I have a whole stable of ancient appliances hidden away in various places around my house. In the interest of figuring out just which ones might benefit from being replaced, I bought one of these doodads. I’ve had it plugged in to Ancient Fridge #1 for a couple weeks now, and finally took the time to look at the output.
Problem is, I’m totally clueless as to what I’m looking at. Can someone give me a hand?
Here’s what I’m getting, going from left to right as I press the buttons:
The last two seem to be the important bits, right? 0357 (I think) is the number of hours this thing has been gathering data - that works out to just under 15 days. So does that mean in 15 days, the fridge has pulled 32.17 KWH of electricity?
My local electric company says I pay $0.0755 per KWH.
So does that mean I paid $2.42 to run this fridge for 15 days? Am I doing it right?
Your math is right. I don’t know if the doodad is accurate, but your math is right.
Having said that: That averages out to be about 89 watts on the average that your fridge is pulling (32.170 kWh / (15 days *24 hours). I think the compressor is going to pull a lot more than that when it kicks in, but it’s not running 24/7. A little cursory Google indicates that a refrigerator compressor runs about half the time. IF that is correct, the 89 watts seems a little low. I would expect most normal fridges to pull 400-600 watts, dividing in half giving 200-300, two to four times more than your doodad is registering, unless this is some dorm-sized fridge.
What does the tag on the fridge say for watts? You could use this formula to get a pretty good estimate if the “compressor on about half the time” is accurate:
Monthly Cost = (watts [from tag on fridge] * 720 [number of hours in a month] * ½ [compressor on only half the time] * kWh cost)
The only number you don’t know in that formula is the watts. (A fridge isn’t going to use “zero” watts when the compressor isn’t running, but it won’t be much, either.)
The fridge is a small fridge (though not dorm-sized. It’s maybe 5’ tall, has a freezer), and it’s in our unheated garage. Right now it’s about 16 degrees outside, and maybe 45 in the garage. Would that make the fridge run less and account for it not pulling much electricity?
Good question. Fourier’s Law would say that since there’s a much lower temperature differential between 45º external temperature and 70+ inside a house, that the “heat creep” is going to be much slower. But how much slower, which would affect how often the compressor turns on, is something I don’t know. But, at a constant 45º, I don’t think the compressor is going to be kicking in very often. Aren’t most fridges set at about 40º? So that $2.42 might not be so unusual after all.
If your frig is in a 45 degree space the the heat gain to the box at 40 degrees is going to be very small; so it will not run very often.
You get billed by the KWH (killowatt hours) so your math is right. How often a frig compressor runs depends on many factors. What is the temperature of the space the unit sits. How often and how long the door is open.
I really cannot see how that can be true, at least with relatively modern devices. I have measured the power usage of my (six years old) refrigerator for months and it only averages a little over 50 watts. Contrast that with the cable receiver which draws a continuous 23 watts, and there does not seem to be a huge amount of difference.
Not all refrigerators and households are equal. Some people have very large, old refrigerators which use a lot of energy. Others have their thermostats set way too low. Still others have kids who are always in and out of the unit through the day, causing the compressor to run nearly continuously from 7:00-11:00.
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The OP is doing her math correctly, but the sole exception I would make is that although your bill may say “X cents per kWh” you probably have to include any local taxes, as well as fees attached to the account which vary as a function of electric use. For example, on my bill the listed cost of energy is close to 7 cents/kWh, but when you include taxes and fees it’s actually about 11 cents/kWh.
And good for the OP, for making the effort to buy one of the meters and use them. That’s the smart way to analyze household expenses.
Oh, I know that. It’s actually a gradated scale as well, so the first 1000 KWH cost me more than the second, etc. But for what I’m doing, I think a simple calculation to estimate usage works fine; what I’m really looking for are the culprits that are pushing my electricity bill up towards $200/month.
Unfortunately, my gut feeling is that it’s all the computers and our sauna, neither one of which I can do anything about. But we’ll see…
it is always good to take 2 or 3 measurements at different times for things like this, if they are widely different then some values may be wrong.
an electric sauna cost could be found by finding its power used (W) and the time it is used. you might find that enjoyable sweating is a large part of your cost.
having a meter like that is a good thing, especially at its now lower price. you can figure device usage or replacement for lighting and appliances. the meter will pay for itself.
replacing an older refrigerator, freezer or air conditioner can have a payback of a few years. measure your device and compare to what is currently for sale in the marketplace. stores that sell these devices (in the USA) will take your old ones and properly recycle them. electrical utilities (in the USA) will frequently have a program to give you money/credit for your old device; it costs less for them to reduce demand than to generate more electricity, they now like conservation too.
You guys really think the sauna costs that much? Our sauna stove is one of these, pretty sure it’s the RAD-7. When we turn it on, it runs constantly for an hour or so. Once it gets to temp, it turns itself on and off a bit.
So how do I figure out what it costs me to run it for an hour straight? Assume it stays on the whole time.
To my surprise, I found that computers were the number one users of electricity in my house (outside of AC). They can easily consume 100-200 watts doing virtually nothing, and when you have multiples to act as file servers, HTPC devices, and gaming systems, it can quickly add up.
I was able to reduce usage by a surprisingly large amount by just replacing my existing power supplies with 80+ rated, high efficiency units. The energy savings realized paid for the new supplies in about a year. Using S3 sleep, and slowly switching to lower power processors (and video cards) helped further reduce the run-time cost as well.
Well, from that page, the RAD-7 consumes 7.5kW. If it’s on continuously for an hour, that’s 7.5kWh, which is 7.5x$0.0755, or about 57 cents at your rate.