Living in a Vacuum

22/12/22 22:28

Sometimes it feels like trying to resolve competing demands, like thermal performance against the limited depth available in a wall or deck build-up, is like trying to post an octopus through a Venetian blind.

The push to improve U-values has run all through my career. We scoffed at the buff-covered copies of the Building Regs which the greybeards had, prescribing walls which didn’t even achieve 0.45 W/m2K. The old-timers each had their own dog-eared copy, but when the new Technical Standards came in later in the 1990’s, the office only bought one copy and it came in a ring binder: all the better to swap pages out each time the thermal performance of walls and roofs became more stringent.

As values rose from 0.45 to 0.3 then 0.2 W/m2K, how best to achieve them became a concern, because material performance didn’t improve so insulation thicknesses just kept increasing. I vaguely remember 100mm kit walls, which soon became 140mm studwork, then 200 or 250mm JJI joists were used as studs to accommodate increasing depths of glasswool, cellulose or rock fibre.

As a result, we've always been up against it with wall linings and timber kit build-ups and rather like computers during the 1990's, as soon as processor speed and RAM increased according to the so-called Moore’s Law, the gain was more than absorbed by a more sophisticated programme carrying out ever more intensive tasks.

Similarly, despite pressure to move from glasswool and stonewool to polystyrene (EPS or XPS) polyurethane (PUR), then poly-isocyanurate (PIR) foams, which offer progressively better R-values: as soon as thinner insulation was developed, the minimum U-value improved too, so you needed more of it. The net gain in footprint won back was nil, because materials technology and the Technical Standards had fought themselves to a standstill.

However, what feels like one of the few genuine pieces of materials tech progress in recent decades has become a commercial proposition: Vacuum insulation, or more accurately evacuated insulation. As you may remember from the teacher’s explanation of the Dewar Flask in Higher Physics, a vacuum, or the absence of air, has no thermal conductivity and that makes it the perfect insulant. Nothing can pass through a vacuum apart from radiation, so no heat is lost to either conduction or convection.

Vacuum insulated panels (VIP’s) have been in use for a few decades in refrigeration plants, cold stores, cryogenic freezers and the like, manufactured by companies like Morgan Advanced Materials (the UK company which was previously known as Morgan Crucible). They’ve only made their way into the building industry in the past decade or so as firms like Kingspan and the German firm Va-Q-tec began production. Around 2005, VIP’s were introduced into the construction industry in Germany, Switzerland and Scandinavia, to begin with as deck insulation on balconies and other locations where deep build-ups cause detailing headaches.

VIP’s are made from fumed silica sand, which forms a porous matrix from which more than 99.999% of the air is evacuated. The silica is encapsulated in a vacuum-tight envelope made from aluminium foil, and the key thing is to make sure that isn’t penetrated by a nail or screw. In 2022 terms, silica is inert so it won’t harm the environment, and it’s not flammable so it won’t go up in flames, like foam insulation frequently seems to do.

In thermal performance terms, vacuum panels have a lambda value four or five times better than the best foam insulations, and one analysis demonstrated that a VIP board 20mm thick achieves the same thermal performance as mineral wool or PUR insulation board with a thickness of 185mm.

At the same time as VIP boards emerged, a new type of double glazing was developed.
Similarly to the ever-thickening walls conundrum, upgrading traditional sash and case windows to double glazing often means using bulky glazing units which ruin the fine lines of the transoms and astragals.

Vacuum glazing is similar to a double glazed unit in construction, except that it doesn’t have a gas in the cavity, it has a vacuum. That vacuum is far more effective than filling a 20mm cavity with a noble gas like Argon or Krypton, and therefore only requires a 0.2mm cavity - hence the unit’s thickness is greatly reduced. Some of the first vacuum glazed units to come to market are the AGC Fineo and the Pilkington Spacia; for example, a Super Spacia unit achieves 0.65 W/m2K, against standard 4+20+4mm double glazing which achieves around 1.2 W/m2K.

Thanks to vacuum technology, finally we have the potential to return to the slim glazing profiles and slender walls of the 1960's… and even more importantly, to use far less raw material in order to save much more energy, and in doing so to reduce the gross floor area of the building. That’s a triple win, and as a result you may not need to post your octopus through a Venetian blind after all.

Happy Christmas when it arrives. :-)

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