Post date: Nov 16, 2013 1:45:02 PM
Keeping cool at night. It appears that my first hypothesis about hot bedrooms in Granada was not valid. The temperature just under the roof is not significantly warmer than the temperature at bed level.
So, how to keep cool?
Let's go back to the beginning. These colonial houses are built of adobe or (more recently) concrete. The masonry walls store a lot of heat. The traditional method (before electricity) of staying comfortable is to open the house during the night, when the outside air is cooler, and close it up mid- or late-morning when the air temperature rises.
This technique works well - as long as the air moves through the room. But modern building techniques have reduce the air flow - partly because having air flowing under or through the roof also means having insects, bats, and birds in your rooms. And most colonial houses have a floor plan that does not allow through ventilation. Two walls of most bedrooms separate rooms and have no windows. A third wall borders the neighboring house and has no window. A room with openings on only one side does not naturally ventilate well.
So we use fans to move the air. But we often install ceiling fans, which move the air within the room, but do not exchange room air with outside air. The moving air feels cooler, but does not make the walls of the room cooler. I notice that when I walk in the 'breezeway' between rooms, the air feels cooler than air inside the bedrooms. So I measured air temperatures last night. The temperature outside was 2.5 degrees Celsius cooler than in the bedroom (or 4.5 F degrees) at 10pm. I checked again in the morning, and the temperature difference was still 2 C degrees, even with the ceiling fan running all night. The outside air temperature had dropped less than 2 Celsius degrees over night.
We need to replace the air inside the room with (cooler) air from outside the room. A ceiling fan cannot do this. A fan in a window or a floor fan blowing (either out or in) a window will exchange the air. Another method is to turn the room into a chimney by adding a large roof vent. I know this works, because our house in Seattle is a large chimney, with air from the cellar moving up through the first floor and out the second floor windows.
In contrast to bedrooms, the Sala (living room) is built across the street side of the house with doors that open to the street and an opening to the garden. This area gets good through ventilation.
There will be times when we don't want the air movement. I colder seasons we need to either prevent cold air from entering (by closing the cellar door, for example) or preventing warm air from leaving (by closing the upstairs windows). Closing a roof vent will be hard because the roof is 12 to 15 feet above the floor. But we can close the door and windows of the bedroom.
I now need to find a house built like this in Nicaragua, or find a bunch of money to build one and see if it works!
Discovery!
I found a good example, in Casa Carlota. The two bathrooms are stacked vertically. Above the showers is an air shaft - the same size as the shower - which draws the damp air from the bathroom up and out. The air shaft also serves as a skylight, making the bathrooms bright (whereas many are dark and dank).
In this case the water storage tank is mounted atop the air shaft, giving plenty of water pressure without need for an electric water pump. Each bathroom is separated from the adjoining bedroom by a closet space, removing the need for a privacy door. This encourages natural ventilation through the bedroom, closet, and bath. No electric fan is needed. This particular property is only 15' (5 meters) wide but about 75' deep. Because the bedrooms are at the rear of the property they are very quiet.