Geothermal Ground Source Heat Pump vs Oil Evaluation - Page 3

 



The problem is you need a 1 ton unit for each 250 ft. bore hole which will
yield 12,000 btu's. so you need 7 bore holes and a 7 ton unit to get 85,000
btu's. If you need 120,000 btu's you need 10 bore holes and a 10 ton unit.
Now that will take a great deal of electricity.

 

Hi Nog;

Nog wrote:


 > hole which will yield 12,000 btu's.

Do you really mean to say that that bore hole can
only deliver 12,000 btu's.
Heck, my furnace can deliver 10 times that amount
every hour. And your bore hole has a lifetime limit
of 12,000 btu's.

That's not very much?


Are you sure con only get 85,000 btu's?

 > If you need 120,000 btu's you need 10 bore holes and a
 > 10 ton unit. Now that will take a great deal of electricity.

That's not very much electricity?

Oh, I understand.
You don't know the difference between energy and power!

Never mind!!!!

Duane

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¶ I guess you don't know what a heat pump is! §
  Nor what one ton-hour of refrigeration is!

 



Much depends upon actual bore spacing and the soil thermal transfer
characteristics ......consider vertical loops set in a sandy aquifer--with a
water table that's always moving downstream, for instance...


Still, it would cost him one hell of a lot less in electricity than if he
was to be running straight heat strips.....

--

SVL

 

good thoughts so far.
As Nick asked, where does the 85000 BTU/hr come from? Is that a peak
load or a typical one?
is this a new house or an existing one? If it's existing, what do you
have now?
If it's a new one, then you can build the cost into the mortgage and
make it much less painful. In fact, I've seen analysis that show it to
reduce your payments because of the savings.
In my house in PA, I was going through several fill-ups of dual tanks
(~500 gallons/fill) with oil heat used for water and heat. I installed
a geothermal last winter and used the oil as backup heat for cold days
(<~15-20F) and the geothermal the rest of the year. I also got rid of
my old "high efficiency" 5-ton Carrier A/C system (~10 SEER).
This summer, my electric usage was down about 25% from last year in
spite of higher average temperatures. Last winter was very cold and the
geothermal was running 10-20 hours/day and the oil 1-5 hours/day during
January to avoid stressing the loop field too much.
I ended up using about 1 fill of oil 500 gallons, instead of 3 fills
AND my electric bills were lower! The reason my electric bills were
lower is because in PA, we get a discount for electric heat, so my kwh
charge is dramatically lower in the winter. My net savings then is
about 1000 gallons of oil and ~30% in electric bills. Back of the
envelope savings then are about $3000/year.
My system is a 4-ton system.
In addition, I've also spent the year doing as much as feasible to make
my house more efficient. lots more insulation in the attic. Low-e
windows. Air sealing every penetration I can find. I'm getting
dense-pack cellulose in the walls and cathedral ceilings next week.

Note - if I were to do it again here in PA, I'd go for a high
efficiency conventional heat pump. The reason is this - in my area,
since the balance point for my system is ~15F,  a good two stage heat
pump(i.e. Lennox XP19) with oversized heating could have a balance
point into the low 20's and work efficiently in the summer, so there's
not much difference there. And instead of paying $20k for the
geothermal install, the heat pump might be $7k. That's a lot of saving
to apply towards the incrementally greater energy costs.

The efficiency of the conventional HP won't be quite as good for the
coldest and hottest months, but in your area, you'll probably run 9-10
months at about the same efficiency as the geothermal system.  Keep in
mind, while the companies will make claims based on your ground
temperature of ~50F, as soon as your system runs in the winter, the
ground temp will drop. I installed temperature probes along with my
loops and monitored ground temp all winter. My loops were operating
below freezing much of the winter so system output and efficiency was
far less than rated.

Just some more food for thought.