One concept for how to reduce the environmental impact of cities is arcologies. The word itself is a combination of the words “architecture” and “ecology”, which neatly sums up the idea of developing self sustaining buildings with the minimum of environmental impact. Such buildings would not only provide housing, public services, shops and businesses, but would also grow their own food within the building (or on the grounds surrounding it), even recycling all of the buildings waste and manufacturing much of its own goods. If you are unfamiliar with the concept this TEDx by Jeff Stein should help. Also I’d recommend this pod-cast by Issac Arthur.
In theory given that the plants inside such a structure could produce enough oxygen to sustain the population you could theoretically put such a building on the moon if necessary, or in a dome at the bottom of the ocean. This concept was first introduced by the Italian architect Paolo Soleri in the 1950’s. While no true arcology exists in the world, its certainly a concept that has influenced eco-building designers for quite sometime, as well as also being a stable of science fiction. So I thought it would be useful to look at the concept of arcologies in a bit more detail.
One misconception we need to get away from is that arcologies have to be tall mega structures. Certainly quite a few of those proposed over the years have tended to be fairly large. For example the NOAH (New Orleans Arcology Habitat) concept, which would be 1,200 ft tall and house 40,000 people. Or the X-seed concept, a 4km high 800 storey building that would support up to a million people.
However, there’s no reason why they can’t be smaller or have a lower floor count. Arcosanti, Soleri’s own arcology concept, is only few stories high. And it isn’t a single building but a cluster of them. Probably the closest to an actual arcology we’ve come is Dubai’s Masdar city where most of the buildings are only a few stories high. However, certainly quite a few of the proposals have been fairly tall, as often the goal is to change how densely populated cities work.
Perhaps the best way to illustrate the pro’s and cons’ of arcologies is to throw around some numbers. So firstly, how much floor area do you need to create a “self sustaining” community? Well in the UK the current recommendation is 50m2 for a single bedroom flat and about 85m2 for a three bedroom flat. So let’s assume 70m2 per person, as I want to assume we’re not cramming people in like sardines. This would also exceed the average flat size per capita in most countries. That said there is an argument to be made for making flats smaller for environmental reasons, but we’ll overestimate all the same.
Next let’s assume about 50m2 per person for public services (e.g. schools, a medical centre, council offices, library, etc.), shops and other amenities and 50m2 per person for gardens, green spaces and public areas. Growing food within a building would most likely involve using greenhouses and hydroponics. These can intensive grow crops, often stacking plants into a very small area, growing them under red light in climate controlled conditions to increase the yield. I’m going to assume 30m2, because I came across a paper sometime ago from some NASA study suggesting that was about enough to support a single person. I’ve lost that paper, but this source here implies 49,210 people could be sustained by 1km2 of aeroponics (implying you’d need just 20m2 per person).
Now granted these studies assume you’re eating nothing but porridge oats or potatoes, while I’m assuming we’ll be more interested in growing fruits and vegetables, which would wouldn’t be as efficient. However this is where I’d question some of the concepts behind an arcology, notably the issue of being completely self sustaining in terms of food production. This “Juche” like concept has never sat well with me. I see the point of trying to reduce environmental impacts, but at the end of the day its going to be a lot easier to grow most crops outside in a field rather than inside a building. So my assumption of 30m2 probably isn’t enough to make the building fully self sustaining. But its likely to be enough to supplement the occupants diet. And we are devoting remember a further 50m2 for gardens and other green spaces, which could include allotments and urban farms.
I’m going to add up these areas and add on an extra 25% to represent the area taken up by services, e.g. risers for lifts, stairs, service floors, etc. One problem with ultra tall builds is the so-called lift conundrum. This states that the higher a building gets, the more of its useful floor area gets devoted towards fitting lifts. An arcology gets around this problem to some degree because we’re spreading people out more, as compared to a normal high rise building. And given that such buildings incorporate shops and offices within them, often on intermediate floors between residential floors, people won’t need to leave the building that often, meaning most journey’s will only be between a few floors and we would probably encourage residents to simply take the stairs.
Either way, adding up all of these areas we come up with about 250m2 per person. Taking this number I will consider three basic designs. For the first one, which I’ll call “arco-cylinder” ,we’ll assume a cylinder 50m in diameter and about 400m high. Such a building would have a floor area of around 250,000 m2 and could therefore house 1,000 people. Next we’ll look at the Sky City 1000 concept. This proposes a building 1,000m high and 400m in diameter, with a total total floor area of 8 km², which could accommodate 32,000 people. Rather than a simple skyscraper, the Sky City consists of 14 dish-shaped ‘Space Plateaus‘ stacked one upon the other, inside which the residents live in a self contained community.
As a contrast to these two skyscrapers I’m going to also include a low rise building just 6 floors high and 40x40m square (likelihood is we’d probably go for more rectangular blocks around a central garden or forum, but it will occupy the same area on site) built to passivhaus standards which houses just 80 people. This will include a further 4,000m2 of garden space on site (e.g. central court yard and park land or allotments around the edges) rather than putting this area within the building itself. I’m only going to assume for this concept that the ground floor is occupied by shops, public services and offices (e.g. about 16% of the overall floor area, v’s the 20% assumption made with the other two). In place of hydroponic farms we’ll put some greenhouses on the roof, where there would be room for up to 1,600m2 of them (about 20m2 per person, so again slightly less than with the previous two, but we’d be using some of the green space around the building for an urban farm as well). We’ll call this one the “eco-block” and its worth noting its not that dissimilar to some existing developments.
So the first question is how many of these would we need to house the current UK population? And what level of population could they support? Well the UK’s cities occupy 27,400 km2 of land area (about 11% of the UK’s total land area). So in theory, taking just 10% of the UK’s existing urban area, our “arco-cylinder” concept could house 700 million people and the Sky city concept could house 350 million. So with just 1% and 2% respectively of the UK’s urban land covered with these, you could house the entire UK population.
The eco-block concept could house 34 million people, which means that using 20% of the UK’s urban land area you could house the entire current UK population with eco-blocks. This is one of the advantages of arcologies, even relatively low rise ones surrounded by green areas are still able to house a large number of people, yet still providing them with a larger floor space in which to live.
Arguably the above comparison wasn’t really fair as it compared the ground footprint area of the two taller ones with no provision for any gap between them, while we factored in a large area of green space around the “eco-block”. So let’s recompute, we’ll take the maximum dimension of the two taller buildings (e.g. the height) and space them that distance away from one another (likely they’d be built as a cluster of several towers closer together, but we’ll assume the same land area allocated to each of them).
So assuming we then built one arco-cylinder spaced 400m apart across all of the UK’s urban land, you could accommodate 230 million people (or just the UK’s current population using 30% of all urban land). With Sky city’s spaced 1 km apart, you could house 890 million people within the UK’s existing urban areas (or the whole of the UK’s current population on just 7% of all urban land). Replace all of the UK’s cities with eco-blocks and you could accommodate 340 million people.
And remember, we’re assuming each of these buildings is now surrounded by a lot of empty space. The footprint of each arco-cylinder will occupy just 1.6% of the land area we are assigning to it, the Sky city only 12.5% and the eco-block 25%. So that’s lots of empty green space that could be used for other purposes, such as urban farms and allotments, or renewable energy systems.
Now I’m not advising covering the entire country in arcologies as a realistic planning strategy, I’m merely pointing out that when someone tells you that “Britain is full” that’s baloney. You could double or triple the UK’s population and not have to build a single home on the green belt. The reason why the UK has a housing crisis is that since the 80’s the rate of house building has been falling and the country’s stock of council houses was decimated by the Thatcher government. Also the population is rising (only recently due to immigration, generally its been people living longer) and household sizes are shrinking (more people living alone) which has increased demand for homes.
Isaac Arthur in his podcast on arcologies estimates that if you put one 125m diameter arcology with 5,000 people in it, one per square mile along the US coast you could house half a billion people, leaving the whole of the US interior either devoted to farmland or as national park land. Its worth noting that Issac applies a larger amount of floor area than I do. In his calculations, he assumes more than enough to render an arcology fully self sufficient, so it won’t really need much farmland to support these buildings. Putting one down every square mile (i.e. one tower occupying about 0.5% of that square mile) across the whole of America and you could support a population in the tens of billions. So no, America isn’t full either, not even close.
Heating and cooling
Isaac Arthur’s video also mentions how arcologies might have a major cooling problem. Well not necessarily, it depends on where you build it and how its designed. But certainly heating and cooling of any buildings is often the main source of energy consumption. This is in fact the very element of the arcology concept that has been most heavily incorporated into modern buildings, as I discussed in a prior post.
Good insulation can limit heat losses in winter while good use of solar shading can limit solar gains and reduce overheating in summer. Natural convection can also be utilised to reduce energy consumption. For example, the double skinned facade can be used to either heat a building in the winter. Or by using natural convection, we can create a stack effect that will draw hot air out of the building.
By positioning the inlets at the ground floor and drawing the air through the ground (which will always be about 10-12’C) we can effectively cool the building naturally. Solar PV facades can perform a similar function, with the added benefit that the air flow will help to cool the PV panels and improve their efficiency. Similarly Masdar uses wind towers to help naturally cool the city down.
The layout of a building can help reduce its energy consumption. Clustering the hydroponics or greenhouses towards the top of our structure (where it tends to be warmest) would produce an immediate energy saving, as well as resolve a number of the issues I mentioned with regard to lifts (as people won’t need to get off on these upper floors as often). Harvesting rainwater and storing it in tanks higher up would also reduce the energy consuming with regard to water pumping (both for irrigation and the needs of occupants). Although it would mean the support columns would need to be a bit thicker to account for all that extra weight (making the building a bit more expensive to build).
Isaac mentions putting a fusion reactor in the basement of arcologies. Well if you do have a cooling problem the worst thing you could do is put a reactor in the basement (for every unit of electricity that reactor generates, its going to pump out at least 2 units of heat!). Of course there’s nothing to stop you building one nearby and then shunting the energy it produces back to the building or neighbouring buildings clustered around it. And while we don’t have fusion power, we do have biomass CHP and fuel cells which can essentially do the same job.
Any sort of thermal power plant can also help heat the building in winter and using the absorption chiller effect you can use waste heat from your power plant to provide cooling in summer. The same applies to solar thermal collectors mounted on the roof.
You will notice how many of the heating and cooling options I’ve mentioned can do both heating or cooling. This is important because in reality we often face both problems, the need to both cool and heat a building at different times of the day or year. Even in Dubai you’ll need to heat buildings on occasions (it gets pretty cold in the desert at night you know!).
The rookie mistake of many architects is to emphasise one of these two at the expense of the other. E.g. they’re designing an office building, they know that cooling tends to be a big problem with office buildings, so they design the building to leak heat away like a sieve. Only trouble is, on Monday mornings in the winter (after the building has been left unoccupied over the weekend), or around Christmas time (when the weather’s cold and occupancy will be lower) its freezing inside and the female staff are going around with massive coats on mumbling something about “winter is coming”.
In another example the double skinned facade concept is only as good as its shading device. Install one without a proper shading device (and I’ve seen plenty of examples of this) and you might actually increase the buildings carbon footprint, because it will be at risk of overheating in summer or on sunny winter days.
So all in all, there are ways we can heat or cool down any building, be it a single story house or a 1km tall arcology, but it does require some careful analysis from the design team. And generally it means considering options that can perform both heating and cooling.
So how much energy would the occupants of our arcology use? Well the current best practice in the EU is 115 kWh/yr/m2 for residential property, 80kWh/yr/m2 for a passivhaus, 125 kWh/yr/m2 for commercial property. These figures include the energy load for heating and cooling, assuming best practice (as outlined above). Hydroponics energy use is a bit harder to estimate, I’ve seen a range of figures going from 12-100 kWh/yr/m2, so I’m going to pick a median value of about 50 kWh/yr/m2 and 20 kWh/yr/m2 for our gardens and green spaces (we’ll need lighting during the night and water pumping). I’m going to slap a further 250 kWh/yr on each occupant to cover things like lifts, shared utilities and parasitic loads. Do the maths and this suggests each occupant of our arcologies would use around 17,500 kWh/yr, against a UK average of 37,750 kWh/yr, so that’s a reduction of 54%.
That said, keep in mind the arcology figure, while it includes some of the transportation, services and food production energy consumption, it doesn’t include all of that allocation. On the other hand, we’ve probably overestimated the floor area and essentially assumed a higher standard of living on the arcology side. Its also going to be a lot easier to incorporate public transport into the arcology model than the way we current plan out cities (the larger ones will have a subway station in the basement, the smaller ones will be clustered around a transportation hub). Making it easier for people to live car free, which significantly reduces energy consumption. We’ve also ignored the benefits of economies of scale that the larger arcologies would benefit from. So my guess is these weighting all these factors, the residents of an arcology should have a lower rate of energy consumption, but by how much lower is the question.
But could an arcology completely generate all its own power? Well if we cover about 50% of the south facing surface area of each of our arcologies with PV panels or solar thermal collectors (for domestic hot water), installed a ground source heat pump, put some wind turbines on the upper parts of the taller ones we could meet between 25% (for the Sky City) and 60% (for the eco-block) of the resident’s total energy consumption.
I would note that I’m not saying that making an arcology completely self sustaining from an energy point of view is impossible (because there are buildings that are capable of doing that right now, earthships for example). It depends on the consumption rates and also to what extend are we willing to compromise the design of the building or increase the construction costs to allow a higher yield of renewable energy. This is often the dilemma faced with BIR’s (building integrated renewables). There’s also the option of a CHP plant (running on hydrogen or biomass), either within the building or nearby (likely feeding power and heat to a number of nearby arcologies), which would easily bring the power levels up to 100%.
And given that our buildings only occupy between 1.6% to 25% of the land we’ve assigned to them, there’s no reason why some of this land couldn’t have solar panels or wind turbines mounted on it. And yes a few quick sums shows that all three easily exceed 100% if we do that.
Although that said, in the same way its always going to be more economic to grow crops in a field outside of urban areas, its always going to be more economic to put a solar panel in a desert or stick a large multi-megawatt wind turbine on a hill in Scotland than incorporate it into a building. Even so generating some significant proportion of a building’s energy use via renewables, in a building where the occupants already consume a lot less energy, is definitely going in the right direction.
Its perhaps worth briefly mentioning fire safety. One issue with draping plants over the side of the building (as some arcology designers like to do), is that this is a potential route for fire to spread. Now, so long as precautions are taken to contain the fire, i.e. there is no way for the fire to get inside the building, or we put the plants inside a glazed facade (but with open windows that can be closed off automatically in the event of a fire) with a sprinkler system (we’ll need to be able to water the plants anyway!), then there’s no reason why this should be a show stopper. Similarly the double skinned facade I mentioned will need fire dampers to seal it off and a set of fire breaks every couple of floors on very tall buildings.
This is all important, because as I’ve discussed before, we’d like to use as much low-embodied energy materials (and easily recycled material) as possible, such as wood for example. Fire isn’t a show stopper for this, so long as adequate fire protection measures are in place to limit or slow the spread of any fire (e.g. fireproof cladding around any flammable material, sprinklers, fire doors, adequate evacuation routes, etc.), giving residence’s time to get out and fire fighters to get in.
The upside down skyscraper
Another idea is the concept of inverting our arcology and building it downwards rather than up. Would this be a good idea? Well its not going to be easy. As I discussed before (with regard to underground nuclear reactors), building underground is expensive and time consuming. Often the phase of any construction project that you try and minimise is the phase involving deep excavation and building the foundations, as this tends to be more prone to delays and unexpected cost overruns.
We also need to consider the issue of water intrusion. Dig a pit in your garden, go in for lunch and you’ll probably come out to find the pit has flooded. So the walls of our upside down skyscraper will have to be fully water tight to stop the building flooding (which isn’t an easy thing to do with concrete, hence why flooding in basements isn’t that uncommon). And the deeper we go, the worse the problem gets because of the rise in ground pressure and thus the head of water trying to push into our building increases.
There’s also the matter of heating, cooling and ventilation. The soil in the UK is generally (as noted earlier) around about 10-12’C year round. Given that soil has a much higher rate of thermal conductivity compared to air, this means we’re going to have a major heating problem year round. Now in a warmer climate this lower ground temperature would have advantages (although note the ground temperature in these countries is usually a bit higher although it will generally be lower than the surface air temperature) as it could help keep the building cool.
But we’re still going to have to provide hot water to residence and ventilation. And given that we now need to pump all of that air and water up and down from the surface (in the other arcologies we can get by with a service area every couple of floors or use natural convection as described). So we’re probably still going to end up with reasonably high energy consumption.
All in all, my guess is that such a structure will be more expensive to build than existing skyscrapers and probably more expensive to run.
Urban planning in reverse
So as we’ve seen, arcologies are significantly more land area efficient. Even the low rise option (the eco-block), where the building itself only occupies 25% of the actual land area assigned to it, would still have a higher housing density than most of the UK’s existing cities, 12,500 people per km2 against London’s current population density of 5,500 people/km2. With shops and public services essentially on site or nearby, we can help reduce (or eliminate) the dependence on cars.
And as noted its not too dissimilar to a number of current or proposed housing developments. Arcologies are more energy efficient, more ecologically friendly and potentially self powering (up to a point!). And while we probably can’t produce all of our food for the resident’s on site (but then again, my point isn’t so much could we? but more should we?) we can certainly significantly reduce the resident’s food miles. So why aren’t we building arcologies?Well quite simply put, only 50% of the floor area of our arcology can be sold on by a developer, while if he eliminates those green spaces and growing areas, this rises to 80% (the balance being taken up by services). There is little economic incentive to build them.
And even this idea of mixing commercial property, public services and residential areas in the same building can be difficult to justify. If you put a building up in the central business district of most cities its going to be more profitable to fill it with commercial property (with maybe a few penthouses on the upper floors). Outside the CBD, the value of commercial property falls and its more profitable to fill it with residential units. Also there’s the small matter of zoning laws. So there is a lack of joined up thinking here.
Building regulations can also be an issue. In most countries the building regulations for an office building or commercial property are often different from those for a residential block or factory. In any sort of mixed development we generally have to apply the most stringent standards across the entire building. This is particularly true when it comes to fire safety. So that’s going to push up the costs. So there would be a need for incentives from government to encourage these sorts of developments. And if anything, the problem in recent years has been that government’s have done the complete opposite.
Governments, both sides of the Atlantic have for too long encouraged strip mall development. Not only is this bad as it creates urban sprawl, but it also decreases the efficiency of public transport and thus increases car ownership, which pushes up carbon emissions. Keep in mind the figure for population density given for London above represents the average for central London. The average population density across the whole of the London metropolitan area is just 1,500 persons/km2. And most UK cities are a lot less densely populated than London.
By contrast Paris or Athens, historic cities with relatively few skyscrapers (but equally less strip mall development) have a population density of 21,000 person/km2 and 19,135 persons/km2 respectively. Indeed, its interesting to note how the planners of cities like Paris, or Edinburgh’s New Town, were closer to the arcology concept than our modern urban planners, given that they incorporated green spaces, commercial property and residential space all within the same development. And they were doing this centuries ago. Indeed, so close is Edinburgh’s Georgian New Town development to the eco-block concept above, I’m wondering if I should just rename it “New Town 2.0”.
So the major obstacle to arcologies, or eco buildings in general, is the fact that we have gone backwards in terms of urban planning and development over the last few centuries. If there’s anything conclusion we can draw from this analysis, its the need to reverse those policies.