THE AIRCRAFT SEAT AS INDOOR AIR QUALITY AND TEMPERATURE CONTROL SYSTEM P Jacobs *, WF de Gids Department of Building Physics Indoor Environment and Energy TNO Environment and Geosciences Delft, 2600 AA, The Netherlands ABSTRACT This paper describes the results of measurements to quantify the convection induced airflow around a seated person and the effect of this flow on the trajectory of a local supply jet. The test results indicate that it is not possible to supply a flow above the shoulders without causing local thermal discomfort. This conclusion has been used to design and construct a seat with displacement ventilation in the headrest. Tracer gas experiments in a mock-up with heated mannequins in each of the seats revealed contaminant removal efficiencies up to 96% in the breathing zone. Local supply of air near the breathing zone of the passengers minimizes the amount of air, enables some humidification and could give some protection against infectious diseases. Due to exhaust of air through the seat and electric heating, passengers can control the surface temperature of the seat. In this concept the seat is the main Indoor Air Quality and temperature control system for the passengers. INDEX TERMS Personalised air supply, aircraft cabins, seat, passenger comfort and health, displacement ventilation INTRODUCTION Fresh air in aircraft is very expensive. At the cruise altitude of 40.000 ft outside air has to be pressurised from 0.2 bar outside pressure up to the cabin pressure of 0.75 bar. For safety reasons the air almost always is pressurised up to 2-4 bar. Therefore the ventilation energy per passenger currently amounts to 2 3 kw, which represents 1-2% of the total thrust. Other problems in aircraft cabins are dry air and widespread concerns regarding the impact of the cabin environment on the health of passengers and crew. Figure 1. Different types of local supply and exhaust Instead of a mixing ventilation system local supply could be advantageous. Local supply systems are developed for office workplaces where the supply air is introduced below the desk (e.g. Loomans 1998) or mounted above the desk (Cermak et al. 2002). When the chair is moved, which is a frequent action in the office, the effect of the local supply is strongly reduced. The same applies to aircraft cabins. Airliners do from time to time change the seat arrangement. To be independent of the seating arrangement the personal supply and exhaust should be mounted on the same seat as it is directed. This is accomplished in figure 1 in the seat on the most right. In this arrangement the convection induced airflow around the person has an effect on the local air supply jet. Knowledge exists on the flow around standing persons (Murakami 2002) or with the plume above a sitting person (Borges et al 2002). Concerning the combination, the flow around a sitting person and the effect on the trajectory of a local supply jet, * Corresponding author email: P.Jacobs@bouw.tno.nl 426
little information is available. This study is aimed to investigate this phenomenon. The data have been used to design and construct a seat with displacement ventilation in the headrest. RESEARCH METHODS The measurements have been performed in a test room (floor area 3,1 x 3,7 m 2, height 2,3 m). The test room has isolated walls and ceiling. To determine the vertical temperature gradient the air temperature has been recorded over the first 2 meters at every 0.5 m. Ventilation air (12 ACH) is introduced with very low velocity (0.008 m/s) via a floor plenum and leaves the room via 4 holes in the upper wall. Tracer gas experiments Figure 2. Front view experimental set up in test room Figure 3. Cross section experimental set up in mock up, with flow field based on smoke tests. To simulate contaminants a tracer gas (SF 6 ) was added to the test room ventilation air. Clean outside air was provided close to the seated mannequin along both sides of the head, see figure 2. By means of filtration paper (Area= 64 cm 2, ΔP = 40 Pa @ 1.5 dm 3 /s) a homogeneous airflow has been made. The distance between the diffuser and the breathing zone is approximately 25 cm. The concentration of the tracergas in the breathing zone of the mannequin was measured by connecting a Multigasmeter with a sample tube positioned between nose and mouth. The volume flow through the sample tube is negligible compared to the flow due to the local supply. The experiments have been repeated in a mock up (30 seats) representing an aircraft cabin to study the effect of the aircraft ventilation system on the local supply. In figure 3 clearly two vortexes can be distinguished caused by the supply slits below the bins. Figure 4. Experimental setup local supply jet trajectory. The position of the local supply is indicated with the circle. Figure 5. Test person with velocity probes in front of supply Convection-induced airflow around a person Instead of a mannequin a male test person (1.83m, 75 kg) has been used. In total 27 positions have been measured. Figure 6 shows the positions in a x,y,z grid. Due to a limited number of hot sphere anemometers the measurement has been split up in four parts. Between the measurements a waiting time for flow stabilization of 5 min has been used. 427
Trajectory of a local supply jet The induced airflow around a person has influence on the trajectory of a local supply jet aimed at the breathing zone. To study this effect the local supply box has been placed behind the left shoulder of a sitting person (x=-0.18, y=-0.05, z=0.75). To quantify the effect 8 velocity sensors have been lined up vertically (x = -0.07, y= 0.17) in front of the test person, see figure 4 en 5. It has been assumed that the highest velocity in this velocity profile (v max ) determines the deviation of the jet. To avoid disturbance by the breathing air, the test person has turned his head to the right. RESULTS Tracer gas experiments in test room During the first experiment the temperature of the local supply was 1.5 K higher than room temperature and the mannequin was not heated. The results are listed in Table 1. With smoke it has been shown that with an air velocity of 0.08 m/s the local supply air rises too much to reach the breathing zone. At higher velocities the concentration of the contaminant is reduced up to a factor 80. However a large range can be seen. Table 1. Contaminant reduction as function of local supply flow rate flow rate [dm 3 /s] Air velocity [m/s] SF 6 conc. [ppm] 0 0 7.9 (7.6-8.0) 0.5 0.08 7.8 (7.7-7.9) 1.0 0.16 0.26 (0.1-0.7) 1.5 0.24 0.53 (0.1-0.8) The mannequins have the option to be heated: the torso 40 W and the upper legs 20 W. Lower legs were not present. With heating on the reduction factor was reduced to zero. Due to the heating skin temperatures of 32 36 ºC are reached. This causes induction of air above the shoulders. As a consequence the local supply air is pushed upwards before it reaches the breathing zone, resulting in a reduction factor of zero. Convection-induced airflow around a person The temperature gradient in the test room was 0.35 K/m. Figure 6 shows the results. The highest velocities are above the shoulders, near the torso and above the head. Trajectory of a local supply jet Tests have been performed at two different start velocities and at five temperature differences between the room air and the supply air. Higher velocities and larger temperature differences are considered to cause thermal discomfort in the neck. The temperature gradient was 0.25 K/m during the over temperature experiments and 0.25 0.7 K/m during the under temperature experiments. Figure 7 shows the deviation from a horizontal trajectory. no person, 0.3 m/s no person, 0.2 m/s with person, 0.3 m/s with person, 0.2 m/s 0.2 0.15 vertical deviation [m] 0.1 0.05 Figure 6. Person in test room, side view with measured velocities in m/s 0-2.0-1.5-1.0 0.0 temperature difference [K] 1.0 1.5 2.0 with person, 0.2 m/s with person, 0.3 m/s no person, 0.2 m/s no person, 0.3 m/s Figure 7. Vertical deviation local supply jet under different conditions The results clearly indicate that with an over temperature the local supply jet is bended upwards. With a person seated this effect is enforced. With under temperature the trajectory remains more horizontal. However, the minimum deviation is 10 cm, with an under temperature of 2 K and a start velocity of 0.3 m/s. As the breathing zone is about 10 cm higher than the shoulders, this makes it impossible to supply air from above the shoulders. 428
Mock up tracer gas experiment For the mock up test a new design for the local supply has been made, see figure 8. The air diffusers are located closer to the breathing zone. Two laminar flow cloths with an area of 0.0075 m 2 each distribute the air. As shown in figure 9, the position of the local supply boxes is adjusted to the size of the mannequin. Several experiments have been executed in which the flow rate of the local supply has been varied, see figure 10. At a flow rate of 2 dm 3 /s per passenger the contaminant reduction in the breathing zone is negligible (results not shown). The initial velocity of 0.13 m/s is too low compared to the buoyancy flow around the passenger and the disturbances of the cabin ventilation. Figure 8. Dimensions head rest with local supply boxes [mm] Figure 9. Set up tracer gas test in mock up, from left to right: seat C, B and A. Figure 10 shows that a flow rate of 3 dm 3 /s per passenger reduces the tracer gas concentrations, mainly for seat A. Further the concentrations vary in time. Probably disturbances caused by the cabin ventilation flow play a role in this variation. A flow rate of 4 dm 3 /s per passenger (initial velocity 0.26 m/s) renders a more stable pattern, with clearly lower concentrations in the breathing zone. The average reduction for seat A is 96%, for seat B 81% and for seat C, which is situated near the aisle, 57%. Figure 10. Measured SF 6 concentrations in mock up, effect of flow rate DISCUSSION Current regulations (FAR 28.831) specify a fresh airflow rate of at least the 5 dm 3 /s per passenger; this is 3.5 dm 3 /s 429
at sea level. This corresponds to a CO 2 concentration of 1400 ppm in the cabin [de Gids et al 2002]. During long range flights relative humidity levels drop to 5 15%. Temperature control by the passengers (e.g. gaspers) is limited or not existing. As discussed in this paper local supply of air near the passengers breathing zone could be a solution to these problems. By exhaust of air through the seat (Jacobs 2003) or electrical heating passengers can control the surface temperature of the seat. In this concept the seat is the main Indoor Air Quality and temperature control system for passengers of collective transport like aircraft, trains and buses. Currently investigations are going on to implement other functions in the headrest like support during sleep and integration of audio. As shown by the right person in figure 11, making use of the audio to watch a movie, requires positioning of the headrest and thus ensures automatically an optimal position of the ventilation supplies [Jacobs 2005]. For all applications research with real persons is needed to determine the perceived comfort and the effect of breathing on the efficiency of the local supply. Figure 11. Impression of audio and ventilation in headrest CONCLUSION AND IMPLICATIONS Persons convection induced airflow does complicate the application of local supply provisions. A practical approach has overcome these difficulties by reducing the distance between provisions and breathing zone. This system can be used in collective transport and may be viable in offices to create an individual climate. ACKNOWLEDGEMENTS This research has been conducted within the European Sixt Frame Work Programme project Cabinair. The contribution of Peter de Jong to the experiments is thankfully acknowledged. REFERENCES Borges CP., Quintela DA., Brites GN., Gasper AR. and Cota JJ. Analysis of thermal plumes generated by a seated person, a thermal manikin and a dummy, Proceedings of the 8 th International Conference on Air Distribution in Rooms 2002, Copenhagen, pp 253-256. Cermak R., Holsøe J., Meyer KE. and Melikov AK. PIV measurements at the breathing zone with personalized ventilation, Proceedings of the 8 th International Conference on Air Distribution in Rooms 2002, Copenhagen, pp 349-352. FAR 28.831, Federal Airline Regulations Gids de WF., Jacobs P., Knoll B., Phaff JC., Kornaat W. and Cox CWJ. Review of current concepts for cabin air distribution and control systems, Cabinair report D7, April 2002, available through TNO. Jacobs P. Methodology design strategy for cabin air distribution, Cabinair report D14, April 2003, available through TNO. Jacobs P. Ventilated headrest with audio positioning, International Patent, to be published July 2005. Loomans MGLC. 1998. The measurement and simulation of indoor air flow Ph.D. Thesis, Eindhoven University of Technology (The Netherlands), 220 pages. Murakami S. CFD study on the micro-climate around the human body with inhalation and exhalation, Proceedings of the 8 th International Conference on Air Distribution in Rooms 2002, Copenhagen, pp 23-35. 430