Solar Powered Air Conditioning Just Makes Sense

http://www.treehugger.com/files/2006/06/solar_powered_a.php

Solar Powered Air Conditioning Just Makes Sense

June 15, 2006 06:22 AM - Lloyd Alter, Toronto



Some concepts just make sense- like when the developer of a solar powered pontoon boat pointed out-"Since most recreational boating is done when the weather is nice, solar power is particularly well adapted to the task." We were thinking that way while looking for a solar powered air conditioner- when do you need it? When it is hot and sunny. We looked at Justin's SolCool but we knew that natural gas fired AC units or propane fridges existed and thought heat is heat- there must be one somewhere, and put google to work. This is the first of a series- the Direct-Fired Absorption system.(DFA)



Gas fired air conditioners work on the absorption principle. "The distinguishing characteristic of absorption cooling equipment is that it produces cooling by using heat energy as an input, rather than by using mechanical energy. For this reason, absorption chillers were once common in facilities that had large boiler plants with excess capacity during the cooling season. Unfortunately, absorption cooling is inefficient, and absorption chillers appeared destined for extinction." ...In large absorption machines, the actual refrigerant is water at very low pressure. An absorber, usually the salt lithium bromide, is used to move water vapor through the system. Crystallization of the salt is a major operating problem that the design of an absorption chiller seeks to avoid."

Direct Absorption (DFA) was developed in Japan in the 60's and now the world's largest maufacturer is Broad Air Conditioning in China. "To power our absorption cycles, BROAD absorption chillers use a wide range of energy sources: oil, gas, as well as solar power, steam, hot water and exhaust. As our chillers do not use electricity as an energy source, they have the potential to dramatically reduce investment in electricity infrastructure in both public and private sectors." They now appear to be extremely efficient and save lots of electricity.

Finally, we find on their site:

"BROAD strives to be like our ancestors that mastered the miracle of fire, like James Watt who harnessed the power of steam, like Thomas Edison with his devotion to testing and retesting. Our goal is to limit the use of fossil fuels and exploit the use of renewable energies such as solar energy to provide cooling and heating needs.

Two years ago, BROAD provided an American customer with our first solar energy powered air conditioning system. This system has performed exceptionally well to date. BROAD's solar energy engineers and salespeople have drafted an ambitious plan to commercialize the solar energy air conditioning system worldwide."

We did not find the home-sized unit we were looking for, but the peak loads in North America are driven by air conditioning in summer- this looks like a good way of taking much of that off the grid. Visit the surprisingly complete and thorough website at ::Broad Air Conditioning and read their ::environmental manifesto here

I'm only paying for AC. And I take it that after a hurricane, we'd still have AC??

of course

...they aren't PV panels. They are solar thermal panels. Picky me :-)

Put my foot in my mouth again

Absorption cooling can be cost-effective when it runs on the exhaust heat from natural gas-fired electric power generation.

It's also possible to generate electric power using methane from landfill gases, sewage gases, or farm animal manure, and use the exhaust heat for absorption cooling.


I like my solar hair dryer -- I just open the car windows, and by the time I get to the office, my hair is dry.

will allow you to use convection and small solar powered fans to move air that is usually about 62 degree. To all you have to do is raise the heat to 72 in winter and increase volume in summer. It is an almost unbreakable system. But if you want a way to save quick and easy

http://www.energymatch.com/features/article.asp?articleid=46

Ground-source heat pump.

I'm not saying that it doesn't work, but on the other hand, it's a bit too vague for me to buy one. The laws of thermodynamics require that in all such systems, heat must be rejected to the surroundings. I'm not sure that I see that anywhere. I see one place where hot heat transfer agents are moving out of the system, but it seems to be rejecting heat from the boiler and not the cooling device. There seems to be some kind of concentration gradient in the system, but no details on how it works. The site seems to refer to the fact that some kinds of mixing and crystallization are endothermic - this is how cold packs work - but it's not clear how this system compares.

In principal, I buy the idea that solar energy is well suited to provide air conditioning, since it is usually available precisely when the demand for air conditioning is highest. Of course, one could go to an appliance store and buy an air conditioner and enough PV solar cells to power it and achieve the same effect. Whether either option is cost effective when compared to other options is another consideration entirely. Clearly a PV powered air conditioner has a low external cost, at least when compared to natural gas or coal based grid electricity. Further one can divert PV power to other uses when air conditioning is not necessary. I'm not sure that one can use the proposed system to charge one's portable PC, for instance, or run an electric dryer.

I note in passing that wind power is not especially suited for air conditioning. One generally needs less cooling when there's a healthy breeze blowing.

In all of these deals, the matter is cost. That system pictured is huge. The mass alone implies a significant external cost. One can often get a rough idea of the environmental impact of a system (and often, economic impact as well) by noting its size.

Is there anything anywhere near the size of a window air conditioner?

Note that a window air conditioner can be very efficient inasmuch as the cooled area is targeted.

The heat exchanger on my central air conditioner in my home is not as big at this things. Neither is it likely to weigh as much, since that heat exchanger is mostly about surface area, and not about a complex series of reservoirs.

I'm skeptical. I'm not saying no, but I'm very skeptical.

I have a great passive cooling system in my house, and don't have to run the air conditioning much. My passive system consists of huge trees.

The ammonia is absorbed in water and the watter heated to release the ammonia as a gas. It is then cooled in a static air cooled coil and is condensed into a liquid and then the liquid is released in the condenser coil inside the box and the expanding gas removes the heat as it is reabsorbed by the watter.
This absorption system is the oldest kind of refrigerant there is It was discovered by Faraday a long time ago.
years ago they had Ammonia absorption AC systems that were fired by natural gas and were sold by the gas companies until somewhere in the 1970s
I actually worked on one that was still in use They were reliable because they had few moving parts, and were only slightly larger than standard units.
There is no reason that I know of that solar heat could not replace the Gas in such a system, only I think a lack of desire on the part of industry to make a system that can be operated free.

The heat is rejected when the condenser cools the ammonia gas.

Thanks also for the remarks about Faraday. I didn't know that.

He didn't invent the gas adsoprtion refrigerator however:

http://en.wikipedia.org/wiki/Adsorption_refrigeration.

To be perfectly honest, I was unaware of the devices completely.

I'm not sure that the reason these systems are not more popular is that industry doesn't want systems that can be operated for free. A competitive selling point for many air conditioners these days is that they can be operated cheaply.

I wouldn't be surprised if another reason may be involved, fear of lawsuits should the refrigerant escape.

And it occurs in nature.
But the first refrigerators were all Absorption types because of the lack of electricity. Once electricity came into wide use the change was made to electric motors that compressed gas into a liquid and removing the heat from that liquid and then using the expanding gas to remove the heat in the box.
But I have seen an absorption type A/C system that worked well. It's heat source was propane gas but I can see no reason why the heat could not come from the sun.

I certainly would not want my kids outdoors when an ammonia system with enough ammonia to cool a house leaks outside. Ammonia is a gas, and it's a pretty strong corrosive basic gas.

Here's the first link I get when I google ammonia and fatalities:

http://www.health.state.ny.us/nysdoh/environ/hsees/ammonia.htm

It reports almost 2000 people being evacuated for 107 leaks. Note that this is the situation without the widespread use of ammonia as a refrigerant.

The wikipedia reference to this technology notes that this is the reason these systems were not widely used in the 19th century.

I have thought over the years of ammonia as a potential liquifiable gas to use to carry hydrogen. I quickly discarded the idea, since I have been around gaseous and highly concentrated ammonia in the lab.

At least in large quantities.
And I do know of a case where a train derailed and a car load of liquid ammonia burst and killed 2 or 3 people.
But that was a train car load. The Refrigerator uses only a pound or 2 of Ammonia and an AC unit no more than 5 to 10 lbs. and it is encased and sealed in a very strong steel system that is not easy to punch a hole in. And remember that in the absorption system the Ammonia is only in a gas form when the water is heated to 170 degrees F and then only at low pressures. Most of the ammonia will be still absorbed in the watter,
But what makes Ammonia such a good refrigerant is that it has a very low boiling point something like -70 degrees Fahrenheit. So the Ammonia stores a lot of BTUs.
Ammonia is still used today in camper refrigerators and in freezers that require a low temperature such as flash freezers and such.

http://www.engineeringtoolbox.com/ammonia-health-symptoms-d_901.html

It is 1700 ppm. By my calculation, using partial pressures and treating ammonia as an ideal gas, 1 kg is enough to contaminate a cube 24 meters on each edge at this level. Many bedrooms are far smaller.

I note that the effects of smaller concentrations are decidedly problematic.

Dimethyl ether, my favorite chemical compound, is also an excellent refrigerant. In fact, it has displaced CFC's in hair spray cans. It can be breathed. It is, of course, highly flammable, but on the other hand, so is ammonia gas.

I think there is too much risk associated with solar powered ammonia air conditioners. If one insists on solar air conditioning, I'm quite sure that a PV cell, an inverter, and a standard air conditioner is far safer than ammonia refrigerants. I'll bet a brazillion dollars its cheaper too.

Not everything that sounds good, is good.

But it's ignition point must be quite hi.
And you are aware that in the AC system the refrigerant is never inside the house. The ammonia cools a brine mixture in the outside unit and the cool brine is what is circulated inside the house.
The big advantage to this system is that there is no moving parts as far as the cooling part is concerned. A circulating pump and fan is all that is needed as far as moving parts are concerned.
But if they wanted to, they could make a standard AC system that runs off of DC power instead of AC and then it could be powered directly from a photo voltaic cell.

The idea is that if we do not have it now then it must not be practical or that there is something wrong with it. And I don't believe that it is true. Most of what we have now is due to the fact that it is convenient for the system to do it that way. What is good for the electrical company is electrical appliances and what is good for the Gas company is internal combustion engines, and so they discourage in every way they can any change.
There are a lot of good answers for the energy problems we face, but none of them are welcomed by the established interests.

Freons are nonflammable, virtually nontoxic and noncorrosive. When they were first introduced they replaced all the volatile fluids previously used in refrigeration -- ammonia, SO2(!), methyl chloride, etc. They really seemed to be the perfect answer, with no drawbacks, so they just took over completely.

As a nice added touch, Freons could be 'fine tuned' -- one carbon, two carbons; one chlorine, two chlorines, etc. -- to give a near-optimal match between the properties of a particulary Freon and the job for which it was being used.

It has a heater in back with 12v or porpane. Some liguid that it heats and loop inside the box. It will freeze items inside if you want. This one is not one of thermo-electric peltier models

Camper refrigerator work with heat also.

Does the heat removed from the box go out with heat from the heat source.

cooler is not larger than an thermo-electric model

The eject heat goes out the "cooling water outlet." FWIW. It would be nice if they miniaturized these (they haven't, though there is one company that make both industrial absorption chillers and standard house sized central ACs so one would think if they applied their engineering team to it...)

Personally I think it may end up being thermoacoustics that can fill this niche -- if you don't have to deal with creating electricity the trickiest part of a thermoacoustic engine goes away (coil pickup), so a simple stack of TA heat pumps with a solar heat source might just do the trick -- essentially that would end up being glass bottles, perforated ceramics, a sconch of He and some exchangers.

RE: wind power: like we discussed months ago that's for winter night-time heating :-)

except on cold still nights, right? Then everybody has to run some other infrastructure, right?

...for that portion of the heating load that is needed due to crosswinds.

I think we will have to accept that all forms of energy have advantages and disadvantages. Personally I believe that wind is an excellent form of energy. It is so good, that it's been in use for thousands of years, and even in the age of oil, never really went away. Now that it has been developed so that it is clearly useful for the generation of electricity, it is more useful than it has ever been.

That said, it has limits. The biggest limit is, of course, that it is sometimes available when it is not needed and sometimes not available when it is needed.

by solar energy. It was also heated with solar and the year-round energy usage was 80% solar and 20% fossil fuel.
The building was later sold to the local school district. I don't know if it still uses solar or not.

I'm not taking any issue with the post you just made here -- the idea of using solar and/or wind power for air conditioning in the summer is one that needs to be considered quite seriously. However, we would do well to look at the way that our living arrangements are designed, and come up with configurations that reduce the need for AC altogether.

Sometimes, the best designs in this sense can be found by looking backward, not forward. A good example would be the way that dwellings were designed in ancient Greece. Many buildings had south-facing openings, were constructed with stone floors and walls, and had overhangs over the front entrance. The overhangs allowed sunlight to enter during cooler seasons, when the sun was lower in the sky. During the summer months, the overhang kept the sun out. The dense building materials acted as heat sinks during the time they were exposed to the sun, absorbing solar energy during the day and radiating it back at night. They helped cooling during the summer by absorbing adjacent heat, much as concrete in a basement currently does.

Measures such as this are relatively simple ones we can use right away -- especially in the use of reflective shutters (reflect sunlight in on cold days, keep it out on warm ones), trombe walls, water walls, porch overhangs, the use of brick and concrete blocks on the interior rather than the exterior, and so forth. And if implemented effectively, they can reduce significantly the need for AC even in warm climates. Combined with a solar-driven system, the result could be a virtually self-contained system requiring no additional power input from outside the house itself.

It works great in my house.

I don't often have to run my air conditioner, and when I do, I often can do it for only very short periods in the afternoon or evening. Since deciduous trees lose their leaves in winter, they allow for passive solar heating using thermal windows.

I'm not sure that rebuilding every structure in the world is an environmentally good idea, but I firmly believe that new structures that are being constructed anyways should incorporate as many passive energy features as possible.

As you note, these kinds of considerations are ancient, which is a good indication that they work.

Unfortunately such thinkng is none too common. Too many times these days, one sees new construction in temperate climates featuring high vaulted ceilings. This is terrible. It's an SUV mentality that builds these things.

I mean the plant, not the human, although sometimes it's hard to tell the difference.

Bushes don't take as long to reach a height that can cool a house. Some grow quite quickly, and they can be planted very close to a house, which make them suitable for small lots and townhomes or as a stop-gap measure while the trees are growing.

My neighbors used to have a mix of deciduous and evergreen bushes practically obscuring the south-facing ground floor of their Cape Cod. Only the windows were visible. They have no trees on their front lawn, which has a southern exposure and would make a great veggie garden.

A couple of years ago they decided to chop down the bushes and replace them with much lower, less dense plantings. Immediately, the temperature of their house shot up by 5 to 10 degrees!

They can afford the extra cost of the AC so that they can have more flowers. They're also older and Global Warming simply isn't real to them. Nonetheless, here in PA, 5 to 10 degrees can make a house habitable without AC for much of the spring, summer and fall, particularly if the occupants use some low-energy electric fans.

I like landscaping that grows to a nice shape without trimming, like mountain laurel or junipers.

juniper or two and some deciduous bushes that I didn't recognize. I know that none of the deciduous bushes had obvious flowers or brightly colored seeds.

I'm sorry to be so unhelpful here, but I grew up in a colder climate, and much of the vegetation here is unfamiliar to me.