Chu, Two and Btu

Bad for the Lab, Good for the Country

Staff at Building Solutions, a home performance
company, install PV on a roof in Oakland. Next year, the renewable
and energy efficiency business will be even better.
Credit: Kate KenkeDr. Steven Chu, Noble-prize-winning physicist, and director of Lawrence Berkeley National Laboratory, was named as President-elect Barack Obama’s nominee for Secretary of Energy. Home Energy is a nonprofit magazine, but our offices are at Lawrence Berkeley Lab and the magazine was founded by Alan Meier, a lab scientist. People around here are saddened by the loss of Dr. Chu as director of the lab, but extremely excited about his nomination as Secretary of Energy. Dr. Chu believes in science and the important place of technology in helping us meet our energy goals and fight global warming—think cellulosic bio-fuels, nanotechnology, and yet undreamed of solutions to the present energy and environmental crisis.

Weatherization Works!

Word in energy efficiency circles is that the funding for Department of Energy (DOE’s) Weatherization Program will increase several-fold with President Obama’s proposed economic stimulus package. The Weatherization Program is managed state by state from money provided by DOE, and the funds pay to retrofit the homes of low-income families. Homes become healthier to live in, more energy efficient, and more comfortable for the occupants. For every one dollar the Weatherization Program spends, almost two dollars in energy savings results. Hundreds of thousands of homes have been retrofit so far, leaving about 99.5% of existing homes. Talk about green jobs potential! Many nonprofit and for profit organizations do weatherization work, and, basically, you retrofit the home of a low-income family the same way you retrofit a mansion. Lots more skilled people will be needed to do the work, and the jobs will provide a good income, benefits, and the possibility of future advancement. Community colleges, unions, professional training organizations, online trainers, and other players are gearing up to train the new green workforce.

How Many Btu Do You Do?

I promised in my last blog entry to explain the concept of heating-degree day and cooling-degree day. Sometimes you will hear that a home uses so many Btu or kWh per heating- or cooling-degree day, per square foot, per year. The degree days indicate the heating or cooling load on a building’s HVAC systems. A degree day is the rise or fall of one degree Fahrenheit for 24 hours. The rise or fall in temperature is measured from a baseline of 65F°. For example, if the average temperature tomorrow is 45F°, than the heating load on your heating system is 20 heating-degree days. If on a hot summer day the average temperature over a 24-hour period is 85F°, than the load on your air conditioner is 20 cooling-degree days. The number of heating-degree days for a winter in New York is around 5,000. Barrow, Alaska has about 20,000.

You can figure out how much energy you use to heat or cool your home by subtracting the baseline energy use. During a month when you are using neither your air conditioner or heater, such as in October or March (called the “shoulder” months), your gas and electric use represent your baseline. The baseline covers energy for lighting, appliances, hot water, and plug loads. Subtract out the baseline from your winter or summer energy use and you have the amount of energy to heat or cool your house. If you know the square footage of your home, and you have weather data for your area (go to www.degreeday.net to find out heating-degree days and cooling-degree days for your area), you are in a position to brag to your neighbors (or not) about your energy use.

At our house we used about 90 therms of natural gas from September 7 through December 7, 2008. There were about 480 heating-degree days (HDD) in our area during that time. Our baseline use of natural gas is about 10 therms per month, for heating water and cooking, leaving 60 therms for heating over the three-month period. Our house is about 1,200 square feet (ft²). Therefore, we used 60 therms/(480 HDD x 1,200 ft²), or about 0.0001 therms/HDD·ft². Since one therm of natural gas contains about 100,000 Btu of energy, that equals about 10 Btu/HDD·ft². That’s not bad, but not great either. How about you?

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