Small-Scale Solar Powered Air Conditioning Is Here (in Spain, Anyways)
by Lloyd Alter, Toronto on 01.17.08
For years we have been saying that solar powered air conditioning just makes sense- if you are boiling in Phoenix the sun is probably shining really hard. We have seen big units, evaporative units that won't work in humid climates, a few vaporware units and even home-made absorption chillers
Now it looks like a Spanish company, Rotartica, has put it all together, by combining evacuated tube thermal collectors with a water-heated absorption chiller, and sized it at 4.5Kw (1.28 tons) for residential use, all packaged in a neat little box.
From an operation point of view it is very simple: you put hot water in, you get cold water out, which you can run to a conventional fancoil. The hot water in can come from any source, but evacuated tube collectors, which used to be very expensive, are pretty affordable now. If you want to get more techie:
In an absorption chiller unit the evaporator and condenser are the same as in conventional systems but the function of the compressor is performed by a chemical absorbent (LiBr) and a
heat generator, with only a pump being required to provide the change in pressure. As there is
no compressor, electricity consumption is reduced significantly.
The diagram is a graphic representation of the Single Effect Absorption Cycle, which
functions as follows:
1. The refrigerant, together with the salt or absorbent in the Generator, evaporates due
to the heat provided by a burner or an external circuit leading to a heat exchanger.
2. The absorbent is conveyed to the Absorber as a solution with a low refrigerant content,
while the refrigerant that has evaporated in the Generator travels to the Condenser
where it is condensed and releases heat.
3. Due to the difference in pressure, the refrigerant flows to the Evaporator where, at a
low temperature and as a result of the low pressure, it evaporates and absorbs heat
from the circuit which subsequently goes on to cool the room.
4. Lastly, the evaporated refrigerant is attracted by the absorbent in the Absorber, where
the refrigerant-rich absorbent solution is created once more and is conveyed to the Generator where the whole cycle begins again.
We don't know the price, (probably expensive) but operating costs will be negligible and it runs when the sun is hottest and electricity the most in demand; once those smart meters become common this may be the only way to affordably cool on the hottest days. If you are worried about being cool at night, perhaps you can add an ice bear. ::Rotarica
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From the description, I'm assuming this is just replacing a mechanical compressor with a thermal compressor, which draws its heat from the water from the solar collector. It's like the natural-gas powered refrigerator in my dad's old VW camper.
Sounds like a great idea, and one that might be easy to replicate using plumbing fixtures. I wonder how long it will take the Makers to duplicate this using parts from old refrigerators.
Another one - cool!
I wrote last week about another solar HVAC on my blog at www.practicaleco.com.
However, that one is for larger applications at 10 tons and bigger. I'm sure solar cooling is becoming viable.
I am surprised about the evacuated tubes. We like them for heating in the cold mountain winters, when the vacuum is needed to separate the hot water inside from the frigid outdoor air. Why would you use this more expensive type of solar collector for cooling if the surrounding air is hot and the water inside is hot too?
This past summer I installed a hvac mister, similar to the misters used around patios and at amusement parks to cool crowds. The hvac mister cools the ambient air before it is drawn through the condenser coils on the outside unit. The mist also wets the coils and improves heat transfer because wet surfaces transfer heat better than dry ones. But to avoid calcium deposits a simple calcium filter is installed in the water line. The misters are turned on with a solenoid valve like the ones in a lawn sprinkler system that is wired into the thermostat line so it comes on and off with the condenser and compressor. No wasted water. Lowered the electrical use of my AC by about 40%. I love it. Talked with the Lennox rep and was told they have a commercial version of evaporative pre-coolers but it is not available on residential units. Should be. Wow the savings are huge.
"Tonnage" refers to the cooling capacity of the unit, not the weight. A home may have between 2-6 tons of cooling, so this unit is on the small side.
Chillers powered by solar hot water have great potential. One of the problems with solar hot water, (especially arrays sized to provide space heating) is that you have surplus hot water in the summer time because the days are longer and hotter. Solar chillers solve this problem nicely, however the size of the array needed to cool a typically home in the US is massive. The technology still needs to improve.
Evacuated tubes, rather than flat plates, are typically used for to drive thermal chillers because they can deliver higher temperatures. Flat plates, even in the summertime top out at 180F, while evacuated tubes can hit 250F.
You do pay a premium for evacuated tubes over other technologies, but performance is far superior.
I think I saw this exact chiller at the solar decathlon in DC last October.
When I lived in India over 30 years ago all the room a/c units had water pans mounted on top. You filled the pan with water each morning and it dripped water down the face of the unit, increasing the cooling power and efficiency of the a/c.
My Condo community has 900ft^2 units. This sounds about right size for them....and I do 'need' a new one, if only to not have a broken one sitting outside gathering dust. Unfortunetely my condo and the AC spot outside face north, and get little sunshine, so I am not sure that this will be useful anyway.
I could see this working great in Texas! Just get a 2-stage thermostat:
Stage 1: Solar cooling, which at 1.25 tons of cooling, would get used over half the time.
Stage 2: Regular 2-3 ton compressor.
Same could be done for heating in the winter, since in TX, we need both heating and cooling (so the evacuated tubes would be beneficial). Stage 1 could run the hot water through a heat exchanger for thoese "cool" days; Stage 2 could kick in a smaller natural gas burner to make up the extra heat needed on those really cold days (like today).
Now, if we could see HVAC installers package a system like this - it'd be absolutely awesome!
Richard - your mister sounds a lot like a "swamp cooler". It would work great in dry climates where adding some humidity would be beneficial, but in areas like the east coast summers are hot and humid. We rely on the coils to condense out the humidity so it can be drained away. Glad it works for you, though.
Doug,
No, Richard's mister is not like a swamp cooler--it doesn't inject the humidity inside. Just assists cooling the outside coils by misting them. The inside coils are still just as cold (or colder) and still condense the inside moisture which still drains away.
You'll find a couple of articles/presentations I wrote on the topic of solar air conditioning on the 'ideas' section of Climate Managers' website: http://www.climatemanagers.com/index.php?option=com_content&task=blogcategory&id=1&Itemid=34
I believe this technology was used in the University of Cincinnati Solar Decathlon house, along with evacuated glass tubes for water heating. Not really sure how effective it ended up being, but just wanted to say that it has been implemented...there may be more info on the solar decathlon website:
http://www.solardecathlon.org/
I am one of few houses in the Palm Springs (Coachella Valley) that have a gas fired air conditioner. Count them on 1 hand. They are very rare, but old technology. ArklaServel (Arkansas-Louisiana) gas company use to manufacture them. It uses 0.75 therms per hour to run, so approximately $1/hour to run. Not cheap. Regarding thisHot water fired unit: For clarity, all the hot water would do is surround a lithium bromide tank, heating the contents to a boil (185 degrees), thus starting the cooling process. In my unit a vertical broiler heats the canister. It's GREAT technology. I love it.
I am one of few houses in the Palm Springs (Coachella Valley) that have a gas fired air conditioner. Count them on 1 hand. They are very rare, but old technology. ArklaServel (Arkansas-Louisiana) gas company use to manufacture them. It uses 0.75 therms per hour to run, so approximately $1/hour to run. Not cheap. Regarding thisHot water fired unit: For clarity, all the hot water would do is surround a lithium bromide tank, heating the contents to a boil (185 degrees), thus starting the cooling process. In my unit a vertical broiler heats the canister. It's GREAT technology. I love it.
This is kind of off topic, or maybe under topic because it's probably dumb. Why can't you take an existing air conditioner off the grid, and attach pv panels?
I have a 6kw pv system that provides all of the electricity I need including the air conditioner. I don't the the arrays would have to be too big--too big a footprint.
Okay, shoot me down.
Don
Don, a 2.5 ton air conditioner has a power consumption of around 3.5kW.
At $5 / Watt, you would spend $17500 in solar panels only to power your air conditioner... that's why...
Does anyone know where to purchase the hvac mister featured on "Living with Ed?" Thanks.
I too would like to have more info regarding the a/c mister that I saw on Living with Ed.
Jeanne
I am doing this on a more appropriate residential scale .......I have designed and installed in 2 different homes 5 tons of chilled water loop central AC systems run on large solar systems.......I am an off-grid developer and luxury home builder here in Baja California, Mexico. My systems combined with a lot of insulation, and good windows make solar powered aIr conditioned luxury effortless for my home owners. It is very possible to live in harmony with the environment without sacrificing your creature comforts. I am proving it in the last frontier, and wish more people realized this was possible.
Mace