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

[Glurth]

I have an airtight container, the "hot-box", filled with air from outside.
I close the two valves to the outside air, and let the sun heat it up.
Once it reaches a certain temperature/pressure: I open/unlock a one-way check-valve that leads to a shaded/water-immersed coil of copper tubing. The tube is open to (indoor) air on the other end.
For simplicity, let’s say the copper coil is long enough that hot & high-pressure air from the container, while passing through it, will be cooled to room-(outside)-temperature by the time it reaches the open end.
When the air finally escapes from the tube, it will expand from high-pressure to atmospheric pressure, further cooling the gas.
The amount of time it takes the hot-box chamber 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* (no longer pushing high pressure air); we close/lock the valve to the copper tube, and open the two valves (top and bottom) exposing it to open air so the hot air inside will be replaced with fresh air, and we can repeat the process.

Is all of this actually correct? Am I forgetting/ignoring something important? Like; will significant pressure be lost due to friction in tube? Or, do I need to consider the air already in the tube if << the air in hotbox?
If this does work, I assume such a device like this already exists, what is it called? ( I saw similar, but not the same, devices here, http://en.wikipedia.org/wiki/Solar_air_conditioning)

If I wanted to use this as a small cooling unit (which would probably require a round-robin array of heating chambers, with temperature controlled valves for each, leading into to the coil, and so forth), will the cooling effect even be noticeable? Or should I be asking, how big or hot would my hot-box need to be for the effect to be noticeable? (I live in rural high desert: powerful sun, low atmospheric pressure, lots of space)
I'm getting a bit lost trying to figure out what’s going to happen to the pressure in the hot-box chamber (and the tube's output), when the air is leaving via the open end of the copper tube, AND still being heated by the sun. E.g. will the decrease in pressure be linear, or exponential? *I think this info will be important in determining when a "cycle" should end, and the hot-box flushed with fresh air.

Thanks in advance for your feedback!

 

[mfb]

This is roughly the basic idea of a fridge or machines that produce liquid air, just in the first step the heating gets replaced by compression as this is faster and does not heat the medium so much.

 

[Glurth]

Indeed, AC's and Fridges are where the idea originated. I'm trying to make it even more KISS, and reduce electric use to powering valves open and closed, rather than running a compressor.

But is it too simple to work WELL, and be worth the effort of making it? (I live off grid, and need to save my PV generated electric for lights and computers, so "worth the effort" has a much lower threshold than for most: just needs to cost less than new PV cells to power an AC unit, and mounting equipment.) Size of those hot-boxes will really effect price. How can I determine how big I'll need to make them?

 

[mfb]

I doubt you get much out of it. Air has a tiny density, has a bad absorption both for visible and infrared light (so heating a lot of it takes a while), and I guess you won't achieve high pressures. Your cooling pipe cannot be placed inside (otherwise the setup heats your room), so a part of the temperature drop just goes to the difference between outside and inside air temperature before any cooling effect starts. And your overall setup would be another heat bridge where heat gets conducted to the inside.

 

[Glurth]

>>has a bad absorption both for visible and infrared light
That's why I would make the"hot-boxes" out of metal, and paint them black. Perhaps even add mylar reflectors to direct more sunlight on them.

>>and I guess you won't achieve high pressures
I think I see your point, this is indeed probably the biggest issue. Just to confirm I have PV=nRT right, I would need to DOUBLE the air temp (in Kelvins), to get just 2ATM of pressure? That does indeed seem difficult (75F -> 620F!)

>>so a part of the temperature drop just goes to the difference between outside and inside air temperature before any cooling effect starts
I'm actually thinking about using a small outside POND that I have, for cooling the tube. The pond will be the average daily temp, which includes those cold desert nights. Evaporation will also help keep it cooler than hot daytime air (and probably even cooler than my house, which does NOT have any AC yet.)

>>And your overall setup would be another heat bridge where heat gets conducted to the inside.
Do you mean the copper pipe will thermally conduct the heat from the hotbox to inside? This I don't understand, won't any given section of the tube be the temp of the air inside that section of tube? If we can cool the heated air inside the tube down to outside-temp, won't the section of tube containing that cooled air also be the outside-temp?

 

[mfb]

That's why I would make the"hot-boxes" out of metal, and paint them black. Perhaps even add mylar reflectors to direct more sunlight on them.

I would paint the bottom and make the top out of glass - that way, you trap more light. And convection works better if you heat it at the bottom.

I think I see your point, this is indeed probably the biggest issue. Just to confirm I have PV=nRT right, I would need to DOUBLE the air temp (in Kelvins), to get just 2ATM of pressure? That does indeed seem difficult (75F -> 620F!)

Indeed.

Do you mean the copper pipe will thermally conduct the heat from the hotbox to inside? This I don't understand, won't any given section of the tube be the temp of the air inside that section of tube? If we can cool the heated air inside the tube down to outside-temp, won't the section of tube containing that cooled air also be the outside-temp?

Unless the pond is directly at the house, there is a pipe in between that can get hotter than the pond temperature. And your pipe needs some connection to the wall, which might not be 100% airtight, and so on.

 

[mp3car]

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

 

[sophiecentaur]

Did you ever consider a cooling tower style of cooler? A tall black chimney will have a vertical flow of air through it. The air flowing in at the bottom is drawn over a 'wick', wetted by the pond water and in good thermal contact with the pond. The hotter the sun, the stronger the updraft and the more evaporative cooling.
No moving parts either. Top up the pond occasionally.
The chimney / tower may need to be quite tall, of course but I have seen a reference somewhere to such a system in PF which works. I will try to find it.

 

[mp3car]

I thought about evaporative too, but it would depend on the size of the pond and the frequency if rain or whatever method keeps the pond full... Wouldn't want to empty the pond I assume, as they are off the grid, they may use a well for water, which would use power to fill back up...

 

[sophiecentaur]

Evaporation could be a problem; true. For a pond that's not too large, there's always the possibility of using plant cover. Plants can be good at regulating temperature by efficient use of water by transpiration.

Alternatively, what about a reflective floating cover?

 

[P K Pillai]

Air heaters

The tank could be fitted internally with finned air heaters powered by photovoltaic cells.This will increase tank pressure substantially.Small dia orfices at the outlet end will reduce the temperature.

 

[Glurth]

I've heard of "swamp coolers" before, but never heard of one using a chimney to power airflow like that. But I'm a bit confused about that idea, won't the sun on the black chimney make the air hot, rather than cool? Is the ouput \ top of the chimney supposed to feed into the area I'm cooling?

I DO use a well for water, so there IS a power cost to pump it up, but pumps are one of the things I don't mind using my PV electric power for. Of course I'd rather power pumps differently, but that's another post.

 

[TechFan]

I think the Pr drop inside the box will be close to exponential anyway as it will take longer to keep increasing the Pr due to heat than the Pr drop because of opening the valves.
I think there are 2 main problems for this approach to be able to produce a useful cooling effect:
-Air as the refrigerant. Reason why they have been using other gases to increase efficiency of refrigeration systems instead of air.
-Open refrigerant circuit.
Perhaps you can still use solar energy for the heating and use a system similar to absorption refrigerators http://en.wikipedia.org/wiki/Absorption_refrigerator. Having a close refrigerant circulation circuit, will allow you to use a much more efficient refrigerant than air.

 

[sophiecentaur]

If you want to go down the refrigeration route then use a 12v compressor-based system, fed from a large PV array. Proper compressor systems have by far the best performance coefficient. Even doing it this way, the problem is that you need to shift 1kW worth of solar energy falling on every sq metre of pond area with what the PV array can produce. Allowing for inefficiency of the whole refrigeration power chain, that means a pretty massive area of PV.
It is far better to stop the sunlight from falling on the pool in the first place - if that's practicable.

 

[TechFan]

"...Proper compressor systems have by far the best performance coefficient..."
That's why they are used more than anything else. Apparently he wants to use sunlight directly in the first place. Since he wants it for lightly cooling a room and not refrigerate goods, perhaps he does not need so much sun power to get the cooling effect he needs. On the other hand, the conversion from sunlight to electricity in the PV, is pretty inefficient anyways and most of the sunlight power will be lost right there. Maybe its better to use sunlight to directly heat the absorption refrigerator system. It could be less expensive also. I don't know.

 

[Glurth]

Great input, thank you!
I read that wiki article on the absorption refrigerator, but I don't think I'm quite clear on it yet: I see how the thermodynamics of it are supposed to work, but I'm not quite clear how the fluids and gases are moved around between the different chambers, does it use a pump, or does the heat gradient itself generate this flow, like a convection cell?
So you think I can buy a commercial Absorption Fridge that runs off, say... propane, and convert it to heat the internal-chamber with solar reflectors instead? I'll need fans to get the cool air into the room I want it, but that should be pretty low power usage. I can even recirculate back to the cooling unit over and over, for better cooling over time. I like this solution.Regarding the pond, which actually has yet to be dug, it's going to be a DEEP and long, kind of like a stream (minimal surface), with lots of plants growing on the banks, and floating potted plants in the water itself to provide SOME shade to reduce evaporation. It may not be enough.

Regarding PV: We have high winds in this area, so mounting a PV panel, costs about as much as the PV panel itself, maybe even more! This can get really pricey really quick, which is why I'm shying away from PV where possible.

 

[TechFan]

-No pump required to circulate the refrigerant, heat does the job.
-Yes, I think you can buy a commercial unit and heat the system with sunlight reflectors, etc. I would suggest you build a temp control system of some kind controlling the amount of sunlight to avoid the thing getting overheated and over pressurized which can make it explode. An overpressure release valve will also be a good idea. Generally speaking, provide safety means to avoid overpressure of the refrigerant which might occur by overheating, leading to explosions.
-I agree, you can circulate the air using a simple fan which takes very little power to operate.
-PVs are expensive and inefficient in energy conversion. I would avoid using them if not really needed.

 

[mfb]

I've heard of "swamp coolers" before, but never heard of one using a chimney to power airflow like that. But I'm a bit confused about that idea, won't the sun on the black chimney make the air hot, rather than cool? Is the ouput \ top of the chimney supposed to feed into the area I'm cooling?

No, this would be a method to cool the pond. Or a smaller amount of cooling water.

If you want to go down the refrigeration route then use a 12v compressor-based system, fed from a large PV array. Proper compressor systems have by far the best performance coefficient. Even doing it this way, the problem is that you need to shift 1kW worth of solar energy falling on every sq metre of pond area with what the PV array can produce. Allowing for inefficiency of the whole refrigeration power chain, that means a pretty massive area of PV.
It is far better to stop the sunlight from falling on the pool in the first place - if that's practicable.

Why do we have to cool the pond now?

 

[TechFan]

"...but I'm not quite clear how the fluids and gases are moved around between the different chambers, does it use a pump, or does the heat gradient itself generate this flow, like a convection cell?..."
Check kerosene or propane refrigerators. They work very similar to compressor driven ones, that is they have a close refrigerant circulation circuit evaporator and so on. They don't operate based on heating air; but the refrigerant inside the close circulation refrigerant system which when boils in the evaporator, absorbs heat from the surroundings. The chambers (I guess) refer to the evaporator, condenser and so on, not the cooling chambers inside the machine where the food is placed and air circulates by convection.

 

[frazelle09]

If your area is not very humid, swamp coolers work alright for cooling. All they are are a box with some absorbant material through which water flows, usually from top to bottom. At one end of the box there is a fan which blows through the box into the room. People usually mount them in windows and they have a small hose which feeds the top of the box.

As i mentioned they are good in hot, dry climates, not humid ones, so your usage may vary.

Have a great morning! :)

 

[sophiecentaur]

Refrigeration cycles that don't use a compressor are unbelievably poor performers. Peltier junctions or so-called 'absorption style' units have their place in appropriate circumstances but when you want to shift serious amounts of heat on Earth, they are useless. On a small scale, a far better solution for camping and boating fridges ( and even freezers- I have one) PV cells driving a compressor system win hands down.
It could be that a large solar collector could yield the right sort of power at the right high temperature to work an absorption cycle. Calculations needed here and throughout this project.
Personally, I like the swamp cooler idea, driven by a tall convection chimney. There is no problem having a hot chimney 'cos the air drawn into the bottom is at ambient temperature.
The only running cost is in replacing evaporated water. To estimate feasibility of this style of cooling, you compare the Latent Heat of evaporation of the water with the amount of heat that needs to be shifted (total solar heat on pond surface per day and required min / max temperatures you want.)
Loads of fun experimenting to be had.

 

[TechFan]

This is just one example of a commercial Air Conditioner using a heat pump. Peltier Elements were not mentioned as a possibility.
https://www.gacjp.com/en/pro/jyu/khp.html

 

[Glurth]

Many thanks for all the suggestions and input.

Regarding primary purpose: I'd just like to help keep my home office a bit below ambient outside temperature. Ideally the cooler air will enter the room near my computer's fan intake, to help keep it from overheating. My comfort is a less important, but existing, goal as well.

Regarding "the pond": We certainly don't need to try and keep it cool, other than shade. I think everyone is rightly concerned about the pond's rate of evaporation in my climate, but that is a different post. I was just throwing it's presence out there as an available heat sink.

I have a few specific questions:
"Refrigeration cycles that don't use a compressor are unbelievably poor performers."
While I see that EFFICIENCY may be poor, that's OK if it just means I need more direct sunlight (I have lots of that for free). It's the cost of buying and mounting the PV cells (plus charge controllers, and all the additional circuitry) that adds up to the BIG $$. So rather than power efficiency, I need to consider my "Cost Efficiency" in terms of TOTAL INITIAL COST vs FINAL COOLING EFFECT. Given this fact, do you stick by your statement, Sophie? (I must certainly grant that the PV output is far more flexible, as I can power ANY electric device, rather than JUST a cooling device.)

Swamp coolers/black chimney: I really like this idea. Swamp coolers work great in this area of low atmospheric pressure and low humidity. A pump (small: ounces per minute) for the water supply will be all the electricity I need, perhaps I can buy a commercial unit, and disable the fan, using the black chimney instead. Am I correct in my assumption that this little pump will require much less power than an AC's compressor?

I could use a bit more explanation of how the black chimney actually works. I mean SOME of the air in there must get hotter, in order to rise and pull in fresh air, right? Is this heating negligible because fresh air is always being pulled in (more heating directly relates to more fresh air)? Or does the expansion of the heated air itself counteract the addition of heat, keeping temperature the same? Design wise; Do I want the chimney to be a constant width, or to taper/expand as it goes up? Do I want to shoot for particular height/width ratio?

Thanks again for all the input!

 

[frazelle09]

" Am I correct in my assumption that this little pump will require much less power than an AC's compressor?"

Yes. Much less.

Have a great day! You're gettin' there! :)

 

[sophiecentaur]

Just a few points. The best solution is very application specific. Swamp coolers are useless in UK and very good in Oz outback (I have heard).
The PV / compressor system needs no charge controller because batteries are not needed. You may need a 'smart' system to supply the starting current for a compressor motor but it can be home brewed. Cooling is only needed when the sun shines.
The cheapest solution must involve a solar heated chimney and evaporation cooling. The hot air is all in the top section. Air is at ambient temp as it is drawn in at the bottom. A wide, shiny half cylindrical reflector would double / triple heat input to a vertical black chimney. Evaporative cooling produces 2,000kJ for every kg of water evaporated.
You have to involve actual figures if you want to have an optimal solution here.

 

[Glurth]

"The hot air is all in the top section."

I thought the output, for the air to be cooled by the swamp cooler, came FROM the top section.
Or do I misunderstand, is there more than one output?

Good point regarding hooking it up to only run when the sun shines, as separate from my existing power infrastructure. Though single-purposing it like this eliminates some of the flexibility electric power provides. I'll look for some DC powered commercial swamp-coolers (fan included) tonight, and let you know what I find. This might just be the simplest-setup route, not sure about cost yet.

Why do they call them "swamp-coolers", when the worst place for them to work is in a swamp?

 

[OmCheeto]

"The hot air is all in the top section."

I thought the output, for the air to be cooled by the swamp cooler, came FROM the top section.
Or do I misunderstand, is there more than one output?

Good point regarding hooking it up to only run when the sun shines, as separate from my existing power infrastructure. Though single-purposing it like this eliminates some of the flexibility electric power provides. I'll look for some DC powered commercial swamp-coolers (fan included) tonight, and let you know what I find. This might just be the simplest-setup route, not sure about cost yet.

Why do they call them "swamp-coolers", when the worst place for them to work is in a swamp?

I think the reason they call them swamp coolers is because the poor people in America live in areas surrounded by swamps, and swamp coolers are the most energy/cost efficient way to keep cool.

As an experiment tonight, I suggest you take a spritz bottle with you, as you go to bed.
Once in bed, cover yourself, with a single bed sheet.
Then, using your spritz bottle, spritz your sheet, somewhat thoroughly.
Then, and only then, will you realize how freaking efficient swamp coolers are.

ps. This is why only poor people use such devices, as you will wake up a few hours later, and have to spritz all over again. It is not conducive to a good nights sleep.

 

[sophiecentaur]

@glurk
I see your confusion here. This is because you have two different applications. For cooling the pond, ambient air flows over the pond surface (with an area of wick to cool by contact). To cool a room, some simple heat exchanger is called for. This is a step up in complexity and would be best with some moving parts. For a big chimney system there would be sufficient power to drive a turbine. But an office has electrical power so a turbine is hardly worth while.

 

[TechFan]

"...Evaporative cooling produces 2,000kJ for every kg of water evaporated..."
These numbers although apparently huge, don't mean much. To properly quantify the cooling effect Watts (Energy/Unit of time) is a more proper unit to use. Its not how much energy is absorbed; but how much and how fast it is absorbed. It could take a week to evaporate 1Kg of water, in which case the cooling effect will be nothing as the heating due to other sources will surpass that considerably. The key is to make the Energy transfer in a way that more heat is evacuated and faster than what is coming in.
Close circulation refrigeration achieves that. The more refrigerant is evaporated per unit of time and the faster it circulates the more the heat absorption at the expense of the energy consumed to do that, of course.

 

[OmCheeto]

... Evaporative cooling produces 2,000kJ for every kg of water evaporated.
...

These numbers although apparently huge, don't mean much.

That number means a lot to me, converted to watt-hours. It tells me I have to evaporate 1 kg of water per hour, to be equivalent to my 500 watt electric air conditioner, which keeps me quite comfortable on 100+ °F days, and 80+ °F nights.

... It could take a week to evaporate 1Kg of water

It probably would, if you had a bucket of water sitting on the porch.

, in which case the cooling effect will be nothing as the heating due to other sources will surpass that considerably. The key is to make the Energy transfer in a way that more heat is evacuated and faster than what is coming in.
Close circulation refrigeration achieves that. The more refrigerant is evaporated per unit of time and the faster it circulates the more the heat absorption at the expense of the energy consumed to do that, of course.

I have an experiment going on in my kitchen at the moment. It started about 4 hours ago. The only thing I've determined, is that I've apparently built a psychrometer. The sheet still feels cool to the touch...

≈80% humidity...

data:
area of evaporative material: 1.25 m²
mass of dry material: 0.16 kg
initial mass of wet material: 0.31 kg
final mass of wet material: 0.17 kg
maximum ΔT: 4°F

conclusions:
tent shaped wet towels in a humid kitchen, will eventually, dry out.
Om is really enjoying an infinite amount of time off.


next project:
tomato cage tower of evaporative doom...
(with aluminum foil)
(and waxed paper)
(and a 5 watt muffin fan, salvaged from my experiment from 20 years ago)

 

[frazelle09]

"... like kids
playing on the seashore ...
finding smoother pebbles ..."

oMMCheeto - i think you've got the idea...

Have a great afternoon! :)

 

[TechFan]

"...That number means a lot to me, converted to watt-hours. It tells me I have to evaporate 1 kg of water per hour, to be equivalent to my 500 watt electric air conditioner, which keeps me quite comfortable on 100+ °F days, and 80+ °F nights..."
Exactly, when time is mentioned it has meaning, without it there is no meaning. That's what I meant.
"...It probably would, if you had a bucket of water sitting on the porch..."
Exactly, it depends where you have it. It was just an example to show time its important and without it there is no meaning to that number. That was exactly what I was saying.

 

[mfb]

I think the Einstein–Szilard refrigerator hasn't been mentioned before, but I'm not sure how practical that is.

It cools with just a heat source and a cooling part (->pond), without moving parts.

 

[sophiecentaur]

I think the Einstein–Szilard refrigerator hasn't been mentioned before, but I'm not sure how practical that is.

It cools with just a heat source and a cooling part (->pond), without moving parts.

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. You would need another (bigger) pond to act as the heat sink.

 

[sophiecentaur]

"...That number means a lot to me, converted to watt-hours. It tells me I have to evaporate 1 kg of water per hour, to be equivalent to my 500 watt electric air conditioner, which keeps me quite comfortable on 100+ °F days, and 80+ °F nights..."
Exactly, when time is mentioned it has meaning, without it there is no meaning. That's what I meant.
"...It probably would, if you had a bucket of water sitting on the porch..."
Exactly, it depends where you have it. It was just an example to show time its important and without it there is no meaning to that number. That was exactly what I was saying.

Taken on its own, of course, it's 'only a number' and you are right to question my bringing it up in the first place. I only introduced the figure to show that there need be very little water loss to achieve cooling. If you needed to evaporate 1kg of water to cool 10kg by 1°C then it would be a lousy system. A similar figure could be quoted to account for why they use the fluids they do use in normal refrigerant cycles. No one would use air (which was an early suggestion in the thread) because you need to work very hard to make up for the fact that a state change wouldn't be used in an 'air cycle' system.

Using water evaporation is a very common low tech form of cooling. You can get specially made pot containers to give you cool water in hot countries, which work very well on that principle. A bit of forced draft will increase evaporation rate significantly (the wind does the job but you need it to be blowing when the sun is strongest and that doesn't happen always.) As everyone who hangs out wet washing knows, it is easy to get rid of several hundred g of water in a short time. People in wet clothes die of hypothermia in high winds. The whole phenomenon is very significant and the numbers are very favourable in some conditions.

Your "500W" refrigeration system is very costly to run (if it does, in fact, run continuously) and is unlikely to be an optimum (sole) solution to your house-cooling requirements (although it's the most convenient, of course). My home is the UK (cooling is seldom a problem) and I have just returned from a holiday in Sicily, with baking Sun, almost overhead, all day. People use AC all the time and everywhere and it worried me. I joined in the system of course; well you can't change the world when you're on holiday. But there must be better ways. I notice that roofs are not insulated and upstairs ceilings feel very warm. People do make good use of external shutters, which are closed for most of the day but they are a bit 'antisocial'.

The trouble with any discussion of this sort is that words like 'efficiency' are not always relevant. A point already made is that 'overall cost efficiency' is really what counts and the natural resources in any particular place are the dominant factors. We have all been selling our own pet solutions - which is what PF is all about - but none of us is necessarily 'right' of 'wrong' about choices - only the Physics involved is right or wrong.

 

[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...