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.

 

[flyingcow]

Rob,
How much oil you use a year to heat your house? And how much$$$'s is your electric bill?

 

[AHNC]

I would suggest that you look at minisplit heat pumps. You will not get the same COP as a water source but you will be very close. As well, with your radiant heating you will find the mshp the ideal compliment. No matter how you try to control it radiant is best when you have a substantial load against it. The lead/lag issue on slabs is a problem in the shoulder seasons, the mshp will do better than the radiant in that condition. Go to miniheat.com and run a few numbers. Pay particular attention to the table showing the hrs/yr at a temp. Buy it for the heating efficiency as, in the north, itis there that you get your return on investment. As well, you get very high effiency cooling/dehu. I must include this disclaimer. I represent Fujitsu in New England, but I use them as suggested in the home I just sold in Feb and the home I'm moving into.

 

[leonz]

Hey Rob,

Another option is building a deep pond and lining it to hold water and then running loops of black PVC and securing the loops down with cinder blocks to hold them down in the deep water for you.

The deep pond will take up less time digging but you need to buy a good pond liner.

 

[KennyG]

I think the original poster has the correct take on the issue. If the ground is only 42 deg, it's not going to be too efficient on heating. However, I'm really surprised that it would be that cold at 6 ft down. To get a good measurement, you have to excavate, bury a probe, fill and compact and then wait for it to stabilize. If you measure the exposed earth after you excavate, I would doubt that it's a good reading.

It would defeat your advantage in doing your own work, but vertical shafts seem to be the preferred way to go these days. Drilling costs are way down in a lot of areas and a few 100 ft. deep boreholes will provide the heat sink.

 

[buckeyefarmer]

In my area, 5' deep trench is adequate. You can make up for depth with more loop. The difference for me from 6' to 5' deep was about 20' more of pipe per loop, which is probably cheaper than digging the extra foot.

GHP are also 4-5 to 1 as efficient as straight electric coil heat.

Search some of the other threads on Geothermal that have been posted here.

 

[Brad_Blazer]

Thanks for your comments but I think you're both missing the point. Geothermal is a closed loop system with the ground temperature being higher than the ambient outside temperature in winter and lower in summer.
That's all well and good but we still have to convert that temperature difference to heat regardless of how we do it. The greater the difference the greater the energy expended to reach the final temperature.

With two systems both being closed loop, one running off geothermal and the other off a heating element in the boiler, the one with the lowest temperature differential will use the least amount of energy.

The first question I'm asking is how can a system that costs anywhere from 15 to 30k compete with a system that uses a 15 dollar heating element from Home Depot? The payback is tremendous.

Secondly, even if my measurement system is incorrect by 5F, which it isn't, I will still be better off with the heating element because the temperature differential is lower than the geo ground temp regardless what source or method I use to capture it.

Rob

You have it pretty mixed up in this post. Electricity is high quality energy. You can convert it directly into heat at 100% effficiency at as high a temperature as your materials can withstand. The temperature difference from a resistance element in the duct to the air in the duct will self regulate to transfer all of the energy to the air as long as there is enough air flow to prevent the elements from burning up.

Electricity can also be converted into work with high efficiency. The work can run a heat pump which pulls ADDITIONAL energy from a low temperature heat source into your home. Any efficency losses convert work into heat which is still utilized as output. The WORST result you can get from a geothermal heat pump is a COP of 1 which is the same as resistance heat at 100% efficiency. ( A conventional air source heat pump could possibly get less since the compressor is outside where it may lose some heat to ambient) The temperatures you listed should yield a COP of at least 4 which means for every KW of electrical power you get 13,650 BTU/hr of heat ransfer (4x3413).

That still doesn't mean it makes economic sense but I just wanted make sure you understand that a geothermal heat pump will always outperform resistance heat.

 

[schmism]

your not understand the geothermal system correctly

you dont take the 45 deg fluid in the ground loop and move the temp of that fluid all the way to 110 deg which you then blow air over to make heat.

you use electrical compressor to move the energy from one "side" to the other.

just like you dont try to cool 95 deg summer hot outside air into 65 deg cold air for inside the house.

its the differential between the 2 temps that you need to move.

so say your house is at 65 and you want to move it to 70... you need to "find" 5 deg of energy.

you could "find" 100% of that energy in pure electricity (in the form of resistive heat)
you could "find" a 100% of that energy in burning a fuel (like coal, wood, natural gas or fuel oil)
or you could "find" that energy in another fluid and simply move it from fluid A to fluid B (were A is the ground loop fluid, and fluid B is the air in your house)

it is the compressor that does the work to move the energy from fluid A to B.

The result is a function of which way you run the circuit. in the winter you make fluid A colder and fluid B warmer... exactly opposite in the summer

while there is an efficiency to worry about when you consider the min/max fluid temps (of either side of the system) i dont think its that significant between 55 and 45 deg ground temps. I may be a mechanical engineer but im not one that designs geothermal systems.


While its great to think you save half or more on the cost of project (which i dont deny is a real possibility especially if doing the ground loop labor yourself)
your obvious lack of understand on how the system works gives me serious concerns that you would know enough of what your doing to have a successful install. at which point you've botched a 10-15K install.

My advise is to talk with a few more contractors and find one to properly explain how the system works and work a deal to allow you to do some of the install work to save on the install price.

 

[Redneck in training]

Heat pump (the key word is pump) doesn't generate heat. It "pumps" large amount of low level heat to smaller amount of high level heat. The smaler is the temperature rise the higher is the efficiency. Typical geothermal heat pump has efficiency about 400% to 450%. In other words every kW os electric power will pump about 4 kW of heat. Some large units (MW size) have much greater efficiencies.

Another thing to consider is selection of the HP for your climate. There is a difference between heating a swimming pool in Florida and heating house in Canada.

 

[sawduster98]

FWIW...when I built my place here in western NY and it came down to installing a heat system I chose geo. I overbuilt the house in terms of insulation and windows and was able to use a 2 ton forced-air system with 2 285' loops. Since an excavator was already on-site it only cost me an additional $480 to dig the trenches. The geo system cost $15k and the ductwork an additional $2k. I also use the system to preheat my hot water. The whole house is electric only. I didn't look at this project in terms of a pay-off period as I'd have to install some kind of heat regardless and quotes I got for high-end propane furnaces were around $10k + $2.5k for A/C. With geo, A/C comes 'free'.
First year results: took a little getting used to and getting everything tweaked in but the worst month total elec bill was $258 in Jan keeping the house at 71 degrees.
What I never counted on was the decrease in my homeowners insurance. Since I have no "ignition sources" in the house, my rate decreased dramatically ($200/yr).

 

[eepete]

Great comments here!

An interesting aspect of geo is that the numbers are more constant. The outside temperature just affects heat loss of your house, and very little the temperatures the heat pump has to work with. As such, one should be able to figure out the:
1) Cost to install a system (be it simple resistive electric or geo)
2) Cost to operate the system.

Since you know the desired output temperature, and have the ground temperature (input temp), the manufacturer of any geo system should be able to get you a power consumption number. It's a little harder to turn that into a "dollars per month in the heating season". I suspect that as long as you are consistent in these approximations you'll have an apples to apples comparison.

The one piece of data you're missing is what is the temperature of the water with a well based system. Perhaps there is someone local to your area has this answer. You can then get power consumption for both the ground loop and well loop systems and see what 10 to 15 degrees warmer water would really mean for you.

Redneck in training's comments about the low cost of simple resistive electric vs. the high cost of geo really draws a focus on the payback period (or if you like, "pay me now vs. pay me later").

Sawduster's comments points out the importance of the cost difference of the systems being looked at in addition/in stead of just the "big cost of geo". Of course, one has to have the up front funds in the first place. It's all about the increase in installed cost of the system vs. the decrease cost of operation. The devil's in the deltas.

Like many financial decisions, wouldn't it be nice to know how much longer you had to live to help with this choice.... After all, some people define a perfect financial life as one where the check to the mortician bounces :laughing:.

When there is just too much information, you have to simplify. I think you can get the installed costs OK. As for the operating costs, I'd try to come up with a BTUs you need, perhaps your current oil consumption will get you close. Now you have your system installation costs, and your operating costs. I'd ignore the possibility (certainty?) of increased electricity costs. In your case, it's much less of an issue and even for the grid dependent, rising cost just work in your favor but should not be counted on.

I'm making a subjective post here, but one last comment. When people get granite counter tops or a bonus room added to their house, they don't go through this "payback period" calculation like they do with HVAC systems. The reason is it adds to the value of the house. If you go the resistive electric with payback period of some number of years, when you go to sell your house it has less value than if it has an efficient heating system. Yes, this is a "Do I fly first class or do my heirs fly first class" problem. None the less, the house that has all of it's decisions based on "pay me later" (a.k.a the "typical" builder spec house) has less value 20 years down the road than one with more insulation and a more efficient HVAC system. My parents 4000 sq ft house that was built in 1960 was just torn down. It was too expensive to heat and cool, and it had a lot of "Deferred maintenance issues" with it. When the house sold 40 years after it was built, it was sold for $50K. It had little value. I fly coach a lot...

I know this doesn't solve your technical evaluations, but I hope it can help you focus on a few numbers, and focus on your personal long term goals and that will help you decide. Yep, I drone on like an inefficient heat pump...

Pete