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-   -   Basement Cooling BTU requirements? (http://www.diychatroom.com/f17/basement-cooling-btu-requirements-72213/)

neilt 05-27-2010 02:07 PM

Basement Cooling BTU requirements?
 
I understand calculating BTU's for a typical room, and found that my basement requires at least 10,000 BTU for cooling, with 12,000 being preferable. However, this basement is entirely underground, with no south facing walls; It's finished and insulated. During hot summer days, the basement typically starts out 10-20 degrees cooler than ambient ground level temperatures.

My question is, I'm wondering if I can get away with a smaller AC unit. A friend recently gave me a window mount AC unit, which fits quite well in one of my window wells. I tuned it up and sucked all the dust out off the condenser and evaporator, and it runs like a champ despite it's age. However, judging by it's size, it looks like a 7,000 BTU unit (The service labels with model numbers are long gone).

Normally, one would think that an AC unit is not necessary due to how cool the basement is typically, but I have 7+ computers in the basement, with two on 24/7. The rest turn on as more people fill into the basement. Needless to say, the 10-20 degrees below quickly disappears.

Does anyone think I can get away with this smaller unit? I'll probably have it on full time while the basement is occupied, to keep it from cycling too often. I'll turn it down at night, of course.

Thanks

beenthere 05-27-2010 02:15 PM

Window well?

The unit won't work well with the condenser drawing in its own exhaust air.

But I doubt you'll need much more then 6000 to 8000 BTUs for cooling.

A person is roughly 450 BTUs of total heat. Even with all your computers on. You don't need to get rid of the full load. Since some of that heat, is still being transferred to the ground around your walls.

Yoyizit 05-27-2010 02:36 PM

Quote:

Originally Posted by neilt (Post 447687)
but I have 7+ computers in the basement, with two on 24/7.

At ~600 BTU/hr for ea. computer, this is how much heat you have to remove.
For more accuracy, read your electric meter over an interval of a few minutes, with and without the computers on. This will give you the watthours and then divide by the time interval you used to get avg. wattage.
1 w = 3.4 BTU/hr of power.

Plus, I think you have to exhaust the 1 kw generated by the A/C motor.

From
http://en.wikipedia.org/wiki/Electricity_meter

"The amount of energy represented by one revolution of the disc is denoted by the symbol Kh which is given in units of watt-hours per revolution. The value 7.2 is commonly seen. Using the value of Kh, one can determine their power consumption at any given time by timing the disc with a stopwatch. If the time in seconds taken by the disc to complete one revolution is t, then the power in watts is . For example, if Kh = 7.2, as above, and one revolution took place in 14.4 seconds, the power is 1800 watts. This method can be used to determine the power consumption of household devices by switching them on one by one."

neilt 05-27-2010 04:01 PM

Window well?

The unit won't work well with the condenser drawing in its own exhaust air.
[/quote]

I was worried about that for a short while, but the window well is actually quite shallow. Less than a foot between the top of the unit and the top of the window well. If all else fails, I'll build a sheetmetal duct. It's cooling quite well now that I built a frame for it.


Quote:

Originally Posted by beenthere (Post 447689)
But I doubt you'll need much more then 6000 to 8000 BTUs for cooling.

A person is roughly 450 BTUs of total heat. Even with all your computers on. You don't need to get rid of the full load. Since some of that heat, is still being transferred to the ground around your walls.

Thank you, that's what I assumed. It seems to be handling the load at the moment.

beenthere 05-27-2010 04:03 PM

Let us know how well it works when it has to run for 2 hours on a hot day.

neilt 05-29-2010 03:26 AM

I cut some sheet metal dividers to separate the intake from the exhaust, and using a pressure differential to my advantage (Smaller volume = greater velocity) and it worked wonders today. 10 people, with 8 computers; half of those people were complaining about being cold.

I'm glad I put the sheet metal in, I could see how it would be a requirement on a much hotter day (today was only 85). The exhaust has to be around 120F or hotter. I'm pretty sure this unit was built before the idea of an Energy Star rating was even thrown around a conference room.


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