[TriLUG] OT: thermodynamics of A/C question

Joseph Mack NA3T jmack at wm7d.net
Sat Jun 23 11:47:22 EDT 2012


On Sat, 23 Jun 2012, Scott Chilcote wrote:

> Hello LUGGers,
>
> I apologize for any potential thread-jacking,

it's about decreasing your A/C bill, so it's close enough 
for me.

> The winter bills were especially bad because the home had 
> hydronic heat,

sounds like something from StarTrek

> Despite the larger initial investment, geothermal was the 
> front runner early in the process.

> We opted for closed loop geothermal, because we did not 
> want to be dependent on the availability of local ground 
> water to have our HVAC system operate. We would have saved 
> about $5000 by going with open source,

OK closed is recirculating water in a closed system through 
pipes in the ground. What is open? I assume cold water comes 
out of the ground. Then what do you do with it?

> Due to the limited space an access in our front yard 
> (residential cul-de-sac with driveways) we had to go with 
> vertical closed loop, in the form of two 300 foot wells. 
> The loops consisted of pipes going in both directions, top 
> to bottom (like a large W with narrow Vs).  So in total it 
> was over 1200 feet of approx 1" pipe, grouted from top to 
> bottom.

interesting details.

> Drilling the wells was the largest expense, and it also 
> threw a big rock into the pond of our quiet neighborhood. 
> It took two days and created noise that could be heard two 
> blocks away.  One of our HOA officers had a tizzy, in 
> spite of the fact that the work was in full compliance. 
> The drilling rig also put some cracks in our concrete 
> driveway, but we were told that might happen in advance. 
> People with lots of yard space can save money on the 
> excavation costs.  I spoke with one fellow in a rural 
> district who rented a vibrating trencher, and installed a 
> closed loop coil field by himself.  He saved thousands of 
> dollars.


hmm.

> We contracted for a 3-ton equivalent geothermal system. 
> The rule of thumb the installer follows is 200' of piping 
> per ton, hence the pair of 300' wells.  The yield on our 
> system turned out to achieve 3.8 tons, and it cools our 
> house effortlessly.  There's no outside 
> compressor/condenser unit, just a quiet water pump mounted 
> next to the air handler in our crawl space.  We've been 
> running the house cooler than we did last summer, and the 
> bills are less than half.

I was at the Reed Gold mine recently

We entered the mine via an adit in the side of the hill. The 
mine tunnels connect to two main shafts at the top of the 
hill. With the rock inside the mine being 55deg, and the air 
outside in the mid 70's, the adit, tunnels and shafts are a 
reverse chimney, with cold air pouring out of the adit. In 
summer you can hardly hold papers in your hands from the 
stiff breeze. In winter the air flows in the opposite 
direction, into the adit and up the shafts.

> The difference over last winter was stark because our gas 
> bills rarely exceed $20 now.  We only use gas to heat 
> water, and the geothermal system (de-superheater) uses 
> recovered waste heat to pre-warm the hot water.

If the water coming out of the ground is cold, how do you 
use it to heat in the winter?

> And to bring 
> the topic back to Linux,

this thread is OT; Linux is not required

> Let me know if I can help with any information on this 
> HVAC project.  I have photos of the installation process 
> online.

OK where?

Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!



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