The thermal effect of humidity on the comfort

The thermal effect of humidity on the comfort of sedentary persons is small, that is, comfort is maintained over a wide range of humidity conditions. In winter, the body feels no discomfort over a range of relative humidity (RH) from 50% down to 20%. In summer, the tolerance range extends even higher, up to 60% RH when the temperature is 24°C; above that, the skin feels sweaty. Nevertheless, some types of industrial applications, such as textile manufacturing, optical lens grinding, and food storage, maintain an RH above 60% because of equipment, manufacturing processes, or product storage requirements. At the other extreme, certain pharmaceutical products, plywood cold pressing, and some other processes require an RH below 20%. In hot dry climate in southern Algeria, compact settlements (known as Ksur, plural of Ksar) have evolved over time to make the best use of locally available materials and resources to provide comfortable shelter for populations inhabiting even the most extreme climates of the world with minimum promotion info consumption. The well known Ksur in the desert of Algeria are M\'zab Ksur (Ghardaia, Melika, Beni Izgen, Bounoura and El Atteuf), the Ksar of Ouargla city, the Ksur of Djanet city (El-Mihan, Azelouaz and Adjahil) located in the Wilaya of Illizi and the Ksar of Knadsa in the wilaya of Bechar (Bouchair, 2013). These settlements were adapted to give shelter for privacy and for thermal comfort (Bouchair and Dupagne, 2003). Privacy includes cultural, social, psychological and religious elements. For thermal comfort, the building must act as a barrier, transforming the outdoor climate to conditions suitable for indoor activities. Numerous studies have been conducted on this topic and several have recognized lessons from the past and demonstrated the usefulness of passive tools in achieving thermal comfort of inhabitants such as wind towers (Bahadori, 1985), storage of coolness in adobe walls (Bahadori, 1985) and solar chimneys (Bouchair, 1994). Unfortunately, modern urban transformations and development have overturned the microclimatic conditions of the settlements because they are not adapted to climatic constraints and have, consequently, mitigated the well being and thermal comfort of inhabitants. This is mainly due to the use of industrialized non-adapted material with low thermal inertia, low albedo, and the use of wide streets and open spaces. An in depth study was made by Boukhabla et al. (2012) to show the effect of urban morphology on urban heat island in the city of Biskra in southern Algeria where the negative implications of unplanned modern urban transformation upon the warming up of the city were shown. This study concerns the city of Ouargla located in the south-east of Algeria. It is one of the Saharan cities which are characterized by hot and dry climate. Ouargla is a true capital of the desert, located at 190km east of the city of Ghardaia, 388km south of the city of Biskra and 160km south-east of the city of Touggourt. It is located between 28° and 32° north latitude and the meridians 4° and 8° East (Figure 1). The hot desert or arid zone is characterized by high mean annual temperatures and low mean annual precipitation. The city of Ouargla is characterized by long periods of overheating and thermal discomfort is felt strongly. The climate of Ouargla is one of the hardest of the North Eastern Sahara. The average annual temperature is 23.44°C. The mean value of air temperature in July, the warmest month, is 35.7°C and for January, the coldest month, is 11.6°C (Table 1). The maximum temperature can exceed in certain cases 50°C under shelter. The average annual rainfall is very low; it is 52.3mm/year (Table 2). Sources of weather data can be obtained through national or regional meteorological stations (Meteorological station of Ouargla, Algeria). The city of Ourgla was originally a Ksar (traditional settlement) surrounded by a rampart provided with three gates each of which is oriented towards the tracks leading to the nearest cities such as Ghardaia, N\'goussa and El-Golea. These three tracks influenced to a large extent the formation of the settlement around the old market. Figure 2 shows the general plan and location of this Ksar in relation to the whole city of Ouargla. It remains in the memory of inhabitants a cultural and spiritual sanctuary. It continues to play the true function of city center of Ouargla, and the new modern expansions become simple specialized districts or suburbs.