Any experience with earth tubes.
 

Looking for advice on earth tubes. (pipes that run underground to collect/dump heat from outside air as it is drawn into the house)

We have a whole house MHRV system i installed during the renovation pf our house, it,s currently hanging on the wall outside our house with a shelter to protect it from the elements.
It will be relocated into a utility room as once constructed, started on the foundations this week. The plan all along has been to connect the inlet to a series of earth tubes to pre heat the incoming air in winter and provide some free cooling in summer.

Now construction is under way it has dawned on me how many services need to run through the foundations from this one small room, mains water, bore hole water, incoming electric, ground source heat pump loops, sewage, rain water drains, and all services to workshop(water electric, network cables etc)

The other thing i,ve just found out is the cost of Rehau's special pipe for earth tubes, over £2000 for 40 meters :eek:

I could use 160mm drainage pipe but 2 runs of that is still £600 and would take an even bigger lump put of the foundations. Also as it's not silver lined it could harbour bacteria as Britain has a wet climate.

Soo, after a bit more research i found a German company producing a system where brine loop/loops collect heat/cool from the ground and condition the air through a big radiator before it enters the MHRV. http://www.sole-ewt.de/sytembeschreibung/?lang=en

This seems too good to be true, a small loop or water pipe, a pump and a couple of car radiators in a housing.

Any thoughts?

I only know some general information from so-called envelope houses in the 80's. Do you have an exhaust up high in the house for passive air flow in the summer?

Years ago I was renovating a house (without AC) located on a hill. I used corrugated metal pipe - two runs of 8" I think it was. The pipe went out the basement wall, across the back yard, and exited on a hillside. A metal frame was welded up with burglar bars and mesh to keep critters out. That frame went on the inside of the poured concrete foundation wall. In front of that was a second frame, hinged to the first, made to hold two thicknesses of furnace filter. An operable skylight controlled by temperature and humidity on the second floor was the other part of the equation. When the skylight opened a noticeable amount of cool air could be felt coming through the furnace filters. The owners were very happy for years to come.

We are not going for passive airflow, don't think it would be very easy to achieve with the design of the house and duct rout's we have done.
We have 3 rooflights on the 2nd floor which can be kept open through summer.

The exhaust will be 2 to 3 meters above ground level but 5 below the ridge of the roof.

Steve

Sounds like a nice system, Was the air much cooler than the outside ambient temp ?


Our climate is 6 months heating and 1 to 2 months cooling.

The summer cooling is only part of why i want to try this, with the MHRV running year round it struggles when temps drop in winter.
If the incoming air is below freezing it stops the intake fan whilst keeping the exhaust fan running to defrost the heat exchanger, i haven't timed the defrost vs running ratio but it seems like it spends more time defrosting than running.

My hope is that earth tubes will warm the air enough in winter to avoid the defrosting and boost the output temp from the ventilation a few degrees therefore reducing the heating load.

Steve

I posted pics of ground tube network I plan to use to temper subzero fresh air to DIY exchanger(in Eco-build thread). Three 100' 6" sewer pipes linked together at foundation. Each run has a nylon rope thru it that can seasonally have a bleach soaked swab pulled thru for cleaning. It will only be used in winter so condensation problems should be minimal. Capped in summer. All tubing was surplus and laid in same trench that day lighted footing drains are in out hill away from foundation.

http://ecorenovator.org/forum/renova...d-started.html

http://ecorenovator.org/forum/attach...d-imgp0023-jpg

I never measured the incoming air temp but yes, it was significantly (a lot) cooler. Over cooling the house wasn't a problem because of the temperature logic on the skylight. Your climate sounds similar. A bonus is the quiet running compared to AC.

I think the way to go is to use plastic pipe and circulate water, plus radiator. As far as brine, use more pipe and rely on water as your heat transfer media. The radiator will be the single site of condensation, and it will be easier to manage, both in terms of dealing with moisture and bacteria.

I think earth tubes are great in dry areas, which your green island is not.

Passive House seems to be going for earth tubes. Maybe research those forums.

Keep us posted!

-AC

We are going for plastic water pipe, either 4 loops of 25mm or 2 loops of 32mm, each loop 100m.


Simpler to run than earth tubes and takes less of a chunk from the foundations. Also more controllable than earth tubes so when the ambient temp on a sunny winters day exceeds the underground temp the water pump can shutdown, same for summer nights when the air temp drops below the underground temp.

Updates on this will be on my renovation thread towards the end of this year when we have the extension up and i can start connecting everything i've been working on the last couple of years.

Thanks

Steve