Week 4 Crux Questions Feedback

Q1. We have two versions for assessing the efficiency: process and overall efficiency. Define each form. Compare how you might use each analysis for the problem of analyzing the efficiency of cooking pizza in a wood-fired backyard oven that you are planning on building. How do the different methods of analysis lead to different ideas for increasing the efficiency of your pizza experience?

Parts of the answer:

• simple/process efficiency = output / input
• overall efficiency = output / (total amount of machinery)
• process would be just how much wood to burn to cook a pizza
• overall would be the energy and materials cost to build the pizza oven to cook some number of pizzas
• reduce wood burned vs. probably building a smaller oven or use the outdoor oven a lot more often
• key comparison is between the two types of efficiciency

Comments:

that's just the net efficiency part of the question

process and overall efficiency are usually analyses at different scales

- the comparison of the two definitions of efficiency needs to be clearer

- you need to compare the two definitions

-- you need to define both, compare them and then comment

the overall efficiency would count in the materials for making the oven

overall efficiency could be multiple uses or including the oven, or both

you need to compare the outcome of the analysis for the two types of efficiency

Excellent answer from a student:

Process efficiency is the output/input of a simple activity. Overall efficiency is the the output of something divided by the sum of all the machinery and their inputs required to make that something. If one is trying to make pizza in an oven, the output would be pizza. The input could be just simply the amount of wood required per pizza baked, which would be a process efficiency measurement, e.g.number of pizzas/pounds of wood. Types of wood or density of wood could be the variables in the input.

An overall efficiency measure might be the comparison of pizza making in an outdoor oven versus a conventional oven in a kitchen. Then many variables could enter the accounting, such as the cost of the machines,e.g. bricks, mortar, building plans; wood to burn; pollution from wood-burning; how often it may not be used because of weather, versus the cost of an indoor oven and of electricity used.  

For example, it is desirable for delivering usable energy, i.e. the "net energy". Make up an example that demonstrates how net energy can be increased through efficiency and optimization. 

However, some cases the objectives for the addressing the problem might not be best met through increasing the efficiency at each step. State why this might not be the case and give an example that illustrates that point. (When would increased efficiency of the individual steps not be the best outcome.)

Parts of the answer:

• give an example that illustrates net energy (2)
• describe the increased efficiency (1)
• what's the example where one step of higher efficiency might not fit
• increased efficiency is not the goal - it might harm the environment

Comments:

good examples of where the increase in efficiency in one process may not be the best are:

• leads to the rebound effect
• creates toxic by-products
• eliminates useful by-products and creates just waste
• doesn't serve the overall benefit, i.e. increased efficiency isn't the goal

I think you have the key concept in the example, but it could be more clearly stated.

You can increase output to increase efficiency, but that may cause other problems. That's why we need to look at larger and longer scales and assess all the impacts.

You need to explain how making one step more efficient might reduce the overall efficiency.

Rebound effect is a good example of how improving efficiency might not pay off.

You gave two good examples of control for more than efficiency - balance the overall process and using the waste