differences for temperature at seat 1A, but in the control condition 2A.
For reports of relaxation no effect of seat (with the exception of seat 8G) was found for the normal temperature. Lowest values were found in the cold conditions and, in addition there is always less relaxation on the aisle side than on the window side. Highest values were reported for the seats 1A and 7F.
Additionally a photocatalytic regenerable adsorption (PCRA) cabin air cleaning device was integrated in the global cabin ventilation system and was tested at the end of each test day. Compounds were injected into the cabin supply air for a period of 15 min reaching the cabin by the personal air outlets (PAOs) above the passengers. Test compounds used were ethanol, hexanal, butyl acetate und Limonene. The subjects evaluated with questionnaires if they could smell anything. Additionally it was measured if the compounds reached the cabin. A proper functionality with the mentioned compounds could be proven. The answers of the subjects differed a lot.
Based on testing and CFD simulation ISPACE gives recommendations on the use of systems for personalised aircraft cabin environment for existing aircraft and solutions for future aircraft. Designing future aircraft, planning of modernisation of the current fleet as well as assessing the status quo need reliable and validated simulation tools for the complex phenomena of individualised cabin environment. These tools are continuously developed and improved and were validated with test data. Technical workshops and stakeholder meetings gathered external experts to provide an additional overview of the workflow and progress of ISPACE.
In the following the recommendations of ISPACE are listed considering the topics 'Concepts for individualised cabin environment', 'Technologies for individualised cabin environment' and 'CFD simulation of individualised cabin environment'. Recommendations are accentuated in bold in a separated box at the end of each subtitle.
1.3.2 Concepts for individualised cabin environment
1.3.2.1 Concept evaluation based on thermal cabin environment simulation
Parametric studies of the thermal cabin environment were performed using CFD simulations in order to evaluate different concepts of individualised cabin environment. In some simulated cases it was challenging to evaluate impact of a specific technology on thermal comfort and local seat environment because the selected combination of the setup could lead to situations when one technology influences others, e.g. seat heating compensates convective cooling by nozzles. Also the cooling effect of ventilated seat mats, which can be controlled by the passenger on demand, could benefit from technology combination especially in high cabin temperature conditions. On the other hand humidified air from personal inlets is in this case not necessarily fed into the passenger's convective plume and thus does not reach the passenger breathing zone what is a disadvantage of such a setup of combined technologies. Side displacement outlets may counteract this as they deliver air in a manner which is supporting the convective plume. In the parametric study a combination of nozzle and side displacement inlets with a seat heating and ventilation mat turned out to achieve best results with respect to thermal comfort assessment based on equivalent temperature and age of air.
This case combines two personal inlets - a nozzle and seat displacement inlets together with the suction of air through a seat ventilation mat. This configuration brings the most efficient fresh air delivery to the passenger. While the side nozzle delivers the air towards the face of the passenger, the displacement inlets help to create enclosed microclimate which is not disrupted significantly by the main ventilation air pattern. For both positions, window and aisle seat, the thermal comfort assessment of virtual manikins show similar profiles.
The release of humidified air must be chosen very thoughtfully, otherwise the humidity will be released to the environment without any effect on the passengers breathing and comfort conditions. This is in particular relevant for provision of humidity through distant nozzles which would need to provide an air jet with high velocity to reach the facial region, and thus would cause a convective drying out rather than an effect of humidification. As shown in the subsequent sections the results of testing yield similar conclusions as the simulative evaluation of the concepts based on the equivalent temperature assessment method: the fully equipped seats (combined technologies) show high thermal comfort values as well as seats with a heating and ventilation mat.
ISPACE recommendation:
In terms of thermal comfort personal ventilation inlets in the form of seat integrated side displacement inlets appeared to be most effective in combination with a seat heating and ventilation mat and eventual additional nozzles.
% Draught issues should be considered carefully for the design of nozzle inlets, however adverse effects may be counter-balanced by an overall better thermal environment. The release of humidified air must be chosen very thoughtfully, otherwise the humidity will be released to the environment without any effect on the passengers breathing and comfort conditions.
1.3.2.2 Impact on perception of thermal cabin environment, physiological load, well-being and comfort
Statistical analysis of passengers' perception of thermal cabin environment revealed that fully equipped F/c seats, fully equipped B/c seats and seats only equipped with seat heating and ventilation mat got the most positive ratings. A comparison of boxplots between the temperature and the seat heater settings of fully equipped F/c seats, fully equipped B/c and seats only equipped with seat heating and ventilation mat revealed that for the latter system medians are often higher than the ones of the other two systems, thus indicating that this system can contribute significantly to increase thermal comfort. Data analysis of the questionnaire ratings and physiological parameters showed that subjects' well-being and comfort was affected by ambient temperature and was perceived differently across seats, they differed systematically between aisle and window seats. Therefore the following ranking of seats is based on window seats only. Based on subjective experience of comfort and well-being the seats with the highest ranking were 1, 4 and 7 and based on physiological load, seats 3, 4 and 5 were highest in ranking. The ranking based on a combined score is:
- Seat 1: fully equipped, F/c
- Seat 4: heat and ventilation, B/c
- Seat 7: fully equipped, B/c
- Seat 5: ventilation side, B/c
- Seat 6: control seat, B/c
- Seat 3: humidification, B/c
- Seat 8: ventilation front, B/c
- Seat 2: control seat, F/c
Whereas between the first three seats no statistical differences were observed, for all three of them the statistical difference to the respective control seat was significant.
Based on the empirical investigation of the impact of individualised climate on well-being and physiological response of human subjects - considering a typical thermal condition in an airplane cabin as well as cool and warm cabin conditions - the results show that most of the technologies investigated (with the exception of ventilation from the front) have an advantage to the traditionally used systems which were integrated into the investigation as the control condition. That means that in particular full climate control in the F/c suite as well as in the B/c seat show the largest advantage to current systems.
However, all other investigated systems, i.e. heating and ventilation, humidification, ventilation from the side, with the exception of ventilation from the front, display a remarkable advantage to the traditional systems.
Moreover, not only well-being in cardiovascular response was affected in a positive way - in particular regarding the fully equipped seats as well as those with individual control of heating and ventilation - but also the investigation showed remarkable results on perceived comfort - whereas none of these results were found for seats with ventilation only from the side or only from the front.
Besides these clear advantages in perceived symptoms, well-being, and comfort, there are also some indications on adverse effects, in particular for the full individualised climate control seat, coming most presumably from additional noise. This seat configuration seems to have the highest potential for well-being and comfort; however a reduction of noise seems advisable.
The present investigation focussed on control of humidity, temperature, and ventilation via individually controllable systems implemented in seats. It turned out that such additional systems if combined most likely with spots of higher acoustical load in the cabin might become an issue of discomfort on a subjective and on a physiological level. Therefore it is recommended that noise reduction in general and also in relation with additional equipment should be a focus of future research.
ISPACE recommendation:
All investigated systems, i.e. heating and ventilation mat, humidification, ventilation from the side, with the exception of ventilation from the front, show a remarkable advantage wrt. well-being and physiological response of human subjects compared to the traditional systems, in particular seats with full climate control.
Thermal comfort was rated highest on fully equipped seats and seats only equipped with a heating and ventilation mat, which should be the first candidate for further development. Besides there are some indications on adverse effects coming most presumably from additional noise, thus noise reduction in general and also in relation with additional aggregates should be a focus of future research.
1.3.3 Technologies for individualised cabin environment
1.3.3.1 Seat heating and ventilation mat
An electrical heating element underneath the seat surface / cover heats up and transfers the heat through the seat cover to the surface. For ventilation ambient air is sucked through an air permeable cover and guided through an air distribution layer underneath the seat cover. With the air flow through the cover and the distribution layer to the outlet of the fan the humidity at the body contact area of the seat can be removed.
During testing this system showed to improve passengers' comfort most and its reaction time was effective to satisfy the subjects demand for thermal comfort. Such systems would be fairly easy to design into an aircraft seat, for both business and F/c applications. However this depends on energy consumption and energy management priority level in competition with other actuators at seat level. Therefor further benefits should be elaborated to achieve similar thermal comfort perception with less and transient energy demand.
Although the used system components are already certified for the car industry, there are specific certification requirements for the passenger aircraft industry. Applicable requirements relate to the materials of an aircraft seat. Especially the materials of the seat heating and ventilation mat need to be certificated. The main attention need to be paid to the flammability requirements for aircraft seats regarding CS/FAR §25.853.
ISPACE recommendation:
Testing has shown that seat heating and ventilation technology can improve passenger comfort substantially under a range of temperature conditions. Such systems yield an almost immediate effect to satisfy the passengers' demand.
Stakeholders within the project were most interested in the technology than any other concept, and saw potential in its use and series introduction.
In terms of design, integrating this concept into a seat should not be an issue. However to enable this, amounts of electrical certification work and some developmental flammability testing on appropriate seat heating and ventilation mat need to be done.
1.3.3.2 Seat integrated ventilation inlets
A piping for ventilation and heating at the side of the seat cushion was integrated into the seats. For additional personal ventilation an air inlet in the backrest of the front seat was installed. Both systems worked with directly recirculated air from the cabin.
The piping into the seat including a temperature control system turned out to be realistic for F/c suites only where piping and outlets can be better integrated and 'hidden' in the furniture. Draft is an issue especially for nozzle systems, where also the feeling of drying out must be avoided. Special attention should be paid to avoid any additional source of noise, which raised discomfort during testing.
Generally such systems could replace the current personal air outlets (PAOs), which are integrated in the hatrack) installations; however implementation for procurement will be a challenge with another supplier structure (e.g. seat manufacturer instead of airframer). For the demonstrated prototype standard parts were used. For a potential serial solution for all non-metallic parts flammability requirements according to CS §25.853 have to be met. For the design of the electrical components of the system specific requirements of the aircraft and requirements according the electrical seat actuation systems specification have to be taken into account.
ISPACE recommendation:
Testing has shown that seat integrated ventilation inlets can improve passenger comfort if draught issues are considered carefully. Especially for nozzles there is a risk of perception of draught and drying out. However, nozzles are fast and effective compared to larger inlets of side displacement - but they introduce additional sources of noise, which must be avoided. Generally such personal ventilation systems are imaginable as replacement of current PAOs.
In terms of design, integrating such concepts into a seat challenges space and maintenance issues. Certification aspects could be met as standard parts can be used; of course flammability requirements and electrical seat actuation systems specifications have to be fulfilled.
1.3.3.3 Local humidification
The tested humidifier was cylindrical membrane humidifier for B/c seats and in a similar design for F/c seats. For humidifying the air stream in the centre of the cylinder was divided from the water reservoir via a membrane. This avoids droplets in the airstream and thus contamination. Over piping and a fan the humidified air was transported to the passenger. The complete system could be integrated at seat level, power consumption and system complexity could be reduced significantly. A water tank of three litres at each seat supplies the humidifier with water for around seven hours flight time.
Humidification up to 15 degrees of Celsius dew point could be achieved with the current system over long durations. During testing the humidifier had problems with water leakage, so major design improvements will be necessary and considerable certification costs have to be expected. Besides no fouling was visible after testing at the membrane, which proved to be an effective technology for which even better humidification performance can be achieved with an optimised air flow within the system. During turn around additional maintenance time is necessary to refill the water tanks at each seat.
Up to now the used system is only a functional prototype. No certification aspects (flammability, electrical characteristics) are considered yet. For further design steps this has to be done beside the major operational concerns.
ISPACE recommendation:
Testing has shown that local humidification technology has potential to improve passenger comfort if systems succeed to deliver humidified air directly to the passengers' facial area without draught. The current design is not yet mature enough to achieve this and needs further development. Additional maintenance during turnaround time for refilling the water tanks at each seat is a high effort. Stakeholders within the project confirmed the generally high demand for humidification, especially in (almost) closed spaces (such as suites). However up to now technologies are too slow or effects are not noticeable enough for the short term satisfaction of passengers. In terms of design, for integrating this concept into a seat several operational and maintenance issues have to be solved, in particular risk of leakage has to be minimised.
1.3.3.4 Personal high-efficiency particulate air filters (HEPAs) for individual seats
The personal HEPAs are designed to remove particulate contamination, including bacteria and viruses from the cabin air supply. This will improve the air quality for the individual passenger.
The personal HEPAs require a small fan supply and have no moving parts. The cost and weight impact of installing this device is extremely small in comparison to other aircraft systems.
The ISPACE project has tested the equipment on the ground, in the Fraunhofer FTF. The next phase of development is to find an airline to carry out an in-flight service trial. This will determine the life of the filter in the actual aircraft environment.
ISPACE recommendation:
With the personal HEPA the ISPACE project adopted and applied a technology which can help to protect passengers and crew from the spread of infectious diseases.
In-flight service trials are to be planned to establish the life of the filter.
For any aerospace equipment, stringent testing is carried out. In order to certify the technology for aircraft installation, further performance and environmental testing is required.
1.3.3.5 PCRA system for cabin system
The PCRA system uses a unique combination of adsorption and photocatalytic oxidation to remove gaseous contamination from the cabin air supply, e.g. odours and volatile organic compounds. This improves the air quality in the main cabin for both passengers and crew.
The PCRA device has low power consumption and no moving parts. The cost and weight impact of installing this device is small in comparison to other aircraft systems. The current PCRA prototype unit is restricted to relatively low flow rates and is likely to require a further process of scaling up in size to be fully effective in the environmental control system (ECS) system. The final choice of adsorbent rotor is still yet to be determined.
The ISPACE project has tested the equipment on the ground, in the Fraunhofer FTF. The next phase of development is to find an airline to carry out an in-flight service trial. This will determine the life of the components and the effectiveness of the solution in the actual aircraft environment.
ISPACE recommendation:
With the PCRA system the ISPACE project developed and tested a new filtration system for VOC odour removal which can help to provide a safe, healthy and comfortable cabin and cockpit environment.
Further test programs to establish the full performance of the PCRA are to be planned to investigate in more detail regeneration strategies, including various lighting sources, and a more extensive range of VOCs.
For any aerospace equipment, stringent testing is carried out. In order to certify the technology for aircraft installation, further performance and environmental testing is required.
1.3.3.6 Focus of future technology development and design
The following operational aspects have to be taken into account for further industrialisation of the components:
Accessibility: For each component access descriptions have to be prepared for the customers and integrators. Mainly for the humidification system, the required water servicing for the humidifier, to be completed during transit, has to be considered in regard to the accessibility to the corresponding interface.
Maintainability: For the ventilation and humidification systems scheduled actions are expected for filters and water servicing. To calculate the scheduled maintenance intervals procedures have to be prepared for customers and integrators.
Servicing: Water servicing for humidifiers is required at each seat where the system is installed and is to be performed during transit time. Since this type of action is not part of today's standard operation, the implementation of additional procedures, tools / equipment, etc. will be required. The impact should be minimised by a service friendly design and servicing instruction should be available for the customer.
Overall aircraft aspects: Especially the humidifier system may have an impact to the air-conditioning and associated cabin regulation. Additional water may accumulate in the cabin. Dedicated investigations, in terms of measurements and simulations, should be performed for further industrialisation.
Human factors: Special attention shall be paid in defining the servicing action to minimise errors which could impact cabin elements serviceability / availability. With regard to leakage risks, sufficient precautions need to be installed.
ISPACE recommendation:
Testing has shown that innovative systems for personal aircraft cabin environment can improve passenger comfort substantially under a range of temperature conditions.
For future technology development and design several operational aspects have to be taken into account, such as accessibility, maintainability, servicing, overall aircraft aspects as well as human factors.
1.3.4 CFD simulation of individualised cabin environment
This section is a summary of knowhow and recommendations for individual cabin climate CFD simulations.
1.3.4.1 Geometry preparation
Different regions were identified based upon their boundary conditions. A list of boundary conditions used in simulation includes:
- Walls: floor, side wall lining, window, ceiling panel, overhead bins, lights, seat surface, passenger surface.
- Inlets: lateral and ceiling air inlet, individual air inlets.
- Outlets: cabin air outlet.
Whenever a variable prescribed on the corresponding surface varied on this surface, the surface was subdivided into several regions to form appropriate boundary conditions. The thermal manikins were subdivided into distinct regions according to the clothing level and heat output (feet, legs, torso, arms, hands, head, etc.). The subdivision of the surfaces should be done after processing of experimental data.
Another issue of great importance were the simplifications made on the input computer-aided design (CAD) model in order to reduce the level of detail of the real model. Inlets and outlets were approximated by generic shapes. Although the discharge characteristics of air inlets can have an effect on global flow patterns, it was expected that the general directional characteristics including volumetric flow and temperature can provide the required accuracy for the aims of the detailed CFD simulations. Unnecessary details of the seats geometry and the body of the thermal manikins were removed in order to simplify the computational mesh.
ISPACE recommendation:
The reduction of the level of detail of the CAD model is very important for the geometry of the CFD model but the simplifications should not influence the accuracy of the simulation significantly. The subdivision of the surfaces into boundary conditions should respect the division of the real cabin and should be made after the processing of experimental data to describe real boundary conditions in sufficient level of detail.
1.3.4.2 Data for boundary conditions
The data from measurements of the real aircraft cabin environment are necessary for an appropriate setup of the simulation, because CFD simulation requires a precise description of the boundary conditions in order to get accurate results. The data from measurements are also required for consequent validation and comparison of CFD model results. The data from tests were analysed to obtain two groups of the data. The first group represents all data used as boundary conditions of the CFD model and the second one represents data which characterizes the cabin environment and heat transfer in the cabin. After post processing of the test data, the first group of the data was used as boundary conditions for CFD simulations. The results were then compared with data of the second group to validate the model predictions.
The first group (main boundary conditions for CFD cabin model) includes: surface temperature of the walls (lining, floor, overhead bins and ceiling); air temperature, air speed, air pressure and relative humidity at the main ECS inlets (ceiling inlets and lateral inlets).
The second group used for validation consists of: data measured on probes located in the cabin interior (temperature and relative humidity near seats), outlet air temperature. During the processing of the data, the problem of instability of the conditions during test day occurred for some test cases. Significant changes of air temperature on main ECS inlets were the typical attribute of these cases. It is more likely to obtain accurate results and predictions from CFD on stable rather than on unstable conditions, thus data sets for validation must be selected carefully. This is caused by the fact that the effect of the change of inlet temperature has some delay in impact on the cabin environment and this change can affect also the consequent position on unstable day. The flow pattern can be also affected by the changing of inlet temperature. Furthermore the impact of these changes on the perception of environment by test persons during tests is unknown and subsequent influence on thermal comfort and answers in questionnaires should be subject of further work to evaluate fluctuating cabin climate conditions.
ISPACE recommendation:
The precise processing of the experimental data is crucial for the accuracy of the CFD simulation. The stability of the data in time should be observed very carefully. The impact of instationary and fluctuating cabin climate conditions on passengers perception should be investigated in more depth.
1.3.4.3 Physical models for cabin environment simulations
Cabin environment and ventilation flows are complex in nature due to the diversity of physical phenomena involved. Complexity is increased by the presence of people acting as sources of heat and humidity. For simulation purposes, a careful selection of models and assumptions is therefore fundamental to achieve a practical solution with reasonable accuracy and reduced time.
Flow assumptions - the following assumptions were made:
- Heat conduction through seats and other solid components was ignored. The heat loads and temperature values at walls were provided and used instead.
- Buoyancy and radiation within the cabin were taken into account. The P1 radiation model included in ICON FOAMpro was used for the detailed simulations. A surface-to-surface (S2S) radiation model included in STAR-CCM+ was used.
- Solar radiation effects were ignored. In terms of assumed ambient conditions this compares with a night flight scenario.
- The flow is assumed turbulent.
Flow characterisation - the air flow in the cabin was characterised as follows:
- Nature of flow: fluid = air; type of fluid = compressible; fluid regime = buoyant turbulent; type of flow: three-dimensional and confined.
- turbulence models: The equations for k and e correspond to the k-e SST turbulence model.
- Gravity: The effects of gravity were considered in order to account for buoyancy with the gravity acceleration of (0x, 0y, -9.81z) (m/s2). The reference density was calculated based on the ideal gas equation, reference pressure and reference temperature were obtained from testing for each case using the specific gas constant = 287 J / kg K.
Thermal models and thermophysical properties:
The energy equation was activated in order to model convective heat transfer within the cabin. Heat loads due to occupants and outer walls, as well as additional heat sources like lights and other minor power sources were included in this model. Heat transfer due to thermal radiation was also considered and modelled using the P1 model available in ICON FOAMpro and the S2S model available in STAR-CCM+. Modelling radiation is fundamental for comfort related problems. Simple CFD test cases organised in the past, and validated against experimental data (e.g. heated cylinder in a room), have suggested that radiation may account for as much as 30% of the total heat transfer in a cabin. The values of thermal conductivity (k) and heat capacity (cp) were left constant. The molecular viscosity was estimated using Sutherland's equation and was set to constant value of 1.85508E-5 Pa.s.
Solution procedure and convergence
The solution procedure employed for the steady state solution was SIMPLE, with a second order discretisation. The corresponding control parameters for this procedure are listed below:
- Velocity: under-relaxation factor: 0.5
- Pressure: under-relaxation factor: 0.2
- Energy: under-relaxation factor: 0.5
- Turbulent energy: under-relaxation factor: 0.7
- Turbulent viscosity: under-relaxation factor: 0.7
- Levels for convergence for most cases reaches values below 110-4.
Specific and relative humidity model
Humidity was modelled utilising the passive scalar approach. This means that effects like gravity force causing the stratification are neglected. The passive scalar of humidity represented specific humidity Sh (g / kg dryair). In the simulated cabin two main sources of humidity were taken into account - humidity which is brought in by air supplied from the main and individual inlets (Shtech) and humidity generated by passengers (Shpass).
The source or humidity from passengers was defined in front of the face of each manikin which represents real person and the value was 7.86 (g1s-1m-3) in sphere of 10 cm diameter. The value of Sh on main ECS inlets and individual seat inlets was calculated based on equation (2). The input values were tair - air temperature, pair - air pressure and RH - relative humidity of air. Achieved accuracy compared to tests
- Air temperature at seat probes: typical value of the absolute error below 1 degrees of Celsius, average error 0.86 degrees of Celsius
- Air temperatures at outlets: results in close agreement with test data, small deviations up to 1.5 degrees of Celsius
- Relative humidity of air: the discrepancies in most cases up to 4 % abs., transient simulations show better agreement, however they are computationally expensive.
- Both codes - STAR CCM+ and ICON FOAMpro - work properly and give almost identical results.
ISPACE recommendation:
Using appropriate boundary conditions and physical models both simulation codes - STAR CCM+ and ICON FOAMpro - work properly and give almost identical results.
Temperatures can be predicted well, the approach of specific humidity for steady state conditions leads to discrepancies with measurements in most cases up to 4 % abs. transient simulations show better agreement, however they are computationally expensive.
Generally the simulation tools are able to reliably predict cabin environment and comfort and may be used as a design tool even for very complex situations to save development time and resources.
1.3.4.4 Thermal comfort prediction based on equivalent temperature
The thermal comfort evaluation was based on the comfort zones diagram method using the equivalent temperature approach (see also ISO 14505-2). This model evaluates thermal comfort on eighteen separated parts of a human body and also overall thermal comfort which is calculated as weighted average where the weight of each part is the surface area of the part. Values of overall comfort for each manikin were extracted and compared with thermal comfort assessed during the subject test campaign in the Fraunhofer FTF. Results from the simulations for a medium cabin temperature situation show the same trend as the results from the subject survey, however MTV on all seats is shifted to colder votes. The main problem in the thermal prediction discrepancy was identified in the values of clothing insulation used for simulations. The values were adopted from ISO 14505-2 but the clothing of real test subjects during tests in FTF was evaluated differently. Therefore the typical dress for a passenger was defined and the thermal resistance was measured using thermal manikin NEWTON. Then the simulations were repeated with the adopted values of clothing insulation under boundary conditions of virtual manikins. The discrepancies are much lower and the prediction on most seats is in close agreement with measured values.
ISPACE recommendation:
The prediction of thermal comfort base on concept of equivalent temperature and the associated comfort zones diagram is a suitable tool for prediction of thermal comfort in aircraft cabins.
An important parameter in simulation is the correct value of clothing insulation, which is applied as boundary conditions on surfaces of virtual manikins in CFD simulation. The simulations under-predict thermal comfort at all seats when the virtual manikins were dressed based on ISO 14505 (summer clothing), after calibration with more realistic clothing the results are in very good agreement.
1.3.4.5 Steady vs. transient simulations
Cabin flow simulations should be conducted as transient. However, due to the time restrictions and the large number of simulations for parametric studies, simulations were mainly performed as steady-state. One case was also run transient in order to provide a rough indication of the average values compared against monitored values.
Although the transient simulation was relatively short, the improvement of relative humidity prediction is evident from results. The flow in the cabin is time dependent and oscillates with a certain frequency. It is evident from the results that certain transient effects may exist in the flow field. This brings a degree of error which appears to be relatively large for the humidity profiles in the cabin. Although all other residuals (U, T, p) gradually reduced, humidity would not converge easily, which is considered to be an indication of transient effects.
ISPACE recommendation:
Cabin environment simulation should be performed as transient simulation due to the fact that cabin flow is transient and main flow oscillations have a direct impact on precision of cabin environment and human thermal comfort prediction.
For transient simulations of complex geometries as an aircraft cabin the main problems are still the computational effort and time as well as the enormous amount of the data generated by CFD solvers.
Potential impact:
ISPACE investigated unique concepts and technologies to reach a step-change in personalised passenger climate control. The overall objective of ISPACE was to provide aircraft manufacturers and the supplier industry with know-how and innovations to address the individualisation of passenger cabin environment. This ultimately provides a step-change in passenger comfort during flight. The general approach of ISPACE is that concepts were worked out and analysed, prototypes were tested and in addition a CFD pre-study was realised which could be validated after testing.
In the end three integrated systems can be noted: seat heating / ventilation, humidification and air purification.
Individualisation of climate at seat level in the aircraft cabin has a socio-economic impact; it leads to higher comfort during flight. The environmental cabin system (ECS) does not need to be separated in several temperature zones if an individual adjustment of temperature and airflow at seat level is possible. Passengers travel one a higher comfort and satisfaction level. Business travellers get to the meeting at their destination perfectly relaxed and are not stressed due to uncomfortable flight conditions. Passengers who are flying on holidays can experience their first step of holiday in the airplane. Airliners with an individualised cabin environment have a better initial point to attract potential customers. It can be conceivable that travellers accept a higher price for more comfort on their flight.
For demonstration of climate individualisation a published link on YouTube in the internet shows how this benefit of comfort can look like: http://www.youtube.com/watch?v=9TH6XcEYp7s&sns=em
Simulation of individualised ventilation in a global cabin environment was a big issue within the ISPACE project. A commercially licensed CFD tool (STAR-CCM+), a developed open source solver (ICON FOAMpro) and meshing tools were compared and proved. This offers customers a cost-effective customisable solution to fulfil their CFD simulation requirements and engineering consultancy with open source based software.
For dissemination of ISPACE project stakeholders were involved from the beginning of project. A questionnaire survey figured out which problems are occurring in the aircraft cabin. Although the feedbacks from the questionnaire were very different it showed that an individual environmental control system would be a good extension to the existing seat equipment for the upper class segment.
In detail, the feedback from the airlines showed, that the individual temperature control and humidification would be the most wanted improvement. The individual ventilation would be the second priority. In addition, there are also many complaints by the passengers which are not related to the climate environment.
At the moment the complaints from the passengers are not always to be resolved with the existing technology and the airlines performed some workarounds to satisfy the passengers. All improvements are mostly expected for high-priced seats (F/c-seats).
One important boundary condition is that the additional equipment must fit into the existing space for B/c- and F/c-seats as there is no further room available inside the aircraft without losing any seat.
One year after the questionnaire interested stakeholders were invited to a project consortium meeting to involve their views and opinions in the final testing of the developed personalised heating, humidification and ventilation systems. After the subject testing a stakeholder test flight was realised. It gave the stakeholders an impression on the developments and the test conditions. An adjacent discussion discovered important aspects. With regard to the installed improved environmental control equipment the seat heating including ventilation was rated as the most beneficial feature. The humidification was rated as 'not existing'. In the feedback round it was discussed, if a longer test period might be necessary to realise any effect from the humidification system. However, the airlines stakeholders mentioned the critical maintenance and operational aspects of this system. For further dissemination the investigated prototypes were exhibited at the Berlin AirShow ILA, September 2012. Several presentations and / or papers at AeroDays 2011, IndoorAir Conference 2011, ICEE2011, NAFEMS2011, EFM2012 and IATA Aviation Health conference 2012 spread the information about ISPACE project. With the ISPACE webpage www.ISPACE-project.eu interested people could get a general overview of the project structure and objectives.
In the end of ISPACE project the results were disseminated to stakeholders from the industry at a final stakeholders club meeting. It took place in October 2012 in Holzkirchen, Germany. For this symposium also Prof. Peter Vink from the TNO were invited as external speaker as a well-known specialist in the field of aircraft interior comfort. After his introduction the ISPACE consortium presented the main topics of ISPACE project.
List of websites: http://www.ispace-project.eu
ISPACE investigated unique concepts and technologies to reach a step-change in personalised passenger climate control. The overall objective of ISPACE was to provide aircraft manufacturers and the supplier industry with know-how and innovations to address the individualisation of passenger cabin environment. This ultimately provides a step-change in passenger comfort during flight.
The first steps achieved within ISPACE were to define the specific requirements and boundary conditions for individualisation of passenger cabin environment and comfort within aircraft cabins. Parameters and aspects which were considered and defined are environmental parameters (such as air temperature, surface temperatures, air humidity, airflow, air quality), human related aspects (e.g. perception of comfort, human physiology, well-being, ergonomics) and technical requirements (such as mass, volume, weight, safety, energy consumption, lifetime, maintenance). Based on these first steps, ISPACE developed concepts for individualisation of passenger cabin environment and comfort within aircraft cabins. The different concepts were evaluated against the requirements identified. For the most applicable concepts possible technology solutions were determined. Subsequently, detailed feasibility studies were carried out by taking evaluation criteria into consideration. Simulative parameter studies were carried out for selected technologies to achieve a preliminary qualitative basis for the judgement of feasibility and to reduce parameter variation for further integration in real scale of these technologies.
Within the second period of the ISPACE project an experimental proof of individualisation of cabin climate and comfort was performed. Experiments were carried out with 42 subjects on ground in a most realistic flight test environment (Flight Test Facility (FTF) at Fraunhofer IBP). Based on the results of the feasibility study a detailed test design was developed to achieve this experimental proof. Selected technologies were tested with the focus on passengers' well-being and their comfort increase due to individualised cabin environment. Dedicated environmental parameters were generated locally at the subjects' seat level to provide maximum flexibility for testing. The goal was to find out by environmental measurements and subject questionnaires which control parameters are the critical ones and how well the cabin climate can be individualised for a single passenger at seat level. In addition, the limiting factors for individualisation (e.g. geometrical, physical) were determined. Parallel with testing a computational fluid dynamic (CFD) simulation of the individual environment was validated with STAR-CCM+ and ICON FOAMpro. Testing showed that individualisation of personal environment lead to higher well-being and comfort level. Fully equipped seats with different personalised ventilation systems achieved the highest satisfaction. Additional seats equipped with seat heating/ventilation mats had a high comfort level.
Within the third period of the ISPACE project the investigated prototypes (individualised seats, humidifier, PCRA filter system and seat heating / ventilation) were exhibited at the Berlin AirShow ILA 2012 which resulted in high interest of the press and visitors. Detailed results were presented and discussed during the Final Stakeholders' Club Meeting (24 October 2012). Stakeholders from diverse aircraft industry branches, ranging from suppliers to airliners, attended the meeting. Besides the presentation of ISPACE and its results they got the possibility to experience the ISPACE prototypes and the testing environment of the FTF. A lively and fruitful discussion on further exploitation possibilities concluded this event and the ISPACE project.
Project context and objectives:
The scientific and technological objectives of ISPACE were the following:
(1) the development of concepts for individualisation of passenger cabin environment and the general prove of feasibility;
(2) the development of technologies for individualisation of passenger cabin environment and proof with subject testing;
(3) the provision of simulation tools for individualised cabin environment and the recommendations for existing and future commercial aircraft.
The project ISPACE was divided in six work packages (WPs). In the following the WPs and their work task (WT) described in detail with respect to objectives of ISPACE project.
Within WP1 'State-of-art of science and technology and their requirements' the objective was the construction of a systematically arranged collection of requirements, prepared on the basis of cross-section of influential factors related to the system: human, space / room, climate, structure / envelope, installations.
The WP was divided into four subtasks:
Within WT1.1 'Existing knowledge and expertise' knowledge and partners' information was collected and compiled as a sound basis for development, testing and final evaluation of the developed technologies.
The output of WT1.2 'Existing technologies and their principles' provided a summary of existing technologies for personalised climate control, their principles and applications with respect to aircraft application.
In WT1.3 'Requirements for individualised cabin environment' information on the requirements for an individualised cabin environment, comprising both general requirements for human comfort and well-being as well as requirements specific for the aircraft environment and the integration of technologies were provided.
In WT1.4 'Requirements and boundary conditions for simulation' knowledge and partners information towards a virtualisation of the problem was collected and compiled as a sound basis for the CFD model which was generated in the parametric study of WP2. WP1 served as a source of target information for the study of possible intervention measures which were treated first of all in the framework of WP2 and the feasibility studies on individualisation of passenger cabin climate.
WP2 'Concept development, selection and test design' had one main objective: to select step change technologies to be developed and their concepts of integration for WP3, which were tested and evaluated in WP4. In WT2.1 'Feasibility' the feasible integration of personal climate control systems into aircraft cabin environments was assessed.
In WT2.2 'Qualitative simulation and parameter study' the parametric study was performed to study the effect of personalised inlets in a first class (F/c) seat using CFD. For the computational study four F/c seats in a row located in a section of an exemplary A380 lining were used. The aim of the study was to find suitable positions of the personalised inlet in terms of fresh air delivery, efficiency of humidity local delivery to the passenger and at the same time maintain thermal comfort.
In WT2.3 'Selection of Concepts' performance and acceptability of the concepts, systems and technologies were assessed. For that purpose, many criteria were evaluated and considered. Generally, systems for personalised air conditioning are more complex systems, which cost more, use more space and have a higher mass than current or no such systems. However, it is expected to achieve higher customer satisfaction and comfort with these systems.
In WT2.4 'Test design' a test design was developed to prove the individualisation of passenger cabin climate in a highly realistic flight environment, focusing on the selected innovative technologies. The test design takes into account physical and chemical measurements, as well as human response parameters of psychological and to some extend physiological measurements.
In WP3 'Technology development and integration' two main objectives were realised:
(a) to develop technologies for the local generation and the control of air temperature, surface temperature, air humidity, air quality, airflow etc. ;
(b) to integrate these technologies into a most realistic test environment - separately as well as in combination.
These objectives were gathered within three work tasks. WT3.1 'Individual temperature zone' considered heating / cooling devices and concepts for distribution of air at seat level. Seat heating elements for backrest, seat cushion, leg rest and foot rest were prepared. Within WT3.2 'Personalised ventilation' a humidification system was developed and a filtration system based on the photocatalytically regenerated adsorber principle. Different concepts for ventilation in / outlets were tested and analysed. The developed technologies were integrated in WT3.3 'Integrated technologies' into first and business class (B/c) seats and installed in a most realistic flight test environment (FTF FTF at Fraunhofer IBP). The main objective of WP4 'Testing, analysis and evaluation of technological concepts' was to prove whether the local climate in an aircraft cabin can be individualised for each single passenger by the technologies developed and integrated in WP3. Within the following four work tasks this could be realised.
In WT4.1 'Detailed simulation of individualised cabin environment' the boundary conditions were finalised for the CFD simulations to match the actual boundary conditions of the seats in the FTF geometry based on the parametric study results and previous studies. The impact of seat integrated local ventilation arrangements was analysed in the context of cold, normal and hot climate environmental conditions.
In WT4.2 'Testing of technologies for individualised cabin environment' system and subject testing was achieved. During system testing the performance of all single in-/outlets was tested and measured. A subject test campaign was performed with 42 subjects under different thermal conditions using different setups of B/c and F/c seats with individualised systems developed in WP3.
In WT4.3 'Analysis of test data' the data of questionnaire ratings and physiological parameters from subject testing and physical measurement data were analysed. The data of the questionnaire ratings and physiological parameters revealed that subjects' well-being and comfort was differently perceived across seats and was also affected by ambient temperature and differed systematically between aisle and window seats.
In WT4.4 'Validation of simulation of individualised cabin environment' the results obtained from detailed simulation in WT4.1 were compared with results obtained during testing in WT4.2.
In WT4.5 'Evaluation of technologies for individualised cabin environment' certification aspects were considered as well as the performance of technology developments during testing and with simulation. The developed technologies were checked for applicability and if they are suited for integration as stand-alone or combined technologies with respect to their impact on passengers' health, well-being and comfort.
The objectives of WP5 'Dissemination and exploitation' were:
(a) to involve stakeholders views in the whole project to streamline technology development and to ensure applicableness of the new concepts;
(b) to guarantee consideration of intellectual property rights throughout the whole project;
(c) to generate an overview of the work accomplished in WT4.5 to emphasise the critical evaluations of the technologies studied in this project for individual passenger climate control. This permits to identify technologies for industrialisation and the key factors to account for industrialisation of these systems;
(d) to draw, from critical evaluations of the WP3 and WP4 results, some recommendations for both future aircraft and the current fleet;
(e) to disseminate these results and conclusions by both publications and demonstration within the consortium and to the outside world, especially to other European organisations working on commercial and business aviation.
WT5.1 'Stakeholders club' included a web-based questionnaire to gather opinions of stakeholders. Stakeholders were informed regularly about the status of ISPACE with newsletters. Stakeholders were invited to a project consortium meeting (September 2011) and took part at a test flight for individualised cabin environment at FTF (November 2011). In October 2012 a final stakeholder club meeting was achieved.
In WT5.2 'Exploitation and protection of results' arose intellectual property rights were considered, patents were reviewed and summarised and exploitation strategies were worked out. CFD tools FOAMpro and STAR-CCM+ were used. ISPACE prototypes were exhibited at the Berlin AirShow ILA in September 2012.
In WT5.3 'Publications and recommendations' several publications were achieved including press releases as well as scientific conference papers and posters.
In WP6 'Management' Fraunhofer IBP as the coordinator successfully set out the management strategy and achieved the proper coordination of the project.
Project results:
Four different personalised ventilation systems were tested with subject testing in the FTF at Fraunhofer IBP. The tested systems are:
(1) ventilation side;
(2) humidification;
(3) heating / ventilation mat;
(4) ventilation front.
These four systems were tested as single components at B/c seats. Additionally all four systems were combined in one B/c and one F/c seat. One B/c and one F/c seat had no personalised ventilation systems and were used as control seats.
Each subject tested each type of seat during one day of flight for at least 20 minutes and evaluated it with a questionnaire. This was repeated at three different temperature conditions of the cabin:
- low temperature (~19.5 degrees of Celsius),
- middle temperature (~23.5 degrees of Celsius),
- high temperature (~27.5 degrees of Celsius).
Each setting was achieved for one day of testing. All subjects participated on three sequent days. Other environmental parameters remained constant for all three temperature conditions:
- Relative humidity: 10 %
- Noise: 74 dB(A)
- Pressure: 7000 ft equivalent height
1.3.1 Analysis of Test Data
In general big differences for the overall temperature ratings can be seen depending on the temperature conditions, but the differences are relatively small for the 1A seat, also for the fully climatised (7F, 7G) and for the ventilated seats (4F, 4G). There are very big differences in the control conditions, so this gives a very clear picture that the climatisation of 1A, 3, and 7 is working, although there is no significant difference between the warm and the normal condition. There are very big differences at the seat 8, for the ventilation front, for both seats (window and aisle), but much more for the aisle seat.
The experienced temperature at feet level is generally perceived somewhat cooler than at the other levels, and shows a comparable pattern with less differences across seats than at the other levels, and most pronounced for the cool condition.
In particular for the cold condition overall draught was perceived as too much, although the difference to zero is not that big in general. However, in the ventilation conditions from the front, there are pronounced effects and relatively strong 'too much' in the cold condition. The ratings are very close to zero, meaning 'good', for the seats 4F and 4G.
Highest comfort ratings independent of temperature - were reported for seat 1A. Compared to the control seat 2A, there are general rather bad conditions. For the blue condition (cool) the window seat 7F had the highest comfort rating.
The main effect averaged over the temperature conditions shows clearly that the most comfortable ones are the seats 1A and 7F as well as 4G. The control seats are worse. To some extent the aisle seats 5G with ventilation side and seat 8G with ventilation front are somewhat bad wrt. sitting comfort.
Ratings on comfort are very close to the ratings of overall temperature, but there are not so much differences between the normal and the warm condition. This may be because there were some problems to reach all the planned ambient temperatures, there may be other reasons, but it is very clear: the more negative, the more uncomfortable, in particular for the cool temperature and it is more uncomfortable in the control than in the climatised seats.
1A reports were on the uncomfortable side for seats 8G/F for the cool condition. The analysis of the number of symptoms revealed a clear effect of temperature. For the cold conditions there are more symptoms in general and no differences for temperature at seat 1A, but in the control condition 2A.
For reports of relaxation no effect of seat (with the exception of seat 8G) was found for the normal temperature. Lowest values were found in the cold conditions and, in addition there is always less relaxation on the aisle side than on the window side. Highest values were reported for the seats 1A and 7F.
Additionally a photocatalytic regenerable adsorption (PCRA) cabin air cleaning device was integrated in the global cabin ventilation system and was tested at the end of each test day. Compounds were injected into the cabin supply air for a period of 15 min reaching the cabin by the personal air outlets (PAOs) above the passengers. Test compounds used were ethanol, hexanal, butyl acetate und Limonene. The subjects evaluated with questionnaires if they could smell anything. Additionally it was measured if the compounds reached the cabin. A proper functionality with the mentioned compounds could be proven. The answers of the subjects differed a lot.
Based on testing and CFD simulation ISPACE gives recommendations on the use of systems for personalised aircraft cabin environment for existing aircraft and solutions for future aircraft. Designing future aircraft, planning of modernisation of the current fleet as well as assessing the status quo need reliable and validated simulation tools for the complex phenomena of individualised cabin environment. These tools are continuously developed and improved and were validated with test data. Technical workshops and stakeholder meetings gathered external experts to provide an additional overview of the workflow and progress of ISPACE.
In the following the recommendations of ISPACE are listed considering the topics 'Concepts for individualised cabin environment', 'Technologies for individualised cabin environment' and 'CFD simulation of individualised cabin environment'. Recommendations are accentuated in bold in a separated box at the end of each subtitle.
1.3.2 Concepts for individualised cabin environment
1.3.2.1 Concept evaluation based on thermal cabin environment simulation
Parametric studies of the thermal cabin environment were performed using CFD simulations in order to evaluate different concepts of individualised cabin environment. In some simulated cases it was challenging to evaluate impact of a specific technology on thermal comfort and local seat environment because the selected combination of the setup could lead to situations when one technology influences others, e.g. seat heating compensates convective cooling by nozzles. Also the cooling effect of ventilated seat mats, which can be controlled by the passenger on demand, could benefit from technology combination especially in high cabin temperature conditions. On the other hand humidified air from personal inlets is in this case not necessarily fed into the passenger's convective plume and thus does not reach the passenger breathing zone what is a disadvantage of such a setup of combined technologies. Side displacement outlets may counteract this as they deliver air in a manner which is supporting the convective plume. In the parametric study a combination of nozzle and side displacement inlets with a seat heating and ventilation mat turned out to achieve best results with respect to thermal comfort assessment based on equivalent temperature and age of air.
This case combines two personal inlets - a nozzle and seat displacement inlets together with the suction of air through a seat ventilation mat. This configuration brings the most efficient fresh air delivery to the passenger. While the side nozzle delivers the air towards the face of the passenger, the displacement inlets help to create enclosed microclimate which is not disrupted significantly by the main ventilation air pattern. For both positions, window and aisle seat, the thermal comfort assessment of virtual manikins show similar profiles.
The release of humidified air must be chosen very thoughtfully, otherwise the humidity will be released to the environment without any effect on the passengers breathing and comfort conditions. This is in particular relevant for provision of humidity through distant nozzles which would need to provide an air jet with high velocity to reach the facial region, and thus would cause a convective drying out rather than an effect of humidification. As shown in the subsequent sections the results of testing yield similar conclusions as the simulative evaluation of the concepts based on the equivalent temperature assessment method: the fully equipped seats (combined technologies) show high thermal comfort values as well as seats with a heating and ventilation mat.
ISPACE recommendation:
In terms of thermal comfort personal ventilation inlets in the form of seat integrated side displacement inlets appeared to be most effective in combination with a seat heating and ventilation mat and eventual additional nozzles.
% Draught issues should be considered carefully for the design of nozzle inlets, however adverse effects may be counter-balanced by an overall better thermal environment. The release of humidified air must be chosen very thoughtfully, otherwise the humidity will be released to the environment without any effect on the passengers breathing and comfort conditions.
1.3.2.2 Impact on perception of thermal cabin environment, physiological load, well-being and comfort
Statistical analysis of passengers' perception of thermal cabin environment revealed that fully equipped F/c seats, fully equipped B/c seats and seats only equipped with seat heating and ventilation mat got the most positive ratings. A comparison of boxplots between the temperature and the seat heater settings of fully equipped F/c seats, fully equipped B/c and seats only equipped with seat heating and ventilation mat revealed that for the latter system medians are often higher than the ones of the other two systems, thus indicating that this system can contribute significantly to increase thermal comfort. Data analysis of the questionnaire ratings and physiological parameters showed that subjects' well-being and comfort was affected by ambient temperature and was perceived differently across seats, they differed systematically between aisle and window seats. Therefore the following ranking of seats is based on window seats only. Based on subjective experience of comfort and well-being the seats with the highest ranking were 1, 4 and 7 and based on physiological load, seats 3, 4 and 5 were highest in ranking. The ranking based on a combined score is:
- Seat 1: fully equipped, F/c
- Seat 4: heat and ventilation, B/c
- Seat 7: fully equipped, B/c
- Seat 5: ventilation side, B/c
- Seat 6: control seat, B/c
- Seat 3: humidification, B/c
- Seat 8: ventilation front, B/c
- Seat 2: control seat, F/c
Whereas between the first three seats no statistical differences were observed, for all three of them the statistical difference to the respective control seat was significant.
Based on the empirical investigation of the impact of individualised climate on well-being and physiological response of human subjects - considering a typical thermal condition in an airplane cabin as well as cool and warm cabin conditions - the results show that most of the technologies investigated (with the exception of ventilation from the front) have an advantage to the traditionally used systems which were integrated into the investigation as the control condition. That means that in particular full climate control in the F/c suite as well as in the B/c seat show the largest advantage to current systems.
However, all other investigated systems, i.e. heating and ventilation, humidification, ventilation from the side, with the exception of ventilation from the front, display a remarkable advantage to the traditional systems.
Moreover, not only well-being in cardiovascular response was affected in a positive way - in particular regarding the fully equipped seats as well as those with individual control of heating and ventilation - but also the investigation showed remarkable results on perceived comfort - whereas none of these results were found for seats with ventilation only from the side or only from the front.
Besides these clear advantages in perceived symptoms, well-being, and comfort, there are also some indications on adverse effects, in particular for the full individualised climate control seat, coming most presumably from additional noise. This seat configuration seems to have the highest potential for well-being and comfort; however a reduction of noise seems advisable.
The present investigation focussed on control of humidity, temperature, and ventilation via individually controllable systems implemented in seats. It turned out that such additional systems if combined most likely with spots of higher acoustical load in the cabin might become an issue of discomfort on a subjective and on a physiological level. Therefore it is recommended that noise reduction in general and also in relation with additional equipment should be a focus of future research.
ISPACE recommendation:
All investigated systems, i.e. heating and ventilation mat, humidification, ventilation from the side, with the exception of ventilation from the front, show a remarkable advantage wrt. well-being and physiological response of human subjects compared to the traditional systems, in particular seats with full climate control.
Thermal comfort was rated highest on fully equipped seats and seats only equipped with a heating and ventilation mat, which should be the first candidate for further development. Besides there are some indications on adverse effects coming most presumably from additional noise, thus noise reduction in general and also in relation with additional aggregates should be a focus of future research.
1.3.3 Technologies for individualised cabin environment
1.3.3.1 Seat heating and ventilation mat
An electrical heating element underneath the seat surface / cover heats up and transfers the heat through the seat cover to the surface. For ventilation ambient air is sucked through an air permeable cover and guided through an air distribution layer underneath the seat cover. With the air flow through the cover and the distribution layer to the outlet of the fan the humidity at the body contact area of the seat can be removed.
During testing this system showed to improve passengers' comfort most and its reaction time was effective to satisfy the subjects demand for thermal comfort. Such systems would be fairly easy to design into an aircraft seat, for both business and F/c applications. However this depends on energy consumption and energy management priority level in competition with other actuators at seat level. Therefor further benefits should be elaborated to achieve similar thermal comfort perception with less and transient energy demand.
Although the used system components are already certified for the car industry, there are specific certification requirements for the passenger aircraft industry. Applicable requirements relate to the materials of an aircraft seat. Especially the materials of the seat heating and ventilation mat need to be certificated. The main attention need to be paid to the flammability requirements for aircraft seats regarding CS/FAR §25.853.
ISPACE recommendation:
Testing has shown that seat heating and ventilation technology can improve passenger comfort substantially under a range of temperature conditions. Such systems yield an almost immediate effect to satisfy the passengers' demand.
Stakeholders within the project were most interested in the technology than any other concept, and saw potential in its use and series introduction.
In terms of design, integrating this concept into a seat should not be an issue. However to enable this, amounts of electrical certification work and some developmental flammability testing on appropriate seat heating and ventilation mat need to be done.
1.3.3.2 Seat integrated ventilation inlets
A piping for ventilation and heating at the side of the seat cushion was integrated into the seats. For additional personal ventilation an air inlet in the backrest of the front seat was installed. Both systems worked with directly recirculated air from the cabin.
The piping into the seat including a temperature control system turned out to be realistic for F/c suites only where piping and outlets can be better integrated and 'hidden' in the furniture. Draft is an issue especially for nozzle systems, where also the feeling of drying out must be avoided. Special attention should be paid to avoid any additional source of noise, which raised discomfort during testing.
Generally such systems could replace the current personal air outlets (PAOs), which are integrated in the hatrack) installations; however implementation for procurement will be a challenge with another supplier structure (e.g. seat manufacturer instead of airframer). For the demonstrated prototype standard parts were used. For a potential serial solution for all non-metallic parts flammability requirements according to CS §25.853 have to be met. For the design of the electrical components of the system specific requirements of the aircraft and requirements according the electrical seat actuation systems specification have to be taken into account.
ISPACE recommendation:
Testing has shown that seat integrated ventilation inlets can improve passenger comfort if draught issues are considered carefully. Especially for nozzles there is a risk of perception of draught and drying out. However, nozzles are fast and effective compared to larger inlets of side displacement - but they introduce additional sources of noise, which must be avoided. Generally such personal ventilation systems are imaginable as replacement of current PAOs.
In terms of design, integrating such concepts into a seat challenges space and maintenance issues. Certification aspects could be met as standard parts can be used; of course flammability requirements and electrical seat actuation systems specifications have to be fulfilled.
1.3.3.3 Local humidification
The tested humidifier was cylindrical membrane humidifier for B/c seats and in a similar design for F/c seats. For humidifying the air stream in the centre of the cylinder was divided from the water reservoir via a membrane. This avoids droplets in the airstream and thus contamination. Over piping and a fan the humidified air was transported to the passenger. The complete system could be integrated at seat level, power consumption and system complexity could be reduced significantly. A water tank of three litres at each seat supplies the humidifier with water for around seven hours flight time.
Humidification up to 15 degrees of Celsius dew point could be achieved with the current system over long durations. During testing the humidifier had problems with water leakage, so major design improvements will be necessary and considerable certification costs have to be expected. Besides no fouling was visible after testing at the membrane, which proved to be an effective technology for which even better humidification performance can be achieved with an optimised air flow within the system. During turn around additional maintenance time is necessary to refill the water tanks at each seat.
Up to now the used system is only a functional prototype. No certification aspects (flammability, electrical characteristics) are considered yet. For further design steps this has to be done beside the major operational concerns.
ISPACE recommendation:
Testing has shown that local humidification technology has potential to improve passenger comfort if systems succeed to deliver humidified air directly to the passengers' facial area without draught. The current design is not yet mature enough to achieve this and needs further development. Additional maintenance during turnaround time for refilling the water tanks at each seat is a high effort. Stakeholders within the project confirmed the generally high demand for humidification, especially in (almost) closed spaces (such as suites). However up to now technologies are too slow or effects are not noticeable enough for the short term satisfaction of passengers. In terms of design, for integrating this concept into a seat several operational and maintenance issues have to be solved, in particular risk of leakage has to be minimised.
1.3.3.4 Personal high-efficiency particulate air filters (HEPAs) for individual seats
The personal HEPAs are designed to remove particulate contamination, including bacteria and viruses from the cabin air supply. This will improve the air quality for the individual passenger.
The personal HEPAs require a small fan supply and have no moving parts. The cost and weight impact of installing this device is extremely small in comparison to other aircraft systems.
The ISPACE project has tested the equipment on the ground, in the Fraunhofer FTF. The next phase of development is to find an airline to carry out an in-flight service trial. This will determine the life of the filter in the actual aircraft environment.
ISPACE recommendation:
With the personal HEPA the ISPACE project adopted and applied a technology which can help to protect passengers and crew from the spread of infectious diseases.
In-flight service trials are to be planned to establish the life of the filter.
For any aerospace equipment, stringent testing is carried out. In order to certify the technology for aircraft installation, further performance and environmental testing is required.
1.3.3.5 PCRA system for cabin system
The PCRA system uses a unique combination of adsorption and photocatalytic oxidation to remove gaseous contamination from the cabin air supply, e.g. odours and volatile organic compounds. This improves the air quality in the main cabin for both passengers and crew.
The PCRA device has low power consumption and no moving parts. The cost and weight impact of installing this device is small in comparison to other aircraft systems. The current PCRA prototype unit is restricted to relatively low flow rates and is likely to require a further process of scaling up in size to be fully effective in the environmental control system (ECS) system. The final choice of adsorbent rotor is still yet to be determined.
The ISPACE project has tested the equipment on the ground, in the Fraunhofer FTF. The next phase of development is to find an airline to carry out an in-flight service trial. This will determine the life of the components and the effectiveness of the solution in the actual aircraft environment.
ISPACE recommendation:
With the PCRA system the ISPACE project developed and tested a new filtration system for VOC odour removal which can help to provide a safe, healthy and comfortable cabin and cockpit environment.
Further test programs to establish the full performance of the PCRA are to be planned to investigate in more detail regeneration strategies, including various lighting sources, and a more extensive range of VOCs.
For any aerospace equipment, stringent testing is carried out. In order to certify the technology for aircraft installation, further performance and environmental testing is required.
1.3.3.6 Focus of future technology development and design
The following operational aspects have to be taken into account for further industrialisation of the components:
Accessibility: For each component access descriptions have to be prepared for the customers and integrators. Mainly for the humidification system, the required water servicing for the humidifier, to be completed during transit, has to be considered in regard to the accessibility to the corresponding interface.
Maintainability: For the ventilation and humidification systems scheduled actions are expected for filters and water servicing. To calculate the scheduled maintenance intervals procedures have to be prepared for customers and integrators.
Servicing: Water servicing for humidifiers is required at each seat where the system is installed and is to be performed during transit time. Since this type of action is not part of today's standard operation, the implementation of additional procedures, tools / equipment, etc. will be required. The impact should be minimised by a service friendly design and servicing instruction should be available for the customer.
Overall aircraft aspects: Especially the humidifier system may have an impact to the air-conditioning and associated cabin regulation. Additional water may accumulate in the cabin. Dedicated investigations, in terms of measurements and simulations, should be performed for further industrialisation.
Human factors: Special attention shall be paid in defining the servicing action to minimise errors which could impact cabin elements serviceability / availability. With regard to leakage risks, sufficient precautions need to be installed.
ISPACE recommendation:
Testing has shown that innovative systems for personal aircraft cabin environment can improve passenger comfort substantially under a range of temperature conditions.
For future technology development and design several operational aspects have to be taken into account, such as accessibility, maintainability, servicing, overall aircraft aspects as well as human factors.
1.3.4 CFD simulation of individualised cabin environment
This section is a summary of knowhow and recommendations for individual cabin climate CFD simulations.
1.3.4.1 Geometry preparation
Different regions were identified based upon their boundary conditions. A list of boundary conditions used in simulation includes:
- Walls: floor, side wall lining, window, ceiling panel, overhead bins, lights, seat surface, passenger surface.
- Inlets: lateral and ceiling air inlet, individual air inlets.
- Outlets: cabin air outlet.
Whenever a variable prescribed on the corresponding surface varied on this surface, the surface was subdivided into several regions to form appropriate boundary conditions. The thermal manikins were subdivided into distinct regions according to the clothing level and heat output (feet, legs, torso, arms, hands, head, etc.). The subdivision of the surfaces should be done after processing of experimental data.
Another issue of great importance were the simplifications made on the input computer-aided design (CAD) model in order to reduce the level of detail of the real model. Inlets and outlets were approximated by generic shapes. Although the discharge characteristics of air inlets can have an effect on global flow patterns, it was expected that the general directional characteristics including volumetric flow and temperature can provide the required accuracy for the aims of the detailed CFD simulations. Unnecessary details of the seats geometry and the body of the thermal manikins were removed in order to simplify the computational mesh.
ISPACE recommendation:
The reduction of the level of detail of the CAD model is very important for the geometry of the CFD model but the simplifications should not influence the accuracy of the simulation significantly. The subdivision of the surfaces into boundary conditions should respect the division of the real cabin and should be made after the processing of experimental data to describe real boundary conditions in sufficient level of detail.
1.3.4.2 Data for boundary conditions
The data from measurements of the real aircraft cabin environment are necessary for an appropriate setup of the simulation, because CFD simulation requires a precise description of the boundary conditions in order to get accurate results. The data from measurements are also required for consequent validation and comparison of CFD model results. The data from tests were analysed to obtain two groups of the data. The first group represents all data used as boundary conditions of the CFD model and the second one represents data which characterizes the cabin environment and heat transfer in the cabin. After post processing of the test data, the first group of the data was used as boundary conditions for CFD simulations. The results were then compared with data of the second group to validate the model predictions.
The first group (main boundary conditions for CFD cabin model) includes: surface temperature of the walls (lining, floor, overhead bins and ceiling); air temperature, air speed, air pressure and relative humidity at the main ECS inlets (ceiling inlets and lateral inlets).
The second group used for validation consists of: data measured on probes located in the cabin interior (temperature and relative humidity near seats), outlet air temperature. During the processing of the data, the problem of instability of the conditions during test day occurred for some test cases. Significant changes of air temperature on main ECS inlets were the typical attribute of these cases. It is more likely to obtain accurate results and predictions from CFD on stable rather than on unstable conditions, thus data sets for validation must be selected carefully. This is caused by the fact that the effect of the change of inlet temperature has some delay in impact on the cabin environment and this change can affect also the consequent position on unstable day. The flow pattern can be also affected by the changing of inlet temperature. Furthermore the impact of these changes on the perception of environment by test persons during tests is unknown and subsequent influence on thermal comfort and answers in questionnaires should be subject of further work to evaluate fluctuating cabin climate conditions.
ISPACE recommendation:
The precise processing of the experimental data is crucial for the accuracy of the CFD simulation. The stability of the data in time should be observed very carefully. The impact of instationary and fluctuating cabin climate conditions on passengers perception should be investigated in more depth.
1.3.4.3 Physical models for cabin environment simulations
Cabin environment and ventilation flows are complex in nature due to the diversity of physical phenomena involved. Complexity is increased by the presence of people acting as sources of heat and humidity. For simulation purposes, a careful selection of models and assumptions is therefore fundamental to achieve a practical solution with reasonable accuracy and reduced time.
Flow assumptions - the following assumptions were made:
- Heat conduction through seats and other solid components was ignored. The heat loads and temperature values at walls were provided and used instead.
- Buoyancy and radiation within the cabin were taken into account. The P1 radiation model included in ICON FOAMpro was used for the detailed simulations. A surface-to-surface (S2S) radiation model included in STAR-CCM+ was used.
- Solar radiation effects were ignored. In terms of assumed ambient conditions this compares with a night flight scenario.
- The flow is assumed turbulent.
Flow characterisation - the air flow in the cabin was characterised as follows:
- Nature of flow: fluid = air; type of fluid = compressible; fluid regime = buoyant turbulent; type of flow: three-dimensional and confined.
- turbulence models: The equations for k and e correspond to the k-e SST turbulence model.
- Gravity: The effects of gravity were considered in order to account for buoyancy with the gravity acceleration of (0x, 0y, -9.81z) (m/s2). The reference density was calculated based on the ideal gas equation, reference pressure and reference temperature were obtained from testing for each case using the specific gas constant = 287 J / kg K.
Thermal models and thermophysical properties:
The energy equation was activated in order to model convective heat transfer within the cabin. Heat loads due to occupants and outer walls, as well as additional heat sources like lights and other minor power sources were included in this model. Heat transfer due to thermal radiation was also considered and modelled using the P1 model available in ICON FOAMpro and the S2S model available in STAR-CCM+. Modelling radiation is fundamental for comfort related problems. Simple CFD test cases organised in the past, and validated against experimental data (e.g. heated cylinder in a room), have suggested that radiation may account for as much as 30% of the total heat transfer in a cabin. The values of thermal conductivity (k) and heat capacity (cp) were left constant. The molecular viscosity was estimated using Sutherland's equation and was set to constant value of 1.85508E-5 Pa.s.
Solution procedure and convergence
The solution procedure employed for the steady state solution was SIMPLE, with a second order discretisation. The corresponding control parameters for this procedure are listed below:
- Velocity: under-relaxation factor: 0.5
- Pressure: under-relaxation factor: 0.2
- Energy: under-relaxation factor: 0.5
- Turbulent energy: under-relaxation factor: 0.7
- Turbulent viscosity: under-relaxation factor: 0.7
- Levels for convergence for most cases reaches values below 110-4.
Specific and relative humidity model
Humidity was modelled utilising the passive scalar approach. This means that effects like gravity force causing the stratification are neglected. The passive scalar of humidity represented specific humidity Sh (g / kg dryair). In the simulated cabin two main sources of humidity were taken into account - humidity which is brought in by air supplied from the main and individual inlets (Shtech) and humidity generated by passengers (Shpass).
The source or humidity from passengers was defined in front of the face of each manikin which represents real person and the value was 7.86 (g1s-1m-3) in sphere of 10 cm diameter. The value of Sh on main ECS inlets and individual seat inlets was calculated based on equation (2). The input values were tair - air temperature, pair - air pressure and RH - relative humidity of air. Achieved accuracy compared to tests
- Air temperature at seat probes: typical value of the absolute error below 1 degrees of Celsius, average error 0.86 degrees of Celsius
- Air temperatures at outlets: results in close agreement with test data, small deviations up to 1.5 degrees of Celsius
- Relative humidity of air: the discrepancies in most cases up to 4 % abs., transient simulations show better agreement, however they are computationally expensive.
- Both codes - STAR CCM+ and ICON FOAMpro - work properly and give almost identical results.
ISPACE recommendation:
Using appropriate boundary conditions and physical models both simulation codes - STAR CCM+ and ICON FOAMpro - work properly and give almost identical results.
Temperatures can be predicted well, the approach of specific humidity for steady state conditions leads to discrepancies with measurements in most cases up to 4 % abs. transient simulations show better agreement, however they are computationally expensive.
Generally the simulation tools are able to reliably predict cabin environment and comfort and may be used as a design tool even for very complex situations to save development time and resources.
1.3.4.4 Thermal comfort prediction based on equivalent temperature
The thermal comfort evaluation was based on the comfort zones diagram method using the equivalent temperature approach (see also ISO 14505-2). This model evaluates thermal comfort on eighteen separated parts of a human body and also overall thermal comfort which is calculated as weighted average where the weight of each part is the surface area of the part. Values of overall comfort for each manikin were extracted and compared with thermal comfort assessed during the subject test campaign in the Fraunhofer FTF. Results from the simulations for a medium cabin temperature situation show the same trend as the results from the subject survey, however MTV on all seats is shifted to colder votes. The main problem in the thermal prediction discrepancy was identified in the values of clothing insulation used for simulations. The values were adopted from ISO 14505-2 but the clothing of real test subjects during tests in FTF was evaluated differently. Therefore the typical dress for a passenger was defined and the thermal resistance was measured using thermal manikin NEWTON. Then the simulations were repeated with the adopted values of clothing insulation under boundary conditions of virtual manikins. The discrepancies are much lower and the prediction on most seats is in close agreement with measured values.
ISPACE recommendation:
The prediction of thermal comfort base on concept of equivalent temperature and the associated comfort zones diagram is a suitable tool for prediction of thermal comfort in aircraft cabins.
An important parameter in simulation is the correct value of clothing insulation, which is applied as boundary conditions on surfaces of virtual manikins in CFD simulation. The simulations under-predict thermal comfort at all seats when the virtual manikins were dressed based on ISO 14505 (summer clothing), after calibration with more realistic clothing the results are in very good agreement.
1.3.4.5 Steady vs. transient simulations
Cabin flow simulations should be conducted as transient. However, due to the time restrictions and the large number of simulations for parametric studies, simulations were mainly performed as steady-state. One case was also run transient in order to provide a rough indication of the average values compared against monitored values.
Although the transient simulation was relatively short, the improvement of relative humidity prediction is evident from results. The flow in the cabin is time dependent and oscillates with a certain frequency. It is evident from the results that certain transient effects may exist in the flow field. This brings a degree of error which appears to be relatively large for the humidity profiles in the cabin. Although all other residuals (U, T, p) gradually reduced, humidity would not converge easily, which is considered to be an indication of transient effects.
ISPACE recommendation:
Cabin environment simulation should be performed as transient simulation due to the fact that cabin flow is transient and main flow oscillations have a direct impact on precision of cabin environment and human thermal comfort prediction.
For transient simulations of complex geometries as an aircraft cabin the main problems are still the computational effort and time as well as the enormous amount of the data generated by CFD solvers.
Potential impact:
ISPACE investigated unique concepts and technologies to reach a step-change in personalised passenger climate control. The overall objective of ISPACE was to provide aircraft manufacturers and the supplier industry with know-how and innovations to address the individualisation of passenger cabin environment. This ultimately provides a step-change in passenger comfort during flight. The general approach of ISPACE is that concepts were worked out and analysed, prototypes were tested and in addition a CFD pre-study was realised which could be validated after testing.
In the end three integrated systems can be noted: seat heating / ventilation, humidification and air purification.
Individualisation of climate at seat level in the aircraft cabin has a socio-economic impact; it leads to higher comfort during flight. The environmental cabin system (ECS) does not need to be separated in several temperature zones if an individual adjustment of temperature and airflow at seat level is possible. Passengers travel one a higher comfort and satisfaction level. Business travellers get to the meeting at their destination perfectly relaxed and are not stressed due to uncomfortable flight conditions. Passengers who are flying on holidays can experience their first step of holiday in the airplane. Airliners with an individualised cabin environment have a better initial point to attract potential customers. It can be conceivable that travellers accept a higher price for more comfort on their flight.
For demonstration of climate individualisation a published link on YouTube in the internet shows how this benefit of comfort can look like: http://www.youtube.com/watch?v=9TH6XcEYp7s&sns=em
Simulation of individualised ventilation in a global cabin environment was a big issue within the ISPACE project. A commercially licensed CFD tool (STAR-CCM+), a developed open source solver (ICON FOAMpro) and meshing tools were compared and proved. This offers customers a cost-effective customisable solution to fulfil their CFD simulation requirements and engineering consultancy with open source based software.
For dissemination of ISPACE project stakeholders were involved from the beginning of project. A questionnaire survey figured out which problems are occurring in the aircraft cabin. Although the feedbacks from the questionnaire were very different it showed that an individual environmental control system would be a good extension to the existing seat equipment for the upper class segment.
In detail, the feedback from the airlines showed, that the individual temperature control and humidification would be the most wanted improvement. The individual ventilation would be the second priority. In addition, there are also many complaints by the passengers which are not related to the climate environment.
At the moment the complaints from the passengers are not always to be resolved with the existing technology and the airlines performed some workarounds to satisfy the passengers. All improvements are mostly expected for high-priced seats (F/c-seats).
One important boundary condition is that the additional equipment must fit into the existing space for B/c- and F/c-seats as there is no further room available inside the aircraft without losing any seat.
One year after the questionnaire interested stakeholders were invited to a project consortium meeting to involve their views and opinions in the final testing of the developed personalised heating, humidification and ventilation systems. After the subject testing a stakeholder test flight was realised. It gave the stakeholders an impression on the developments and the test conditions. An adjacent discussion discovered important aspects. With regard to the installed improved environmental control equipment the seat heating including ventilation was rated as the most beneficial feature. The humidification was rated as 'not existing'. In the feedback round it was discussed, if a longer test period might be necessary to realise any effect from the humidification system. However, the airlines stakeholders mentioned the critical maintenance and operational aspects of this system. For further dissemination the investigated prototypes were exhibited at the Berlin AirShow ILA, September 2012. Several presentations and / or papers at AeroDays 2011, IndoorAir Conference 2011, ICEE2011, NAFEMS2011, EFM2012 and IATA Aviation Health conference 2012 spread the information about ISPACE project. With the ISPACE webpage www.ISPACE-project.eu interested people could get a general overview of the project structure and objectives.
In the end of ISPACE project the results were disseminated to stakeholders from the industry at a final stakeholders club meeting. It took place in October 2012 in Holzkirchen, Germany. For this symposium also Prof. Peter Vink from the TNO were invited as external speaker as a well-known specialist in the field of aircraft interior comfort. After his introduction the ISPACE consortium presented the main topics of ISPACE project.
List of websites: http://www.ispace-project.eu