Night Ventilation
Source: DeKay, M., Brown, G.Z. 2014. Sun, Wind & Light Architectural Design Strategies. Hoboken, NJ. WILEY.
(Nikolaos Giannoulas)
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In hot humid climate one of the most crucial considerations is the night ventilation. Through the use of tree lines and ground slopes the air must be guided, especially on night hours, when humidity can reach its highest level, in order to cool both the ground and the buildings. Having that in mind, the buildings must be placed in lots and the courtyards must be wide in order to achieve the goal of ventilation.
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Human thermal comfort
Humans are comfortable only within a very narrow range of conditions. Our body temperature is about 37°C, despite the fact that the body generates heat even while at rest: we must lose heat at the same rate it is produced and gain heat at the same rate it is lost.
The main factors influencing both physical and psychological human comfort are:
▪ temperature ▪ humidity
▪ air movement (breeze or draught)
▪ exposure to radiant heat sources
▪ exposure to cool surfaces to radiate, or conduct to, for cooling.
Humans are comfortable only within a very narrow range of conditions. Our body temperature is about 37°C, despite the fact that the body generates heat even while at rest: we must lose heat at the same rate it is produced and gain heat at the same rate it is lost.
The main factors influencing both physical and psychological human comfort are:
▪ temperature ▪ humidity
▪ air movement (breeze or draught)
▪ exposure to radiant heat sources
▪ exposure to cool surfaces to radiate, or conduct to, for cooling.
http://www.yourhome.gov.au/passive-design/shading
Urban density for wind flow
The importance of density in an urban pattern is highly considerable. Depending on the streets width and the buildings height, we decide to allow or not the amounts of air that flow in the city. Therefore, determined by the strategy, we maximize or minimize the flow in order to achieve cooling or protection from undesirable winds.
The most essential factor that influences the wind velocity, when parallel to main streets, is the width of that roads and the wind-ward face of the buildings in height and width. A way to calculate the wind velocity is by finding the blockage ratio for buildings and streets organizations which is defined as:
Rb= (W x H) / (W+L) 2 where W is the width of the building
L is the width of the street
H is the height of the building
The importance of density in an urban pattern is highly considerable. Depending on the streets width and the buildings height, we decide to allow or not the amounts of air that flow in the city. Therefore, determined by the strategy, we maximize or minimize the flow in order to achieve cooling or protection from undesirable winds.
The most essential factor that influences the wind velocity, when parallel to main streets, is the width of that roads and the wind-ward face of the buildings in height and width. A way to calculate the wind velocity is by finding the blockage ratio for buildings and streets organizations which is defined as:
Rb= (W x H) / (W+L) 2 where W is the width of the building
L is the width of the street
H is the height of the building
![Picture](/uploads/6/9/0/4/69048233/5228364_orig.jpg)
-The graph predicts average wind speed in streets as a fraction of prevailing unobstructed speed. The graph assumes regular building layout, buildings that fill the block, forming a continuous street wall on the windward side, and wind perpendicular to the block face and parallel to the major streets. (Sun,wind,light p.223)
In hot and humid climates, it is important to take advantage of the cooling breezes for the removing of the excess heat from the streets, and thus to reduce the solar gain.
One way to achieve the removal of hot air of the urban environment is by creating converging ventilation corridors. Through that strategy, the cooler air is entering from upslope and outlying areas, and through avenues and green corridors, to the urban zone. In that way, the hot polluted air is rising forced by the cooler.
Plantation, condensed as in parks or along the streets is necessary, because plants have the property of cooling by shading and by evaporating.
For the cooling of the buildings through the access of them to breezes, the designing have to include wider distances amongst them.
For the cooling of the spaces between buildings and therefore the natural ventilation of them, the designer should take advantage breezy or calm streets. The configuration and orientation of streets and buildings promotes or retards air movement.
(T.M)
One way to achieve the removal of hot air of the urban environment is by creating converging ventilation corridors. Through that strategy, the cooler air is entering from upslope and outlying areas, and through avenues and green corridors, to the urban zone. In that way, the hot polluted air is rising forced by the cooler.
Plantation, condensed as in parks or along the streets is necessary, because plants have the property of cooling by shading and by evaporating.
For the cooling of the buildings through the access of them to breezes, the designing have to include wider distances amongst them.
For the cooling of the spaces between buildings and therefore the natural ventilation of them, the designer should take advantage breezy or calm streets. The configuration and orientation of streets and buildings promotes or retards air movement.
(T.M)