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Community and Q&A

Ground loop in bottom of new footings

Nick Smith | Posted in Energy Efficiency and Durability on

Hi folks,

I like to experiment and try new things, so I’d be grateful for any constructive thoughts on the below. I’m respectfully asking for helpful views which may improve the system and help make it a success. I’m not going to pay for an engineer to design me a system. This is a DIY job to take the edge off in the winter, no more, no less. I’m digging trenches anyway, I just need to know if this stands a chance of working.

I live in a temperate climate (UK) where the outside air temp rarely gets lower than say -5°C (23°F) overnight. I have a heavy clay soil and will shortly be laying footings 1 meter (3 feet) deep for a new 2-bay oak frame workshop. To supplement electric heating and frankly just to take the edge off things in the workshop, I’m considering running some 50 mm (2 inch) corrugated plastic pipe in the bottom of the footings, with both ends terminating at head height in the workshop. I’ll then install a low-speed inline 50 mm 12 volt electric fan, driven from a solar panel and spare yacht battery I have, which will drive air from inside the workshop through the 50 mm pipe in the bottom of the footings and back into the workshop, hopefully raising the temperature inside to around 8-10 degrees Celsius (46°F to 50°F), which is much better than -5°C!

The workshop will be well insulated with Celotex or equivalent in both the walls, floor and ceiling and should be fairly well draught proof.

I’m confident that 1 meter depth where I live will give me a fairly steady 8-10 degrees Celsius, but I’m not sure whether laying concrete on top of the pipes rather than covering with dirt will reduce the heat transfer and negate the benefits I’m trying to achieve.

For various reasons, I can’t dig additional trenching away from the footings without incurring additional cost, and as I will already be digging 1 meter deep trenches for the footings, I wondered if this would work for what I require. Worth pointing out that I’m not trying to heat a whole house; just take the edge off the temperature in the workshop so I only need a small but steady temperature rise to achieve that.

With thanks for your help in advance.

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Replies

  1. David Meiland | | #1

    My opinion: such a setup will create almost no measurable temperature rise, could actually lower the indoor temp, and could cause IAQ problems. I wouldn't do it.

  2. GBA Editor
    Martin Holladay | | #2

    Nick,
    A few observations:

    1. Most experts have moved away from buried ducts because of mold and moisture concerns. These days, most ground loops are made of PEX, and circulate a liquid glycol solution. These loops are usually connected to a copper heat transfer coil in an air handler or ventilation duct.

    2. Even people who still believe in buried ductwork have concluded that (a) the ducts must have a larger diameter than the ducts you are planning to install; (b) the ducts have to be quite long; (c) the ducts have to be buried deeper than 1 meter. Even when these rules are followed, the soil near the ducts tends to get colder and colder as winter progresses, and warmer and warmer as summer progresses. For more information, see My Earth Tube Story.

    3. It's your project, and you sound like you enjoy DIY challenges. So experiment away, and report back on the system's performance.

  3. Charlie Sullivan | | #3

    I'd switch to the modern version: run propylene glycol/water mix in your tube, rather than air, and then run it through a water-to-air heat exchanger. Maybe get a PC liquid cooling kit that has the pump, heat exchanger ("radiator") and fan, all efficient 12V units.

    I'm not sure you'll get a high enough temperature to make it worthwhile, but if you are willing to let it be pretty cold, and just want to avoid very cold, it could help.

    What it will accomplish will be similar to what an uninsulated slab would do. Is your floor an uninsulated slab? The main advantage of the glycol system would be in the summer, where an uninsulated slab could potentially be cold enough to get condensation, which would be bad, but if you have a heat exchanger with condensation, that can be a good way to dehumidify, if you have a drip pan.

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