Archive Monthly Archives: May 2011

Our Energy Baseline

Because we chose not to live in the house until the renovation is done, we don’t have an exact way to measure the energy performance improvement from the renovation.  It would be fantastic if we could say, “Our annual energy consumption at the house was 100 before the renovation and and after the renovation it dropped to 20, so we realized 80% improvement.”  That would give us a nice clean comparison, but we don’t want to live in the house while construction is going on.  So, we will be using relevant data for this “before and after” comparison.  The former resident of the house, Bob, was kind enough to provide us with access to his past utility bill data.  This provides us with an approximate baseline of how much energy was used at the house “before” renovation.  Thanks Bob!

Along with the attribute of the house, the lifestyle of the occupant plays a role in the energy consumption — what kind of electronic gadgets used in the house, what’s the preferred thermostat setting, what kind and how much cooking is done, and so forth.  You may remember that we’ve been going to various energy efficiency classes and several of the instructors suggested we gather and analyze our utility bill.  So, I did just that last week for our current home.  Our current home is a 1,300 sq.ft., 3-bedroom, 2-bathroom, 2-story condominium where we share 2 walls with our neighbors.

First, I logged on to our home account on the website of our local utility, PG&E,  and gathered data from our past billing history.  The Excel spreadsheet with the basic data looks like this.

Next, I took the gas data and graphed it over a 12-month period.  This is useful because I can tell how much gas is used for heating the condo from the shape of the curve.  How?  In our mild climate we don’t need to heat the home during the summer months.  You’ll notice that the gas usage in the months of August, September and October is constant at 10 Therms per month.  Because we have gas furnace, gas water heater, gas oven, gas cooktop and gas clothes dryer, the 10 Therms per months represent our normal usage of hot water, cooking and clothes drying.  Anything above 10 Therms is for heating.  You can see the gas usage goes up in the winter and down in the summer, where in December we’ve used up to 35 Therms to heat the house.  Here’s what the graph looks like.

Then I graphed the data for electricity.  This turned out to be pretty uniform throughout the year.  In July we were on vacation so both gas and electricity usage dipped a bit.  There is a slight bump in electricity usage in December.  I’m guessing that  we used more lights around the winter solstice when days are very short.

Interesting, isn’t?  We can further analyze the electricity data by doing some detective work.  There is a little device called, “Kill A Watt,” which measures the electricity usage of an appliance by plugging in the Kill A Watt device into the electric outlet and the appliance you want to measure into the device.  A couple of years ago Kurt went around our home and measured different equipment and found that his stereo equipment had quite a bit of vampire load or standby load.  This means that the equipment uses electricity for just being plugged in, even if the equipment is not turned on.  He immediately put his stereo on a separate power strip and turns off the power strip when he’s not listening to music.

By the way, we got a bonus credit of 20% from PG&E in March for low energy usage. They sent us a lovely email expressing their appreciation for conserving gas.

I don’t think we were consciously trying to reduce energy consumption this winter, but we were curious. So we did a little experiment to find out, “How cold does it get in the house?” by turning down the thermostat to about 50 degrees Fahrenheit.  The answer?  In the range of 60-65 degrees Fahrenheit.  Actually, I’m glad that experiment is over…