Smart Utility Bill Disaggregation

April 30, 2012
May/June 2012
A version of this article appears in the May/June 2012 issue of Home Energy Magazine.
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Energy auditors use a simple, well-known approach called a utility bill disaggregation to analyze a home's overall energy use. Here's a quick summary of that technique as detailed in Krigger and Dorsey's Residential Energy:

  1. Collect 12 months of gas and electric bills.

  2. The monthly domestic hot water use is the average of the three lowest gas bills multiplied by 1.1. The 1.1 adjustment compensates for higher winter hot-water use masked by the heating load.

  3. The annual heating load is the annual gas consumption minus 12 times the monthly hot-water use.

  4. The monthly electric base load is the average of the three lowest electricity bills multiplied by 1.1. The 1.1 adjustment compensates for higher electricity consumption in the winter months.

  5. The annual cooling load is the annual electricity consumption minus 12 times the monthly electric base load.
Steve Mann
is a HERS rater, LEED AP+ Homes, Certified Energy Analyst, serial remodeler, and longtime software engineer.

This is an excellent, gross-level algorithm that can give you a rough snapshot of a home's utility consumption based on the current occupants' behavior.

It does, however, have shortcomings. For instance, there are no adjustments for weather conditions—the analysis can be skewed in years with unusually hot or cold seasons. Also, the calculations clearly won't work for all-electric houses, although with some adjustments, they might provide you with some useful information.

Smart Meters

Thanks to "smart" utility meters, we are entering a new era of remote utility monitoring and analysis (see photo below). Smart meters give utilities and authorized third parties a way to monitor consumption on a much more detailed basis than once a month. Some can be read on a real-time basis; others less often, perhaps once an hour.

Detailed utility monitoring and recording can benefit both consumers and utilities. For instance, utilities can set pricing based on season and time of day, rewarding customers who shift their loads to off-peak times. (California's energy code already uses this approach by calculating energy efficiency benefits based on what is called time-dependent valuation, or TDV, metrics.) Consumers can use the information provided by their smart meters to monitor consumption and perhaps manage their energy use (see Figure 1).

More than 40 million smart meters have been deployed in various European countries. In the United States, programs are under way in California and Texas to outfit approximately 15 million households with smart meters. Pacific Gas and Electric Company has installed 10 million units in California to date. Various utilities in Austin, Houston, Dallas, and San Antonio are responsible for installing the remainder.

Right ImageA typical Pacific Gas and Electric smart electric meter. (Steve Mann)

Smart Disaggregation

Now that smart meters can provide so much more consumption data, it makes sense to update the (now) old-fashioned utility bill disaggregation process. That's just what Steve Schmidt, founder of High Energy Audits (HEA), decided a few years ago. Steve spent years in the software side of the semiconductor industry, where they're used to dealing with millions of data points when analyzing chip designs. A former climate change denier, Steve—faced with rising swimming pool bills and under pressure from friends and family—started investigating his own electricity consumption. One thing led to another. He ended up joining the Environmental Committee in his Northern California town and was charged with investigating utility consumption as a path to reducing greenhouse gas emissions.

He and another committee member started out auditing houses using The Energy Detective (the "TED 5000"), Kill-a-Watt meters for individual load identification, HOBO loggers, and extensive Excel spreadsheets (see "Evaluating Energy Use Feedback Devices," HE July/Aug '08, p. 36). With the introduction of smart meters, Steve realized that there could be a much simpler approach using cloud-based software.

HEA has developed a web-based tool for doing a detailed analysis of a home's energy consumption, water use, and greenhouse gas production. The process starts with your smart meter data, pulls some information about your house from public records, and then requires you to answer a brief survey. The questions cover such topics as

Right ImageFigure 1. Pacific Gas and Electric’s My Energy portal lets homeowners monitor their electricity and gas usage by using smart meter data. (Steve Mann)
  • water features (pools, ponds, spas);

  • food-handling equipment (refrigerators, freezers, ice makers);

  • home entertainment systems (TVs, computers, game consoles, music systems);

  • lighting;

  • thermostat settings;

  • water use; and

  • driving habits and air travel.
Right ImageFigure 2. High Energy Audit’s primary graph breaks out five different categories of energy consumption loads. (Steve Mann)

Once you finish the survey, the software presents you with a detailed analysis of your energy use, water use, and greenhouse gas production, compares the findings to findings for other households locally and in California, and makes suggestions for improvement.

The software can easily identify heating, cooling, and base loads. In addition, using the smart meter data, it can break out from the base load your idle mode and your recurring and variable loads, all areas for potential reductions (see Figure 2). Idle mode is that portion of your base load that is active 24 hours a day. Recurring loads use electricity at the same time each day. Variable loads occur all year, but not at regular intervals (see Figure 3). Variable loads typically represent devices like laundry equipment, computers, and other household electronics.

Right ImageFigure 3. Variable electric loads, typically representing electronics and laundry equipment, can be tracked on an hourly basis. (Steve Mann)

The software identifies excessive loads, which it calls leaks, and recommends specific ways to reduce those leaks. For instance, for high base loads, it recommends installing smart power strips, unplugging unused devices, or for the really big base leaks, getting a detailed electrical audit of your home. For high idle modes associated with the use of games and computers, the software recommends configuring the power-saving mode on those devices. For excessive heating or cooling loads, based on BTU per square foot thresholds, the software recommends a whole-house or HVAC audit to identify opportunities for upgrading the shell or the home's equipment and/or appliances.

This level of analysis presents many opportunities for reducing energy consumption. At a very basic level, the analysis can inform homeowners how and when they are using the most energy in much more detail than was previously available. The program's recommendations can be used to develop a long-term reduction plan or identify the most cost-effective upgrade measures. The analysis may help program implementers identify the best weatherization opportunities without ever having to visit the house. For whole-house contractors and auditors, the analysis provides a great starting point for a whole-house project by identifying specific problem areas.

The Future

Even though this auditing service is available at no charge to households in the six participating Northern California towns—Atherton, Los Altos Hills, Monte Sereno, Portola Valley, Woodside, and Mountain View—the sign-up rates have been lower than expected. That may be because of HEA's small marketing budget, or because residents of the Bay Area tend to downplay the importance of energy efficiency. The climate is so mild that many households have relatively low utility bills. Many homeowners see little need to reduce their energy consumption.

learn more

Krigger, John, and Chris Dorsey. Residential Energy: Cost Savings and Comfort for Existing Buildings. Saturn Resource Management, May 2004.

Get more information about HEA.

Steve Mann can be contacted at steve@green-mann.com.

Five Bay Area municipalities originally funded HEA using EECBG (Energy Efficiency Community Block Grants) money from the 2009 federal stimulus package. This funding ran out in 2011. The company is currently talking to various funding sources and energy efficiency stakeholders to continue and expand the service. In the meantime, HEA continues to gradually sign up users in the target municipalities while it refines the program's modeling.

Schmidt is confident that HEA will still be around in a year, with a reach that extends beyond the Bay Area. Perhaps one or more of the utilities will see the value of this detailed analysis and will figure out a way to apply it on a mass scale. We have smart meters; now it's time to use them smartly.

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