Obtaining Practical and Accurate EIL Measurements—Part I

August 11, 2008

Energy Input Labeling (EIL) is fairly new. The immediate goal is to provide ball park figures of Energy Added Inputs calculated and reported in good faith. Following the Standards helps to provide consistency.Taking extremely scientific and accurate measurements may be very difficult for most businesses, especially small ones who are just starting out with EIL. This post discusses how I start out. This methodology is targeted towards business people, not engineers, so please do not get too offended by the roughness of the measurements. The calculations below may look scary, but with patience and a calculator, they will become fairly simple and second hand.

The product I have begun with was a short book that is sold commercially. The Energy Added Inputs by my firm include human labor to compile, write and layout the book. Energy used to produce the physical book itself is also included. I don’t know the energy to transport the book, since I generally outsource that to the U.S. Postal service or other delivery firms.

I use a computer and a desklamp during these operations. I live in San Francisco, so I don’t use much HVAC. My lamp burns a constant 0.060 kilowatt hours per hour. I know this because the lightbulb in my desk lamp states that it is a 60 Watt lightbulb. 60 Watts is not perfectly accurate despite the label, but it is a good enough ball park figure for now. I’ll make even rougher assumptions later. 60 Watts x 1 hour = 0.060 kilowatt hours. (Note that “kilo” = 1000).

My body burns energy at a mean value of about 100 Watts. My body might burn more or less energy depending on whether I am out running around conducting field research or just sitting passively in front of the computer. Since I am not highly physcially active all of the time, I’ll just use the baseline 100 Watt figure. So, 100 Watts x 1 hour = 0.1 kilowatt hours per hour.

How should I determine the energy input from my computer and printer? If I were an electrician, I could use special equipment to measure the actual current over a period of time, and the actual voltage if that varied much. This can be dangerous work! If you are not a qualified electrician, you should not use this method unless you can obtain the services of such a person. In my case, I do have the equipment (a volt meter and a current clamp), but I would have to rip apart my cable in order to accurately use the clamp, and I do not wish to do that.

There are devices that I could plug my computer into, and those would report the power usage. This may be a good alternative for businesses who wish to purchase such a device. If you use such a device, very carefully follow any safety instructions. Even plugging in and unplugging devices can be dangerous. Science education catalogs often sell such devices.

My computer has a maximum current rating of 1.875 Amps. Many items of electrical equipment are labeled with this information, particularly those that use wall current. It is often stated in the user manual. This figure is not the mean usage value, but the most the device is expected to use (such as during peak usage). An engineer would shudder, but I am going to use this as my energy input rate for my computer. Let’s be clear. This figure tends to significantly overstate the energy input from this device. However, since I am understating or neglecting the energy inputs from so many other sources, I feel that this practice is not unreasonable and does not overstate the overall Energy Inputs. It is further justified by its ease of adoption and relative safety. My computer operates at about 120 Volts. So I multiple 1.875 Amps x 120 Volts to get an energy input of 0.225 kilowatt hours per hour. (Note: 1 Volt x 1 Amp = 1 Watt).

Say that I required 100 hours of time to compile, write and layout the book. Let’s assume that I am using my computer and desklamp the whole time, or I am at someone else’s office using at least that much energy. So my total hourly energy input rate is 0.060 kilowatts for the lamp, 0.100 kilowatts for my human body and 0.225 kilowatts for my computer, for a total of 0.385 kilowatts (or kilowatt hours per hour). The total time x input rate equals the input. So 100 hours of work x 0.385 kilowatts hours per hour is equal to 38.5 kilowatt hours (kwh). This is the total input to compile, write and layout the book.

However, say that I expect to sell about 200 copies of the book. It is of local interest, but is unfortunately not likely to be a national bestseller. I would call this a batch of books. Some firms would call this a “run” or a “Lot”. I would then take the the above total input and divide it by the batch quantity, so that 38.5 kwh / 200 units of product equal 0.193 kwh per copy. If my book were a purely digital version and I outsourced distribution, I would be finished. The books could be labeled “Energy Added Input: 0.193 kwh”. If the energy sources were known, they could be included as well. Here, the label would continue “Sources: 11% human energy, 89 % electrical energy”. If the sources of the electrical energy were known, the figure for electric energy could be further refined, such as “11% human energy, 25% hydroelectric, 64 % coal electric”.

Since physical copies of the book have been produced, will energy inputs in production need to be determined as well? Read the Standards (pdf) or wait for the thrilling answer in a soon-to-come future post!