## Flows and partitions

##### Apr 29, 2008

Andrew M., a new but loyal reader, didn't like the flow charts used by the EPA to illustrate cleantech.  We had some lively discussion on flow charts before.  The bottom line seems to be that they are difficult beasts to tame, especially when the relationships are complex.  The example shown by Andrew (below) is not particularly horrid in this scheme of things.  It's the abundance of annotations and colors that cause dizziness.

Here's a view of the same data, using a partitioning approach.  The inputs are fixed at 100 units, which I find easier to comprehend, while the original fixed output at 30 units of electricity and 45 units of heat.  And of course, it is a tremendous service to readers not to have to work out the efficiencies.  Tacitness is a vice, not a virtue, in graph-making.

Reference: "Catalog of CHP Technologies", US EPA Combined Heat and Power Partnership.

You can follow this conversation by subscribing to the comment feed for this post.

I am a fan of Sankey diagrams and agree with Kaiser that the original is not particularly bad - just very busy.

For simple flows like this, it is also often possible to get away with a standard 'waterfall' chart. Here is an attempt:

http://www.flickr.com/photos/24579696@N05/2453689923/sizes/l/

I followed Kaiser's lead and framed it as a 'constant input' chart to make it easier to understand. I do understand why the original chart chose to look at it as from a 'constant output' perspective: It is frequently more natural to ask the question: 'given my electricity and heating needs, how little fuel can I spend' rather than 'given a fixed amount of fuel, how much electricity and heating can I generate'.

I like the format of the second chart better, but it may have a slight problem: How do you know that it's linear - that a ~30% decrease in input results in the same decrease for all outputs?

Dreikin: that is a great question. I don't know. Since the original uses the arbitrary outputs of 30 and 45 units, it seems plausible that these numbers are scalable. But true, it may very well not be.

The comments to this entry are closed.