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Cooling by Solar heating air?

by Glurth
Tags: cooling, heating, solar
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Jun24-14, 12:43 PM
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Quote Quote by TechFan View Post
"...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:

Quote Quote by mfb View Post
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.....
Jun24-14, 12:47 PM
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Quote Quote by TechFan View Post
". 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.
Jun24-14, 05:20 PM
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Quote Quote by sophiecentaur View Post
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?
Jun24-14, 06:35 PM
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Quote Quote by OmCheeto View Post
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.
Jun25-14, 08:05 AM
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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.
Jun25-14, 01:20 PM
P: 37
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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