Geothermal 6 ton vs two 4 ton

10 years ago

Hello, we are looking at a geothermal Bosch system for our new build. Our home will be 2700 main 2200 second floor slab construction. We originally planed for a 6 ton unit but the HVAC contractor wants to do two 4 ton units (one on main, one on second). Does anyone have and advice on this?

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fsq4cw

10 years ago

last modified: 10 years ago

This site SUCKS! (too many letters!)

Part II

Will the ground loops be
connected in parallel or series, how many feet per ton, how many boreholes, what
diameter HDPE pipe?

Are you planning to install
gas irrespective of the HVAC?

Are the HPs variable speed
compressors & blowers, 2-stage or single stage compressors?

What’s the plan for hot
water?

These are just some of the
vitally important questions to understand – even before you ask a contractor, so that you will know how to evaluate
their answers. They all impact
efficiency, reliability, comfort and your overall satisfaction.

Geothermal is not cheap;
you’ll love it if it’s done right, curse it if it’s not.

Proceed with extreme caution
– but proceed – Caveat Emptor!

IMPO

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Comments (7)

mike_home
10 years ago
A house as big as yours should have a system for each floor. Two systems can keep both floors are the desired temperature and will save money.

Where are you located? Is natural gas available? Is the contractor providing you with a load calculation?
grant0830
Original Author
10 years ago
We are in Omaha, NE. Natural gas is available. We are awaiting for the load calculation. Let us know if you have any other thoughts or suggestions
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mike_home
10 years ago
In most parts of the country, it is currently cheaper to heat a house with natural gas furnace than a geothermal set up. Cooling is usually cheaper, put it can be close depending on what AC condenser you choose.

Post your gas and electric rates. We can look at the numbers to do a cost comparison.
grant0830
Original Author
10 years ago
Natural Gas is $.72 per Therm

Electric rates are...

Summer (June 1 – Sept. 30)
- 11.48 cents/kWh for all kWh
Winter (Oct. 1 – May 31)
- 10.56 cents/kWh for the first 100 kWh
- 9.13 cents/kWh for the next 780 kWh
- 5.23 cents/kWh for all additional kWh
mike_home
10 years ago
Here are some numbers you can use a general guidelines. These are the approximate costs for 100,000 BTUs:

Furnace @ 95% efficiency: $0.76

For the Heat pump I assumed a COP of 3.5. This will can be adjusted based on your geothermal equipment and outside temperature:

Heat pump @ 10.56 cents/kWH: $0.88

Heat pump @ 9.13 cents/kWH: $0.76

Heat pump @ 5.23 cents/kWH: $0.44

Your electric rates are unusually low. Do these prices include both service and delivery?

The winter design temperature for Omaha, NE is -2F. The geothermal heat pump is going to need an auxiliary heat source. If it is electric heat strips, then it is going to be more expensive than heating with gas. You could install gas furnaces as back up, but that gets to be an expensive installation. It is difficult to calculate the overall costs of the heat pump plus auxiliary heating versus just the gas furnace.

For cooling the EER for the geothermal is higher than any air sourced AC. The inverter type AC condensers like the Carrier Greenspeed can achieve an EER of 16. You have to find out the EER rating of the heat pump for temperatures in the 80-95 range to do a fair comparison. The summer design temperature for your area is 92F.

I suggest you get quotes for both systems. Your low electric rates make the geothermal system competitive for heating. You have to decide whether the higher initial costs are worth any potential savings.
fsq4cw
10 years ago
Part I

Will your GC or will you
directly hire the HVAC contractor?

How experienced with
geothermal is the contractor; what are their geothermal accreditations?

Will they provide the Manual
J load calcs & Manual D duct design?

Will this be forced air
distribution & in-floor radiant or just forced air?

Where will the mechanical
room be located?

Will the ground loops be
horizontal, vertical or diagonal; 2-separate ground loop systems if 2-heat
pumps or 1-combined ground loop system; pressurized or non-pressurized?

What gauges will be
installed on the ground loops that will allow you to monitor the systems, i.e.
temperatures and flow rates?

SR