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Wednesday, November 22, 2006

Passive Cooling

Part I) Passive Cooling and Zeer Pots
By Scott A. Meister

If you happen to live in an area that depends on a lot of electricity, and you’re finding electricity to be rather expensive...or would rather wisely eliminate as much of that expense as possible so you could spend your hard earned money on other things, then you need to be looking for ways to reduce or eliminate your electrical use as much as possible. Where can we cut our electric bills?

We’ve all heard of changing our lightbulbs to the new and improved warm fluorescents (no, they no longer turn your skin green). Of course, we can shut off our lights when we’re not in a room, shut off all electrical appliances we aren’t actually using. After all, there’s really no need to have all the lights on in the house, the stereo blazing and the TV on with no sound while we browse the internet. Those kinds of things are easy to see, and cutting back on them does a lot of good. But a large portion of the energy going into a household is actually used for heating and cooling rooms, food and beverages.

Even if you think you’re rich enough to waste your money on electricity, you still need to be concerned about emergency situations when the power companies stop giving you what you need. If you lived through the LA blackouts as I did...then you know what I mean. Believe it or not...there are a number of free and effective ways to nip your electrical cooling bill in the bud while also be prepared for power-outages.

We can consider passive solar cooling and air-conditioning. Please note that we are not talking about the use of photovoltaic solar panels, those are active solar devices. I’m talking about passive solar cooling. A lot of people have trouble imagining that the hot summer sun, can actually cool your house, but it can. The second law of thermodynamics is our best friend, and it works endlessly for free (or at least as long as the sun exists).

Heat rises (in the case of hot air), heat can radiates outward from warm surfaces, and heat will always move toward cooler areas, and if it happens to draw liquid with it, and that liquid evaporates...the inside surface of what just evaporated will be cooler. Solar chimneys, underground cool rooms (the old fashioned cellar), and the zeer pot, are just a few ways that use these aspects to our advantage to help us cut our power needs forever, and for free. After all, isn’t that what we all want? Why should we slave away at work all day and then spend our hard earned money on things that we can get for free?

To the surprise of many, the world’s cheapest refrigerator/cooler costs less than $2 dollars to make, uses minimal resources to produce and runs completely without electricity. It’s called a zeer pot, or the pot-in-pot and was developed by Mohammed Bah Abba, who realized that he could put the second law of thermodynamics and transpiration to work for him. The zeer pot, is actually two earthenware pots (I’m assuming they are both unglazed), one pot smaller than the other. The smaller pot is put inside the bigger pot, and the space in-between them is filled with sand. The sand is made wet with water (twice a day) and a wet towel is put on top of the two pots to keep warm air from entering the interior. As water in the sand evaporates through the surface of the outer pot, it carries heat, drawing it away from the inner core, thus cooling the inside of the inner pot which can be filled with soft-drinks, water, fresh fruit, vegetables or even meat. A damp cloth placed on top keeps the inside pot away from hot air. In this way, fresh produce can be kept for long periods of time without the need for electricity, or camping coolers made high embodied energy. Tomatoes and peppers will last for up to three weeks, and African spinach, or rocket, which normally would spoil after just a day in the intense African heat, can and will remain edible for up to twelve days. Eggplants will keep for up to 27 days instead of three. It can even be used for storing sorghum and millets for a long time since it protects from humidity, thus preventing fungi from developing. The zeer will keep water (and other liquid beverages) at about 15 degrees Celsius (maybe acceptable for Guinness), and even meat can be kept fresh for long periods.

The new technology is now being used by farmers at the market. Fresh produce is kept inside, with just a couple fresh items displayed on the damp towel resting on top. In this way, most of the produce is kept hidden away from both warm air and insects. In the past, all produce was displayed in the open air, attracting flies resulting in stomach disease such as dysentery. Now food can be kept fresh for longer and kept away from flies...even miles away from electricity or ice. The key however, is a certain degree of aridness, for at a certain amount of humidity, the benefit of evaporative cooling tends to dissappear.

Although many people are excited about promoting this technology in developing countries, I see greater potential for this technology in the developed western cities, suburbs and countryside.

Instead of having humming, heat producing, electrical, bank-sapping refrigerators and freezers, we could have zeer pots stashed away in or near the garden, by the back door, out on the porch or balcony...anywhere. We could have them on the truckbeds of roadside vegetable stands, in cross-country delivery the local farmer’s market. We no longer have to make choices about freshness based on expensive camping coolers, refrigerated trucks, ice machines and electrical outlets. We can provide our own endless supply of refrigeration for less than two dollars.

For further information on zeer pots, please see the following sites:

Part II) Passive Air-Conditioning and Refrigeration
by Douglas JE Barnes

In permaculture, we look to a problem as being a solution. Much money is spent battling the cold in places like Canada, Scandinavia, Scotland, Tasmania, Russia, Argentina, and so on. But the cold can also be a valuable resource. Unfortunately, the cold is a largely untapped resource in most places. That said, there are some hopeful developments being made. For example, many office towers in Toronto, Canada are now cooled using a deep water cooling system that draws frigid water from Lake Ontario. While the buildings themselves are not sustainable, this method is less energy intensive than powering large air conditioning units to cool each building.

There are techniques for the rest of us – passive cooling techniques – that we can use to beat the heat.

Food needs to be kept cool for preservation purposes. The zeer pot described above is one cheap solution. But if one has the means, it is possible to design a passive cold cupboard that doesn’t require energy to operate. In almost any region of the Earth, the ground is going to be cooler than the surrounding air in the summer season (areas of geothermal activity are an exception to this and offer heating potential instead of cooling potential). A cold cupboard makes it possible to replace a large part of one’s cooling needs with a system requiring no outside energy inputs.

The cupboard itself would be a fully insulated space within the home with the same magnetic seal on the doors that refrigerators have. Cool air is drawn in to the bottom of the cupboard through a pipe running under the house with the pipe itself 4 to 6 feet (1.2 to approx. 2 metres) underground and with an opening to the surface outside. (See diagram - click to enlarge.) A drain should be installed in the pipe to allow for condensation forming in the pipe. A second pipe at the top of the cupboard vents to the outside of the house. The external portion of this vent should have access to full sun and be painted black. This will cause the air inside it to heat and rise, which in turn causes cool air to be sucked in through the bottom pipe.

To cool the house itself, a similar technique can be employed. In this case, a closed circuit of pipes is laid 4 to 6 feet (1.2 to approx. 2 metres) beneath the ground outside the house. A small fan is then used to force air through the system and blow cold air into the home.

One variation on this is the have one end open to the surface and draw the air out through a vent pipe as is done in the cold cupboard described above.

Another variation is the wind chimney, which is sometimes employed in deserts. In the direction of the prevailing cool winds, a scoop-like vent is placed and a pipe is laid under the ground from it to the house. Where it reaches the house, the air passes over a container filled with dampened charcoal. This causes evaporative cooling of the air before it enters the home. Charcoal is used both as a sponge to hold the water and as a means of keeping the water fresh.

Another strategy put into effect in tropical and sub-tropical areas is the shade house. A shade house is simple an area on the shaded side of a home with a vine-covered trellis to create a shaded sanctuary. Often these shade houses will contain an outside kitchen to prevent the heat of cooking from entering the home. Subtropical areas would have two kitchens, one inside for the winter, and one outside for the summer. Urban temperate areas suffering from the thermal island effect would also benefit greatly by the shade house strategy.

If you are living in a tropical or sub-tropical region and building a new home, you can increase airflow through the home by substituting the simple “box” design for one with more corners in it (see diagram). This will allow greater airflow through the home.

In tropical regions, it is beneficial to design a traditional tropical home with wall vents and a vaulted roof of permeable material to draw cool air in and push hot air out. (See diagram.)

These strategies are not only sustainable cooling solutions, they also save money by using available cold as a resource.


Anonymous said...

Great ideas. I have often thought about the buried pipe to draw earth-cooled air into a house and appreciate your drain to eliminate accumulated condensed water. However, I also worry about the inherent damp environment within the pipe causing molds. Is there a design feature that could be added to allow for periodical cleaning of the pipe? For instance, line running through the pipe to which could be attached a cylindrical brush or rag-ball that could be pulled through to scrub the insides of the duct? Do you see any validity to this concern?

Thanks! 9anda1f

DJEB said...

Hey 9anda1f, glad to have you come by.

Molds are an issue and your concern is valid - some people are very sensitive and susceptable to this problem. For this reason, you would want 1) a slope to the pipe leading to a drainage point, and 2) a HEPA filter filtering the incoming air. Do that and there should be no problems.

Your brush idea wouldn't hurt (unless the string pulling it broke), but you would still need that HEPA filter.

Scott A. Meister said...

Y'know...I had the same concern about mold, I've also considered pipes with the bottom half filled with charcoal, and perhaps perforated for drainage...don't know if that would help much for mold though, what do you think?

Also...for DJEB, I'm a little leary of the physics behind the diagram where the hot air re-enters the floor. Heat wants to rise (and I would prefer it to do so) therefore I would think that a pipe leading to a lower entry point in/under the floor in cooperation with a solar chimney, or other sort of ceiling/roof ventilation might be a little more effective, with a screened and covered in-flow pipe a few meters away. I think that kind of system is what Bill Mollison presented/illustrated in Introduction to Permaculture.

DJEB said...

Charcoal certainly wouldn't hurt...

About the diagram, you are taking it too literally. For reasons of scale and mediocre drafting skills, I simplfied the drawing.

Anonymous said...

A UK charity called Practial Action are teaching people in many 'third world' countries to make the fridge pots similar to the ones you describe so the they can store food for longer.

Scott A. Meister said...

DJEB, thanks for clearing up the diagram. I was hoping that was the case...but thought it would be better to make sure, and make that clear for everyone.

Scott A. Meister said...

dear anonymous,

Thanks for the info. Now I'd love to see them teach a class to the citizens of the UK, and North America, and here in Japan. If we can show the "1st World" countries how to massively reduce their energy resource inputs, then perhaps there would be more to go around for the rest of the world, including those in the "third world," and then we wouldn't need charities.

DJEB said...

Anon, I'm very glad to hear that Practical Action is spreading the zeer pot in the two thirds world. It is amazing the simple solutions to problems that exist if people only know about them.

Scott, like 9anda1f's question, better clear than confused...

Crusoe the Painter said...

Heat Pumps already use the underground pipe to increase cooling/heating efficiency.

Ground heat pumps use the temperature of the ground as a source of cooling, or a dump for heat depending on the season.

But yeah, those pots are cool.

DJEB said...

Thanks for oyur post, Crusoe. This is true. But heat pumps are expensive pieces of machinery, are not passive, and are definitely not sustainable. It would be lighter on the pocketbook and the environment to employ one or more of these passive systems.

kathaclysm said...

I've heard of those pots before, and I definitely like the concept, and you are right; the world would be a better place if even those of us who could afford electricity would use such simple technology.

I'm now picturing a huge pot-in-a-pot-house (not that kind of pot!) by the ocean, where salt-water could be utilized for the cooling effect.

This also made me think of Thermal-Storage-Cooling, where off-peak energy is used to freeze balls of ice over-night, and during the day air is blown over them to cool the building:

Scott A. Meister said...

Crusoe the Painter,

I see what you mean, and a ground coupled heat pump might be attractive if it wasn't for it's high cost, installation, and higher embodied energy audit.

The point of the science we presented here, is to reduce, the embodied energy audit and cost, while at the same time providing cheap, simple and efficient cooling for the long term, without the need for electricity, or complex mechanization. If I'm not mistaken (correct me wrong, maybe I didn't read the wiki piece correctly), heat pumps require things like a compressor, and a refrigerant, or a compressed gas, or the complicated digging of wells, and burying coils which add to manufacturing costs, time, labor, and possible cost to the earth as well...but yeah, heat pumps are "cool" (pun intended). I just happen to think they're a little too copmlicated and high-tech for something that doesn't need to b at all.

DJEB said...

Kathaclysm, it's funny. Scott and I are currently in Tokyo were the summers are hellish with the heat island effect; and I was joking about doing just what you suggest. A pot-in-pot apartment woudl sure beat the current place I'm in.

Scott A. Meister said...


It's funny you should mention the zeer-house. When I first showed that part of the article to DJEB, he said, "I wonder if we could make a pot-in-pot desert house" with the sand fed water via drip-irrigation. But we came to the conclusion that you would need to build two houses, because you'd probably freeze to death at night in the zeer-pot-house. Not a bad idea really.

The cryogel ice-balls do I say it...cute...but...they make me wonder.

Scott A. Meister said... thinks DJEB and I are posting our comments at the same time! Get out of my head!

kathaclysm said...

Ohh... I didn't think about nights in the fridge-house... that would probably be cold.

I work in HVAC, and we had one of those ice-balls floating around the office, we use it as a paper-weight, I've never actually worked on a building that applied that technology. But I think it's an interesting idea.
The army-engineers research it too:

Anonymous said...

kathaclysm -
I'd be interested in your calcs for the amount of water and convection needed to keep a house relatively cool in Tokyo in the Summer. I grew up in the middle of the USA, August being 90 degF and 75% rel. humidity (similar to Tokyo). I now live in Phoenix where 30% RH feels "sticky" and "swamp coolers" work ok during the summer. In the midwest, there are no swamp coolers, because as the humidity goes up the cooling affect goes down.

The comments on the heat pumps being complex and ineffecient are relative. Compared to an earthen pot, yes they are complex, but compared to a typical a/c unit there are more reliable and significantly more efficient. In areas where the groundwater is close to the surface the ground source heat pump is a wonderfully efficient piece of equip. and pays for the higher initial installation costs in 3 to 5 years with the savings of conventional freon type a/c. The one my parents have uses a closed loop water source, and has reduced their monthly electric bills substantially. So, as always, appropriate use of technology is best.


BobRainbow said...

One problem that I found in the developed world was that our pots don't seem to be porous enough. They are fired too high and don't allow enough evaporation. You also need quite a high ambient temperature to make them work. I tried some while it was coolish and they did absolutely nothing... I was annoyed as I'd had dataloggers in them for a week to see how cool they got!

kathaclysm said...

"I'd be interested in your calcs for the amount of water and convection needed to keep a house relatively cool in Tokyo in the Summer."

Aw crap... calcs? I didn't become an engineer to do math.... I just look things up in the handy-dandy data-tables... maybe I can find a program for that somewhere... If I get really bored over the long weekend, maybe I'll take the time to figure it out thou.

Anyhow, I didn't say it was a practical idea to apply evaporation-cooling to a whole house; just an interesting idea.

gardenlen said...

g'day douglas,

not sure if i need to be subscribed to comment so here goes:

with using evaporation to cool a house in the tropic/sub-tropics can it be that increased humidity can make things less comfortable at some time maybe later in the day.

great ideas hoepfully get more thinkignoutside the square, but even in permaculture circles many still locked into designs that are known to be inefficient, hard to beleive that there is a power shortage on the way hey?

is it ok by you that i put this link on our page?


Jonathan said...

Nice blog. I enjoyed the readings. Thanks for another interesting perma resource.

Best regards,


DJEB said...

Rainbow Bob, thanks for that bit of info. It is helpful for people out in the field.

Len, glad to have you stop by. The wind chimney employing evaporative cooling is something that Geoff Lawton suggests for deserts and was employed at the location of the last Jordan project. I think your concern about increase humidity in the tropics and sub-tropics is warranted. In muggy weather, the last thing you want to do is make things more humid. In those cases, another strategy is better.

And by all means, feel free to link us or repost this piece.

Jonathan, thank you very much for your kind words. We hope to have more posts soon.

S. Drumm said...


Good post. To Rainbow Bob's point, the ambient humidity reduces the enthalpy of the system which in turn lowers the amount of heat that can be removed by evaporation.

In short, techniques which rely on water-based evaporation work great in the mountains and desert...and not at all in the humid mid-South (where I live).

Fully passive cooling won't get you the necessary results in humid climates, but there are still alternatives:

1. Ground Source Heat Pumps.
2. Glycol-based chillers (see for info).
3. Solar Adsorption Cooling - not yet available commercially.

The only other choice is to stay in the shade or the basement (which we also don't have in the mid-South).

DJEB said...

Thanks for the input, S. Drumm. Air that is saturated or nearly saturated with air won't allow one to employ evaporative cooling. In those cases, it is better to start with a home design that is appropriate for the climate.

Scott A. Meister said...

S. Drumm and Rainbow Bob, thanks for the comments.

As for Rainbow Bobs comments about the clay not being porous enough. I believe there is a point to be made there. There are many different types of clay, and I imagine you'll get different results from different kinds of clay. I think the clay they're working with in Africa, probably just happens to be perfect for the job.

Just out of curiousity, I'd like to know what area you were using the pots in?

As for S. Drumm's comments. I agree. It's important to use the right tool for the right job. Unfortunately, for where you live, some of the options presented here might not be suitable, but as you mentioned there are loads of other choices, and perhaps through discussions such as these, we may be able to come up with better, cheaper, simpler solutions to fill everyones needs.

We also might want to consider lowering our standards a bit. I think we've all been spoiled by modern AC. Afterall, it wasn't that long ago that we humans didn't have such technology, and many people still don't. Although they may not have the comfort of Trump Tower, through some good, intelligent design, they can live in comfort.

Anonymous said...

kathaclysm -
ewww - yep calcs, after reading through those I had to go look up the psychometric chart to see if I remembered how to do the stuff I learned in Thermo - whew that was awhile ago.

Now - S. Drumm the solar absorptive /heat refrig that's an idea used in the industrial word and super neat (although NH3 is kinda nasty) - a/c using waste heat from some process. I always wanted to do something like that in my backyard - AZ, USA the hotter the summer, the better the cooling. I forget which cycle that was - but at aprox. 800 w/m^2 it takes a lot of reflected sunshine to create enough heat to keep a room cool when it's 115 F outside.

These are some great thoughts - and the discussion is very provoking.

here's an interesting study -

you know, if you want to model the thing ;o)

The solar chimney is used now for keeping the outhouses at National Parks a little more odor free - nice use of appropriate technology.


DJEB said...

" see if I remembered how to do the stuff I learned in Thermo - whew that was awhile ago."

Wow, memories. All I remember these days from thermodynamics was that I went to the lectures. I am sure glad you didn't ask me for any calculations.

Anonymous said...

The only real problem I see
is that, most places where it's
dry enough for evaporative cooling
to work really well, there's not
enough water to waste on it.

Where there *IS* enough water,
the historic technique is to
put whatever food you're
trying to preserve/cool,
in a waterproof container,
and drop it down a well on the end of a rope.

And where you are trying to
cool living space, fountains
work a whole lot better
than straight evaporation through


lindsey said...

i'm following this conversation with interest, being an architecture major with a focus on energy conservation. but having been submerged in the available literature the past couple of years, i'm pretty frustrated by the lack of efficient cooling for humid/muggy climates. i grew up in the south where the relative humidity never dropped below 74%, but out here in AZ where i am studying, all they preach is evaporative cooling. please, can anyone tell me something smart about passive dehumidification? dessicants? anything? i've been studying solar air conditioning on my own time (the adsorption system mentioned above?), but from what i can tell, it's mainly in europe, mainly for large scale architecture, and far far away from the american suburban home which is where my interest regarding energy guzzling lies.

comment about something hinted at above:

yes, human thermal comfort is relative. when it's 110 outside, 85 inside feels really good. and because of that you may say we should reacquaint ourselves with the temperatures our recent ancestors used to live in. condition ourselves to reaccept it, so to speak. but it's not sustainable to say the answer to our energy crisis is for the human race to readapt to the temperatures we used to live with. it's too idealistic, like thinking we should all live in strawbale construction. when we lived in 'comfort' without air conditioning in the past, we organized our days differently. we had siestas. we worked early in the morning, did nothing active mid-day, and worked again in the evenings. but as members of today's economy, who is in a position to shut down their productivity in the middle of business hours? the schedule in which we make our living is divorced from our environment in ways it used to not be. you could even argue we enabled this economic model by learning to manipulate our enviroment and make comfortable building interiors 24/7. but frankenstein has gotten away from us and we cannot go backward. who is going to volunteer to tell wall street to chill out between noon and four pm when the day is most hot and new york is baking?

i want solutions though. you all seem well versed in the options out there. what are some real, acceptable cooling options in humid climates? besides specifying a triple digit SEER...

9anda1f said...

Found mention of an "earth tunnel" similar to what Douglas describes:

Note the diameter of the pipe being used! 9anda1f

9anda1f said...

Any interest in a solar icemaker?


DJEB said...

"can anyone tell me something smart about passive dehumidification?"

Lindsey, you've gotten my mind clicking now. That's an interesting one. Unless someone already has a solution, I'll be thinking about that one. Dry air tend to make it easier on asthmatics and people with emphysema, so a solution would be helpful.

If it's just straight cooling, then the underground pipes mentioned above (which happen to be employed in some North American homes) would serve to cool the air. This cooling would cause some dehumidification, but the effect might not be that great overall.

I've lived in Toyko most of the last 14 years and it is painfully muggy in the summer. I have noticed that it is tolerable in stand of trees, however. While I doubt the humidity drops at all in the trees, the shade certainly helps with the comfort.

I actually think that reacquainting ourselves with our own environments is sensible. I came from early winter in Canada 2 weeks ago to fall here in Tokyo and everyone here keeps complaining about how cold it is. I'd believe them if I could stop sweating.

As for the other points, straw bale, siestas, I understand the point you are trying to make, just not in the way you are making it. Switching more homes to straw bale construction would be a good idea in that it would not only give people more efficient homes requiring less wood, it would also give them more comfortable and attractive homes than the drywall eyesores that are the industry standard. As for siestas, you get what you allow people to do to you. If I had the choice between working 2 or three jobs to make ends meet because the CEO gets over 400 times my own salary, or living in New Zealand where people usually work a 30 hour work week (they happen to value different things in life than North Americans), then I would choose the latter.

Again, I understand what it is you are getting at. I'm just not agreeing with the points you use to get there.

As for how to bust out of the rat race, well, that, in a way, is what this site is about. There is no one answer to that one. It takes a total lifestyle change. Like the Kiwis, you have to decide which lifestyle it is that you want.

9anda1f, thanks for the links. In the first one, that's one bloody big pipe. I am sure 6" would be fine if the circuit were long enough. Also, a smaller pipe has more surface area per unit of air passing through making it better for cooling the air. And the solar icemaker is great. It is giving me Mosquito Coast flaskbacks.

Scott A. Meister said...

Well put DJEB, you beat me to the punch again.

Just to add my own two cents to clarify...

I wasn't suggesting we all go back to the dark ages and re-adjust to the conditions of our ancestors. However, I was suggesting that we are overly spoiled, and need to pull back on the reigns a bit to be more reasonable.

To illustrate:

One of my former bosses in Los Angeles, was silly enough to put his desk in a southern bay-window so he could sit in the hot summer sun all day long while keeping the a/c for our unit of offices on the lowest temp possible...thus freezing the heck out of the rest of us who didn't have windows (and giving us all colds in the process). Boy, was HE bummed when the blackouts hit! And, he got what was coming to him. That kind of silliness just has to stop, and way too many in the "developed" world live like that.

My point, is rather that we should design better houses and settlements with passive solar in mind, southern facing aspect, more sufficient insulation (like was mentioned with straw-bale, or perhaps even earthbag, or mud-brick etc. (we didn't even mention living rooves!)) while also incorporating things like underground cooling tunnels, attached shade houses, solar chimneys, proper length eaves, abundant greenery surrounding our abodes to take advantage of shade and transpiration etc...basically use everything in our bag of tricks that we can think of that DOESN'T take an insane amount of energy or we can live a very comfortable life aimed toward sustainability.

The way we live right now is just rediculous, and not sustainable therefore, it, and the current economy cannot continue.

Now that we've realised that fossil fuels are not "endlessly abundant," and you can't just make more (but thanks for that bit of nonsense anyway Mr. Julian Simon) there is no way that this economy, and lifestyle can continue as-is. We will be forced to pull back on the reigns sooner or later, wether we want to or not. (it follows that the sooner we all pull back on the reigns, the later the end of our use of fossil-fuels will come)

On a lighter note I personally wouldn't mind a siesta, a lot of people are getting along just fine while holding onto that tradition. I also wouldn't mind a 30 hr work week. If I were using the rest of my time wisely to provide things for myself, instead of working for a boss making 500% more than I do, in hopes that he will do the respectable thing and pay me enough money to provide the things I need, I think I'd probably be a lot bettter off anyway.

From my experience, the upper echelon doesn't ever want to give up their "gross" profits, to provide a better life for their employees. The drive for status through greed always gets the best of them.

But even aside from that, like I said before (in the beginning of the article). Why work so hard to get money to then pay for something that you could provide for yourself, for free?

It is entirely possible to live a reasonable and comfortable life, full of abundance, while doing honest work for ourselves (I've recently seen good examples of this lifestyle at work in New Zealand, but they exist all over the place if you look). We just have to design our lifestlyes accordingly, and use our time and money wisely...on things that give back more than they take...and on things that matter most.

For more on successful sustainable lifestyles, you can follow these two examples below, but there are other's abound, and in the most unlikely of places, but the following links should give you a start.

If we work with, and give back to mother-nature, she will pay us back 10-fold , but if we throw her out the window, she'll come back though it with a pitchfork. I believe that right now, she's climbing back up the trellis with that pitchfork in hand, and a rather non-plussed look on her face. Now's a good time to start thinking of ways to try and make her smile again. (this is my own severely enhanced and para-phrased version of a Masanobu Fukuoka quote).

I believe this, as DJEB stated, is precisely what I hope everyone is able to find here on this blog in the future: positive, simple solutions, to serious problems.

Scott A. Meister said...

Regarding passive dehumidification:

It's my understanding (please correct me if I'm wrong, it's entirely possible), that as air cools, condensation occurs thus removing the moisture from the air.

With this in mind, looking at the first diagram, and previous posts, it seem to make sense to me, that if the air is cooled coming through the pipe going underground, condensation is bound to happen on the surface of the pipe, thus removing that moisture and creating drier air (before entrance to the abode) and dew, which can be either collected (at the bottom of the pipe, if it is angled downward into the lower level of the home, underground) or drained back into the surrounding soil (via the charcoal filled tubes with perforated bottom halves, which I mentioned before).

The collected dew could be reused elsewhere, and the later would help to insure a droughtproof garden.

Either way...through the creation of condensation, shouldn't you be getting drier air?

If not, there's always iso-thermically compressed air (and therefore dry air) via trompe (do as the Romans do) just need a water source with the proper amount of head.

DJEB said...

Scott, the cold surface of the pipe would lead to condensation, which, in turn, would mean drier air. How much drier is hard to say until you try it out. I occurs to me that the use of small diameter (small because of the expense)copper pipe would inhibit mildew forming in the pipes. Whatever the material, however, HEPA filters should be used to clear the air entering the house as I mentioned above.

As for collecting the condensation from inside the pipes, while possible, it would be rather impractical. The extra work or extra material needed to do this would not be likely to be considered sustainable after an energy audit.

The use of a trompe would be... amazing. But the right geographical conditions are rather rare, and the initial building and installation would be very expensive.

Scott A. Meister said...

Actually, I think there is a simple way to collect the condensation, you just have to stop complicating things by thinking like an engineer. Probably the simplest way is to let the water condensation seep back into the ground via drip irrigation holes in the tube.

As for the trompe, that can be simplified too, and there is a sustainable way of creating the right conditions, even if you don't happen to live by a waterfall.

However, I think that it will take some experimentation and tweaking. Anybody want to give me a grant to work this all out for the benefit of all mankind?

DJEB said...

A drain is going to have to be made in the pipe at any rate to deal with condensation as mentioned. In this case, it is going to be put into the ground.

As for trompes, you are going to need both drop and a steady flow of water - something which is not available on every site.

Scott A. Meister said...

"As for trompes, you are going to need both drop and a steady flow of water - something which is not available on every site."

Probably one of the reasons why it never caught can't be pre-packaged and sold to everyone...therefore, it's not considered economical by today's standards.

Of course drop and steady flow of water may not be available on EVERY site, but it's available on quite a few, and if people happen to be blessed with it...then, it can be taken advantage of. It's another thing we can add to our bag of tricks, and use where applicable.

Basically, drop can easily be created (how you do it so it's efficient and sustainable is the trick), so if drop can be created, steady flow is all that is necessary. Therefore, if you live near a river or're half-way there. But, really, all of this should saved and put in another post for later.

Speaking of settlements on rivers...I think it's interesting to note, that U.S. cities and towns were almost always built on rivers and streams, but somewhere along the way, thanks to the ability to import resources, people decided to build massive settlements in insane places like Las Vegas and Los Angeles.

Rather silly, eh?

DJEB said...

In the right spot, a trompe would be a great option for a community to build. The costs of building one would put it out of reach of individuals.

While it would be possible to create the needed drop, the depth needed would make it very impracticle and would make it's manufacture costs skyrocket. Not something I'd recommend.

Don't get me started on Las Vegas. At the rate it drains the groundwater, it has got 20 years tops before it needs to import all it's water. I wonder if they will still waste it by spraying it on grass when that time comes.

9anda1f said...

"Human thermal comfort is relative..." Can't agree more. I've come to the conclusion that we surround ourselves in comfortable environs to excess. If our airconditioned offices, cars, malls, homes, etc keep our environs always at 70 degrees F, our bodies become intolerant to anything else, and our "comfort zone" becomes extremely narrow. My personal experience says that we can "acclimatize" ourselves to the changing seasons/environment, if we only forego the blanket of comfort provided by artificial means. This is not to say that extreme temperatures need to be tolerated, rather to propose that we can widen our tolerable temperature comfort zones according to the swings of the natural season.

I have lived/worked in desert temperatures (110 deg F +), tropical (100 deg F/99% humidity +), and cold (temps <40 deg F for months, often below freezing). It is the willing exposure to these conditions that "acclimatize" me to tolerate them. In the autumn, I let the house cool down to about 62 deg F, where it remains all winter. At first it feels "chilly", but soon becomes "normal", and with physical activity, pleasant. If just sitting, a sweater or light jacket is all that's needed for "comfort".

I guess that all I'm saying is that by consciously widening our zone of temperature tolerance, we can eliminate the need to control our immediate environment temperatures to the nth degree. Our bodies are amazingly adaptable, if we allow it.


Scott A. Meister said...


I couldn't agree more. I planted a small garden on my balcony this last year with vines growing across the rail to provide food, shade beauty and transpiration, I was determined to cut my a/c use down considerably, opened the windows and bought an electric fan instead...and you know what? It worked...but I think it's also because I was determined to acclimate my body to a more reasonable sense of "cool." Instead of running 2 A/C units the entire time I was in the apartment, attempting to cool the whole apartment, I used only one, and only when it was unbearably humid and hot. For the most part, windows were open, and a breeze was blowing through my balcony garden into the window. Sitting on pillows placed on a bamboo matt on the floor, instead of carpet also seemed to have a cooling effect as well. Also, we don't have to actually be cool, but it's more important to feel cool and comfortable.

Now I just have to figure out way to get through the miserable cold, damp and grey winter in the non-insulated and drafy apartment without doing major modifications.Hmmm...I smell another article coming on...passive heating.

DJEB: I think you are being too pessimistic about something we know very little about. There's not enough information and data available to support your claims.

How big does a trompe absolutely have to be? How small can it be scaled down? How much do they cost? How long will they last? How much maintenance is involved? How much energy can they provide, and for how long? None of these questions have absolute answers right now, because there aren't enough examples in existence to collect data from, and nobody is currently experimenting with it, because we're all in love with more high-tech, big-engineering projects with LED displays, gears, valves, conductors, etc. etc.

True, the one operational trompe in existence is enormous, and was probably very had to be, because it was and still is providing sustainable power to all the power tools driving a gargantuan mining operation in Canada.

However, as for costs...I'm sure the cost of construction has more than paid for itself over the lifetime of the system...and it's continueing to provide renewable energy with very low maintenance, and just a few simple moving parts.

So...I think our image of trompes is that they have to be enormous, expensive, and require difficult to attain drop and depth but I think things can be scaled down to suite a smaller fact, I know they can. I read about a guy who built a small, table top version of a trompe, and the blow-off shot water quite a distance up in the air. Do enough googling on trompes, and you can find it.

The fact of the matter is, nobody has explored this technology in depth, therefore there isn't enough information to either shoot it down, or promote it effectively.

Engineering schools, are usually more interested in big projects involving lots of different kinds of technology that show off their knowledge, they usually aren't interested in experimenting with simplicity (i.e. things like passive cooling, and zeer-pots). So things like the trompe have never been developed to see the full range of their capabilities.

I also think the problem with scales of thought needs to be addressed. Modern science and technology doesn't usually attempt to create things that operate on a small local scale, because they're still focused on "bigger is better". If a technology can't work on a large scale, and in every situation, it usually falls by the wayside. This is because modern science and technology is driven by the market, not by the actually needs of society (people) who live in small localised communities in a variety of environments, and situations.

There simply needs to be more experiments, examples and data collected on simple, sustainable technologies, before we start shooting down good ideas.

This is why places like the Permaculture Institute at Tagari Farms, and Rainbow Valley Farms, and the people at Path to Freedom are so important. They are willing to try experimenting with new things and old forgotten ideas, that can benefit people living in different situations. They're willing to take chances on things that experts insist on shooting down.

I remember Joe Polaisher at RVF, tell me that all all the experts told him that sugar cane wouldn't grow on his property, but he took the chance anyway, experimented, and now it's now one of many very successful and useful plants on his property.

DJEB said...

How big does a trompe have to be? A large drop is needed to hold the trapped air under enough pressure. If you've got the topography to pull that off, it's a fantastic idea, assuming you can finance it. A drop could be artificially be dug into the ground, but getting it deep enough to have significant pressure would tend to be prohibitively expensive for most.

Water exerts a pressure of 0.433 psi per foot of water. So a trompe with a 30 foot drop (a big hole in the ground with accompanying drain) would only generate 13 psi. A 100 ft drop gives 43.3 psi, and 200 ft gives 86.6 psi. So, to get the kind of benefits that make a trompe worthwhile over just microhydro, a big drop is needed. While it would be possible to dig a 100 to 200 foot deep hole in the ground to artificially create the needed drop, and while it would eventually produce more power than was required to build in (assuming no colossal failure before that payback occurred), the magnitude and expense of the project wouldn't make it feasable.

Now, I need to be clear that this is not shooting down the idea of a trompe. There are definitely situations in which the trompe would be a wonderful source of sustainable power. But to try to place it in unsuitable topography would be an unwise use of effort, in my opinion. Trying new things is great. But trying to force an idea in places where simpler and easier solutions are available burdens one unnecessarily, I think.

lindsey said...

i do agree with all of you, as an individual, when you talk about widening our thermal comfort zones. as a single individual who cares about sustainability and conserving resources, i can and do do all of those things.

but as someone who also wants to pitch resourceful living to the rest of the plebians in the world (who cannot all move to new zealand and work 30 hr weeks with the kiwis, unfortunately) there has to be something 1) sellable to people who may not give a damn enough to deprive themselves of something they think they need and 2) doesn't mean giving up their livelyhoods to become (what they perceive to be) hippy homesteaders. here in academia i have met so many lovely people with lovely ideas about how to save the world, but their ideas mean nothing after i join a firm if i can't pitch those ideas to clients. part of the business plan has to be to account for people's fallabilities, weaknesses, and indulgences and have a good solution anyway. it's the only way to sell to the masses - and you need the masses on board because just a few of us is not enough.

so that is what i meant when i said it's not realistic for all of us to live in strawbale construction. some people can and will, others need some other way to contribute. it's one of the reasons i like LEED, even though there are holes in the concept that you could drive a mac truck through. at least it spurs people who don't really care (developers!) to impliment some form of sustainable strategy that they wouldn't have otherwise (by offering them a shiny trophy). those of us who know better can go above and beyond LEED, and we should. but getting people who wouldn't otherwise participate to do so is worth all the silliness of that is LEED.

i am looking for those same kind of middle-ground solutions when it comes to heating/cooling/ventilation. i make do with a $35 energy bill every month, and even that is because my rental has a lousy hot water heater, but ask my mother to do with less than $120 and she says, "No way!" i need something i can pitch to the masses without them feeling deprived.

fun conversation, btw!

DJEB said...

Hi Linsey,

Yeah, unfortunately, there are those who would only accept the less-damaging option, and only if there is benefit in it for them (i.e. reduced costs). They still want all the creature conforts that don't contribute to happiness. And that is where the mentioning of New Zealand (or most of Europe) comes in. While Kiwis are reasonably well off, they seem to value their lives more. That is to say that they value their time: time with friends and family. If companies push them to work longer or get replaced by some despirate soul who will, the vast majority of the population will not play that game. And if one has one's own land and can cover taxes and other reasonable expenses (not Armani suits, for example), one can live that way too - provided there are no status wars with the neighbours and there is self-taught immunity to advertising campaigns.

Getting most people to understand this may be rather difficult, though. And unfortunately, for whatever reason, a number of "permaculturists" in North America seem to think that permaculture is about praying to the sun god or some such idiocy (the hippy homesteaders you mention). Not even Bill Mollison's repeated belittling of these folks has prevented them from promoting permaculture as a way to get in touch with the great earth spirit, etc. Unfortunate.

Good examples by regular folks are what is needed. I'm happy to report that all of the people I've met in Canada are just regular people looking to lead cleaner, happier, healthier lives. When regular folks start to see good examples of people not dedicating their entire lives, save two weeks a year, to monetary pursuits, but to enjoying their own lives, more and more will want to join in. What our task is is not to start that trend - it has already been started - but to promote it.

9anda1f said...


After much thought regarding your approach and requirements, it occurs to me that the solution revolves around a system of tempering the living environment using thermal mass in conjunction with substantial insulation and solar gain (basic solar principles). I lean towards earth sheltering overall. It is hard for me to accept an "adjunct" system as a retrofit to existing, poorly designed shelter. Thoughts?


9anda1f said...


Here is a very interesting article on "Intertial Ventilation", which is an adjunct system. Both direct ventilation and "thermal phase shifting" are discussed, based on work done in Brazil. The article also mentions that buried pipe ventilation has been noticed in Europe over the last decade.

So much for my purist posting! = )


9anda1f said...

Oh...and the article:


DJEB said...

Thanks for that info, 9anda1f. Interesting stuff.

lindsey said...


High thermal mass inside a highly insulated building envelope is precisely what I'm modeling in my Master's Thesis. The site is in upstate SC, on a lake. Very high humidity. I'm using Calpas3 to evaluate it (as it's the only software my committee chair knows that allows you to model natural ventilation). The scheme helps, although I am still dealing with a mean temp of 84F in August. But I'm not done combining strategies, so I think it'll get better.

Then again, all this site-specific strategizing equals high architect/engineering fees for the average joe wanting a house, which I am not in favor of. And I don't think my thesis strategies would work quite as well in high density urban locations where the ability to passively cross-ventilate your thermal mass might be compromised (and who wants to cross-ventilate with car exhaust?). So if by adjunct system you mean a HVAC system, I am in favor of smart adjunct systems.

9anda1f said...

Thanks Lindsey, sounds like you're doing good work. Although a "start from scratch" engineering approach would drive architectural fees sky high, wouldn't a "toolkit" of analysis processes and previously modeled solutions help to minimize the impact? Sounds to me like you're in the process of developing such a "kit".

Do you have plans to validate your model by actually constructing the solution? 9anda1f

Scott A. Meister said...

One thing to keep in mind regarding architectural fees, costs, etc...

The one-time "high" architectural fees for the site-specific design of a passive-solar home are well worth itin the long run if it means you don't have to install and run a central air-conditioning/heating unit indefinitely over the lifetime of the abode.

Installation costs of central air-units are high, and the costs of running them are even higher over time.

We have to always be thinking of the costs over the long-haul. Our world is currently designed with short-sightedness and instant gratification without regard to sustainability.

jon said...

Guess I'm a few months late - but two comments:

Re: 9anda1f
"I guess that all I'm saying is that by consciously widening our zone of temperature tolerance, we can eliminate the need to control our immediate environment temperatures to the nth degree. Our bodies are amazingly adaptable, if we allow it."

Hot & muggy weather tip honed over 5 summers in Taipei: sleep on a large towel, as thick as possible. Without it, you will be sleeping in an uncomfortable puddle of sweat. The towel absorbs the sweat and still feels dry. It's best not to place anything over your body, but you may need to sleep under a mosquito net to do this. But a strong electric fan may make the net unnecessary, because mosquitos can't handle strong air movement. And keep water handy, regardless of the humidity you will be dehydrated in the morning and possibly sooner.

Re: Scott A. Meister
"I also think the problem with scales of thought needs to be addressed. Modern science and technology doesn't usually attempt to create things that operate on a small local scale, because they're still focused on "bigger is better". If a technology can't work on a large scale, and in every situation, it usually falls by the wayside. This is because modern science and technology is driven by the market, not by the actually needs of society (people) who live in small localised communities in a variety of environments, and situations."

After seeing some cities in Asia and living in Taipei, my opinion is that America's population density is well below world average, and it will rise sharply in the future. The average American just doesn't understand that we are sitting on prime real estate while much of the wold is crammed into very tight spaces. Respectfully, I feel that we will have an acute need for technologies which can be applied on a large scale, and also that high-density urban areas are vital to our future, if for no other reason than they reduce the massive amount of energy used to transport people and food.

DJEB said...

Thanks for your comments, Jon.

I fear that the game will be over before North American population densities can approach anything near those in places like Taiwan or Japan. And I don't believe that continuing the cycle of technological fixes to problems created by technological fixes to problems created by technological fixes is going to do anything but make the ultimate bill more painful to pay.

Aaron said...

wow, I'm impressed with the quality of discussion. I really feel as if I'm meeting people who think like me, people i didn't think existed. even some sites like Inhabit are full of posts that seem like 14 year olds or hardened, stubborn zealots. Now I feel like I'm full of #$%, as if I'm in a better category. but I mean it--thank you all. I just read the entire blog straight through.

I'm a physician in NC, but architecture is a hobby of mine (studied in college) and ecology is a concern of mine. A very daily concern. It's funny how all things are connected, the health issues, for instance obesity and asthma, which are largely due to the controlled comfortable boxes we've built for ourselves. That's simplifying, but true. The ecological impact of these "modern" behaviors is having a feedback loop effect, the dreaded downward spiral. As we heat up and consume our environment, our lifestyle becomes less and less affordable.

I will at least, when I get out of residency, be building or modifying my house to be sustainable. As for now, it's 85 in the summer, and 65 in the winter (I agree you can acclimatize to some degree)--and I ride a bike to work and own no car. I came to this site to get ideas for house design (my frequent daydream) But I hope you guys get this figured about by then--I think I'll have to hire Lindsay and 9anda1f as consultants.


DJEB said...

Thank you for your comments, Aaron. Expect some new posts and an update soon.


Shea said...

The zeer pot house an actual house is not a good plan, since freezing to death isn't an option. Would the same idea work using a small out-building and then venting the cooler air into the main house (at least a room). Or would venting from the zeer building defeat it's cooling effect?

DJEB said...

Zeer-pot style evaporative cooling is only possible in dry conditions (i.e. low humidity). While it would not cause freezing if brought on a huge scale such as a house, it would be tremendously wasteful of water - never a good idea.

You would be better to try the wind chimney, trying the "natural air conditioner" and/or designing to allow greater wind flow through the building described later on in the article.

Santa Fe Dehumidifers said...

I could suggest in addition to a HEPA filter, you could use a dehumidifier to help control moisture in the pipes.

DJEB said...

A possibility, though perhaps not a sustainable one.

Anonymous said...

I am late to the discussion and not as knowledgeable as many herein, but I thought I'd add a few thoughts. I live in the humid and hot southeast. 50% of the cost of cooling a home is related to dehumidifying the air (research by Dr. Norman Witriol -- a friend of mine formerly of Louisiana Tech University).

Passive cooling seems improbable in humid environments. To save energy a house must be sealed tight from humidity infiltration. And yet air exchange is a REQUIREMENT of good health and of building codes. Active measures are required to exchange air in a sealed house, and the resulting energy expense to exchange dry air in a sealed house is cheaper than to repeatedly remove humidity during cooling of an unsealed house. Most of the cost of "cooling" in a hot humid environment is repeated removal of the moisture from the air.

In other words, the cheapest way of making a home habitable in hot, humid environments (even down to 80 degrees in the southeast summers that reach 103 F with 90% humidity), is sealing a house to avoid duct leakage and infiltration through joints and walls, and even sealing and conditioning the attic to avoid the expense of humidity infiltration into the home from an open attic and then using "efficient" active cooling methods.

I'm on this site, because I am researching how to build the house I'm planning. I am going to use insulated concrete forms and foaming insulation to completely seal the envelope of the house. I am designing the house with the "time proven" colonial plantation style with a two-story wrap-around porch, a full basement open on two sides of my lot, and a widow's look-out on the peak of the roof that will serve as a heat escape.

I'm building in substantial thermal mass for passive heating in the winter. My house has a rear southern exposure and the southern side of the wrap-around porch will be enclosed with windows in the winter as a solar collection room and opened as a screened in porch to shade the house in the summer. I'm also considering adding a very fine mister to the edge of the porch to accomplish about a further 10 degrees drop from evaporative cooling on the porch edges. With the house closed and sealed the humidity on the covered porch won't make it into the house, and the lowered temperature differential between the porch and the air-conditioned home will reduce heat gain inside the house.

The passive solar heating with the solar mass should keep the house comfortable for most of a northeast Alabama (near Atlanta) winter. The covered porch and deciduous trees combined with my natural heat chimney through the widow's look-out should give an extra month or two of comfortable open window natural ventillation time in the spring and the fall.

But once the house has to be closed and actively cooled to keep it below 75 degrees, it will not make sense to turn the air conditioning off or open the house up again (Even if an unseasonably 65 degree day comes after a rain storm) until the cool fall days are gauranteed to be consistent. The energy expense of re-dehumidifying the air is far higher than any expected gains from opening the windows, turning off the air conditioner, and passively cooling for a brief few days or even a week. Besides, with my wrap-around porch and sealed home with substantial thermal mass, the air conditioner probably won't kick on on those cooler days anyway! But allowing humidity to re-enter my home will expend ENORMOUS amounts of energy to re-dehumidify.

To keep the humidity out (in order to save energy) and to keep the house comfortable and healthy during the hottest months, it appears I am essentially required to use active cooling and active conditioned air exchanging mechanisms here in Alabama for at least a few months. And believe me... I've been looking for over a year to try to find some way to avoid the energy consumption and cost of an active mechanical system. It looks like I will resort to some form of active geothermal cooling system with a dehumidifying, conditioning air exchanger.

On the positive side, such a super-pressurized, sealed house will be easy to become rated as a "safe house" in the event of a chemical disaster. [I live near a chemical weapons incinerator -- grin/groan].

I am exploring the concept of an earth cooled underground air pipe with passive air circulation as a means of perhaps further extending the non-active cooling season of my house. I too was concerned about humidity, condensation, and mold, but I like the ideas of the charcoal and the hepa filter. If I did use such an underground air-cooling pipe, I think I would make it active and tie it into my conditioned air exchanger system and just make the system work a little more energy efficient. That way I can dehumidify the air and avoid the mold/mildew problems the moisture can otherwise lead to here in the southeast.

I'm just not sure I'm willing to make my dream house an experiment for this without the air exchanger/conditioning...

As far as cleaning the underground pipe goes, that is no problem. Any sewer cleaner company can use a high pressure water jetter to occasionally clean and if desired simultaneously disinfect the pipe. I just happen to work for a company that has its own sewer jetting equipment [grin]...

Anyway, I thought I'd contribute my thoughts as I read this old thread, hoping someone might find something useful herein.

Grant W.

Anonymous said...

For the moderator...

I couldn't seem to get my Google ID or any other method to work so I posted as anonymous...

My email is if you would like to share any comments to further my education.

Anonymous said...

A "geothermal well can be used without a heat pump. Ambient Earth temperature water is pumped through a shrouded radiator (like an automobile radiator). Air is blown across the radiator, which cools and dehumidifies it without a compressor-based air conditioner. Photovoltaic solar electric panels produce electricity for the water pump and fan - eliminating conventional air-conditioning utility bills. This concept is cost-effective, as long as the location has ambient Earth temperature below the human thermal comfort zone. (Not the tropics).

Found this on Wikipedia... It looks like there is a more environmentally friendly way of using geothermal cooling. The dehumidification is handled as well as the cooling.

Anonymous said...

Here is another interesting very low energy means of humidity control while cooling.

Anonymous said...

I mentioned the need for a heat exchanger to avoid humnidity problems in the home while permitting air exchange. At the same univrsity site as the passive dehumdifier I just shared, I found an excellent entry regarding such "energy recovery ventillators" including the one the professors say is exceptionally energy efficient. said...


I am currently working on the details for a small building in central Florida with Photovoltaic Modules (solar panels) on 90% of the roof. The concept is that the PV modules operate as a second roof shading the actual roof effectivly eliminating the direct heat gain from the sun (not a new concept). Does anyone know where I can find some information about double roof systems? I have lots of questions like how far apart should the PV panels be mounted above the roof? is there a rule of thumb for lateral spacing (places for the heat built up below the PV panels to escape) The main roof is 100' x 26'. Any other considerations? If anyone has come across a similar project, I would greatly appreciate some direction. Thanks.

DJEB said...


I seem to recall info on your typical Australia double roof in Derek Wrigley's "Making Your Home Sustainable". Unfortunately, I do not have access to my copy as I am out on a job at the moment.

I can't recall the spacing he used, but it wasn't a tremendous amount. I would think that in your area, you would also worry about strong winds from thunderstorms and hurricanes as well.

You might also see about the cost of a radiant barrier. They are not so effective at keeping heat in (something Canadians like to do), but they work well at keeping it out.

Jose Pino said...

Great information! I can't believe how simple can be the items that keep us cool.

I hope you provide more posts with more earth-friendly info.

Anonymous said...

Excellent commentary. My wife and I are planning to reconstuct a log house (circa 1850) on a passive solar 24' x 28' ICF foundation set into a south-facing slope in southeastern Pennsylvania (north latitude approximately 40 degrees). Any suggestions about materials and depth of the solar slab? For us, summer cool(th) is as important as winter warmth.

DJEB said...

Hi, I would go concrete. Used as a thermal mass it is sustainable.
Make sure the sides are fully insulated as is under the concrete. The number 4" keeps jumping out in my mind. I do know that beyond 4", you get into diminishing returns in terms of heat storage. Give your concrete pourer the final say if he or she says 4" is not enough. Building too strong a foundation is not a problem. Building too weak a foundation invites expensive problems.

HomeBizDiva said...

I've seen the houses made out of the one long continous sand bag...they look like bee hives...I love them.
I had a thought.
How about a house whose walls are pvc pipe filled with water????

DJEB said...

Hello Homebizdiva,

The late and very great Nader Khalili is known for his innovative work with the structures you are speaking of (known as earthbag construction). Providing one can get ahold of the bags necessary for construction, the method is a fast, inexpensive and easy way of building.

Water can and has been used as a thermal regulator in homes and greenhouses. Your idea could work, but you could save a lot of money using some other system of thermal mass to keep temperatures steadier.

Anonymous said...

Hello, i'm from malaysia, a tropical country, and is very interested with the passive dehumidifier.

Living directly on the equator is very uncomfortable, since it is both very warm and very humid. It also causes maintenance issue such as the need to clean things in the house (especially fabrics) VERY often. If you can work out this passive dehumidifier to be highly usable (our standard of living here is not exactly very high, but still most can afford normal air-cond) i believe you'll get yourself a lot of money. Definitely people here will buy.

I think utilizing dessicant is a good idea. I do not exactly know the mechanic of the machine (since i'm just a civil engineering student) but electricity i think is not a problem here.

Equatorial country is blessed (cursed? :p j/k) with 90 degree sunlight right above our head. Meaning, with recent discovery on cheap solar film which can generate electricity despite the angle of incoming sunlight, power is not a problem. A large portion of electricity can be generated at home only by using solar films.


DJEB said...

Thank you for the comment Amadeus! Passively controlling humidity is something I looked into, but if there is a realistic solution to the problem, I am not aware of it. The humidity certainly can be a nightmare - causing damage as well as discomfort.

Active systems that are solar powered are an option. But that is just making a minor change to the current method of air conditioning. It is unlikely that this will yield a system that fits the definition of sustainability (i.e. energy saved or stored is greater than the energy needed in the creation of the system). Many of the buildings people live in in Southeast Asia are concrete, but concrete does not make a very comfortable building to live in without the aid of air conditioning. It captures and stores the heat of the day, releasing it into the home after nightfall. The cheapest solution, and least expensive one, would be to shade the building from direct sunlight. I used this strategy as much as I could in Tokyo, which gets around 40°C with near 100% humidity in the summer, and it worked out pretty well. One could shade with plants (outside green walls and green roofs)or with shade cloth like Coolaroo, Coolaroo being more expensive, I suspect - certainly less sustainable.

Noddy said...

The real challenge to passively cooling houses is to do it successfully in the humid tropics. Probably the best solution is a combination of deep shading of the building, and having a heavily planted area next to the house with damp ground, that you draw cool(er) air through, into the house and out the top somewhere.

However, as somebody who has lived in the deep tropics all his life, I have to say that, while a lot can be done, there are still serious limits to the power of passive cooling in hot, high humidity climates.

And the mould issue is also a real problem in some situations

DJEB said...

Noddy, you are absolutely right. The humid tropics are no small challenge. People think tropics and they think paradise. In reality it is tenacious and deadly diseases, lethargy from heat, and decay from the humidity you point to. This article is certainly not the end-all, be-all to passive cooling - it's merely an introduction. There is more in Bill Mollison's Designer's Manual, but the bulk of it is incorporating the excellent points you made. After designing as best as one can, you just have to come to terms with the fact that you live in a hot climate.

Hamishmac said...

What a great discussion! Makes it hard not to think outside the square.

I'm no engineer but...with regards to passive cooling in humid environments, particularly in the tropics and subtropics, does the designing of roofs shaped like an aerofoil/ plane wing towards the prevailing wind offer any beneficial properties in terms of the small pressure differential generated? Does this cause a tendency for heat/cool, condense/evaporate of one side over the other? Could water be dripped off one edge for...? What about upside down wing shape? Or dark & light sides? Or stacked? What about the airflow vortices created?

Or is the reality that to have a useful cost effective benefit you would need prevailing winds of such a speed that cooling wouldn't be the problem, rather stopping the house from taking off?


Hamish, SE Queensland, Australia

DJEB said...

Wow, a lot of great questions there, Ahmish! Thanks!

For the humid tropics, doldrums tend to be the wind, or rather lack of wind, that is available. At least, this is the case along the equator. In your area (Brisbane?), you certainly wouldn't want to catch the North Westerlies off the desert. That would take away the humidity, but heat you up fiercely.

Regarding all the questions about roof design, I think you could hire an engineer to do all that to a degree, but, as you say, would it be cost effective? Would it be cost effective when you've got your house surrounded by trees (for shade and food) that would cut the wind anyway? And any strategy at evaporative cooling in the tropics would exacerbate the unwelcome humidity problem.

Perhaps there is a new design along your lines that would work brilliantly. But I personally would not stray from time tested traditional methods of cooling. There are already the cost effective strategies outlined; and as Noddy pointed out above, it is the tropics - you have to accept a certain level of discomfort. The heat can be horrible, I know. To help with perspective, we had to deal with -26°C two nights ago where I am. But then again, we don't have things like Ross River fever to deal with...

Kim said...

Dehumidification improves subsequent evaporative cooling.
A Liquid Desiccant Waterfall removes humidity with very little energy, greatly reducing the job of the air-conditioner (used only for cooling). Calcium chloride, a highly absorptive salt, is mixed into the waterfall, where it captures moisture out of the air. Heat from the solar hot water collectors is used to regenerate the desiccant.
dehumidifier utilizes refrigeration to cool the incoming air stream below its dew point. This cooled and drier air is used to pre-cool the incoming air stream. After the pre-cooling stage, the processed air is reheated by passing through the condenser coil. The heat removed by the evaporator coil is returned to the air stream, resulting in an overall temperature increase of the air leaving the unit and building.
Precool dehumidifying using the return heat aircon
Dehumidifying heat pipes absorb heat from the aircon return air before it reaches the cooling coil, lowering the operating temperature of the evaporator coil and increasing moisture removal 50% to 100%. The heat absorbed by the pipes located in the warm return air is transferred to the second section to reheat the cold supply air for humidity control. Lower-humidity indoor air feels more comfortable, so cooling temperature thermostat settings can be higher to save more energy.
_Personal notes_
Massive evaporative cooling via _air_heat_exchanger_:
pool in shade with humid draft exchange?
waterfall or coolgardie drip sheets against under house upward air channels [cross ventilation evaporates]
dense wet shade vegetation under house or pool to cool up vented/down sealed air pockets between the joists. Pre roof eaves to slow exit of relatively cooled strata. Have pool under abutting cover for maximum flow/exchange?
open sub floor on wind _side_ and close opposite side and updrafting ceiling vents. Also, upstairs updrafting curtain wall on opposite side to prevailing wind
wet clothes.
chain link fenced under house?

deep shade tree cover?.
trellised vines 5cm+ above roof? Passionfruit?
rockwool batts are very sound absorbent
Cyclone resistance?
Off coast breezes and down valleys in late evening and early morning
Lovered sunshade to direct air down through windows
Channel air via vegetation

DJEB said...

Thank you, Kim. I tend to like the final suggestions the best as the others are active dehumidification and cooling. My hope is to promote the usage of low-tech solutions that have minimal embodied energy and require little or no energy inputs to maintain and operate the cooling system. Your shading suggestions fall right in line with that!

Anonymous said...

thank you for the inpiration.
i just thaught about, when you are camping you could pull jour sleeping bag insideout put in stuff to cool and inside moisten the "outside".The (now)inside cloth would keep the filling the evening the filling should be cold and the sleeping bag dry.

DJEB said...

Anonymous, I suppose you could. I don't think I'm up for trying that, mind you.

UnknownWarrior said...

Hello DJEB!
I had read already about zeer pots on practical action's site. But was searching someplace where I could post my question. Nice to have found your blog. And nicer to see that you're responding to each of the posts. Have only read half the posts yet though.

OK, with my question: I'm in a metro city in India called Mumbai.

Mumbai has a tropical wet and dry climate. Mumbai's climate can be best described as moderate temperatures with high level of humidity.

Now, if I use the zeer pot, will it work in this humid climate? Its raining these days.

Also somewhat offtopic I guess, I have read quite a bit about ultra lpw cost solar water heaters and solar stills which produce little water out of air.

I would like to make all these solar projects to cut down on costs as well as have an alternate means of water during bad times.

Would these things work in the humid climate or are these useless in this climate?

DJEB said...


A zeer pot (I forget the Hindi term for them) will not work in a humid environment. The cooling comes about as a result of the evaporation of water that slowly percolates through the unglazed vessel. They are common in the drier regions of India, however.

Happily, your efforts to adopt solar water heating will not be affected by the humidity.

UnknownWarrior said...

Thanks for replying Douglas,
Well, atleast the solar water heater will work.

I'm now searching for alternatives to the zeer pots which could work in humid climates too.

Just found something interesting

DJEB said...

An interesting find. Thank you!

Anonymous said...

Ok, help me out here. i am bound and determined to live as self sustained and offgrid as i possibly can in the worst of places to try and do so- i live in an old poorly built apartment above my parents business- in muggy high humidity indiana. until i save enouigh money to move somewhere else and build a home correctly with passive solar design- i have to make do with what i have. which isnt much.

heres my question- the Clay pot fridge must have hot dry surroundings to work- but does anyone know the exact temp and humidty scale for this?

is it possible to build an enviroment to stay within that scale? like perhaps building a box with a small fan to create airflow and bunch of calcium chloride in a pan or vessel of some kind to dehumidify? it would take upkeep- i imagine youd have to have the calcium chloride on a rotation everyday- a fresh batch to replace the soaked batch while you evaporate the soaked batches liquid.
if you evaporated it with a solar cooker and you solar power charged the batteries for the inside fan- it would be free offgrid running.

i can imagine everytime i reached in for veggies or fruits- (two to three times a day)- i would water the pot and empty the chloride pan.

which does not bother me any.

but the main question is what temperature does it need to be at? my house is never below 80 degrees in the summer. would that keep the box hot enough? or would i have to put it outside in the sun to get it hot- the temp is always between 80 and 100 here in the summer)?
would this work at all?

in the winter it gets cold and keeping food cold is not a problem- but during the summer months- can i create a small suitable enviroment for a pot fridge? because its my only option on my budget, current location and my desires for offgrid self sufficient living.

any fresh food i try to keep in my unair conditioned house immediatly spoils.

can someone help me. any ideas?

DJEB said...

The temperature is ok, but I think that the humidity is going to prevent you from getting the effect you want. I don't think there is a way around the humidity. I'd be delighted to be proven wrong, though.

Solomon said...


I was wondering... I'm going to be going on a camping holiday this summer to portugal with only the items on my back. I would love to be able to have a zeer pot but obviously the logistics of carrying two large clay pots with me is not exactly feasible!

My thoughts are the following, and I would appreciate any thoughts or feedback on these, that I would create a zeer pot using fabric with a DIY frame to hold it together. The fabric is obviously taking up most of my thought process here. Do you agree that if I used a breathable water resistant fabric, one that allows "sweat vapour" out but water particles out as well?

I think that like an unglazed clay pot, this would allow for slow release of the water inside, taking away the water vapour and leaving the smaller framed fabric "box" inside cooler?

Obviously this would massively reduce weight and space taken up.

Many thanks in advance,


DJEB said...

Hello Solomon,

Your good idea is one that people do use. Items wrapped in a wet towel cool down as heat is lost to evaporation. It won't get cold like a fridge, but it will help.

Tiberius Iulius said...

Very good article. I had no idea that the Africans knew that.

John said...

Its like we're going back to the past. The solution to our problems is using only the resources around us.Nowadays we use process cooling chillersfor cooling building ,then someone invented the Passive Air-Conditioning and Refrigeration that uses only pipes under the house. Because of our problem of loosing much energy, we are now looking alternatives ways to conserve it.

Anonymous said...

Perhaps the best way to cool your house is to have a way to occasionally spray (not drench) your roof with a fine mist on a hot day. No water should leave your roof (either by draining or falling) and you don't want to soak or wet your roof, just slightly moist it. Water has a high heat of vaporization and as it evaporates it takes a lot of heat with it keeping your house cool.

Anonymous said...

I am doing a project about the pot-in-pot cooler for one of my engineering design classes at Penn State. Would it be possible for me to have permission to use the images of the cooler from your article in my project? It would be a huge help!

DJEB said...

I believe Scott gleaned them and used them under fair use.

Gadzira Chirumhanzu said...

mine is not a comment but a question or advice. is it possible to build a cold room from cement or farm or soil bricks where one can keep lets say 1200 bottles of beer and where the temperature is low that these beers can be consumed nicely