Hi,

I have propane heat and got hammered this winter on cost so looking at geo...

New member questions: (pardon me 'greeness' (no pun...)

I have about 3100sf finished spaced in 2 story home built in 2004 (plus 750sq basement finished (poured concrete) - but no ducts - baseboard heat) in SE PA.

I got multiple quotes and all contractors and most of them said i need a 5 ton system. (tranquility 27)

1) Based on the above info - does that sound right for system size?

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Also got multiple drilling quotes - because of property need 2 vertical bore holes. I got quotes for 2 375's and 2 400's. (1 1/4 pipe with methanol)

2) What would be proper depth for loop?

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Also - one driller uses 'thermal grout' which he packs down the entire hole, where the others use stone up to waterline, then regular bentonite.

3) Does thermal grout make a difference in heat transfer, enough for me to save or justify a slightly higher cost?

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Also - going to get desuperheater - was told to feed into 40gal buffer then into 60gal or 80gal electric hot water tank.

4) Is that a good/safe/efficient set up to control hot water costs?

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Anything else a newb needs to know?

Ty in advance.

One often-neglected but crucial element to the system's success will be properly designed and installed ductwork. CFM for each room should be calculated and designed.

5 tons sounds reasonable for the described house but that's a sight-unseen internet-based shot in the dark. Ask each bidder if they did ACCA manual J and D calculations and how much auxiliary heat will be needed and its estimated cost of operation.

I'm based down south (though typing this while in Montgomeryville, PA for a few days), and I often read that 150' per ton is ballpark for vertical systems up north, so your proposed wells sound about right in length.

I like to see a desuperheater feeding a buffer tank sized for a full day's hot water use, and the finishing heater sized for the worst hour's hot water use. If room permits consider enlarging the proposed buffer for optimum recovery.

I'll leave the grout issue to the well experts here, but my off-the-cuff guess is that the grout won't make much difference in the wet sections of the bores - water is a great heat transfer medium, so it helps for it to be in contact with the loop lines.

Pay most attention to the integrity, experience and reputation of the contractor.

Thanks for the fast reply - im about 30 mins sw of Mongomeryville! Great info thanks.

So are you saying a large buffer tank? SAy 60g or 80g? could it be larger than regular hot water tank?

And you think water is better than thermal grout?

Enjoy PA lol.

blackflag,
I think if you ask you will find most drillers grout, to protect aquifers from cross contamination and ensure good loop contact with surrounding soil (and to satisfy local regulations).
Your BTU loss for the home would determine heat pump size. I be suprised if a new home the size you describe wouldn't find a 4 ton heat pump capable of satisfying 92+% of the load.
Ask installers to show you operating cost comparisons between different sizes. Find out balance point (temperature at which auxiliary heat comes on) and don't be afraid of a designer who uses auxiliary coil as stage 3 vs emergency heat. I loaded a 3,300 SF two story recently in my area (Mid MI) and was perfectly comfortable recommending a 4 ton which covers 97% of load required without auxiliary. Mind you this is new construction with 2X6 walls etc that you may not have, but it is also colder here ( winter design temp 1* vs Allentown's 8*).
Read the shoppers checklist. It is my feeling that if you take care of item 1 most of the others will take care of themselves. Buffer tank size, loop length and even heat pump tonnage are more subjective.
Good Luck,
Joe

thanks Joe,

i was told its better to not be undersized, but its ok to be 10-15% over for those cold days...

i have 2x4 walls and insulation to code minimums

"Buffer tank size, loop length and even heat pump tonnage are more subjective"

can you elaborate?

thanks

Simulation says use stone below the water level and thermal grout above. And you may be able to go with a small 85% system on geothermal and use your existing system for the remainder (depending on your propane and electricity costs).

also few more questions: - is it better to run a larger system without using aux, or a bit smaller with aux?

also i have been reading here that there should not be dramatic setbacks. how many degrees would you recommend max setback in winter? and also difference in summer? (not sure if its called setback for summer lol)

jonr - is water better than thermal grout below water line?

in spite of what simulation says, proper loop install requires grout from the bottom of the loop to the top. Most State laws require the same.

Posted By blackflag on 13 Apr 2010 10:15 PM
thanks Joe,

i was told its better to not be undersized, but its ok to be 10-15% over for those cold days...
Well now you have had someone else that has told you it's not necessarily good advice:)

i have 2x4 walls and insulation to code minimums
I's all speculation without BTU load

"Buffer tank size, loop length and even heat pump tonnage are more subjective"

can you elaborate?

Short answer lots of ways to skin a cat. Concern yourself most with getting a good contractor and less with minutae.

thanks

j

geodean - thanks

so if grout all the way down - does thermal grout make a differerence for a 5 ton residential install? (is it worth the extra cost?)

and would you go 2 x375 or 2 x400?

Blackflag,

I would go 2 x 400 as long as conditions allow.

I would not pay more for thermal grout. There is no payback. We don't charge more for thermal grout since sand is cheaper than grout.

Posted By blackflag on 13 Apr 2010 10:27 PM
jonr - is water better than thermal grout below water line?

1) As always, "it depends" -- on both the rock and the grout.

2) Water tables move. Simulations ...not so much.

3) Grout prevents contamination of aquifers with surface water,
and cross-contamination between aquifers. Regardless of
local code requirements, bottom-to-top grout is the only
environmentally responsible approach.

...BTW, simulation isn't nearly as much fun,

Looby

> is water better than thermal grout below water line?

Thermally, yes, for any grout you are going to feasibly use. Your driller should have knowledge of the aquifers, water table ranges and local code.

Posted By blackflag on 13 Apr 2010 10:27 PM
jonr - is water better than thermal grout below water line?

Posted By jonr on 13 Apr 2010 11:13 PM
Thermally, yes, for any grout you are going to feasibly use.

Actually, quiescent water is a remarkably sucky thermal conductor --
it's not even as good as non-thermally enhanced 20% Bentonite grout.
OTOH, a moderate amount of water greatly enhances the conductivity
of granular solids such as sand (or rock drilling fines):

Water ......................................... 0.34 BTU/(hr-ft-°F)
20% Bentonite grout .................... 0.42 BTU/(hr-ft-°F)
20% Bentonite + 40% quartzite .... 0.85 BTU/(hr-ft-°F)
Coarse sand + 5% moisture ......... 0.8-1.4 BTU/(hr-ft-°F)
Coarse sand + 20% moisture ....... 1.4-1.7 BTU/(hr-ft-°F)

In the final analysis, a 2" thickness of [whatever] in the
well bore won't make much difference -- compared to the
thermal resistance of several yards of surrounding soil.

...don't sweat the small stuff,

Looby

thanks looby

so it sounds like grout all the way down is best way to go - regardless of type.

and looby would you recco. 2 x400's for 5ton?

Posted By blackflag on 14 Apr 2010 12:17 AM
thanks looby

so it sounds like grout all the way down is best way to go - regardless of type.

and looby would you recco. 2 x400's for 5ton?

I'm just a geeky homeowner/engineer (not in the HVAC trade), so I
wouldn't "recommend" anything. You really need a thorough design
by a competent geo professional -- with excellent references.

Just as one data point, I've been extremely happy with my 3-ton WF
Envision (NDV038) and a single 450 ft bore (in Chester County, PA).
After the first 10', it's water-saturated solid rock all the way down.

BTW, 900-1000' is about the maximum length of 1.25" pipe that'll
work in a non-branched loop with a single UP26-99 circ pump at
9 GPM (and then, only with methanol antifreeze). Etc., etc. ....

...that's why good engineers/designers haul-in TheMediumBucks™,

Looby

> quiescent water
> a 2" thickness of [whatever] in the well bore won't make much difference

Of course quiescent isn't the case and convection makes a huge difference. And what is in the well bore does make a significant difference. Try air if you don't believe this.

Posted By jonr on 14 Apr 2010 01:58 AM

> quiescent water

Of course that isn't the case.

With standing water in the bore and little/no advection, it
would be the case -- for example, a well with no backfill
and grouted only from the surface to the water table.

Thanks for the fast reply - im about 30 mins sw of Mongomeryville! Great info thanks.

So are you saying a large buffer tank? SAy 60g or 80g? could it be larger than regular hot water tank?

And you think water is better than thermal grout?



No reason why buffer can't be larger than main tank. I like a large buffer because DSH recovery works slowly over hours of heat pump operation, and during a typical day heat pump peak hours are often quite removed from peak hot water use hours, A large buffer tank bridges that gap, essentially storing a full day's maximum potential recovery for use during the day's hot water needs even if those events are many hours apart.

I'm a bit out over my skis with the grout / water question, so I will both leave it to the experts and agree with Joe that it is a trifling issue compared with selecting the most competent and honorable contractor. he / she will know the most cost effective and local code-compliant grout and well bore length solution for your area and situation.

As to the question of advection (groundwater moving sideways or perpendicular to a geo loop bore's long axis): If it occurs it will be very helpful for heat transfer, but I do not know how to predict or measure it.