Friday, 6 June 2014

Positive energy

A renovated office block in Norway has laid claim to being the world’s first energy positive building.  PowerHouse Kjørbo, at Bærum outside Oslo, was designed by Snøhetta, with consultants Asplan Viak, property management firm Entra, construction company Skanska, aluminium companies Hydro and Sapa and the environmental organization ZERO.

During the course of its design life of 60 years, Powerhouse Kjørbo will generate enough energy to cover the total amount of energy used to produce the building materials, construction, operation and disposal. The building’s energy system is based on geothermal for heating and cooling, as well as the largest rooftop solar photovoltaic system in Norway.

In taking this cradle to cradle approach, the designers are going well beyond the claims of the Bullitt Center in Seattle with its design to the Living Building Challenge. The Living Building Challenge's Net Zero Energy building certification, for all its apparently lofty ideals, doesn't take the energy used to produce the building into account.  In fact, the Norwegian building seeks to introduce the term PowerHouse as a subset of the European voluntary PassiveHaus approach.

The definition of a Powerhouse is a building that shall produce at least the same amount of energy from on-site renewables as the energy used during construction, manufacture of materials, renovation, demolition and operation, but excluding energy used during manufacture of equipment such as PCs, coffee machines etc. Importantly, the exported energy shall on average not have less quality than the imported energy. This implies that produced and exported electricity can offset corresponding amounts of imported energy for both electricity and thermal purposes.  Exported thermal energy cannot offset imported electricity. The building must also as a minimum fulfil all the requirements of the Passive House standard according to NS 3701.

Bærum is located at approximately 60 degrees north latitude, and with an annual average outdoor temperature of about 5.9°C and an annual mean solar irradiation on a horizontal plane of about 110 W/m² (955 kWh/m²a).  For anyone who knows what they’re looking at, these figures for potential energy harvesting look dauntingly low, while the climate is obviously cold enough to require artificial heating for human comfort almost all year round. 
So why is it that it is possible to at least contemplate an energy positive building in frigid Norway, rather than balmy climates with spectacular solar potential, like Australia?  As counter-intuitive as it may first seem, it’s completely logical.  For operational energy, you just have to remember your second law of thermodynamics.  All high-grade energy used in the building ends up as low-grade heat.  Lighting, office machines, even lifts are all contributing to the artificial heating.  If you can achieve a thermally efficient building envelope, you can prevent most of that internally produced heat from escaping.  Basically, your dedicated heating bill can be reduced to near zero.  
In contrast, in overheated climates the external heat load and the internal heat production are additive, and all have to be overcome by cooling.  A much more difficult proposition, requiring much more sophisticated passive building approaches and esoteric technologies.  

If you can lay down enough area of even modestly efficient photovoltaics, you can equip a low rise building in a cold climate to be a net energy exporter.  What then remains to solve is limiting the embodied energy of the building materials.  At this point it should become blindingly obvious why it was always going to be a renovation or adaptive reuse to claim the title – as I am fond of repeating, the most sustainable building is the one that’s already built.

So here is the irony. The best potential for ‘healing buildings’– the ones that produce more than they consume, is in 'climate rejecting design' in some of our least comfortable climates. And it isn’t the sophisticated new build, but the thoughtful renovation. It isn’t the aggressive high-tech high-rise, but the land consuming low rise, simply because it has to have enough site area to harvest the required total amount of solar energy.

However, I can’t help pointing out the one little niggling problem with this rosy picture.  It still relies on the concept of swapping excess energy produced on site, for imported energy, every single day of the building’s life.  That is the energy required to run the building when the sun is not shining, at night, and on many days during the northern winter.  Until we solve the problem of truly large batteries, far beyond our tentative attempts at small scale load leveling, such imported energy from the grid is still likely to be sourced from non-renewable fossil fuels, unless we are willing to adopt the nuclear option.  Although it occurs to me that in Norway, with its small population and abundant snow melt, there may be some finessing the figures, involving hydro electricity.

But I don't want to be a spoilsport.  PowerHouse Kjørbo is a worthy advance in showing that architecture can be part of the solution to global sustainability, rather than part of the problem.

Unusually, it isn't hard to find at least some of the technical information on this project.  So go beyond the usual Treehugger and ArchiSource sites that you can google yourself, download and read at least the presentation made at the PassiveHus Norden conference.Or even better, the comprehensive project description under the IEA SHC Task 47 Renovation of Non-Residential Buildings towards Sustainable Standards.

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