How I used Space Shuttle tech to insulate the living room
Radical DIY with space gel
Now that the Space Shuttle is being decommissioned, what are we to do with all that lovely high-performance insulation that protects it from the heat of re-entry?
Silica aerogel is an amazing material: a solid foam consisting of over 95 per cent air, about the least material and the most 'hole' per unit volume and thus the lowest bulk density of any known solid. It is made from the most abundant elements on Earth, is non-toxic and doesn't burn. What's not to like?
Aerogel makes for fantastic insulation, providing about twice the resistance to heat per unit thickness compared to the next-best materials, and is used in everything from super-energy-efficient skylights and industrial refineries to keeping warm the electronics at the heat of the Mars Exploration rovers. (OK, the Space Shuttle LI-900 insulation tile core is not quite aerogel, but is a very close cousin made of silica glass fibres and 94 per cent air by volume and can withstand temperatures of well over 1000C.)
So how does aerogel manage to outdo every other insulation material by such a margin, and do goats and the environment need to be sacrificed to make it?
With off-the-shelf building insulation such as rigid foam and glass wool loft insulation, the performance is dictated not so much by what the material itself is made of but rather by the (small) holes in it neither available to conduct heat nor convect. Those holes are filled with air or a gas such as pentane.
Silica aerogel basically has more hole than other insulators, and thus conducts less heat through what is left, which is itself is a poor conductor.
The embodied energy of aerogel (ie used in manufacturing it) is less than most alternatives other than wool, and unlike foam, nasties such as toxic "blowing agents" aren't required so leaks/emissions can't happen, and nor can there any ensuing degradation in insulation performance over time. Aerogel insulation should be good for 50 years or more.
One downside of the material is that it costs several times that of other products, but that might well drop if aerogel were suddenly to be made fashionable by Grand Designs or its ilk. Another is that it can be hard to work with (and my builders quietly though unconvincingly vowed never to touch it again: see below).
Aerogel can also be bought in various forms and from many suppliers - Cabot amongst others offers translucent granules and 'privacy' glazing with very good thermal performance (it is also a strong absorber of infrared), diffusing light and preventing anyone seeing straight in; good for skylights and ground-floor windows.
Aerogel was first made in 1931 by Samuel Kistler, in Stockton, California. He went on to invent the silica-based Monsanto Aerogel, which was marketed until the 1960s. It was forgotten until many new scientific and industrial uses were found for it in the Eighties (see History). The blanket style now in my walls has been around for about a decade. And, no, it doesn't seem to taste of anything much.
In the home
I've been working for the last two or three years towards making my family home (and office) "zero-carbon" for electricity and gas. I caught the conservation bug in late 2007 and I was able over a couple of years to reduce electricity consumption at home by about 80 per cent, and then take us negative by putting lots of photovoltaic paneling on the roof.
I also wanted to see what we could do about gas heating.
It was not at all clear how we could insulate the walls of our timber-framed house without giving up too much space, so I concentrated on improving the living room where the family spends much of its time. The decor was a bit of a mess anyway, so we could potentially kill two birds with one stone.
My big idea was to 'dry line' the existing walls with insulation, leaving the existing structure intact (mainly to help ensure that thermal performance could not get worse, but also so that no building control is needed). The best performing material on the market in terms of insulation for a given thickness is (as you'd now expect) aerogel, for example under the Spacetherm™ brand from Proctor Group in the UK, and provides roughly twice as much long-term insulation per cm as products such as Kingspan Kooltherm K17 rigid phenolic insulation but at many times the cost to achieve the same level of insulation. Aerogel pays off where space is at a premium.
What every spacetherm enthusiast should see on Christmas Day. This is the aerogel as delivered
The same tech that keeps the Mars rovers warm should be able to keep us warm too.
As our living room is not huge at 15m^2, and I wanted to test a bleeding-edge technology to let other people know if it's worthwhile, I decided to go for 40mm of aerogel bonded (as four 1cm blankets) to plasterboard. K17 would have been about £170 for somewhat less performance at a similar thickness. With a fairly generous discount from Proctor, the aerogel came in at about £1500.
The blankets are silica-gel-derived aerogel with embedded polyester fabric to reduce brittleness. This blanket form snags drill-bits and saws and requires a bit of practice to get used to, and only an electric skilsaw seems to be really effective.
Working aerogel generates a fine desiccating dust that dries the skin and that you don't want a lungful of. The builders claimed that neither would bother them, but it did.
The Spacetherm-style blankets-on-plasterboard style also requires mechanical fixing with steel screws which will knock the edge off its effectiveness a little; due to thermal bridging.
But the relatively small thickness required to triple the insulation of our walls meant that we were able to replace two large old and ineffective radiators with one half-size double-skin modern one (and now place furniture right up to the end-walls of the room), and so we've not noticably lost any space at all from the drylining, far better than I'd thought.
We now boast exterior walls that beat the latest building regs by quite a significant margin.
By the time all the building works were done including replastering and painting and so on, the aerogel was nowhere near a majority of the cost.
I'm also intending to upgrade the windows from double- to triple-glazed, and in the interim we've put up multiply-lined curtains, as well as adding more insulation above the ceiling plasterboard. Putting back the internal door from the corridor will have done as much as the aerogel to keep cold draughts out.
As any decent engineer will tell you, the building elements cannot be successfully tackled in isolation if the desired overall effect is warm toes on cold nights.
Hot Hot Hot
To date the wonder aerogel seems to be working for us: the room's exterior walls are barely cooler than the interior walls and are far warmer than the double-glazed windows when it's cold outside. As the temperature drops we should get a clearer idea, and I'll hire a thermal camera to check.
By my calculations, if all four of us are in the living room then it should stay at about 18C even if freezing outside just from our body heat, ie given London's average temperatures we should in principle stay warm year round even if the central heating failed.
For a full blow-by-blow account, with bonus graphical aerogel porn, see my write up here.®
Damon Hart-Davis is an IT consultant who has spent most of the past 15 years in the City, with a long-standing interest in small and low-power devices and various flavours of UNIX. He founded one of the first British ISPs, virtual credit card company, and once edited a supercomputer magazine.