vent pipe for underground house 2

[redun]

I designed and am building an underground (dirt on the roof) house. The south wall is exposed like a walk out basement,the roof is covered with 18" of soil as well as the entire back wall.Most of the side walls are covered also.
I installed a 4" PVC pipe under the floor slab. and it comes up to the floor level at the 2 back corners of the house where I will put 4" diameter grates level with the floor slab. The 4": pipe goes out thru the front foundation wall about 3 ft below grade. Grade slopes away from the house. My plan is to dig a 3ft trench for about 100' away from the house and extend the 4" pipe in the trench out to where it will daylight at an exist bank.
Here I will build a concrete box around it and cover with screening to keep bugs,snakes,etc. from entering.The idea of the pipe is that it will provide ventilation and in summer when its 90+ degrees and 90% humididty, as the air moves up thru the pipe, the humidity will condense on the pipe walls and run out the end so cooler dryer air enters the house because the pipe is surrounded by 55degree soil. In the winter this would heat the air some justthe opposite effect if its say 32 degress outside of colder. At least this is the premise that Ive read.
The question is what mechanism pulls the air up thru the pipe? Is it some natural movement of air inside the house? Or must I have a tiney fan that has a small vent hole in the top of the front concrete wall to get air flow thru the pipe?
Anyone have any experience with such a Vent pipe?

 

[dvd]

Sounds like kind of a pipe dream.

For the air to move on its own it will have to be less dense than the air in the house: your cool air will be more dense, especially after condensing out the moisture.

Where does the air already in the house go?

If you are condensing moisture on the wall of the pipe it very likely will mildew.

Spend the money on your (ground source) heat pump if you want to take advantage of geothermal exchange.

 

[MikeHalloran]

I've read of vaguely similar closed-loop schemes where house air was run through a network of underground ducts (with considerably more surface area than you're proposing), and brought back into the house. ISTR the ducts and the system were abandoned because the mold and mildew couldn't be controlled.

How about putting a U-trap in your pipes, calling them floor drains, and installing a nice ground-source heat pump?

To answer your question, air would be drawn into your pipes as warmed air left the house through roof vents.


Mike Halloran
Pembroke Pines, FL, USA

 

[redun]

Ok It sounds like I will need some little fan to pull the air up thru the 4" pipe. So i must cut a hole in the very top of the front wall so the little fan can blow air out thru that hole in the wall. The house is about 23ft wide x 42 feet long and has 9 ft high wall in front and 8 ft high wall in back. So I have about 8200 cubic feet of air in the house.

Any ideas on how big a fan I need just to get "some" small movement of air into the house?

You may be right this could be a useless pipe dream. I sure hope it at least provides ventilation. I am a Civil/structural engineer so I really dont know much about this issue other than all the references Ive read on underground houses.

Regarding the mold/mildew problem, if the pipe is on a continuous slope to it's daylighted end, then no water should accumulate in the pipe. it should run out the end. Being that the pipe is smooth wall PVC, even if the insides are damp sometimes, could mold/mildew actually grow if there is no "food" source? Wouldnt the PVC material preclude mold growth as PVC is not a food source ?

Do you think that a hundred feet of pipe may not be enough to let hotandhumid air drop out its water while flowing up the pipe?

I must look up ground source heat pump as I dont know how they work. I assume you need electricity for that system?

THanks for your comments and anymore you can add. I appreciate your responses.

 

[IRstuff]

Well, even a single air exchange per hour 8200 cf/hr = 137 cfm


"even if the insides are damp sometimes, could mold/mildew actually grow if there is no "food" source"

I would agree with others that typical passive moisture removal systems like this, and even some active ones, are Legionella factories waiting to happen. Warm, moist, air is the perfect growing environment for a host of organisms. And, there are plenty of food sources in the air, notably, you, or more precisely, the dead skin, etc., that you slough off every minute of every day.

TTFN

FAQ731-376
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[hydtools]

I would not expect pvc pipe to be very good for heat exchange. Moisture will cling to all id surfaces, that is where mold will grow. Spores will flow up the pipe with the incoming air.

Ted

 

[redun]

This is sounding really bleak.

The main article i read was about what they called an "umbrella house" it was dome shaped and had these passive heat exchange pipes as they called them. The inside temp of this umbrella house was very stable and no mold or mildew problems. You can Google it and see the aricle. Its pretty short.
Are you thinking that just the incoming air would have enough food source within it to grow the mold/mildew?
The new densglass drywall's claim to fame is because it has no paper mold and mildew wont grow on it. wouldnt it be the same for the pipe?
I too have the same concern about mold/mildew in the pipe but Im just not sure.
I like the idea of the pipe vent but I'm not sure about it either.

I would be nice when the place is locked up for say a month in the summer, to leave a very tiney fan running and have this vent system work to keep humidity levels down in the house while it is vacant.

 

[ornerynorsk]

There are some subteranean "AC" systems being used in Israel that I've read about. Chimney effect, heat rises, which can easily work against you in a system designed wrong. A roof vent or skylight will do more to circulate air than anything, provided you've got some windows :>)

The mold and mildew problem is a real concern in your 90% humidity area. UG houses were a fad in Minnesota 30-35 years ago, and they just didn't pan out. Houses need to breathe well in such climates.

Good luck on the project.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[MikeHalloran]

When our Public Safety building was new, it had some kind of super-green cooling system that was going to be wonderful.

I was in the building once.
It was uncomfortably humid, not nearly cool enough, and was clearly breeding its own hordes of mosquitoes. ... inside. ... and it stank of mildew.







Mike Halloran
Pembroke Pines, FL, USA

 

[SnTMan]

These passive heating / cooling projects are wonderful things to design and build for OTHER PEOPLES' houses and budgets

Regards,

Mike

 

[flash3780]

I think that what you really want is a fan pulling fresh air into the house and into the HVAC system. You'd tap the duct right into the return duct and size it to provide some rate of air changes in the house.

You'll pull fresh air into the house and slightly pressurize the air inside of the house. The latter will prevent hot/cold air from coming in through an open doorway when people enter/exit.

 

[asimpson]

http://www.asknature.org/strategy/e27b89ebcdec8c9b5b2cd9ac84b8f8a0

 

[redun]

ornerynorsk and flash3780,
The house is a simple rectangle with a single pitch shed type roof. It has windows all along the south side and 1 small window on the east and west side where the side fill allow enough room, so these little winodws are about 6 ft from the south wall.From there back,(about 16 ft) there are no more windows.
This is located in northern,Pa. so most of the time hot and humid weather is not a concern,however in summer as you know hot and humid weather can and does occur. The house will be heated with a small effeicnet woodburning stove and i will put in a few baseboard electric heaters that I may want to turn on once in a while to take the chill off when its just slightly chilly.
Thats it as far as heat. I will have a dehumidifier just in case I need it in spring and summer.
Do you know anyone who had a passive underground pipe vent system like this that worked ok and didnt grow mold?

 

[ornerynorsk]

All the passive or quasi-geo systems I've read about are in very arid climates, so I can't lend anything further in that respect.

Fresh air intake for the woodstove? If you've had wood heat before, you already know how it dessicates the house in the winter. The ultra-dry air excaberates the effect of any mold spores present in the air. (EG: bronchitis, respiratory irritation, etc)

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[hydtools]

Put a vent above the south wall and a vent through the north edge of the roof and soil to encourage ventilation. The warm south wall air will rise, the cooler north wall air will fall.

Why add both electric baseboard and wood stove? The house should be well sealed except for the controlled vents and require only a small heat source. Hedging your bets seems to indicate you don't trust the design. Might as well add an air conditioner, just in case.

Check out temp controlled RV vent fans. They run on DC power.

Ted

 

[KENAT]

The only way I can see this working entirely passively is if you've got some kind of chimney effect as briefly mentioned above. Even then I'm not sure, it's not like you have a significant heat source at the base of the chimney to encourage convection. You're essentially relying on the wind a ways above ground level usually blowing at a reasonable klip so you can take advantage of the venturi effect. With the length of underground pipe and inherent drag there in, it seems optimistic.

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[IRstuff]

Chimneys work, when the effluent gas is 1500°F, and when there's a bit of Venturi going at the top. Air that's 10°F hotter, good luck with that, the convection rate is quite pitifully slow.

TTFN

FAQ731-376
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[KENAT]

Hey, I didn't say how optimistic.

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[redun]

hydtools If its 50 degrees and I want to bring it up to say 67 degrees I might just turn on the electric heat real low for awhile rather than crank up wood stove. If its 10 degrees or lower outside and it getting to say 40 degrees inisde I might stoke up the wood stove a burn a little wood.
I figure its cheap to put a few baseboard electric heaters a few places just for convenience.
The vent pipe would sereve as air sourcefor stove also.

I guess the big questions are still
.how big a hole do I drill/cut thru the top of the front wall for the chimney effect to let hotter air out when air is coming in thru underground vent pipe
.If i decide to put tiney fan at that hole in wall how tiney a fan do i need to bring in enough ventilation thru the vent pipe
.is a hundred feet of underground 4 inch pipe enough to get the condensation effect in action for hot humid air coming thru pipe.
This I guess is a thermodynamics questions combined with gas flow-if velocity of air is too fast thru pipe then maybe it doesnt have time to do the heat exchange thing.
.will mold grow inside pipe even though it is on a steep pitch to daylight so no standing water can occur.

 

[hydtools]

Look in this ref. about page 30 for ASHRAE air exchange rate chart for whole-house ventilation.

http://hvi.org/assets/pdfs/HVI_FreshIdeaslores_31Dec09.pdf

You don't want to pull too much air or you may backdraft your stove and draw smoke into the house.

Ted