Beating the heat with geothermal cooling


A while back, [Erich]’s oil heating system was due for a few repairs. Given the increasing price of fuel oil, and a few incentives from his Swiss government, he decided to go with a more green heating solution – geothermal heating. The system works well in the winter, but it’s basically useless in the summer. [Erich] decided to put his 180 meter investment to work for the summer heat, and made his geothermal heating system into a cooling system with a fairly low investment and minimal cost.

The stock system works by pumping cold liquid from [Erich]’s under floor heating into the Earth. In winter, the surface is always colder than the ground, thus heating [Erich]’s home. In the summer, the situation is reversed, with the cool earth insulated by the baked surface. All that was required to reverse the heating system was a few slight modifications to the heating controller.

Stock, [Erich]’s heat pump controller doesn’t have the capability to run the system in reverse, so he turned to a Freescale board to turn the compressor off and the pump on. With the additions, [Erich] is using 50 Watts to pump 1.5 kW of heat directly into the Earth below, a fairly efficient cooling system that’s basically free if you already have a geothermal setup.

25 thoughts on “Beating the heat with geothermal cooling

    1. my first guess would have been that
      to prevent excessive condensation UNDER his floor,
      he would need the pipes encased in HUGE heatsinks to distribute the cooling with greater surface ares thus increasing the temperature per square cm thus possibly reducing or eliminating condensation???

      anyway thats what i would think would work best, and it could cost a lot for metal.
      BUT thats where recycling a few or 50 ariconditioners,
      lay out 20 or so of the pipe+fin under the room’sss floors
      then sell off the remaning scrap (and the gas you recovered, right?)

      wait, scratch that, just weld em pipes onto (inside) a two-layer metal floor!

      1. I was involved with pouring a concrete floor with baseboard heater cores (copper pipes with aluminum heatsinks soldered to them) embedded in them for a geothermal cooling system. It was actually really effective once they fixed the condensation problem with a coat of vapor barrier paint on the concrete. The concrete ended up a bit porous because of the heatsinks, though. Not a problem, since it wasn’t structural.

      1. yes sure. it’s called radiant flour. It’s really common just the same as bricks in the walls…
        The use of heating/cooling pumps depends on the house itself, sometimes it’s not worth it, sometimes people use solar, sometimes people use a mix of several things.
        I’ve one too. It’s deep 70meters in the earth. pumps the fluid.

        I really can’t understand this post.

  1. So…….no efficiency comparison between a normal 10 KW system and this one? I am wondering also about the installation cost……maybe $q5-20K U.S.? Looks expensive, what’s the paypack compared to heating with fossil fuels, both in terms of financial outlay…..and carbon footprint….?

    1. In the US it is significantly cheaper than using fossil fuels or the grid, except for natural gas in some areas. With the savings from power usage and the federal rebate, most installations recover cost in 6-8 years. The carbon footprint is much lower because power is used only to circulate the refrigerant, not to actually do the cooling. Overall, it is not so expensive, but it can be disruptive. With a horizontal array, you have to rip up your whole garden. With a vertical array, you need to allow a heavy drilling machine onto your plot and clean up afterwards. Nevertheless, it is still a worthwhile investment, pays for itself relatively quickly, and adds to the resale value of your home.

      1. It can be more expensive to repair if something breaks though. My workplace has geothermal cooling and last year the refrigerant started coming up through a section of the parking lot. The fix involved ripping out a large-ish section of asphalt and likely a soil cleanup of some kind. I’m assuming this and the resulting lost day of productivity weren’t cheap.

  2. Geothermal and ground-source are not the same thing. This is ground-source.

    It’s trendy to call ground-source systems “geothermal” but it is not correct. Geothermal systems extract thermal energy out of the ground. Ground-source systems use energy to pump heat in and out of the ground.

    1. I’m confused, was his system geothermal before he made it capable of cooling too? What’s an example of a geothermal system that isn’t ground source then? Only the geothermal electricity generators?

      1. Geothermal systems are used in places like Iceland, where the heat from the ground is used to run electrical generators and to heat large buildings and houses.

        Geothermal in one area in California is controversial because it changes the frequency of earthquakes – apparently pumping water through the deep soil lubricates the rock and allows for slippage. However, this may actually be a good thing, since many small earthquakes are better than one big one. But I digress.

        Ground source can be used for heating, cooling or both. It is more effective than using air-source heat pumps since you are using a source that is warmer in the winter and cooler in the summer than the air. If you get deep enough underground ( a few meters) the temperature is fairly constant year round – about +10C to +15C where I live. Contrast that to air temps that can vary from -40C to +40C.

        Note that it is not more efficient thermodynamically, since maximum efficiency goes with maximum temperature difference, in general. However, if you are trying to heat a house with air-source when it is -35C outside, the thing consumes ridiculous amounts of electricity – at that point air-source systems switch to resistance heating to save electricity and cost. This doesn’t happen with ground source and, while slightly lower in efficiency, it is much more cost effective.

  3. I considered the same option where I live but the heating with natural gas is about the same price but the installation cost is about 5-10 times cheaper for gas. With good house isolation it just did not make sense.

    In addition to the cooling of the floors I also considered extra cooling of the ventilation air (I’m pretty sure that this guy also has balanced ventilation with hear recovery).

    1. For most the initial cost is the biggest hurdle. It sounds like that was that case for you. Forgive me for assuming too much but It also seems like you didn’t really look too far into the future and take into consideration the future costs of fuels vs cost of electric. Both are on the rise, but natural gas and oil are beating out electric in the race to “absurdly high”. Having a system like that installed would be highly desirable and would drive your house value up when it came time to sell.

      1. When I calculated the cost of heating with the heat pump and gas heater then I got about the same result (sorry, this happened few years ago and I do not have the calculations any more).

        The problem is that the efficiency of the condensing gas heaters is really high and the loss of the energy during electricity distribution is high too.

        Besides the heating need in small properly insulated house is low so it is hard to gain big advantage in absolute terms.

        I could still install the heat pump in the future when the balance between electricity and gas prices changes because the investment to have the gas heating was negligible.

        But I’m currently more interested about installing solar water heating in the future. I’m also considering DIY solar air heating when I should have more time at hand.

      2. “natural gas and oil are beating out electric in the race to “absurdly high”.

        Not sure where you live but in my country we just discovered about a hundred year supply of natural gas. It’s so cheap in the U.S. the power plants are switching to it, as it is cheaper than thermal coal….

  4. Just build a couple of solar water heaters and use those durring winter. There is a guy where I live that installed two on his roof and it circulates warm water via some sort of flex tubing under his tiled flooring.

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