Cooling ponds: Nature's air conditioning system - Grand Designs Magazine
cooling ponds: nature's air conditioning

How a pond can keep your home cool

Kevin McCloud on making the most of nature's air conditioning systems

By Kevin McCloud |

There was a medieval time when meteorologists blamed meteors for the changes in the weather. Comets were responsible for the crops failing and the populous starving. Now it is all our fault and climatologists point to the climate as the driver of big change in our weather systems. Our winters are becoming milder and wetter, and our summers warmer.

Weather is of not necessarily an indication of longer-term climate change. Weather patterns fluctuate in any case. But the past few years have brought a flavour of what is to come. Heat waves, dry landscape and temperatures approaching 40°C. It is as though what they said would come true is becoming a reality, but much quicker than anyone thought.

house for theo oskar - accessible home - grand designs

Solar shading over south-facing windows, as shown here in the House for Theo and Oskar, can help keep homes cool. Photo: Andy Matthews

Climate change is happening

Climate change is happening, we’ve all come to understand that. But in our lifetime? We all thought we had a few more decades to turn our boilers up in winter and ramp up the air con in summer.

And air conditioning is a big contributor to greenhouse gases. Although modern machines use refrigerants which are much less damaging to the atmosphere, older units – the vast majority on the planet – do not. They are slowly leaking their gases, which are hundreds of times more contributive to global warming than CO2.

Meanwhile developing countries are turning to air con as a technology for their burgeoning middle classes. According to the International Energy Agency, cooling buildings accounts for 16% of all electrical use in buildings and the market for air con globally has risen 4% every year since 2000. To give you a sense of scale, the number of people on the planet equals seven billion and the number of air conditioning units is two billion.

So will one more make a difference? If you have air con installed this summer will it alter the course of our climate’s destruction? The answer is, of course, yes, because you are a contributor to the bigger number – as we all are. It’ll also dent your bank account. On a positive note, there are some good alternatives.

Identical twins Nik and Jon built twin houses in Sheffield

Trees and a cooling pond help keep Nik and Jon Daughtry‘s homes temperate. Photo: Fiona Walker-Arnott

Air-conditioning alternatives

But looking at the offering from property developers you wouldn’t think so. The average new home has no solar shading, almost no thermal mass, poor cross-ventilation, no stack ventilation and no evaporative cooling. And yet all these technologies can be yours.

You don’t need to be building a new home either. You can exploit the magic of these scientific principles in your own house or flat. Solar shading? Fit external shutters or a deck and canvas awning or a posh brise-soleil to form a canopy over your windows. Or just plant a deciduous tree to shade your home and cool it using the tree’s own mantle of cool humidified air. Trees are nature’s air conditioners.

Thermal mass is very hard to retrofit into a home but it’s not the be-all and end-all. Ventilation is more important. You could fit a light-well over your stairs with an opening skylight above for stack ventilation. It would mean remodelling the roof a little but it would give you a ‘chimney’ through which warm air in the building can rise and then ‘purge’ itself out. The delight of this principle is that just as warm air rises up and out, so it will draw in cool air from open windows and doors at ground level.

This brings me to windows, which should be securely left – but strategically — open in hot weather. If you can work out where a breeze is coming from on any day you can maximise its cooling effect by opening windows on the side it’s coming from and on the opposite side of the house too, to provide cross-ventilation.

There was a medieval time when meteorologists blamed meteors for the changes in the weather. Comets were responsible for the crops failing and the populous starving. Now it is all our fault and climatologists point to the climate as the driver of big change in our weather systems. Our winters are becoming milder and wetter, and our summers warmer.

Weather is of not necessarily an indication of longer-term climate change. Weather patterns fluctuate in any case. But the past few years have brought a flavour of what is to come. Heat waves, dry landscape and temperatures approaching 40°C. It is as though what they said would come true is becoming a reality, but much quicker than anyone thought.

house for theo oskar - accessible home - grand designs

Solar shading over south-facing windows, as shown here in the House for Theo and Oskar, can help keep homes cool. Photo: Andy Matthews

Climate change is happening

Climate change is happening, we’ve all come to understand that. But in our lifetime? We all thought we had a few more decades to turn our boilers up in winter and ramp up the air con in summer.

And air conditioning is a big contributor to greenhouse gases. Although modern machines use refrigerants which are much less damaging to the atmosphere, older units – the vast majority on the planet – do not. They are slowly leaking their gases, which are hundreds of times more contributive to global warming than CO2.

Meanwhile developing countries are turning to air con as a technology for their burgeoning middle classes. According to the International Energy Agency, cooling buildings accounts for 16% of all electrical use in buildings and the market for air con globally has risen 4% every year since 2000. To give you a sense of scale, the number of people on the planet equals seven billion and the number of air conditioning units is two billion.

So will one more make a difference? If you have air con installed this summer will it alter the course of our climate’s destruction? The answer is, of course, yes, because you are a contributor to the bigger number – as we all are. It’ll also dent your bank account. On a positive note, there are some good alternatives.

Identical twins Nik and Jon built twin houses in Sheffield

Trees and a cooling pond help keep Nik and Jon Daughtry‘s homes temperate. Photo: Fiona Walker-Arnott

Air-conditioning alternatives

But looking at the offering from property developers you wouldn’t think so. The average new home has no solar shading, almost no thermal mass, poor cross-ventilation, no stack ventilation and no evaporative cooling. And yet all these technologies can be yours.

You don’t need to be building a new home either. You can exploit the magic of these scientific principles in your own house or flat. Solar shading? Fit external shutters or a deck and canvas awning or a posh brise-soleil to form a canopy over your windows. Or just plant a deciduous tree to shade your home and cool it using the tree’s own mantle of cool humidified air. Trees are nature’s air conditioners.

Thermal mass is very hard to retrofit into a home but it’s not the be-all and end-all. Ventilation is more important. You could fit a light-well over your stairs with an opening skylight above for stack ventilation. It would mean remodelling the roof a little but it would give you a ‘chimney’ through which warm air in the building can rise and then ‘purge’ itself out. The delight of this principle is that just as warm air rises up and out, so it will draw in cool air from open windows and doors at ground level.

This brings me to windows, which should be securely left – but strategically — open in hot weather. If you can work out where a breeze is coming from on any day you can maximise its cooling effect by opening windows on the side it’s coming from and on the opposite side of the house too, to provide cross-ventilation.

Image: Two Cocks Farm, built by grand designers Phil Palmer and Michael Butcher, has a cooling pond. Photo: Tim Brotherton

Cooling ponds

The masterstroke of a smart building systems manager – that’s you – is a technology which transcends all of the above. It combines the best of stack and cross ventilation while mimicking the evaporative cooling processes of a tree. It operates at different levels of complexity and involves no building work. At least not to the house. It is a pond.

My first ecological cooling pond belonged to the progressive social architect Jon Broome, who I visited more than 20 years ago. The second was constructed by the great architect Peter Aldington and his wife Margaret some 50 years ago when they built their home near Aylesbury, Buckinghamshire. We filmed it last year for the second series of The Street.

Then, in the last series of Grand Designs, there was the giant swimming pond built alongside the ravishing home of Dan and Nina, which you can take a closer look at in next month’s magazine. All three promote biodiversity and offer beauty, dancing reflections and delight. And all three cool their houses.

grand designs pond house in chichester with natural swimming pool

Dan and Nina’s natural swimming pond doubles up as a cooling pond. Photo: James French

They do so in an obvious way by cooling the air that passes over them – they are all right against the buildings. The air they cool is sucked into the building as part of either cross or stack ventilation.

But they also exploit another phenomenon known as phase change, the same physical process that makes an air-conditioning unit work, or helps a tree to cool the air around it. Liquid moisture is wicked away by warm air, which it readily absorbs as water vapour. To change from dense liquid to light gas, the water needs to draw energy, as heat, from somewhere to help it over the hump of that change. Humans have their own phase-changing technology called sweating.

With a pond, however, there is no need to sweat. The cool air moistens your skin and a second opportunity for phase-change evaporation happens. Bingo. You’re even cooler. You and your pond are your own air-conditioning unit. Add a tree and you become part of a wider environmental control system – a microclimate machine able to alter the air quality, temperature and health of where you live.

That’s what I call air conditioning.

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