Written by: Laurel Kruke, Sustainability Manager
Last week, I spent time at a seminar with people who I didn’t know before the week. Inevitably, the question “what do you do?” came up; when I started talking about energy conservation and the simple behaviors people can do to reduce their energy consumption, I got a variety of responses (all positive, just different). My favorite reaction was of shock and awe at the amount of money that one can save by just turning off and/or unplugging appliances they don’t need or use. For example, when I told a friend that the mini-fridge many of us keep in our offices/classrooms/houses can cost around $35-$100 a year to run (depending on location and price of electricity, and age, size, and model of appliance), he was floored. I got to thinking about awareness, and how oftentimes, people just don’t know how much they are spending on various appliances.
I thought I would take some time in this week’s blog to share some calculations, and bring to light how much we actually spend on our everyday appliances. Here are some assumptions we’ll use throughout our calculations: the average cost/kWh in Arizona is $.10; a month is 30 days; 12 months in a year (as opposed to 9 months in a school year). A refrigerator's cooling system runs on cycles, so while it is plugged in for 24 hours/day, the Department of Energy recommends dividing the total time plugged in by three for a more accurate representation of how long refrigerators run to keep their interior cool. Therefore, we will use approximately 8 hours/day for a refrigerator. Keep in mind that these calculations are based on these assumptions, so are not exact, and may differ based on location, cost of electricity, and appliance use/run time.
Let’s look at our refrigerators. I’ll share information about a full-size standard refrigerator, and a mini-fridge to show the difference. The full-size refrigerator example I’m using is 22 cu. ft., which is a typical size for a full-size refrigerator. A 22 cu. ft. refrigerator, on average, uses approximately 540 W (watts), and is "on" and running approximately 8 hours per day. Converting this to kWh (kilowatt hour) consumption requires dividing the wattage by 1000, and multiplying by 8 hours, which equals 4.32, or rounded 4 kWh per day. Multiply this by 30 days then 12 months, you have consumption of 130 kWh/month, and 1,555 kWh per year. If you multiply these numbers by $.10/kWh, a full-size refrigerator costs approximately $13/month to run, or $156/year.
The mini-fridge example that I use is a 3.2 cu. ft. mini-fridge. According to the specifications, this mini-fridge uses 391 W, and again, is typically plugged in 24 hours a day, but is cooling about 8 hrs/day. When this is converted to kWh, the average kWh consumption of a mini-fridge this size is about 3 kWh per day. Over the course of a month, then a year, this mini-fridge is using 94 kWh/month, and 1,126 kWh/year, respectively. The cost of running this mini-fridge equates to $9/month, and $113/year.
You can see by this comparison that a full-size refrigerator is only a little bit more energy-intensive, and costs just a little bit more to run per year than a mini-fridge. But it can hold a lot more volume-wise than a mini-fridge, so it could be considered a more energy-efficient appliance. Appliance and equipment run costs can add up and can be a significant amount of our electric bill over time. A question to ask about our appliances is what are they used for, and are they being used to their fullest potential. For example, in your workplace, classroom, or school facility, do you have multiple mini-fridges spread around when you could consolidate and use 1 full-size refrigerator instead?
You can do these calculations on your own for other appliances and equipment as well. How much does your phone charger cost when it is left plugged in during the day when nothing is charging? How much does it cost to leave your computer on sleep-mode (rather than turning it completely off) all the time? By asking some of these questions, and doing some quick math, you could uncover some potentially significant opportunities to save.