I'm nearing the end of design of a new ICF-walls, SIP-roof house with 3,000 SF conditioned space. Single story shoebox shape oriented east-west, with a central service corridor running the length between north (bedrooms) and south (office and living) sides. It's in Austin, Texas, a hot-humid climate, and our hill country geology is fractured limestone.

Austin doesn't seem to have been hit by the housing downturn, and I've had difficulty getting people for design work, for independent Manual J and D calculations, for example.

Anyhow, a well regarded geothermal contractor proposes:

 o WaterFurnace Model 049 4-ton heat pump with hot water option.
 o Four 300-foot wells with 1-inch U-tube polyethylene pipe with 1.25-inch polyethylene connecting pipe to the unit.
 o Metal ducts. Two zones by dampers.
 o ERV
etc.

For $42,000. I currently have no basis for evaluating this figure. My architect thought it expensive and didn't believe the suggested five to eight year payback. (We're all electric.)

Can I get any words of wisdom here to help evaluate this or alternatives? Or maybe leads to other experts in the Austin area?

Thank you!

Depending a lot on your electric rates, I'd be surprised at a 5-8 year payback on that amount.

As far as the amount itself, it sounds like a very reasonable price.

If you have the land available, a Horizonal design should shave at least 5k or so off that price.

TechGromit, in Austin's climate you'd have to get a really deep and large field. I think it would be worse digging through limestone for a horizontal field than it would be to drill. (Aside from which, our property is covered with trees that we don't want to disturb.) But thanks for raising an alternate approach.

TuffLuckDriller, thanks for your comment. I don't need an eight year payback to justify it. My wife and I want to set an example of energy efficiency (as well as having great comfort and reliability). If something is a reasonable cost for what it is, AND it makes sense compared to alternatives over the long haul, then we're for it.

You should definitely get other bids to compare to, but I say go for it. When installed, sized, designed correctly, you'll be a very happy customer.

I'm north of you in Dallas, with WaterFurnace Envision units one size smaller (3 ton) and one size larger (5 ton) than the 4 ton you're looking at.

Your well depth and number of wells/ton is same as me, along with 1" HDPE pipe.  I've got 2" pipe connecting the loop field to my units, except for the last 10' or so which is 1.5".

Assuming that you're speaking of the Envision 049, and assuming you're using a WaterFurnace IntelliZone panel, check that each of your planned zones can handle at least 900 cfm - in heating mode 900 cfm is as low as you can go.

If you need assistance with WaterFurnace installers in Texas, contact Rick Horvath, WF's Texas territory manager - his contact info is obtainable from WF's web site.

Best regards,

Bill

Bill, thanks much for those two pieces of information. I'll certainly contact Rick.
--David

David, Rick Horvath is quite familiar with my installation.  Feel free to tell Rick I encouraged you to contact him.

Also, if you're unable to find his contact info, let me know.  It should be pretty straight forward from WF's web site.

Best regards,

Bill

Seems a little high, but maybe not (wishy-washy answer, I know)

Drilling is expensive, and so is metal duct. WF is justifiably proud of their high end Envision systems. Intellizone and dampers adds even more. Make sure the geo flow center is supplied and installed as part of the job - I assume its included, you didn't list it.

Intellizone may be overkill for 2 zones of approximately equal size. A cheaper Honeywell controller might suffice (Not meaning to micromanage the bidder, just an idea)

I have 3000 SF in JAX, FL, ICF walls and spray foam roof Andersen windows and fairly decent shading. All I've needed up to 95 DB 75 Dewpoint weather with 77 F indoor is low stage on an Envision 038 (right at 30 kBtuh). That's right at what my load calc indicated as well, so I'm confident in the calc process. (System now open loop but sized in case of future closed loop)

I hope manuals J and S calcs have been done for your house incorporating your walls, doors, windows, roof, overhangs, shade, summer+winter design temps and indoor design temps and that the 049 has been selected as a result. It sounds reasonable.

I'm skeptical of a 5-8 year payback unless Austin electricity costs a heckuva lot more than the national average. A premium conventional air source system with backup strips could probably be installed for half of the proposed $42k, and my seat-of-the-pants guess is that it would cost no more than an additional $1k per year to operate, probably not even that much.

Of course if you are trying to be green and / or hedge against future energy cost increases then simple payback may not be a priority.

David, later I realized why I have 2" HDPE pipe from my loop field to almost my GSHP units.  It's because when both units are running (like they are at the moment), I'm pumping close to 30 gpm (at about 85 kBTU/h heat rejection).

Best regards,

Bill

The WF supplied dampers are very high quality, with Belimo motors that are heavy duty commercial quality.

You may have to use WF's IntelliZone panel for zoning if you want to avoid using a dump zone or a bypass duct.  The IntelliZone panel is the only way to get a PWM signal to the Envision's ECM2 fan - varying the speed of the Envision's ECM2 is a proprietary interface.  With any other panel, you're looking at only one fan speed available for 1st stage and one speed for 2nd stage.

(Still, the IntelliZone panel is not sophisticated like the Infinity - with the IntelliZone you only get 2 speeds to work with for each stage.)

I don't have a 'geo flow center' nor do I know if I need it.  I do have two purge ports in my 2" lines outside in my loop field.

Best regards,

Bill

I remember, 2-3 years ago, being really impressed with the Infinity system and asking Climate Master (Supplies Carrier geo) whether Infinity could be integrated with Climate Master - no dice: "we've been waiting for lab time..." he told me. I imagine he is still waiting.

My takeaway was that Geo is a red-headed stepchild in the huge Carrier scheme of things, and that became a point in favor of Waterfurnace.

I like the flexibility and the 'whats-going-on-right-now' LED indicators on the Intellizone board, but dip switches are so 1990s, and I'd like for dehu mode to be a tad smarter than just a one-and-done dipswitch setting...like maybe the 'stat would advise the board of high humidity and drop CFMs only when needed rather than all the time.

I had trouble nailing this down (Don't have ASHRAE Fundamentals book) but Austin design temps are about 5 degrees worse than North Florida in both directions: 98 summer and 25 winter according to one doc I found.

 

Exactly.

It's interesting to see how WaterFurnace went to advanced PWM technology to implement the 12-step speed control offered by the IntelliZone Panel, but, didn't at the same time offer a set of 'Dehum' terminals to connect a humidistat to instead of a DIP switch setting that isn't controllable by anything.

Best regards,

Bill

The geo flow center is what circulates the fluid through the ground loops and heat pumps.  Every closed loop system has one.  They are called different things by different people.

My (Grundfos) pumps are up in the attice, very close to my GSHP units.

My purge ports are out in the front yard, somewhere between the manifold and where the 2" pipes come up out of the ground to go to my attic.

I think I have the equivalent of a 'geo center,' just in generic parts.

Best regards,

Bill

Shouldn't the purge ports be high in the system to better catch any air?

Or does the flush cart's high water velocity overcome gravity and pull any air sitting higher in the system piping down and out?

(GeoDean - I'm asking you...)

Thanks

Higher purge ports are better, but not mandatory as long as you have enough velocity. An air trap in the highest spot is also a good idea.


Our goal when purging is to flush at twice the recommended flow. We have two purge carts hooked in series and we can move a lot of water.

Thanks

Wow!  Two purge carts in series.  That's a lot of water flow.

That's also a considerable investment.  And that means you've got to find 2 readily accessible, separate 20 Amp circuits to plug in to.  And that means you've probably got a significant investment too in extra-heavy duty high capacity extension cords (that are heavy).

I now understand why my pumps are up in the attic (short electrical connection to GSHP units) while my purge ports are outside shortly after the loop field manifold (not possible to haul one, let along 2 purge carts up into the attic).

I've got SpiroTop air vents at the highest points of my lines.  Is this something you install too?  And do they make it such that you don't have to get every last bit of air out of the line with the purge cart(s) because you know the air vents will finish the job over time?

Best regards,

Bill

You all have been so helpful and knowledgeable. I am grateful to you.

I've started a new thread "Unusual zoning proposal for Austin geothermal" related to this one. Hope to see you there.
--David