Subject: Re: underground air conditioning

From: [email-masked] (Dave Wood)
Date: 20 Jul 1996 20:59:50 GMT

In article <[email-masked]>,
   "Kirk Harnack" <[email-masked]> wrote:

>
>I'm working on a commercial application for cheap cooling and heating and
>I need some guidance.
>

One thing, a 12" duct has a cross section of 1 sq ft. 1000 CFM through a
1 sq ft duct has a velocity of 1000 ft per minute or 17 ft per second.
Does that qualify as low velocity air for your purpose? At 17 feet per second,
the air only has about 12 seconds to transfer heat in a 200 foot pipe. Off 
hand, I'd guess that that is too fast to cool the air off much. 

-Dave

---

From: Robert Landry <[email-masked]>
Date: 23 Jul 1996 03:25:07 GMT

Your idea is an interesting one.

My experience is that air conditioning is often the Achilles heel of 
transmitter installations.  Air conditioners seem to fail far more 
often than transmitters, and while transmitter manufacturers usually 
have someone available by phone 24 hours a day to deal with emergency 
situations, HVAC contractors, or at least the ones my employers have 
used, do not.

Using the earth as a heat-sink makes a lot of sense; it should require
less electricity and involve fewer mecahnical components.  There used
to be a hotel built over Howe Caverns in upstate New York which was
cooled using air from the cavern instead of air-conditioning. 

>Well, here's what I want to do.  I'm building a site with a 10kw and a 1
>kw transmitter.  Their combined heat output will be about 5000 watts.  I'd
>like to construct an underground system of 12" (or so) duct about 150 to
>200 feet long.  Air would be drawn in by an above-ground intake box
>located on the North side of the building (out of the sun), through air
>filters (lots of square foot area for low velocity), then through the
>underground duct system where it would (hopefully) get cooled in the
>summer, and finally into the transmitter building.  The ductwork would be
>about 6' underground and would snake its way around the large field around
>the building.  I hope that when the air gets to the building, it'll be a
>bit cooler than it was at the intake.  In the dead of winter, I hope that
>it'll be warmer than the outside air.

The viability of this approach will likely depend on the difference in 
temperature between the air in the duct and the surrounding ground and 
the length and surface area of the duct.

My approach would be to use, not a single duct with a single intake,
but a number of small plastic tubes or pipes, perhaps 1" or so in
diameter, each with its own intake, converging from different
directions to a central fan/filter unit in the building.  The combined
cross-sectional area of all the tubes would be equal to that of your
12" duct, but their surface area will be much greater. 

There is almost certainly a formula, involving the temperature 
difference, surface area, and rate of flow, that can be used to 
predict how many tubes you'll need and how long they should be. 

You'll also have to keep water, dirt and animals out of the system.

Let me know how you fare; this sounds like a really cool (pardon the 
pun) idea!

Rob Landry
WCRB Classical Radio Boston
[email-masked] * [email-masked]
http://www.cybercom.net/~umar/radio.html

---

From: [email-masked] (Donald Kulha)
Date: 23 Jul 1996 03:25:06 GMT

Kirk Harnack ([email-masked]) wrote:
: 
: kw transmitter.  Their combined heat output will be about 5000 watts.  I'd
: like to construct an underground system of 12" (or so) duct about 150 to
: 200 feet long.  Air would be drawn in by an above-ground intake box
: located on the North side of the building (out of the sun), through air
: filters (lots of square foot area for low velocity), then through the
: underground duct system where it would (hopefully) get cooled in the
: summer, and finally into the transmitter building.  The ductwork would be
: about 6' underground and would snake its way around the large field around
: the building.  I hope that when the air gets to the building, it'll be a
: bit cooler than it was at the intake.  In the dead of winter, I hope that
: it'll be warmer than the outside air.
 
    I believe an aquaintance by the name of Gary, owner of the Exeltech
inverter company in Fort Worth TX (817)595-4969, did something similar. I
believe (you should check with him though) that his system worked for a
few days (cooling) and then basically stopped being of any benefit as the
ground around his buried tubes became heat soaked. Give him a buzz and ask
him about it though.

DCK

P.S.-Recalled from a conversation at the Solar Expo and Rally in Willits
about 2 years ago.....