Still Seeking the Solar Powered Air Conditioner
by Lloyd Alter, Toronto on 04.24.07
Almost a year ago we wrote about how wasteful running air conditioning in the hot sun was, that all that solar energy was going to waste heating buildings when it should somehow be captured and used to cool the building (read here). Obviously a sunshade of solar panels might do the job but they are still expensive and we were looking for something more direct. The post has been generating comments all year and we have learned a lot:
1) Been there, almost done that in 1929: The Crosley Radio Corporation introduced a water-ammonia mixture refrigerator in 1929: "The Icyball is an intermittent heat absorption type of refrigerator. A water/ammonia mixture is used as the refrigerant . Water and ammonia combine easily. So, they combine in the hot ball at room temperature. When the hot ball is heated, for about 90 minutes, the ammonia evaporates first because it has a lower boiling point than water. The other cylinder is in water to help condense the ammonia in the cold ball. When the balls are fully charged, the cold ball is placed in the insulated box, as the ammonia evaporates to recombine with the water in the hot ball it removes heat, cooling the inside of the refrigerator for 24+ hours." They are still found in garage sales and junk stores. ::Crosley Ice Ball and you can build your own, ::Instructions here. Add a solar hot water heater and you are set.
2) Doing it right now: The Energy Concepts Company designed and built the ISAAC Solar Icemaker, acronym for Intermittent Solar Ammonia-water Absorption Cycle. Designed for third world use, we learn from Sustainable Village:
During the day the solar collector focuses the energy of the sun onto the ammonia generator in the collector trough. Solar heat distills pure ammonia vapor from the water-ammonia solution in the generator. The vapor condenses in the cooling coils and collects as liquid ammonia in the receiving tank in the evaporator.
At the end of the day, the user switches three valves from the Day to Night position to allow the ammonia to evaporate in the ice compartment, providing the refrigeration to freeze the water. The resulting vapor is absorbed back in the generator. Critical to the operation of Isaac is a passive thermosyphon that operates in the Night mode to remove the heat from the generator and allow the ammonia vapor to absorb into the solution at lower pressure and temperature.
At the beginning of the day, the operator harvests the ice from the ice trays, operates a drain sequence to remove traces of absorbent from the evaporator, and places the unit back into Day mode to begin the next cycle.
This was designed for third world use: "Energy Concepts has adopted this technology to a machine which uses the sun as the only energy output. The particular advances in the design and configuration have resulted in a low cost and reliable method of making significant quantities of ice in areas without electricity." the biggest unit, at costing $ 17,000 can make 150 pounds of ice per day.
The company also makes a waste heat fired icemaker and a very interesting Thermosorber gas fired heat pump that provides both hot water and refrigeration.
I think better building design could counter most of this need. Simpe solar siting, better insulation, passive solar treatment, and suddenly the need for an AC is cut in half or more!
I have a 50-year old Canadian-made Servel refrigerator that uses the ammonia sorbtion cycle. These and competitive brands are still commonly used throughout the developing world or even in bush cabins of Canada where people are off grid. Efficiency is high and there are absolutely no moving parts, meaning they last forever. The only problem is that the direct fired ones (kerosene, natural gas, LPG, or wood) have to be properly vented and vermin have a tendency to nest in the exhaust pipe, presenting a fire hazard. Solarizing the heat source eliminates that problem so its a marriage made in heaven.
No flourocarbon refrigerants needed either!
We had a natural gas Servel for 40 years. They were great! We only recently replaced it with a Roper.
Mechanically powering an a/c compressor with a windmill, waterwheel, or stirling is probably more efficient, but really the power required for a/c is so immense that I can't imagine it's at all doable. Stirling powered ventilation fans are about the best you'll be able to do. Plant some trees around your house, get awnings, and open the windows.
Smaller houses, better building techniques. Less energy per individual is the one and only basis for solving our needs.
There is an individual in my area that is building themselves a 10,000 sg ft house..to bake in the Florida sun. They had to take the trees down to make room for the house on the lot. WTF
Palm Springs, CA:
There are 3 old ARkLA (natural gas powered ammonia air conditioners on the property. Southern California Gas company services them every year and keeps them running. ARKLA (arkansas & Louisana gas company) Used to manufacture them, but when Ammonia was made a hazzardous material the license to recharge the ammonia became too expensive. So if one is purchased today you just have to hope your "closed system" doesn't need to have ammonia charged in for 20 years. A good bet, for in the desert, it would pay for itself in 2 years.
Looking at my unit, it looks like It would be fairly easy to convert from gas to solar. Just remove the gas burner (looks like a big broiler like the one underneath your stove) and focus a parabolic solar collector on the bottom of the cannister (bottom for heat rises). This process may take 1 collector focused on the sun and 1mirror focused down on the ammonia tank.
Remember the ammonia only needs to heat up to 140 degrees. So the thermostat that turns the gas on and off (at 140 degrees) by way of standard ingnition wire (like in your car) would need to turn the solar mirror "off" as well.
FYI: The gas unit burns .75 therms per hour, Gas costs $1.21/therm (w/ discounts $0.95/therm). Although the technology is "cool" it costs $1 per hour to run the unit ($15/day $450/month).
With the addition of 1 simple solar collector, the country could have unlimited cool air, and practically leave the doors open if they wanted.
Solution to the Iraq war: Americans have spent $5,000 per household on the war (since inception). The next President (Clinton) can spend the same $150 billion per year but give it to local utilities and local contractors to install these solar ammonia units on every house in america. $2,500 goes to the manufacturer, $2,500 goes to the contractor. Creates massive jobs, ongoing service work, and huge savings in gas (remember even electric AC's use gas, it's just burned at the power plant not at your house). If we're not wasting $400-$1000 per month on AC we can spend the money on fueling our Hummers......"What's good for the country is good for GM". :-)