The discussion centers on comparing the energy efficiency of new paper versus recycled paper. Participants explore various factors that should be considered in this comparison, including energy units, transportation costs, and the overall energy required for production processes.
Participants express various viewpoints on the factors to consider in the energy efficiency comparison, and no consensus is reached on the best approach or the inclusion of costs in the analysis.
Participants note the importance of defining the scope of the comparison and the potential for missing assumptions or errors in data collection. The discussion highlights the complexity of measuring energy efficiency across different processes.
Zryn said:Joule is the unit of energy (kilojoule = 1000 joules, megajoule = 1000 kilojoules etc), and to compare the energy between processes, converting each process to similar units sounds good.
When comparing these processes however, be wary of different time periods (J/s compared to MJ/year), keep in mind costs like transport (how big a truck/ship, and how far to travel), think about the entire time line of the process (does the energy to grow / harvest / transport trees factor in) and figure out early on what is relevant and what is not (discuss the scope of the problem with people for different viewpoints)!
Zryn said:If it takes $100 worth of diesal (?? MJoules/litre; I can't remember the value) to fill a truck with a 50 litre capacity tank and a 15% efficient engine which can carry 10tonne of new paper per delivery and the driver can drive back and forth 3 times between the paper manufacturer and the wholesaler, then you can figure out how much energy it costs to send each tonne of paper, as you will end up with joules/tonne. Do the same for the other modes of transport and you have your cost in energy instead of dollars.
The question is, do you want Joules/sheet of paper, Joules/ream of paper (500 sheets) or perhaps Joules/tonne of paper?