Humanity is consuming more and more energy every year and, since much of the world depends on fossil fuel based resources, our total carbon emissions continue to climb as well. In the effort to curb this trend, energy conservation is imperative. One area where conservation efforts can make a particularly large impact is in our nation’s buildings where 40% of our national energy expenditure is consumed. [1] This is a powerful motivation to construct buildings that are more energy efficient. Researchers from the National Research Council (NRC) are attempting to do just that with a promising new technology called the vacuum insulated panel (VIP).

It is important to digress somewhat here.  What does it mean to make a building more energy efficient? Well, we have to actively heat and cool our buildings. In other words, we continually supply energy so as to maintain a constant temperature. If we need to supply it constantly then that means we must be losing it somewhere.  The energy expended to heat or cool a structure is lost through the walls, windows, floor, roof, etc. An “energy efficient” building would lose less.

This is what insulation does. It helps to maintain the difference between the interior and exterior temperature by slowing the rate of heat transfer between them thus requiring less energy to heat and cool the structure. The best insulation possible is a vacuum. This is because heat needs some medium through which to travel and a vacuum is essentially the absence of a medium. Everyone knows that a thermos can keep liquids hot for a long time and this is the reason why. It is insulated with a vacuum (in actuality it would not be a perfect vacuum).

This is the same idea behind VIPs. They are constructed from an open nano-porous material that is strong enough to remain intact under atmospheric pressure. The air is evacuated from the panel and then the whole thing is sealed in a gas barrier to prevent any air infiltration. It is essentially a portable, rigid container that holds a vacuum. In terms of performance it blows the competitors away.

Cross-section of a VIP

Cross-section of a VIP: The core is made from a porous material. (Picture from ref.)

The ability of a material to prevent heat loss is given by its R-value per unit thickness. Familiar insulation materials like mineral fibre or cellulose are less than R-5 per inch. VIPs can achieve R-values as high as R-60 per inch. This is incredibly high and anyone in the building industry would be very skeptical of such a number. However, that’s just the power of a vacuum.

So why haven’t we seen the widespread proliferation of this wonder-material? There are several reasons. Cost is the most prohibitive factor. VIPs are currently more expensive than the alternatives. However, the researchers at the NRC claim that once economies of scale kick in the cost will come down considerably. Another major issue is  uncertainty in the long-term performance of VIPs. The research has yet to establish how this technology degrades over time. They are certainly less robust than convention materials, as a single pinhole in the gas barrier will compromise the vacuum.  Nevertheless, it is a very promising technology and perhaps not too far away from more widespread adoption.

For the NRC paper on VIPs  see:

Mukhopadhyaya P., M.K. Kumaran, F. Ping and N. Normandin. Use of vacuum insulation panel in building envelope construction: advantages and challenges. May 2011. NRC-53942.

http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc53942.pdf

-Erik Janssen

(Engineering Physics, MASc, Year 2 at McMaster University)


[1] Mukhopadhyaya et al.

Advertisements