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

[TechFan]

"...You surely can't think I was 'getting at' anyone here??..."
Thanks for the clarification. My reference to existing commercial products, was just to prove the point that these things exist, and they work, despite many theoretical analysis here which contradict that. We all know DIY projects are better at the lowest cost; but sometimes it saves a lot of time and money, as I do with many of my projects, just to get a used machine and modify it somehow. We have Craigslist, Ebay, Pickers, Garage Sales and neighbors dumping all kinds of things. No one fixes anything, as it is more expensive than buying a new one, they don't even care about looking at a fuse and use whatever minor problem, as excuse to get a new thing they like more and dump the old one. Sometimes they trash things, just because there is no place to store them and they are in perfect working condition. For the Project I'm working on now, I've got a working Mini-Refrigerator from a Picker for $20.00. Perhaps, he ripped me off on that one; but I needed it right away and had no time to drive around trying to find one myself or get a better deal. The modified Microwave I'm using, I've got for free from a friend. That was the thinking, perhaps he can just get his hands on one of these used absorption fridges for cheap (or for free) and modify it for his project.

 

[sophiecentaur]

My issue is with the sellers of systems, not individual products. They say "Do it this way", when that's the way that gives them most profit - or (in the case of Politicians) glory. Europe is littered with an ever increasing number of wind farms. As a monument to the guy (government minister) who put it there, the wind farm is great. To the public who are subsidising it, it may not be so great - especially when the blades seem to be still most of the time.

 

[TechFan]

As mentioned before, I do not necessarily disagree with all you've said.

 

[OmCheeto]

>> The only problem I couldn't figure out, was how to survive, amongst 70,000 crazy people. Ahhhhhh!
Finally, one I can answer: go crazy yourself! (and some practical advise: having your tent inside a bigger tent REALLY helps with temp, sun, dust and noise)

>>Sorry that I'm having so much fun with this thread
Don't be sorry, its great!

Actually, staying clean was my worst nightmare. Which is why I was going to bring along a 55 gallon drum, and 75 gallons of water. I was not interested in taking just a tent, as my truck barely holds enough supplies for a 3 day trip to the OCF(read: Hippy Fair, without all the ambulance trips).

Anyways, I find it odd, that after 6 1/2 years at this forum, I think I've finally wrapped my head around the gas laws, because of this thread.

My guess is, that I had been too busy.

Anyways, I'm curious if anyone understood my modification to your OP air powered system: replacing the air with water as the working medium.

Here's a quick doodle:

The blue stuff, water, in section A is heated by a parabolic reflector.
As the water turns to steam, it pushes the piston, along with the pink solar shield, turning off the power source, allowing the heat to dissipate through the cooling fins, returning section A to its original position.
Section C, the refrigerant compressor, is attached via rod F to section A.
The fluid from section C, is sent to section D, which, having a smaller volume, will dissipate heat more efficiently.
The fluid is then sent to section E, which is in your bedroom.
Components G & H, are, well, my makeshift, off the top of my head, valve and fluid reservoir, awaiting a better engineering solution.

Anyways... Every single component of the above diagram has a myriad set of thermodynamic equations, related to their operation.

Yours, is not a simple problem.

Might be why, it is so much fun.

-------------------------------
Note to Mentors: Ok to delete, infract, and ban.
My friends and family will not leave me alone.
This post normally would have taken me 12 hours to clean up...

 

[Glurth]

>>Actually, staying clean was my worst nightmare.
This was my actually my greatest lesson of the cooling power of evaporation. Heat up your water with a solar shower, then take the shower, with hot water, in the heat of the 90F day. Out on that playa, the SECOND that water stops flowing, you will be utterly FREEZING. For about 40 seconds.

I don't quite get your design. Doesn't the compressed refrigerant need to expand to a larger volume (and lower pressure) in section E, in order to cool?
>>having a smaller volume, will dissipate heat more efficiently
Doesn't this depend upon surface area, not volume? (Perhaps you meant that given two tubes of the same volume, the one with the smaller radius will have more surface area?)
>>it pushes the piston
How the HECK does one make a durable but airtight, pneumatic, DIY piston?

 

[sophiecentaur]

>>Actually, staying clean was my worst nightmare.
This was my actually my greatest lesson of the cooling power of evaporation. Heat up your water with a solar shower, then take the shower, with hot water, in the heat of the 90F day. Out on that playa, the SECOND that water stops flowing, you will be utterly FREEZING. For about 40 seconds.

I don't quite get your design. Doesn't the compressed refrigerant need to expand to a larger volume (and lower pressure) in section E, in order to cool?
>>having a smaller volume, will dissipate heat more efficiently
Doesn't this depend upon surface area, not volume? (Perhaps you meant that given two tubes of the same volume, the one with the smaller radius will have more surface area?)
>>it pushes the piston
How the HECK does one make a durable but airtight, pneumatic, DIY piston?

The only remote chance would be to use a bladder of some sort. That wouldn't leak (for the first few hundred operations - before it perished or split). But the cylinder in a commercial refrigeration system doesn't need to have a perfect seal as the whole thing is operated in an enclosed system.
But the whole notion of doing the refrigeration cycle based on air is just not worth considering - surely. They spent decades finding the ideal type of refrigerants and that is far and away the best option. The standard system uses a mixture of lubricating oil and refrigerant and the oil helps to make a good enough seal for the compressor, I believe. If you move a compressor fridge about, it takes a while for the two fluids to find themselves in the right places for it to work properly. An absorption system is even more fussy.

 

[TechFan]

"...I don't quite get your design. Doesn't the compressed refrigerant need to expand to a larger volume (and lower pressure) in section E, in order to cool? ..."
Yes. Its also missing a check valve between sections C and D to avoid the refrigerant coming back to C when the piston returns. I don't see how this Engine will deliver any cooling effect.

"...How the HECK does one make a durable but airtight, pneumatic, DIY piston?..."
Good question.

"...But the whole notion of doing the refrigeration cycle based on air is just not worth considering - surely..."
Agreed.

"...The standard system uses a mixture of lubricating oil and refrigerant and the oil helps to make a good enough seal for the compressor, I believe..."

Sorry; but disagree on that one. The oil just lubricates the compressor piston otherwise it will over heat, expand and get stuck in the cylinder. It also helps lubricate the bushings for the crankshaft converting the circular motion of the motor into a linear one for the piston. The system is similar to a car engine. The seal is achieved by check valves (flaps like) sitting on the head of the cylinder. In normal conditions the oil sits at the bottom of the compressor casing. When the motor is running there is a pump action achieved by a worm (screw type) hole in the center of the motor shaft lifting the oil which then gets out at the top and sprays the mechanism to keep it lubricated. When the fridge is moved and it gets inclined, the oil enters the refrigerant tubing coming out of the compressor and then wait is necessary until it flows back by gravity to the bottom of the compressor, otherwise it circulates through the system and takes time to return decreasing efficiency in the process and I don't know what else may happen.

"...An absorption system is even more fussy..."
I don't know how that can be possible because absorption systems do not use compressors or moving parts therefore no lubrication required and no oil in the system.

 

[TechFan]

"...and the oil helps to make a good enough seal for the compressor, I believe..."
Rethinking on that one, yes that's another role played by the oil.

 

[OmCheeto]

...
I don't quite get your design. Doesn't the compressed refrigerant need to expand to a larger volume (and lower pressure) in section E, in order to cool?
>>having a smaller volume, will dissipate heat more efficiently
Doesn't this depend upon surface area, not volume? (Perhaps you meant that given two tubes of the same volume, the one with the smaller radius will have more surface area?)
>>it pushes the piston

I'm mostly trained as an electrician. I'm basically teaching myself how to build a refrigerator from the ground up.

Going over the basics of a refrigeration cycle, it appears you know more than I do.

How the HECK does one make a durable but airtight, pneumatic, DIY piston?

If you look back at the image, can you tell me why cylinders A and C can't be redesigned as a continuous cylinder? I can't. Engineering problem #1 solved.

...the cylinder in a commercial refrigeration system doesn't need to have a perfect seal as the whole thing is operated in an enclosed system...

See. Even the pro's have figured it out.

One more thing, I just ran across an actual device which does exactly what you are looking for. Although, from my calculations, it will take about a week(perhaps longer) to do what you want done, NOW*!

Solar Refrigeration: A Hot Idea for Cooling
How to build a solar refrigerator: The brighter the sun, the better it works
Oct 20, 2008
...
Making cold out of hot is easier than one might think. A group of students last year at San Jose State University built a solar-powered ice maker with $100 worth of plumbing and a four-by-eight-foot (1.2-by-2.4-meter) sheet of reflecting steel. No moving parts, no electricity but give it a couple hours of sunshine and it can make a large bag of ice.

From a couple of other articles, I found it was ammonia based, and 14 lbs of ice was its daily capacity.

And this is why I asked that you to calculate the heat capacity and R-values. I just interpolated my whole house numbers, to my bedroom, which is the only place I need cooled.

Here we go!
(all numbers are rounded to 2 significant digits, because this is just for fun)
Ice produced per day: 6.4 kg
Heat energy absorbed to melt ice: 2.1 billion joules
Volume of my bedroom: 33 m^3
Th = 32°C
Tc = 21°C
Energy required to cool the air in the room: 360,000 joules
Yay!
We have way more than enough cooling power to cool the air!

ummmm... wait... What was that about "heat capacity"?
Heat capacity of my bedroom: 2.3 billion joules / °C

hmmm...

That tells me, that a bag of ice, can change the solid contents of my room, by ≈1°C.
And it can do that once. And it takes all day for that "motor-less" device to make a bag of ice.

So, by my rough calculations, the device will be able to cool down my bedroom 11°C, but it will take 12 days.

Ha! Didn't I say that the other day?

...
The fact that it has no pumps, puts it in a "Carnot Engine" category, IMHO.

Great for textbooks, but I don't have all week for my air conditioner to cool me down now.
...

Not even off by a factor of 10. Woo Hoo!

*I suppose you could stuff the 14 lb bag of ice inside your sleeping bag. Then it might work. Never tried it myself.

 

[TechFan]

"...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.

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. They are real despite all your experiments and calculations to 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.

 

[OmCheeto]

"...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.

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?

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​

"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.

Sweet!

umm... Sorry. I appear to be getting off topic. But I get so excited!

 

[TechFan]

"...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.

 

[OmCheeto]

"...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:

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...

 

[sophiecentaur]

". 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.

 

[OmCheeto]

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.

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?

 

[OmCheeto]

...
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.

 

[TechFan]

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.

 

[Glurth]

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.