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Help with Sizing/ Cost of Geothermal System

Posted by DelawareMama (My Page) on
Wed, Jun 27, 12 at 8:50

Hello everyone,
I've never posted here but started reading posts on geothermal systems and got pretty confused! I'm hoping someone can help at least figure out what questions we need to be asking. My husband and I are planning a build of a 2-story, 3200 sq foot home in Delaware on 2 acres (flat land). We have received bids from 3 builders so far and they have given us the following specs and prices for the geothermal (all closed-loop)

Builder 1 - 5 ton, trench installation, $22k

Builder 2 - 7 ton, well installation, $39k

Builder 3 - 5 ton, well installation, $32k

Builder 2 says that even if we ended up needing just over 3 ton on 1st floor and just over 2 ton on second, they will round up, with would be how we got to 7.

My questions - should they be rounding up or could an oversized system be detrimental? How can we figure out which size we should be going with?

Is there a big cost savings between the well vs trench?

Basically, any insight would be wonderful so that we can go back and ask the right questions.

Thanks in advance for any help!


Follow-Up Postings:

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RE: Help with Sizing/ Cost of Geothermal System

The size of the system should be based on Manual J heat gain/loss calculations. 2 extra tons of capacity is an expense you may not need.

Check out the credentials & references of the installers carefully.

There may be a substantial savings by installing a horizontal ground loop, linear or slinky. Any properly designed & installed ground loop configuration should be fine. Would these ground loops be configured in series or parallel?

Are you looking at 2 separate systems or 1 system with zoning? Is this 2 stories plus a basement?

Post the proposals in greater detail.

SR

Here is a link that might be useful: International Ground Source Heat Pump Association


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RE: Help with Sizing/ Cost of Geothermal System

fsq4cw - Thanks so much for taking the time to reply. I'm sorry it's taken me so long to follow up. We've been dealing with frustrating issues with our lot and it has caused me to want to avoid all house building stuff. Now, I'm back to it!

Unfortunately, I don't have more information. I did hear from Builder 3 who had the 7 ton system that each floor was just over the tonnage (just over 3 tons on first, just over 2 tons on second), so that each floor was rounded up for a total of 7 tons.

So my main question now is:
Will this create an inefficient system or would we have trouble with an insufficient system if we rounded down to 5 tons?

We are planning two systems (not zones) although perhaps zones would be a better way to go? It's not something we had considered. The house is 2 stories on a conditioned crawl, about 1700 sq feet 1st floor with 9 foot ceilings, 1400 second floor with 8 foot ceilings.

Again, any insight is appreciated.


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RE: Help with Sizing/ Cost of Geothermal System

I would like to be clear on the structure, 1700sq ft 1st floor, 1400sq ft 2nd floor, and no basement, just a conditioned crawl space under the 1st floor?

Has or will a Manual J and Manual D calculation be/been done?

What accreditation do these installers have?

7 tons seems rather large for the square footage you are planning, especially new construction.

I would ask any contractor suggesting 2 systems why this instead of 1 system with or without zoning? Although zoning would be better.

My first choice would be 1 system with zoning, probably 5 ton, 2-stage compressor with ECM variable speed blower fan. 2 separate systems would in effect provide zoning and may provide more DHW in that there would be 2-desuperheaters (one for each HP) feeding 1-buffer tank.

The system MUST be properly sized for cooling; there are no cheap second chances for a fix here. Too small and you will not have adequate cooling. Too large and you won't have adequate dehumidification. 2-speed compressor and variable speed blowers reduce these risks should a system be somewhat oversized.

Regarding heating mode, an undersized system can be supplemented with auxiliary resistance or gas heating and would be less expensive to install.

I would suggest asking the installers whether their design includes a pressurized or non-pressurized flow center. Pressurized may be even more desirable particularly with horizontal ground loops as there would be less likelihood of the material on top of the loop compressing the pipe at any given point.

I would also suggest asking if headers for a paralleled installation (preferred) would be placed inside the mechanical room or buried outside. Both have their advantages, headers within the mechanical room would provide for easy isolation of individual ground loops for both flushing and troubleshooting should a problem arise.

I would highly recommend the installation of a transparent flow meter (see link below) for anyone to be able to measure the flow rate at any time and to possibly see visually if air is present in the loops.

Ask if they will use a commercially manufactured, insulated flow center or would they 'build' their own, commercially built would be better. The same thing for the headers.

Any installer MUST provide COMPLETE documentation, 2 copies, one for you to keep in a safe place and another to remain with the heat pump in the mechanical room detailing the design of the system and ALL start up measurements and parameters to serve as a baseline so that any qualified service person can come on site and completely understand what's going on - particularly if your installer is no longer available or out of business! This must include detailed drawings of EXACTLY where the ground loops are located - particularly buried headers! These documents are called an 'As Built Book' and are ESSENTIAL! This is also important to have with regards to the resale of your property. A qualified home inspector will appreciate this and it would be mentioned in a report or to the client if it were present.

Become your own expert - hire accredited, experienced, recommended professionals; you'll be glad you did!

SR

Here is a link that might be useful: Blue - White


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