Understanding Residential Energy Consumption
Some years back my company began to "double meter" some of our new homes. We wanted to understand how homes consumed energy in the north central Texas area. Our goal was to make our homes more energy efficient and to do so we needed to know where the energy was being consumed.

What Is a "Base Load?"
We installed the second meter between the regular electric company utility meter and the heating and cooling equipment. Our meter only showed us how much energy was being used to heat and cool our homes. By subtracting our meter reading from the overall utility reading, we found out how much power is required to run the lights, refrigerator, freezer, dryer, hot water, and everything else that isn't part of the heating and cooling equipment. We call the power needed to run everything but the heating and cooling equipment the "base load" of a home. The monthly base load represents all the energy used to run a home each month except for heating and cooling.

After monitoring these homes for several years, we made several interesting and important revelations. Each month the power consumption by the rest of the house (base load) remained fairly constant throughout the year. People tend to use about the same amount of hot water, lighting, etc., every month.

Texas Does Have Spring and Fall!!
We also found that almost always there was a month in the spring and fall when the meter on the heating and cooling equipment moved very little or not at all. With the mild spring and fall weather, the heating and cooling equipment wasn't being used. This meant the utility company meter reading was identifying the base load. Suddenly we realized that we could figure out the base load of a home without the second meter.

Our Discovery Goes to Work
We realized that if you looked at a 12 month history of the utility bills, the lowest monthly reading (almost always a fall or spring month) could be called the monthly base load of the house. That was a month that the heating and cooling was used very little if at all.
FYI: If you use gas, your gas base load is usually during the summer.

You Can Do It, Too
Now all we had to do was to request a 12-month history of utility bills on any home and we could understand how that home performed. For the past five years, each of our homebuyers signed a letter to their utility company giving us permission to request a history of their utility bills for monitoring purposes. You can receive your own utility history from your utility company-just call and ask!

A Real Example
Below is a copy of some of the data you will find on your utility history printout. This is actual data from a home we built several years ago. This year the heating and cooling bills on this home were a little higher than in past years. Of course when you look at this past summer's record number of days of over 100 degrees, it is still pretty good. This home is all electric and has 2340 square feet of heated and cooled area. It is located just north of Waxahachie.

Date	KWH	Total Bill
8/26/99	2170	174.58
7/28/99	1777	143.95
6/28/99	1892	130.95
5/27/99	1147	83.16
4/28/99	1028	76.18
3/29/99	1007	74.74
2/25/99	900	71.27
1/27/99	1237	84.90
12/29/98	1470	102.05
11/30/98	936	70.81*
10/28/98	1115	93.98
9/28/98	1959	160.70
TOTAL	16,638	1267.27

What We Can Learn
Now we can analyze this 12 month history and learn a lot about this home. We can figure out how much is spent to cool this home. We can figure out how much it cost to heat this house. And we can understand how much we spend on everything else that uses electricity in this home.

The Overall Monthly Utility Bill
This data shows that for the year ending 8/26/99 this house used 16,638-kilowatt hours and paid $1267.27. If you divide the annual bill of $1267.27 by 12 you find this home had an average monthly electric utility bill of $105.61.

The Base Bill
The November bill was the lowest at $70.81, so it is our base load bill. This past year was a little strange since November was our mildest month. Multiplying the monthly base load bill of $70.81 by 12 months, you get $849.72 for an annual base bill. Subtracting the total annual base bill of $849.72 from the total annual bill of $1267.27, you get $417.55. This number, $417.55, represents the total annual amount paid to heat and cool this home. Dividing the total heating and cooling bill of $417.55 by 12 months you find that this home averaged $34.80 per month for heating and cooling. If you just look at the Spring through Fall bills, every dollar spent over the base load bill of $70.81 each month was spent on cooling. Likewise, if you look at the Fall through Spring bills, every dollar over the base load bill of $70.81 was spent on heating.

Increase your Knowledge, Increase Your Power
By studying the utility record, you begin to understand how your home consumes electricity. Once you understand where the energy is being used, you can identify where you should spend your efforts for energy improvements.

What Should I Do?
When I review the home with the above history, I see that they spent $49.73 on heating and $367.83 on cooling. They also spent $849.72 to run everything else in their home. Spending money to reduce their heating bill can't really save very much. Even if they did something to cut their cooling bill in half, they would only save $183.92 a year. Because of the way this home was constructed there isn't much room to improve heating and cooling expenses. The base load is the best area to look at for savings. So they could start by seeing what they could do on things like the hot water heater, refrigerator, freezer, dryer, light bulbs and fixtures, and general life style.

Caveat
I have found that the above method works almost as well as actually double metering a home. I have also found that a lot of things can go wrong. If you take a vacation in the Spring or Fall you may have a low utility bill that would not represent an accurate base load. Also be watchful of outside Christmas lights, they can really skew a winter bill. After reviewing hundreds of these printouts, I can usually spot something out of line. I think as you begin to study your home's utility usage, you will understand abnormalities. If your base load seems really high, it is possible that your are actually having to heat or cool throughout the year. In that case, I would suggest that you look at your cooling problem first.

by: Jim Sargent, owner of:
Bentwood Custom Homes, Inc.
1214 Creek Circle
Waxahachie, Texas 75165
972-938-9997
www.bentwood.com