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

[TechFan]

I do not necessarily disagree with all you've said. Actually, I mentioned the heat pump refrigeration as an alternative solution, which I think is more efficient than the original post using air as the refrigerant by evaporation. That I know, will not produce enough cooling and that was what I was referring to. I never discarded water evaporation as a method. It was a bit confusing though, you mentioning the 2000 KJ/Kg from evaporating water without accounting for the time it takes to do so, which is a key element there (as you know) and it looked to me that you had mentioned a number to prove the point, which was not really helping as evidence of that. That was all.
As you mentioned this is just a good discussion place where we all learn from each other.
Thanks and good luck.

 

[sophiecentaur]

Yes. Time is relevant (i.e. the Cooling Power). I was using an intuitive appreciation and my informed / subjective experience of hand driers and wet clothing and I am 'remembering' that the cooling effect on a moderately small area with an air speed of around 1m/s is significant. The low power involved in shifting the air is a small contribution to the cooling power of the system. Imagine and compare the puny amount of friction heating that a similar amount of kinetic power could produce.

I guess the real question would be how much KE a cooling chimney could impart to the air across the evaporation surface. There must be some Heat Engine parameters in there somewhere which could give a ball-park answer..

 

[Glurth]

>> Einstein–Szilard refrigerator
Checked out the wiki article on this, but I'm not quite clear: Is this the same principle used on those propane based commercial fridges we talked about? Looks like a fairly simple machine, but Ammonia, and butane... definitely excludes it from my DIY skills.>>But the "pond" is to be a heat source (we want to take heat out of it) and not a heat sink in this case.

I'm not sure how I gave you this idea, but it is incorrect. The goal is to cool a room, not the pond. Here in the high desert, we have very cold nights (and very hot days). Since the pond will be the average daily temp, this is sure to be less than the daytime air temperature, thus I was going to use it as a possible heat sink (during the day, at least). Though I suppose, thinking about it, it COULD act as a heat source(heat-reservoir actually) when compared to cold night-time air- whatever that advantage could be.

Question about the hot air chimney: While I obviously don't want to pump the hot air into the room to be cooled, I feel like this simple setup has great potential. In science class have seen suction and blowing action use "T" connectors: Where connecting the pressure differential to the two TOP ends of the T, forces air through the bottom of the T. I don't quite get why this happens (I'll guess it's faster air=>lower pressure?), but I wonder, could a T shape like this be used with the chimney setup? Such that HOT air is let out the top, to outside, while un-heated air is pushed/pulled in/out of a third opening (like the T connectors).

The 2000KJ/Kg is, I think a useful number, even if only energy, rather than power. How much water am I going to have to pump (energycost) up to the swamp cooler, in order to cool the room. e.g. If my swamp cooler is too high above the water reservoir , there will be better ways to use the power for cooling. Though that's of course the ideal scenario, and we'd like to know the over-time quantities in real life... but I also suspect these quantities will be based upon IMMEASURABLE values, like the room's heat-loss/gain rate (which will be highly dependent on temperature of the room vs. outside). I feel like the important factor to take away from the temporal consideration: we want to pass as much air as possible over the evaporation surface, as quickly as possible.

 

[OmCheeto]

... but I also suspect these quantities will be based upon IMMEASURABLE values, like the room's heat-loss/gain rate (which will be highly dependent on temperature of the room vs. outside). ...

Why do you consider these immeasurable? I did it. Not for each individual room, but for my whole house. I know both its heat capacity(BTU/°F), and thermal resistance(R-value). It's not that difficult to do. It just requires a bit of time, and a few instruments: Two thermometers, a clock, a pencil, and a piece of paper.

And you can clean the house in between measurements. That's what I did yesterday during my towel in the kitchen science experiment.

ps. You should really consider investing in some insulation. My house stays comfortably cool even on 100°F days. It's when the nights don't drop below 80°F that things get icky. I traded one of my 50 watt solar panels for a 500 watt window air conditioner about 3 years ago. Best trade I ever made.

 

[sophiecentaur]

500w for most of the day would cost around 1GBP per day in UK. Quite a lot per year / summer. Used in conjunction with passive methods and a strict regime of shutter closing, the AC could make life sweet for much lower running cost.

I have never seen AC used in Europe with a pond heat sink. That should be very economical. Is it ever done? The performance factor could be way up.

 

[OmCheeto]

500w for most of the day would cost around 1GBP per day in UK.

1.50 USD around here.

Quite a lot per year / summer.

They have thermostats, so they don't run at that rate constantly.

Used in conjunction with passive methods and a strict regime of shutter closing, the AC could make life sweet for much lower running cost.

Indeed. If I didn't think there was merit to the idea, why else would I perform kitchen experiments?

I have never seen AC used in Europe with a pond heat sink. That should be very economical. Is it ever done? The performance factor could be way up.

Nor have I seen one installed in a private residence over here. Though my previous employer used an industrial sized evaporative cooler. I also see that they use them in the UK.

Fog clouds produced by Eggborough Power Plant (UK)​

We had a similar tower just down river from where I'll be spending the day today. Unfortunately, after the plant closed, people complained that it was unsightly. I thought it was beautiful. The plonkers won.

https://www.youtube.com/watch?v=qMTQSC8I8Zo​

ps. I like the idea of your cooling tower. Though as I mentioned, I'd add aluminum foil to the design. With just a cloth tower, moisture would be evaporating both from the inside and out. Adding an inner layer of foil would force all the evaporation to the outside surface. The cloth, in contact with the aluminum foil, would absorb the heat from the inner column of air, creating a moisture free, natural down draft. I would have built it yesterday, but my friend just bought her first boat, and we've been getting it ready, and plan on getting it out today. But tomorrow it's supposed to be 80°F, so I'll be able to build a double ended tomato cage cooling tower, very similar in shape to the big cement towers. Outside this time.

And depending on those results, I'll decide whether or not I need the waxed paper & muffin fan forced convection upgrade.

 

[Glurth]

>> It just requires a bit of time, and a few instruments: Two thermometers, a clock, a pencil, and a piece of paper.

I'm not sure I understand how this works. Doesn't the outside temperature change all day long, in which case we will have a variable rate of heat exchange. I must be missing something...given the following tiny set of sample data, how would I determine the R value?
8am inside:75F outside: 75F
9am inside:76F outside: 78F
10am inside: 78F outside: 85F

 

[mfb]

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.

 

[sophiecentaur]

1.50 USD around here.They have thermostats, so they don't run at that rate constantly.Indeed. If I didn't think there was merit to the idea, why else would I perform kitchen experiments?
Nor have I seen one installed in a private residence over here. Though my previous employer used an industrial sized evaporative cooler. I also see that they use them in the UK.



We had a similar tower just down river from where I'll be spending the day today. Unfortunately, after the plant closed, people complained that it was unsightly. I thought it was beautiful. The plonkers won.



ps. I like the idea of your cooling tower. Though as I mentioned, I'd add aluminum foil to the design. With just a cloth tower, moisture would be evaporating both from the inside and out. Adding an inner layer of foil would force all the evaporation to the outside surface. The cloth, in contact with the aluminum foil, would absorb the heat from the inner column of air, creating a moisture free, natural down draft. I would have built it yesterday, but my friend just bought her first boat, and we've been getting it ready, and plan on getting it out today. But tomorrow it's supposed to be 80°F, so I'll be able to build a double ended tomato cage cooling tower, very similar in shape to the big cement towers. Outside this time.

And depending on those results, I'll decide whether or not I need the waxed paper & muffin fan forced convection upgrade.

Expensive things, Air Conditioners - despite the occasional operation of a thermostat. The ones I see seem to be running their compressors and fans most of the time. The delivery of 'cool' to a building seems to be treated much less carefully than the delivery of 'warm'. The regime for people living in Alaskan winters is very tight. There are more people living at the high end of the liveable temperature range (I think) and the possibility of improved economy seems to have been explored much less where it's hot. Your experimental approach is very creditable and should be followed by more people imo. What price the notion of air conditioned football stadia in Dubai? Such a waste of resources when there exist places with ideal football playing temperatures. That's politics for you.

There are some excellent designs for heat exchangers for heating buildings by recirculating the heat and not the air (stinky). Why not use the same thing for cooling?

 

[OmCheeto]

>> It just requires a bit of time, and a few instruments: Two thermometers, a clock, a pencil, and a piece of paper.

I'm not sure I understand how this works. Doesn't the outside temperature change all day long, in which case we will have a variable rate of heat exchange. I must be missing something...given the following tiny set of sample data, how would I determine the R value?
8am inside:75F outside: 75F
9am inside:76F outside: 78F
10am inside: 78F outside: 85F

I think I forgot the ruler.
You will need the surface area of the interior of your house.

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.

Absolutely. At the time I did this, none of my single pane windows were thermally insulated. After some calculations, I determined that roughly 1/2 of the thermal losses were through my windows, even though they comprised only 5% of the surface area of the house.

There can also be no significant heat sources or sinks during data collection. This means no cooking, no doors or windows left open, etc.

My determining the heat capacity and R-value of the house were in no way meant to be other than an approximation, but my numbers told me a lot. I purchased the house in May of 1989, and by November, I'd determined the head capacity was approximately 5000 BTU/°F, and the R-value was a dismal 6.3. This told me there was something very wrong with the house. I discovered later, that there was no insulation in any of the exterior walls. And the insulation in the attic was about 2 inches thick, and composed of a material which I had never seen before. It was kind of fiber-glassy, but was completely black.

I fixed most of this.

 

[sophiecentaur]

I think there needs to be some significant modification to the assessment of performance in respect of heat loss in a cold climate if you want a useful figure for how well a house will keep cool inside. In the daytime, in full sun, I would guess that the main influence will be the 1kW per square metre of incident solar energy. Reflection, rather than internal insulation will have greatest effect per $ / £ spent.

The 'greenhouse effect' from windows will be very significant - much more significant than when keeping warm is the aim. We all know what a long pay back time is involved for investment in double glazing in temperate to cold climates.
@ Omcheeto. Keep up with your experiments. You may well identify a crucial factor that will make a real difference to your comfort, yet not cost you an arm and a leg. White walls and shutters and a shiny roof are probably the way forward.

 

[OmCheeto]

I think there needs to be some significant modification to the assessment of performance in respect of heat loss in a cold climate if you want a useful figure for how well a house will keep cool inside. In the daytime, in full sun, I would guess that the main influence will be the 1kW per square metre of incident solar energy. Reflection, rather than internal insulation will have greatest effect per $ / £ spent.

The 'greenhouse effect' from windows will be very significant - much more significant than when keeping warm is the aim. We all know what a long pay back time is involved for investment in double glazing in temperate to cold climates.
@ Omcheeto. Keep up with your experiments. You may well identify a crucial factor that will make a real difference to your comfort, yet not cost you an arm and a leg. White walls and shutters and a shiny roof are probably the way forward.

You nailed it.

My sister just arrived from Texas yesterday morning, so I had to do my social obligations, and left the house from 11 am to 8 pm. When I got home, I checked the relevant temperatures:
Inside: 68.1°F
Outside: 65.6°F
The maximum daytime temperature was reported to be about 70°F (ref)

I scratched my head, and went to bed.

This morning, when I woke up, I decided to look for a heat source culprit.
All I had to do was open my eyes. My bedroom faces south, and I install a black cloth covered frame there during the colder months. It was still installed. Installed in this case means: Propped up on a bookcase, leaning against the wall, in front of the window. It took me 60 seconds to uninstall and store, until next November, behind the bedroom door.

The window is almost a full square meter, but I don't get that much sun, due to the forest of trees, so it shouldn't have warmed the house to almost outside ambient temperature. But I also have a huge living room window that also faces south. The mini blinds had been left open. That was another 2 square meters of solar heating source, as everything in the vicinity of that window is fairly dark, if not black.

3 square meters of solar heating for just two hours, yields a lot of energy.

I would continue, but I've been summoned to more, social duties. Gotta love friends.

ps. Current temperature conditions in °F:
inside: 65.2
outside: 56.6
attic: 62.9 (above R-13 rated insulation, and below the roof, midpoint between ceiling and peak)
crawlspace: 60.9 (no insulation down there except on the inside face of the foundation. again R-13)

I permanently installed temperature sensors in my attic and crawl spaces, 24 years ago.
My house is wired, for science.
Yes, IFLS. Always have, always will.

-----------------------------
And now I'm off to an island, with friends. It's a lovely place. Really.

 

[OmCheeto]

I should probably mention, that I've been following this thread, from day one, and have laughed at many of the comments. Not because they were stupid, but, because I had either performed experiments, or researched the advertised technologies, myself.

I have an airtight container, the "hot-box", filled with air from outside...

Stirling engine technology. Thumbs down.

http://en.wikipedia.org/wiki/Solar_air_conditioning)
...

Awesome list of options. :thumbs:

2 Photovoltaic (PV) solar cooling
3 Geothermal cooling
4 Solar Thermal Compression Technology
5 Solar open-loop Air Conditioning using desiccants
6 Passive solar cooling
7 Solar closed-loop absorption cooling
8 Zero-energy buildings

As an advocate of poly-hybridization, I would say; "All of the above".
Though I didn't read it front to back, so I might throw one or two ideas out.

My favorite line in the wiki article was:

Solar Thermal Compression Technology
...
The poor use jargon and dubious technical explanations makes the section highly suspect.

in PF parlance; "Crackpots!"

... I'm trying to make it even more KISS, and reduce electric use to powering valves open and closed, rather than running a compressor.

That's how I do everything. Although "KISS", in my case means; "I have no money, so everything has to be made out of sticks, old pop bottles, duct tape, and will be lubricated with WD-40"

But is it too simple to work WELL...

"too simple" is a relative term.

I doubt you get much out of it. ...

Bingo! (meaning; "Doch!")
The quote from Hyperphysics came to mind, regarding a "Carnot Engine";

The conceptual value of the Carnot cycle is that it establishes the maximum possible efficiency for an engine cycle operating between TH and TC. It is not a practical engine cycle because the heat transfer into the engine in the isothermal process is too slow to be of practical value. As Schroeder puts it "So don't bother installing a Carnot engine in your car; while it would increase your gas mileage, you would be passed on the highway by pedestrians."

What about circulating the pond water through a heat exchanger in the house?

I tried that. It did not work.
Data collect from that experiment: This doesn't work.

Did you ever consider a cooling tower style of cooler?...

Going through my 3 ring binder yesterday, labeled "Thermodynamics", I discovered that I'd actually experimented with evaporative cooling about 5 years ago. It was a dismal failure.
Data available on demand.
But it wasn't a tower design, hence, my interest in this thread.

-No pump required to circulate the refrigerant, heat does the job.

See "Carnot Engine" reference, above.

-PVs are expensive and inefficient in energy conversion. I would avoid using them if not really needed.

I disagree. They are dirt cheap, if you know how to cheat.

...It's even cheaper, when you're more than 100% efficient:
Let's see... 24 watts of electrical input over 3.5 hours yields 84 watt hours consumed.
Energy gained by the system was 2300 watt hours.
2300 - 84 = 2216 net watt hours
system efficiency: η = P_out / P_in
= 2216/84 = 2338% efficiency
...
Dullards have apparently never heard of the Kobayashi Maru. When in doubt, cheat.
...

>> Einstein–Szilard refrigerator
Checked out the wiki article on this, but I'm not quite clear: Is this the same principle used on those propane based commercial fridges we talked about? Looks like a fairly simple machine, but Ammonia, and butane... definitely excludes it from my DIY skills...

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.

----------------------------------------
Aside: I can really appreciate SETI's search for extraterrestrial intelligence, after going through my 25 year old, 150 page binder of thermodynamic home improvement notes: "This person was way smarter than I am, but I have not a clue what he was doing. This is pure, unintelligible, un-annotated, numerical, gibberish. hmm... perhaps with some curve fitting...

 

[TechFan]

..." Quote by TechFan View Post

-No pump required to circulate the refrigerant, heat does the job.

See "Carnot Engine" reference, above. ..."

Absorption refrigerators work and have been in use for more than 100 years https://www.gacjp.com/en/pro/jyu/khp.html

 

[OmCheeto]

..." Quote by TechFan View Post

-No pump required to circulate the refrigerant, heat does the job.

See "Carnot Engine" reference, above. ..."

Absorption refrigerators work and have been in use for more than 100 years https://www.gacjp.com/en/pro/jyu/khp.html

bolding mine

Show me one today, that doesn't use at least one pump.

Or, have we redefined "pump"?
def: a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action.

Components, from the KHP image:

Engine*: = pump
Fuel injection pump = they said it
Compressor: will always be a pump in my mind
Engine starter: external fuel source other that "solar" implied. See above.


*If anyone starts a philosophical discussion about what an "engine" is, I will...
take a nap...

 

[TechFan]

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

 

[sophiecentaur]

bolding mine

Show me one today, that doesn't use at least one pump.

Or, have we redefined "pump"?
def: a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action.

Components, from the KHP image:

Engine*: = pump
Fuel injection pump = they said it
Compressor: will always be a pump in my mind
Engine starter: external fuel source other that "solar" implied. See above.


*If anyone starts a philosophical discussion about what an "engine" is, I will...
take a nap...

I think this is a cross post but I'll post it anyway.
Are we talking at cross purposes here? Electrolux (afaik) are still making gas / DC / AC absorption fridges for Camper Vans and boats. There is no 'pump' in these. Absolutely no moving parts apart from the circulating fluids. They have a very low COP compared with compressor types. If you're talking about Air Con units then a fan would be needed for circulating room air. Is that the 'pump' you are referring to?

The COP of a compressor unit is so good that, even when powered from a PV panel (say 1m², which would give you 200W), you could expect at least 1kW worth of cooling (very sloppy terminology I know) over a temperature difference of 20C

 

[TechFan]

"...Absolutely no moving parts apart from the circulating fluids..."
Exactly.
"...They have a very low COP compared with compressor types..."
That was already mentioned and we agreed on that; but we also discussed the original poster wanted to use direct sunlight and no PVs. The Absorption refrigerator was an alternative solution in that case which uses no pumps, motor, compressor or moving parts, except for the circulating fluids as you have mentioned.

 

[OmCheeto]

... Electrolux (afaik) are still making gas / DC / AC absorption fridges for Camper Vans and boats. There is no 'pump' in these. Absolutely no moving parts apart from the circulating fluids. They have a very low COP...

How low a COP do they have? I can't imagine a natural circulation device suited for the "real world"*.

Camper Vans and Boats, in your context, are still on my horizon.

*Except in "Economies of Scale" cases, of course. I'm familiar with the wiki entry on the S5G.

 

[sophiecentaur]

"...Absolutely no moving parts apart from the circulating fluids..."
Exactly.
"...They have a very low COP compared with compressor types..."
That was already mentioned and we agreed on that; but we also discussed the original poster wanted to use direct sunlight and no PVs. The Absorption refrigerator was an alternative solution in that case which uses no pumps, motor, compressor or moving parts, except for the circulating fluids as you have mentioned.

I know he started off with that view but, once I had pointed out that you need neither a battery nor a charge controller for the 'midday sun' situation, he seemed more interested. The bald statement that PVs are not efficient is not very relevant unless the efficiency 'with respect to what' is stated. They are cheaper than they used to be but still take up significant area (for instance on a boat). They last pretty well, too and can be used for other things when needed.

I think this thread has more or less run out until a tighter specification is made for the requirement. There are many ways of skinning this particular cat. In the world of DIY projects, the best solution is often the one involving free or cheap materials - or what may be acceptable, visually, to neighbours (OmCheeto may know about that!). One thing is for certain: the best solution for the individual is seldom the best solution for the flashy Green Salesman! Money changes everything.

 

[TechFan]

"...One thing is for certain: the best solution for the individual is seldom the best solution for the flashy Green Salesman! Money changes everything..."
I don't see the connection of that statement with this thread, nobody is trying to sell anything here as far as I know, we are all giving our opinions and discussing a physical subject trying to help the original poster.

__________________

 

[OmCheeto]

I know he started off with that view but, once I had pointed out that you need neither a battery nor a charge controller for the 'midday sun' situation, he seemed more interested. The bald statement that PVs are not efficient is not very relevant unless the efficiency 'with respect to what' is stated. They are cheaper than they used to be but still take up significant area (for instance on a boat). They last pretty well, too and can be used for other things when needed.

I think this thread has more or less run out until a tighter specification is made for the requirement. There are many ways of skinning this particular cat. In the world of DIY projects, the best solution is often the one involving free or cheap materials - or what may be acceptable, visually, to neighbours (OmCheeto may know about that!). One thing is for certain: the best solution for the individual is seldom the best solution for the flashy Green Salesman! Money changes everything.

And on that note, let me try and sell you on my original idea, which popped into my head on day one. I've been working out the engineering kinks since then, so I haven't mentioned it, as I can't imagine myself building the beast.

Rather than heat up some air, why not heat up some water, in the original contraption? 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. @ 250°F, the steam would have a pressure of around 15 psi. I used 15 psi, as that's what most automotive cooling systems are rated at, and you can get that stuff from the junk yard for dirt cheap.

Now I also know that water at room temperature will boil when the pressure is reduced. What I did not know, is what is demonstrated in the following video, as, although I've boiled room temperature water in a hypodermic syringe before, I have never taken this experiment to this level:

https://www.youtube.com/watch?v=pOYgdQp4euc​

Those bloody brits made ice! At room temperature!

I'm going back to the drawing board. That was too cool not to research.

ps. Just ignore my first two paragraphs here. Kind of.

 

[OmCheeto]

My kitchen, currently, looks like Austin Power's suitcase, exploded...

Those clear tube things are Bethesda Research Lab gradient formers. I got them at surplus. They looked like they would make perfect vacuum chambers. Which they are, if you can figure out how to seal the top openings. It took me an hour. Cellophane does not work. Condoms stretched over a 16 oz inverted plastic lid, work perfectly.

Unfortunately, the tubing is not designed for a vacuum, so I'm having difficulty continuing. My fish tank air bubbler tubing is not quite the correct diameter.

(one hour later)

Eureka! I successfully evacuated 90% of the water from the gradient former. Unfortunately, I was pumping the water from the bottom, and the temperature didn't change. Of course, after the fact, I'm pretty sure I understand why. Doh!

---------------------------
ps. Sorry that I'm having so much fun with this thread, but "high desert" living conditions, were exactly what I was looking forward to a few months ago. And I worked out solutions to all of the problems. Zero local water, high daytime temps, freezing cold nighttime temps, living in a cardboard box like structure. Fortunately, all the tickets for Burning Man sold out too quickly. I now have 14 months, to figure this out.

The only problem I couldn't figure out, was how to survive, amongst 70,000 crazy people. Ahhhhhh!

 

[Glurth]

>> 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!

 

[sophiecentaur]

"...One thing is for certain: the best solution for the individual is seldom the best solution for the flashy Green Salesman! Money changes everything..."
I don't see the connection of that statement with this thread, nobody is trying to sell anything here as far as I know, we are all giving our opinions and discussing a physical subject trying to help the original poster.

__________________

You surely can't think I was 'getting at' anyone here??

I am just pointing out that what is advertised commercially may not be anything like optimal for a PF member. The marketing blurb input could be very significant to many readers of this thread. Your flashy green salesman would not be in business if he / she were running a charity for the practically minded.

 

[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.