Salvaging an improper geothermal install

[Astro]

A GSHP installer grossly undersized the vertical loop field on my system
and won't make it right (yes, I have offered to pay), so I'm left with
looking for alternate solutions. Bear with me on this question, as it
might be educational for other GSHP installers as it's not your typical
home-owner question. Also, for any of you prospective GSHP buyers - don't
belive the claims of 100ft/ton for a vertical direct exchange system.
Unless you're only running the system for an hour or two per day, the
ground will quickly freeze and you'll get half the rated heat out of the
system.

The 4-ton direct exchange system was installed with four, 100ft ground
loops. Ground is solid granite from 8ft down. Loops backfilled with sand.

Normal ground temperature is ~50F. Operational ground temperature runs
from 43F to <32F within 12 hours of operation.

With this system, the loops freeze after one day of normal winter use,
reducing BTU output of the system to <30,000 BTU/h, so system therefore
has to be cycled, day of use, day of rest, to provide the loop field time
to recover back up to around 43F and thence be able to produce closer to
40,000 BTU/h. Still far less than the rated 48k BTU/h.

Options are:
1) add vertical ground loops - this requires getting the original
installer involved again, and they have done a "hit-and-run", refusing to
return my calls, so this is a non-option.

2) add some system to replenish some of the energy extracted from the loop
field

3) deal with it - not acceptable. The system runs decent when the ground
temp is >40F, so I want to salvage it.


Evaluating options, I've been looking at (2) - how to replenish the energy
extracted from the loop field. This brings up other options

1) Run open loop - add running water to the vertical loops to bring in
ground temperature water. At 8-10gpm, at a dT of 10F, this would bring in
40-50k BTU/h.
Problem with this - I would have gone this way originally if i had a water
source capable of supplying that much water. a 950ft well on the property
yields only 1.25gpm.

2) Run solar and pump the heat into the loop field.
This is an intriguing idea, but at roughly 25kBTU per DAY per panel, it's
not practical. During the winter, the system is extracting 300-400
kBTU/day at 50% run time. It would definitely help though and is
advantageous because it's renewable. On the downside, this won't help in
the Summer when the loop field heats up and is unable to keep up with the
home's cooling load.

3) Run solar and heat the house directly with it.
If one installs solar hot water panels, may was well put it to direct use
and add radiant heating where possible in the house. This would directly
reduce the percent on-time of the GSHP and hence put less strain on the
loop field.
Same disadvantage as (2) in that it doesn't help during the Summer.

4) Add a horizontal slinky field, and circulate the heat transfer fluid in
the vertical loop field.
This option works by my calculations. Adding four loops and circulating
the fluid from each of these (closed) loops down alongside the exising
vertical loops can provide ~15kBTU/h per loop at a flow rate of ~3gpm with
a dT of 10F. Subtract off for inefficiencies, and it seems that this is
just about the right capacity to achieve the balance point.

I still need to compute the energy capacity of the ground in the slinky
field as obviously it will get colder as the energy is pumped out.
However, at the very least, it should greatly reduce the load on the
vertical loop field since granite has a Cp of about the same as sand, and
considerably less than clay or moist soil.

an added downside is the energy consumption of the circulator pumps.
Circulating 3gpm through 1000ft of 3/4" PEX requires a fairly hefty
capacity, I'm calculating a pump head pressure of 55-60 ft. (depending on
the viscosity of the transfer medium), though I'm not positive about that
figure. That would be times 4 to get the desired overall system energy
transfer. So If one has to run an extra kilowatt of pump to circulate
enough medium, that's going to largely negate the benefits of the added
COP yielded by heating the ground. Though it would be feasible to add PV
panels and just run the circulators while the sun is out, though Ideally
you'd want to run them when the load is highest.

If this all sounds like a Kluge, I agree. During the lead-up to the
install, I had been questioning the manufacturer about exactly these types
of questions because I was dubious about their claims that 100ft/ton was
adequate. I'd actually upgraded and ordered the 150ft/ton system but the
installer broke his drilling rig during install and insured me that the
system wouldn't suffer by dropping back to 100ft/ton.

So there's the situation. Can anybody add to this equation (other than
telling me that I've been robbed)?

tia.

 

[geoman]

You have been robbed and should sue the crap out of them!

I normally do not answer home owners questions, but this post upsets me.

This is the very reason that the costs of geothermal are going down.
EVERYTHING in the world is going up in price but Geothermals are going DOWN
!! One must ask WHY?

The reason, CRAPPY installers who don't know what the heck they are doing
AND non-engineered systems.

You cannot salvage the existing system, that is, you cannot without great
effort and headaches try to add more to this system, it is junk! I guarantee
the Reynolds numbers are wrong, pumps are wrong, header is wrong, and we
KNOW that the field is wrong!! I would even bet the load on the house is
wrong along with the ducts not being engineered correctly!!

If you promise to sue this jerk or company I will offer my services for
sizing the loop for free! But only if you PROMISE to sue them! They need
to be put out of business so they don't ruin this industry by reducing the
prices and giving the systems a bad name.

Post your reply here, and if you promise to sue them then list where you
live so I can run the numbers. I also need the equipment that is installed.

Man, this really ticks me off. I loose so many quotes from dealers like
this!

OH, BTW, find out if this driller is certified for this type of work! Just
because he can put wells in doesn't mean he's approved to put vertical loops
in.



Rich

 

[geoman]

I have a water well. Can it also be used as part of a geothermal system?

EPA wont let you mix the two. IF the well is tested to allow enough GPMs
then it may be possible.

 

[William P.N. Smith]

a 950ft well on the property
yields only 1.25gpm.

Are you using that well? How about running it thru a heat exchanger
and dumping it back down the well. Worst case you've just added
another 950-foot loop...

So there's the situation. Can anybody add to this equation (other than
telling me that I've been robbed)?

Uh, news flash. 8*} Can you talk to your state's attorney general?

 

[Jon Elson]

A GSHP installer grossly undersized the vertical loop field on my
system and won't make it right (yes, I have offered to pay), so I'm
left with looking for alternate solutions. Bear with me on this
question, as it might be educational for other GSHP installers as
it's not your typical home-owner question. Also, for any of you
prospective GSHP buyers - don't belive the claims of 100ft/ton for a
vertical direct exchange system. Unless you're only running the
system for an hour or two per day, the ground will quickly freeze and
you'll get half the rated heat out of the system.

The 4-ton direct exchange system was installed with four, 100ft
ground loops. Ground is solid granite from 8ft down. Loops backfilled
with sand.

Can you get to the level where the top of the sand is? How about
pouring tens of gallons
onto the sand, and possibly "topping it up" every once in a while? You
might want to
install pipes of hoses to apply the water.

That solid granite is not typical in general, but might be common in
your area. The driller
should have notified the installer of what he found when drilling, as it
should have been taken
into consideration as the system was built. They should have drilled
deeper, or made more
holes. I'm sure that 400' of GT wells would work fine in a place with
wet, sandy soil all the
way down.

Normal ground temperature is ~50F. Operational ground temperature
runs from 43F to <32F within 12 hours of operation.

With this system, the loops freeze after one day of normal winter
use, reducing BTU output of the system to <30,000 BTU/h, so system
therefore has to be cycled, day of use, day of rest, to provide the
loop field time to recover back up to around 43F and thence be able
to produce closer to 40,000 BTU/h. Still far less than the rated 48k
BTU/h.


1) Run open loop - add running water to the vertical loops to bring
in ground temperature water. At 8-10gpm, at a dT of 10F, this would
bring in 40-50k BTU/h.
Problem with this - I would have gone this way originally if i had a
water source capable of supplying that much water. a 950ft well on
the property yields only 1.25gpm.

You could install a larger pump, and make the system semi-closed loop,
by returning the
used loop water to the well casing.

2) Run solar and pump the heat into the loop field.
This is an intriguing idea, but at roughly 25kBTU per DAY per panel,
it's not practical. During the winter, the system is extracting
300-400 kBTU/day at 50% run time. It would definitely help though and
is advantageous because it's renewable. On the downside, this won't
help in the Summer when the loop field heats up and is unable to keep
up with the home's cooling load.

3) Run solar and heat the house directly with it.
If one installs solar hot water panels, may was well put it to direct
use and add radiant heating where possible in the house. This would
directly reduce the percent on-time of the GSHP and hence put less
strain on the loop field.
Same disadvantage as (2) in that it doesn't help during the Summer.

3 HAS to be more efficient than heating the ground, too! However, your
loops may be so well
isolated from groundwater that they form a pretty good thermal storage
mass, too.
Jon

 

[daestrom]

an added downside is the energy consumption of the circulator pumps.
Circulating 3gpm through 1000ft of 3/4" PEX requires a fairly hefty
capacity, I'm calculating a pump head pressure of 55-60 ft. (depending on
the viscosity of the transfer medium), though I'm not positive about that
figure.

One thing to keep in mind is the head loss through a pipe goes by the
inverse of the diameter raised to the fifth power (no, that isn't a typo, I
really said '^5' So if your head pressure is 55 ft for 3/4" ID, then it
would drop to only about 13 ft with 1" ID pipe. And 4.28 ft head with 1
1/4" pipe. You also get slightly larger surface area

The downside is you get a lower velocity in the tube (for the same gpm), so
the internal heat-transfer film coefficient won't be quite as good. For the
1" ID pipe, velocity would be ~56% of that in the 3/4, and 1 1/4" would be
down to 36% of the 3/4.

A lot of heat-exchanger manufacturer's shoot for a water velocity of between
5 and 7 ft/second when using water for the medium. This seems to be the
'sweet-spot' between best heat-transfer coefficient and pumping losses for
water. I suppose other fluids would target a different spot based on
visocity and thermal conductivity of the fluid though.

daestrom

 

[George Eberhardt]

I talked to the manufacturer of a GSHP a while ago. I was told that I
needed 10 to 16 vertical loops of about 75 to 100 feet, drilled at 45
degrees. From your comments this appears about right. I would talk to the
manufacturer about what remediation you need. They will have at least one
engineer who actually knows what it will take. Then I assume you will have
to drill additional vertical loops.

And could you tell us just who is the manufacturer of your GSHP?

 

[Astro]

Astro

Just to clarify

You are talking about a direct expansion system where you are
circulating refrigerant?

Thanks for all the replies! I'll try to summarize my answers here to
reduce bandwidth...

- this is a direct expansion system - R22 circulates in copper ground
loops. Sorry that wasn't clear in the earlier post. I'm getting too used
to using lingo.

- Heat load: over the last couple years, I've had a number of people in to
propose replacement heating/cooling systems. All estimates have come in 4
or 5 tons at a design temperature of 0-5F, except one that came in at ~8
tons (heating). I ran a manual-J using commercial software and came up
with ~4 tons as well as doing a manual calculation of my own and came up
with somewhat less, but this did not include infiltration losses which
could add considerably. Anyway, this in fact really doesn't come into the
numbers I've calculated as I will discuss later...

- I have access to the entry points of the loops. The original backfilling
was done totally improperly so I had to do it myself. It was supposed to
be (and is) filled with all sand, no grout. This is done because the loop
temperatures are much more extreme than a water loop which can cause
cracking and separation of the loop from the grout.
As such, when I backfilled, I flushed the sand in with hot running water.
Lots of it. When you do the calculations, you'll find that the heat
capacity of the water is relatively low compared to the amount of energy
that's being pumped out, though it does help the heat conduction.
One plan was to add an irrigation system to the loops, exactly as Jon
Elson suggested. But with the minimal capacity of my wells, the numbers
just don't add up to a winning situation.

- Prior to install, I exchanged a number of notes with the manufacturers'
engineers and the installer regarding system performance. I questioned the
100'/ton figure they gave because everything else I've read indicates that
you want 200'-300' of vertical bore per ton. They assured me that the
thermal capacity and diffusivity of the granite would be ample to support
the load. However, to be on the safe side, I opted for the upgraded system
with 150'/ton. Unfortunately, as noted, that didn't work out because the
installer broke his drilling rig.

- The installer did the drilling himself. This isn't a small-time
operation either. This company is specializing in GSHP systems and came
highly recommended by the manufacturer!

- I did geologic research prior to install and discussed the ground
composition with the manufacturer and installer. They knew that I was
sitting on a solid diabase intrusion. Further, I told them that the ground
water movement was near nil up on the hill where I live. They said that
the diffusivity of the granite should be a benefit and that I shouldn't
worry. The diffusivity of granite is indeed good, but nonetheless, there's
only so much heat that can be extracted from a 100' section of granite if
you're drawing heat out faster than it can migrate back in.

- Given the research done prior to install, I opted to install temperature
sensors on each of the loops and in a control bore so that I could monitor
ground temperature. Everything was tested/calibrated prior to install and
all sensors showed a ground temperature of ~51F at install.

- The BTU output of the system was calculated by measuring the air in/out
temperature at the air handler and knowing the approximate flow (1600CFM).
Calculations have been done using a variety of assumptions to give a range
of outputs. Even with the most liberal figures, I'm getting a temperature
rise of 23F. Under normal conditions, the dT is more like 18F after maybe
8 hours of use.

- Regarding winter temperature reduction of loop field - I kept my
existing baseboard hot water heating system to use as backup heat. This is
run as the primary heating source every other day so that the loop field
can recover back up to 40F-43F after 25-36 hours.

- Daestrom - thanks for the note on head vs. pipe diameter and typical
figures for flow rates. It's good to know what works in practice.

- Abby Normal - In retrospect, I should have gone with a 5 ton system.
Even though I researched this extensively prior to install, I hadn't
realized how fast the ground temperatures drop during use. Therefore, my
assumptions on the balance point of the system were flawed. The system
would be perfect for all but the coldest days here if it were putting out
40k BTU/h steadily, but when it drops to below 30k BTU/h when the ground
freezes), it's fighting a losing battle and I have to turn it off for a
day to thaw out. Right now, this is the case if it runs for a couple days
of around 30F outdoor temperatures, not what I'd call real cold!

- I've kept daily run time data along with heating degree days, average
temp, backup-heat usage, etc. This shows me quantitatively how the system
is performing vs. the heating load. Basically, it supports my observation
that when the loops freeze, the system is incapable of supplying enough
heat. to be worth running.


On the positive side, I've learned a lot about HVAC/R and GSHP systems
I have a lot of respect for quality HVAC/R people, because this field does
require a broad array of in depth knowledge and you really have to be on
your game to be good at this.

 

[Astro]

I talked to the manufacturer of a GSHP a while ago. I was told that I
needed 10 to 16 vertical loops of about 75 to 100 feet, drilled at 45
degrees. From your comments this appears about right. I would talk to
the
manufacturer about what remediation you need. They will have at least
one
engineer who actually knows what it will take. Then I assume you will
have
to drill additional vertical loops.

And could you tell us just who is the manufacturer of your GSHP?

How big a system was that for? My guess is that if I had 12 loops, I
wouldn't be having these problems today.

The manufacturer specs 50 or 100 ft loops and stated that installers
prefer the 100ft. loops because it reduces setup/install time. More 50'
loops would be typically better because of increased ground area.

Something else I forgot to mention - the loops are supposed to be about
15' apart based on the IGSHPA. The loop field that my guy made put the
loops a scant 6' apart.

I had a couple good contacts at the manufacturer but once the install was
done and the checks cashed, they stopped communicating with me. Likewise
for the installer. They are totally ignoring my requests for remediation.

At this point, I'm not going to name names. While I'm exceedingly
frustrated with installer and manufacturer, I don't want to totally burn
my bridges. However, if they persist in ignoring my requests for help, I
won't hesitate to let everybody know about their business practices.

 

[Gunnar]

[snip]

At this point, I'm not going to name names. While I'm exceedingly
frustrated with installer and manufacturer, I don't want to totally burn
my bridges. However, if they persist in ignoring my requests for help, I
won't hesitate to let everybody know about their business practices.

This sounds like a horror story. I hope you have written communication with
the manufacturer, looks better in court if it gets that far. Sue them sooner
than later!

How much has the installation cost you so far? It would be nice to see a
breakdown of cost if possible.

Best of luck in resolving this.

Gunnar.

 

[Astro]

[snip]

At this point, I'm not going to name names. While I'm exceedingly
frustrated with installer and manufacturer, I don't want to totally burn
my bridges. However, if they persist in ignoring my requests for help, I
won't hesitate to let everybody know about their business practices.

This sounds like a horror story. I hope you have written communication
with
the manufacturer, looks better in court if it gets that far. Sue them
sooner
than later!

How much has the installation cost you so far? It would be nice to see a
breakdown of cost if possible.

Best of luck in resolving this.

Gunnar.

system install was ~$17,000. No breakdown. Single supplier for equipment
and drilling.
This included Trane variable speed air handler, drilling/installing 4,
100ft vertical loops, compressor setup and patching into my existing
ductwork.

They did not have to install new ducting and did not install new
vapor/liquid lines.

It took about a full day of drilling to drill the 4 1/2 bores (before the
drills broke). Drilling done by one of the company principals. Two kids
did the rest of the system install up to system startup where the
principal did the vacuum and refrigerant work.

One of the kids was a trained plumber and very competent and careful. The
other was a trainee. Took them two days. Conditions were miserable - cold
and rainy. I spent about half the time out in the mud with the guys,
bought them pizza, coffee etc. and tried to learn while staying out of
their way. They were real troopers. Tipped them each $100 since they were
honest, hard workers.

Throughout this entire thing, I've tried to be as congenial as possible. I
understand that we're "married", as the system will need maintenance. So I
want to treat them as partners. Unfortunately, they don't seem willing to
play their part.

As geoman noted, it's unfortunate that companies like this exist as it
gives the industry a bad name. I think the technology itself is excellent
and, properly installed, has the capability of greatly reducing our
national energy demands.

c'est la vie.

 

[William P.N. Smith]

Throughout this entire thing, I've tried to be as congenial as possible. I
understand that we're "married", as the system will need maintenance. So I
want to treat them as partners. Unfortunately, they don't seem willing to
play their part.

Explain that to them again in writing, and offer to get your state's
Attorney General involved if that will help you resolve your problem.

You _MUST_ document all (successful and failed) communications
attempts for future use, as "Your honor, I called them a lot and left
messages a lot and they never called back." is far less effective than
"Here's a list of dates and times that I called, what messages I left,
who I spoke to, and what they said." which in turn is far less
effective than "Here's a copy of all correspondence." Get the
manufacturer involved, and explain that the installer they reccomended
is making their system look bad.

As always, be unfailingly polite, just state that you've spent a ton
of money and are unhappy with the performance of the system, you want
them to make it right, and if they can't/won't communicate with you in
a spirit of resolving problems and making the customer happy, you're
willing to involve the law to get things straightened out. Once the
Attorney General explains that their business license is at risk I bet
they come to you hat in hand asking what they can do to make you
happy. They might even learn something about the systems they are
installing and quit cutting corners, make more happy customers, and
have a more profitable business.

 

[George Eberhardt]

How big a system was that for? My guess is that if I had 12 loops, I
wouldn't be having these problems today.

Sorry, I intended to include this information. It was for a 5 ton system.
The reason for the 45 degree drilling is that the heads of the bores had to
be in a 16 foot diameter maximum circle. And by drilling at 45 degrees, you
increase to separation of the bores at depth. I had an estimate of $15,000
to drill the bores and install/grout the copper; I live in New Jersey, and
the regs here are apparently very expensive.

 

[geoman]

Explain that to them again in writing, and offer to get your state's
Attorney General involved if that will help you resolve your problem.

If his State Attorney is anything like Ohio's he has a better chance of hell
freezing his loop before he gets any satisfaction.........

 

[geoman]

Thanks for all the replies! I'll try to summarize my answers here to
reduce bandwidth...

- this is a direct expansion system - R22 circulates in copper ground
loops. Sorry that wasn't clear in the earlier post. I'm getting too used
to using lingo.

Abby, GREAT question! I was thinking, "who would go vertical with this
design with a ground loop!!"

Now that its determined that its a DX system I can't help you out since I
have no engineering data or experience with them

Rich

 

[daestrom]

Thanks for all the replies! I'll try to summarize my answers here to
reduce bandwidth...

- this is a direct expansion system - R22 circulates in copper ground
loops. Sorry that wasn't clear in the earlier post. I'm getting too used
to using lingo.

- Heat load: over the last couple years, I've had a number of people in to
propose replacement heating/cooling systems. All estimates have come in 4
or 5 tons at a design temperature of 0-5F, except one that came in at ~8
tons (heating). I ran a manual-J using commercial software and came up
with ~4 tons as well as doing a manual calculation of my own and came up
with somewhat less, but this did not include infiltration losses which
could add considerably. Anyway, this in fact really doesn't come into the
numbers I've calculated as I will discuss later...

- I have access to the entry points of the loops. The original backfilling
was done totally improperly so I had to do it myself. It was supposed to
be (and is) filled with all sand, no grout. This is done because the loop
temperatures are much more extreme than a water loop which can cause
cracking and separation of the loop from the grout.
As such, when I backfilled, I flushed the sand in with hot running water.
Lots of it. When you do the calculations, you'll find that the heat
capacity of the water is relatively low compared to the amount of energy
that's being pumped out, though it does help the heat conduction.
One plan was to add an irrigation system to the loops, exactly as Jon
Elson suggested. But with the minimal capacity of my wells, the numbers
just don't add up to a winning situation.

- Prior to install, I exchanged a number of notes with the manufacturers'
engineers and the installer regarding system performance. I questioned the
100'/ton figure they gave because everything else I've read indicates that
you want 200'-300' of vertical bore per ton. They assured me that the
thermal capacity and diffusivity of the granite would be ample to support
the load. However, to be on the safe side, I opted for the upgraded system
with 150'/ton. Unfortunately, as noted, that didn't work out because the
installer broke his drilling rig.

Well, I don't have any direct experience with GSHP's, but I'm doing a little
'noodling' around with numbers on a spreadsheet here and this is what I've
figured out so far.

If you treat a bore hole as 1 ft diameter and 100 ft long cylinder
surrounded by granite, the calculations of temperature gradient across the
granite are pretty straightforward if you assume the steady state and the
surrounding granite is uniform temperature. One could add on the lower
hemispherical region as well, but maybe later. Looking around on the 'net,
I found a few numbers for granite, ranging from 2.3 to 3.9 W/m-K. Assuming
2.5 W/m-K as sort of towards the worse end of the spectrum, that's 1.44
BTU/hr-ft-R (if I got my units right ;-).

With To - Ti = q/(2*pi*k*l) * ln(Ro/Ri) for a cylinder, and assuming you try
and pump 1 ton of heat out, then in the steady-state you would have a
temperature gradient in the first foot moving outward from the bore of
app...

To - Ti = 12000/ (2*pi*1.44*100) * ln(1.5/.5) = 14.5 R. Moving out to
distance 3 feet from the bore center, it would seem to be =
12000/(2*pi*1.44*100) * ln(3/.5) = 23.7 R. Frankly, these seem like pretty
strong gradients for natural rock, but what the heck.

Applying some calculus we can find the theoretical temperature gradient at
any distance. The gradient drops to less than one degree/ft only when the
radius gets out to about 13 foot radius. At that radius, the central bore
is 44 F cooler than granite at 13 ft. If the ground temperature is only ~45
F to begin with, this means the central bore would *have* to be around 1 F
to sustain a long term heat output of 12000 BTU/hr. Mind you, this is
just out to the 1F/ft radius, that probably isn't the true radius of
influence of this bore, I just chose 1R/ft as a guess.

So with multiple bores as close as 6 ft, it is clear that their 'radius of
influence' overlap. And that's bad. The temperature gradient to get 12000
BTU/hr must be even steeper on the sides away from neighboring bore holes to
make up for the interference caused by the neighboring bore hole cooling the
granite on the sides between neighbors

Of course you don't need to run continuous (at least most HVAC systems are
designed not to require that), but on really cold days (like this on in NY
where we broke some records at -11 F), you might need/want this much
capacity.

The hemispherical zone at the bottom would help this a bit by allowing
conduction from directly below the end of the bore. But there are other
factors that make further refinements kind of moot. Things like the
temperature gradient going down the bore is probably not uniform, and the
area near the surface is influenced by the surface temperature.

Water in soil will generally improve the situation since water's thermal
conductivity is higher than diamotaceous earth (~0.4 BTU/hr-ft-R vs ~0.04
BTU/hr-ft-R). But it needs to permeate the entire soil around the bore
whole. And that's something you don't have (IIRC you indicated these bore
holes were in solid granite).

Frankly, using these calcs for normal soil seems to show that 1ton/100 ft is
not a practical number there either. Either my calcs are off because I
missed something, or 100ft / ton is wildly optimistic. And the 'radius of
influence' would seem even larger for poor thermal conductivity soils. Or
they conventionally rely on *moving* ground water to increase the heat
available by convection.

One thing I'm not clear on, is if the liquid refrigerant enters the bore
hole through an pipe and descends to the bottom, then vaporises as it rises
up a second pipe, it would seem some of the heat gained in the deep part of
the bore is lost as the refrigerant passes out the last 10-15 ft near the
surface. That is to say, the flowing refrigerant is warming some of the
frozen rock near the surface with deep well heat, instead of coming into
your home. Or do they insulate one pipe to avoid this?

Thoughts??

daestrom

 

[Jon Elson]

One thing to keep in mind is the head loss through a pipe goes by the
inverse of the diameter raised to the fifth power (no, that isn't a typo, I
really said '^5' So if your head pressure is 55 ft for 3/4" ID, then it
would drop to only about 13 ft with 1" ID pipe. And 4.28 ft head with 1
1/4" pipe. You also get slightly larger surface area

The downside is you get a lower velocity in the tube (for the same gpm), so
the internal heat-transfer film coefficient won't be quite as good. For the
1" ID pipe, velocity would be ~56% of that in the 3/4, and 1 1/4" would be
down to 36% of the 3/4.

A lot of heat-exchanger manufacturer's shoot for a water velocity of between
5 and 7 ft/second when using water for the medium. This seems to be the
'sweet-spot' between best heat-transfer coefficient and pumping losses for
water. I suppose other fluids would target a different spot based on
visocity and thermal conductivity of the fluid though.

This may be to optimize size and materials for an all-metal heat exchanger.
The heat flow per square foot in this case is VASTLY lower due to there
being
negligible fluid flow on the outside of the pipe. So, I think the
thermal diffusion
becomes significant when the turbulent flow is not dominant. Anyway,
the owner
of this disaster probably wants to avoid pulling up the loops that are
already in.
And, running several thousand feet of large-diameter pipe horizontally
is going to
get darn expensive, too. Probably running parallel loops of smaller
pipe spread out
in the field will end up performing better than one big pipe.

Jon

 

[Jon Elson]

How big a system was that for? My guess is that if I had 12 loops, I
wouldn't be having these problems today.

The manufacturer specs 50 or 100 ft loops and stated that installers
prefer the 100ft. loops because it reduces setup/install time. More
50' loops would be typically better because of increased ground area.

Something else I forgot to mention - the loops are supposed to be
about 15' apart based on the IGSHPA. The loop field that my guy made
put the loops a scant 6' apart.

Oh, MAN! That's certainly reason to sue, right there! He just
blatantly decided to ignore
the expertise of those who had fought this battle before! Fifteen feet
is just about the MINIMUM,
especially in the solid granite!

You need to check out the small claims procedures in your state. The
fix for this, however,
may well exceed the limits of small claims court.

Jon

 

[Sylvan Butler]

Options are:
1) add vertical ground loops - this requires getting the original
installer involved again, and they have done a "hit-and-run", refusing to
return my calls, so this is a non-option.

This seems by far the only real solution. Can the manufacturer
recommend another installer in your area that will do the work?

BTW, if you have any warranty issues, you will want to have proper
service available...

4) Add a horizontal slinky field, and circulate the heat transfer fluid in
the vertical loop field.

Or simply use the horizontal as supplemental heat transfer area. Or is
splicing into the existing lines the reason why you need the installer
for option #1?

How deep would you be able to place the added field? Obviously it has
to be significantly below the frost line, or you get nothing.

an added downside is the energy consumption of the circulator pumps.

Which is yet another advantage to adding it to the existing system
rather than trying to add heat/cool to the existing vertical loops.

Larger pipe will reduce the energy needed to overcome friction, as will
parallel rather than serial loops.

sdb

 

[geoman]

Sorry, I intended to include this information. It was for a 5 ton system.
The reason for the 45 degree drilling is that the heads of the bores had
to
be in a 16 foot diameter maximum circle. And by drilling at 45 degrees,
you
increase to separation of the bores at depth. I had an estimate of
$15,000
to drill the bores and install/grout the copper; I live in New Jersey,
and
the regs here are apparently very expensive.

The idea of drilling 45 degrees is very interesting! I have never heard of
this practice before but I can see several advantages to it, having a slight
cave in before putting the tubing in isn't one of them!

Now, as to Astro's drilling, I have had the same problem with a driller when
I put our first system in. He came up with a 'rule of thumb' and I was too
green to catch his stupidity. He drilled for a GSHP system 150 feet per ton
spaced 6 feet apart. Guess what, It didn't work! Now that I calculate things
myself I have never quoted anything less than a total of 200ft per ton
vertical and a minumum of 15 feet apart. But this is NOT a rule of thumb,
there is NO such thing as a rule of thumb, ever when it comes to designs in
geothermals.