[jeffvail]

Occasionally I go on a rant about how critical energy independence, energy decentralization and vernacular energy technology are to freedom. Or, how energy centralization creates empire. Every day I hear about how some new technology will save us from oil prices or pollution or whatever. What seems to be continually overlooked is how easily these problems -- and the danger of a solution that increases the centralization of energy production (nuclear...) -- can be solved: PASSIVE SOLAR.

I say this a lot, and I get the impression that the definition isn't really well known. There are those ugly solar photo-voltaic cells (ACTIVE solar) that you can put on your roof, but the energy required to make one (mainly derived from oil) is just about equal to the energy that they will produce over their lifetime, and they require centralized manufacturing and high-technology to produce. No, passive solar is simply the harnessing of the sun's power directly. Ever notice how a room with lots of windows that face the sun gets hot? OK, that's the whole concept... now let's explore how this can be applied effectively, simply, cheaply, etc.

Pretty much everyone can figure out how to heat a home with passive solar. But most people aren't aware at how effective passive solar can be for cooling, cooking, ventilation, waste disposal, etc. Let's take on the most difficult challenge: Cooling a home in Phoenix in the summer with only passive solar. Bill Mollison's "Permaculture: A Designer's Manual" outlines a passive solar cooling system which I have adapted into the graphic below.



For example, while in Phoenix it may never get below 90 at night during some points in the summer, the temperature of the earth at 10' underground is always a nice 55-65 degrees F. A simple solar chimney on your home (roughly, imagine a normal chimney x 50%, with a single-glazed window on the South side and a black-painted vent pipe inside) will heat up and pull air rapidly out of your home. Now, for air intake, lay a "radiator", a network of pipes 10' underground that acts as a heat-exchanger with the thermal mass of the earth. As the solar chimney draws air out, you get nice, cool air blowing in through vents in your floor. 0 energy cost, 0 moving parts, simple technology, and it keeps your (well insulated) home at a comfortable temperature and well ventilated, even in Phoenix in August. Similar technology has been in use in vernacular architecture in the Middle East for thousands of years.

Here's the catch: because it's vernacular technology, and can be easily implemented in a decentralized fashion, there isn't much money to be made off this through a centralized/industrialized economic mode. But it works... this is the very stuff of freedom.

~Jeff
http://www.jeffvail.net/

[jeffvail]

Apologies... I meant to post this to the "Energy Technology" section.

Moderators?

[Petro]

wow this is interesting stuff...I have been trying to figure out, here in florida, some solutions to the A/C thing...This is brilliant. I'm interested in the specifics of the heat-exchange construction however. Wouldn't it make more sense to place the incline in the opposite direction since the coolest temps are lower? or is this a non-issue?

[jeffvail]

Good point... the graphic that I adapted this from had the incline in the opposite direction as you suggest. The key part is that there is a condensation sink (a deeper area filled with gravel or the like) rather than let condensation run into the house. But that could easily be placed directly under the home inlet...

There are a variety of commercial options for geothermal heat exchangers (see www.climatemaster.com ). There are also a number of commercial providers of solar chimneys (see www.azsolarcenter.com ). However, I've been unable to find a commercial provider that combines the two. The air-geothermal heat exchange is simple enough, any contractor could put one together, but the solar chimney is (so I've read) a bit trickier, and may be best if it's at least designed by someone with some solar experience...

The Alhambra (600 year old Moorish palace in Spain) used a system like this that drew air past fountains to increase the humidity. There is probably something similar that could be done specifically to decrease the relative humidity for Florida...

[Petro]

Thanks for the links...I'm very intrigued. I can however see some issues, primarily those you address. The issue of condensation could prove challenging here in Florida, as whenever you dig deeper than 6 feet you usually hit water. Hrmm interesting.

[DomusAlbion]

Thomas Jefferson used a similar idea at his estate, Monticello.

[Caoimhan]

In the case of a high water-table, a closed liquid ground loop can be installed like a regular heat-pump's ground loop. The warm air convection then draws air through an exchanger with that ground loop. A small wind or PV power source can be hooked up to a pump to increase the flow through the ground loop, if necessary.

[Caoimhan]

Just another thought...

It's sadly funny that most homes are insulated heavily from the ground, isolating them from the geothermal temperature moderation. The cave-man lived in caves for a reason. The prehistoric Orkney islanders lived in round houses built mostly below ground level, heated by a central hearth. Modern construction could do much the same, except with a masonry heater. That would be a very efficient home in any climate.

[Devil]

I agree with you that traditional house design in the countries within a few hundred km of here are designed to promote coolth in the summer and, as a result, they are hell to keep warm in winter.

However, the extreme heat (40-47°C) in this country is for only a few days/year and it is uneconomical to construct houses for these conditions.

The problem with passive cooling, as you describe, is that it is not really effective when you need it the most. As I write this, it is 34.3°C outside with a RH of 27% and is quite comfortable, in and out. We have no aircon switched on. The problem arises after dark: the temp will drop to about 25°C by 2000 h but the RH will shoot up to ~60% RH and it is at this time that we need aircon, when we are sitting, watching TV or reading a book, etc. with an inside temp of 28°. Passive systems will shut down by then and we would become stifled (windows closed because of insects). However, I agree that the system is useful for daytime use, albeit very expensive in capital cost.

The Roman atrium construction was also designed to promote convection currents, with an updraft from the paved yard pulling air through the rooms.

Also, it is important to have outside-the-window shutters closed during the day and opening the windows only at night (unlit rooms because of insects).

$this->bbcode_second_pass_quote('', 't')he energy required to make one (mainly derived from oil) is just about equal to the energy that they will produce over their lifetime

[Caoimhan]

I am familiar with the European aversion to screens on windows. I don't know why that is.

Actually, in the evening passive solar cooling doesn't have to stop. Place a thermal mass in the solar chimney, such as black sealed barrels of water, and it will continue to operate long into the night.

[Devil]

$this->bbcode_second_pass_quote('Caoimhan', 'I') am familiar with the European aversion to screens on windows. I don't know why that is.

Actually, in the evening passive solar cooling doesn't have to stop. Place a thermal mass in the solar chimney, such as black sealed barrels of water, and it will continue to operate long into the night.

[Petro]

Instead of a solar chimney, why not just use the considerable heat that builds up in the crawl spaces(read attic but with less than standing room), that are prevalent in the homes of Florida. I measured the temp for awhile before deciding to reinsulate and 120F is not uncommon here in Miami in the crawlspace. We have many months on 90F + temps.

[EdF]

$this->bbcode_second_pass_quote('Caoimhan', 'J')ust another thought...

It's sadly funny that most homes are insulated heavily from the ground, isolating them from the geothermal temperature moderation. The cave-man lived in caves for a reason. The prehistoric Orkney islanders lived in round houses built mostly below ground level, heated by a central hearth. Modern construction could do much the same, except with a masonry heater. That would be a very efficient home in any climate.

[jeffvail]

Devil,

www.gaiam.com lists a 165 Watt PV panel at $940. Not quite $200 for 150 Watts. And that's with government subsidies, and not counting the very expensive (and short lived) batteries, the intertie, etc.

But let's assume your figure of $200 for 150 watt panel, and let's assume that it will last 30 years:

The total energy required to produce a product can be considered equal to its price, as the concept of oportunity cost translates equally across energy, labor, and all other economic inputs. So, being generous and assuming a $60 barrel of oil (even though the recent price rises have yet to be incorporated into retail prices), one $200, 150W PV panel requires 3.33 barrels of crude to produce. 3.3 barrels of crude is equivalent to 5.6 MWH, which is just over half what you predict your panel will generate in 30 years. If you use actual panel prices (as I mention above, which is 4.3 times as expensive as your example), then a $940 165 W Panel only generates 45% of the energy required to produce it over 30 years. Either way, it's a very poor return on a 30-year investment.

So in simpler terms: With $940 you can buy either one 165W panel or 15 barrels of crude oil. Over 30 years, you'll get 45% as much energy out of the panel as you will get right now out of the crude.

The EROEI on PV Solar is terrible -- it's critical to remember to calculate not just the energy used in the PV panel manufacturing plant, but ALL the energy used in the entire production chain: energy to power the mining equipment, the ore processing equipment, the transportation of the raw materials, the transporation of the finished product, the energy required to feed, cloth & house the workers, etc. Because if you cut that part out of the equation, no solar panel. EROEI = <1

~Jeff

[DriveElectric]

jeffvail, please define EROEI and what it really means. Nobody on this website seems to know, including a few Physics professors. Perhaps you can enlighten us. Does anyone even use it?

If you have a defined formula, please run the numbers for us.

[Kez]

I'm in Texas (hot!) and I often go outside for just a minute and the heat is just amazing. I often think that there has got to be a passive way to capture all this heat, without resorting to using a million mirrors boiling salt and whatnot. I have studied these cooling systems and the passive ovens a little bit.

Looking at the chimney, does anyone think it would be possible to build such a chimney or other solar collecting area that absorbed the sun's energy and converted that to air pressure by rising, such that the pressure could be used to turn a turbine? Of course it would be pretty weak energy created, but at least the construction is simple and there is no fuel source. The air would heat up and rise through a tiny valve to create enough pressure to turn a turbine and at least recharge batteries or something small.

The part that I don't think is possible, is how do I let more air in at the bottom even though I want to keep the pressure of the system very high so that it can actually create the air pressure needed to create enough power.

[jeffvail]

From the ]EROEI Thread:

$this->bbcode_second_pass_quote('jato', 'J')ohn you bring up a good point. A standard must be made in regards to calculation. However, EROEI is still a very important CONCEPT relevant to declining energy.

[jeffvail]

Kez,

It's a fascinating concept. See:

http://www.enviromission.com.au/index1.htm

I have no idea how well this would work on a home scale, but I'd love to see any resources or links that people have on this??

[jeffvail]

Back to EROEI as a concept... from an anthropology standpoint I'd argue that aggregate EROEI across humanity is proportional to aggregate population and economic growth. That seems to sum up much of the threat posed by peak oil...

[Petro]

I love this whole concept. That its origins are archaic only reinforces my philosophy that" 'Simple is best.' I do see that to implement this type of cooling system, in a modern environment, will require more thought, and perhaps substantial improvements on the basics. This is an interesting challenge, and I will spend some intellectual capital on it.

Some interesting issues:

1) condensation: very solvable, though will require some inginuity.
2) day/night transition: this could prove problematic, but solvable.

any info that addresses these particular issues would be appreciated