Calculating the cost of Summer

Found this in Drafts, lol.

Our house doesn’t have air conditioning. We keep cool in the summer with a combination of open and closed windows, the large overhang, and shade trees. (Well, the city’s cut down some of those, the jerks.)

With screens on most of the windows, our house is decent at moderating temperature. During the summer, our large overhangs keep the direct sun off the house, and the plentiful and giant windows catch any passing breeze, which helps immensely in terms of keeping us cool. There are only a few days when we’re genuinely miserable. (This year, there was the memorable 2 weeks when the overnight temp was still in the 90s/100s – I don’t think we’ve ever been that miserable before.)

Our windows will not accommodate window (or portable) AC units (except one in the kitchen which is double-hung). They are sort of like casement windows, but very deep and very large. I won’t say it’s impossible to use window units, but it would require a lot of custom carpentry.

So…. We rely on fans to help augment the breeze, or to make one on those days when the air is still.

— BEWARE. LOTS OF GEEKY MATH AHEAD.—

If you’re interested in learning more about keeping energy useage down in summer, but don’t care to read the details of KWH used in my house during the summer, this website has a nice amount of information along those lines.

— YOU HAVE BEEN WARNED —

In addition to being curious about whether it would be cheaper to use an AC or to use the fans/windows, I also got curious about something I’ve heard recently – that one window AC is actually cheaper than two fans plus one dehumidifier. So I started doing some math.

According to this website dedicated to energy savings, a large window AC uses 1071 kwh/month, assuming 24 hour a day useage for 31 days. A medium sized unit would use 670. A household fan uses 74, and a dehumidifier would use 116 (a figure which came from here). Two fans and a dehumidifier equal 222 kwh/month.

So, though you’re certainly more comfortable with an AC, it’s definitely not cheaper than 2 fans and a dehumidifier. It’s actually comforting to know this, because our own experience with energy bills has been that, on months when we turn on our tiny kitchen AC, our energy bill goes waaaay up, whereas it’s a barely noticeable rise when we switch from those few no heat/no fan weeks to using the fans 24/7.

Now, let’s look at my house. We don’t use a dehumidifier in the main floor. (I mean, that would be a lot like running the heater with the windows open. There’s no possible way a dehumidifier can keep up when the windows are all open.) We do use one in the basement because there’s not very good air circulation down there. We would use a basement dehumidifier whether or not we had window ACs on the main floor. So the dehumidifier is not a factor.

Our bedroom uses two fans plus the ceiling fan (which weighs in at another 55 kwh/month). So, while we’re running 203 kwh/month in the bedroom, it’s less than even a “tiny-ass” (quote from the energy website) window AC would (500). Since we all sleep in there, there would be no reason to consider a window unit in the kids’ bedroom, which is more of a play room that happens to also have  a bed in case anyone spontaneously decides to sleep in there.

Moving out to the main living area: dining, living, school room, and kitchen. We usually run the kitchen AC on really hot days. I think it qualifies as “tiny ass” since it’s a small window and the more powerful units wouldn’t fit, so 500 would be the 24/7 useage. (we don’t have it on nearly that much) Then fan in front of the AC (74), and a total of 4 other fans (74 each = 296) and one more small ceiling fan (55). Total energy useage, assuming the AC is on 24/7, which is is not: 851.

If we were to cool the same square footage with window ACs, we’d need at least two medium sized units in addition to the tiny kitchen unit. That weighs in at 670*2, or 1340.

And now for the grand total, on our main floor, what is our energy cost for cooling, per month during the summer? 1543 kwh/month. MidAmerican, our energy company, says it charges an average of $0.0835 per kwh. $128.84 per month.

For comparison, if we were running three mid sized window units (1 in bedroom, 2 in main living area) plus the kitchen unit, we’d be running 2510 kwh/month, or $209.59 per month.

Now the real question – would it be worth it?

(and I have to say no – particularly considering the amount of work it would be to even get portable or window ACs to fit in our windows.)

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About sarahtar

Our Family lives in central Iowa. We are Christians, conservatives, and crunchy granola heads. We love the outdoors, photography, and lindy hop. Turn ons are people who are polite, honesty, and really good root beer. Turn offs are mean people and people who make my life more difficult.

Posted on September 14, 2011, in Personal. Bookmark the permalink. 1 Comment.

  1. you are teaching my boys advanced math — you lost me, but i trust you

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