Monday, April 14, 2014

Green Roofs Can Cool Cities, Learning From an Endurocap

Green roofs really do cool buildings through plant transpiration and I proved this yesterday to myself by example with an inexpensive but highly effective cap called the Mission Enduracool cap.
My Mission Enduracool cap teaches me about green roof cooling effects.
Green roofs and Mission Endurocool cool based upon the same principal as air conditioners  - that of heat being absorbed into a liquid and the liquid transitioning from a liquid state to a gaseous state.

On green roofs and across my cooling cap the liquid is water.  Plants transpire water out of their stomata during the photosynthesis processes and I sweat water and salts.  Air conditioners usually evaporate a refrigerant like freon, but all there cooling processes are based around heat being absorbed into a liquid and the resulting gaseous phase that takes place with heat adsorption.

According to the US Geological Service (USGS) about ten percent of the humidity in the air is due to plant's transpiration.  That is a lot of water!

So because I cycle most everywhere I go, my head (just like a building's rooftop) gets hot from both metabolism and from solar gain.  I always wear a helmet but that piece of safety equipment does not do much to cool except provide a bit of filtered shade.

We have talked of green roofs and their insulation value before, several times in this blog, but cooling offers additional benefits over insulation.  Cooling actually removes heat whereas insulation just blocks heat.

My first bicycle trip out with the cooling cap was to Publix, our local grocery store.  Per the cap's instruction sheet, I soaked it  in water and proceeded to wring most of the water out, leaving the cloth slightly damp.  Snapping it over my bald head I took off down the road after turning my bike's safety lights on.  The cooling effect was immediately noticeable and amazing!

Green roof plants and their transpiration right away popped into my mind.  "Hey!  This is what is happening to a building with a green roof as plants loose water to the atmosphere through evaporation", I told myself.

There are many web resources pointing out the benefits of green roofs, and their cooling potential for the urban core.

For me the maxim, 'seeing is believing' rings so true.  I learn mostly from experience.  The cooling cap taught me yesterday about the power of plants on a roof and cooling the cities.

Riding my bike I felt as if I had an air conditioner in my cycle helmet.

Sometimes short, simple life experiences can teach us more than an entire college course.  Green roofs can cool cities, I knew this before but I am so much more convinced now.

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