Did you ever walk bare foot over asphalt that is so hot you are sure getting blisters and then step onto a patch of nice cool grass? Why is the grass so cool? Well, the answer is that plants work hard to stay cool; in fact their primary work is not to grow and produce fruit and seed but to stay cool or in another way of putting it: to not overheat. That is the unrecognized function of the plant kingdom - to keep this plant from turning into one large oven (at least around the equatorial parts). The loss of greenery is what has created most deserts and explains why they are expanding. We bust up the natural ecology and turn it into farm land. We gradually exhaust "farm land" and turn it over to livestock grazing until it is gradually converted into desert. The bread basket of the ancient world is now the desert land we refer to as the Middle East and North Africa.

In a desert you will find a natural temperature swing (day high to night low) of over 100F as sand, rock and dry earth as direct exposure to the midday sun is followed by a chilling clear night sky. But the urban Grey Zone? of concrete, asphalt and conventional roofs are also a desert that produce the urban Heat Island effect. Plants cannot tolerate such large temperature change; the roots alternately bake and then chill. On the other hand the ground temperature in a forest changes little from day to night. It remains at about the average wet bulb temperature. The sun never reaches the ground level. There are three stories of plant leaf canopy to intercept the solar radiation.

Only a tiny fraction of solar radiation is used for plant growth; all of the rest of the radiant energy (that's typically about 99%) would become except that the leaf has the amazingly powerful Phyto Mechanism? (a mechanism) of transpiration to use to release this excess energy and prevent the Leaf Temperature from rising above a metabolism controlled maximum. This transpiration cooling is able to convert biochemical energy into the latent energy of water vapor that a leaf canopy will breathe out. This moisture is absorbed by the air surrounding the leaf, so long as the air is not saturated, this transpired moisture is produced at a rate that is nearly exactly proportionate to the radiation that is incident on the leaf surface. This will typically amount to 1 to 2 pounds of water transpired per square foot of leaf surface per day.

The higher number would be typical of a Texas summer day and the lower number a gray Chicago winter sky. Going far to the north affect these numbers quite as much as you would expect. At the peak hour of midday you could get a third of a pound of water vapor given off by each square foot of leaf surface. In a closed atmosphere greenhouse of 1000 square feet that is filled with a mature crop you would have a ton of vapor produced per day from the plants. The plants will be perfectly comfortable as long as they have access to that much water to take up from their roots.

This capacity of living plants to transform sensible into non sensible latent molecular energy of water vapor is an order of magnitude more efficient than any mechanical process even the best or technology can only produce a fraction of the output from a given input energy. Conventional fuel powered mechanical process can use energy more intensively whereas the solar resources are distributed and limited to the energy available from the solar radiative intensity available from the sun, which is typically 3 to 8 Kilowatts per day per square meter.

The Sola Roof works by supplying Cooling Liquid over the topside of the Inner Cover of the Sola Roof greenhouse. This water based liquid will be supplied at say 60F. The water cooled skin of the greenhouse will attract and condense the transpired moisture according to the temperature difference between the skin and the air temperature in the greenhouse. Here is a typical reading: the plant leaf temperature is 74F - the air temperature around the leaf canopy is 80F - the temperature of the air near the water cooled glazing is 60F the temperature of the cooling water is 60F. The relative humidity (a delta T of 20F) is maintained at about 50%.

All of the energy that is given up as latent energy of transpiration becomes sensible thermal energy when this moisture condenses on the cooled roof and walls of the greenhouse. These surfaces will be streaming wet with condensation (an anti-drip coating on the plastic is needed or it will be raining under this roof). The Inner Cover is composed of thin Sola Fabric sheet material which transfers this thermal energy to the turbulent Liquid Film flow. On a winter day the thermal heat can accumulate in the Liquid Thermal Mass system (which is tons of water) and gradually raise the temperature a couple of degrees during one day. At night this low temperature energy is used (and dissipated) to maintain the roof and wall Cavity Space at that same temperature (60 to 62F) by making dynamic Liquid Insulation? (bubbles) that fill the building envelope cavity spaces, and give up the low grade heat very slowly.

In the summer the heat that is absorbed by the Cooling Liquid is dissipated to a heat sink such a cold ground water, lake water or ocean water. In the tropics we will additionally resort to multiple leaf canopies, one of which may be over the roof top. This creates a cool shade canopy and rejects the largest component of the solar heat gain before it can reach the climate controlled space. Another advantage of this system is the possible use of cold ocean water (see Cold Water Resources) as the primary cooling water system on the inner covering layer of the greenhouse space while the interior produces transpired moisture from plants that will form condensate at a rate that is 5x that which is possible using the best available thermal/mechanical solar distillation. Again - plants to the rescue! Look out California - the new California Cold Rush is at hand! This is the discovery of unlimited off-shore energy can eliminate 25,000 Mega Watts of peak power demand!

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December 2017


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