Week of June 28, 2009

My other venture is building to a crescendo. We have received funding on our advanced energy storage project and we are filing a new patent. We are also working on a proof of concept prototype which will determine the feasibility of the basic approach.

Our prospects appear good. We have identified a solid electrolyte which has a voltage breakdown of several tens of kilovolts per millimeter and a dielectric constant of over 50 at all charge levels up to breakdown. We have also found an electrode capable of high voltage operation which presents a succession of smooth surfaces and which has hundreds of times the surface area of a flat plate per the same dimensions of length and width and which has a thickness of a fraction of a millimeter. If we can achieve an intimate connection between the solid electrolyte and the electrode we should be able to exceed the energy density of a lithium sulfur battery, the current state of the art, while still maintaining enormous power densities. Furthermore, our storage capacitor should be capable of sustaining hundreds of thousands of full charges and should have recharge time of only a few minutes provided a high current industrial charging circuit is available.

There may be some reason why the concept won't work. Nobody has ever succeeded in making a capacitor with very high capacitance operating at very high voltages except for some rather impractical designs utilizing cryogenic dielectrics. Then again not many people have tried.

But back to the book. I am presently completing a chapter having to do with passive solar design, an area on which a good deal of prior material is available though nothing comprehensive so far as I can determine. The really glaring omission in most of the prior texts has to do with what is known as passive cooling. I've found a single book on the subject that is now about fifteen years old and out of print, but no single source that is up to date.

So how do you cool a house using sunshine? You don't, at least not directly. You cool a house primarily by avoiding sunlight, by fending it off. Specifically, you try to connect the house to a thermal mass that is lower in temperature than the ambient air during daylight hours and then attempt to transmit excess heat from the house into the thermal mass.

Perhaps the most obvious example of such a cool thermal mass is the nighttime sky which is generally several degrees cooler than in the daytime and sometimes as much as fifteen or twenty degrees cooler. If you can admit a lot of cool air into the house at night and keep it there during the day then the house will average only a few degrees hotter than the overnight low.

That, however, is easier said than done. Most houses are not sufficiently well insulated as to able to block the transfer of heat from the out of doors, and very few climate control systems are designed to pull in large volumes of cool outside air during the evening. One can always open windows but that's of limited usefulness. If that weren't the case air conditioning would never have found a market.

A couple of approaches have been tried with some success. One method that works is to use a device called a windcatcher combined with a thermal mass under the house such as bed of pebbles. The windcatcher is oriented to face prevailing winds and to draw them through conduits to the thermal mass. Since in most places winds tend to intensify at night you get plenty of cool air entering the area containing the thermal mass.

In the day another device known as a thermal chimney sets up convective currents within the house and draws cool air out of the basement—air conditioning with zero expenditure of energy. The thermal chimney is an enclosed space positioned to absorb direct sunlight on a heat collector and to use the sunlight to heat that air. The heated air then rises and flows out of a vent pulling cold air out of the basement by means of convection.

Another scheme uses a pool of water on the roof known as a thermal pond which is covered with insulation during the day but exposed to the cool night air. The temperature of the pool stays lower than that of the ambient air during the daytime and absorbs heat from the interior of the house.

Generally, hybrid systems utilizing fans or powered evaporative coolers produce better results than the purely passive systems, however, and I will consider them in the next post.

passive cooling

My father bought a house at auction years ago, that had some peculiar characteristics. It had oversized lumber for the walls, the roof area, and under the floors. The roof is made of concrete shingles, an imitation red tile. It's faded in most places, but still works at keeping the rain out. I calculated that for the 5000 square feet of living space, there is about 55 tons of concrete on top. The place has a very long lag time between when it gets hot outside and when it gets hot inside. The major drawback is that it stays cold all winter. Thermal mass is real, but it works both ways. The house tends to stay warm in the evening, as it cools down outside in the evening, during the summer. I equate it to an "above ground cave". It's in Sylmar, not too far from Burbank.