Electricity measurements give insight into energy and money-saving products and strategies.
- Section 1 – How to use an energy meter.
- Section 2 – Electricity measurements around the house.
- Section 3 – Lessons learned about saving energy.
Lafayette Residents – Borrow a "WattsUp?" energy meter from the Lafayette Public Library (check availability).
Other libraries in Xcel Energy's territory (and elsewhere) may also have this program, so it's worth asking.
Students and Teachers – Electricity measurements are well suited for fun and meaningful projects or assignments.
1. How to Use an Energy Meter – There are 2 key measurements: Watts and kWh.
- Watts (W): This is how much electricity something is using right now. Most things use about the same amount of power all the time, but others like refrigerators use different amounts of power as they cycle on and off.
- Watt-hours or kilowatt-hours (Wh or kWh): This is how much total electricity something uses over a period of time. Multiplying Watts times Hours gives Watt-hours. A tv that uses 25 Watts of power for 4 hours has used a total of 100 Watt-hours of energy (or 0.1 kWh, since 1 kWh = 1000 Wh).
- Refrigerators are tricky. They cycle on and off, and they must work harder when warm food is added, or the door is opened, or the defrost cycle kicks in, or if the house is warmer. An accurate measurement needs to average over at least a couple of days.
- Using a "WattsUp?" meter. There are 2 buttons – "Mode" and "Select". Mode chooses the type of measurement, and we only care about the first two: Watts (power), and Watt-hours or kWh (total energy since the WattsUp was plugged in). The Select button cycles through secondary values for each Mode setting (like maximum and minimum values). For refrigerator measurements, hit Select once when on the Wh/kWh Mode setting to see the monthly average value (kWh/month). Read the manual for more details.
- Read "Power and Energy (Watts and kWh) in a Nutshell" for more on electricity measurements, and some examples.
2. Household Electricity Measurements
- Different brands and technologies use very different amounts of energy to do the same thing, so these measurements will differ from yours. The idea is to buy the most efficient model that does what you want.
- The sum of a few big energy users plus many small energy users adds up to your total monthly electricity use. In my case this is about 160 kWh/month (1/4 the national average), or 5.3 kWh/day.
- Even if something uses a lot of Power (Watts), it may use very little total energy (Watt-hours) if it's only used for a short time. Or, it may use only a few Watts, but if used 24/7 it can really add up to a lot of Watt-hours.
- WattsUp can't measure 240 V appliances (stove/oven and dryer) or hardwired things (furnace blower). However, I have a whole-house energy monitoring system (this one) that lets me figure these things out.
- See Section 3 for Lessons about Energy Efficiency learned from these measurements.
About Standby Power and Vampire Loads: Some things use power even when they're supposedly "off". This includes anything with a clock, or a light to tell you it's off (ironic!), or anything with a remote control (because it must constantly check to see if you pushed a button). Things with "wall cubes" like battery chargers can suck power (like a vampire) even when nothing is attached (so unplug them). Some newer devices have very low standby power (much less than 1 Watt), but others use several Watts continuously, which really adds up. See "Steps to Cutting Standby Power".
- Lighting – See the Lighting Choices page for details on energy use.
- Bottom line: Old-fashioned incandescent lights waste over 90% of the electricity they use as heat; CFLs are very energy efficient but have a few downsides; LEDs are the most efficient and are the light source of the future.
- Refrigerator – I've had 3, each more efficient due to energy efficiency regulations updated in 1991, 2001, and 2014.
- Current fridge: A 2014 GE 18.2 cu ft top-freezer (model GTE18ITHWW), Energy Star rated at 369 kWh/year (or 31 kWh/month). But measurements show that in winter and with my use patterns it only uses 17 kWh/month (a real energy-sipper!). It will probably use closer to the rating in the heat of summer.
- Previous fridge: A 2004 Kenmore model, Energy Star rated at 440 kWh/year (37 kWh/month), and I measured it at about 35 kWh/month in winter and 45 kWh/month in summer. However, it was so much more efficient than my old 1980s fridge that it paid for itself in energy savings in 6 years.
- Old fridge: Classic 1980s gold model (before Energy Star ratings) was measured in summer at 150 kWh/month, but based on whole-house energy savings when I got the 2004 fridge it used an average of 1500 kWh/year (125 kWh/month). I recycled it even though it was still working, and saved a ton of money! I bought the WattsUp to make this measurement, and the conclusion to get rid of that energy hog easily paid for the meter.
- Microwave: 1300 W cooking. 3.3 W continuous (equals 2.4 kWh/month). (interesting microwave factoid)
- Coffee Maker: 1000 W while brewing or when the warming plate cycles on (zero standby power...no clock, not programmable). Total energy: 150 Wh to brew, then 75 Wh/hour to keep warm. Assuming a daily pot and 2 hours warming, that's 9 kWh/month. I put the rest of the coffee in a thermos after drinking two cups.
- Toaster: 785 W while on. 30 Wh to toast half a bagel. No standby power (it's a basic model). Unfortunately, both slots heat up even when only one slot is used, wasting half the energy.
- Breadmaker: 240 Wh per 1 pound loaf (max 480 W while baking).
- Washing machine: 255 Wh per load (or 0.255 kWh/load)
- Dryer: 4500 Wh/load (4.5 kWh/load), almost one day's total electricity use for me. I'm thinking about line-drying!
- Garage door opener (single): 375 W opening and 330 W closing (for 17 seconds each); 10.8 W for 5 mins while light is on after use (9 W CFL bulb); and 5.0 W continuously (on standby). So, the daily energy used to open and close the door twice a day is: 3.5 Wh to open + 3.1 Wh to close + 1.8 Wh for the light + 120 Wh on standby. So, 93% of the energy is used on standby just to watch for a remote signal to open!
- Furnace blower (1979 80% efficient natural gas forced-air furnace): 480 W for 7 min cycle (1°F temperature increase) = 56 Wh/cycle. First cycle in the morning is about 25 mins (6°F temperature increase) = 200 Wh.
- Entertainment and Communication
- tv: 23 W on, 0.0 W standby (26" Samsung UN26EH4000F). LED/LCD tv's are much more efficient than plasma.
- Comcast DVR: 23.5 W continuous (equals 17 kWh/month, or 10% of my total electricity use). Still uses 22.5 W if turned "off" (so "off" is meaningless!) Must unplug it, but that's unrealistic for a DVR. Come on Comcast!
- DVD player: 7.2 W idle, 9 W playing, 0.8 W off (standby). When not in regular use, I unplug it.
- VCR player: 7.8 W idle, 11.5 W playing, 1.6 W off (standby). When not in regular use, I unplug it.
- Stereo receiver: 24 W radio on, 0.0 W standby
- Laptop (Macbook Pro, 6 years old, plugged in and fully charged): 22 W typical, 30-40 W working, 0.0 W sleeping
- Phone (landline, cordless): 3.1 W continuous (equals 2.2 kWh/month)
- Modem: 2.8 W continuous (equals 2.0 kWh/month)
- Clocks, chargers, fans, etc.
- Clock radios: 3.6 W (=2.6 kWh/month); 2.7 W (=1.9 kWh/month); 1.2 W (radio only, =0.9 kWh/month)
- Drill battery charger: 2.0 W to maintain charge, and 1.7 W even if battery is not attached to charger (so unplug it). This battery loses its charge very slowly, so it doesn't need continuous charging.
- Dustbuster 18V charger: 3.2 W to keep it fully charged (=2.3 kWh/month). Often batteries don't hold their charge very long after they're a few years old, so they must be charged continuously to be ready when needed.
- Razors: 2.9 W (2.1 kWh/month); 1.6 W (1.2 kWh/month). Wall cubes alone use 0.6 W and 1.0 W.
- Oscillating fans: 28 / 35 / 46 W and 23 / 28 / 38 W (Low/Medium/High)
- Window fan: 63 W on high; 1.4 W off (standby) so I unplug it. This is my summertime cooling so it's on all night. For 12 hours/day that's 22.7 kWh/month, which is substantial (14% of my electricity use), but it's peanuts compared to A/C or even a swamp cooler. My swamp cooler became unnecessary after putting R-50 (or 16") of insulation in the attic, which keeps the house from overheating in summer and saves on heating in the winter.
- Cell phone charger (just a dumb flip phone): 1.4 W if fully charged; 0.0 W if phone is removed from charger.
Baseline (minimum) electricity use. My energy efficient house uses about 160 kWh/month (1/4 the national average). If smoothed out over time, this is equivalent to using 222 Watts of power continuously [*]. From my whole-house energy monitoring system I know that my baseline energy use in the middle of the night when the refrigerator and furnace and radio are off and the computer is sleeping is about 70 Watts. This is the total of all clocks, chargers, the DVR, phone, standby power, etc. That's a lot! The little things that use power continuously add up to almost 1/3 of my total electricity use (70/222 = 31.5%). It's important to address the bigger things like refrigerator, lighting, cooling, and wasteful habits, but it's also important to consider standby power and vampire loads. A handy factoid to keep in mind is that 10 Watts of power used continuously equals 7.2 kWh/month.
[*] The math: (160 kWh/month) x (1000 Wh/kWh) / (30x24 hrs/month) = 222 Watts.
3. Lessons about Home Energy Efficiency
- Aim for an LED light in every socket, but start with the most-used fixtures. Replace incandescent lights ASAP!
- Turn off lights when not in use. Consider using fewer lights regularly, and using 1 bulb in 2-bulb fixtures.
- Refrigerator – is it an energy hog?
- When was it made? Can you borrow or buy an energy meter?
- Consider these refrigerator buying tips.
- Replace 40 W appliance bulbs with a CFL or LED, and remove any freezer bulb (a heat source in a freezer?!).
- Do without a second fridge if possible. Some utilities have rebate programs to promote second fridge recycling.
- Reduce wasted standby power and vampire loads.
- Buy Energy Star rated products (at least!).
- Energy Star doesn't mean the MOST efficient, but it's a good start.
- I often consult TopTenUSA.org to find the most efficient models, then visit manufacturer websites for more info.
- People tend to like what they're used to, but we quickly get used to new ways, especially if they're as acceptable as the old ways and/or if the benefit of saving energy and money is considered. For example...
- I like it less bright in the house, but in the past I had more lights on just because I never tried alternatives.
- It's easy to get in the habit of deciding what you want before opening the refrigerator door, or of setting all the groceries on the counter so it's quick to put them in the fridge.
- It saves on heating if windows are kept closed when the outdoor temperature is below the indoor temperature.
- Lower the thermostat in winter and put on long clothes (I like 66°F in the day, and 60°F while sleeping). It's actually nice to be a bit chilly and snuggle under a blanket in the evening.
- Install a programmable thermostat to automatically turn down the heat at appropriate times.
- Air conditioners use a lot of energy, so there's a payoff for any steps that reduce its use or allow for downgrading to a more efficient swamp cooler or window fan. After having 16" of insulation blown in my attic ("R-50"), my house wasn't as hot in the summer so I could get rid of a noisy swamp cooler and just go with a window fan at night for cooling.
- Try accepting a summertime indoor temperature of 78°F or higher.
- Remember that indoor fans only make you feel cooler, as the motor is actually a source of heat. If no one is in the room then they're a waste of energy and should be turned off.
- Control "solar gain" by closing blinds (ideally white) on the sunny side of the house.
- Close windows when the outdoor temperature is higher than the indoor temperature.
- Synergies. Sometimes one change can lead to more than one benefit...
- Having an energy efficient refrigerator means that less electricity is wasted to produce heat that is dumped into the kitchen, so the house's cooling needs are lower.
- Adding insulation in the attic not only reduces heat loss in winter, it also reduces heat gain in summer which reduces the cooling load. My attic reaches 130°F in summer, and in places like Arizona it can reach 170°F!
- Solar panels are expensive. Any solar-powered home benefits greatly from making the home more energy efficient so that the size of the solar array can be reduced (or so that the solar provides a greater percentage of your electricity use). See these clear examples and this one.