This post first appeared on the Green Building Advisor Website.
Part of my job working as an energy auditor is educating homeowners on electricity usage, reviewing and analyzing historical electricity usage is part of the process. Checking service conductors and individual branch circuits in an electrical service panel is also sometimes needed. This information lets me know if an appliance, motor, or other device is operating as expected. How about electricity usage of an appliance or other equipment over time? My visit to a home is usually under four hours, hardly enough time to figure out how often a device operates. For this, we need tools that can record data.
Case Study
A few months ago, I was asked to perform an energy assessment for a customer of a local electricity provider. The customer had an increase in their electric bill of about $80, or more than a 500 kilowatt rise per month from normal. The increase had started several months earlier, but they were unable to find the source.
My process starts with asking questions, any new appliances? Is there any electric space heating equipment in operation? Are you using a vehicle block heater? (Something us in cold climates are familiar with.) How about farm animals? Any tank heaters for cattle or horses? Do you have any chicken? All the answers were “no”.
My next step is testing inside the electrical panel. I’ll let you know what the source of the increase was later in this blog.
Testing Inside an Electrical Panel
When diagnosing a high electricity bill complaint, I have a few different methods at my disposal, testing inside the electrical panel is where I typically begin. First, I view the electrical panel with my thermal imaging camera. If a circuit breaker is, or was recently on, often the breaker will be warmer than the surrounding circuits. This gives me a starting point of where to look.
Thermal imaging is effective when the electrical draw is constant. Sometimes loads are intermittent, which can be frustrating for the person trying to diagnose the issue (me). Intermittent loads don’t always present using thermal imaging. At that point, you have to be lucky to catch the problem using another method.
The next step is to utilize my clamp-on multi-meter to confirm electrical usage. (Monitoring electrical loads inside a live electrical panel is not something untrained people should attempt.) I start by measuring the load on the two main service conductors. This will indicate the entire draw of the panel.
After measuring the load on the main service conductors, I next begin measuring the individual branch circuits, trying to determine if any are drawing an unexpected amount of electricity. I start with warmer breakers that were indicated by thermal imaging.
Again, this work should be performed by a trained electrician. The work is performed inside a live electrical panel, injury or death can be the result if a mistake is made.
Individual Appliance Tracking
There is a way to check individual plug-in appliances for their electrical usage. The opening photo shows a few different plug-in monitors that are available to purchase for around $30.
These devices for checking the electricity usage of plug-in appliances have been around for decades. One of the more popular models is the Kill-A-Watt meter, a simple meter that plugs into a wall socket. The appliance then plugs into the meter. Some meters will only display the real-time usage without recording any data. Most newer watt meters will record usage over time. I recently purchased this Masterforce watt meter (sold at Menards) for $25. Toggling through the display (pushing the DISP button), the meter displays real-time power draw (displayed in wattage), cumulative power usage (displayed in kilowatt-hours), the amperage being used, the voltage being supplied, the frequency (not used for calculating energy costs), and the amount of time the meter has been recording. The meter will continue to record until the reset button is pushed for 5 seconds, it even stores the data if the meter is unplugged or there is a power outage. Very simple and safe to use. The one drawback, the meter only works with 120-volt plug-in appliances and equipment.
Converting the Information to Cost
Before we get into converting the information to a dollar figure, we should have a brief discussion about the units we use for the calculations, a few basic electricity definitions.
Voltage-The pressure that pushes charged electrons through an electrical circuit. In the United States (and I believe Canada), the line voltage for most residential applications will be 120/240 volts. The letter E represents voltage and stands for electromotive force.
Amperage-The strength of an electrical current, often referred to as an amp. We protect electrical devices from damage that may occur from too much current flowing in a wire or through a device by using circuit breakers, which are rated in amperage. For instance, a 12-gauge wire is rated to carry up to 20 amps of current, typically protected using a 20-amp breaker or other overcurrent device. Amperage is represented by the letter I.
Resistance-The opposition to electrical flow, which is measured in ohms. The concept is similar to friction, heat is one product of resistance. In calculating the cost of electricity for residential applications, resistance isn’t typically a part of the equation. Resistance is represented by the letter R.
Wattage-Wattage is defined as the rate of doing work, and is also how electricity billed, kilowatt-hours. It is also what we are trying to solve for when using Ohms Law to calculate the cost of electricity. Wattage is represented by the letter P.
I first learned about Ohm’s Law back in 1985 in my high school basic electricity class. The basic illustration below shows how to solve for one unknown. As I mentioned in the definition for wattage, it is the information we need to calculate the cost of electricity. Let’s use my dehumidifier as an example. I’ve plugged in my recording watt meter and toggled through the display. I find that the dehumidifier uses 4.24 amps and is operating at 120 volts. I want to solve for wattage or P.
The formula to use according to Ohms Law is P=I x E or power (in watts) = current (in amperage) x voltage. 4.24 amps x 120 volts = 509 watts. The 509 is wattage consumed in one hour (the recording watt meter will also display the wattage; this example shows how to solve if you do not have that information). The problem is we are billed by the kilowatt-hour, or 1000 watt-hour. The 509 watts is a little more than one-half of a kilowatt, we need to move the decimal point over three places, to .509. Or you can use the equation wattage/1000 watts = kilowatt. 509 watts/1000 watts = .509 kilowatts. Again, we are billed by the kilowatt-hour, the 0.509 kilowatts are what is consumed in one hour.
Next, we need to know the cost of the power. The average cost across the United States is a little more than $0.15 per kilowatt-hour ($0.1545 to be exact). If we multiply our 0.509 kilowatt-hour times the cost, $0.15, we find the dehumidifier is costing $0.07635 per hour to operate. If the dehumidifier is running non-stop for 30 days, the cost is $54.97 ($0.07635 x 24 hours per day x 30 days).
Another way to determine energy use is by reading the nameplate. This dehumidifier has a listed amperage of 7.2 amps and is rated at 115 volts. Plugging these numbers into the formula and we find the dehumidifier will consume 828 watts or 0.828 kilowatt-hour costing nearly $90. This nameplate is from my dehumidifier, which I measured using the recording watt meter in the example above. As we can see, the listed data is substantially different than what is actually used. I prefer to measure usage as opposed to using the nameplate rating whenever possible.
There are other ways to track electricity usage. Newer electrical panels have technology either built into the panel or inside the breakers that are capable of recording electricity usage. There are also aftermarket monitoring systems that are installed inside an existing electrical panel. These monitoring systems use a device called a current transformer that clamps around a current carrying conductor. The Sense Energy Monitor has a learning algorithm built in; it learns which devices are using power. An advantage to this system is it uses only the main conductors entering the panel as the source. It takes several months for the system to “learn”. Another system uses several current transformers clamped around not only the main conductors, but also several branch circuit conductors. There is no learning curve with these systems, but there are a lot of wires that are added inside an electrical panel. Emporia Vue is an example.
One other way to track electricity is through your electrical meter. Many electricity providers have switched to “smart meter” technology. The provider I work with uses a meter that transmits data over existing power lines. (A customer is able to view their power usage on a mobile app or computer). The meters have the capability to record energy usage down to the hour (some down to the minute). The meters can even notify the provider if power is not being supplied, handy for quick responses during power outages. The drawback is the information shows all the devices using power. It cannot disseminate between individual devices and equipment.
Back to the Case Study
What was the piece of equipment that caused an $80 increase in an electrical bill? It was a well pump in a rural home. We tracked the issue to either a bad pressure switch or a faulty check valve that wouldn’t allow the system to hold pressure, forcing the well pump to run continuously. I didn’t dare turn the system off for further diagnostics. My fear was the pump, or some other part of the system would fail and the family living in the home would not have water for an extended period of time. As is the case for most energy assessments and building investigations I’m sent to, I have no idea how the homeowner resolved the issue.