What is the best way to use solar heating to cool a living space?

In summary,The sun heats the "hot-box" container filled with air from outside, to a certain temperature. Once the temperature is reached, a one-way check valve is opened, and the air is admitted into a water-immersed copper coil. The air is then cooled by the water, and finally escapes to atmospheric pressure. The amount of time it takes the hot-box to stop pushing air (1atm) depends on the friction of air in the copper tube, and size of the hot-box. When the hot-box reaches 1atm, or close-to-it*, the valve to the copper tube is closed, and the two
  • #71
TechFan said:
"...So, by my rough calculations, the device will be able to cool down my bedroom 11°C, but it will take 12 days..."

Then what you do is to increase the size of the thing and use a fan to circulate air through the evaporator and you have come up with a motor less solar AC unit.
I just researched the cost of mirrored stainless steel. The sheet in their design costs roughly $300. One article claimed they made the rest of the system for about $100. So that's $400 for a single unit. To be an effective air conditioner, for me anyways, I would need 12 units. That comes out to $4800. 12 of these units would also take up a lot of space, and would require all trees be removed. hmmm... There's another factor. How much do my 60+ foot tall trees in my front yard contribute to the non-heating of my house? That will be my experiment for the day. :smile:



You are trying to discard a system (motor less absorption refrigerators) which has been in use for a hundred years. It works , its proven science and the technology has been around for decades before this thread. That's why I posted the links to commercial existing systems.
Are you talking about the link in this post?


TechFan said:
Here are many images of kerosene and propane refrigerators. They do not use a pump or compressor to circulate the refrigerant; but the heat delivered by the burner does the job. That's what I meant in case you didn't realize. You want to start the philosophical discussion about pumps, not me. I'll take the nap...
https://www.google.com/search?q=ker...tric_Freezer_with_Basket_with_CE.html;800;600

Those all look like refrigerators and/or freezers. Gurth doesn't want a refrigerator nor freezer. Well, maybe he does. But that's another thread. hmmm... Maybe not. See below.

They are real despite all your experiments and calculations to prove them wrong.
Can you point out where I said they don't work. If that's what you mean by "prove them wrong".

The "pro's" (as you call them) have come up with different results for their experiments and decided it was doable and began to produce them. By the way, I did not invented, designed, modified or improved them in any way. They exist before I was born and independently of my thinking, input and original disbelieve. It was really shocking for me also to believe in their existence when I first learned about them, because it "looks physically impossible" that heating the gas one can get cooling on the other end. That disbelieve is particularly accentuated when one learns about them after a life time marriage with a compressor type unit. Its also difficult to accept that without using an electric motor, why they were not in use from the time of Newton, Galileo or Davinci?. These geniuses could have invented them, there is nothing in the technology which wasn't available in their times... except for the knowledge to do so...(I guess).
They aren't the most efficient systems, agreed, by they do the job without consuming electricity and they seem to be a reasonable and feasible solution for someone who wants to live off the grid.

If you think I'm dissing absorption refrigeration, guess what my first question was for this guy:

Larry.Schlussler.phd.CEO.Sunfrost.2008.07.11.OCF.jpg

Larry Schlussler, phd, CEO Sunfrost 2008.07.11 @ OCF

"OMG! Does it use the Einstein-Szilard process!?"
He said; "No. It utilizes an electric powered refrigeration unit, just like yours at home. Mine's a bit different though". (probably not an exact quote, but that was 6 years ago)

Garth, if you're still with us, I consider Larry to be the guru of off-grid living. I think it's all he thinks about. And then he actually does it.

I think it was last year that he displayed a solar powered tack welder.

pf.ocf.solar.tack.welder.2013.09.28.1135am.jpg

Sweet!

umm... Sorry. I appear to be getting off topic. But I get so excited! :redface:
 
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  • #72
"...I just researched the cost of mirrored stainless steel. The sheet in their design costs roughly $300..."
These are hypothetical calculations which do not necessarily have to be what implementing the system can cost him. As a doer yourself, you know, individual cost depends and varies greatly depending on your ingenuity to recycle and reuse things like the old fan you've mentioned before. Also, he just wants to lower the temp a few degrees in a certain area. Making a fully operational AC system is a pro's job costing a lot of money. I don't think he is trying to achieve that. Your are taking cost analysis to the extreme worst case scenario with this example.

"...Are you talking about the link in this post?..."
Yes, that one and the previous one.
The purpose of that link was to show you these systems do not use pumps, compressors or moving parts.
When you requested to show you one which did not used them. Even though he wants an AC unit, I was trying to show him the principle with these refrigerators and the possibility of its implementation, which I believe for his needs and purpose, can be done by somehow converting one refrigerator like that. The OP clearly said he just wanted to lower the temp surrounding his computer area a few degrees.
"...If you think I'm dissing absorption refrigeration, guess what my first question was for this guy:..."
It seemed to me you were; but if you say so, then we agree on that one.

To be honest, I don't have a clear idea about what solution you are for: swamp coolers, OP's original design, absorption refrigeration, your sun powered compressor cooling system, cooling tower, PVs??. So many postings and experiments, got me confused, I admit it.
 
  • #73
TechFan said:
"...I just researched the cost of mirrored stainless steel. The sheet in their design costs roughly $300..."
These are hypothetical calculations
Everything is hypothetical, until you "do it".
which do not necessarily have to be what implementing the system can cost him. As a doer yourself, you know, individual cost depends and varies greatly depending on your ingenuity to recycle and reuse things like the old fan you've mentioned before.
It so far has cost me nothing, except for my time, to do these experiments.
Also, he just wants to lower the temp a few degrees in a certain area. Making a fully operational AC system is a pro's job costing a lot of money. I don't think he is trying to achieve that. Your are taking cost analysis to the extreme worst case scenario with this example.
From the sounds of it, he wants to lower the temperature a lot of degrees, in a significant volume.
"...Are you talking about the link in this post?..."
Yes, that one and the previous one.

The purpose of that link was to show you these systems do not use pumps, compressors or moving parts.
I pointed out that the device from your "previous" link does use pumps.
When you requested to show you one which did not used them. Even though he wants an AC unit, I was trying to show him the principle with these refrigerators and the possibility of its implementation, which I believe for his needs and purpose, can be done by somehow converting one refrigerator like that. The OP clearly said he just wanted to lower the temp surrounding his computer area a few degrees.
"...If you think I'm dissing absorption refrigeration, guess what my first question was for this guy:..."
It seemed to me you were; but if you say so, then we agree on that one.

To be honest, I don't have a clear idea about what solution you are for: swamp coolers, OP's original design, absorption refrigeration, your sun powered compressor cooling system, cooling tower, PVs??. So many postings and experiments, got me confused, I admit it.

It is quite confusing. But I just completed the calculations from my experiment from yesterday, and came up with a few conclusions:

mfb was more correct than he probably knows:

mfb said:
Houses are not a single object with perfect internal heat conductivity - different parts of the house will react at different speeds to outside air temperatures. Air temperature can change quickly (opening a window for a minute is sufficient to change it significantly in this room), but most of the heat capacity is in the walls, floors and other solid objects and reacts way slower.

I had 9 temperature sensors, took readings on average every 51 minutes, and everything came out wrong. From the data, my house should have cooled down by a degree, but the temperature rose by 3.5°F.

The experiment started at 9:15 am, and concluded at 3:10 pm. (I got somewhat bored, and nothing was turning out as expected, except for my tree. She came through with flying colors.)

Temperature changes were as follows:
1.5 Crawl Space (62-63.5)
3.5 Inside my house (69.1-72.6)
10.1 Ambient outside temperature (68.3-78.3)
12.9 At the base of my 60 ft tall big leaf maple tree (65.0-78.0)
14.6 South facing exterior (70.7-85.3)
26.6 East facing exterior (66.2-92.8)
55.6 Attic (63.5-119.2)

As mfb stated; "different parts of the house will react at different speeds".

The crawl space and attic, exchange heat with the inside of the house via natural convection, conductivity, and perhaps via radiation. The outside of the house has to deal with forced convection and conductivity. (There was a light breeze all day)

The tree as I mentioned, provided the most interesting number. It was 5°F cooler at the base of the tree vs ambient temperature. Proof that evaporative cooling works. Had there been no breeze, the number may have been higher.

I should mention that my calculated heat capacity and sum R-value was derived from data collected during the winter months, as there is so little effect from the sun at that time of year, I really didn't have to worry about it.

My conclusion is that a massive heat sink, aka the crawl space, would be the cheapest and most affordable means of cooling a space.

A 55 gallon water filled insulated drum, chilled via a pair of heat exchangers during the cold nights, might also be a viable solution, depending on the night-time temperatures.


--------------------------
ps. My cooling tower of doom, although quite unimpressive to look at, was a bit of a waste of time. Mainly though because it kept drying out between readings. I simply can't sit for 6 hours waiting for a towel to dry... (Maximum cooling effect: 2.2 °F, 40" tall, 8" average radius.) But then again...
 
  • #74
TechFan said:
". So many postings and experiments, got me confused, I admit it.

Me too. But it has been fun.
A lot of hot air, one could say.
 
  • #75
sophiecentaur said:
Me too. But it has been fun.
A lot of hot air, one could say.

Hot air? I hope you're not referring to me. :eek:

ps. Does anyone know the absorption coefficients for the solar spectrum of a single folded white bed sheet?

I stapled one onto the south face of my exterior, right next to an unshielded identical surface. The bed sheet shielded portion ended up being 6°F warmer than the unshielded! I decided that it was acting as an insulator, and moved the bottom portion away from the house. I later checked the no load voltage of one of my solar panels behind the sheet, and it was the same as without the sheet.

I discovered a few years back, that solar panels can also measure light intensity. My notes in that post are a bit lacking, but I believe it was no load voltage.

So it would appear that the sheet had no solar thermal shielding effect at all. Which I thought was odd, as when it's sunny out, I just wear a shirt, no sunscreen, and never get a sunburn. It always worked.

hmmm... Perhaps this is because, UV and infrared are at opposite sites of the spectrum?
 
  • #76
OmCheeto said:
...
everything came out wrong. From the data, my house should have cooled down by a degree, but the temperature rose by 3.5°F.
...

I was sitting on my front porch thinking about this, decided that the air in the crawl space was probably stratified, and probably contributed little to the whole house heat equation. So I removed the 22,000 BTU it would have absorbed. The net BTU gain turned out to be 14,000 BTU, which, at 5000 BTU/°F, yields 2.8°F, which is very close to the 3.5°F temperature gain.

The only other significant heat source in the house was the refrigerator.
 
  • #77
I'm kind of exhausted from this thread already. Trying to understand and find meaning to so many posts and experiments made me loose interest on this. I’m out until it gets interesting again.
 
  • #78
First let me say, thank you to everyone who has contributed here, this has been a GREAT thread!
I think I was a bit misleading in my OP, allow me to clarify: I’m still living in an RV, and am in the process of designing the house (and pond). I’m going to implement “green” building techniques, and be using highly insulating materials. My solar power system, and water-well are already in place.
Based on everyone’s input, the swamp cooler AND “solar tower” ideas will both be used as follows:
An AIR intake will be located on the north side of the house, near the ground. A duct will lead from there into the basement. This duct will have an evaporation material/screen inside it, kept wet by a pump. (Need to determine how to trigger/throttle the pump)
The air will be forced through the duct as follows: The south side of the house will have many windows with curtains, to let in a certain amount of sunlight. Vents in the floors on this side of the house will allow the sun-heated-air to rise to the roof, where a close-able (for winter) vent at the top allows the hot air to continue up and out (sucking fresh air into the house behind it).
It appears this type of solar generated air flow is common practice in green building, I’m just adding the evaporator in the intake duct.

While I certainly love DIY stuff, once things get beyond a certain complexity, my DIY skills are insufficient. This is why I think modifying a commercial propane/natural gas fridge, would be the way to go, at least for me. It’s got those special refrigerant chemicals for better heat transfer, and most importantly: SEALS those chemicals in, better than I could.

Electric powered compressor based AC unit: Sophie you made an excellent point about only needing the cooling when the sun is up, eliminating the need for batteries. Unfortunately the commercial DC powered air-conditioners I have found all require a battery bank and charge controller, in addition to the solar panels. This makes sense, designing a motor of any-kind, to work properly on a VARIABLE DC voltage (a solar panel’s direct output), is very tough/impossible. Still , if I spend money to increase the capacity of the existing solar power system, I should also factor in the additional flexibility more electric power will provide.

>>Going over the basics of a refrigeration cycle, it appears you know more than I do.
I just know the ideal gas law: PV=nRT : Pressure x Volume = number of Moles * ConstantR * Temperature
I DON’T know how various refrigerant types behave differently from this IDEAL gas law. But note that this law is only for an “ideal” gas and so does not take phase changes into account.

>> I determined that 10 cc's of water starting @ 60°F could be turned into steam in about 7 seconds with a 2 meter parabolic reflector.
Good gosh! This raises a whole new set of possibilities! It could pass through a turbine (to provide rotational power to a compressor/pump, generator, WHATEVER!) It could be used to distill my well water (water treatment plans will be my next post). It could keep help keep my house warm in the winter. It could pre-heat the hot water. I really like the idea of having steam as a power source, even if only during the day. Thinking about it now, I have indeed seen this technology in use- they use long tubes and curved reflectors. I’m going to research some of those systems now.
 

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