Monday, July 5, 2010
A Truly Green Device
Since residential energy use comprises about 26% of all the energy used in the state of Florida and in south Florida, about 35% of this annual residential energy expenditure is for cooling the home during Florida's 5- to 7-month-long summer, I started to look for a new device that I could use to reduce the energy consumption of our home. I got ideas from an AC guy and I learned a lot about insulation and glass shading co-efficients and such, but I found what I was looking for in my back yard. A tree!
Glass windows and doors can account for between 30 and 60% of a building's total heat gain in the summer. As much as 270 Btu’s of direct and diffused solar radiation can enter a home or building through each square foot of glass on the east and west sides. For example, direct sunlight on a clear glass window on a west wall can require more than one ton of air conditioning to remove the heat gained from this source alone. This is more than eight times the heat gain caused by conduction and infiltration. We don’t use clear glass anymore, but you can get the point.
So what would be a more aesthetically pleasing way to shade this window than a tree. Naturally this assumes that this doesn’t place a tree between your window and the Gulf of Mexico. Placing a tree to shade a home involves consideration of the angle of the sun's rays in summer and winter, mature tree height and structure height. In general, the target areas for shading during Florida's warm months are the walls on western, eastern and southern exposures, in that order. Though an exposure facing due south receives little direct sun on June 21, by August the sun will be lower and as we Floridians know, it’s real hot in August.
It’s possible to achieve as much as a 30% reduction in cooling and heating costs through careful landscape planning. Landscaping can reduce direct sun from striking and heating up building surfaces. Trees can prevent reflected light from carrying heat into a house from the ground or other surfaces. Shading the air conditioner can also improve its efficiency by as much as10 percent. Trees can shade a roof and walls from the hot summer sun. They can also create a cooler atmosphere around the home, cooling sidewalks and driveway that normally reflect heat.
So again it’s possible to trump the use of technical gadgets with good design and common sense! Go plant a tree!