Most efficient window for an air conditioning unit?

[Feiel]

Hello everyone,

I have a practical problem I am looking to solve.

In my tiny 300 sq ft apartment in NYC I have 3 windows with exposure to the East, West, and South. It is very hot. I just purchased an 8000 BTU window unit, so in which window will the unit operate with the most efficiency?

Intuition tells me to put it in the Westerly facing window, as I imagine the air is cooler on that side of the building for the majority of the day, allowing it dump the heat more efficiently there. This is a life or death decision, because at $.25 a kWh I will either die from heat exhaustion, poorness, or my girlfriend if I get this wrong... or not if the potential gain from this is minimal.

 

[russ_watters]

Welcome to PF. I would think east would be better (though it depends on the exact direction). When the sun is east, it is morning and not very hot out, so you won't use much AC. Late afternoon is when you use the most, so that's when you won't want the unit in the sun.

I doubt the potential gain is very big, though.

 

[SteamKing]

8000 BTU is a monster A/C for your closet ... uh, I mean, your apartment.

 

[russ_watters]

Maybe not. An old apartment building may be very poorly insulated.

 

[zebidieB]

It depends on the direction. An old place can't be well ventilated so you must find the the perfect place for your air con.

 

[pallidin]

...
I doubt the potential gain is very big, though.

Yeah, my cars' air-conditioner works just fine no matter what direction I'm going.

 

[pallidin]

8000 BTU is a monster A/C for your closet ... uh, I mean, your apartment.

Hopes he meant 3000 sq/ft versus 300 !
And 8000 BTU is not usually residential.

Sounds like some type of homework question.

 

[russ_watters]

I'm not sure where you live, pallidin, but where I live (Philadelphia), 8000 BTU is not far off for 300 sq ft (450 sq ft/Ton). For example, I have a 2.5 Ton unit for 1500 well insulated square feet (600 sq ft/Ton).

 

[pallidin]

I see, well, I surely stand corrected. Thanks.

 

[russlhenley]

The west window is likely the best location due to wind, which I assume still blows from the west in NYC. In zero wind the sun becomes the major factor due to radiant heat, but remember that the a/c unit condenser fan is using convective heat distribution for cooling, therefore the greater the wind the more cooling is achieved. Also, your a/c unit is drastically oversized. Used properly a 5k btu will cool the average home in the northern US. The key word is properly, though. Leave it run day and night to remove humidity and build a cold sink. Most people turn their a/c on and off depending on whether they are home, etc. It costs way more to do that than to let a smaller unit run continuously. And remember to reduce the heat load by keeping other windows closed, radiant sunlight out when possible, and not adding heat from cooking when possible. In Ohio our kw price is less than half of yours and my a/c unit costs me roughly $30 per month for a good size home. Usually we get complaints that our house is cold and our bill is still far less than our friends' who run the big central units. Right now it is 89 deg outside and 71 inside our three story house with a relative humidity of 43%, all from a 5k btu window a/c unit which is mounted on a south facing window at the top of our stairs. The physics is the same for a/c as it is for heating, so calculate your cooling load as you would a heating load and work the numbers. Suprisingly ASHRAE still uses benchmarks developed in the last century so it's understandable that you bought an 8k unit for your apartment.