Air conditioning - Egyptian tomb

air coNDitioNiNG EgyPTian TomB air to the throNe Excessive relative humidity is threatening priceless wall paintings in the tombs of Egyptian kings. Essam E Khalil, of Cairo University, explains how his research into the ventilation and conditioning system of one such chamber could help preserve them E very year, the Valley of the Kings attracts hundreds of thousands of tourists to Luxor, all keen to see the final resting places of the Egyptian pharaohs. By far the most famous of these is Tutankhamen but, 14 years before the boy kings burial chamber was discovered, archaeologists uncovered King Horemhebs tomb (KV57), on 25 February 1908. Horemheb was the last king of Egypts 18th Dynasty, and was a Great Commander of the army. The decoration in his burial chamber and other parts of his tomb was left in various stages of completion, and so provides scholars with a fascinating glimpse into the processes involved in preparing painted reliefs. It reveals, for example, that wall decorations were created by following a grid system in red ink, over which figures were drawn in black before being carved and painted. It is also the first burial chamber in the valley to show the ancient Egyptian funerary text, the Book of Gates, while other decorations depict deities and Horemheb with the gods. Such priceless antiquities, however, are being threatened by excessive relative humidity (RH) in the tomb; this can affect the mechanical and physical properties of the materials used to create the wall the first consists of the entrance and a corridor, which leads to a well chamber; there is then a second axis that leads to a six-pillared burial chamber (see Figures 1 and 2). The tomb is 5.36m at its highest and its width ranges from 0.66m to 8.94m. It is 127.88m long, has a floor area of 472.61m2 and a total volume of 1,328.17m3. My research builds on earlier studies by AbdelAziz1, Ezz Eldin2 and Mohamed3; it was a numerical study carried out to further investigate the air-side design of the tombs air ventilation and conditioning system to provide optimum comfort, healthy conditions, and optimal energy use (see panel Numerical investigations below). Air-side design types were considered for the tomb passage of KV57, including different visitors in alternative positions to test the designs ability to provide optimum characteristics. The air supply and mechanically extracted ducted air play an important role in shaping the main flow pattern. The flexible ducts are above the raised wooden floor, and run less than 0.2 m above the original stone flooring. Simulation and discussions To design appropriate ventilation systems, simulation of actual airflow patterns and near-wall velocities to avoid erosion of the tombs wall paintings. The number of simultaneous visitors to the tomb should also be restricted to limit the relative humidity inside. paintings, as well as raise the levels of bacteria and fungus inside the chamber. Currently, whenever condensation forms on the walls, KV57 is closed. As this has happened frequently over the past five years, the tomb has only been opened to the public for around 10% of the time. To try to preserve the wall paintings from these harmful factors as well as improve the comfort of visitors to the tomb I recently undertook research into the effect of mechanical ventilation systems on airflow patterns, temperature and RH inside KV57, as well as the thermal comfort prediction, using commercial computational fluid dynamics (CFD) package Ansys Fluent 15. It was found that the optimum air-side system design should allow air to pass through all the enclosure areas before being extracted, with careful selection of introduction The restoration of the Valley of the Kings started in the late 1970s with the Theban Mapping Project3, which fully documented its tombs in contour and engineering form, as built drawings of the various burial chambers. Horemhebs tomb is located in the west branch of the south-west valley, and its opening just above the valleys ancient floor is low in the south side of a hill that projects eastward into the central valley from the cliff face where the tomb of Amenhetep II was cut. It is composed of two parallel axes: Axis 1 Axis 2 Fig. 1: Tomb of Horemheb configuration schematic geometry eadE Rmor TomB dimEnsions Fig. 2: Tomb schematic geometry heat transfer behaviour were carried out. Air outlets were located on the raised floor to keep the archaeological scheme unaltered. The air outlets may be located either near the side walls or at the floor centre, allowing a diversity of air-side system designs. The CFD grid independency check was achieved for a grid size of about eight million nodes. The comparison was made through line plots at a location above the sarcophagus. The burial zone is of prime importance because visitors group around the sarcophagus. The tomb model design incorporated 52 grilles (1.0 0.15m) taking up to 8% of the tomb area for mechanical air extraction to limit the air velocity near walls to prevent scouring erosion. Figures 3 and 4 show that a velocity higher than 0.12 m s-1 is only found in the entry of the tomb, after which velocities are low to prevent erosion of the surfaces. Temperatures decrease from 313K (40oC) to 305K (32oC) inside KV57. Temperature contours are shown in Figure 5. The predicted RH indicated that the max RH at the wall is 70% and that RH varies from 63% to 69% in the burial chamber, as shown in Figure 6 for RH at the mid-plan axis two. The comfort zone is based on predicted mean vote (PMV) values of between -0.5 and +0.511-12 and the predicted percentage of dissatisfied (PPD) value is 25%. The different number of occupancies shows that the RH decreases when the number of people inside the tomb goes Numerical investigations Governing equations The governing partial differential equations are typically in the general form, Khalil4 and Kameel,5 in 3D configurations under steady state conditions as: U + V + W = y z , eff , eff + x y y , eff + + S z z Where: = Air density, kgm-3; S = Source term of ; = Dependent variable; U, V, W = Velocity vectors; , eff = Effective diffusion coefficient. The diffusion coefficients and source terms for the differential equations can be found in this reference by Khalil6. Boundary conditions assumption The following boundary conditions assumptions were made in the investigations: down; however, this decrease is very small. The max RH decreased from 75% (85 people) to 73% (65 people) and then to 70% (42 people). The high RH can be attributed to the high moisture content air drawn from outside the tomb for ventilation; this means the RH inside the tomb is highly dependent on the outdoor air conditions, which vary with the time of the year. The effect of outside air conditions from simulation indicates that RH increases at all times of the year except June, July, August, and September so opening the tomb only during these months will save it from the excessive relative humidity that causes problems with mould, corrosion, decay and other moisture-related deterioration. Figures 3-4 show RH% predictions for July and November. (1) The inlet air condition is taken as the average day maximum of 40C and 30% relative humidity (humidity ratio = 0.0138), representing August conditions, Egyptian code7. When air is admitted freely to the tomb, the turbulence intensity was assumedto be 5%, and the length scale assumed to be 1m. (4) The visitors bodies were treated as a wall at a constant temperature (isothermal), where the skin temperature is a function of metabolic rate. Visitors have an assumed metabolic rate of 116 W.m2 (2 Met) equivalent to 32.5C skin temperature andthe body is assumed to have zero diffusion flux. (2) The air outlets are set as outflow conditions, where the specification of the airflow distribution can differ from one outlet to the other in order to allow more flexibility. (3) The walls are deep inside the earth; they are treated as a block kept at constant temperature, which is the wet-bulb temperature or dew-point temperature for outside air condition, representing August conditions. Using the psychrometric chart, one can obtain the outside air wet-bulb temperature of 25C. The walls were assumed to have zero: mass transfer of species, water vapour, and diffusion flux. Fig 3 RH contours for July with 85 people inside tomb (outside conditions 41C DBT, 28% RH) (5) The visitors faces were also considered as isothermal walls, kept at the human skin temperature of 32.5C. The sweat effect in moisture gain to the tomb airflow was taken into account. Computational results More than eight million computational cells were used to map the tombs total volume at 1,328.17m3; more than 1,500 iterations were necessary to achieve the convergence criteria. The application of CFD simulation in the indoor environment is based on conservation equations of energy, mass and momentum of incompressible air. The turbulence model used in the numerical model is the widely used standard k- model 8,9. Fig 4 RH contours for November with 85 people inside tomb (outside conditions 30C DBT, 49% RH) the challenge of preserving historic artefacts By Tim Dwyer Designers of building environmental control systems are normally focused on occupant comfort, to deliver a healthy and productive environment. In historic buildings, however, it is often the fabric, the surface finishes and the artefacts that command the environmental criteria. The thermal mass of a structure or an artefact such as a book can mean that its surface temperature is significantly below the (dry-bulb) temperature of the surrounding air. This is particularly so when the space is heated swiftly by, for example, crowds of visitors who, conclusions The aim of my study was to enhance the understanding of flow regimes, thermal patterns and ventilation-system characteristics in the tomb. It found that RH is not affected greatly by the number of people inside the tomb, but is highly affected by the outdoor air conditions. The maximum RH in June, July, August and September is 75%, while, in other months it is above 75%. It is, therefore, not recommended to open the tomb for visitors at these times. Air velocity inside the tomb should not exceed 0.12 m s-1 to avoid creating undesired drafts. The velocities near the floor-mounted extracting grilles are expected and accepted to be higher than the limiting value of 0.12 m s-1, while the velocities in the rest of the domain are generally less than 0.12 m s-1, particularly near the walls. Velocities higher than 0.12 ms-1 are only found in the entry of the tomb up until the well chamber, after which the velocity is low to prevent erosion of the paintings. cJ coincidentally, act as very effective room humidifiers or by warm and often humid outdoor air. This may mean the relative humidity in the overall space must be controlled at a level not primarily to provide occupant comfort. In the worst scenario, this will ensure the cooler air next to the surfaces does not approach its dew point so risking condensation or, where there are absorbent materials (fabrics and paper), prevent it rising beyond a safe maximum humidity. See CIBSE Guide to building services for historic buildings, and CIBSE KS19 Humidification. TomB dimEnsions Maximum height: 5.36m Minimum width: 0.66m Maximum width: 8.94m Total length: 127.88m. Floor area: 472.61m2 Total volume: 1,328.17m3 References 1 O Abdel-Aziz, Flow regimes, thermal and humidity patterns in ventilated archaeological tombs, kings valley, Luxor, The burial zone has unfinished paintings on its walls MSc thesis, Cairo University, 2005. 2 H Ezz Eldin, Thermal comfort prediction CRC Press, Taylor and Francis, structures and the environment, Building and assessment ventilated archaeological November 2013 and Environment 24 (1) (1989) 3-110 tombs, Kings Valley, Luxor, MSc thesis, 6 R Kameel, E E Khalil, Computer-aided 9 B E Launder, D B Spalding, The Cairo University, 2006. design of flow regimes in air-conditioned numerical computation of turbulent 3 O Mohamed, Flow, thermal patterns spaces, in Proc. ESDA2000 ASME 5th flows, Computer Methods in Applied and moisture distribution in ventilated Biennial Conference on Engineering Mechanics and Engineering 3 (2) (1974) archaeological tombs, Kings Valley, Luxor, Systems Design & Analysis, Montreux, 2000 269-289 MSc thesis, Cairo University, 2008 7 Egyptian HVAC code, Ministry of 4 K Weeks, Theban Mapping project, Housing, HBRC, Vol. 1, 2014 AUC, Egypt, 1999 8 E H Mathews, Numerical solutions 5 E E Khalil, Air Distributions in Buildings, of fluid problems related to buildings, ESSAM E KHALIL FASHRAE is professor of mechanical engineering at Cairo University, Egypt