Monday, June 4, 2012

Re-Thinking my AC Strategy

For the first 12 years that I lived in this house I never had air conditioning. At the time I was working afternoons and evenings, so I was seldom home during the heat of the day, plus it was one of those luxuries I figured I could do without.

The house has an attic fan which pulls in outside air through open windows and pushes all of the hot air out of the attic. It does a reasonably good job of keeping the house cool once the outside temperature cools down. But during the heat of the summer, you pretty much have to run the thing all night long in order to get much cooling effect, because the outside air temperature never falls much below sixty degrees.


The main problem with the attic fan is that you have to have the windows open to run it, which, during allergy season made it sort of a "pick your poison" proposition. I could either suffocate from stifling heat or suffocate from the high pollen count.


Still, by employing the unheated waterbed tactic, and the occasional camping trip to the basement when it got really unbearable, I got by.

But then once I quit working and was home during the heat of the day, the weaknesses of my strategy started becoming quite apparent.


It was all made worse by the fact that my home office is on the west side of the house and has a sliding glass door, so that room just cooks in the afternoon sun, getting well over 85 degrees or so. During the worst of it, I'd actually sit at my computer with my feet in a bucket of ice water, wearing a wet t-shirt with a fan blowing on me just to make it bearable.


Soooo, when the government offered some nice tax rebates for installing high efficiency furnaces and air conditioners a few years back, I decided that the time had come.


I replaced the original 1954 furnace (which ran at about 40% efficiency) with a 95% efficient model and a central AC/air source heat pump. (A heat pump is basically just an air conditioner that can run either direction... so it can both heat and cool. They are much more efficient than any sort of a furnace when the outside temperature is above freezing. Once it gets really cold though, their efficiency plummets and you switch over to the gas furnace.)

Anyhow, my basic strategy had been to use the air conditioning only during the heat of the day to keep it below 80 inside, and then once it cooled off outside I'd switch back to my attic fan system. I'm used to the heat and I really don't mind it that much.


But recently a new problem has arisen. A family of skunks has taken up residence in our neighborhood. We're not quite sure where they're living, but they're out and about after dark most days, and trust me... those suckers are fragrant even when they're not spraying anything, and you do NOT want to pump a bunch of skunk scented air into your house at night!


So with great amounts of environmental guilt, sometime around the middle of last summer I started keeping the windows closed and running the AC at night. And to my utter amazement, my electricity bills actually went down!


I thought it was a total fluke, but then CatMan gave me a long lesson into the inner workings of an air conditioner, and it started to make sense. I won't pummel you with the details (and to be honest, I can't remember the details) but suffice it to say that an air conditioner works by moving heat from one place to another. This is accomplished by compressing and decompressing a gas trapped within the system. But it has certain physical limitations, namely that it can only heat/cool the air by about 30-40 degrees.


This is why the heat pump only works well when it's above freezing outside. Once it gets too cold, it just can't get the air warm enough. But it also means that if you run the air conditioner when it's 90 degrees outside, the temperature of the air coming out of your AC vents will be about 50-60 degrees. This will cool the house, but the AC has to work fairly hard to do it.

If, on the other hand, you run the AC at night when the outside temperature is 60 degrees, the air coming out of your vents will be closer to 20-30 degrees, meaning that it is able to cool the house down in no time flat.


Sooooo I now have a new strategy which is to run the AC at night to cool the house down to the low 70's. It really only takes about 20 minutes to get the house that cool. Then during the day I've got it set at 80 - but it has yet to come on during the day. Even with 95 degree heat outside, the inside temp is still holding steady at  a comfortable 76 degrees.

In the evenings I open the windows and run the attic fan for 15-20 minutes just to clear out any hot air that's still lingering up there, and leave them open for an hour or two, but close them before "the skunking hour" begins.


So far it's working great, and it's much nicer to sleep at night in a house that's 73 degrees as opposed to one that's 78 or so! Plus, it's really nice not to have to hear the noise of the attic fan running for hour upon hour.

So waddya think? Any thoughts on this new strategy? I'd love to hear how you utilize your AC to stay cool without breaking the bank.





23 comments :

  1. We fire up the engine and head further up the mountain. YMMV. Although, 7000' is feeling extremely perfect right now.

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    1. Ha! My parents have a similar strategy... it's called condo in Steamboat Springs!

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  2. We're lucky to have a nice evening breeze for a good portion of the summer, so if it cools down around dusk, I'll turn off the AC, open up and let nature do the work. If it doesn't cool off or the breeze doesn't pick up (and this happens for a couple/few short, miserable weeks in August/September) we will leave the air on at night. But my brain fights it. We don't have an attic fan, as we have no attic, not even a crawl space. Just vaulted ceilings with reasonably good insulation.

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    1. I actually LOVE to have the windows open at night, but with the skunks... umm... not so much! There are also a few stray tomcats in the area that drive my boy kitties nuts. Those lovely breezes are not so much fun when they are punctuated by screaming yowling hissing fe-lions!

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  3. Oh, and ceiling fans! I love those babies!

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    1. I have thought about ceiling fans, but I think they'd need to be very strategically placed so that crazed psycho cat could't attempt a ceiling fan leap!

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  4. Hmmmm, you're making me think again. I've been employing the method of my Southern heritage...open up the house at night, throw the window fans in the windows overnight, then in the morning I close it all up, close the blinds, close off extra rooms, etc. It stays fairly cool *up to a point*. The temps at night make/break this scenario though. If it hasn't cooled off enough outside by bedtime we run our window a/c rather than window fan. During the day, I've been leaving the main window a/c set to turn on at 76 but in the afternoons I have to lower that as it's too hot in here (split foyer house - living area is upstairs). Wonder how I could tweak that to make it more efficient?

    YIKES about the skunks! I'd be closing up the house too!

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    1. Well, the fact that my house is fairly well insulated, and I have a big shade tree helps quite a bit to conserve the indoor temperature. I've also recently installed a make-shift awning (which I'll do a post on soon) to shade the deck and sliding glass door on the west side of the house. It makes a BIG difference in the afternoons.

      The other thing that seems to be helping is that when I had the new roof installed last fall (after the hailstorm took out the old one) the roofers had to install a bunch of new attic vents to bring everything up to code. I don't have an attic thermometer, but I'm pretty sure it's helping to vent out the super heated air up there.

      CatMan lives in a two story house and his work space is on the top floor. He keeps the basement windows open and uses an attic fan for a few minutes every few hours throughout the day to blow the hot air out of the attic. He says it makes a BIG difference.

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  5. I grew up in a one story house, in a room with big French windows. Even on hot summer nights, I was never, ever allowed to sleep with the windows open. (Polly Klaus was kidnapped from her home not too far away and my mom was paranoid.) One of the pleasures I associate with being an adult is waking up slightly, refreshingly chilly with the morning fog coming in my window. I'm on the second floor, so no skunks or kidnappers! My condo faces south and gets lots of light and warmth in the winter but remains pretty cool in the summer. I think I'll look for that feature in all future houses.

    I've only lived in California (near the coast) and England, so AC hasn't really come up.

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    1. Fog! That's something I have seldom experienced in my land locked little life.

      My father also suffers from "intruder paranoia." It's risen to totally crazy levels IMHO. I mean he's nailed most of the windows shut, even on the second floor! It's totally crazy. I think the truth is that it's much more likely that there will be a fire or that they will die from heat stroke than it is that some bad guy will try to break in. But as we discussed earlier, humans are not logical creatures when it comes to assessing risk!

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  6. Easy peasy. My strategy is to continue living in England. Works a treat so long as you don't mind the occasional case of trench foot.
    ;o)
    Cathy (totally, and I mean t-o-t-a-l-l-y, sick of the Jubilee)

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    1. Ahhh, the wonders of the temperate climate. Sigh.

      And the media blast for the Jubilee has been rather amazing even here in the states. I hate to think what it's been like there!

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    2. Hey Cathy, Wales beats England for cool, wet weather ;-) It's not a bad place for avoiding the jubilee, either.

      I have to keep reminding myself that AC means air conditioning, not alternating current. Don't be too jealous, Cat, we froze at a festival all weekend and our carnival (OK, we didn't entirely avoid the royal thing) was very nearly rained off.

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    3. Rain... I'd do just about anything for some rain right about now. They've officially declared a drought here in Colorado... our snowpack (which is where we get most of our water from) was at 7% of normal, and we've only had about an inch of moisture total since the beginning of March. It's sort of like trying to garden in dust, and there are forest fires everywhere.

      But... maybe this will be motivation to finally install that drip irrigation system that I've been planning for nearly a decade now!

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  7. We might have to revisit our AC strategy. I checked the utilities for our new apartment -- ouch! I know it's a bigger space, but it looks like we'll be paying a LOT more to cool it (although we're keeping our fingers crossed that the last tenants were just really big energy hogs ;-) ).

    Anyhow, we're not home during the weekdays, and even if we were, I'm not sure your strategy would work in our triple-brick construction buildings in St. Louis (i.e., brick ovens). The brick just absorbs so much heat during the day and just keeps pumping it out at night.

    Your set-up, with a well-insulated (I'm assuming frame) house, attic fan, and efficient HVAC system sounds pretty ideal -- something to aspire to if/when we buy a place of our own!

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    1. Oh yes, the dreaded brick oven apartment. I lived in one of those for a few years. I really am lucky in that respect. Even though I pay a premium to get all my electricity from wind power, my total utility bills (gas and electric) average less than $100/month.

      Insulation is worth it's weight in gold - and there is still more I could do in that respect. I have a small amount of insulation in the walls, but could use more. I almost had a company do blown in wall insulation a year or so ago, but they wanted to drill holes to blow it in from the inside, and there are issues of lead paint - plus a good chunk of the house has fake wood panels on the walls, so it would have meant doing a complete interior remodel, and I wasn't quite ready to go there. I think with a little ingenuity, I could probably pour loose insulation into the walls from above, although the prospect of climbing around in the attic is somewhat less than appealing!

      Anyhow, I think I've read somewhere that if you have a space that you have to cool 24/7 it's more efficient to keep it cool rather than to let it get hot and then try to cool it once it's hot. But I don't know if that's true or not. You'll probably just have to experiment and see how it goes.

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    2. I second both those points. Insulation is very important (and we need to get some more) and it's more efficient to maintain a comfortable temperature than letting a house heat up and cool down (I'm talking heating here, but I'm sure the principle's the same for cooling).

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  8. I agree about the insulation. Our little wood and tin home has only foil in the walls and roof : ( We have put bats under the floors (were on stilts) and also in the rooms with ceilings but most of the house is cathedral ceilings. The only way to increase the insulation would be to replace the roof and walls! Anyhow- our A/C strategy is in direct conflict with the frugal advice to stay away from shops- we go to the shopping mall. But only if it gets over 40oCelcius. We prefer the beach but sometimes its just too hot for that too so we go to the mall and watch the zoo go about its business- we see amazing things! Im allowed a coffee and partner buys his own pie but I do see people bringing sandwiches and sitting in the food hall. We dont have animals or young children (when the grandchildren come I put on the A/C because they are just too small to cope with the heat) If your A/C straegy works I say go for it! Nothing like a cool sleep when its hot and humid : )

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    1. Wow... who builds a house without insulation? Well, you're in Australia right? I hope your climate is a tad bit more temperate than outs! Is there space in the interior of the walls and/or cathedral ceilings? If so, you might be able to do the blown in insulation thing... but you might also be left in the same position I was - having to completely redo all of the interior walls. UG.

      Anyhow, your strategy sounds reasonable to me... let somebody else pick up the tab for the cooling costs!

      And I had to chuckle at the "hot and humid" comment. Humidity is something we never experience with our near desert climate!

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  9. What did you do to your walls Eco Cat? Im always on the prowl for inspiration. I cant see us solving the lack of insulation any time soon (other than continuing to adapt to the temperature or leave the house for survival! I imagine when the time is right all the little snippets of info I have gathered will connect the dots...........

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    1. I actually ended up not doing anything, but I considered having loose fill insulation blown into the wall cavities. Not sure if this is an option for you, but most frame construction houses have a cavity between the inside and outside of the wall. I didn't do it because it would have required drilling holes in the interior walls - which would have meant a complete interior remodel/redecoration since there is wood paneling on most of the walls. Not sure how your house is made so this may or may not be an option for you.

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  10. Your method is pretty much what everyone here in the desert is going. We crank the air at night to truly chill the houses and then they stay somewhat cooler during the days. Glad to see that your a/c is working so well for you now!

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    1. A Ha! Well, you desert dwellers would certainly know the best way to use the a/c! Glad I stumbled upon this method!

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