Geothermal for Residential Home

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Jimmy7

Senior Member
Location
Boston, MA
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Electrician
Hello,

I have a customer who wants to add geothermal to his single-family home. The homeowner has already hired his geothermal contractor which is ready to start in the next week or two. The homeowner said he would eventually like to upgrade his service from 200 Amps to 400 Amps because he states his current panel is filled to capacity. As a result, he is asking me if his current 200 amp panel can handle the additional load of the geothermal system. According to the geothermal contractor, he will need a 60amp, a 40 amp, and two 30 amp circuits to run his system. With all this being said, I guessing that I will need to utilize 220.83, but do I use A or B?
 

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What exactly does “Adding geothermal” mean? Doesn’t the home already have an HVAC system that this is replacing?

And to state the obvious: Just because the panel has no open slots to add breakers does not mean the service is maxed out.

It seems 220.83(B) would apply.
 
retirede said:
What exactly does “Adding geothermal” mean? Doesn’t the home already have an HVAC system that this is replacing?

And to state the obvious: Just because the panel has no open slots to add breakers does not mean the service is maxed out.

It seems 220.83(B) would apply.
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They are currently drilling new geothermal wells, and adding a new geothermal system. I'm assuming that they are ripping out all of the existing HVAC system.
Yes, I'm aware that just because there are no available slots doesn't mean that the panel can't have any additional load. I just wanted to make sure that I'm using the correct code section.
 
Jimmy7 said:
They are currently drilling new geothermal wells, and adding a new geothermal system. I'm assuming that they are ripping out all of the existing HVAC system.
Yes, I'm aware that just because there are no available slots doesn't mean that the panel can't have any additional load. I just wanted to make sure that I'm using the correct code section.
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Geothermal should be more efficient than the old system. I’d expect the new calculation to yield a lower number than existing.
Unless it is replacing gas or oil heating.
 
retirede said:
Geothermal should be more efficient than the old system. I’d expect the new calculation to yield a lower number than existing.
Unless it is replacing gas or oil heating.
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If there is existing central air then there should be at least one double pole breaker slot opening up. I'm assuming that any existing A/C is going to be pulled, not left as standby.
 
While a ground source heat pump is more efficient, it is also going electric heat strips. While the heat strips may be seldom used they are definitely going to add to your load calc. That's probably what your 60 and 40 amp circuits are for but I wouldn't trust the HVAC guy for amperages of circuits. Get the make, model or nameplate info.
 
tank728 said:
While a ground source heat pump is more efficient, it is also going electric heat strips. While the heat strips may be seldom used they are definitely going to add to your load calc. That's probably what your 60 and 40 amp circuits are for but I wouldn't trust the HVAC guy for amperages of circuits. Get the make, model or nameplate info.
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If there is not electric heat now, I would not even consider adding it. I would use an outside thermostat to switch to what ever heat is currently being used when the temperature is too low for the heat pump to supply all of the heat.

With a ground water source heat pump, that really should not happen, but it happens all the time with an air source one.

I had an air source one in my house at one time and the cost point and the thermal break points for the heat pump were both around 32°F. When it got to that temperature the outside stat shut off the heat pump and turned on the gas furnace.
 
LarryFine said:
Not all systems do that; some run both over a temp range.
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You can make the control system do whatever you want too.
There is no way that I would install electric heat as part of a geothermal system if I didn't have electric heat before. My system was not designed to work that way...it was designed by the manufacturer to have electric heat and turn that on when needed...I just made some control changes and added the outside stat to make the switch over at a calculated temperature.
 
James L said:
Not at all.

Geothermal has a bore into the earth about 1/8 mile down.

Ground source heat pump uses something like a lateral field about 5 to 6 feet underground.

But they function similarly
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I disagree. I admit "geothermal" has become a common term for ground source heat pumps utilizing wells, but whether it's a lateral field or a well it's the same thing, a ground source heat pump.
 
electrofelon said:
I disagree. I admit "geothermal" has become a common term for ground source heat pumps utilizing wells, but whether it's a lateral field or a well it's the same thing, a ground source heat pump.
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I believe you to be correct.

True Geothermal is use of Heat generated by thermal venting or taping of heated water from volcanic activity or hot springs.
US Department of Energy state:
"Geothermal energy can be usefully extracted from four different types of geologic formations. These include hydrothermal, geopressurized, hot dry rock, and magma. Hydrothermal reservoirs have been the most common source of geothermal energy production worldwide."
 
electrofelon said:
I disagree. I admit "geothermal" has become a common term for ground source heat pumps utilizing wells, but whether it's a lateral field or a well it's the same thing, a ground source heat pump.
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get-green-now.com

Geothermal Energy vs. Ground Source Heat Pumps: What’s the Difference? - Get Green Now

There is widespread confusion between the terminology of geothermal energy and ground source heat pumps, also known by their acronym, GSHPs. This confusion is understandable when we consider that the two terms are used almost interchangeably, particularly in North America. There is also a true...
get-green-now.com get-green-now.com
Screenshot_20230726_073553_Chrome.jpg
 
The people in my neighborhood with homes on our small lake have the lateral field in the lake. I don’t know if there’s a different moniker for that?
 
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