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?

 

[hydtools]

Have you read about the REHAU system?

http://na.rehau.com/files/REHAU_ECOAIR_Installation_Guide_7.09.pdf

They use 8" and 15" pipe. Buried 5-6ft to get into the constant temperature ground and below the frost line.

Ted

 

[redun]

hydtools Thanks for that link. looks like the same principal,except I guess that is for big commercial use and it looks like must be in flat land where they must have sump pump. Luckily I dont need a pump as i am on side of the mountain so any condensate can just run out via gravity flow.

 

[btrueblood]

A suggestion after having thought about this for a while. Seperate the condensate drain function from the air intake, i.e. in the trench for your air intake, first lay a perforated drain pipe, and bed it in washed rock (classic "french drain"). Your air intake duct should then be perforated, and laid, perf's down, atop the gravel bed for the drain line. This should help keep the duct drier, and reduce (but probably not completely prevent) mold/mildew formation.

In the (now) 100+ year old farmhouse that I grew up in, we had a "cooler" built into the north wall of the house. Essentially a cupboard with slatted shelves, and two vents (upper and lower) through the north wall. Stored vegetables and certain adult libations there, more as an overflow for the fridge. It sorta worked. It also tended to be a source of drafts whenever the north winds blew (winter).

 

[hydtools]

btrueblood, that sounds like you would get 'ground odor' into the house and some creepy-crawlies.

We lived in a brick house built in the 30's and couldn't understand why the dishes in one kitchen cabinet were always cold. The cabinet had been built over a cooler that had top and bottom vents through the wall.

redun, a larger pipe would give more surface for heat exchange and lower air velocity to allow more condensate to drop out in the pipe. Yes,the slope away from the house would carry the condensate away. I thought the numbers used in the link would be of interest; moisture condensed and temperature rise or fall. I didn't find mention of length of pipe for their figures. Curious.

Good luck. Let us know how it works out.

Ted

 

[unclesyd]

I've seen very similar systems tried (Alabama and Florida) and each failed in about one solar cycle. I think the air/air heat exchanger is a much better solution, with only minimal increase of the carbon footprint. This type system will avoid the sealed air syndrome which can be quite harmful to your health from VOCs, Mold, etc.
Depending on your total environmental envelope you could easily add a small high efficiency (high SEER) heat pump type air conditioner. You effectively have a super insulated house so air quality will be a problem.

I haven't run out any details the units from BPE might be the best approach.

http://www.bpequip.com/residential.dws

Addenda:
I ended up with my shop being super insulated and quickly learned that air quality was problem everytime I did anything in the shop. I had to put in an air exchange system. I took the penalty of a small in loss of efficiency as my current heating and cooling system are too big for the reuired load.

 

[boo1]

Several factors to consider: Fresh air requirement, piping design, and temerature/mosture control.

Fresh air ~10 cfm/person assume 6 people max capacity = 60 CFM
100 ft 4" pvc pipe gives .27 inches water head loss
5 elbows add gives .135 inches water head loss
Cap and screen gives .135 inches water head loss
Total loss 0.64 inches of water
so your pump must be a 60 CFM at .64 inches of water head

60 CFM in a 4 inch pipe give 688 ft/min pipe velocity. This velocity may be too high to condense water out of the make up air. Consider a 6" pipe, 60 CFM will be 306 ft/min pipe velocity at .08 inches of water head. A test would be easly constructed and evaluated for both temp and humidity.

 

[gerhardl]

Interesting reading!

It seems that there is some reasonable doubt that the ducting systems can be kept mouldfree.

If you rephrase your problem it could read as:

How to minimize installation, operation/maintenance and consumption cost for a 'green' temperature and energy system controlling humidity and temperature in an underground house. If possible by utilizing earth warmth and natural ventilation by ducts (PVC).

Summary and comments on 'known facts'

1. PVC pipelines seems smooth, but even good quality plastics have pores and will present growth possibillities for milddew and bacteria. Aging process of plastics, although slow. Lifetime xx years?

2. Known problem with superinsulated houses: air quality will often be low, as air circulation often is set/regulated several times lower (up til 1:5 or 1:10?) lower than by older constructions. Air circulation from inside out and vv. should be controllable and amount at a level upholding quality. Higher underground necessary than above?

3. With humidity/temperature higher outside than inside, air intake will give condensate on colder surfaces.

4. Walls, roof (and ceiling), and inner walls to be constructed to give protection against humidity coming from surrounding earth penetrating to inside of house. (Else excess and constant drying and ventilation necessary.)

5. Inner surfaces of house isolated or protected against humid air from outside to give condensation on colder inside surfaces. (Else air intake more needed to be dried)

6. A wood burning oven construction as often used in Scandinavia:

A pipeline for air intake from outside of house led directly into oven to avoid draft in house, diameter depending on capacity of oven, normally used about 2". Might be buried in floor.

Pipe for smoke and hot air from oven (smokestack), even one meter (metal) free will give as much as 1 kw extra. Might also construct larger heat magazine (brick, clay Mexican construction, 'kakeloven' or other).

The direct air intake construction will not necessarily need extra drafting from room/house (possible excemption when lightening with open door or room vent) if smoke-pipesize and intake is dimensioned sufficient to oven capacity. One can however regulate air intake into the house by opening door oven vent intake and open vents (normally above windows)

7. Modern electrical panel (ovens) have metal heating magazines of some size and very narrowbanded thermostats (0,3deg C) and can be adjusted at low cost to give low-cost 'warm-air curtains' in front of (glassed) cooling surfaces.

8. The house entrance(s)should be built with an airlock (closed smaller room with extra door to minimize uncontrolled air exchange.

9. Additional to 'main controlled' air intake the house should have some smaller (2-4") manually adjustable / controllable / shutable / easily cleanable (with chlorid water) vents. About 8 feet above floor, over windows?

And finally comes the key questions:

With the house construction as described, the earth and hence the house temperature would be relatively stable, somewhat cooler in the winter than summer.

If we now add 'living in the house' as some extra heating sources (warmwater, electrical equipment, lights, cooking, people) and some air exchange what will the temeprature be over the day7night and seasons? (This can be calculated!)

Will the living be sufficient for a stable comfortable temperature?

The answer is no.

At a guess mostly heating will be necessary. In spring, summer and early early autumn perhaps partly during day by sun intake, and shading when to much heat?

If extra heat needed: as in winter.

In winter heating could be done by burning wood, electrically by air/air heat exchanger (as cheapest for circulating inside air wich will also give higher conmfort circulation alone about 10W) and heating (100-300W) at air temperature about 8 deg C or higher). Figures approximately for a 250m3 house.

Cooling in summer at a guess mostly/all by surrounding earth?

The main problem then is mainly to control humidity in the air intake in summer.

This problem might possibly be solved by a 'technical room' where the air/air heat exchanger is placed, where straight cleanable/accessible ducts are placed, and air intake into the room perhaps passes 'some suitable cool metal plates' to remove excess humidity in summer above what is condenced in pipeline (or last part of pipeline stainless).

Note: air amount balance necessary to give heat to heat exchanger is not calculated! Duct size and need of forced air not calculated! (Can be calculated!)

In winter the technical room will have air temerature about earth temerature.

The technical room to be isolated from the living area, and will in summer work as dried air intake reservoir. (Possible to control air temperature by having several pipes to different levels (shorter cooling length, throttable vents? Somewhat forced intake from technical room to house? Sunpanel/battery powered fan)?

'Normal' visible draining from ducts in the technical room into small reservoir (cleanable)and normal draining system out together with gray water from the house.

In winter (low humidity) air intake should be directly from outside, throtteled and controlled to balance comfort and running heating sources: wood, electrical or air to air or combinations as suitable.

Sorry about the lengthy comments, but I got really carried away by the concept!

Good luck!

 

[Ron]

boo1 nailed it. You need a larger pipe. Not only for the required air exchanges, but to keep the noise of air exchanges down.

Further, I can't imagine by any stretch, that 40F is comfortable inside. Maybe I'm a bit jaded since I live in the southern US, but even 65F inside is uncomfortable to me.

I have seen very few of these systems work for the long term.

 

[redun]

boo1, Thanks for your specs., calcs and suggestions. Unfortunately I allready bought the 4" pipe. Maybe I can use a smaller fan to slow down the velocity of air coming thru the 4" pipe. Typically there will be no more than 2 people in house and 1 dog,so that may help some. Your analysis gives me good reference information.

gerhardl, Thanks for your long list of thoughts and issues for consideration.

I must try and digest all the info. posted here so far. I must do some calculations of my own and see what I come up with and post an update. In the meantime ,any more thoughts are Welcome

 

[boo1]

From the Moody diagram, f is about 0.03 for smooth PVC pipes at the flow rates which are most likely. f tends to decrease at large Reynolds numbers for very smooth pipes, but less so for slightly rough pipes. Because the internal roughness of the pipe is not closely controlled, f is assumed to be .03 for all flow rates.

The transition from laminar to turbulent flow in pipes occurs at Re between 2000 and 4000.

Re = VD/v

Where: v, the kinematic viscosity of air at sea level is 1.6 x 10-4 ft /sec.

For a 4 inch pipe, this gives a transition velocity of 1 to 2 feet per second.

For fully turbulent flow, hf = f x (L x V2)/(D x 2 x g)

Where:
hf is the head in feet of air (which must be transformed into inches of water).
f is a friction factor which is a function of pipe roughness and other parameters.
L is the length of the pipe.
V is the velocity of fluid flow.
D is the pipe diameter.
Re is the Reynolds number.

The pressure drop h is given in feet of air in the Darcy-Weisbach equation may be converted to inches of water by multiplying by 0.0147.

Solving for head loss in inches of water for one foot of pipe yields the following:

Head loss (inches of water) = 0.0147 x 0.03 x 1/D x V2/64 for 4 inch pipe, this yields 5.7 x 10-9 x v2 per foot

The cross sectional area of a 4 inch pipe is 0.09 sq ft, so assume 30 CFM flow for 3 people, will require a velocity of 344 ft per minute.

344 squared times 5.7 x 10-9 = 0.00081 inches of water column per foot.

For the calculation of pressure drop, the equivalent pipe length should be used. This means that 10 times the diameter (in feet) of the pipe should be added for each elbow and size transition to be used.

Assume 100 ft pipe and 5 elbows
~0.16 inches water head required for a 30 CFM fan

WARNING
Don’t forget fresh maybe required for cooking and heating.
Consider CO and O2 monitors

 

[ornerynorsk]

I've been letting these thoughts percolate over the weekend, and I think in the same situation, I would seriously consider geothermal. Solar panels on your "roof" could possibly help power the system, in addition to shielding the berm from excess solar absorption, at least in the summer. The ground should help temper the winter and give you a net gain vs the snow and cold.

Many utilities have rebate or assistance programs to implement these systems. Tax breaks or incentives for the solar, as well, not to mention depreciation.

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.