Posted: Tue May 20, 2008 11:38 am Post subject: Solar home cooling
I'm starting this thread because of this.... I cant let it go, I dont want to get off topic in the other thread, but I have more stuff to add now that I'm doing some additional research. I'm finding some cool alternatives for home cooling.
If anyone has any questions about home cooling or heating feel free to ask me.
tsakach wrote:
burtonridr wrote:
I understand that designers are the experts in their prospective feilds, I design HVAC, plumbing and mechanical systems for a living.
Since you have experience in HVAC systems, what are your thoughts about running these systems on solar?
A little bit pricey but it does the job in the desert where temps get up to 120F. Some people also convert an AC swamp cooler to DC using a 12v radiator fan to drive the air through the evaporative cooling pads.
Obviously HVAC is a major energy consumer, but my unit only draws about 85 watts. It would be nice if there were more energy efficient options in this area that could run off a small solar system. Geothermal with a heat pump might be worth experimenting with as well.
I dont want to get off topic with this, however I want to answer your question quickly as well as point out some things you should think about.
First about the little unit you are using, without doing a cooling load calc on the living space you are using it to cool, I cant really tell you much. I'm sure it works, and actually it is probably less efficient than most units on the market. Most units are 80% or better on the efficiency aspect. Efficiency is the measure of how well something converts energy. There is a lot of technology built into other units, they use more electricity, there are more types of energy than electricity.
The page on the link says they recommend using it to cool a 300 sq ft room. Sometimes manufacturers will make a claim, but what they dont tell you is what kind of environment it is recommending or what it was tested in. If they tested it in a 300 sqft room, what was the wall insulation value? What was the roof insulation value? Floor insulation value? How many windows? If there are windows, which way do they face? south? north? Also what was the temperature difference between outside and inside the living space?
300 sqft is a whole lot of space to cool. If you have 10 ft ceilings thats 3,000 cubic feet of air you have to cool. Now that unit blows 1,200 cubic feet per minute. that means every 2.5 minutes you have circulated the air within the space. That is a lot of air movement for a single 300 sqft space... To give you an idea of just how much air that is, we typically use a unit that blows 1,200 cfm for about 900 sqft of office area.
Now you are somewhere that gets up to 120 degrees, just to cool the air down to 90 degrees is a temperature difference of 30 degrees.... So it will take a lot to cool that air down, off the top of my head I'm not about to figure it out.
But if, and this is a big if, that little unit cools the temp 30 degrees that would mean it is providing 3,600 buth of cooling.
Now another thing that units requires is a constant inflow of water. What is pumping that water to the unit? how many watts is it requiring? Can your solar system handle the load from the pump? Do you live near a reliable water source?
There really isnt any information provided on that website to provide more accurate numbers.... _________________ Tired of high gas prices? Then stop driving to work, duh..... Learn to Work from home
If you have a typical attic space where the insulation lays on top of the ceiling, un-insulated attic space, this could help keep your home 10 degrees cooler, or more. Not only that, but the moisture it helps to removed will also help keep the ceiling insulation value from decreasing due to moisture. This is especially true if you have blown in insulation.
In the winter, you would want to turn it off to help retain heat in the attic. _________________ Tired of high gas prices? Then stop driving to work, duh..... Learn to Work from home
Joined: Jan 03, 2005 Posts: 1183 Location: western Wisconsin
Posted: Tue May 20, 2008 12:05 pm Post subject: Re: Solar home cooling
The May/June 2008 issue of "Solar Today" magazine has a good section on "Cool Naturally with Passive Solar Design", with about 16 pages of good basic info and ideas.
Posted: Tue May 20, 2008 1:54 pm Post subject: Re: Solar home cooling
burtonridr wrote:
Now you are somewhere that gets up to 120 degrees, just to cool the air down to 90 degrees is a temperature difference of 30 degrees.... So it will take a lot to cool that air down, off the top of my head I'm not about to figure it out.
But if, and this is a big if, that little unit cools the temp 30 degrees that would mean it is providing 3,600 buth of cooling.
When running the unit, I measure the inside and outside air temperature and humidity. At 12% humidity, there is a 28 degree temperature drop on the air coming directly out of the unit. The indoor humidity increases to about 40%. However, if the outdoor humidity goes up by 10% the temperature drop goes down to around 20 degrees, and the indoor humidity is still around 40%.
So in dry conditions, the unit works well and according to your calculations it provides nearly 3,600 btu of cooling.
burtonridr wrote:
Now another thing that units requires is a constant inflow of water. What is pumping that water to the unit? how many watts is it requiring? Can your solar system handle the load from the pump? Do you live near a reliable water source?
The unit consumes about 3 gallons per hour when running. It has a water pump inside that circulates water from a small tank to the cooling pads. The tank is kept full by a float valve fed by city water pressure. To run the main fan and water pump, the unit needs 80 watts.
burtonridr wrote:
I'm sure it works, and actually it is probably less efficient than most units on the market.
Why you think it is less efficient than most units on the market? Do you know of a more efficient unit? I would definitely be interested.
As far as passive cooling is concerned, I have added extra insulation to the ceilings and painted the roofing material with white elastomeric paint. This dropped indoor temperatures by about 12 degrees.
The next area of improvement is to shade the structure with trees or some type of shade structure, like shade cloth or maybe camo netting?
I have several ideas on how to improve my cooling setup. With evaporative coolers, you are cooling a constant inflow of air from the outside and exhausting it back to the outside through an open window. To increase the amount of air flowing through the unit I was thinking of setting up a secondary fan to exhaust the air.
I am also thinking about ways to provide the cooling unit with a source of cooler air from the outside, such as ducting air from a shaded area, or possibly blowing air through tubing submerged in underground water storage. The main drawback with evaporative coolers is that they consume water, so I am still actively looking for alternative cooling methods.
Providing HVAC for off-grid solar/wind systems is definitely a challenge, especially when you are working with a limited amount of watts. I am definitely interested in any ideas on how to stay cool on a limited energy budget.
So effective has been the windcatcher in Persian architecture that it has been routinely used as a refrigerating device (yakhchal) for ages. Many traditional water reservoirs (ab anbars) are built with windcatchers that are capable of storing water at near freezing temperatures for months in summer.
Main drawback here is that it is rather elaborate to construct. But think of how much energy it would save over the years! A smaller scale version of this that is simpler to construct would be ideal.
Here are a few modern variations of the windcatcher and qanat:
Posted: Tue May 20, 2008 2:44 pm Post subject: Re: Solar home cooling
WisJim wrote:
The May/June 2008 issue of "Solar Today" magazine has a good section on "Cool Naturally with Passive Solar Design", with about 16 pages of good basic info and ideas.
Posted: Tue May 20, 2008 2:56 pm Post subject: Re: Solar home cooling
tsakach wrote:
The unit consumes about 3 gallons per hour when running. It has a water pump inside that circulates water from a small tank to the cooling pads. The tank is kept full by a float valve fed by city water pressure. To run the main fan and water pump, the unit needs 80 watts.
What happens if the power grid goes down? will your pressurized water still be available?
tsakach wrote:
Why you think it is less efficient than most units on the market? Do you know of a more efficient unit? I would definitely be interested.
It may be the best suited application for your needs, which is to make the best use of minimal electricity. Efficiency ratings take more into account than just how much electricity they consume, it is a measure of how well they convert energy.
It is by far the best low power application I have seen, I was just arguing the use of the word "efficient"....
tsakach wrote:
I have several ideas on how to improve my cooling setup. With evaporative coolers, you are cooling a constant inflow of air from the outside and exhausting it back to the outside through an open window. To increase the amount of air flowing through the unit I was thinking of setting up a secondary fan to exhaust the air.
I wouldnt be to concerned with another fan, having a little back pressure is actually a good thing. It helps keep the fan in check, plus it will push air through cracks in the walls and things to help keep dust out of the house. It wont increase the airflow enough to make much of a difference. It would be good if you wanted to close the window during a storm though.
However, if you have enough air rushing out of the window it will be just fine.
What is the size of the window opening? I will run a calc and see if you need a large opening or anything.
tsakach wrote:
I am also thinking about ways to provide the cooling unit with a source of cooler air from the outside, such as ducting air from a shaded area, or possibly blowing air through tubing submerged in underground water storage. The main drawback with evaporative coolers is that they consume water, so I am still actively looking for alternative cooling methods.
Do you have a crawlspace? _________________ Tired of high gas prices? Then stop driving to work, duh..... Learn to Work from home
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Then stop driving to work, duh..... 
