Tuesday, February 13, 2007

Intense commentary plus a/c from heat

Wow!, while I admit that my intention is to promote discussion, I am surprised (and delighted)by the intensity of the comments on my last post. So, where do I begin to respond?

First, let me say I sincerely appreciate the comments, despite...No, because of, their intensity and diversity.

Jay, you make some excellent points. For example, with my comments in red:

  • Energy drives our entire economy. Quite correct, energy supply is a serious matter which has wide reaching effects on our way of life.
  • Solar energy is the source of all energy on the earth. Wind, wave and fossil fuels all get their energy from the sun. Fossil fuels are only a battery which will eventually run out. There may be a few other exceptions, such as nuclear and tidal energies, but the point is well taken. Many do not recognize that even fossil fuels are essentially just a capture and storage mechanism for past solar energy.
  • the direct conversion of sunlight with solar cells, either into electricity or hydrogen, faces cost hurdles independent of their intrinsic efficiency. Ways must be found to lower production costs and design better conversion and storage systems. Agreed, hence my comments that photovoltaics are far from viable economic alternatives to the grid in the current environment.
  • Mandate net metering. Since utilities are generally government sanctioned monopolies, government has the right and obligation to mandate appropriate controls on the monopoly.

However, before I retreat to my area of expertise (technical), let me be perfectly clear. I believe very strongly that free enterprise will produce the best solutions at the appropriate time. In general, neither the federal government nor big business has either the mandate or the ability to solve these problems by edicts outside those demanded by free enterprise. Both government and business will effect solutions when, and only when, their customers demand it. Regulations and actions outside those demanded by free markets divert valuable resources and decrease the efficiency of the system in solving problems.

Only education about the possibilities, the science, the technologies available can improve the efficiency of the free market, hence this blog.

Now, off the soapbox and on to the issue of cooling with heat.

Jeremy, thanks for your question about using solar heat to generate air conditioning. As I mentioned in my previous post, this area is one of the least understood and therefore least recognized alternative energy resources. And, of course, it seems contradictory. At the same time, the technology is well proven. Most RVs have propane refrigerators which use the propane to generate heat, and thereby refrigeration by a process known as adsorption. You may remember natural gas powered air conditioning systems, although they are pretty rare now. They work on the same process. Variations of both this and other cooling process, such as steam vacuum are widely used in industrial processes to provide cooling through application of heat.

Very simply, the process looks like this:

  • Use desiccants (materials that naturally attract water vapor) to attract moisture.
  • Evaporate water to supply the moisture demand created. Cooling results from the water evaporation.
  • Regenerate the desiccant by using heat to drive moisture out.

As I said, this is a well proven process. I realize that, to most, the term desiccant is foreign, but it simply means materials which attract or have an affinity for water, and there are many well known examples. Salt is a desicant...you've seen water extracted from the air into salt to create a wet mixture in a humid area. Popcorn becomes less crisp when exposed to humidity for the same reason. Ethylene Glycol (antifreeze) is added to your radiator because it attracts water and therefore makes the water mixture less inclined to boil and escape the radiator. Ethylene Glycol and ammonia are dessicants widely used in industrial processes for drying and/or cooling. And there are desiccant pellets such as silica gel manufactured specifically for drying air and natural gas to eliminate freezing, corrosion and other negative effects in processing. These are also used to remove moisture from packaging. You've probably seen the small packets of silica inside packaging. They are there because they absorb moisture from the air and therefore prevent moisture related problems.

So, all that remains is to select the appropriate desiccant and to generate sufficient temperatures with solar heat to apply the process to solar air conditioning. Importantly, this process has synergy with solar heating which makes both more attractive. Everyone knows, of course, about solar heating. But one of the problems is that heating demands are high, but short lived. A solar heating system designed to meet a significant portion of heat demands in a home sits idle much of the year. And, even worse, the highest heating demands occur when there is the least sunshine, ie at night or cloudy days. If the same heat collector and storage mechanisms can be used for air conditioning, the economic viability of both solar heat and air conditioning can be significantly improved. And the highest air conditioning demand largely corresponds to the periods of maximum sunshine.

So, what does this collector look like? You've seen them and could probably do a pretty good job of building one yourself, but here is where I get most excited. I believe that with relatively minor modifications you could collect enough energy in your attic to supply most of your air conditioning and heating requirements. And you would further improve the efficiency of your house in the process by increasing ventilation and temperature in the attic.

I'll leave you with that, although I know some may want more details. If there is a demand, perhaps I'll get smart enough to post sketches and schematics in the blogs and explain further.

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