geothermal questions and possible DIY

[buckeyefarmer]

Back up heat for a geothermal?

Modern air to air efficiency makes a closed loop an even harder choice to justify.

In my training they recommended backup. My 2 ton unit uses backup when outside temps get in the teens. My 3 ton unit never even got the backup connected, isn’t needed.

I like not having an outdoor unit. Geothermal is quiet.
But I agree, the advances in air to air makes cost hard to justify unless you self install.

 

[jigs_n_fixtures]

All heat pumps need to have a backup heat source. Depending on how many Amps you have coming in, and how far it is from the transformer, it can rapidly get very costly to run the wire to upgrade. I’ve been researching the costs of various options, because I have two old Forest Service houses with 125-Amp services I need to upgrade, from their 1962 oil burners we can’t get parts for.. I’m looking air to air with propane backup.

I did cost comparisons of various systems, and the increased cost to install geothermal loops, in our soils will exceed the cost savings from the higher efficiency in about thirty years. System design life is 20-years.

If you dont have ducts already, a MiniSplit system may make more sense. It has the advantage that each zone can independently control their own temperature. Saw some MiniSplit heads designed to go into the dead space at the top of closets. Which would eliminate the “wall wart” look.

 

[71bronco]

View attachment 782538

I bought backhoe and did it myself.

Our installer said this was not the ideal way to install. It will warm or cool the ground depending on the season and won't be as efficient as having a separate line in 4 or 5 runs. Ours was installed with a line borer 20' deep with separate lines coming into a manifold. 1 ditch about 12' long for the manifold and line bored to a 3' square hole to run 2 lines into the basement.
Our whole backyard is septic field so the lines run under that. Plus minimal mess.

Jeff

 

[Popgadget]

All heat pumps need to have a backup heat source……

If you dont have ducts already, a MiniSplit system may make more sense. It has the advantage that each zone can independently control their own temperature. Saw some MiniSplit heads designed to go into the dead space at the top of closets. Which would eliminate the “wall wart” look.

I agree completely with the second statement, but not at all with the first.
A geothermal heat pump running an open loop will not see heat exchanger water input temps below 50 degrees which is still in the sweet spot for making heat, and awesome for AC. The reason for backup heat on an air to air heat pump is that it’s capacity is greatly diminished as the heat exchanger input temp falls below 30, whether it’s air to air or a closed loop. If a closed loop is sized so that it’s temp gets close to freezing, and requires glycol for freeze protection, that’s a hint that it is not properly sized, nor as efficient as an open loop.

As far as the cost to properly size a closed loop system, that’s a whole other discussion. Most large scale closed loops use vertical wells that are grouted to conduct heat to and from the earth or bedrock, making them quite expensive. I also recognize that many sites are unsuitable for an open loop. But that doesn’t change the physics.

As I have stated before, faced with a new system today, I’d look at open loop or mini splits if efficiency was the foremost consideration.

 

[buckeyefarmer]

Our installer said this was not the ideal way to install. It will warm or cool the ground depending on the season and won't be as efficient as having a separate line in 4 or 5 runs. Ours was installed with a line borer 20' deep with separate lines coming into a manifold. 1 ditch about 12' long for the manifold and line bored to a 3' square hole to run 2 lines into the basement.
Our whole backyard is septic field so the lines run under that. Plus minimal mess.

Jeff

The design software will give you the correct amount of pipe required any way you want to configure the loops, in the end slinky’s take up less space, or less digging, but you need the area available. I expect using boring machine to be much more costly, but less tearing up of the yard. All part of the final cost.
I also installed the headers inside, and have valves on each loop, so it can be flushed with the circulation pump, instead of a flow cart. Been in 10 yrs now.
Trenches allow you to backfill around the pipes with good topsoil for the best heat transfer. Soil type also goes into the loop calculations.

 

[LD1]

If the electric heat is running in the geothermal it was probably undersized. We have had temps well below zero and my backup electric heat doesn’t kick in. The only time it kicks on is if you start jacking with the thermostat and turn it up more than one degree at a time.

Or some idiot contractor convinced the homeowner that the unit needed sized based off cooling load. See it all the time here. People spend $25-$30k for a geothermal system.....and still have to run strips when temps get down in the 20's and below

 

[LD1]

View attachment 782538

I bought backhoe and did it myself.

Looks exactly like my install

 

[buckeyefarmer]

Mine heats more than it cools. Wouldn’t think that being on the coast.

 

[ponytug]

@arto98607 That explanation makes complete sense to me. Thanks!

All the best, Peter

 

[arto98607]

I have no idea as it's not my wheelhouse, it's his. I'll never have geothermal anyway. I have biomass and all my corn is free so I have basically free heat. I heat the house and shop and my total electrical consumption is about 300 watts per hour for both stoves. Keeo the house at 70 and the shop at 65 no matter what the ambient is and the entire cost is basically free.

In order to heat my shop etc. we get the firewood from our own forest by using:

• Tractor for running chipper & hauling logs.
• PTO wood chipper for cleanup.
• Couple of chainsaws, wedges, axe, log cant, slings, tow chain with hooks etc.
• Wood splitter.
• ATV & trailer for hauling wood.
• Safety gear & work clothing etc.
• Fuel & lube the above.
• Firewood storage.
• Hurt my finger accidentally.

None of the above was free - corn sounds great!

Cheers