Monday, May 14, 2012

04b - Good ventilation habits

To be comfortable a building with insulation and good ventilation still depends on the participation of its occupants.
Walls that are built with earth and clay based materials, such as cob, mud bricks or rammed earth, absorb and release heat at a much slower rate than walls built with reeds, concrete blocks or corrugated iron sheets. This is called high thermal capacity and thermal inertia.

We can and should use this ability to retain heat to control the warmth or coolness inside a dwelling. And this happens when the dwelling occupants adopt simple practices that can contribute in a big way to the comfort level within the building. 

In warm weather
We want the building to be cool during warm and hot weather. But the air will only be cooler after sunset. When the night air starts to cool off we want to open the intake air vents close to the floor and the exhaust air vents close to the ceiling/roof. This will let the cool night air in and, or at a minimum, will let air circulate due to the induced stack effect (or chimney effect).
At night this cooler air circulation will help cool off the walls and release any excess humidity that may have accumulated during the day. This cooling effect is, in reality, the release of heat accumulated in the walls during the day. And so air circulation inside the dwelling will release excess heat and humidity.

In the daytime we want to preserve this coolness accumulated during the cool hours of the night. To do this we close all air intake vents to stop the hot outside air from entering the building.
During the day the outside of the walls could be exposed to direct sunlight and absorb a lot of heat. This will not help us keep the dwelling cool during the day. During hot sunny days we should try to keep the sun away from the building walls. Wide roof overhangs, the shade of trees or other shading solutions are the best approach.
In cold weather
During cold weather we want to do exactly the opposite to what we do during hot weather. We want warm air to enter the building during the day and at night, or when it is cold, we do not want this warm air to get out of our warm dwelling.
To warm up the walls we want to open the intake air vents during the day. We also open the exhaust air vents to create good air circulation. We want to make sure that the air going into the building is as warm as possible. We want the air from the sunny side of the dwelling.

When the sun starts to go down and the temperature starts to drop we want to close the intake and the exhaust air vents to keep the warm air and the warmth accumulated in the walls to stay inside. 
An insulated and ventilated building that is built with earth based materials will maintain most of its warmth until the sun comes up again. We are still dependent on the weather, but we can take advantage of the benefits that nature provides.
These good practices are simple and will contribute the physical comfort we can obtain in an insulated building with control over its ventilation.

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