In a geothermal system—not the kind in Iceland, which confusingly has the same name—pipes are buried underground where they stay at a constant temperature. Refrigerant circulates in the pipes, warming air and water in the winter and cooling it in the summer.
This is the greatest thing in the world: essentially free energy. Oh, you still need pumps to keep the refrigerant circulating, but that's not much. And of course it's entirely carbon free.
It's also expensive, though not wildly so. So why isn't it more popular? Why don't states like California require it for all new residential housing? Am I missing something about its greatness?
About ten years ago I looked into geo thermal as part of the construction of a new home (northern CA).
First, it was hard to find firms that would do a residential project.
Second, unless I one uses geo thermal as the sole source of heating cooling, this would be a very expensive secondary system.
Third, once I got a firm to come out and bid, they admitted a 20% - 25% 'failure' rate: one in four times geo thermal materially under performs its projections and creates very little value.
I think you'll have a problem with moisture in California. You want the soil around the heat exchange pipe to stay damp to facilitate conduction. If you're pumping a lot of heat into the ground, it will tend to dry the ground out. Perhaps you can combine it with a grey water system that drains into the same soil.
The first time I even heard of geothermal it was on This Old House. If it was on This Old House you can safely assume there are only a small handful of qualified contractors and the price is insanely prohibitive.
I don't know about that show (not in USA) but HP systems are well understood. But it's a niche market so finding a contractor to do it could be problematic.
Right now, with the shortages of materials and labor, I don't imagine contractors will even bid for something out of the ordinary. They are having enough trouble doing the work they are contracted for - and long waiting lists of clients and potential clients.
My understanding is that geothermal is more appropriate for states like Washington. Also, it's kind of a big problem to fix when one of the pipes springs a leak, because they are so deep in the ground. It's expensive.
My own feeling is "geothermal" is more accurately described as "ground sourced heat pump". It is like conventional heat pumps except it uses the ground as a thermal reservoir instead of the air. Given the ground is cooler than the air in summer and warmer than the air in winter, it makes great sense from a thermodynamic standpoint.
The reservoir can be vertical or horizontal. Large buildings typically use vertical plumbing which costs more because of the drilling but has a smaller footprint. A large building will have multiple wells, so failure of one is not a showstopper. Residential houses typically use a horizontal system from 3 to 5 feet deep. This is cheaper but takes a large footprint.
A friend successfully built two buildings for a small university that used ground sourced heat pumps. The first one used 25 wells but was so successful that the second one only used 5 wells. The first building was required by code to use a closed-circuit system, but with the second building a few years later they were allowed to use an open circuit system. One curiosity was that the one building contained numerous computers, and on many winter days the system was effectively just moving heat around, removing waste heat from the rooms with computers and sending it to the rooms that didn't have computers.
"Geothermal" is a bit of PR.
Ground Source Heat Pump is the more correct term.
However in America, and in particular in the Southeast, "Heat Pump" is a v common form of heating and cooling. And that means Air Source Heat Pump (essentially an AC system that can also run in reverse).
The Coefficients of Performance of the best Japanese systems get to around 4.0 (1 kwhr electricity moves 4 kwhr of heat) in a heating function (I think that's with air temp around 20 degrees F - but you can look up the ratings online in the manufacturer manuals). US manufacturer systems tend to be not as good because they are optimized as AC.
A GSHP (geothermal) might get to 5.0. So say 2-3x capital cost, for a marginal improvement in efficiency at very low temperatures. Not worth it, generally.
I’d never heard of a heat exchanger for a house until I moved to the Pacific Northwest near Portland. The one at my house provides very cool air in summer heat. The heat part mostly (I think) comes from the electric furnace, which thanks to Bonneville power is pretty economical.
Most heat pump systems can maintain a satisfactory temperature in the winter but have little thermal reserve. Nighttime temperature setbacks are typically not used because it takes more power to warm the house with electric resistance heating in the morning that it does to just run the heat pump all night.
I am not sure alternative forms of heating system (such as natural gas) have "thermal reserve" either?
It's simply the way modern North American houses are built w timber framing and lightweight materials. They don't have large thermal mass. Given the prevalent problem in much of the Continent is hot humid summers (so no cooling off at night) that makes sense?
The point about HPs is that their efficiency is inversely proportional to gap between input and output temperatures. Thus whereas a gas furnace can run "hot and fast" -- don't waste energy heating the house when you don't need to (it will only leak to the outside air and
heat the outside).
Whereas a HP runs best "low and slow" with a lower output temperature, but running all the time. That's why they work particularly well with underfloor heating (the thermal mass of the concrete screed holds the heat and releases it slowly) - at least in a European home w a concrete floor. And in a well insulated home, the temperature will get to the desired level, and stay there.
My new Honeywell "smart" thermostat lets me specify that the auxiliary resistance heating will never be used unless the outside temperature drops below (in my case) 20°F. (My ground-source heat pump isn't affected by outside air temps, but I want to avoid using the inefficient resistance heating as long as possible.)
Air Source HPs are very common in the US Southeast -- because they are basically ACs that can run also in reverse, and winter temperatures are not low.
As long as your winter temperatures are above about 20 F, generally, an ASHP is probably a good solution for heating (if you do not have gas).
An electric bar furnace (which is what a HP runs on at low temperatures - check the manual to see where it kicks in) is about the most inefficient system one can have**
** fingers crossed. A gas furnace is only c 90-95% efficient (a modern one). By definition an electric bar is 100% efficient. But gas costs a fraction of electricity everywhere in the USA (except perhaps parts of New England - but even there I suspect the ratio is merely 2 or 3 to 1, not 4 or 5 to 1).
It's pretty expensive to install (roughly $10,000-$30,000) compared to a conventional furnace or air source heat pump (the latter two are pretty comparable in installation cost).
Air Source Heat Pumps have gotten a lot better at handling cold temperatures, as well. They used to be rather unreliable at temperatures below 40 degrees F, and you'd have to supplement them with electric resistance heating. Cold Climate Air Source Heat Pumps can usually now handle temperatures below zero, although if it gets extremely cold (< -20 degrees F) then you still need resistance heating.
I doubt that latter happens often in California.
Yes - why would builders pay that cost, when they can just pass it on to the consumer in the form of higher utility bills?
It's basically a market thing. Plus the fact that when one fails and needs repaired, I bet it's a headache since it's underground. Maybe I'm wrong on that part but if it's similar to other underground utilities...
At the densities we are supposed to be building today, it has to be vertical bore holes for ground loop heat pumps. Rather deep at that. For my home it has been suggested three or four hound 200 to 250 feet down. That would be for a 1900 square ft single family home.
On the order of $40k for the drilling alone.
The ground source heat pump has an advantage in that below the frost line the earth never gets below 32 deg F. The thermodynamic limit on the efficiency of a heat pump = Th/(Th-Tc) where Th and Tc are the temperatures of the hot and cold reservoir expressed in absolute degrees (Kelvin or Rankine). Using a cold source that is closer in temperature to the hot cycle gives a big boost in performance, allowing efficiencies of several hundred percent.
For not only efficiency's sake, but also cost savings, it seems like such a system could be done on a larger scale to be shared by a number of houses. Each house's usage would then be separately metered at each branch of the distribution and billed accordingly.
That's likely to be a dealbreaker then. HOAs and other organizations assembled to deal with problems at the level of "a number of houses" are generally total messes in the US. It's highly likely that any such number of houses that shared a single geothermal system would skimp on the maintenance fees until the system failed and needed to be completely replaced... at which point, I could easily see one or more households opting out and installing whatever is cheaper than the per-house fee for installing a brand-new geothermal unit in the neighborhood.
The original development in Reston had a community heating/cooling setup--I think because it was right next to Lake Anne it used the lake rather than in-ground piping. It developed problems which I haven't followed closely, but I think it's partly maintenance and partly management. As you say, HOA's don't do great management--too many of us are freeloaders relying on the few conscientious enough to devote their time to the effort.
some idea of life at end of lifespan geothermal
https://www.restonnow.com/2021/02/11/frustrations-boil-over-as-lake-anne-residents-deal-with-no-hot-water-since-dec-1/
The good news is the failure would hit hard and hit everyone. No hot water or electric induction heating (ouch expensive).
The service issues should not be too chronic. But there will be periodic big bills for replacement (every 20 years or so?).
District heating is quite common in Europe, and increasingly they use Heat Pumps (rather than gas or oil fired boilers) because of the potential for zero emissions.
Like everything house related, it's a *local* technology with local choices.
Your question should not be: why don't we use geothermal more; that's like asking: "why don't we use wind power more, I don't see any windmills in Irvine".
Windmills of course are great -- but not appropriate for every house in a city!
So what's required for geothermal?
I would assume some combination of
- the building on soil, not rock
- the right sort of soil (wet enough)
- how much land is required (both for the installation/repairs process, and for the equipment itself?)
- how much "space" around it is required to be free of other stuff?
The answer to these questions may be that it's essentially irrelevant to cities and suburbs. Even if you have to qualifies as a reasonable sub-urban garden, between where the electrical, water and gas pipes are coming in, where the house foundations are, and where various tree roots are, there simply aren't any practical installation locations.
What about large entities like campuses? I suspect the density of storage just isn't high enough relative to demand to be interesting for a central location, and if you disperse to every building, well you'e back to the suburban "no good locations" issue.
So who's left? Farmers and semi-rural folk. Now we may be talking non-technical issues. How will the financing work?What's the business model ("the music man blows into town for six months, installs ten systems, then moves on to the next town over?" -- but then what's the support/repair story?) Who's taking the risk between the claims of "it will deliver so much heating/cooling" and the cases when it does not deliver?
All this stuff is hard enough for rooftop solar -- which as the advantages that it can operate in a city with all the density benefits of a city.
And of course it is a *mining* technology, or at least it usually is; you are pushing the ground temperature higher in one direction.
In the past this could have been like ground water, something where someone should at least run the numbers and figure out a plan -- including a fight over "what do we consider long term, and why should we care?"
But in 2021 think of these issues before you start the investments:
- who "owns" "ground cold"? If you install a mega system next to my house and suck away all my cooling, so that my system stops being useful after five years, can I sue? Or flip side, do I want to install a mega system if any rando within a kilometer can claim I am stealing his cold?
- will you be killed by environmental impact statements and random weirdos who start insisting that by warming the ground you will be changing the environment for moles, worms and suchlike and this is unacceptable. As usual, there will probably be one element of truth in this to 9 parts hysteria and bad faith, but you will have to deal with the lawsuits and demonstrations.
I believe Cornell several years ago did something using Cayuga lake's waters. Don't know how that worked for them.
Geothermal systems benefit from scale. A single home project would cost a lot more per BTU than a much larger one. Drilling and piping are big fixed costs, and, as others have pointed out, you want a buffer larger than practical on the typical house lot. In addition, the system would still need a heat pump for operation. You don't want the interior of your house at the same temperature as the earth beneath it. In most parts of the country, you want it warmer. The advantage of geothermal is that the earth temperatures vary only slightly while air temperatures vary widely
Geothermal systems are fairly common in the Northern parts of Europe. The apartment complex where I currently live has such a system, and we installed one ourselves for our single family house where we used to live before. That investment paid off in about five years, with costs for other energy sources being what they are in Sweden. We also got quite a bit more because of it when we sold our house.
My guess is that as long as other sources of energy remain much cheaper, it will be hard to make a case for this kind of investment, and from what I understand fossil fuel is simply too cheap in the US. I guess that is why Kevin mentions making such systems mandatory for new housing projects, as you would find it hard to sell the idea to individual families for simple economical reasons as it stands today. Hence it would have to be a political thing.
Furthermore, of course there has to be a governing agency handling permits for these systems, to ensure there is enough distance between boreholes, make sure you don't hit some critical infrastructure, take various environmental issues into account, etc.
" . . . fossil fuel is simply too cheap in the US . . ." Therefore, carbon tax, everyone. It's the main answer to unlocking every low-emissions technology. Right now, it's still on the table in the Senate for the reconciliation bill. Call your Senator and tell them "Dammit, don't wimp out on a carbon price!"
Yes, it's politically difficult, just like everything else that would actually WORK.
It's not JUST that "fossil fuels are too cheap in the US"; that was the point of my post. It's that THE US IS NOT SWEDEN!
There are parts of the US that are like Sweden, yes, and for them "soil-based" heat pumps make sense. But much of the US is like CA or AZ and this is just not an appropriate tech, especially in cities, not when solar photo-voltaic works so well.
This dismissive attitude to "oh the US sucks in every way" is getting old.
CA already generates a lot of electricity from geothermal -- real geothermal.
How much? 6% of its electricity. But that pales compared to the 15% or so from solar PV along with an additional percent or two from solar thermal. And solar is growing massively in CA -- net generation has tripled since 2014 and will likely continue once the glitch caused by covid is over.
Looking at ONE type of tech and saying "the US doesn't use that much, therefore they suck" is as dumb as me looking at Sweden's paltry use of solar PV and saying they therefore suck! Different tech is appropriate to different locations -- unless of course your goal is scoring points rather than understanding.
The US has 1.7 million geothermal heat pump installations (compared with Sweden's 350,000). OK, the US has more people, sure. But only about 30..40M of them live in a Sweden-like climate -- compared with 10M Swedes. Unfortunately I can't find numbers for the more directly comparable value of "energy saved by the heat pumps" and that would surely be something that is likely defined and measured differently by different localities.
Look if people want to have opinions about US politics, whatever. But when it comes to actual questions of FACT, can we at least try to retain Jabberwocking as a reality-based environment?
OK, rant over. Feel free now to explain to me why everything I said was incorrect and in fact the US is even worse than we all imagine, that they are deliberately running their heat pumps backwards to increase global warming, or whatever.
Where did you get the idea that the intent of my post was to complain about the US? I was providing some hopefully interesting facts about certain technology used in my country, and how it worked out for me there. Also a guess on why this technology would probably be hard to sell in the US. I don’t know enough about the geological situation in various parts of the US, but my guess is that our variant of geothermal (vertical borehole through bedrock) would work in many places
Sorry, posted too soon: However, whether or not other solutions like air pumps may work better is up to each individual situation to decide. What remains is the need for support and financial incentive from politicians, as Kevin hinted at.
Why so prickly? I try to contribute when I have some information that may be of interest to the discussion, and in this case quite a lot of personal experience. Whether or not this is translatable to conditions in the US is not for me to say.
Solar PV and Ground Source Heat Pumps are not competing technologies. Solar PV generates electricity which is what powers GSHP.
GSHP probably work better in communal heating systems, where the fixed costs can be amortised over more consumers. However there's limited incentive for a developer to specify & install one, since they do not have an ongoing interest in the costs to residents.
As an example, Toronto Canada has a communal AC system for many downtown office complexes. A giant heat exchanger coil which runs out into Lake Ontario. Analogous to the NY City steam tunnels - one of the defining characteristics of Manhattan on a cold morning is the steam emitting from pipes and manhole covers at various intersections. (there's also a district heating system, which is gas fired at the moment - but you could use a heat pump powered by electricity).
https://www.enwave.com/case-studies/enwave-and-toronto-water-tap-into-innovative-energy-source/
District Heating Schemes are more common in Europe, where there is a lot of collective social housing. Russia and Scandinavia, especially.
Geothermal power (electricity generation) in California has the advantage of being semi-despatchable. As the amount of intermittent renewables on the grid keeps growing, that becomes more and more valuable. Particularly as we aim for 100% decarbonisation.
Calling a GSHP as geothermal, as is done in the USA, hugely confuses the issue. GSHP is a heating/ AC technology, not an electricity generation technology.
Agree that usage will conform to local conditions - that's true of any technology of course. But incentives matter as well.
My understanding is that air source heat pumps are so much cheaper that ground source is rarely a win.
Maybe it can be in the NE tip of the US and much of Canada?
Also maybe if the underground part can be shared by half a dozen or more houses.
One problem is that the underground part is a big investment, but it isn't clear if it will have a long term payoff. Will you be able to re-use it when the mechanical part wears out or will it not fit the machines sold in 30 years?
So check back in 30 years. It might eventually grow market share.
It's not a big problem because there are no moving parts underground.
However the line will have to be cleaned out, periodically. That's where my relation in Ontario had a problem - the maintenance people used the wrong sort of cleaner. Eventually the insurance settled.
You can in fact pull the coil up and start again - the borehole will still be there.
Geothermal made sense when the efficiency of heat exchangers was low. With a modern heat pump made within the last ten years, air is a perfectly acceptable medium to either extract heat from or dump heat into and the installation cost is nearly an order of magnitude lower. Also there is significantly more going on than just using the equalizing the temperature between ground and house by pumping some liquid. The actual output from a heating vent is probably 40C above soil temperature.
Assuming a ground temperature of 10 deg C (50 deg F) and a heated air temperature of 50 deg C (122 deg F) gives a temperature difference of 40 deg C. If the air temperature is -4 deg C (24.8 deg F) the ground source heat pump will have an efficiency limit of 800% compared to 598% for the air sourced heat pump.
As long as we're talking about heating...California residents should be aware that they statewide TECH (Technology and Equipment for Clean Heating) program. There are exceptional rebates for heat pump water heaters and heat pump space heating starting in January 2022.
We replaced our old gas water heater with a heat pump water heater last year and we're replacing our gas furnace with a heat pump in 2022.
Our new heat pump water heater provided an extra plus during last summer's heat wave, as our furnace room (now air conditioned by the hot water heater) became our emergency refuge from the heat.
Green Building Advisor has done extensive analysis of this, and as others have said, air source heat pumps have gotten so good that the added cost of ground source heat pumps is very rarely worth it, both cost-wise and energy-wise. The one scenario where a ground source heat pump makes sense on a residential scale is when you already have a suitable pond on the property to act as the "ground."
This is key. Thanks for pointing that out.
I have read Green Building advisors who have said they no longer recommend GSHPs ie geothermal, given how good the ASHPs have gotten.
This was 15 years ago but was told you need to do it in areas that have enough moisture
We were all disappointed when my father didn't add geothermal when he had the well redone. He was already paying a ton to drill the well, so making it work for geothermal at the same time would have worked well. For him it was likely all about politics.
Most people arent interested in the expense of a new well or the disruption of digging huge trenches (if you even have the space for them).
It can be difficult to justify, especially when upgrading to a more efficient new furnace is a fraction of the cost, but still reduces your energy needs.
An acquaintance lives in a very large development of over 55'ers, likely 300 or more homes, just east of Vancouver, BC. They are, and have been heated and cooled, by geothermal. She said it is very inexpensive when she moved in, year round. I haven't heard anything more.
It would be. BC Hydro (electricity) has low rates!
Also it generally doesn't get too cold on the BC coast. HPs efficiency is inversely proportional to gap between input and output temperatures. So if your winter air temperature is say above 32F, most of the time, then that's not as big a gap.
There were various Canadian programmes to encourage these. A relative installed one on a farm on a ridge Central Ontario and it provided trouble free heating and AC for over 2 decades (trench not vertical bore). They did also have an airtight wood fireplace which they used pretty constantly in winter.
As the alternatives were propane or oil it was a pretty good savings.
This is my recollection that Los Alamos, which sits near the edge of the vast Valles Caldera, tried out geothermal, but people didn't like it because it was stinky -- small amounts of sulfur-tainted emissions. (Please, correct me if I'm misremembering or are otherwise misinformed!)
But I agree with the other folks that geothermal isn't meant to be a house-by-house investment, like your home solar panel. Why we don't have a more distributed electrical network, with many smaller sources, than relatively few huge points of failure, is beyond me. This "economy of scale" business has been debunked so many times.
Oh, and that goes for widespread heating systems, too. They almost of necessity need to be localized, but not "atomized."
"Geothermal" is a misnomer.
A geothermal system, such as you describe, taps onto an underground hot water source. Hence the sulphurous smell. Hence Iceland (volcanic).
Geothermal HPs used to be called "ground source HPs" and that's a much closer description. Nothing special about the ground you put the loop into. Normal ground temperature (around 50 degrees F once you get below the frost line) will do.
Re electricity production. "Economy of scale" has not been debunked. An Internal Combustion Engine, generating electricity, has a sub 30% efficiency. A gas fired combined cycle over 50%. Plus all the problems of capacity & maintenance associated with the former.
Some technologies, like steam turbines, just scale very well. Until Con Ed installed "Big Alice" - the 1000 MW steam turbine, there was a pretty constant increase in economies of scale for thermal generation (coal and nuclear), leading to large cost savings for consumers.
One went from something like Bankside Power Station in London, c 80 MW turbines & sub 200MW station, built in the 1930s, to Drax Power Station in Yorkshire, built in the late 1960s (and for a time the largest power station in Europe): 6 x 500 MW units.
The economics of electricity favoured large, centralised, despatchable (non-intermittent) units, backed up by Open Cycle Gas Turbines (aircraft engines) for peak power.
Tying it all together was the miracle of the 60Hz (50 in Europe and half of Japan) electricity grids, which meant that any point of consumption could have as much electricity as it wanted (that its circuits could take) when it wanted. A grid controlled and balanced in real time. Large failures were rare enough (1964? 2003 in the Northeast) that they are heavily documented and storied events (people in Toronto getting out of their cars and directing traffic through intersections when the lights failed).
Where we are now is that it's all about decarbonisation. That speaks to economies of scale in wind (the latest offshore turbines will be 12 MW each, and windfarms of 500MW - 1.5 GW) and in utility-scale PV (100MW+ farms in the deserts in the US and Australia). This has driven the cost of new wind (onshore) down to below the cost of any other new capacity, even gas-fired.
Of course there will be distributed generation. People will want to have solar panels on their homes. In Australia it's something like 10% of homes already. The actual installed cost is c 2x utility scale PV but distributed generation, if coupled with local electricity storage, offers the opportunity to reduce the load on the grid at peak times (peak is normally c 4-9pm on weeknights. For most utilities that's summer b/c of the AC load, but some also have a winter peak).
The grid is far from obsolete. In fact in a world where you are going to have absolutely huge power flows over quite short time periods - as the wind drops, or it's raining, or sunset and sunrise -- the grid will be more important, not less.
Yeah, I think manufacturers have adopted the "geothermal" misnomer because it sounds sexier than the correct "ground source".
When I had mine installed 25 years ago, "ground source" was the term used.
Can you say whereabouts you installed this? (geographic location)
My sense is it only works well, at North American energy prices, in the extreme cold locations. Upper Midwest, NE, Canada, perhaps some of the mountain states.
It’s been on my remodel/rebuild wish list for a while, but drilling in rocky soil is expensive and I’m not sure we actually have enough space on our 1/6 acre lot (iirc the wells need to be 15 feet apart). I know schools and some office developments around here are using it; you can see the tubing protruding from the ground before the fences go up. But in fairly dense residential single-family-oriented neighborhoods, it can be a real logistical challenge.
Look at the best Japanese air source HPs. Which are available in the US.
You will get COP of 4.0 - within shooting distance of the 5.0 that you might get with a GSHP.
GSHPs are basically not worth it, unless you have very cold winter temperatures (and no access to natural gas).
If burning gas worries you environmentally then find a way to forgo flying a couple of times a year. Drive an EV if you can. Invest in rainforest preservation charities - far and away the most effective "bang for buck" in decarbonisation terms.
My 25 year-old ground source "Water Furnace" heat pump has an advertised COP of 3. Presumably I could replace it with a newer model, while keeping the same buried coolant loop, and increase that substantially.
(One objection people have to heat pumps is that the air coming out of the heater registers isn't toasty warm. My attitude is "Too bad. Get over it.")
It is why they work better with well insulated homes (or homes w large thermal mass e.g. stone hearth etc). Once they are heated to the desired temperature, they stay there.
Gas furnaces are often used in homes w much poorer insulation (my Victorian has solid brick walls - a modern window is almost better insulation than my walls). These are leaking heat to the outside world, so they need a high heat input from the heating system to stay anywhere near desired temperture => high rad water temp or high output air temp.
For a geothermal system, you either have to have a really large lot for a more horizonal configuration of the pipe system, or a way of drilling down several hundred feet for a vertical configuration. You also have to have the right kind of soil for optimal energy transfer or it doesn't work very well. And even though it pays for itself after a number of years, the upfront costs are really quite high. (about $15-20k).
They're more and more common here in WI, especially for commercial and government projects. The local university constructed 2 new buildings within the last 5 years and both have integrated geothermal systems -- I've been told the costs savings has already exceeded expectations.
When we lived in Wisconsin we installed a geothermal system, essentially a heat pump that used the stable temp deep down. It worked great, you're basically plugging your house into a cave. (We weren't getting actual air from down deep - the vertical pipes contained fluid and the heat pump drew or dispensed from it.)
Anyway, I think geothermal systems are an obvious choice for buildings in the continental U.S., where the temperature varies widely between summer heat and winter's cold.
The system went in without a hitch and functioned beautifully. The only problem was that when we sold the house, nobody appreciated what we had done. It was invisible and our realtor sucked at presenting the advantages. I suppose now, 8 years later, the heathens that bought our house have noticed that their HVAC costs have been remarkably low. (I wouldn't be surprised to learn that they removed the solar hot water system - I know they bulldozed my gardens and cut down the fruit trees.)
I think in new construction, it makes a lot of sense. For retrofitting an existing HVAC system, there are a lot of issues: you either need to lay the cooling tubes horizontally, and severely tear up your yard, or vertically, and have some really heavy equipment set up on it. And that's before considering if anything needs to be changed inside your house.
Inexpensive?!? Kevin, you should seek a quote. I’ve been quoted on the order of $40,000 - for the drilling alone…. I may yet go ahead and do it, but inexpensive it ain’t.
Air Source HP will most likely do what you want. The best Japanese units, available in America, get COPs of say 4.0 v 5.0 for a GSHP.
If you live someplace really cold in winter, like WI or MN say, this might not work.
Technical correction: it isn't "free heat", requiring only pumps to keep the coolant flowing. The laws of thermodynamics state that moving heat from a cooler place (the ground) to a warmer place (your house) requires energy. Yes, it's a lot *less* energy than simple resistance heating: modern heat pumps have a "coefficient of performance" in the range of 3–5, that is, resistance heaters would require 3–5X as much electricity.
Also, "geothermal" is actually a misnomer. The heat these systems pick up doesn't come from deep within the earth; it's from ground warmed by the sun. So in essence it's a type of solar heating.
That's not accurate. below a certain depth, the temperatures remain almost constant year around. Here it's somewhere around 56F so the geothermal provides heat in the winter and cooling in the summer.
That is only true for a certian depth and a a specific location. The earth warms the deeper you go accfording to the geothermal gradient at the specific location. Generally geothermal gradients are lower in sedimentary rocks and higher in matamorphic or igneous terrians.
Where I live (Alberta, Cananda) air heat pumps are marginal in winter (we can get -40 c or F cold snaps) but ground source heat pumps are a valid alternative to conventional heating and cooling. They are significantly more expensive so low cost financing woiuld be critical for more widespread usage.
And Alberta .. home of the Canadian oil and gas industry.
The technology worked well for a relative in Central Ontario - where -40 is pretty rare (but -20C is not). And it was really good for air conditioning as well (increasingly needed in this day and age). Their "backup" was an airtight wood fireplace w an absolutely massive chimney
In the 1990s there were government grants. And they had a farm so could use a trench and avoid cost of deep boreholes. It worked very well.
You're right about nearly constant temperature. But it's not because of heat emanating from the Earth's core. It's a long-term average of solar heating. Check any of the websites of companies trying to tap actual geothermal heat: the required depth is measured in kilometers (except in cases like hot springs where the heated water is at or near the surface).
What a great discussion by a lot of smart folks! Kevin should have a really good handle on his question now.
I had a geothermal heat pump installed in 2010 with the help of the Obama stimulus and $200/ton from my rural electric co-op. The total cost was about $19k; after the subsidies about $13k (I think). It is a 3 ton unit and uses 3 x 200' deep wells. The well are in the front yard about 20' apart. I think the wells were about half the cost.
I've love it. There were two relatively minor problems over the first 10 years covered under warranty. It is beautifully quiet. It has heating strips for emergency heating only but they've never turned on. No blue light on the thermostat.
My old conventional heat pump was a disaster. I'm tempted to elaborate, but most of them are fine.
Anyway, most of the South is perfect for geothermal heat pumps. Heating and cooling requirements are pretty close. Drilling wells is not a problem in most areas. The problem is initial cost and that most people don't plan to be in the house long enough for it to pay off. It is also complicated to do. The solution is government: We need a scheme where some entity can certify and line up the contractors, buy the equipment at wholesale, and insure the installations.
I proposed this along with some other ideas to a former SC governor. SC owns a very large electric utility: Santee Cooper. The governor had just killed their last attempt to build a coal plant. The suggestion was that Santee Cooper should take this on. He actually proposed something somewhat similar a couple of months later. Then he went hiking on the Appalachian Trail as it is called when one is visiting one's Argentine lover. That was then end of that. Santee Cooper invested billions to buy 40% of an eventually abandoned nuclear plant instead.
I have a ground source heat pump for my house
When I was building the house I looked at local installations - they were terrible!
Most cost about $60,000 for the ground source alone
So I ran the numbers and did mine myself (hired a digger and driver) - cost $1,500
The problem is that its unfamiliar technology and the contractors size it very very conservatively
My $1,500 ground source is probably twice as large as it actually needs to be
Is your system vertical or horizontal?
Dirt is not a good heat conductor so you need a large unit which drives up cost.
We are installing air driven heat pumps for hot water and HVAC. The eco-cute hot water heaters use CO2 as the working fluid and operate to well below zero degrees F. We are using a multi-drop HVAC system which is nice because you only need to heat or cool the rooms you are using.
In general, as others have expressed, people are very reluctant to pay one dollar extra up front for equipment.
Split incentive problem.
A landlord has no incentive to invest in highly efficient systems, because the tenant usually pays the utility bills.
A homebuilder has no incentive to anything 1 bit above standard grade. As long as the new home buyer doesn't mark the property down because of its absence, there's no advantage.
Nicer kitchen counters & better brand name appliances will have a far bigger effect on the sale value of a new home, than a heating system that no one will understand the benefits of.
Also homebuilders are conservative because of warranty claims-- post sale liabilities. Gas furnaces and air source heat pumps (for AC) are well understood by the building trade, are pretty standard & come with product warranties if there is a problem.
Gosh, if I didn't know better I might call this a classic market failure, which would suggest government action to correct it. How about low- or zero-interest financing of the added cost of energy efficiency? Everybody wins (except the utility company).
Some Public Utility Commissions have introduced schemes which reward the utilities for incentivizing customers to install energy-efficient equipment.
The avoided cost of, say, a power line upgrade in the local Low Voltage network, can be very large. Thus benefits to consumers overall if that can be avoided. HPs would generally work in the other direction.
The problem with HPs is the power utility's gain is the gas company's loss (although the infrastructure for both may be owned by the same company).
The UK is looking at banning new domestic gas connections from 2026. However for the existing stock of homes (much less well insulated) gas may be the optimal heating fuel. That implies a solution like hydrogen.
When I think of the promise of geothermal energy, my interest is in large geothermal plants to produce electricity. If you dig deep enough (think miles down), there is plentiful geothermal energy all over the planet. It seems like the US should be investing much more in Deep Geothermal. The cost of drilling is expensive and has to be worked.
An issue with deep geothermal plants is that fluid is pumped into the ground and extracted elsewhere. This is a fracking approach, and thus there are negatives. The company Eavor has been working on a closed-loop system to avoid injecting fluids underground. That would be a big breakthrough.
MIT did a big study on the potential.
One problem is earthquakes. Systems that inject water into the ground to get back steam, can cause earthquakes which leads to claims for building damage. Dutch natural gas production (in its northernmost province) has been sharply curtailed because of a similar effect.
Another problem is you need to have sufficient water - and that can count out much of the western USA, where the doctrine of prior use of water rights prevails. You'd have to find someone else's water rights & buy them & get a legally recognised transfer. That's relatively easy I think if you have a farm, but not so much so if you have a novel use like resource extraction (ie geothermal).
Agree that if you can get closed loop systems using efficient heat transfer medium that would address a lot of the problem.
I've been following Eavor as well. They avoid perturbing the fluids underground, and can get geothermal power out of a much wider range of places than standard methods. They can also make use of a lot of oil/gas expertise and financing, and so give fossil fuel companies a future.
One of their problems is doing drilling through really hot rocks, like 200C and above, because that's not standard oil well practice. Instruments with silicon-based electronics stop working at those temperatures. If they could get to 300C, they could really get a lot of power out.
Forget the company names, but at least a couple of ventures are using millimeter-wave radiation to bore through otherwise intractable rocks.
One goal is to be able to drill a deep well next to pretty much any existing fossil fuel-fired power plant, and use the superheated steam to drive the turbines. Just shut the boilers down. Huge if it works.