Air conditioning tips?

August 1, 2006 3:08 PM

This may seem like one of those "duh" questions, but I've just put in my very first air conditioner (thanks to MeFites) and have a few quick questions.

First, do you usually leave your air conditioner on during the day? (My concern on this issue was prompted by this webcomic.) If so, how much do you crank it down, if at all? I have a cat, so I'd rather keep the poor guy comfortable (although he was seemingly okay even on the toughest of days) — but I'm just wondering how people handle this question.

Second, around what temperature level do you change your policy on the above? For example, although Chicago's in the midst of a well-above-100 heat index as we speak, later this week we're going to have highs that are drastically lower (say, high of 80). I can't see leaving the air conditioning on then. I imagine this one's more a matter of personal taste, but I'm curious as to opinions.

Third, my air conditioner has an EER of 10.8 — according to the little guide, that's only 0.2 from the max energy efficiency of 11. My power bill shouldn't jump huge, should it? With a lot of fans running often, my ComEd bill was $25 for July, if that makes any difference ...

Fourth, the A/C is tipped slightly back so it drains outside. The control panel is a little unflush with the rest of the unit, but not horribly so. The unit seems to have enough insulation around it to prevent any air leaks. I'll be keeping the shades drawn most of the time. Given these items, any other advice about running an A/C?

posted by WCityMike to home & garden (26 comments total)

Well, if youre going to lock a pet in your house yuo really have no choice but to keep at AC at a comforable temperature (cats nd dogs have heat tolerances like a human.) Or you could open all the windows and put up fans like you used to do. This will save you quite a bit of money.

A window unit like yours can double or triple your electric bill. A good strategy is to leave it running when youre home and switch to fans on cooler days.

I asked Alan Turing here in hell about how much this would cost. He calculated that a 10,000 btu unit uses 1200 watts of energy (thats with a high energy saving rating). Lets say you pay 11 cents per killowatt hour. At 12 hours a day you'll end up paying 47 dollars a month.
posted by the ghost of Ken Lay at 3:23 PM on August 1, 2006 [1 favorite has favorites]

1) I absolutely do not leave my air conditioner running during the day (and I have a cat). Instead, I pull the window shades, and make sure as little light as possible enters the apartment. I've been having 100-degree days too, and the apartment is warm when I get home, but not unbearably so.

2) I have no idea how much energy that A/C might use, but I have an in-wall unit that runs on 220 volt power (which is crazily efficient) and doesn't raise my power bill by more than $10, and I have a tiny window unit in the bedroom that raises it by $30-40. (I suspect I'm paying more for power than you are -- my average in the cool weather is $55-60, and I don't have electric heat.)

Keeping the shades closed should keep the apartment comfortable enough for your cat. Turn it on when you get home (don't crank it up -- that makes it colder, but not any faster), turn it down at night to conserve energy, and turn it off when you get up. If it's the weekend and you're planning on sleeping in past sun-up, you might not want to turn it down as much the night before.
posted by CrayDrygu at 3:40 PM on August 1, 2006

I asked Alan Turing here in hell about how much this would cost. He calculated that a 10,000 btu unit uses 1200 watts of energy (thats with a high energy saving rating). Lets say you pay 11 cents per killowatt hour. At 12 hours a day you'll end up paying 47 dollars a month.

Say 'hi' to Al for me. That amount is based on the assumption the condenser runs for all 12 of those hours.

According to the earlier post, your apartment is 500 sq feet. If you run it over night and turn it off in the day, it will still be noticeably cooler than the outside when you get home. I have a 5000 BTU which ran last night in my bedroom (200 sq feet). I closed the door when I left this AM and it was still quite comfortable ten hours later, despite an outside temperature of 100 and 90 in the rest of the apartment.
posted by justkevin at 3:45 PM on August 1, 2006

I set my AC on power save mode at 80°F during the day. I believe it hardly kicks on at all at this setting, and the apartment isn't unbearably hot when I get home. When I'm home, I'll drop it to 74 or 72, depending how I feel.
posted by knave at 4:00 PM on August 1, 2006

Looks like you got yourself a nice, efficient unit. WCityMike.

If you crank your unit's temperature set point up to something like 80° or 82° during the day, your compressor won't run as much as it would trying to keep the place at 72°, and you'll provide a survivable max temperature for your cat, with the least hit to your power bill. Overall, watt hours and degree days are your balance points for keeping your power bill in check. If you can be reasonably comfortable at 76°, you'll pay about 10% less for electricity, than if you must have 72° temperatures for comfort. The less the differential you are trying to maintain between inside and outside, the lower your power bills.

Much of the comfort of having an air conditioner comes from its ability to de-humidify. If you have drier air, and want to run a small fan into other rooms for internal circulation, you might find that 76° temperature setting is great.
posted by paulsc at 4:01 PM on August 1, 2006

Regarding cost to run the AC, 10kBTU at an EER of 10.8 is 926 Watts. ComEd charges 8.275 cents per kWh. Which for your unit means $0.077 an hour. If you left you AC on the coldest setting 24 hours a day, at the end of the month you would get a bill for $55.17 more than what you are currently paying.

(.926 kW * 24 hours * 30 days * $0.08275)

However, since your AC won't be running 100% of the time, your bill will be less. You can make a better educated guess at what fraction of the time it will be running.
posted by darkness at 4:07 PM on August 1, 2006

rock on midwest! electricity is $0.35+/KWh here in the bay area, at the 300% over "baseline" level. and the baselines are so low that i dont know anyone whose not in the top tier...
posted by joeblough at 4:31 PM on August 1, 2006

Indeed, PG&Es rates are insane. My power bills are regularly $200+, and I don't have AC.
posted by darkness at 4:48 PM on August 1, 2006

I also have an in-wall unit that is connected to a 220V outlet (Cleveland area) and our bill only went up by about $15/month if we leave it on for 16/24 hours a day. One other way to decrease your power bill as well as the heat in your apartment would be to turn off any computers you might normally leave on during the day when you're away.

I started turning my PC off when I was not using it and I cut almost $25 off of my electricity bill.
posted by vkxmai at 4:53 PM on August 1, 2006

Thanks, guys, for everything so far.

In addition to the stuff I've asked, I've had two other questions that've come to mind —

First, this thing's been running nonstop since I plugged it in about four hours ago — no off-then-on or anything. Then again, I don't think it's reached its target temparture yet, is my guess. Makes sense too, though, right, given it's still 96 degrees, 52% humidity outside?

Second, air conditioners are fine when it rains, yes?
posted by WCityMike at 5:10 PM on August 1, 2006

Be very careful about those electricity rates. In Ontario the 'official' rate is about $0.05/kWh, but if you add the variable incidental fees (like delivery) it gets to around $0.10/kWh (and then there are a couple of fixed fees).
posted by Chuckles at 5:13 PM on August 1, 2006

Yeah, it will take many hours to drop the temp in the room, since all the objects in the room are at 96 degrees. It takes some time to cool them down. Patience, Grasshopper ;)

Yep, the AC unit itself is fine when it rains, but depending on how well it is installed, some water might leak in the window.
posted by darkness at 5:23 PM on August 1, 2006

Our air has rarely been turning off in this heat, so yours is probably still cooling stuff down. If it feels too cold to you, turn it off (or turn the temp level up, which is what I do in here). And you're sure it's the air and not just plain fan you're hearing?

And yes, it'll be fine when it rains. Though at my last place when I had a window unit, the "pinging" of the rain on the unit sometimes got annoying. I just put an old towel on the top of the unit and it muffled the sound.

Is Chicago supposed to get rain? It'd sure feel nice about now.
posted by bibbit at 5:27 PM on August 1, 2006

Last night, I had the brilliant idea to put one of my fans (a 10" tornado/Vornado-type fan) underneath our window unit, pointed through the output toward the ceiling. We moved into our smallest, northernmost bedroom a week ago so that the window unit had a fighting chance (we're in Ft. Worth, it is not insignificantly hot here) at cooling the room, but we weren't getting very cool and the dogs were freezing at the foot of the bed right by the window unit. The fan made an astounding amount of difference; I woke up at 5am so cold I actually pulled the sheet up, and the dogs did not get in bed to put their disgusting hot dog bodies on us.

Those little high-efficiency units really don't blow so hard, so a little fan seems to be a great investment if you're not getting good circulation. During the day, I set the window unit at 78 on the "energy saver" setting, and turn the fan off so there is a pool of cold air for the dogs. The cats haven't even gone in that room, though, since we moved in. They spend the day in the hottest room, or outside on the patio.
posted by Lyn Never at 6:50 PM on August 1, 2006

Thanks for all the answers, guys.

If anyone's still reading this thread, here's one last question — the lights in the apartment seem to dim considerably but then go back right up (we're talking total time of a half a second, perhaps) when the air conditioner does something inside itself. Any thoughts from the electrically minded as to what's going on and if it's a concern? I've noticed it happening a number of times over the last half-hour ... my computer is in the same outlet (I have no other choice) and I see no problem whatsoever on the computer screen.

Could be a side effect, perhaps, of when the fridge's compressor kicks in, an electrical load thing?
posted by WCityMike at 7:29 PM on August 1, 2006

Yeah, it's a sharp, brief increase in the electrical load. It would be a good time to learn where the breaker is, if you don't know already.
posted by MrZero at 7:42 PM on August 1, 2006

It is an electrical load thing, though I am not electrical enough to say whether it's really bad or how to fix it. We flipped a breaker last weekend plugging the weed eater (outside) into the same (inside) circuit as the A/C. I live in a crappy rent house with a number of circuit issues, so I'm used to balancing things. I don't know how many circuits you might have to choose from to switch things out, but I have noticed that I don't have the light-blinking problem when the unit is not on "energy saver" mode, though that doesn't completely make sense to me. I would think the compressor kicks on and off harder in that mode.

Unless I plug in something really amp-hungry, like the vacuum or the weed eater, I don't have a problem. I can overlook the light flickers to be comfortable.
posted by Lyn Never at 7:43 PM on August 1, 2006

Is it anything to worry about, MrZero, or is it normal?
posted by WCityMike at 7:43 PM on August 1, 2006

The compressor requires an extra burst of current to get started. Because of the high current, resistance in the wires causes the voltage droop a little. Once the compressor gets going the current demand goes down to the 7-10 amps it is specked at (7-10 depending on which numbers above you believe).

I suspect you have too many things on the same circuit. How many lights of what type, and what kind of computer?

If you are running a modern power hungry desktop and a 21" CRT as well as two or three 100W light bulbs.. Well, that could be half the circuits capacity already. The air conditioner on top of that and you are really over doing it. (The lights could be on a different circuit and still dim somewhat when the compressor starts..)

You should add up all the loads on that circuit!
posted by Chuckles at 7:46 PM on August 1, 2006

I put it on Energy Saver mode, actually, and still notice the same problem ... but then again, it's in that stage where it's still de-heating and de-humidfying the entire apartment while still dealing with a very warm weekend, so it's having to work very hard at the moment. Hopefully wouldn't have to in the future! (Also, it has a 10.8 of a max of 11 EER, which means it normally shouldn't be a power hog.)
posted by WCityMike at 7:47 PM on August 1, 2006

Just to clarify, the last posting was a reply to Lyn Never, and this one's a reply to Chuckles' comment.

Chuckles, I've got a computer (Intel iMac), external hard drive, and laser mouse plugged into a power strip sharing the same outlet with the A/C. I have no other option, due to the placement of outlets in the apartment.

The light is a ceiling light — I don't know from which area of my apartment it draws power.

My refrigerator is probably occasionally kicking on and off as it sees fit; it, along with a microwave, is on an outlet in the kitchen.

A DVD, VCR, cable, router, cable modem, and television are plugged into a different outlet. None (aside from cabel modem and router) are in active use at this particular moment.
posted by WCityMike at 7:57 PM on August 1, 2006

We can only have one tv on when the ac is on. And we can't run the microwave while a tv and the AC are on. It gets complicated.

And our bill leaps from 30 to 70/monthly when we use the AC.
posted by DieHipsterDie at 8:06 PM on August 1, 2006

Well, a long time ago, after some stiff proding, I realised:

You should not be relying on the breaker to tell you when you have overloaded the circuit. The breaker is your safety mechanism, it is supposed to be a back up, it is not your first line of defense. You should know how much load you are putting on a circuit, and you should make sure that you don't overload it.

My statement did imply that you could use the breaker as a gauge for when you have over done it. That is not correct!

posted by Chuckles at 8:20 PM on August 1, 2006

in re: the flickering thing

i have the same thing in my apartment (fullerton and western) with my window unit. it has, on occasion, made my linux box kinda crashy. I bought a UPS. Problem solved.

Ben
posted by rbs at 11:00 PM on August 1, 2006

Well, after a night of running, it now seems to have gotten to the point where it can periodically shut off for a while. That's good. I thought this thing was gonna run forever. :)
posted by WCityMike at 4:51 AM on August 2, 2006

It was 105 degrees in Chicago the past couple of days, so yeah, its going to run quite a bit during a heat wave.
posted by the ghost of Ken Lay at 5:28 AM on August 2, 2006