by John Brouwer
"Can I have another bottle of your wine?" What the member probably doesn't realize is that my home brew is a side benefit of a natural cooling system which is reducing summer heat buildup.
Our co-op was designed to use passive solar heating. The passive solar works very well on those cold but sunny winter days when the sunshine heats our living room to 25+C and the furnace fan (gas off) circulates this warm air throughout the house at no cost to us, to our environment, or to global warming. Because the solar well connects into the basement the concrete walls and floor heat up and store this warmth. At night curtains are closed and the concrete radiates the stored heat to minimize gas use during the evening. Works well!
The problems start to occur around June when this same passive solar continues to work and heats the house to 35+C. The concrete retains the heat and ensures that the house never cools down at night. The design breaks down because the architect didn't consider how to deal with the summer heat, except for solar blinds which have now all disintegrated.
The original design did not incorporate the principles of passive cooling. The basic approach is to use some type of barrier to keep the sunlight out of the windows in the summer. The original blinds were one approach but the longterm approach is to use plant shading. Trees and vines (on trellises) are used to shade the south walls, windows, and asphalt in the summer and as these leaves drop in the fall they allow sunlight to heat the units and help clear the pavement in the winter.
The longterm solution is to use judicious placement of trees and vines to provide the natural shade to promote cooling. "The best time to plant a tree is 20 years ago (when our co-op was built), the second best time is now." Our site design doesn't have trees and vines to facilitate summer cooling. For example, the oak trees along the road are on the north side of the units leaving the southern sides fully exposed to the sun. As the solar blinds are now all worn out, in most cases there is no shading barrier to summer sunlight. We can correct this design oversite by judicious planting of trees now, but of course, something has to be done in the interim.
Natural cooling advocates stress the need to use fast-growing vines growing over some type of trellis extending over the south window and walls to provide fast summer shading. On our unit we planted a grape vine on a trellis over our back deck, which provides shade to the window as well as the deck. It took 4-5 years for the grape to cover the window area and now ten years later it covers the whole deck and extends to the neighbours' yards on both sides. In our case this is supplemented with a cherry tree extending beyond the trellis so that we have good summer shade. The grape and cherry have the additional benefit of providing fresh fruit and a source of the afore-mentioned wine.
Although natural cooling is hardly covered in the building design literature, a google search does uncover programs and studies which use trees for cooling. Sacramento (an extreme climate) provides free 5-6' trees to residents along with urban forester consultation to ensure the trees are placed to promote maximum cooling. Chicago, Boston, and New Westminster, B.C. both promote tree planting for cooling but without the free trees.
Studies have shown that a mature deciduous tree can transpire up to 100 gallons of water per day. That transpiration absorbs a huge amount of energy and is equivalent to around 10 room-size air conditioners running 20 hours per day. Of course, that tree's cooling isn't inside a house but the studies have found that trees will reduce the cooling demand by 30-50%. A supplementary cooling strategy is to plant trees to shade heat absorbing pavement and sidewalks as these surfaces are major heat contributors.
On a national scale planting shade trees could reduce the need for power plants. Data from California shows that 50 million shade trees planted in strategic, energy-saving locations could eliminate its need for seven 100-megawatt power plants. The American Forestry Association estimates that 100 million new trees would absorb 18 million tons of carbon dioxide and cut US air conditioning costs by $4 billion annually.
A natural cooling strategy would use mechanical shading for the short-term – awnings, blinds, glass coatings. It would use vines and trellises to provide natural shading over the intermediate term and trees for the really long term. In our case, we would need to take into account that the original layout probably didn't consider shade tree placement in the location of sewers, water and gas supplies, and parking. These would have to be identified before vine and tree planting can be planned and in most cases one would have to choose varieties having tap root systems which won't extend into sewers or be damaged when gas or water mains have to be serviced.
Imagine a vineyard growing at the second floor level on trellises above our south-facing solar windows and sugar maple and nut trees proving shade and habitat for birds, small mammals, and children. Our fall fair could include a cornucopia of grape crushing, wine fermentation, and nut gathering while sugar maple beer and wine flow freely through the evening, all as a side benefit to natural cooling. The solution to global warming involves more partying!