Ground Source Heat

[Steven Prentice]

This was just some mild musings. Thought I'd ask the question see if there is someone out here who knows these things

If I buried 50m of garden hose under the lawn, say 1m deep (hand dig so not too deep, 25m garden so up and down once), blew air through it with a fan (or extracted air through it), what would happen.

My thinking here is that at a certain depth the ground temperature is fairly constant, in the winter hotter than air temperature, summer cooler of course - which is the basis of a wet ground source heat pump. So for a mega simple system, bury pipes, blow air through, duct into the garage near the work bench, would it come out at nearly the 8 degree ground temperature the internet reckons is around here or will it be a lot lower? (then heat this air with a small fan heater, happy days).


Costing, 50m hose, about £50. Small fan, about £20, a few fitting, so all in £100 maybe - as I started for a bit of amusement. However don't want to spend a weekend digging if it will do not a lot

 

[Mike13]

too little to make a useful source of heat, need to do it much larger to make it pay. Also using air to extract the heat limits how much heat you can remove.
A fan has a low stalling pressure and could not drive a useful flow down 50 metres of hose.

 

[stem]

If the underground temperature was 8C and you were drawing 5C air down a garden hose. [You would need a high pressure blower to get a flow of air through 50 metres of small diameter garden hose] garden hose is somewhat insulated and has a very small surface area, so any air passing inside won't pick up much if any heat. Then there's the source of the air. If it's from outside, then today at 1 degree, it might manage to pick up 1 degree on its travel through 8 degree soil, so you would be bringing into the garage at 2 degrees, so if your garage is warmer, than that already you would be actually be cooling it.

Also, introducing air from outside means that when it enters the garage, air already inside the garage that you have heated by your fan heater would be forced outside and lost.

If you want to re-circulate air from inside the garage through the hose to stop the loss to outside, then once the garage was above the temperature of the ground, heat would be lost to it rather than the other way around.

You would be lacking one vital ingredient. The refrigerant a vital part of any heat pump: a fluid that moves in a circuit, soaking up and releasing heat as it goes, the important thing is that it has a very low boiling point -15C. There's a good explanation here.

 

[Ivor Windybottom]

If you do that you'll make your house ever so slightly colder than it already is, as the ground is normally cooler than your house in winter. But it will make so little difference it probably won't be measurable.

This is not how a heat pump works, it's cleverer than you think it is. Read the link above, wikipedia or whatever.

 

[Steven Prentice]

A bit late responding whoops. Garage is external, no other heating but it needs none unless I want to do stuff in there. Like I said just a thought and wondered if it could be done or why not. Aim would be the background heat, and then fan heater on after if necessary (I have a jumper, probably never need another heater)

Appreciate of course the simple mathematics that you are never going to get the output air as warm as the ground temperature.

So limits to this is the dimension of the hose - length, wall thickness and diameter and also the power of the fan (500m thin walled hose, with a decent fan and it might work..... or I can add a pair of gloves to the jumper combo)

Cheers.