4.1 Experiment in Ghardaia, Algeria
The main points:
• With controlled ventilation (night ventilation only) full advantage can be taken of the lower night temperatures.
• The ventilation during nighttime has only a minor effect on the daytime temperature.
• The gypsum construction keeps the temperature at a very even level.
Source: Research project by Lund University, (LCHS) and CNERIB, Algeria, carried out by Hans Rosenlund and Djamel Ouahrani. [ 101, 157 ]
4.1.1 Geographical location and climatic characteristics
Ghardaia lies in an extremely hot and arid region in the desert of Algeria, 600 km from the coast, at an altitude of 500 m above sea level and a latitude of 31.5o North.
The climate is hot and dry in the summer with temperatures variation between a maximum of around 45°C and a minimum of 20°C, thus giving a large diurnal temperature swing. Winter temperatures vary between a maximum of 24°C and a minimum of 0°C. Solar radiation is intense throughout the year with a maximum of 700 W in winter and 1000 W in summer, measured on the horizontal surface.
4.1.2 The project
In 1981, an experimental building was erected in Ghardaia. The purpose of the building was to measure the influence of different parameters on the indoor climate. The building contains two identical rooms, where one room can be manipulated while the other is kept as reference. A series of tests was conducted.
The building has walls of gypsum blocks, 40 cm thick; a roof of gypsum mini-vaults, 8 cm thick, resting on concrete beams and covered with 5 cm thick concrete plaster; and a concrete floor resting on the ground.
A characteristic feature of the building is the ventilation box consisting of a raised roof with an upper window.
4.1.3 Influence of night ventilation
One experiment was to monitor the influence of night ventilation. In the reference room the window and roof ventilator were kept closed, whereas in the experimental room they were opened during nighttime. The effect of the night ventilation is clearly seen as a remarkable drop in temperature when the window was open. During the night the indoor temperature approaches the outdoor one. This means that the number of air changes per hour is important.
4.1.4 Performance of gypsum
During the daytime the temperatures in both rooms vary only slightly, which means that with this type of construction the cool of the night can hardly be maintained during the next day. The temperature is remarkably even throughout the day. This can be explained by the properties of the massive gypsum construction, which has medium thermal storage capacity but rather good thermal insulation value. Therefore, the exchange of heat between the air and the surface is small and, when the windows are closed, the indoor temperature is even. This structure performs in a similar way to the mud house documented in chapter 4.4.
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