Monday, May 28, 2012

Naturally Air Conditioning a Room

(Thermodynamics - 101)

(Click on image to see full size)

My Study is an east facing room with bay windows on the second floor of an old building in Leslieville, Toronto, Ontario, Canada - a badly insulated wood frame house.

In the winter the light I get through those wonderful bay windows is essential to maintaining balance through the short, low-light days of winter - as I try to manage clinical depression without medication.

In the summer though, the room is a green house - good for the cactus plants that I husband in the bay window - but an impossible room to work in with out Air Conditioning. The house has central air conditioning, but the system is too small to make a difference in the morning, in this room.

Last year I noticed that the back of the house was a lot cooler in the morning than the East end of the house. I figured out that it's because at the back of the house there is an urban forest. There are seven 100 foot tall maple trees in a huge open area between the backs of the houses facing Jones Av and the backs of the houses fronting on Coady Av. The forest canopy keeps that Commons area at least 10 degrees cooler at all times of the day. In the morning - before the sun reaches it's zenith - the temperature remains close to that previous evening's low (depending on wind speed and direction).

This morning I set up a oscillating fan (not oscillating) into the north facing window of the bay window set. Next I cut an exact cardboard shape to fit between the circular housing of the fan and the square opening of the window (with all the sliding windows and the screen removed). The result is a high efficiency air evacuation system. 100 percent of the air being expelled through the window is flowing into the room through the doorway (no blow-back turbulence at the window). The doorway connects to a hallway which leads to the back kitchen door, where cool air from under the tree canopy is sucked into the house down the hall, and into my study.

I did this last year as well - but without all the efficiencies I've now perfected.  I've discovered that the small fan in the centre of the room that I added this morning is a *really* important component. With the addition of the small central fan - the room itself  becomes very efficient Heat Exchanger!

Last year I had the fan pointing *at* the window (screen and sliding windows in, less that 1 square foot of area for air expulsion (really inefficient, lots of counter-current turbulence). The cool air from under the tree canopy simply traveled straight across the room and out the window. The only heat exchange happened along a band of air - 7 feet high, conical in shape (I surmise), and 14 feet in length. Some turbulence along it's length created some heat exchange - but generally much of the cool air stayed in the core of the column and flowed directly out the window - never coming in contact with hotter air, and thus never affecting an exchange of energy.

Now, with a strong flow of air, and the small fan directing the column towards the corner of the room, the column becomes a thin sheet of air - which flows around the edge of the room - forced to change directions at least three times - once, as the two columns of air collide, and twice more at the corners of the room (dotted line in drawing).

The result of this set up has been magnificent!

The Bay windows on the left of the drawing face east - into the rising sun. In it's morning arch the sun's most intense point is about 10:00am (direct into window, combined with the least dampening from distance travelled through earth's atmosphere) - the room can easily reach 40°C. With this set up, at 11:45am the temperature of this room was 20°C. Outside temperature at 12 noon: 26°C.

Amazingly, while I was writing this up I had to put on a long-sleeved pull-over - it's too dam cold in here! :)


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