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Building Technology
 
Cooling by evaporation
Would Evapo-Transpiration Strategy helps Cools Buildings in the Tropical Climate? Passive Cooling Concept in Tropical Living, Evaporative Cooling Strategy for Thermal Comfort, Micro Climate - the immediate "Filter" as design options...
Rajeh Salleh
Responses
 
Cooling by evaporation
I don't see why not. However the question we have to raise would be how to integrate such a function into the built form.

As demonstrated in a non-tropical situation, and as a temporary structure, the British Pavilion, Expo 1990, Seville, Nicholas Grimshaw Architects used a glass curtain wall with a continuous sheet of water on its front facade, a 50mm deep evaporating reservoir in its metal roof, and cargo containers as its rear facade, filled with water.

It was to me an excellent precedent for architecture of the tropics to assimilate, as the devices suceeded in lowering the internal temperature of the pavilion by about 5 degrees Celsius, a dramatic decrease that toes the difference between unbearable and comfortable.

Apart from the mentioned methods, the pavilion was also set within a shallow pool, which added to the effect of cooling by a water body.

The design has a philosophy that can easily be adapted to fit the tropical situation. However, evaporative cooling might not be very effective in certain tropical areas due to high humidity. The saturated air would not allow sufficient evaporative mass to escape the surface of the water to create any significant change in temperature. What do you think?
Zaihan Kariyani
Cooling by evaporation
I had an interesting experience with evaporative cooling in a open air restaurant. It uses a primitive form of evaporative cooling with a sprinkler system on its zinc roof. When the sprinkler is on, the place felt humid and hotter than when the sprinkler isn't on.

I tried to analyze the reason, and thought maybe it felt more humid because the water flowing down from the zinc roof formed a screen which trapped air inside the restaurant, not allowing any natural ventilation. Therefore, instead of cooling the space, it made it more uncomfortable.
Boo Chung Ang
Cooling by evaporation
In a world where the lack of quality water to drink is increasing is this wise?
Jorge Campos
Cooling by evaporation
In respond to ABC's experience of the open restaurant- the water sprinkled over the roof should have been collected into a gutter and not let poured down the roof edge. The heated water would just transfer its heat through wind blowing into the building. I am still looking for some models to the above concept applicable to Tropical Malaysian climate. I have surveyed Langkawi's taman padi - its the same effect with spraying the roof with water and let it drips down the roof edge - the inside temperature at 2.10pm is 33C - one degree lower than outside DBT with RH around 84%. One possibility would be shading the taman padi to reduce the radiant heat during the day but open it to the sky at night for cooling. Any comment?.
Rajeh Salleh
Cooling by evaporation
Lets make sure we know the difference between evapo-transpiration which relates to vegetation (trees and shrubs...) naturally adding moisture to the air, and evaporative cooling which relates to an intended and more controlled process of introducing moisture to the air (sprinklers, ponds,...). In general, as contributed earlier, adding moisture to the air is signiicant in dry weather conditions, maximum cooling achieved is limited by the wet-bulb depression (difference between DB and WB temperature). The more saturated (moist) the air the harder it becomes to add moisture via evaporation and the less beneficial. The only passive strategies that should be emphasized in humis weater seem to be shading and promoting for wind movement. Certainly, humid climates are the most challenging.
Iyad Alhalis
Cooling by evaporation
Relative to Peninsular Malaysian Climate- at certain time of the day - ie.between 1.30pm to 4.30pm - where the extreme heat were experienced - the humidity level would fall between 55%-65% - at this time evaporative cooling (passive means) could contribute to energy saving - by letting cool air passing through wetted screens into the building. Some mechanical fan needed to help when natural ventilation is dorman. States up north like Perlis and Kedah do experiences 3 to 4 months of dry period- they could benefit through the idea of evaporative cooling design techniques.
Rajeh Salleh
Cooling by evaporation
You should consider studying the green roof buildings, wich are truly an evapo-tranpiration strategy for cooling buildings.
In Tropical weather these roofs have some problems with managing run off water, keeping humidity off the structures and certainly, controling plant growth.
Non of these are imposible to manage, they just have to be considered.
What this strategy actually helps with is the hot tempetures that cities generate because of the lack of greeens.
Helga Ruiz Alvarez
Cooling by evaporation
Evaporative Cooling is effective, EVEN in Hot Humid Climates, but nos as effective as in dry climates. A simple prove is sweating in humans, it works. Ventilation is promoted as the main strategy for hot humid climates, but one of its purposes is to increase Evaporation Rate on humans skin.Spray water in your arm in a hot humid day and then blow on it, you will feel better. Evaporative cooling can be used in indirect ways cooling the building structure without increasing humidity levels. Wet bulb depression is a reference of Evaporative cooling potential. This can be for example 7 even as high as 10, 12, 14 degrees in the mid of the day in a hot humid location, and this can help to temperature reductions of 2, 5 or more degrees at indoors, depending on other conditions of the building. If evaporation works in humans in hot humid climates it works in buildings. If possible read "Roof cooling with Intermittent Water Sprays" article by John Yellot, look the discussions at the end, roof cooling with water was still effective in humid location like Florida, US.
I hope this give a better perspective to what is commonly misunderstood.
Claudio Diaz
Cooling by evaporation
If I recall correctly, a vertical fountain of falling water called a "sebil" is or was the traditional method in Egypt and elsewhere to cool indoors spaces.

Similarly, in a book by the Egyptian architect Hassan Fathy, there is an image of a large unglazed water pot set placed at a window, so that air passing over caused evaporation and thus cooled the air.

As regards the efficiency or otherwise of using evaporation to cool spaces, this is of course affected by the amount of humidity in the air.
Frank John Snelling
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