Tuesday, May 8, 2012

01 - Heat and humidity

The two main contributors to an unhealthy and uncomfortable dwelling are:
  • Heat (and lack of heat, cold)
  • Excessive humidity in the air
We have to try and control both factors in the simplest and most economical manner to obtain a more comfortable environment for the building occupants.

A human being can tolerate heat and humidity within some limits. What these limits are depends on each person's physical built, the amount of clothing one is wearing at any given moment, the wind conditions, and the humidity of the surrounding air.

If we ignore the effect of the wind and of the direct sunshine we can say that a person wearing a thin cotton blouse or a T-shirt will start feeling cold when the temperature drops below 20ºC (68ºF) and will start feeling hot when the temperature climbs above 25ºC (77ºF).

So, generally speaking, we feel cold when:

  • The air temperature drops
  • The humidity is high
  • The wind blows harder
  • We are wearing less clothing
And so, when it is cold, we want to:
  • Raise the temperature around us
  • Make the air dryer
  • Reduce our exposure to the wind
  • Wear more clothing
Similarly, we feel hot when:
  • The air temperature goes up
  • The humidity is high
  • The wind is not blowing
  • We are wearing more clothing
And so, when it is hot, we want to:
  • Lower the temperature around us
  • Make the air dryer
  • Increase our exposure to the wind
  • Wear less clothing
Some of these factors can be controlled in order to make us feel more comfortable, but not all of them can be controlled without the use of equipment that can be expensive.
Air temperature and humidity can be controlled with air conditioning equipment. Air circulation (the equivalent of wind) can be controlled with fans. And, in most cases, we can chose the amount of clothing we are wearing.
But all solutions based on equipment can be expensive and need electricity to operate, something not always available. And so we have to take advantage of simpler and often more efficient solutions.
Even though we cannot control the temperature and the humidity of the air outside, inside our dwellings we can:
  • control the inside air temperature - by taking advantage of the shade of surrounding trees, building shading surfaces, and using insulation on walls and roofs,
  • reduce the inside air humidity - by circulating the air inside the building to exhaust the humidity from the kitchen, from the bathroom and toilet, and the humidity released by the human body to avoid a buildup of the level of humidity in the air,
  • reduce the effect of the existing humidity - providing or increasing exposure to the prevailing wind and/or creating a natural air circulation of the inside air. The effect of this air circulation can be very pleasant and greatly improves the level of comfort inside the building.

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