13 November 2005

Embedded Energy Metric

Using thermodynamic laws it is usually fairly straightforward to analyze the efficiency of various systems of turning energy (more properly termed exergy) into work or heat. E.g. we can compare the ability of a heat pump next to electric resistance heaters to transform electricity into space heat. However it's often necessary to slide-slip away from the issue of the initial energy investment required to produce a baseboard heater compared to a heat pump because the data are proprietary or simply not gathered.

This energy investment in a product is known as the embedded energy. It is equivalent of capital investment in the money dimension. For example, in order to compare wind turbines to a combined-cycle thermal-electricity plant we should compare not only the CO2 offset by using wind rather than natural gas fuel to produce electricity but also the energy invested in the construction of the infrastructure as well. The steel and concrete in a wind turbine has an associated energy and CO2 production embedded into it during its manufacture. This embedded energy must be amortized over the lifespan of the turbine in order to properly determine the CO2 emissions that are offset.

The trick is how to determine the embedded energy in a product with adequate accuracy? To a certain extent this issue has stalled my investigation into the use of anerobic bioreactors to produce biogas from crop waste along with difficulties finding data on reaction rates as a function of temperature. Well, this being the blogosphere, an order of magnitude calculation on the back of an envelope should suffice. My thought is that if I could establish a metric for some common materials then I could simply estimate the embedded energy based on the mass of material in a product. The embedded energy problem is potentially simplified but it still remains challenging. Just try to find the mass of an air conditioner on a vendor's webpage, for example.

As a rough measure every material in the energy world can be subdivided into the following categories:
  • Steel
  • Aluminium
  • Copper
  • Plastic (polyethylene)
  • Silicon
  • Concrete
While these are certainly broad categories I am only searching for an order of magnitude metric. It's worth noting that some of these items, namely aluminium, steel and concrete have an associated CO2 production associated with them through reaction with carbon in addition to the basic energy inputs.

Rather than try to determine the energy embedded in a particular alloy I am hoping that StatsCan will have industry-wide figures for both production and energy consumption which will result in a more inclusive result. Hopefully I will be able to arrive at a reasonable set of metrics by the end of the week. Of course it would be desirable to actually check the results. Most likely there will be a need to introduce a fudge factor to account for the transformation of sheet steel into an automobile.


Anonymous said...

did you ever work out the embedded energy for those materials?

Robert McLeod said...

No, it ended up looking more like a master's level project.

Anonymous said...

As far as the amount of embedded energy hidden in the materials that interest you, I should be glad if you could a glance at the adress :http://www.greenhouse.gov.au/yourhome/technical/fs31.htm. Tell me what you honestly think about it.

Anonymous said...

You could, for instance, find the amount of embedded energy in materials that interest you at the following adress (by the way, sorry if the last message was beheaded):

Have a good day.

Anonymous said...

Sorry, Robert. It seems to occur each time I'm sticking an adress.So shall I, this time, cut it into pieces :


I hope you'll find interesting thinks; I'm myself involved in the measure and the reduction of embodied energy in the field of building and civil engineering.