Wednesday, 2 April 2014

When Zero isn't Zero

I usually hesitate to write about something that is almost entirely technical, but this one has been bothering me too long to ignore.

There is apparently declining public interest in the issues of climate change and sustainability.  Despite this, the reality is that we are working with considerable momentum on both technologies and regulations for energy efficiency, renewable energy sources and various other initiatives to reduce the impact of future development.  But the progress towards understanding what we are doing, even amongst professionals, is hampered by misinformation, whether that misinformation is motivated by greenwash, or simply sloppy thinking by people who should know better.  The concept of 'Net Zero Energy Buildings' is a case in point. 
You would think that the definitions of net zero energy buildings would be easy; that a NZEB would be one that produces at least as much energy as it uses.  But it is not that easy, primarily because of the problem of 'system boundaries'.  So we have competing definitions related to whether the energy for running the building has to be offset on site, or allowed to be imported, etc.  It gets ever more complicated as you try to factor in energy generation efficiency, or whether the energy used to produce the building also has to be offset.
This sort of complexity is bad enough to derail useful communication with decision makers, design professionals or the general public.  But what bothers me most is a more fundamental underlying sleigh of hand.  Take the deceptively straight forward attempt to clarify this issue, by Allison Bailes on the Energy Vanguard Blog in her article 4 Ways to Define Net Zero Energy Use in BuildingsTo make my point, I quote her first 'way' in its entirety:
1. Net Zero Site Energy
In the first definition, an NZE building produces as much energy on-site as it uses on-site over the course of a year. If the building uses 10,000 kilowatt-hours, it's got to produce 10,000 kWh or more, ideally on-site within the footprint of the building.
This definition doesn't account for the type of energy used, though. Where this becomes important is if the building uses natural gas, propane, or some other fuel besides electricity.
Let's say your home has a natural gas furnace, and it's 95% efficient. For every 95 kWh of heat that your home needs, your furnace is burning 100 kWh of natural gas. (Pardon the units, but since the energy produced is in kWh, I'm going to stick with that.) That means you've got to provide 100 kWh of site-generated electricity.
If, on the other hand, you had a heat pump, it would need maybe 40 kWh of electricity to move 95 kWh of heat into your home. Rather than having to produce 100 kWh of electricity, then, you'd only need to produce 40.
As you can see from this example, this definition of net zero favors on-site electricity use. It's also the simplest of the four definitions.
I wonder if you can see the problem.  It isn't immediately obvious, because the concluding paragraph seems to be so clearly suggesting the preferred solution: use a heat pump, and you have to generate less electricity, and you don't have to bring non-renewable fuel on site.  Which is where the initiative should aim to get you.

Unfortunately, the preceding paragraph makes clear that the 'Net Zero Site Energy' definition does allow non-renewable, off-site derived fuel to be used, albeit with a more onerous on-site offset.  The author's example glosses over the fact that heat pumps become less efficient exactly when the heating need is greatest.  Unless you commit to a ground source heat pump, the chances are that in heating dominated climates, you will either need to generate as many KWh of electrical energy as you use for electric heating, or favour gas fired space heating.

Of course, I am not the first person to notice these problems.  The concept of 'Zero carbon' is introduced to try and overcome the issue with different forms of energy. By the time the issues are teased apart sufficiently, and some self-interested people translate everything into  dollar costs rather than energy units or tons of CO2, I count at least eleven variations on the Net Zero idea.  Almost all of which misses the real point.  The problem word is the 'net' not the zero.  That accounting will always allow 'offsets' and 'conversion' calculations, and will always beg the question of the system boundaries.

The bottom line is that if you are burning a non-renewable fuel, no gymnastics with the conversion numbers will ever reinstate that loss of a resource.  It will have been used up. The whole 'net zero' construct is an illusionist's trick.

See the full article at


Anonymous said...

With reference to Allison Baile’s article, I feel that the definition of a zero energy building is somewhat flawed in its own as it neglects to take into account a fundamental idea which includes the real ‘cost’ in production of such goods.

In addressing Allison’s first and second point about heat pumps and energy source: while there is a point made that heat pumps will consume less energy compared to a gas furnace, there was no mention by the author in regards to the embodied energy of goods and at what cost this alternative comes at in running it. An article at cautions this idea by noting that ‘the energy and carbon overheads associated with this energy source should be taken into account when accessing overall environmental benefits of such schemes’. Expanding from this idea, a post by has indicated that a natural gas furnace would still a better choice because it does not use secondary fuel (whereas heat pumps do as it uses electricity) and is also more cost effective ( In which cases, a heat pump would be consuming electricity which would have been produced from another source such as coal, uranium, natural gas or oil.

Ultimately, it would probably boil down to the question of whether this unit is going to be in operation long enough to reap the benefits this would have to outlay the cost to the environment but as you mentioned in this post and also a previous post titled “The Greenest Building in the World (posted 20/02/12)” the problem lies in the way how ‘net zero energy’ is defined..but moreso, how it could possibly be defined as a zero energy building when it uses non-renewable sources.

My search for an alternative solution brought me to a fairly recent blog post titled “What’s cool in building design? Think net positive, add water” (dated 12/02/14). This particular post spoke about how regenerative design could be the new solution to the topic of net zero energy by taking a ‘cradle to cradle’ approach by focusing on the synergy found between water and energy. While the statistics given only apply to the United States, The numbers itself look rather compelling and indicate that “20 percent of electricity and 30 percent of natural gas is used to move water and waste around nationwide.” and “As a result, we emit 45 million tons of greenhouse gas emissions a year from moving water and waste”.





Eva B said...

The concept that is revealed in this article reveals an aspect of the general situation going on in the world, but especially Australia, today. It is not actually about saving energy or the environment and coming up with solutions to create sustainable energy, but about finding the own benefit and making it look like one is taking care of the environment.
Australia, being the country with a huge hole in the ozone layer, it should more than any other country be the one who takes care of their future, their environment and their land. It is necessary for Australia to start considering the development of sustainable energy, sustainable housing and a sustainable industry in order to secure living for future generations in this country.
25% of the world wide emission of greenhouse gases is caused by electricity and heat. This is a big number, which could be minimized by coming up with sustainable housing, actual Zero- Houses, that save on heating as well as on electricity, even though that might mean to invest money in the first place.
Coming from Overseas and having seen German energy politics, I know that it is possible to subsidize renewable energy sources. The awareness found in Germany for a sustainable lifestyle is not on a level where it should be, but it is moving towards it. 20% of the need for energy in Germany is met by renewable energy sources, in comparison to Australia having 10% met by renewable energy. Even though Germany is not known for having the most sun hours, it still invests into the development of that technic, whereas in Australia there are way more sun hours and the sun being much stronger, but the investigation in that area does not seem to be of high interest. Houses being built in Germany will have proper insulation, a proper heating system and often even private persons will invest into photovoltaic in their buildings. Personally, I have not seen that in Australia. The heating systems, (I understand that it is not as necessary as in Germany) are poorly developed and the ways to heat a building takes up a tremendous amount of energy, there is no insulation and the idea of using solar energy to meet the needs has not been that strongly developed as it could have been having a look at the great opportunities Australia has been given concerning the climate and the sun.
Having said that, I think it is unenviable for Australia to come up with a solution to build buildings that are actually Zero- Houses that consider their environment and the future of this planet. It should not be about trying to get the numbers to look pretty and pretend to be eco-friendly, when it actually still uses up the black coal and with that pushes up the numbers of the greenhouse gas emission.
Architecture is able to have a leading role in the change that has to happen. But it has to stop to look like change and instead be the change that it claims to be.