Patience has rewards, young grasshopper...

The premise that "bigger isn't always better" often has to swim upstream in American culture, but there is grace and elegance (not to mention substantial savings) in having the courage to right size rather than oversize systems.

do I size the electric Aux heater so it can cover 100% of the load if Geo unit goes down? (which is the 7.6KW unit for 25900 BTU)
For some reason all the quotes have a 9.6 KW for 32700 BTU)

Posted By towpro on 17 Feb 2013 04:50 PM
do I size the electric Aux heater so it can cover 100% of the load if Geo unit goes down?

Since electric resistance heat is 100% efficient, the operating cost per BTU is
independent of the aux unit's capacity -- when the compressor isn't running.

OTOH, when used as a supplemental boost to the heat pump, it would be
desirable to use as little aux heat as possible -- but that's not necessarily
the lower capacity aux heater. For example, my 10 kW (Waterfurnace) aux
heater is actually two 5 kW units, that are controlled independently by the
heat pump's internal electronics (i.e., the thermostat logic is not involved).

When the thermostat calls for an auxiliary boost, the heat pump initially
uses only 5 kW, and doesn't turn on the full 10 kW unless/until the call
for aux heat persists for a while (5 minutes, for my system, I believe).
It's probably not a big difference, but time-sequencing two 5 kW units
may be marginally less expensive than a single higher-capacity element.

I also loved the fact that our aux heater could handle 100% of the load --
because our heat pump installation was completed almost a month before
the well driller finished the loop. So, we burned the last of the fuel oil and
switched over to aux heat for 2-3 weeks -- in the dead of winter.

yes I see that now (after digging up the paperwork on the Aux heat unit).  It will stage between 4KW and 8KW as controlled by the internal ECM.

Now the loop design.
Geology maps show my ground as
Chickies formation
Light-Gray, Hard, Massive, Scolithus-bearing quartzite and quartz schist; thin, imterbeded dark slate on top' conglomerate (Hellam member) at base.

when I use Geodesigner and click "auto size" in geo source selection, select 1 Utube at 1.25", (using Average Rock) the report shows me bore length= 245'
max cool 89 deg (average 66)
Min heating 30 deg, average 42
min freeze protection 10 deg.
Htg stage 1: = 97% Htg
Clg stage 1: =100% Ctg.
Aux heat required 1 kW with an Aux Bal point of 11 deg F

My current well will support the above, (plus 75' trench, 8' deep for feed)

local results:
First well digger wants to bring in his rig and make it deeper. Sure the numbers look better with a deeper well, but the above numbers are the results of GeoDesigner telling me how deep I need.

Which one would you pick?
everyone local (I have talked to) designs for 150' vertical loop per ton for residential.

Geo will be a 2 stage, 2 ton unit, with deheater, and AUX heat.
Building load 1700 cooling, 2500 heating.

this is using current well, then adding 1 new well deep enough to cover below loops (loops will be same length in each well)
all with 1.25" pipe. 2 parallel loops (1 in each well), manifold outside, (plus 75' each way to the house which will be average 6' under ground which is not in formula below)
 

2X 150' loops = 300'
Geothermal source
max cool 81 deg
avg cool 63 deg
Avg heat 44
min heat 33
Min freeze protect 13 deg.
Heat 3.54 COP
cooling 19.4 EER
Aux balance point 9 deg (my design low is 11 deg for my area).
cost per year $712.00

2X 200' loops = 400'
Geothermal source
max cool 72
avg cool 59
avg heat 47
min heat 37
min freeze protect 17
Heat 3.66 COP
cooling 20.6 EER
cost pear year $698
aux balance point 5 deg.
(adds 30% to well cost over 2x 150 loops)


2X 250' loops
geothermal source
max cool 67
avg cool 57
avg heat 49
min heat 40
min freeze protect 20 deg
Heat 3.74 COP
cooling 21.4 EER
cost per year $691.00
(adds 60% to well cost over 2X 150 loops)

I don't think I should quote actual prices but 30% cost is more then 1 years operation cost.

Thanks again for your opinion.

Posted By towpro on 20 Feb 2013 06:02 PM
Which one would you pick?

Have you considered a single bore 300' to 400' deep?

That has the advantage of simplicity: no manifold, fewer connections,
and excellent flow turbulence (high Reynolds number). Also, a deeper
bore yields somewhat more constant deep earth temps, and a higher
probability of getting most of the loop into water-saturated rock/soil.

I've had excellent performance with a single 450' bore (+ 50' trench)
feeding a 3-ton WF Envision. 1.25" HDPE throughout. One Grundfos
UP26-99 circulating pump gives me 8 GPM flow with 20% methanol.

In my 4th GSHP season now without the slightest problem. I'm just
15 miles from you, (near Thorndale), so geology is probably similar.

...simple is better than better,

Looby

The installer will be on site next Thursday to finalize prices.

You just gave me an idea.

If its X dollars to drill a new 150' well, then add a loop to my current well at 150', I end up with 300'.
If its the same X dollars to back up to my current well, then add 150' (to my 265' well) I end up with 1 400' loop

But if I only need 300' for 2 ton, why not just add 50' to my 265' well for 1 300' loop.
I am sure they have a min price, but its a good question to ask the driller next Thursday.

I would put two loops in the bore you have, grout with TE grout and be happy!
Eric

Thanks Eric.
I ran the software using 2-1" tubes in the same hole (6" id of steel casing).
It drops the average summer water temps around 3 deg and raises the average water temps around 1 deg in winter compared to 1-1.25" x 250' loop in the same well.
The same software shows 1-1.25" loop that is only 20' longer would preform the same as 2 1" loops in the same hole.
I know there is interaction, but I did not know it was that bad.
But this is only what software shows me. You do this for a living.

I read your website, there is some good pointers there for people looking for there first Geo system.

Sorry, I posted the same question on a different website this morning, and you answered me over there. I use the same user name on both sites.
Thanks again for you help.

Posted By towpro on 21 Feb 2013 08:01 PM
I know there is interaction, but I did not know it was that bad.

i don't think it's so much 'interaction' between the loops, but
more a case of heat available being limited by the amount of
rock/soil in close proximity to the bore. Toward the end of a
long winter, it doesn't matter much whether you've extracted
BTUs gradually with a single U-tube, or slightly more quickly
with two U-tubes in the same bore. Either way, you've pulled
the same total amount of heat out of the same rock/soil.

Just because I drill for a living, does not mean that I advocate that expense as a solution for everything. Thanx for the web site comments. Alot of time off duty goes into creating and maintaining that resource.
Eric

Posted By towpro on 09 Feb 2013 11:40 AM

But there is a superfund site within 1/2 mile (that's why they hooked me up to city water). the aquifer actually goes the other direction from my well (mine has always tested clean), but If I suck water out of the well (more then say washing a car or watering the grass), I could spread the contaminates from the super fund site over my directions. they have several test wells setup (in fact they were using mine as a test well). they would know it if I started to spread the contaminates.

Since that is the case, are you sure you can even get a permit from the powers-to-be to use your existing well, let alone drill a new one. I have serious doubts you will be able to do anything, except maybe drop a loop or two into the well and grout it in completely.

I have already talked to the powers that be. Yes they will give me a permit for Geo wells because they are grouted. In fact they would prefer I pull the pump and convert it to Geo. Once my current well is grouted, they can take if off there database of well locations in the county.

I am NE of the site, The aquifer heads to the SW, so the water is still clean on my side of the site.(was tested by EPA every 6 months, even after they hooked me up to city water).
But if I "pumped and dumped" I might draw the contaminants in my direction.