Tag Archives: getting back to basics

It’s Not Rocket Science #6: The Stack Effect

The Stack Effect is when air is moved into and out of buildings by means of a difference in the buoyancy of the air on the inside and on the outside – between air that is colder and air that is warmer, in other words. Buoyancy can be either positive or negative – in the sense that warmer air can rise to be replaced at the bottom by cooler air, or cooler air can sink to replace warmer air at the bottom. Positive buoyancy is when warm air rises, and negative is when cool air something sinks. Got that? Both are good, if you’re trying to keep a building cool.

Or warm. Before I go any further, let’s not forget chimneys, sometimes called chimney stacks. Here’s a link to the history of the chimney. The first known English example of a chimney is at Conisbrough Castle from the 12th century, but they didn’t become common in houses until the 16th. Until then, life without chimneys was very very unhealthy.


It still is, in many parts of the world. According to a World Health Organization report, “Nearly 2 million people die prematurely from illness attributable to indoor air pollution from household solid fuel use.”

Early chimneys were an improvement, but weren’t perfect. Count Rumford, whom you’ve already met, invented the Rumford Fireplace in 1797. He made two important improvements – one was to change the shape to direct more radiant heat back into the room, and the other was to restrict the size of the chimney at the bottom to increase the speed of the smoke going up the chimney. The streamlined smoke flow generating the stack effect had the added advantage of sending the non-smoky but heated air back into the room.  Importantly, existing fireplaces could be easily modified.

To many, these new and better fireplaces looked strange. They were shallow and their sides were angled and they were taller than they were wide.

Rumford Fireplace

Rumford Fireplace (Photo credit: bensheldon)

Lloyd Alter, over at treehugger, can tell you more about modern Rumford fireplaces. Interestingly, a fireplace has an optimum burn rate that is set to something like “roaring” – the heat should be burning off the soot at the front of the fireplace, as in the photo above. (Thanks for that Lloyd.)

Finally, to end this introduction to the stack effect, here’s a photograph you’ve seen before, of some chimneys that may have been admired by Walter Gropius for their stack effect. Or maybe not.


Conventional chimneys make use of positive buoyancy from the bottom, as do some solar chimneys that have been recently proposed to generate electricity.

English: Solar Chimney prototype at Manzanares...

English: Solar Chimney prototype at Manzanares, Spain. View from South 8km away  (Photo credit: Wikipedia)

Here’s a schematic configuration of a solar chimney power generation plant. [Thanks climateandfuel.] It’s usually proposed that the space beneath the heat trap be used to grow tomatoes. Whatever.

solar tower 200MW

Other solar chimneys use the sun to create a positive buoyancy in the air at the top of a chimney and thereby draw cooler air into the building to replace it.  Here’s a CAD model that’s easy to understand. Chimney heats air, causing it to rise and draw air through the building albeit at different rates for each floor.

English: Solar Chimney; CAD model (in TAS) use...

English: Solar Chimney; CAD model (in TAS) used to investigate solar chimney performance. Image by Nikolaos Angelis (Photo credit: Wikipedia)

This principle is used by the University of Washington’s University of Phase 1 Molecular Engineering Building (MEB) except that the rates are the same as each floor now has its own solar chimney. You’ll find more facts and performance data here. These stacks are really turbine ventilation inducers in which

a glazed panel was incorporated in the west-southwest orientation of the stack, inducing a solar assist to airflow by increasing the buoyancy of exhaust air during peak summer months.

zgf_uwmeb_3dsection_300Here’s a schematic of a building that uses passive energy to draw passively cooled air through a building.

English: This solar chimney draws air through ...

This solar chimney draws air through a geothermal heat exchange to provide passive home cooling. (Photo credit: Wikipedia)

It describes exactly the same principles known in Persia in the first millennium BC.

English: Diagram of a building cooled by a qan...

English: Diagram of a building cooled by a qanat and wind tower natural ventilation system. (Photo credit: Wikipedia)

Here, this windcatcher is coupled with a qanat which, you’ll remember from the post on yakhchal, is an underground canal (aka underground heat exchanger). Windcatchers come in many types depending upon their function and the direction or directions of the wind. They also trap a lot of heat because the µ-value of mud brick isn’t that high. This means that they function as solar chimneys when there’s no wind.

English: Windcatcher exhibit at the Dubai Muse...

English: Windcatcher exhibit at the Dubai Museum within Dubai, United Arab Emirates. The museum is located in the Al Fahidi Fort. (Photo credit: Wikipedia)

A windcatcher doesn’t have to be made out of mud brick to catch wind. However, if mud brick is what you have to build with, then you also have a solar chimney and a stack effect. This stack effect still exists when the tower is wind-driven but is insignificant compared with air movement generated by the pressure difference caused by the Bernoulli EffectGiven their names, it’s unsurprising that the stack effect of windtowers and windcatchers is overlooked but, even if wind had nothing to do with driving them, they would still be a tribute to human ingenuity and intelligence, providing cooling when and where it was needed.

* * *

The term ‘solar chimney’ threw up this image, from www.jeremylevine.com. I’m including it as an endnote because it seems to link the stack effect with recent concerns such as courtyards, gardens, biophilia, and SANAA.

Pocket Courtyard

Pocket Courtyard (Photo credit: Jeremy Levine Design)

Pocket Courtyard
An internal pocket courtyard acts as a light well, open air shower, and ‘solar chimney’. Working as a solar chimney the courtyard allows heat to escape up the vertical space, drawing cool air into the house through the oversize sliding glass doors that open up both ends of the house. This kind of passive/non-automated, climate control method gives the home’s occupants an interactive relationship with their microclimate that lessens their dependence on the carbon hungry air conditioning system.
The tree and plants act as ‘natural air scrubbers’, devouring the C02 and other airborne toxins, replacing it with oxygen.
Behind the tree is an open air shower tied to the grey water recycling system through a drain concealed under smooth beach pebbles.


It’s Not Rocket Science #5: Night Sky Radiant Cooling

If ever you’ve noticed cloudless nights are colder than cloudy ones, then you’ve experienced Night Sky Radiant Cooling.  

The temperature of the surface of the earth is relatively constant so the amount of energy lost in the form of heat from the surface of the earth at night must be more or less the same as the amount of energy gained by the sun at the rate of approx. 1.5 x 10^19 kJ per day. Otherwise, the planet would overheat. Of course, one of our problems right now is that Earth is overheating a bit but, for the time being, we can still say that most of the Earth’s heat is radiated back into unheated space at night as thermal infrared radiation. Please allow me to introduce you to Count von Rumford.


Two centuries ago he invented a more efficient and smokeless fireplace. For this, he received instant celebrity and the eternal thanks of ladies in London salons. He was a bit of an expert on heat transfer and, on his travels, noted that “the inhabitants of certain hot countries who sleep at night on the tops of their houses in order to be more cool and comfortable, do wisely in choosing that situation to pass their hours of rest.” He concluded that “frigorific rays” arrive continually on the surface of the earth from “the heavens” to cool the planet.

We know now that heating is the transfer of heat into an object and that cooling is the transfer of heat out of an object. Whether it’s heating or cooling depends upon the direction of the radiation but the effect of cooling is the same as if there actually were incoming “frigorific rays”. It’s not a bad way of thinking about night sky radiant cooling.


A previous post about yakhchal described how, around 400BC, the Persians used night sky radiant cooling to make ice in winter. Yakhchal of the domed type were common in Yazd (smack in the middle of Iran now) where the climate was especially suited.

yazd location

Here’s a year’s worth of hourly temperature reports for Yazd.


FREEZING (blue) 0°C COLD (dark green) 10°C COOL (light green) 18°C COMFORTABLE (yellow) 24°C
WARM (light red) 30°C HOT
 (medium red) 38°C VERY HOT (dark red)  

We know the Yazd ice-makers knew about night sky radiant cooling because

  1. walls to the east, south and west sheltered the ice-freezing areas from the radiant heat of the sun 
  2. these walls also kept the air behind them still to further reduce the temperature of the air immediately above the ice
  3. the ice-freezing pools were covered with straw during the day to minimise heat radiation from the daytime sky
  4. this straw was removed at night to increase heat radiation to the night sky
  5. yakhchal were built on the edges of towns
    (In their paper, “Assessment of Ancient Fridges: A Sustainable Method to Store Ice in Hot-Arid Climates”, Mahdavniejad and Javanrudi report that yakhchal were built in the countryside because of their large land usage and the high cost of land in cities. Possibly, but if the ancient Persians understood about night sky radiant cooling then they would of course site their ice-making facilities away from cities and their heat islands.) This is a sketch of the ice house at the edge of the city of Kashan, from 1677.

ice house chardinIt’s well known that the process could produce ice even when the ambient temperatures were above freezing. Once produced, the ice was then moved to the yakhchal and stored through the summer. However, I don’t think the use of night sky radiant cooling ended once the ice was stored. In “An Overview of Iranian Ice Repositories, An Example of Traditional Indigenous Architecture”, Hosseini and Namazian state that

one of the advantages of these vaults was that they could be built step-like with stairs to help workers to cover the external crust of the vault with thatch [straw] to protect it from rain, snow, sun and atmospheric variations. They built smaller stairs between these stairs to make it possible for workers to ply. So people could maintain or repair them easily.

close up of ice house construction


If this stepped construction allowed the dome to be easily covered with straw during the day for whatever reason, then that straw would also protect the dome from daytime heat buildup. Moreover, and with equal ease, the stepped construction would allow that straw to be easily removed at night and so enable night sky radiant cooling to cool the dome during summer nights. I suspect this is what Hosseini and Nazamian meant by this.

In the heat of summers especially in central regions, the sun heats the Yakhchal dome. This method was also employed in order to prevent the ice stored to melt during hot seasons.

A 250 mm mud-brick wall has a U-value of 0.36 and a 350 mm wall has a U-value of 0.26.  [Ref.] Mud brick walls have low thermal resistance and are good at storing thermal energy. Unfortunately, this is exactly not what was wanted. Covering the domes with straw during the day and removing that straw at night is the sensible thing to do. The same process that worked when making the ice also worked when storing it. dome

Interest in night sky radiant cooling waned with the development of refrigeration.

* * *

The following brief summary of late 20C developments in night sky radiant cooling applications is largely taken from the research “Potentials of Night Sky Radiation to Save Water and Energy in the State of New Mexico” by the architect Mark Chalom practising “the design and construction of environmentally appropriate buildings”.  

In 1967,  Harold Hay and John Yellott built a one-room, single-story building and on its roof was a series of ponds with a total area of 170 square feet and covered by movable insulating panels. This is all there was to it.

036-123-01afirst skytherm test building

During the day, the panels were closed so that the water would not heat up and at night the panels were retracted to expose the water to the night sky and radiate the heat it had gained during the day. In winter, the process was reversed and the water was exposed on sunny days and covered at night or cloudy days. Here’s what happened. It’s good.


In 1973 they built a second house in Atascadero, halfway between Los Angeles and San Jose on the California coast. This time, the house was about 1,100 sqft and the water was contained in plastic waterbed-like bags. The system had no pumps, compressors, piping, or ducts, and could be easily operated by the occupants. Indoor temperatures stayed between 68°F and 72°F degrees while outdoor ambient temperature fluctuated between 32°F and 68°F.


It’s been heating and cooling without electricity for the past 40 years now. Its only recognition was the 1976 Bicentennial awards for the categories of environmental and solar energy. [ Ref. ]

Whilst Hay and Yellott were exploring night sky radiation cooling for roofs with their Skytherm houses, Steve Baer was exploring its use in Water Walls. His 1972 house in New Mexico used a stack of 55-gallon drums filled with water to provide thermal mass. The south walls were glazed with single-pane glass but had insulated, reflective covers that are lowered on sunny winter days and closed at night. [pic from here – thanks Batiactu!]


The inside.

water wall

Since then, Steve Baer and Zomeworks have developed the Double Play Solar Heating and Cooling System which is both a passive solar heating system and a radiant cooling system for buildings. The Double Play system uses one or more absorber panels attached to the south side of a structure. (Mark Chalom’s research has shown there is only a 25% reduction in the cooling effect if the night sky radiators are vertically mounted.)

Double Play test building

Double Play test building

There is water storage in the ceiling and radiator/absorber cooling coils on the roof.


The system works.

double play

Zomeworks has also developed CoolCells which are highly insulated, passively cooled, outdoor enclosures that protect and prolong the life of batteries and low-power electronic equipment. They work too. [Here’s some performance graphs.]

cool cell

* * *

In the climates that allow it, the use of unglazed radiators for cooling can provide large cost savings because NSRC is cheaper than refrigeration in creating coolth, and because pumps are more efficient than fans in moving it around. According to Steve Baer, the radiator plate becomes a “sensor” that reacts to the multiple weather variables surrounding it, like wind and cloudiness, producing a coldness that is the coldest useful temperature available at that moment. 


Thinking about all the factors this way simplifies the calculation of the Night Sky Radiant Cooling Rate but, for us, all we need to understand is that night-sky radiant cooling uses 90-95 % less energy than air conditioners and 65-80 % energy than evaporative coolers to provide the same amount of cooling.

It’s Not Rocket Science #4: Humidity Control

The building you see above is the oldest timber building in the world.
It was built in the year 756AD.
Hats off!


It is the Shosoein Treasure House in Nara, Japan, built to house the treasures of the Emperor Shomu (701–756). Buildings like this are the only traditional Japanese buildings that don’t employ post and beam construction. This type of Japanese-style “log cabin” is called azekura construction and was popular around 300BC to 800AD. It was probably a Chinese import from Neolithic times (Late Stone Age: 10,000BC – 2,000BC) but all the examples that still exist are from the 8th century and all of these use the azerkura  construction on an elevated floor.

One of Dedicaory Records of Todaiji temple, , ...

One of Dedicaory Records of Todaiji temple, , top detail, dated June 21, ACE756, 1470.0cm length, 25.8cm height, Shosoin Collection, Nara, Japan (Photo credit: Wikipedia)

In Neolithic times, a similar type of construction had also been used in Europe for the storage of grain. The  Shosoein Treasure House is the oldest surviving example and was used to store the Emperor’s treasures that included furniture, games, musical instrument, art, books and things from as afar as Persia.

In Japan, storehouses such as the Shosoein Treasure House may be traditional buildings but they are not vernacular buildings. Firstly, their owners had to be wealthy enough to own things worth preserving, the owner also had to have sufficient land to separate them from other buildings for reasons of fire protection and, the timber was expensive and expensively worked. Much care was lavished on their construction so they could preserve their contents but only Shosoein has done so for 1,200 years.

It’s widely believed that the timber and the method of construction of these storehouses is responsible for regulating the internal humidity and so help preserve what they contain. The timbers are supposed to expand on rainy days to block the gaps between them and prevent further entry of moisture, and then contract on dry days to allow interior moisture to escape. However, this has never been proven – according to Terunobu FUJIMORI, all-round architectural historian, architect, and professor at the University of Tokyo’s Institute of Industrial Science. (Hmm, his name seems familiar.) I imagine him saying something like that would make him rather unpopular but whether or not it’s a hygromyth is easy enough to prove. I expect this paper, “Temperature and relative humidity environment of the North section of Shoso-in repository [in Japanese]”, does so but haven’t yet been able to access it and find out for myself.


Terunobu Fujimori’s “Too-tall Teahouse” needs no damp-proof membrane (Photo credit: japanese_craft_construction)

Fujimori believes that simply elevating the building off the ground matters more, but although the actual azekura construction may not work the way people would like to believe it does, it nevertheless does slow down the rate of moisture entry on wet days and the rate of moisture exit on dry days. So rather than maintaining a constant humidity, the amelioration of sudden changes in humidity does improve the storehouses’ performance in preserving precious objects.

It should be mentioned that the doors of these storehouses are sealed shut and opened only on ceremonial occasions and then only in autumn when the humidity is both low and stable but this too shows an awareness of the link between humidity and preservation.


It’s Not Rocket Science #3: Yakhchal

By 400BC, Persians had developed a system for making ice in winter and storing it throughout the summer and in a hot desert climate, in buildings they called yakhchal.

yakhchal_01 Most of what you’ll find written about yakhchal on the internet seems to come from wikipedia. Most diagrams come from one academic paper but images are from several private sources. Yakhchal and the idea of ice cream before refrigerators appeals to many people – some for its sheer ingenuity and inventiveness, some for reasons of cultural grandstanding, some for the genius of vernacular problem solving, and some for the low-energy aspects of energy storage that may have application today. Not least of all,

thermal energy storage using ice is practical because of the large heat of fusion of water. One metric ton of water, one cubic metre, can store 334 million joules (MJ) or 317,000 BTUs (93kWh or 26.4 ton-hours). In fact, ice was originally transported from mountains to cities for use as a coolant, and the original definition of a “ton” of cooling capacity (heat flow) was the heat to melt one ton of ice every 24 hours. [W]

The following is a summary of what’s involved.

  1. Even cities in Persian deserts were serviced by a system of underground canals called qanat. Here’s how they work.Qanat_cross_section
  2. In winter, water from these qanat was led into channels and allowed to freeze overnight. High walls shaded these channels from the sun from the south and often from the east and west as well. The walls also protected the channels from the wind to facilitate freezing. Ice was made in layers over several evenings, and when it was about 50cm thick, was cut into blocks and stored in the domed yakhchal building. The door was sealed at a special ceremony and opened in summer at another.
  3. This all sounds very simple. However,if we have a piece of ice in shallow ponds with a determined height, and some water with a diameter equal to “s”, the following relationships can be expressed to determine the size of the ice made, where Eq 1 describes the cooling of water up to freezing point and Eq 2 describes the freezing of water in a layer of water at zero degrees.
    Eq 1: (Qr1+Qe1+Qc1-Qs1)∆t1= ρw*As*Cw*twi
    Eq 2: (Qr2+Qe2+Qc2-Qs2)∆t2= ρw*As*hif
    Qr1: transitive heat of radiation
    Qe1: transitive heat of evaporation
    Qc1: transitive heat of convection
    Qs1: transitive heat of water above ice surface
    ∆t1: Time to cool the water to zero degrees C
    ∆t2: Time to freeze the water
    ρw: Density of water
    As: Area of ice surface in cavity
    hif: Freezing enthalpy
    twi:  Primal temperature of the water
    Cw: Specific Heat of water
    Therefore, the size of the ice the can be made can be calculated from Eq 3.
    S´=ρw * s/ρi* ∆t
    where ∆t=∆t1+∆t2 [thanks Mahdavniejad and JavanrudiI only mention this to show that even just making the ice involves many factors that need to be understood empirically, if not theoretically. Just filling a hole with water on a winter’s night will not guarantee timely, sufficient and good quality ice.
  4. The yakhchal storehouse itself was designed to keep the ice frozen for as long as possible and it did this by several means.
    1. Thermal mass: The section shows two parts – the dome and the pit beneath it. Warmer air rose and was vented from the top of the dome, whilst cool air remained in the underground portion that was already insulated by the ground. The pit could be as large as 5,000mand the dome span as much as 11m.Untitled
    2. Insulation: The walls of the dome were at least two metres thick at the base, and made of mud brick coated with a special waterproofing render composed of sand, clay, egg whites, lime, goat hair, and ash. This mortar had excellent insulating properties. I can’t find any information for how the optimum ingredients or mix for the mortar were discovered. I can imagine the goat hair may have functioned like the glass fibres do in fibreglass, but what properties do the egg whites add to the render? And how did anyone know they had those properties? There must be some lost science here because the idea of adding egg whites and seeing what happens is not random. Somebody thought about it and said “I think adding some egg whites might do the trick!”
    3. Evaporative cooling (?): Here, accounts differ. One of the most reblogged sentences about yakhchal states that the “continuous cooling waters that spiral down its side keep the ice frozen throughout the summer” but I could find no reference to these domes being shaped to allow water to spiral down the exterior, evaporating, and thus evaporatively cooling it as it “spirals down”. Presumably, somebody would have to climb onto the building and pour water over it. However, Hosseini and Namazian write that

      One of the advantages of these vaults was that they could be built step-like. They used stairs to help workers to cover the external crust of the vault with thatch to protect it from rain, snow, sun and atmospheric variations. They built smaller stairs between these stairs so workers could maintain or repair them easily.

      This seems more likely, especially since the domes don’t look especially spiral. (See also archnet.) However, it could just be that the stairs were used to cover the vault with straw during the day to prevent heat buildup, and the straw removed at night to facilitate night sky radiant cooling of the dome. We already know that the ancient (and not so ancient) Persians knew about night sky radiant cooling to make ice, so why not use it to cool the dome as well? Hosseini and Namazian say the straw is to “protect the dome from atmospheric variations” – and so it would during the day but, removing the straw at night would cause the dome to act in synergy with atmospheric variations.

English: Yakhchal of Yazd province

English: Yakhchal of Yazd province (Photo credit: Wikipedia)

Applications: The ancient Persians had already worked out how to passively cool  buildings. Their knowledge of orientation, sun angles and their invention of different types of wind towers for different uses is well documented. The most common type of wind tower draws air out of the building so it can be replaced by air cooled by those same underground qanat.  Such wind towers (called bagdir = Persian: بادگیر‎ bâdgirbâd “wind” + gir “catcher”) were often positioned in fours around water cisterns. In the sense that yakhchal use the off-peak power to store energy in the form of ice, they are the forerunners of modern-day thermal energy storage systems. Since A/C was sorted, the manufactured ice was used in summer to cool drinks and make

Faloodeh, faludeh or fālūde (Persian: فالوده‎), which is a Persian cold dessert consisting of thin vermicelli noodles made from corn starch mixed in a semi-frozen syrup consisting of sugar and rose water and is often served with lime juice and sometimes ground pistachios. [W]




The recipe for this has not changed since 400BC. At that time, faloodeh, ice cream and other chilled desserts and drinks would have been only for the wealthy only but, by 1870

there were plenty of yakhchals in Isfahan; some of them were for private use. Nevertheless, the poor could also use the yakhchal to cool water. Sherbets and fruit were preserved with ice in all shops. Huge chunks of ice were carried by donkeys and sold all over the province. In Isfahan, people could buy ice either in the bazaar or straight from the yakhchal building. (Ernest Holster*)


A “yakhchal”, built near Kerman, Iran (Photo credit: Wikipedia)

Further reading:

(1) “An Overview of Iranian Ice Repositories, An Example of Traditional Indigenous Architecture”, Bahareh HOSSEINI, Ali NAMAZIAN 

(2) “Historical Ice Houses: Remarkable Example of Iranian Cultural Heritage”, Amirkhani ARYAN, Okhovat HANIE, Pourjafar Mohammad REZA, Zamani EHSAN

(3) “An Overview of Some Vernacular Techniques in Iranian Sustainable Architecture in Reference to Cisterns and Ice Houses”, Amir Ghayour KAZEMI & Amir Hossein SHIRVANI 

(4) “Assessment of Ancient Fridges: A Sustainable Method to Storage Ice in Hot-Arid Climates”,  M. MAHDAVINEJAD, Kavan JAVANRUDI

*Ernest Holster was a German photographer kicking around Persia at the time.

It’s Not Rocket Science #2: Ventilation

Many architects look to Nature for inspiration for how to make their buildings look more natural even though buildings are very unnatural objects. Instead of actually growing out of the ground or landscape like plants, buildings are constructed from putting lots of building materials together and it takes a lot of people, resources and money to do that. We can conclude two things from this.A building that looks as it it’s built out of lots of building materials will:

  1. have more integrity than a building that, say, is trying to look like a rock or a tree or a cloud or a river and
  2. will therefore cost less than an equivalent building encrusted with ornament or trying to look like something it’s not.

As you would expect, misfits is totally against biomimicry in the sense of making buildings look like the result of natural processes like, say, this building does

forest refugeor the architecture of Greg Lynn

gregh lynn

(and its brand extensions).


However, misfits is all for the use or adaption of natural world processes if better performing buildings in the artificial world are going to be the result. Biomimicry is passive design, basically. Biomimicry is to building performance what ‘organic’ was/wasn’t to building aesthetics.


The air conditioning system design for the Eastgate Building in Harare, Zimbabwe is famously mentioned as an exemplar of biomimicry for having been modelled on the configuration that Macrotermes michaelseni (termites, to us) use to maintain the temperature inside their nests. Dave Parr, over at biomimicron.wordpress.com, coins the word biomythology for the claim that these termites maintain a temperature of 87 ± 1°F inside their nests, and offers us the following graph from this interesting paper.

Parr,D., 2012, Biomimicry Lessons for Building Ventilation, Submitted for qualification of Environmental Design of Buildings MSc, at Cardiff University – Welsh School of Architecture. (Thanks Dave – good luck!)

The graph shows that the temperature is anything but constant and sometimes even greater than ambient temperature. From this I conclude that this entire system, ingenious as it is, is to encourage ventilation in order to prevent excessive heat buildup rather than regulate to temperature per-se. But let’s give the architect, Mick Pearce and those nice folks at Arup some credit for trying to learn something from termites.

Let’s also give the termites some credit because – unlike the Eastgate Centre – they don’t use any electricity to open and close the air intake vents and nor do they use fans to regulate the flow of air and the internal temperature. If ants can develop such a system perhaps we should at least try to do something similar for our own structures and maybe even improve upon it if we can. With these termite nests, all the action is really happening underground where there’s less diurnal variation in temperature.


For the ants, the towery bit adds to the convection effect. For the architects, juxtaposing photos of their own towers adds to the eco-cred effect.

images (1)


Leafcutter ants and their nests are perhaps even more impressive but don’t get as much publicity since they don’t build towers but high-density lo-rise. Here’s what a leafcutter nest looks like above ground. The average population of a nest is about 5 million. The average size of a nest is about 3-4 metres across like this one.

006b2700800e0c512fcd78c70306638e Here’s a link to a larger one being excavated.


Again, most of the action is underground. Now these leafcutter ants are pretty amazing creatures.

  • There are 3 types of leafcutter ant: the queen, soldier and worker and there are five types of worker ant: foragers, gardeners, those that chop up leaves, tiny ants that distribute leaf bits to the fungi and those called minimae that tend the fungus and dispose of waste produced by the fungus. Different types have different sizes.

    Leaf-cutter ants can take over when predator p...

    A forager ant (Photo credit: Wikipedia)

  • The forager ants leave a chemical trail so they can always find their way back to the the nest. They collect leaves from all layers of the forest, from the floor to the upper canopy. They are capable of carrying over 50 times their own body weight. They will travel several hundred metres in search of the right kind of leaves.
  • Leaves brought back to the nest are used as a fertiliser for a fungus ‘garden’ in the nest. This fungus is the big grey mass at the centre of the nest. This fungus is the only food source for the ants. Not only that, if the ants bring the wrong kind of leaves, the fungus will create a chemical to tell the ants. Wild ants collect leaves from all layers of the forest, from the floor to the upper canopy.

There are other amazing things about these ants but here’s a schematic of a nest.


  • When the nutrients have been removed from the leaf material, the waste is transported to the peripheral dump chambers where dead ants and dead fungus are also placed.

Kleineidam C, Ernst R, Roces F have researched how these nests are ventilated. This is the abstract of their paper,


Wind-induced ventilation of the giant nests of the
leaf-cutting ant Atta vollenweideri

“Surface wind, drawing air from the central tunnels of the nest mound, was observed to be the main driving force for nest ventilation during summer. This mechanism of wind-induced ventilation has so far not been described for social insect colonies. Thermal convection, another possible force driving ventilation, contributed very little. According to their predominant airflow direction, two functionally distinct tunnel groups were identified: outflow tunnels in the upper, central region, and inflow tunnels in the lower, peripheral region of the nest mound. The function of the tunnels was independent of wind direction. Outflow of air through the central tunnels was followed by a delayed inflow through the peripheral tunnels. Leaf-cutting ants design the tunnel openings on the top of the nest with turrets which may reinforce wind-induced nest ventilation.” (Kleineidam et al. 2001:301, from asknature)

Biologist Bert Hoelldobler at Arizona State University says that ant colonies provide scientists with an invaluable way to gain empirical data around how living in societies developed. Compare the biological blueprint of an ant society with that of humans, he says, and you quickly see that much of human society is built on culture rather than genetics. The basic blueprints for society in our genes are much simpler than those coded within the ant’s.

Biologists Wilson and Hoelldobler have proposed a new class of life: the superorganism. “A superorganism is a closely knit group that divides labour among its members altruistically,” says Wilson. “There are individuals who reproduce in the group and are promoted to be reproducers, and those that do not reproduce and are workers. This allows the group to function as a giant organism.”


In their recent book, Superorganism, Wilson and Hoelldobler describe their idea by comparing each ant in a colony with a cell in, say, the human body, each one specialised for a task and working  for the good of the organism as a whole.

Hoelldobler says a superorganism has a sort of intelligence where an ant colony acts as a problem-solving unit (or even a simple brain). “When you look at the incredible nest structures of these leaf-cutter ants – 8 metres down, an area of 50 sq metres – no single ant could do that, or even has the concept of it, but the interaction, the behaviour of millions of individuals that react to particular stimuli that are created by other workers, leads to these fantastic structures. An ant colony is a problem-solving instrument, in a way.” [guardianonline]

The most impressive thing of all is that leafcutter ants have been around for about THREE MILLION YEARS doing exactly the same thing. If we’re talking about future generations and stuff, I think that’s as sustainable as sustainable needs to get. For most of those three million years, leafcutter ants have been the most complex and ecologically successful social systems on the planet. And probably still are.

About 60,000 years ago Homo sapiens began to spread out from Africa, were established in Europe 42,000 years ago and in Indonesia about the same time. About 20,000 years ago, they crossed the Bering Strait to Alaska and had colonised most of the Americas by 15,000 years ago and most of the remaining parts of the Pacific by 3,000 years ago. Check out this book for the relative achievements of ants and humanity.


Man learned how to use fire to catch animals and birds about 45,000 years ago and, by about 10,000 years ago, had worked out how to make tools, weapons, containers, and how to clear and cultivate land. The first known city in the world was probably Eridu from about 5,400BC and the first permanent settlements not that much earlier. The oldest pyramid is from about 4,900BC.

Humans have really only been in a position to control their environment for the past 60,000 years. But now we know how to use fire and make tools and telescopes, play the piano, understand the rules of perspective and some other stuff as well, it might be time to think about how to work together in groups to solve problems like how to grow enough food to feed ourselves, how to design our structures so their climate can be effortlessly regulated and how not to screw up the environment while we’re at it.

It’s still early days.

It’s Not Rocket Science #1: Thermal Mass

This is part of the village of Kandovan, on the Iran side of the border with Azerbaijan. Dating from the 13th century, the original inhabitants allegedly escaped to these strange mountains of volcanic ash, to get away from invading Mongols – as one does. You can find more pictures of Kandovan here.



Local residents say that the homes are not only strong but also unusually energy efficient – the homes require minimal supplemental heat during the long cold season and remain cool in the summer.  [Thanks environmentalgraffiti.]  

Something very similar happened in Cappadocia, in Anatolia in what is now Turkey. There are several towns like this one, Goreme. Their main purpose, allegedly, was to provide a place where the (very) early Christians could be secure against Romans out to get them. It goes back that far, apparently – although, to me, carving houses out of rock doesn’t convey any sense of urgency as far as finding safe refuge goes. I doubt those insecure Cappadocians gave much thought to the benefits of thermal mass, but I suppose the less time spent gathering firewood when the hills are alive with Romans, the better.



No account of the history of thermal mass would be complete without a mention of The Pyramids. The temperature of what little inside there is, is a cool 68°F (20°C) and does not change – ever. This is interesting  but not very useful. Of more practical use to people actually alive, is the town of Coober Pedy in South Australia. Opals are mined here.


Why people choose to carve their dwellings instead of construct them above ground seems to attract myth and speculation whatever the century.

Supposedly, many soldiers returning from the First World War moved onto the opal fields and easily adapted to living in the dug-outs they had made looking for opal. They found the temperature in their dug-outs was consistently in the low 20s; cooler than outside in hot weather and warmer than outside in the cold weather. (Thanks travellingaustralia.)



As you might expect, these houses aren’t much to look at on the outside but their construction cost is comparable to that of a ‘surface house’. Running costs are, of course, much less. Most countries have had some form of semi underground or cave house. Here’s some in Germany.


Rotswoningen in Geulhem, gemeente Valkenburg aan de Geul
Foto door Cicero, 23 april 2005

Here’s two views of a nice one in Tunisia. Some people may recognise it as the Tatoonie home of Luke Skywalker who was a character in a movie called Star Wars.

Bernard Gagnonhttp://commons.wikimedia.org/wiki/File:Matmata_house.jpg

Bernard Gagnon

The cave dwelling is now the hotel Hotel Sidi Driss and you can stay there for just $12 a night. Nearby is the Dune Sea where R2-D2 and C-3PO crashed in Episode IV.



Traditional Berber pit-houses show a perfect solution to the difficult problem of adapting the zone’s extremely warm climate – the best defence against summer heat.  According to the historians, the Matmata Berbers built their underground homes to escape the notice of their enemies and to protect themselves from Arab incursions. Underground houses were also very practical from construction point of view. It was easier to dig into the mountains’ soft cohesive sandstone rather then use it as a building material.

The pits are circular and around 30 feet (9 metres) in both depth and diameter. An open air entrance starts some distance away to allow gentle slope through the side of the hill. Above the entrance you may find painted blue symbols of fish, star and a hand of Fatima which may protect inhabitants from bad luck. The fish is a good luck charm and the hand and five fingers represent the five pillars of Islam. Houses have an open air courtyard (haush) which is surrounded by the 20 feet long rooms. In summer, the temperature inside the house can be around 30 degrees cooler than in the midday heat above the ground level. [Thanks for that geographicaladventures – the Star Wars stuff was interesting, but it was the temperature thing I was interested in.] 

Sooner or later, Architecture was going to come along and mess with what is basically a nice idea. The problem of course, with building inside a mountain or underground is that you need to own a mountain or some ground to go under. Building in mountains or underground will never be mainstream. Ever. Most people don’t own land, let along mountains. dezeen_Wadi-Rum-by-Oppenheim-Architecture-16

Florida-based practice Oppenheim Architecture + Design have released these images of their proposals for 47 desert lodges at a resort in Wadi Rum, Jordan. [Thank you Dezeen, thank you Oppenheim Architecture + Design.]

If you think that’s scary …

wadi rum

… it won in WAF’s Future Commercial and Future Experimental categories. Thinking about it, where would an architectural competition be without those categories eh? There was and still is no green or sustainable category btw. If there had been, then Oppenheimer A+D would surely have won that as well because of this compelling justification you can see on their website.


If I was any of those critters, I’d be very worried about their Construction Waste Management Plan. Anyway. The climate in Wadi Rum, Jordan isn’t really that extreme – I think it looks rather pleasant. I suppose a bit of fancy glass would stop any thermal advantage from being totally wasted.


What we are seeing here is an architectural statement of course, the unnecessary proof that anything can be used to justify anything. The most recent example of architecture not driven by thermal mass is Villa Vals – you know the one, by SeARCH [!].

1260367826-villa-vals-search-7923The planners were pleased that the proposal did not appear ‘residential’ or impose on the adjacent baths building. The scheme was not perceived as a typical structure but rather an example of pragmatic unobtrusive development in a sensitive location. [Thanks ArchDaily.]1260367236-section-01-1000x707The villa is thermally insulated and features ground source heat pump, radiant floors, heat exchanger and uses only hydroelectric power generated by the nearby reservoir. [From the architects’ website.]

Once again, thermal mass is not mentioned. The only reason this house is underground is so that people in Zumthor’s famous baths nearby don’t have to look at it – as you can see from the following two images. The house lies between the baths and the building you can see in the background in the second photograph.


The desert people seem to get it right. Thermal mass works best when there are large day-night temperature variations.

The wall predominantly acts to retard heat transfer from the exterior to the interior during the day. The high volumetric heat capacity and thickness prevents thermal energy from reaching the inner surface. When temperatures fall at night, the walls re-radiate the thermal energy back into the night sky. In this application it is important for such walls to be massive to prevent heat transfer into the interior. [Thanks W.]

Skyscrapers, City of Shibam,Yemen


Plus, you don’t need to mess with your mountains. In the thousand-year old city of Shibham in Yemen, the walls are mud brick and thick. Many of them are shaded by other walls. The narrow streets channel what breeze there is and, importantly, helps dissipate heat stored in the walls. The uneven rooftops disturb the smooth flow of that breeze, extracting maximum value from it. I’m not saying that the old ways were better but only that people did extract quite a lot of performance from what they had, and with only observation and acquired experience to go on. Today we pay consultants.

A high-density artificial city such as Shibam with its various passive (read, cheap) ways of doing things is always going to be a winning prototype for modern commercial development so it’s no surprise to find these lessons applied in Transsolar’s conceptual guidelines for Masdar.