Air

Post date: Nov 10, 2013 2:03:16 PM

In a hot, humid climate such as Granada’s, air movement is your friend. The colonial architecture here, however, seems to block air movement. To me this is a bit strange, because the colonialists were Spaniards, who had inherited some of the north-african moorish architecture.

Colonial houses have a masonry wall adjoining the sidewalk. To admit air it has door(s) with window(s). While this lets in breeze, it also admits all the street noise. The plan shows our rented house, with the street entry at the bottom, large front room for dining and TV, kitchen and sitting area behind the front room rear wall, pool (in place of a garden) and two bedrooms, each with bath. At the rear is a utility area.From the several houses I have seen, the cross-section of a bedroom has one masonry wall with a door (and probably also window) to the courtyard, a parallel masonry wall that abuts the neighboring house (and therefore no window), a tile floor, and a sloping roof line with no ceiling.

The lower edge of the roof line in the bedroom might be ten feet above the floor, while the upper edge 14 or 15 feet from the floor. The sun beats on this roof all day, making the air in the upper regions of the bedroom hot. Because of the open door (ours are never closed) the lower part of the room is roughly the same temperature as the outdoors.

The sleepy resident heads for bed and promptly turns on a ceiling fan, which then blows the hot air onto the beds. While the air movement itself helps the sleeper feel cooler, it seems strange to trap all this hot air in the upper reaches of the bedroom. Because the bedrooms are adjacent to the neighboring property, there is no way to have cross-ventilation.

I would propose to ventilate the peak of the roof. How I could do this without drowning in a rainstorm is still a good question, since most eaves overhang the walls by about 7 feet - both inside the houses and over the sidewalks. But the natural ventilation provided by the chimney effect of an open vent at the top of the roof should move cool air from the garden that is within most houses through the bedroom. However, the vent must be big in order to be effective. This means at least 12" across for a room. (The vents on pit toilets in US national forests are about 10" diameter and the 'room' is only about eight feet square.) And the ventilator must be able to handle strong wind-blown rain.

Why is this preferable to a ceiling fan? First the fan costs money to install and operate. Electricity here on the last bill cost US$0.30/kwh (kilowatt hour). We have fans in every space: over the dining table, above the TV, in the kitchen, in the sitting area by the kitchen, in each bedroom, and in the sitting area in the back of the garden. Seven, so far. (No ventilation in the bathrooms - the opposite of North American practice.)

A typical fan may draw 75 watts. If it runs for ten hours each night, electricity would cost US$6.75 each month, per fan, or 22 cents per night. Not bad, but much less than air conditioning.

Now I need to find a way to let the hot air out of the roof peak without letting in birds, insects, and torrential rains. Good luck!

...

Just measured the temperature under the roof vs. the temperature mid-way up the wall. Only 0.3 C difference. This roof structure has a foil-faced insulation between the visible ceiling (of 1" diameter reed rods) and the clay roof tiles. I'll need to check the temperature difference in a clearly uninsulated roof. Most newer roofs here have galvanized, corrugated steel sheet metal between the rafters (and/or ceiling) and the clay roof tiles. The clay tiles themselves are good insulators and the corrugated sheet metal aids ventilation beneath the tiles by providing rising channels for the heated air. It may be that there is sufficient air gaps around the loosely laid roof tiles to allow hot air from under the tiles to escape. This would explain the reasonable temperatures at the peak of the ceiling.

Even if the air inside upper reaches of the room is not hot, added air movement gained by a roof ventilator will provide similar comfort to an electric ceiling fan without the expense of electricity.

The communities called 'Los Pueblos Blancos' are along the north-south ridge just east of the Pacific coast. This area is windy - so much so that there are several wind turbine farms. Houses there can use the breezes for cooling.

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