The Power of the Earth
December 13, 2019 7:03 AM   Subscribe

The use of geothermal heating goes back thousands of years, with bathing culture built around the latent energy from the earth. However, the history of the ground source heat pump is far more recent.

Instead of using ambient air temperature, a GSHP or geo exchange uses the rather consistent temperatures hundreds of feet under the earth to create high-efficiency heating and cooling systems that can be around 4 times as efficient as electric heating and over twice as efficient as traditional air conditioning. While installing a geothermal heating system often took over $40K to install into your home, recently Dandelion Energy has made inroads into replacing upstate New York's oil furnace systems by reducing costs and standardizing drilling procedures. Schools and other large buildings have started to use GSHPS to efficiently heat and cool large building complexes. Combined with renewable electricity, GSHPs offer the ability to control climate with a far smaller environmental impact and increased safety. For this same reason, Massachusetts is currently debating setting up "microdistricts" that would replace natural gas lines, allowing houses to use community geo exchanges for heating and cooling.
posted by Lord Chancellor (16 comments total) 18 users marked this as a favorite
 
I was peripherally involved in a construction project for a large public building (school) that used geothermal. They really are very neat systems. However, it did take a LOT of drilling; they basically did a grid of wells/boreholes under one of the athletic fields, it seemed like on 10 or 15' spacing. Apparently the number of boreholes you need depends on the ability of the subsurface soil to source/sink heat, so maybe it's better in other areas, but it struck me as something that's not practical for every house to have.

But if it scales well and could be used for "district heating" that would be pretty nice. It's clearly a superior technology to resistive heat and burning fossil fuels, for sure.
posted by Kadin2048 at 7:36 AM on December 13, 2019 [4 favorites]


Here in the Midwest, we only drill vertical wells if there isn’t enough space to go horizontal. Horizontal fields are either put in place via directional bore (if you need to preserve the surface) or by trench (if you are regrading the surface). You only need to get down about 8 feet and the ground stays in a pretty narrow temperature range year-round.

One thing to note: ground source heat pumps really only are efficient when run year-round. If you think about it, you are putting heat into the ground in the summer that you then pull out in the winter. My company built a dormitory for a local college and geothermal was eliminated pretty quickly because they were unoccupied in the summer. I also did a project for a biotech company that generated far more heat than they could use in the winter so they had to install cooling towers to bleed off excess heat. Iirc, their geo field was pushing 90 degrees Fahrenheit latent temperature at the end of the summer.

The other issue is geothermal doesn’t deal well with large temperature swings. It is a slow process to inject and extract heat from the ground. As a result, once the system is turned on, you need to keep it running. You don’t turn off the system and open the windows on a nice day because that is detrimental to overall performance .

In short, geothermal is best suited for large, inefficient structures but it is not as good as building an inherently efficient building because the greenest energy is the energy you don’t use.
posted by Big Al 8000 at 7:37 AM on December 13, 2019 [11 favorites]


I saw something like this on TOH last month, I think. It's definitely a great development in geothermal heating/cooling. Unfortunately, at least according to the TOH piece, while it's definitely lower cost than traditional geothermal systems, it's still somewhat prohibitively expensive for most people.

FWIW, the house we are in came with an older ambient heatpump that failed soon after we moved in. It was replaced by a modern ambient systems and I'm amazed at how much heat the thing puts out even down into the mid/low teens.
posted by Thorzdad at 7:38 AM on December 13, 2019 [1 favorite]


When I was a kid, my grandpa - son of a northern Minnesota millwright, 8th grade education, northwoods logger, Air Corps pilot, maker of the bows and arrows I used in the labyrinths he mowed in the tall grass out back of the barn - invented the Terra-temp, a geothermal livestock waterer, which he patented back in 1980. Its purpose was to prevent the water from freezing out on the range without having to run electrical power to the unit.

They lived about a quarter-mile down the gravel road from us, and I got to help with the testing. Every day through the winter, the bus dropped me off at their house instead. I'd check the temp in the unit, run up the driveway, and tell Grandpa, who'd write it in a little notebook next to the air temp. Then I'd eat Grandma's cookies :)

He got an award from the governor and also a Department of Energy Innovation Award a few years later. It was SO EXCITING to see him on the morning farm report talking about this - I even got a shout-out as a his research assistant! There were brochures printed, hats made up, and everything. I still have a couple of the hats - very Eighties Feed Corn style - somewhere in a box.

Sadly, it did not take off, and the business never generated any income. But it seems a lot of the patent's ideas were cited in other applications, so maybe it lives on its own way. I'll have to ask my dad for some more detail. I have a feeling he had a hand in writing the patent, which contains this passage:
When downward force is removed from said float element 82, it returns to its quiescent position, touchingly adjacent stationary element 84 and atop water 34.
And now I learn - what a coincidence - that the patent apparently expires TODAY. That's a little melancholy.

In any event, I'm going to read all these links, because geothermal energy feels like family history.
posted by Caxton1476 at 8:09 AM on December 13, 2019 [28 favorites]


I spoke to an engineer in Houston a few years ago about ground source cooling. He said that cooling loops placed into drill holes are more energy efficient than a traditional air source cooling system. However, he also mentioned the concept of heat exhaustion, where the earth warms up over time around the borehole, reducing efficiency until it eventually does not work. The solution is to drill deeper holes, or more of them, at greater costs. It seemed that the optimal arrangement was one where the system was exhausted in about 30 years.
posted by Midnight Skulker at 8:22 AM on December 13, 2019


heat exhaustion

If you're in the right climate, in the winter you are taking back the heat that you put down there in the summer.
posted by 1970s Antihero at 8:32 AM on December 13, 2019 [1 favorite]


There are many approaches and philosophies to all the systems lumped in the “geothermal” bucket. It’s a bit like saying “combustion engine” and then describing benefits and drawbacks without noting whether you are referencing a two-stroke, four stroke or diesel.

For example, I disagree with the conclusion that they are only useful for inefficient buildings. In contrast, because of the costs of borings, they are most applicable when the building’s energy profile has been lowered as much as possible through basic efficiency.

It is true that they work most efficiently in a balanced set-up. It is possible to heat or cool the surrounding earth to a point where the system either loses efficiency benefits or stops functioning. But ground is not a perfect insulator so this is always an economic balance in amount of exposure length to install versus natural heat transfer as impacted by annual heat insertion/extraction patterns. I know of systems that use existing subsurface groundwater flow to access an essentially stable temperature point indefinitely (and are sized to limit groundwater temperature change due to the system to 2 degrees).
With the increased efficiency of variable refrigerant systems, particularly to low temperatures, the window of geothermal appropriate projects may be narrowing slightly.

My experience based on life cycle costing and energy impacts I’ve seen is that the biggest deterrent to uptake is how cheap fossil fuels are and the lack of cost/incentives to reduce greenhouse emissions.
posted by meinvt at 8:39 AM on December 13, 2019 [3 favorites]


I wonder if there's a version of this technology that can piggy-back on existing deep water well boreholes. That could help rural areas with implementing this type of geothermal system.
posted by tobascodagama at 8:39 AM on December 13, 2019


My home in suburban Boston is heated with a Ground Source Heat Pump. When we built the house we were looking into green energy options and our lot wasn't suited for solar, so we decided to go with a GSHP. A vertical closed loop system was our only option so we drilled two 400' vertical shafts. It was a messy operation that ended up costing a bit more than we expected due to the fact that they didn't hit bedrock until about 200 feet. Everything above the bedrock had to be encased in iron pipe.

It's tough to say how much it saves us. We have a big fat electric bill in the heating and cooling months but no oil or gas bill. We also have no source of combustion in our house, but the fire department still required us to put a CO2 detector above our "furnace." The house is well-insulated, which helps with some of the savings.

It's a quiet, so-far reliable system and I'm happy with it. We keep our house at a constant 68 degrees with no night-time setbacks. It's not like an oil or gas system where you can just crank it up, it's better when you go slow and steady. We found when we lowered the temperature at night if the outside temperature dropped significantly the system would take a long time to catch up in the morning. We have some backup electric coil heaters in the ducts (one upstairs, one downstairs) that are supposed to kick on in times like that but we've kept them shut off since day one.

In the summer it all works in reverse to give us AC, which I'm told is much more efficient then regular AC. Again, I really have no way of determining just how much.

I guess the ground works like sort of a battery, where we're pulling heat from it in the winter and putting it back in the summer when we use the AC.

We have a wood stove in the living room that we use a lot in the winter, just to keep the living room cozy when we're hanging out. The house would be perfectly comfortable without it though.

Not sure what the downsides are. Initial investment was larger due to the drilling. The air ducts blow slightly-warm air but you don't get those "hug the warm radiator" moments like you do with oil or gas. Again, slow and steady.

Find yourself an HVAC company that has experience with these systems. Ductwork is a bit more critical, you want well-designed, smooth ducts for efficient airflow.

Would I recommend it? Hard to say. Getting it built was difficult in 2005, though I'm sure there are more companies now that can do it.
posted by bondcliff at 8:52 AM on December 13, 2019 [6 favorites]


If you're in the right climate, in the winter you are taking back the heat that you put down there in the summer.

I was at a Ground Source Heat Pump presentation this morning. One of the possible issues in the UK is that running a heat pump bidirectionally, letting you have heating in the winter, cooling in the summer, gives air conditioning where it likely wouldn't have been in the past (AC is common in commercial buildings but is only in about 1% of dwellings). This potentially increases comfort, improves the winter Coefficient of Performance for the heat pump but increases how much electricity it uses and thus potentially the carbon emissions, depending how the electricity mix changes. I wonder whether the volume of PV on the system here now means this is moot though.

You only need to get down about 8 feet and the ground stays in a pretty narrow temperature range year-round.

Interestingly, if you are only going down to 8ft then the heat you are bringing up is actually solar rather than geothermal. This is the case down to about 10m IIRC. So if this is the set up then it may negate the concern about heat exhaustion. The summer sun will heat the top 10m or so ahead of the winter. This is only an option where you have enough land to use shallow trenches rather than a deep hole for the HP slinky.

I wonder if there's a version of this technology that can piggy-back on existing deep water well boreholes. That could help rural areas with implementing this type of geothermal system.

I don't know about bore holes but people have been looking at using mine water in old mines in a number of locations and I think it has been done in a few places, some links here.
posted by biffa at 9:00 AM on December 13, 2019 [3 favorites]


I am getting so excited after reading this...
My end of the year get-away after working marketing through the holidays is a short venture from Dallas to Hot Springs, AR and spend New Years in a hotel room where they pump spring water into the bathtub as well as visiting the Bath House Row and getting a good soak in different temperature baths, followed by massages.
I can attest the last trip of the healing powers - I injured my tailbone and could barely walk or get up / sit down. After a few days there I was full-on hiking in the park for hours on the last day pain free.
GET ME THERE NOW.
posted by hillabeans at 9:10 AM on December 13, 2019 [1 favorite]


Semi-related: it's not a borehole, but the Nashville airport is using a flooded quarry near one of the runways as a heatsink for all of the air-conditioning. Seems to be working pretty well, too.
posted by jquinby at 9:21 AM on December 13, 2019 [1 favorite]


If you're in the right climate, in the winter you are taking back the heat that you put down there in the summer.

The hydrology of the specific site has a lot to say about this too.
posted by nickmark at 9:26 AM on December 13, 2019 [1 favorite]


Full disclosure: I got the Dandelion install this year in about May. The federal incentives are a whopping 30% (plus a lot of state and local incentives in NY), so the final cost was about half of what it was. I have a 50s house that had a very inefficient oil furnace and no AC (I spent $700 on heating oil in one month), but now I have heating, cooling, and hot water no problem. Like all Dandelion installs, it was a vertical loop (mine went down to 420 feet *dabs*).

In general, it's been a real delight to have a quiet, constant temperature, season-round. I have solar panels, so besides the install loan, I just pay $20 to be hooked up to the electric grid. Lot's of money up front, but very cheap now.

In a place like Houston where you have more cooling than heating, remember that you're still using the system to heat hot water, because even in Texas, people like having hot tap water for reasons, so it still probably would be efficient and workable.
posted by Lord Chancellor at 9:32 AM on December 13, 2019 [6 favorites]


For example, I disagree with the conclusion that they are only useful for inefficient buildings. In contrast, because of the costs of borings, they are most applicable when the building’s energy profile has been lowered as much as possible through basic efficiency.

Perhaps I worded my first statement poorly. When you get down to residential scale, I’m skeptical of the benefits of ground-source heat pumps over other technologies. When you’re looking at sub-3000sf dwellings, it is possible to get the loads down with base efficiency methods (insulation, high performance fenestrations, LED lighting and high performance appliances) where other technologies such as air-source heat pumps or residential chillers are able to do the job at lower install cost. They may be slightly less efficient overall, but the scale is small enough that the cost of drilling more than offsets slightly lower operating costs.
posted by Big Al 8000 at 12:05 PM on December 13, 2019 [4 favorites]


Trying to remember the details of GSHP installed at Shepherd's Barn in Lanchester, Durham. The grid is about 6' deep in the adjacent pasture. The barn is also heated with a mechanical ventilation with heat recovery (MVHR) unit. So they are not relying on one source. But the system accommodates open windows, wood burning fire, and the like. One end of the barn is fitted with a triple-fold glazed door that opens onto a large stone patio. Seems pretty adaptive to me.

http://leap4.it
https://passivhaussecrets.co.uk
posted by rustipi at 4:42 PM on December 13, 2019


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