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Throwing Hot Water on the Prometheus Development

by Eugene Cordero

As I watched the Internet recording of the Environmental Planning Commission meeting of Feb 10th, one of the statements Mr. John Moss (of the Prometheus Real Estate Group) made about their ‘green practices’ made me pause.  Mr. Moss stated that the biggest sustainability-related feature associated with the development is the proximity to public transit.

As many of us know, estimating how important proximity to transit (and downtown) is to reducing vehicle miles is challenging. A Mountain View study found 9% trip reduction at a transit-oriented development; some academic work, and advocates of such developments, project greater potential reductions.

The question that came to my mind is: ”If Prometheus adopted green initiatives like solar hot water or photovoltaics, how would those carbon savings compare to transit-related reductions?”  I decided to compare the adoption of solar hot water to transit reductions using a back of the envelope calculation.  I chose solar hot water because these systems are typically simple, have an excellent return on investment, and can reduce emissions of greenhouse gases very effectively.

The results are shown in the following chart where we compare the CO2 reductions associated with a 10% reduction in auto miles with CO2 reductions associated with a solar hot water system.

The calculations show that the reductions of CO2 are similar for a solar hot water system compared to a 10% reduction in driving miles.  Although proximity to transit and the services our downtown offers may reduce driving miles even further, it’s fair to say that additional energy-efficiency measures like solar hot water have a similar potential to reduce emissions as transit-related ones.  In fact, if the above calculation was made for a family and not an individual, the reductions may be larger for solar hot water, especially if you have a teenager (or other family member) who regularly takes 20-minute showers!

The main point is that there are various ways to effectively reduce emissions of CO2. While smart growth and access to transit are certainly very important, there are other pieces to our personal carbon footprint including our use of electricity and natural gas.  I would encourage the Prometheus staff to give serious consideration to solar hot water for their Minton’s proposal and for other developments.  With California’s new $350 million rebate program for residential and commercial users, solar hot water is now an even more cost effective way to reduce emissions.

Assumptions made:
The calculations are made for a one-person household that uses 30 gallons of hot water per day.  I assume the installation of solar hot water would reduce the use of water heating by electricity or natural gas by 75%, a fair estimate for our sunny climate and with good access to the sun.  I also assumed that the development location would reduce auto miles by 10%, that the average resident drives 10,000 miles per year, and that the average car gets 25 miles per gallon.  These assumptions are based on averages given in government reports or published studies.
Eugene Cordero is a professor of the Dept of Meterology and Climate Science at San Jose State and co-author of a new cookbook, Cool Cuisine, which explores the multiple connections between the food we eat and global warming.

Eugene Cordero is a professor of the Dept of Meterology and Climate Science at San Jose State and co-author of a new cookbook, Cool Cuisine, which explores the multiple connections between the food we eat and global warming.

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