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Old 06-04-2009, 10:16 PM   #1
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cooling coil formulas?


Can anyone give me some formulas to attempt a calculation of this:

I am aware of "free area" for coils, so we don't need to address that.

But I would like to install a coil in my forced air system (for cooling).
Feed it by cold water supply.

For cold water i am interested in this:
run insulated water lines from cooling coil in forced air airstream to a coil outside the house. Have fan running on outside coil plus having water trickle over the coil to promote cooling.

will it work?
is there some formulas some one can give me to help me calculate this?

thanks,
Tin

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Old 06-05-2009, 02:44 PM   #2
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cooling coil formulas?


It will not work very well. You would need an evaporative water cooled condenser to cool the water down for recirulation.And they won't cool the water below the dew point to eliminate humidity.

Your idea is really no more than an a swamp cooler. But unless you live in a desert climate it will never work for you.

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Last edited by hvaclover; 06-05-2009 at 02:48 PM.
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Old 06-05-2009, 04:35 PM   #3
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cooling coil formulas?


Even the best cooling towers won't get the water temp low enough to remove moisture from the indoor air. If you try to do it the way you posted.

Your water temp from the cooling tower, will generally be 10F warmer then your outdoor wetbuld temp.
Thats why you won't be able to remove moisture from your indoor air.
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Old 06-05-2009, 05:23 PM   #4
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cooling coil formulas?


Thanks for the reply, I'm glad I asked before starting out on some great adventure, only to fail.

Ok, different idea. Instead of exterior coil and fan, i run pipe underground below the frost line and then have a pump with appropriate GPM.

Is there a formula to calculate the amount of pipe and and GPM based on temperature underground (which I'd have to measure). What kind of flexible pipe would I use?

Would this work?

This would be more expensive for me to implement even more so than traditional AC, but I like "green" technology.

thanks,
Tin
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Old 06-05-2009, 05:40 PM   #5
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cooling coil formulas?


There are formulas for it somewhere.

You have to know what kind of ground you have. So you know what your BTU transfer rate is for your ground. Then you need to know what your ground temp is at what depth.

From there it starts to get easier. After you know that above info, you can then size the length of your ground loop, and determine if you have enough lenght of ground to trench for a straight loop, or if you need to use a slinky loop, which means you have to make your trench wider.

From there. you just look up the table for the coil your going to use, to see what GPM water flow it needs.

Keep in mind, that you need about a 50F water temp average in the coil. Sometimes you can get away with 55F. Depends on how humid your area is.


Not to burst your bubble. BUT.

Since you want to be GREEN. How much carbon dioxide will the trencher/backhoe produce digging your trench.
How much carbon dioxide will the factory produce making your ground pipe, that is only used for cooling.
Etc, etc, etc.

Then compare that to how much carbon dioxide will your utility make for you to use a regular A/C.

Some GREEN technology produces more pollution during its manufacturing, then it saves in operation.
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Old 06-05-2009, 06:23 PM   #6
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cooling coil formulas?


Quote:
Originally Posted by beenthere View Post
There are formulas for it somewhere.

You have to know what kind of ground you have. So you know what your BTU transfer rate is for your ground. Then you need to know what your ground temp is at what depth.

From there it starts to get easier. After you know that above info, you can then size the length of your ground loop, and determine if you have enough lenght of ground to trench for a straight loop, or if you need to use a slinky loop, which means you have to make your trench wider.

From there. you just look up the table for the coil your going to use, to see what GPM water flow it needs.

Keep in mind, that you need about a 50F water temp average in the coil. Sometimes you can get away with 55F. Depends on how humid your area is.


Not to burst your bubble. BUT.

Since you want to be GREEN. How much carbon dioxide will the trencher/backhoe produce digging your trench.
How much carbon dioxide will the factory produce making your ground pipe, that is only used for cooling.
Etc, etc, etc.

Then compare that to how much carbon dioxide will your utility make for you to use a regular A/C.

Some GREEN technology produces more pollution during its manufacturing, then it saves in operation.
Thanks Beenthere,
so assuming I have a good transfer rate for my ground, and I can keep the water temp at about 50 degrees F, the ground should be able to absorb the heat from the water?
So basically coil in furnace, pump to circulate water, and underground pipe would be all I need?


As far as being green, you raise some valid points.
I will think about it.
Also it makes me wonder if the plastic pipes are recyclable.
Lots to chew on in the green department.

thanks again.
Tin
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Old 06-05-2009, 06:41 PM   #7
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cooling coil formulas?


i get green when I become irregular
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Old 06-05-2009, 08:08 PM   #8
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cooling coil formulas?


You'll also need the specific heat of water: 1 BTU per pound per degree F.

One pound of water per second will remove 1 BTU of heat and raise the water temp. by 1F.
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Old 06-05-2009, 08:33 PM   #9
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cooling coil formulas?


Quote:
Originally Posted by Yoyizit View Post

One pound of water per second will remove 1 BTU of heat and raise the water temp. by 1F.
One pound of water a year will remove 1 BTU and raise the water temp by 1F.

If the U factor is sufficient in either example.

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