[uuddlrlr]

There's a 52-home community in Alberta that provides ~all of their winter heating by storing heat in the ground throughout the summer:

https://www.dlsc.ca/borehole.htm

It gets up to nearly 80C, but took a few years of operation to get there.

The website covers it really well and I'd recommend checking it out.

[infogulch]

Wow that's amazing! Basically a community-sized thermal battery. I find the design curious; they use insulation around the outside, but still bored 144 holes on the inside, I guess the bottom is just left alone as solid rock.

They heat it with solar energy, and pull out heat during the winter. I wonder how well this would work to provide both AC/cooling during the summer and heating during the winter in climates that experience both, like the midwest US. Perhaps using the pumped water as a stable, biased thermal source for a reversible heat pump.

[mythrwy]

Yes I think that would work.

Check out this guy, he grows oranges in Nebraska in thermal heated greenhouses. As I recall he talks about cooling as well. He has tubes around 8 feet under the ground running around the yard.

https://www.youtube.com/watch?v=ZD_3_gsgsnk

[shagie]

> I wonder how well this would work to provide both AC/cooling during the summer and heating during the winter in climates that experience both, like the midwest US.

If there is a difference in the temperature, then the heat can be moved around. However, that doesn't mean you can run the entirety of the heating for the house in the winter off of the heat battery.

https://dnr.wisconsin.gov/topic/Wells/Geothermal.html

> Geothermal works on the principal of using the earth's natural underground temperature and a geothermal heat pump unit to provide heating in the late fall, winter and early spring and cooling in the late spring, summer and early fall. In Wisconsin, the average underground temperatures range from about 52 degrees in the south to 42 degrees in the north. Below about 20 feet in depth, the influence of surface temperature variations begins to dissipate rapidly and becomes the average of all surface temperature values.

Note the heating in the late fall and early spring and cooling in late spring to early fall. The Canadian one is stuffing more heat into the battery which gets it above where it is efficient for cooling in the summer.

Aside - the wikipedia article for the Canadian one - https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community

> On October 5, 2012 the DLSC set a new world record by covering 97% of space heating needs with solar thermal energy. In the 2015-2016 heating season, 100% of space heating needs were met with solar energy.

The location is just a bit south of Calgary ( https://www.google.com/maps/place/Drake+Landing,+Okotoks,+AB... )

For 2020, Calgary had 4835 heating degree days based on 18°C and 72 cooling degree days (2021 has had 174 cooling degree days)

https://calgary.weatherstats.ca/charts/cdd-yearly.html and https://calgary.weatherstats.ca/charts/hdd-yearly.html or https://portfoliomanager.energystar.gov/pm/degreeDaysCalcula...

Using that last one It's provided in °F too. hdd: 8780 °F and cdd: 117 °F

Going back to Wisconsin for the midwest datapoint... https://www.aos.wisc.edu/~sco/clim-history/7cities/madison.h... - though this data is in °F. The ten year average for heating degree days is 7200 in °F. The ten year average for cooling degree days is 620 in °F.

So... Calgary compared to Madison:

* 8780 vs 7200 hdd (65 °F)

* 117 vs 620 cdd (65 °F)

Based on this, and that there is still a lot more hdd than cdd - it would probably be more worthwhile to try to offset the heating costs on the heating degree days than the air conditioning costs on cooling degree days.

And just for comparison, Houston, TX is has 1000 hdd 65°F and 3444 cdd 65°F. San Francisco is hdd 2467 °F and 190 °F for cdd.

As another note that heating and cooling costs don't scale linearly with heating or cooling degree days.

[guerby]

I looked up the following paper:

https://www.researchgate.net/publication/326121453_Drake_Lan...

They get around 2000 GJ/year out of the storage, so 555 MWh, so 10.7 MWh/home.

Estimated current price of the system 4 millions USD (excluding one off 3 millions USD R&D costs) so 77000 USD/home.

7.2 USD/kWh of yearly thermal storage.

LFP battery is probably currently below 100 USD/kWh, so for this use the thermal battery is 10x cheaper.