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Energy Consumption: Home vs. Transportation

by Mark Hutchinson last modified Jan 04, 2012 02:32 AM
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by Mark Hutchinson last modified Oct 29, 2010

There are many appeals to living in a Postgreen home. Some like them for the modern look, some for the increased comfort of a home that has no drafts or spots of significantly varying temperatures, some for the extremely clean air, and many for the very low utility and water bills. It is that last [...]




 

 

There are many appeals to living in a Postgreen home. Some like them for the modern look, some for the increased comfort of a home that has no drafts or spots of significantly varying temperatures, some for the extremely clean air, and many for the very low utility and water bills. It is that last sliver of the population that I will focus on now, specifically for the corollary to those low utility bills, which is very low energy consumption.

After spending a lot of time researching buildings and adding a bit to standard construction costs we’ve been able reduce the energy consumption of our buildings to roughly half that of your typical code-built home, which is about as low as is possible without adding solar PV and/or forcing our occupants to drastically change their habits. This is a great achievement and we look forward to building as many buildings to this level as possible. However, what is interesting is that at this level of energy use other aspects of peoples lives, most notably their habits for transportation and recreation, become an even more significant portion of their total energy consumption.

For example, the rough numbers show that if Chad and his family (who live in the 100k House) took one round trip flight to Hawaii, their portion of the planes total energy use would be equal to the energy consumed in their house over an entire year (it’s also equal to 2 flights to San Francisco and 6 to Chicago or Atlanta). Similarly, if each person in the house drove just 10 miles a day in a standard car (or 20 in a spiffy new hybrid) then this driving would also consume the same amount of energy as the house uses all year (as would a daily ride of 28-miles on bus or rail).

My summary? If you like our homes primarily because of their low energy consumption then its good to be aware of all of the other pieces in your energy pie and see if you can adjust them accordingly.

If you would like to calculate these numbers on your own, I found it easiest to use kilowatts as the standard energy metric and be sure to use source energy (this accounts for the energy lost in burning fossil fuels to create electricity and refining crude into gasoline). For driving, a standard 20 mile per gallon car uses 2.14 kWH/mile and a hybrid uses half of this. For flying we assume 0.17 miles per gallon and 400 passengers to get 0.75 kWH/mile. For bus travel we assume 4 miles per gallon and 14 passengers to get 0.75 kWH/mile. For commuter rail we use Amtrak’s reported number of 0.86 kWH/mile. For light rail we use Portland’s Tri-Met reported number of 0.75 kWH/mile. Finally to calculate your homes energy use multiply your annual electricity usage (already in kWH) by 3 and multiply your annual gas usage in CCF or Therms by 30 (this converts CCF or Therms to kWH) then divide this number by the number of occupants. If you find any better sources for these numbers please let me know in the comments below.


 

 

 
 
 

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