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...
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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).**
