If we see energy efficiency as a topic that has something to do about sustainability than sooner or later you are confronted with words like exergy and emergy. Energy is a word we all know and it means the ability to cause work were work is defined as any useful energy transformation. In all kinds of work, one type of energy is transformed into another where some of the energy going into a used form that no longer has potential for further work.
Not all forms of energy are equivalent. While they can all be converted to heat one cannot say that joules of one form of energy are equal to joules of another form in their ability to cause work. This concept of quality required a new concept of energy. Exergy quantifies the useful work that may be done by a certain quantity of energy. But energy has also another aspect, it has a history. Embodied energy or Emergy is defined as the available energy that was used in the work of making a product. Embodied energy is an accounting methodology which aims to find the sum total of the energy necessary for an entire product lifecycle: raw material extraction, transport, manufacture, assembly, installation, disassembly, deconstruction and/or decomposition.
In this energy transformation chain at each transformation step some energy is degraded and some is passed to the next step in the chain. The emergy of one type required to make a unit of energy of another type is called transformity. These Energy Transformation chains can be described with the help of the Energy Systems Language (ESL) of Howard Thomas Odum. See Emergystems.org. A simple example of data center energy chain presented as an ESL diagram is given below.
Emergy aims to provide an ecocentric value of industrial products and processes instead of the economic value, which is anthropocentric. Emergy analysis claims to provide a more holistic alternative to many existing methods for environmentally conscious decision-making. All though there is still discussion about the practical usefulness of emergy in an engineering environment if you want to make some effort on sustainability it is worthwhile to spend some time on it. There is a very nice EMERGY SIMULATOR available. This Java application is written by Raphael Valyi and you can find and download it on Sourceforge
So the new question can be what is your data center emergy. Enjoy your new sustainability project!