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AIR FLOW REGIMES AND THERMAL PATTERNS IN CLIMATIZED TOMBS IN THE VALLEY OF THE KINGS

Eng.Omar A.A.Abdel-Aziz and Prof.Dr.Essam E.Khalil

Cairo University, Faculty of Engineering, Egypt ABSTRACT Airflow characteristics in ventilated and air-conditioned spaces play an important role to attain comfort and hygiene conditions. This paper utilizes a 3D Computational Fluid Dynamics (CFD) model to assess the airflow characteristics in ventilated and air-conditioned archeological tombs of Egyptian Kings in the Valley of the Kings in Luxor, Egypt. It is found that the optimum airside design system can be attained, if the airflow is directed to pass all the enclosure areas before the extraction with careful selection of near wall velocities to avoid any wear or aberration of the tomb-wall paintings. In this model conditioned air is allowed to enter the tomb from its entrance with a large area of admission in order to maintain low air velocity while extraction points are distributed along the tomb axis. The mode of evaluation should assess the airflow characteristics in any tomb passage according to its position in the enclosure and the thermal pattern and air quality. INTRODUCTION To design an optimum HVAC airside system that provides comfort and air quality in the air-conditioned archeological spaces with efficient energy consumption is a great challenge. Climatic control in tombs for visitors and artifact can be identified as the conditioning of the air to maintain specific conditions of temperature, humidity, and dust level inside an enclosed space. The levels of the air conditions to be maintained are dictated by the local environment, type and number of visitors and required climate and the required visitors comfort and property reservation. Comfort conditioning is defined as “the process of treating air to control simultaneously its temperature, humidity, cleanliness, and distribution to meet the comfort requirements of the occupants of the conditioned space”. 1 In the present work, following other earlier similar work 3-5, a numerical study is carried out to identify optimum air flow regimes’ design for the tombs ventilation and air-conditioning systems. These would provide the optimum comfort and healthy conditions with optimum energy utilization. The present work made use of packaged Computational Fluid Dynamics (CFD) programs. The present paper introduces a description of the computational solver and its validation with steady state results of the previous properly related literatures. Basically, airside design types are considered here for the tomb passage of King Ramsis VII, including different visitors (simulated flow obstacles) alternative positioning to introduce the capability of designers to provide the optimum characteristics. The full description of the parametric cases’ parameters is discussed later. The primary objective of the present work is to assess the airflow characteristics, thermal pattern and energy consumption in the different tomb ventilation configurations in view of basic known flow characteristics. The paper ends with a brief discussion and conclusion. PROBLEM FORMULATION

The proper tactical airflow distribution is required in all applications in the tomb of Ramsis VII which is of simple single axis passage. The airflow distribution in its final steady pattern is a result of different interactions such as, the airside design, objects distribution, thermal effects, occupancy movements, etc. The airside design and

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internal obstacles are the focus of the present work. The free air supply and mechanically extracted ducted air play an important role in the main flow pattern and the creation of main recirculation zones. The internal obstacles would naturally obstruct the airflow pattern in different ways and means, by for example increasing the recirculation zones size ,relocating these and or deflecting the main airflow pattern. METHOD DESCRIPTION MODEL EQUATIONS The program solves the differential equations governing the transport of mass, three momentum components, energy, relative humidity, and the air age in 3D configurations under steady conditions 6. The different governing partial differential equations are typically expressed in a general form as:

ΦΦΦΦ +���

����

�

∂Φ∂Γ

∂∂+��

�

����

�

∂Φ∂Γ

∂∂+��

�

����

�

∂Φ∂Γ

∂∂

=Φ∂∂+Φ

∂∂+Φ

∂∂

Szzyyxx

Wz

Vy

Ux

effeffeff ,,,

ρρρ

Where: ρ = Air density, kg/m3 Φ = Dependent variable. SΦ = Source term of Φ. U, V, W = Velocity vectors. ΓΦ,eff = Effective diffusion coefficient. The effective diffusion coefficients and source terms for the various differential equations are listed in the following table.

Table 1: Terms of Partial Differential Equations (PDE) Φ ΓΦ,eff SΦ Continuity 1 0 0 X-momentum U µeff -∂P/∂x +ρgx Y-momentum V µeff -∂P/∂y +ρgy(1+β∆t) Z-momentum W µeff -∂P/∂z +ρgz H-equation H µeff/σH SH RH-Equation RH µeff/σRH SRH τ-age equation τ µeff/στ ρ k-equation k µeff/σk G - ρ ε ε-equation ε µeff/σε C1 ε G/k – C2 ρ ε2/k µeff = µlam + µ t µ t = ρ Cµ k

2 / ε G = µt [2{( ∂U/∂x)2 +(∂V/∂y)2 +(∂W/∂z)2}+( ∂U/∂y + ∂V/∂x)2 +(∂V/∂z + ∂W/∂y)2 +(∂U/∂z + ∂W/∂x)2] C1 = 1.44, C2 = 1.92, Cµ = 0.09 σH = 0.9, σRH = 0.9, στ = 0.9, σk = 0.9, σε = 1.225

THEBAN CLIMATIZATION CONTROL PROJECT As a part of the plane for the complete restoration of the Valley of the Kings that started years ago, the Egyptian government had set a handsome budget for the scientific committee in order to achieve this goal. After the work of the Theban Mapping Project (TMP)7 that had fully documented the valley’s tombs in contour forms and engineering as built drawings of the various individual tombs, which are already on the Web site created by TMP, attempts were made to systematically investigate and assess the flow pattern, heat transfer and relative humidity in theses

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tombs in order to set the appropriate working conditions and allowed number of visitors per tomb. In the present work a preliminary attempt to investigate one of these tombs; Ramsis VII, was carried out to reach the proper airside system design. This tomb is simple in construction in a single axis as shown here in Figure 1, where the top is the isometric and the horizontal cross section at the bottom clearly identified three zones. The entrance zone that extended to over 12 m with door locking the second zone that descended with steps down to another door locking the burial zone where the sarcophagus is located. Figure 2 shows a photographic view of the sarcophagus zone and the wall paintings around it.

Figure 1: Schematic representation of Ramsis VII tomb with the visitors inside and the outlet ports locations

Outlets

Visitors

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Figure 2: Ramsis VII Tomb interior

COMPUTATIONAL RESULTS Over 97000 computational cells were used to map the tomb total volume of 618 m 3, the maximum computational volume was 2.505587e-02 m3 and the minimum was 1.976608e-05m3 .Computational grid coordinates extend as follows X-coordinate 0.0 to 44.26 m ,Y-coordinate: -4.30 to5.74 m and Z-coordinate:-0.66 to 4.26 m The minimum cell-face area: 5.630187e-04 m2, the maximum being 1.882718e-01m2. About 300 iterations were necessary to achieve the convergence criteria of residuals being less than 10-3 in computational time just under one hour. Figure 3 below shows the change of residuals with the number of iteration. The two-equation turbulence model yielded poorer results than those of the Large Eddy Simulations incorporated in the present work. The present grid size yielded grid independent results within 3% of the resulted shown here.

Figure 3: Residuals versus number of iteration plot

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RESULTS AND DISCUSSIONS In pursue of the appropriate air conditioning system designs, simulation of actual air flow patterns and heat transfer behavior was carried out with the above computational scheme 8,9 with simulation of visitors as shown in figures 5 to 8 in the following paragraphs at wall temperature of 295 K while modeling the visitors as walls of constant temperature of 310 ºK. The proposed simulated design is to extract air through floor-mounted ports each 1.0x0.15 m at four different locations as shown in Figure 1, with air entering the tomb at different temperatures of 290, 292,294 and 295 K. Figure 4 depicted the predicted velocity vectors distribution in a horizontal plane at 1 m showing 33 visitors located along the tomb passage.

Figure 4: Predicted Velocity vectors contours at 1 m above ground, m/s, (not all

visitors are identified, some are overshadowed by plots) These visitors are located in the most likely positions where tomb paintings are to be viewed. Bearing in mind that the air velocity in the tomb should not exceed 0.12 m/s in order not to create any undesired drafts, Figure 6 indicated flow velocities at Ti=290 K. It is very interesting to observe the higher velocities in the middle section of the tomb as a result of the zone height reduction. The proposed simulated design concept incorporated extract air through floor-mounted ports at four different locations as shown in Figure 7 that indicated the near wall velocity to be of very low values typically less than 4x10-4 m/s. Such values are very important to ensure that air flow would not result in wear of wall paintings or alter any of the tomb geothermal characteristics. The isovelocity contours are shown in Figure 8 and 9 at Ti =294 K and Ti =294 K respectively, and once more it indicated low velocities.

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Figure 5: Predicted Velocity vectors distribution at middle plane, m/s, Ti=290K

Figure6: Predicted Wall-Vicinity air Velocity distributions, m/s ,Ti=292 K

Figure 7: Predicted Wall-Vicinity air Velocity distributions, m/s, Ti=294 K

Figure 8: Predicted Wall-Vicinity air Velocity distributions, m/s, Ti=295 K

On the other hand, the corresponding isothermal lines are shown in Figure 9, 10, 11, and 12 below for a wall temperature of 290, 292, 294, and 295 K respectively. Now considering the requirements lay out by archeological scientists and tomb restoration experts, the temperature is not allowed to vary around the walls of the tomb and thus it is better to have low temperature gradient near the wall. As shown in Figure 9, if the air inlet temperature is reduced to 290 K there would exist medium temperature gradient near the walls of the entrance and second zones, this gradient tends to diminish inside the burial zone. Proceeding to Figures 10 and 11 it was found that the closer inlet temperature to the wall temperature the better thermal design is achieved. Once more air is introduced to the tomb at a temperature that equals that of the assumed wall temperature of 295 K; it was noticed that temperature gradients are of smaller values allover the tomb as demonstrated in Figure 12.

Figure 9: Predicted Temperature distribution at X-Y middle plane,

Ti=290K.

Figure 10: Predicted temperature distributions at X-Y middle plane,

Ti=292K

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Figure 11: Predicted temperature distributions at X-Y middle Plane,Ti=294 K

Figure 12: Predicted temperature

distributions at X-Y middle Plane, Ti=295 K

Figure 13 indicated the resulting static pressure distribution at middle X-Y plane where small static pressure differences of the order of 0.013 Pascal’s were shown.

Figure 13: Static pressure distribution (Pa) at middle plane X-Y.

DISCUSSION AND CONCLUSION

The main flow pattern of the free supplied air and floor mounted extracts is slightly influenced by the extraction ports locations. In the second zone, one extraction port is used at midway between the entrance zone and the burial zone. On the other hand two extraction ports are put in the burial zone as this is the place where visitors stay for a long time to see the paintings and the sarcophagus. The last extraction port is put at the last chamber to extract the remainder air. The flow rate weighting factor differs from one outlet port to the other. In this model the used flow rate weighting factors are 0.2, 0.2, 0.3, and 0.3 for outlets 1, 2, 3, and 4 respectively. This setup allow for fresh air effect to be persistent along the tomb axis. As for the set point for conditioned air entering the tomb, it is found that the optimum set point is that one equal to the wall temperature as it reduces the temperature gradient near the wall to

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almost zero. This design would be the most economical and efficient design as air is not cooled to lower temperature than required thus reducing the amount of refrigeration capacity. The optimum utilization of the air movement to ventilate and reduce temperature can be attained by locating the extraction ports to minimize the recirculation zone and prevent the air short circuits. Ideally, the optimum airside design system can be attained, if the airflow is directed to pass all the enclosure areas before the extraction. Still all shown predictions clearly indicated the usefulness of floor extracts that do not disturb the archeological value of the tomb and do not install any artificial materials in the tombs .The influence of the recirculation zones on the visitors’ occupancy zone and also on the fresh supplied air were investigated. RECOMMENDATIONS

To reach optimum airside system design, the proper air conditioned set point should be selected close to the average wall temperature in order to minimize the temperature gradient near the wall. This setup is important as a preservation procedure for the tomb status. Future work should include the humidity effect in consideration in order to achieve the recommended working condition for the tomb. The model should give the maximum allowed simultaneous number of visitors in the tomb so that the air conditioning equipment works properly. ACKNOWLEDGEMENTS

The authors would like to acknowledge the technical support of the Supreme Council of Antiquities, ministry of Culture, ARE and the CAPSCU of Cairo University. REFERENCES [1] ASHRAE Handbook, Fundamentals 2001, ASHRAE, Atlanta, USA. [2] Stoecker, W. F., and Jones, J. W., 1985, Refrigeration and air conditioning, Second Edition, TATA McGraw-Hill Publishing Company LTD., 1985. [3] Khalil, E. E., 2000, Computer aided design for comfort in healthy air conditioned spaces, Proceedings of Healthy Buildings 2000, Finland, Vol. 2, Page 461. [4] Kameel, R., 2002, Computer aided design of flow regimes in air-conditioned operating theatres, Ph.D. Thesis work, Cairo University. [5] Cho, Y., Awbi, H. B., and Karimipanah, T., 2002, A comparison between four different ventilation systems, ROOMVENT 2002, 181-184. [6] Kameel, R., and Khalil, E. E., 2003, Energy efficiency, air quality, and comfort in air-conditioned spaces, DETC2003 / CIE – 48255, ASME 2003, Chicago, Illinois USA, 2003. [7] Weeks, K., 1999, Theban Mapping Project, AUC, Egypt. [8] Abdel-Aziz, O.A. and Khalil, E.E., 2004, CFD-Controlled Climate Design Of The Archaeological Tombs Of Valley Of Kings, Proc, Sustaining Europe Cultural Heritage, London, September 2004. [9] Khalil, E.E. 2004 “Indoor Air Climatic Design Of The Tombs Of Valley Of Kings”, Invited Paper, Proceedings, Room Vent 2004, Coimbra, Portugal, September 2004.