I couldn't agree more with what Ross said both from a technical as well as politcal point of view.
Technically what he describes is what we have here in Brasilia: collectors are placed in the roof. The botton of the tank is higher than the top of the collectors. The cold water tank it still higher. It is common practice to have a 7% minimum slope in the pipe that goes from the top of the panel to the tank. It is also said that the hot pipe should not be longer than 5 meters. (this is not always observerd) I've never seen any prescription maximum lenght of the cold pipe. Now, as to the way we are spending energy, I have no other words but folly, arrogance and prepotency. The big powers tend to be arrogant and prepotent. Third world (like us) are just fool. A vast proportion of Brasil is between the 23.5 degrees South and 4 degrees North. On the average this country has about 5 hours of direct sunlight per day. Some cities (in the Northeast part of the country) have move than 8 hours! In spite of that we are bringing hydroelectric power from 2,000 or 3,000 kilometer away! New Buildings in Brasilia are build as if we were living in the polar region. They have a lot of glass, they are completely tight. Now we have to pump cold air in, hot air out night and day, non-stop. Since the sun is so strong (in Brasilia you can have several weeks without a single cloud) and the walls and windows have so much glass either you spend more energy cooling it down or you put blinds and other protections everywhere. So life goes. We spend energy as if we could have it forever. And as if this way of life was not anti-life. Well, sorry for being so long. I just wanted to agree with Ross. - fernando Ross McCluney wrote: > The Shaws wrote: > > > I have always wondered why solar panels are put on a roof. > > Up there, they are higher than the hot water tank (well, > > they are in the UK, where the temperature gets down a bit, > > and the storage tank is indoors), and so temperature > > sensors, one way valves and pumps have to be involved. It > > seems more logical (or am I missing something) to put the > > panels on ground level, or at least below the height of the > > hot water storage tank - the thermal syphon then does all > > the work with no moving parts. > > South Florida had a lot of experience with thermosiphon solar systems > earlier in this century. The collector was indeed placed on the roof to > avoid vandalism, to get better solar access, and to keep them out of the > yard. The tank was placed in the attic, higher than the collector so > that the hot water would indeed thermosipon into the tank during sunny > days. At night the hot water would remain in the tank, the highest > point, and the collector would get cold and radiate heat away, but since > there was little heat in the collector and the cold water had no way of > displacing the hot water in the insulated tank above, the system worked > well with no moving parts and no need for auxiliary electricity. > (Except during the few prolonged periods without sunshine.) > > These thermosiphon systems only worked in warm climate areas, because a > decent winter freeze could cause the water-filled pipes in the collector > to burst from the expanding ice inside them, causing water to cascade > down off the roof when the ice melted and a costly repair. Because of > nightime radiant cooling, this can happen even if the outside air > temperature is several degrees above the freezing point of water. > Modern solar water heaters have various means of hopefully protecting > themselves from freeze damage. > > Since all water tanks leak eventually, the installers of the South > Florida systems in the 20s and 30s made sure that drip pans were placed > under the tanks, with drain pipes to the outside. In some cases, > unfortunately, over the years the drain holes would get plugged up, by > various critters inhabiting the attics or by other means, and when the > tank did leak after many years of good service, the drain pans would > overflow and the residence below would be inundated with water through > the ceiling. This is not what killed the industry in the 40s and 50s > however. What did that was incredibly cheap electricity. > > Electricity, and other forms of fossil-based energy, remains immorally > cheap still today. It is immoral because selling it so cheaply means > that it is treated cheaply, without the respect is really deserves (for > the durable products it produces and the incredible geological and > ecological history which produced it), and it is wasted by combustion up > smokestacks and out tail pipes into our precious, though declining, > atmosphere. As if that were not enough, global overpopulation and > continued population growth insures that these problems will get worse, > not better. > > The result of this is a severely compromised future for our children and > grandchildren, their futures compromised by a fouled air supply and > increased global warming, with it's very long time-constant, meaning > that instant cessation of the introduction of greenhouse gases will > still be followed by many years of global warming. > > Much of this, and other disrespect to Spaceship Earth, our home and our > Earthly life-support system, results from a severely inappropriate > world-view, of the citizens and leaders of the industrial nations acting > as if they think the Earth is here for us to use, abuse, and take from > without concern for the future. The "resoning" seems to be little more > than a claim that we simply must, at any cost, protect our current high > level of material consumption, mistakenly equating this with quality of > life. Less well developed countries, incredibly, are intent on > immulating the disasterous path being followed by the polluting > industrial nations, virtually guaranteeing a demise of the planet for > viable human habitation sometime in the next century. > > This is why the solar industry that once was thriving in the U.S. is now > a hollow shell of its former glory. For less-developed countries, those > without extensive electric utility grids in place to deliver relatively > inexpensive energy to their homes, solar energy remains the one great > hope for reaonable access to that precious commodity of modern > industrialized nations -- energy. In a nutshell: Solar energy provides > just enough. Just enough to meet reasonable needs for auxiliary energy > in our lives, but not enough that you can be wasteful with it, trying to > meet the high energy consumption levels of modern, wasteful > industrialized buildings with their isolation from the outside world, > and with their high levels of electrically powered illumination (when > solar lighting is there, just outside, for the taking) inside, and with > their high dependence on fossil fuel powered interior comfort zones. > > In conclusion, thanks to the Shaws for the question. In answer to it, > life as we know it is doomed because we don't have enough thermosiphon > water heating systems in the world today. Perhaps we should take this > discussion off-line so that subscribers to the sundial list can read > about sundials, rather than the coming collapse of civilization. > > Ross McCluney, Cocoa, FL, USA -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br mailto:[EMAIL PROTECTED] Fone: +55 61 321-2433 Fax: +55 61 225-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
