[TriLUG] OT: thermodynamics of A/C question

[Scott Chilcote]

Hi Joe,

Responses interleaved.

On 06/23/2012 11:47 AM, Joseph Mack NA3T wrote:
> On Sat, 23 Jun 2012, Scott Chilcote wrote:
>
>> The winter bills were especially bad because the home had hydronic heat,
>
> sounds like something from StarTrek
Hydronic heat (also called hydroheat) uses hot water to warm a house.  
Instead of having a radiator in each room, it has a radiator coil in 
each air handling unit (upstairs and down).  It pumps water from an 
extra-capacity water heater when the system provides heat.  In our case 
it was driven by a 100K BTU gas water heater, vented through the crawl 
space wall.  It has a powerful blower that sounds like a jet engine.  
Not very pleasant, since it's fairly close to the outside wall of the 
bedroom.
>
>> 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?
Open loop geothermal uses a standing column well system as the water 
source.  Image: http://www.cdhenergy.com/ghp/haverhill/Haverhill_well.gif
Water is pumped from the bottom of the well.  After going through the 
system's heat exchanger, it is returned to the top of the well.  It 
drains down through the well to complete the cycle.  Since the well is 
simply a covered hole, the water is free to circulate as part of the 
underground aquifer.
>
>> 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?
We know that a heat pump system is capable of generating temperatures 
greater than the source medium, or the 55 degree water would not be able 
to provide us with 70 degree warm air in the winter.  According to our 
installer, the de-superheater is like an additional condenser that warms 
the incoming water supply to 95 degrees year round before passing it to 
the gas water heater.   This is more economical to provide in the summer 
than it is in the winter, I'll grant you that.  But if the water from 
the municipal supply is colder than 55 degrees, you get that much 
warming for cheap.  The process that warms it from there up to 95 
degrees is still much more efficient than the natural gas burner.
> I have photos of the installation process online.
>
> OK where?
>
Sorry, here's the link: 
https://plus.google.com/photos/103715902949329457118/albums/5738857024861784257?authkey=CJGJhfyp2cfSywE

Great questions!

     Scott C.