THE EFFECT OF WIND-CATCHERS EL-MALAQEF- ON THE INTERNAL NATURAL VENTILATION IN HOT CLIMATES WITH SPECIAL REFERENCE TO EGYPT: A STUDY ON SMALL PHYSICAL MODELS تأثير الملاقف وخصائصها الهندسية على التهوية الطبيعية الداخلية الناشئة عن ضغط الرياح لتتلائم مع المناخ المصرى الحار (دراسة لنموذج مصغر للملقف)

THE EFFECT OF WIND-CATCHERS EL-MALAQEF- ON THE INTERNAL NATURAL VENTILATION IN HOT CLIMATES WITH SPECIAL REFERENCE TO EGYPT:

A STUDY ON SMALL PHYSICAL MODELS

Ahmed Abdel_Wahab Ahmed Rizk (Ph. D.)

Associate Professor, Department of Architecture, Faculty of Engineering, Tanta University

E-mail: rizk2003@yahoo.com

Mohamed Abd Elmawgoud Abd Elghaffar (Ph. D.)

Assistance Professor, Department of Architecture, Faculty of Engineering, Tanta University

E-mail: Mawgoud@hotmail.com

EXPERIMENTAL DESIGN:

                Experiments are carried out using small physical models (15Ï15Ï50) cm, 11Ï11 cm surface area of the inlet opening and finally 11Ï11cm area of the outlet opening.

                By studying the effect of the geometrical characteristics of wind catcher on air speed at both entry opening and exit openings, it is easy to derive the optimum geometrical chara-cteristics of actual wind catchers that depends on the calculation air speed at both entry. And exit openings.

RESULTS AND DISCUSSION:

                The effect of the geometrical characteristics of wind catcher on air speed of both entry openings and exit openings.

1-Entry Opening’s Orientations (Inlet Orientations):

                It is found that the effects of different orientations of air entry openings according to wind direction, air speed at outlet openings are as follows:

• · It equals to 90% of the speed of the external wind, when the long axis of the wind catcher’s entry opening is perpendicular to the wind direction.
• · It reaches to 50% of the speed of the external wind, when the long axis of the wind catcher’s entry opening is at an angle between 10° to 80° to the wind direction.
• · It is nil, when the long axis of the wind catcher’s entry opening is parallel to wind direction as given in table (1). It is concluded that air speed at outlet opening reaches its maximum value when the inlet opening is perpendicularly placed to the wind direction. It also vanishes when the surface of inlet opening is placed parallel to wind direction as shown in figure (1).

2-Locations of Outlet Openings to Inlet Openings:

                Air speed at outlet openings varies according to the location of the outlet with respect to the inlet openings. When the outlet opening faces the inlet opening, air speed increases to a double value of that when the outlet opening located in the same side of the inlet opening as given in table (2), and shown in figure (2).

3-Location of Outlet openings to Ground Level :

                It is found that the air speed at outlet opening increases when it is near to ground level as given in table (3), and as shown figure (3).

4-The Number of the Outlet Openings:

                The number of outlet openings-the surface area of each one of them equals 11Ï11 cm- affects air speed at outlet opening. The smaller of the number of outlet openings, the increase of air speed as given in table (4), and as shown in figure (4).

5-The area of the outlet openings:

                It was observed that the percentage of the wind speed increases by the increase of the area of outlet opening as given in table (5) and shown in figure (5).

6-The cross sectional-area of the air tunnel :

                It was observed that air speed at outlet openings increases when the cross area of air tunnel decreases as given in table (6), and as shown in figure (6).

7-The Angle of Wind Catcher’s Roof:

                Studying the different angles of wind catchers’ roof, several values of air speed at exit opening are recorded:

• ·The maximum value reaches 94% of the external wind speed when the angle of wind catcher’s roof equals to 30^O.
• · It Reaches 85% of the external wind speed when the angle of wind catcher’s roof equals 0^O (horizontal position).
• · It Reaches 57% of the external wind speed when the angle of wind catcher’s roof equals to 45°.
• · It reaches 30% of the external wind speed when the angle of wind catcher’s roof equals to 60°.

                It was found that the effect of the angle of wind catcher’s roof depends on two factors, the location of the outlet opening to the ground level, and the area of the outlet opening.

Table (1): Air speed and orientation of inlet opening

Table (2): Location of inlet/outlet openings and air speed

Table (3): Location of outlet opening to the ground level

Table (4): Number of outlet openings and air speed

Table (5): Air speed and area of outlet openings

Table (6): Air speed at outlet opening/and cross-area of air tunnel

Table (7): Air speed and the angle of wind catcher’s roof

Fig. (2): The effect of location of outlet openings according to face inlet opening

A-The location of the outlet opening:

                Air speed Increases at outlet openings when the outlet is near to the ground level, when the angle of wind catcher’s roof equals to 30^o, air speed at the outlet openings nearly equals the external wind speed. While when the outlet opening is located in the upper part, air speed at the outlet opening decreases to be just 80% of the external wind speed, as given in table (7-a), and as shown in figure (7-a).

B-The area of the outlet opening:

                Air speed at the outlet opening decreases as the area of outlet decreases, at the half area of outlet opening air speed records only 50 to 60% of external wind speed, as given in table (7-b), and as shown in figure (7-b).

                The table (7-c) was summarized the three factors; the angle of wind catcher roof, the location of outlet openings and the area of outlet openings.

Table (7-a): The effect of the location of outlet opening according to ground level with the angle of wind catcher roof in the case of complete outlet openings

Table (7-b): Average air speed, area of outlet, and the angle of wind catcher’s roof

Table (7-c): Air speed, outlet location, area of outlet, and the angle of wind catcher’s roof

CONCLUSIONS:

                From the above study, it can be concluded that the effects of the geometrical characteristics of wind catchers on the air speed at outlet opening, takes the following forms :

• · When the long axial of wind catcher’s inlet opening is perpendicular to wind direction.
• ·When the outlet opening faces the inlet opening.
• ·When having fewer number of the outlet openings.
• ·When the surface area the outlet opening increases.
• · When the cross area of air tunnel decreases.
• · When the angle of wind catcher’s roof equals to 30^o.
• ·When the outlet opening is located near of ground level.

RECOMMENDATIONS:

                Aerodynamic studies should be encouraged to reach the thermal comfort in the indoor environment to reduce the loads on energy used in air conditioning and artificial ventilations.

                Future studies should be carried out to investigate the performance of real models similar to the models studied in this paper.

REFERENCES:

1-Bahadori, M., Viability of Wind Towers in achieving Summer Comfort in the Hot Arid Regions, Brighton, Elservier Science Ltd, 2000.

2-Elmualim, A., Dynamic Modeling of a Windcatcher/Tower for Natural Ventilation, Building Service Engineering, Vol. 27, No. 3, UK, 2006.

3-Elmualim, A., Modeling of Windcatcher for Natural Ventilation, National Renewable Energy Laboratory, Denver, Colorado. USA. 2004.

4-Fathy, H., Natural Energy and Vernacular Architecture, Chicago Press, 1986.

5-Givoni, Man, Climate and Architecture, Elsevier Publishing, 1969.

6-Harris, D., Web, R., Wind Towers' Old Technology to solve a New Problem', 17 th.  AIVC, Gothernburg, Sweden,1996.

7-Koenigsberger, Ingersoll, Mayhew, Szokolay, Manual of Tropical Housing and Building, Longman Group Limited, London, 1974.