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Discussion Starter #1
We are building an earth-sheltered home concrete walls x3 buried with conventional front wall. R-49 insulation front wall and a standing-seal steel roof (for water collection) which is at ground level in back and most of way to front. This includes the normal soffit & facia needed for air circulation into the rafters etc so it does not rot. Question is with air circulating from the front wall through ceiling and out through soffit and spinners on top of roof do we need HVAC? We are going with a steel roof for 2 things: cost savings over concrete dome roof and water collection. In a well-insulated (i.e. earth) sheltered home including the roof no HVAC is needed, and will this work the same for us? R-49 insulation front wall and ceiling. Any comments welcome. We are doing a Rocket Mass heater at 1st opportunity, house situated SE (so we can see pond) with 4 foot overhang in front and double pane, non-low-e windows to allow heat in in winter.
 

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Hello, hello....is there anybody in there.....?
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I'd install some air intakes that route the air through underground drainage pipes.
If they are long enough and deep enough, the pipes will either cool or heat the air to the ambient ground temperature, cooling it in Summer and warming it in Winter. It will also remove some of the moisture from the air when cooling.

With a few of those and a some roof vents that can be opened and closed you can control both fresh air flow and temperatures.
 
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Otiose Endomorph
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If you can swing it, I'd go for a Heat Recovery Ventilator (HRV). In the old days, houses were sieves, and air exchange wasn't needed (they breathed). As we go for tighter houses, it gets harder to get fresh air supply in house. An HRV can control not only fresh air, but humidity (like from a shower or cooking). Plus, it captures heat from expelled air, if need be.
The newer units are getting cheaper and more efficient.
https://www.amazon.com/s/ref=nb_sb_ss_i_1_14?url=search-alias=tools&field-keywords=heat+recovery+ventilator&sprefix=heat+recovery+,aps,878&crid=O9OT6W12X04Z&rh=n:228013,k:heat+recovery+ventilator
My ideal unit is called a 'magic box'...it has HRV and a Heat Pump built into one unit...they are still pricey, so not in the cards, yet.
The magic box would refresh, recycle (filter), and recover air, plus heat and cool. Does it all.
 

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Just to chime in with a couple of thoughts.

Many variable depend on your region: climate zone, temp swings (hottest to coldest), frost depths and so on. It's important to know such details as you are trying to harness the most out of what Mother Nature is providing you in your spot. Therefore the advice without such info won't be that helpful and could possibly (likely) have negative effects.

- You will need Fresh Air intake(s) as you will be using a wood burner and your in a pretty sealed building. Bathroom venting & kitchen (range hood) venting will be essential to get moisture out - again these will require air in to building as well to replace that which is exhausted.
- Earth Tubes work well when done right OR can be a nightmare if done wrong with mould, mildew & more. That requires more detail discussion and much more detail. These can be a huge power saver and give a good benefit in both summer & winter.
- HRV systems as Melli pointed out are pretty important. They allow for Heat Recovery by warming the incoming air with the outgoing stale air, there are many variations and they are not "universal". Again these largely depend on your climate zone and other factors... In some regions not needed where a simpler Air Exchanger will do as heating is a non-issue BUT then one for cooling incoming hot air from outside can apply in some regions...
- Insulation ! Must be very cautious about what type and how / where you use the different types. Fore anything underground, closed cell foams are best and they have their pro's & con's too...
- Radon Gas also must be considered, as this is earth sheltered you will be getting a certain amount of it in and how to mitigate and manage it is very important and needs to be part of the build plan.. A Good barrier between soil & structure, air management and monitoring with a detector may be required.

BTW: I built my own air-exchanger rather than buy a prebuilt one (they were outrageously priced for a really small unit to suit my cabin with is 500 sq feet floorspace + 250 storage loft. Here is a link to what I based mine off of: https://www.wildsnow.com/17884/how-to-build-air-cross-flow-heat-exchanger-budget/ DIFFERENCES I used smooth aluminium pipe instead of corrugated and my exit / termination end outside is from a Gas Venting system as I wanted something that looked nice too. ** Should'a went with 12V variable speed box fans running from a wall-wart, instead of the 120V fans for even more power saving (120's don't use that much but every watt counts to an off-gridder).**
 

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Otiose Endomorph
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Just to chime in with a couple of thoughts.

Many variable depend on your region: climate zone, temp swings (hottest to coldest), frost depths and so on. It's important to know such details as you are trying to harness the most out of what Mother Nature is providing you in your spot. Therefore the advice without such info won't be that helpful and could possibly (likely) have negative effects.

- You will need Fresh Air intake(s) as you will be using a wood burner and your in a pretty sealed building. Bathroom venting & kitchen (range hood) venting will be essential to get moisture out - again these will require air in to building as well to replace that which is exhausted.
- Earth Tubes work well when done right OR can be a nightmare if done wrong with mould, mildew & more. That requires more detail discussion and much more detail. These can be a huge power saver and give a good benefit in both summer & winter.
- HRV systems as Melli pointed out are pretty important. They allow for Heat Recovery by warming the incoming air with the outgoing stale air, there are many variations and they are not "universal". Again these largely depend on your climate zone and other factors... In some regions not needed where a simpler Air Exchanger will do as heating is a non-issue BUT then one for cooling incoming hot air from outside can apply in some regions...
- Insulation ! Must be very cautious about what type and how / where you use the different types. Fore anything underground, closed cell foams are best and they have their pro's & con's too...
- Radon Gas also must be considered, as this is earth sheltered you will be getting a certain amount of it in and how to mitigate and manage it is very important and needs to be part of the build plan.. A Good barrier between soil & structure, air management and monitoring with a detector may be required.

BTW: I built my own air-exchanger rather than buy a prebuilt one (they were outrageously priced for a really small unit to suit my cabin with is 500 sq feet floorspace + 250 storage loft. Here is a link to what I based mine off of: https://www.wildsnow.com/17884/how-to-build-air-cross-flow-heat-exchanger-budget/ DIFFERENCES I used smooth aluminium pipe instead of corrugated and my exit / termination end outside is from a Gas Venting system as I wanted something that looked nice too. ** Should'a went with 12V variable speed box fans running from a wall-wart, instead of the 120V fans for even more power saving (120's don't use that much but every watt counts to an off-gridder).**
Really like the home built Air Exchangers, but condensation seems to be a problem, especially in humid locales.
Would really like to build one, whenever time and money permits...good idea for my well shed. I suppose smooth wall dryer tube would facilitate better draining. Has to be a way to limit condensation...maybe spraying dryer tube with a rough texture rubber paint or something similar.
Thanks for reposting that link...I totally forgot about it.
 

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Condensation is not a problem, I used White 4" PVC Sewer piing on the exterior with the aluminium pipe inside. The Aluminium pipe is held together with foil tape and centered in. The white PVC is screwed together and where it joins the gas vent fitting I used a rubber coupler, it has a slope ratio of 1/8" per foot and any condensation stays outside or goes out. Mine is 11' long and runs slow, works peachy pretty much, although, using the corrugated aluminium would have added more turbulence (which may have improved heat transfer) I'm happy with it.

Below is a photo of the IPEX System-636 Concentric Vent Kit I used for mine. I got one with my On-Demand Heater for the radiant floor and thought it was the perfect solution for my air exchanger too, so $60 later voila. 3" inside going to centre of the cone, 4" outside. Note how the end Y is made, that makes and the PVS Sewer pipe is a perfect connection. I just left a stub of the 3" original CPVC on both ends which allows for the smooth aluminium to literally slip right over nice & snug too. I can tear it all apart in < 5 minutes if I need to. Ohh... I did wrap bug screen over the outside front before installing the cap with the supplied bird screen. As this is not for a LPG heater, not a problem and I figured it's better than leaving a nice entry for bugs. ** Cheapest to order off of E-Bay ** Rheem has a variant with a slightly different cone for the exhaust. I could'a gone a bit cheaper & more cludgy but wanted a nice finish outside.

REF from E-Bay:
https://www.ebay.com/sch/i.html?_osacat=115968&_odkw=3"+concentric+vent+kit&_from=R40&_from=R40&_trksid=p2334524.m570.l1313.TR0.TRC0.H0.X3"+pvc+concentric+vent+kit.TRS0&_nkw=3"+pvc+concentric+vent+kit&_sacat=115968
636-concentric-kit.jpg
 

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Discussion Starter #8 (Edited)
We will have a dehumidifier, and the soffits/facia will allow air circulation from under the eaves and then out through the front of the house, which will have 13 windows & 2 doors, with some ventilation through the structure itself (or we can open windows at times) per the contractor.
We will also have a Rocket Mass Heater for the worst days, but I understand that often just cooking meals, running light bulbs, TV's & computers (2 always on when home) helps with heat too. We will have the propane cooking stove venting directly outside to prevent toxic fumes, & ventilation in the bathroom, & for the dryer, (although in winter I will route it through a bucket with water in the bottom to capture heat & humidity. My searches, though, for images of an earth-sheltered home with a steel roof only turns up ONE with a view from the back only, and it is flush to the ground from that view like ours is. It will be a peach to keep the leaves off as the nearest trees will be 80 feet away, and the 4-12 slope will allow wind to clear most of them. I am still reading everyone's comments and it is interesting to say the least.
 

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what is SIPS??
Structural Insulated Panels (System)...good starting point to learn about 'em: https://en.wikipedia.org/wiki/Structural_insulated_panel
Be aware of this problem with OSB SIPS and "hot roof" designs: http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/how-make-sip-roof-better
And note that the underlying problem there is moisture. Moisture management is key factor in design & construction of structures. Especially any kind of earth-sheltered structures.
 

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Structural Insulated Panels (System)...good starting point to learn about 'em: https://en.wikipedia.org/wiki/Structural_insulated_panel
Be aware of this problem with OSB SIPS and "hot roof" designs: http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/how-make-sip-roof-better
And note that the underlying problem there is moisture. Moisture management is key factor in design & construction of structures. Especially any kind of earth-sheltered structures.
This.....
Also test for Radon......
Circulation is always a good idea.............
 
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Discussion Starter #12
We will have natural circulation with soffits/facia and air passing through front wall or the reverse, fans in kitchen bath etc & a rocket mass heater ASAP. We will no doubt make some small changes as time passes like a 45 degree angle greenhouse along the front of house with doors at each end to keep certain foods herbs etc available as we are planning to be self sufficient as much as possible, and with 5.25 acres 98% open that will not be a problem. I asked my contractor if SIPS will be used on the wall and will meet with him soon and ask about the roof then.
 
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