Here are the results of our experiment:
When the termometers had been under the dry clay over six minutes, the temperature went up from 36° to 38.5° C. Under the wet clay, it dropped to 31° after the first minute and then started to rise after three minutes. The temperature under both concrete tiles increased, but less so for the wet one.
Wet clay did have a cooling effect, dropping the temperature by 5° in one minute. We believe the temperature started to rise again because the water in the clay had mostly evaporated. We could tell this by touching the clay.
The concrete did not have much of a cooling effect. We believe this is because it did not absorb much water. There was some water on the surface of the concrete tile, but this evaporated quickly.
We remembered that when we put the clay in water there were air bubbles coming out of it. There were no bubbles coming out of the concrete. We think that the clay is more porous. It has more little spaces that held air, and then water. With more water in the clay, there was more to evaporate and a greater cooling effect.
It is interesting that in Malaysia and other tropical countries the traditional clay tile roofs have largely been replaced by other roofing materials, including concrete. Maybe these are easier and cheaper to manufacture, but the beneficial cooling effects of clay have been lost.
We could try
- keeping the clay tile wet over a longer period of time and see how that effects temperature.
- doing the experiment at night when there is no direct sun on the tiles.
- doing the experiment on a cloudy day.
- checking the relative humidity and seeing how the evaporative cooling effect varies depending on humidity.
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