Re-thinking geothermal

[BruceWard]

Rob,

I am having a geothermal heat pump installed in the house I am building. My bid is $25,500 for a 4.5 ton system including the wells, heat pump, duct work and everything else needed for new construction. My system will have 4 220' deep vertical closed loop wells. In my area the ground is too rocky to consider 6' deep trenches so we have well drillers drill 4" diameter holes that a loop of pipe is grouted into.

Also the Feds are offering a 30% rebate on geothermal systems. With the 30% rebate the geothermal is very close in cost to a normal heat pump.

 

[Rob-D]

Rob,

I am having a geothermal heat pump installed in the house I am building. My bid is $25,500 for a 4.5 ton system including the wells, heat pump, duct work and everything else needed for new construction. My system will have 4 220' deep vertical closed loop wells. In my area the ground is too rocky to consider 6' deep trenches so we have well drillers drill 4" diameter holes that a loop of pipe is grouted into.

Also the Feds are offering a 30% rebate on geothermal systems. With the 30% rebate the geothermal is very close in cost to a normal heat pump.

Yes,
I think you're right to go with it on a new house in your location of the country and I wouldn't hesitate to do it myself down there. The prices they are getting here to do it are ridiculous. I'm still waiting for one bid to come in but I think these guys are figuring that they'll make a little extra because they know we get 30% back from the government. Also I imagine there is more competition in your area where these things are more feasible.

Rob

 

[eepete]

It's simple math, 1 KWh will give you 3412.12 BTU's. You can get it from a heat pump or an electric element in your boiler but the efficiency difference isn't much.

If I had a ground temp of 56F that would change things drastically but we don't and I've seen 30 below here.
Rob

I seem to remember a "rule of thumb" for heat pumps that was something like they are 3 times as efficient as resistive electric. It's a rule of thumb because it is very dependent on the air (or for geo, the ground) temperature.


I had two 3 ton units (exact same model numbers) on my geo system. One used a loop in the ground, one used a loop in a pond. These are air units, not radiant floor units (need AC here in the south).

A pond water temperature of 40 degrees gave me 77 degree air at the 1st stage of the compressor, and 89 degree air when at the 2nd stage.

A ground water temperature of 56 degrees gave me 90 degree air at the 1st stage, and 96 degree air when at the 2nd stage. Note that 90% of the time, the units are at the 1st compressor stage.

I ended up abandoning the pond loop and putting in more ground loops. I wish my geo installer had this data before hand, he had never actually measured the difference between a pond and the ground in this area. But the point here is I think you'll want to get the exact KW to BTU for the geo unit at a given water loop temperature in order to compare it to resistive electric.

Did you price vertical wells to a ground loop? While they can cost more, maybe the water temperature would come up enough to get the efficiency you need?

Unfortunately, geo heat tend to be a 7-10 year payback item, much like solar PV panels. Various government incentives can move that around some. Right now, my energy cost are about 2 cents per square foot per month on an annual average. Have both geo heat and PV panels. But 7 more years and I'm golden!

Pete

 

[bironacad]

I did a lot of research on the Geothermal units a couple of years ago, even looked at opening a local dealership while there was the government grants. The bottom line is if everything works well you will be running at 1/3 what you would be paying in electric heat, remember that fans and pumps still use electricity. I looked at the costs and the paybacks and outside of it being better for the green deal there is no way that I could get the payback to cover the expense. That is with me doing the install and having a refrigeration mechanic cousin, lol. Also I am not sure what you pay for qualified service in your area but the more technically advanced the system, the greater the number of components, which means service. I opted for high efficient windows, over code insulation and passive solar design in the cottage. Low tech high tech. An ECM motor is expensive to replace and could take a couple of years fuel savings to change it out not counting computer boards, IMHO. My first house was $40,000 that is what you could pay for a GTH unit. Conservation will save you money. My wife and I think we can save on heating by going south and turning down the stat, lol. Good luck.

 

[Rob-D]

I did a lot of research on the Geothermal units a couple of years ago, even looked at opening a local dealership while there was the government grants. The bottom line is if everything works well you will be running at 1/3 what you would be paying in electric heat, remember that fans and pumps still use electricity. I looked at the costs and the paybacks and outside of it being better for the green deal there is no way that I could get the payback to cover the expense. That is with me doing the install and having a refrigeration mechanic cousin, lol. Also I am not sure what you pay for qualified service in your area but the more technically advanced the system, the greater the number of components, which means service. I opted for high efficient windows, over code insulation and passive solar design in the cottage. Low tech high tech. An ECM motor is expensive to replace and could take a couple of years fuel savings to change it out not counting computer boards, IMHO. My first house was $40,000 that is what you could pay for a GTH unit. Conservation will save you money. My wife and I think we can save on heating by going south and turning down the stat, lol. Good luck.

Yes, I think we're on the same page. Actually one of the reasons I wanted geo is so that I could stay with friends in the south during the winter and the house would run on low power. I built this house in 92' and I over insulated for the time also.
It's not that I use exorbitant amounts of oil but it's what I consider a wild card. That is, we have no way of controlling the expense. If oil goes up to 250 bucks a barrel than geo will be on everyone's table.
-----------------------
I just got the estimates from my excavator and I can put in a geo for around $6,800 after the 30% payback. My thinking is that I'll leave the oil boiler in and maybe the geo will work for me. Of course that's with me doing all the work except for the trenching (I'll do the backfill and reseeding). With the excavating costs I think I can go down another foot (6' deep) and still be way ahead.
The jury is still out, I'm not 100% convinced yet. More numbers to crunch but it's sure good to get everyone's views from both sides.
Rob

 

[Rob-D]

I seem to remember a "rule of thumb" for heat pumps that was something like they are 3 times as efficient as resistive electric. It's a rule of thumb because it is very dependent on the air (or for geo, the ground) temperature.


I had two 3 ton units (exact same model numbers) on my geo system. One used a loop in the ground, one used a loop in a pond. These are air units, not radiant floor units (need AC here in the south).

A pond water temperature of 40 degrees gave me 77 degree air at the 1st stage of the compressor, and 89 degree air when at the 2nd stage.

A ground water temperature of 56 degrees gave me 90 degree air at the 1st stage, and 96 degree air when at the 2nd stage. Note that 90% of the time, the units are at the 1st compressor stage.

I ended up abandoning the pond loop and putting in more ground loops. I wish my geo installer had this data before hand, he had never actually measured the difference between a pond and the ground in this area. But the point here is I think you'll want to get the exact KW to BTU for the geo unit at a given water loop temperature in order to compare it to resistive electric.

Did you price vertical wells to a ground loop? While they can cost more, maybe the water temperature would come up enough to get the efficiency you need?

Unfortunately, geo heat tend to be a 7-10 year payback item, much like solar PV panels. Various government incentives can move that around some. Right now, my energy cost are about 2 cents per square foot per month on an annual average. Have both geo heat and PV panels. But 7 more years and I'm golden!

Pete

Hi Pete,
Good to hear from you, your knowledge is always welcome.

Here's the wild card, I'll have a lot of PV along with wind and microhydro in by the end of the summer. In fact if I don't get the hydro in I'll still be up around 8.2Kw output or so from my system. Right now I'm cruising along with 1400 watts of PV.
My intertie will off set the heating element but I'm not sure I want to rely on it completely. Geo will be completely off set by the PV so once I bite the bullet for it payback will be in 3 or 4 years the most. (I usually run around 400 gallons a year oil now)
Excavating is only coming in at around 1200 to $1400 but I think it's a good idea to get an appraisal for three 200 foot wells. I would say if they come in at under 5k I'll have to start thinking about it hard but the geo PE who came out said they get 10 to 15 bucks a foot which puts them out of the running.

From what I've gotten so far the ground around here is ~42F, with your figures that won't run my radiant heat but these guys are telling me that I'll have 115F at my radiant tubes.
Rob

 

[JimRB]

I know it is not apples to apples. My house is down around Atlanta I make hot water for bathing from the waste heat recovery of the geothermal. When we have good cold snaps and the geothermal is running, I do not have the electric water heater elements turned on. In the summer the electric for the hot water heater is never turned on. All I am saying is the leftover can make hot water in the winter. But I guess my soil temp is 20F warmer. Seasonal Temperature Cycles We have an air system as AC is important. No extreme heat or cold discharge which to me makes for a more comfortable house. Not as nice as radiant floor heat but still rather comfortable.

 

[Rob-D]

The thing that keeps bouncing off my brain is Pete's comment that the ratio is 3 to 1 for geo and a heating element.

Rob

 

[bironacad]

The thing that keeps bouncing off my brain is Pete's comment that the ratio is 3 to 1 for geo and a heating element.

Rob

Remember that hydro goes up with oil and is usually more expensive BTU to BTU.

 

[Redneck in training]

The geothermal heat pump for floor hydronic system has ratio over 4 to 1 because of lower temperature rise. At least that is what the manufacturer of the heat pump says. It doesn't include consumption of pumps and fans though.
I would ask different question:
The heat pump cost about 5 to 6K, ground loop about 5 to 7K. If you need AC the 3 fan coil unit split systems would cost you about 3.5k each and you might need two for your house. The rest is the same regardless of source of heat. That is about 15K not counting installation cost.
If you can invest the amount that you save by going with direct electric heat into increasing of your own energy production you might be better off. Not to be hostage of energy cost has some value too.
Another thing to consider is almost zero maintenance for direct heat element and absolutely silent operation.