the physics of keeping cool

June 3, 2010 10:47 PM

i need pretty specific advise on how to keep an apartment cool. but because i'm incorporating multiple cool making appliances, i was hoping to get to explain a little better and see if anybody could help.

i know there's been a billion questions about keeping an apartment as cool as possible during the summer, but i figured mine is unique in the way we would like to combine fans, portable air conditioners, airflow, sun position in the sky... the physics of it blow my mind. i was never good at science.

so i made a blueprint!

my roommates (s & m - hee) and i all want to cool down our bedrooms. almost all of the air flow in the apartment happens down by the dining room and living room. we have a screen door we keep open with a very large fan right in front of it, and that cools the living room and maybe the hallway a bit. we all use small fans in our rooms, but it's just not cutting it.

so we're thinking of getting a portable air conditioner. once we buy it, we have one of two options - pass the unit around between the bedrooms, or else position it somewhere in the hall combined with some kind of fan positioned somewhere to blow the air into our rooms.

god, i'm confusing myself with this stuff.

additional possibly helpful information:
-- the hallway is about 17 feet long
-- the sun rises on the dining room/living room side of the house and sets on the back of the house, facing mine and m's room.
-- as i'm sure anybody who knows could possibly help me with this, we need to put the air conditioner somewhere that we can run a hose out of the window.

so, in simple terms we're looking for a place to put an air conditioner, a place to put a fan, and what type of fan it should be.

please feel free to ask questions about the things i'm sure i'm not explaining clearly.

thanks!

posted by dithmer to home & garden (8 answers total)

I had a bit of a cooling problem at my old apartment. My advice:

First things first: eliminate excess heat generation:
* If you haven't already, swap out all your incandescent light-bulbs for compact florescents; because they're more efficient, they run much cooler for a given amount of light.
* Shut down any computers/TVs/etc when they're not actively in use.
* Close the blinds on your widows unless the sun is on the other side of the apartment, and make sure they're all closed when you're not home. Direct sun + windows = more heat than your portable A/C can probably deal with.

Box fans are the best for this kind of thing: they're cheap, quiet on the low setting, and move a lot of air.

To cool the bedrooms with a window A/C and the fewest number of fans, I'd put the A/C in your room with a box fan blowing from your room into S's room (or the other way around) and another box fan (positioned somewhere in the fan-wash of the 1st fan) blowing into M's room.

If you're using an A/C like this, you'll probably want to shut your windows and see if it can catch up and cool the apartment by itself, maybe with another fan cooling the common areas.
posted by cosmic.osmo at 11:16 PM on June 3, 2010

Get fans that you can put in the windows, like box fans. Have them balanced, so for example two fans on intake in two bedroom windows, and the large fan at the door on exhaust.

If you do get a portable air conditioner you're going to want to seal it up in the room that it's in, meaning door and window closed -- and if the room can't be sealed don't even bother. It's not going to be strong enough to cool the whole place.
posted by Rhomboid at 11:19 PM on June 3, 2010

Go with two portable air conditioner units (they are pretty cheap) or just use fans. Go with Rhomboid's suggestion and direct some of the fans outwards. For example have the bedroom fans point OUTSIDE and all the rest of the fans point inwards. Prop all the doors open and let the cool breeze pass through your rooms.
posted by saradarlin at 11:52 PM on June 3, 2010

Fans blow air across your skin causing energy loss from the moisture on your skin resulting in a cooling feeling as energy is removed from your skin. Fans also are essentially heaters. A 30 Watt fan is outputting 30Watts of energy in the form of heat and air vibration into the room just as a 30 Watt heater heats up the room. I'm not saying get rid of the fans but its something to consider. If the fans can be used to draw cooler air in from the outside then this is a moot point. Good insulation at doors, windows, walls etc will also help.

If you don't want to use an AC unit but want something better then fans, you can make or buy a swamp cooler (evaporative cooler.) Making... I don't know if I'd recommend because I don't know the skill level involved and it involves water and electricity. An evaporative cooler works on the same principle as a fan does on your skin as previously mentioned. Water is circulated and air is blown through it. Usually there is some sort of mesh trickling system for the water to slide down on where the air is circulated through. The water gains energy from the air, cooling the air.
posted by ebrummer at 12:14 AM on June 4, 2010

We heat mostly with wood in the winter and mostly cool mostly with outside air in the summer, so I've spent a lot of time playing around with air. Personally, I prefer lots of moving fresh air to stagnant A/C air.

Maybe this is obvious, but you should only be exchanging air with the outside when it's hotter inside than out. During the day, I keep windows and curtains closed until the house starts to warm up. At night, they're all open with fans pulling air into the bedroom windows and out the other rooms.

Also, it's probably most efficient to draw from one side of the house to the other, in the direction of the wind. The low pressure on the downwind side of the house can really help suck the air out. It's hard to work against the wind.

If your windows are double hung, you can usually reconfigure the screens/storm windows so that the top is open on the exhaust windows and the bottom is open on the intake ones, or that both the bottom and top are open (this is your best bet if you don't have fans).

All else being equal, move cold air to warm spots rather than trying to move warm air. Cold air is more dense, so has the ability to push the lighter warm air out of its way. Warm air tends to hit pockets of cold air and bounce off.

If you've got box fans in windows, block off the area that the fan doesn't occupy to create a bit of a seal.

If you want to go with straight up natural ventilation I'd do this:
Assuming it aligns OK with the prevailing wind, I'd suggest fans pulling air into your window and M's window, possibly a powerful fan (I love my Vornado for this) on the floor of the hallway blowing air towards the other side of the apartment. Fans blowing out the windows in the dining room and bathroom to exhaust the humidity and warmth of showers, computers and food cooking. S's room might be in kinda a dead spot, but a fan in that window blowing inward would probably help.

If you want to make that window A/C unit work:
Put the A/C in your window. Prop your door open and put box fans in the other bedroom doorways blowing air into them (the warm air will escape above the fan). One more fan in the living room blowing air out the window there (yes, even with the A/C running...by the time the air gets to the living room it'll be warm). Place that fan as high up as possible to get that warm crap near the ceiling. If your bathroom has a vent fan, run it non-stop and see if that helps. If your A/C unit allows it to use outside air rather than inside air, do that because you need some air exchange to keep things moving down the hallway towards the living room.
posted by pjaust at 5:54 AM on June 4, 2010

And yes, fans heat up, so try to only run them when you're actively trying to cool things down. Don't run them to circulate stagnant air around a room.
posted by pjaust at 5:55 AM on June 4, 2010

It's not clear where you are, or how hot it gets.

I'm a big fan of ceiling fans (no pun intended). I leave mine on all the time in the summer. You might ask if you can get your landlord to install them, but even if not, it wouldn't be an intolerable expense to bear.

You might also look into installing sun-blocking films on the windows of the sun-facing side.
posted by adamrice at 8:53 AM on June 4, 2010

One thing we always did was to put a big bowl of ice directly behind the fan. The fan will draw the air across the top of the ice, cooling it down before it blows it around. If you can get a broiler pan with a rack (like this) you can put the ice on top and have space for the melting water to drip into. It works great if you do it in the morning to bring the inside temp down before it can get hot during the day.
posted by msbutah at 9:00 AM on June 4, 2010 [1 favorite]