ENVS 101: Personal Energy Audit

Benchmarking with Electric Heat

The personal energy audit is an example of why it is important to perform quantitative analyses. Sometimes these analyses require estimates, as the sources of data are not exactly as we wish they would be. In this case, we do not have data on natural gas use because it is not used as the heating source for the house. What we have to do is to divide our electricity use between what is used for heating and what is used for everything else in the house, such as lights, electronic devices, and appliances.

Professor Floyd’s Procedure for Allocating Electricity Use

1. Make a table of your electric consumption, in kWh, for each of the 12 months in your year of data.

2. Identify the two lowest months in terms of consumption. Typically, one will be in the spring and one in the fall, as these are times when neither heating nor air conditioning are used. This low level of consumption represents your baseline use of electricity for lights, electronics, appliances, and the like. We will assume that your use of these things is the same every month, that your baseline consumption is constant.

3. Identify the months during which you are heating your house. Typically, this is the interval between the month of low use in the fall and the month of low use in the spring.

4. For those heating months, subtract the baseline consumption from the total kWh on the bill for that month. This is the kWh used for heating.

5. Add up the consumption for heating, in kWh, over the heating season. This is your annual energy use for heating. Convert the kWh to Btu with the appropriate conversion factor, and you have the Btu information you need for the home benchmarking.

For Part 2 of the Personal Energy Audit

1. You are asked to find your electricity consumption for the year. In an audit, you do not want to double count anything, and you have already accounted for the energy to heat your home. Therefore you have to adjust the electricity consumption you report so it does not include the electricity to heat the home. There are a couple of ways to do this, but I suggest this one. On your table above, make an extra column for non-heating electric use. For the heating season, the months for which you subtracted the baseline use to get the heating kWh, enter that baseline consumption as your non-heating kWh. For the rest of the year, enter the full amount of kWh from your electric bill.

2. Add up the consumption in the non-heating column to get your kWh of electricity use excluding that used for heating. This is the amount that you will use for electricity use in your personal energy audit. As a check, add up what you got for your heating kWh and what you got for your non-heating kWh. Now add the kWh for each month directly from your electric bill. The two totals should be the same.

3. There is one more step, and that is to allocate the cost of your electricity between heating and non-heating. First, find the total cost of your electricity by adding the cost from each month directly from your bills. You will allocate this based on the fraction of your use in each category. To get the fraction for heating, divide the kWh used for heating by the total kWh you used for the year. Multiply this by the total cost to get the cost for heating the house. To get the fraction for non-heating, divide the kWh used for non-heating by the total kWh. Multiply this by the total cost to get the non-heating cost. As a check, add the heating cost and the non-heating cost, and the total should equal the total cost you calculated from your bills. If they check, enter the heating and non-heating costs in the appropriate places in your personal energy audit.