Thermal Stability in Earth Sheltered Houses

• At a depth of a few metres below the surface of the Earth the temperature (anywhere on the planet) varies very little all year round, and is roughly equal to the Average Annual Air temperature of the air directly above the surface.

• An Earth Sheltered House has thermal stability because it is built into this stable environment with most of the outer surface of the structure is in contact with the Earth.

• In most places in Australia the AAA temperature will be between 13 and 18 degrees . . . which is within the human comfort level. 

• However in many other parts of the world the average annual temperature is much lower, even well below zero . . . in which case they are building into the permafrost.....Brrrr!

There are two different types of earth sheltered house :

COLD CLIMATE TYPE  and HOT CLIMATE TYPE

They are different in the way they work . . . . and how they need to be designed.

COLD CLIMATE  - suitable for the climates in Europe and the USA :

• Because the temperature of the ground is often well below human comfort level, these houses use huge blocks of Styrene foam on the outside of the structure to isolate themselves from that cold surrounding ground.

• They are internally heated either by natural sunlight, or by a generated heat source. 

• They store this heat in the thermal mass of the building structure.

• They are a total 'thermal mass' type of structure.

• Their energy pricing structures are vastly different to ours in Australia.     Some places have to heat their (traditional) homes 24/7 all rear round!

• They often incorporate a heat exchanging system which requires the structure to be fully sealed in order to work properly.

HOT CLIMATE   -  the Australian type :

• We embrace the temperature of the surrounding ground - it's just fine.        So we don't need all those outer foam blocks (which aren't very eco-friendly).

• We allow our outer walls to adopt the stabile surrounding ground temperature and continually radiate it into our houses . . . and because it is the Earth . . . it will never run out.

• Any small amount of heating that we may require in the depth of winter can be achieved with a slow combustion heater, if the sunlight through the glass is insufficient.   Our houses exceed the Australian Building Code (BCA) requirement for external wall insulation, so it doesn't take much heating.             Why? - we are only heating the air within the room - not the structure.

• Our houses are not the 'thermal mass' type - the Earth surrounding our houses is continually at a comfortable temperature. The notion that we can "store heat in the structure and surrounding ground" is a fallacy . . . it comes from an earlier era when this form of house was not properly understood.

• There may be value in some thermal mass within the structure, but we advise caution if it is to be a primary direction for winter heating. Our climate swings can be quick and the thermal mass could be caught 'out of sync' with the weather patterns of the period. Better to let the Earth do its thing on the structure and the internal temperature of the house adjust itself accordingly.  

• In reality, for a considerable part of the year, our houses can be left open for healthy ventilation and to embrace the surrounding environment and outdoor lifestyles. 

• As mentioned in 'Design Concepts' on the Home Page - our houses have very effective air-flow and natural lighting to all habitable rooms (as required by the BCA).  Our light/ventilation courts act as 'hot air chimney' drawing air  from the rooms surrounding them and across the house from the front external windows and sliding doors.  The top of the courts have adjustable glass louvres to control the winter/summer air movement.  It's something our Open House Tour guests always remark on. (They are also a great place to have a washing line which can be hoisted up to the sun.)

• In times of extreme temperatures and adverse climatic conditions our houses can be completely closed up to take advantage of their thermal stability and safety . . . but a lot of the time they can be left open to catch the breezes, just like any other house.        

So, let's be clear - the Cold Climate and Hot Climate types are completely different.

Northern Hemisphere practices will usually not fit our Australian conditions - there are exceptions, but they are rare. 

There's a lot of information on the internet that's either out of date or not applicable to our climates or the Australian Building Codes. 

We in Australia have terrific climates, from the temperate and alpine southern regions to the northern tropical and sub-tropical zones . . . most of the year we Aussies can spend a lot of time outdoors, and so we at ShelterSpace advocate the use of readily accessible outdoor living areas that capture the breezes and shield the occupants from harsh sunlight. We like to see them as being part of the overall design . . not a last-minute addition or just part of the landscaping. 

Well integrated outdoor spaces can totally transform the way a house performs - well worth the effort and cost. 

We in Australia should think of outdoor spaces as fundamental parts of any design. 

A typical internal yearly temperature range within our homes is between 15 to 25 degrees.

My place once reached 26 degrees inside. . . . but it was 46 degrees outside, and it had been in the 40s for two week prior to that!

Usually in summer the inside temperature stays around 22 degrees.

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THE RADIANT HEAT EFFECT :

An earth sheltered house derives thermal stability not only from the stable ground temperature being conducted through the outer structure, and from there by convection through the air within the house . . . but also by the stable temperature of the surrounding ground and structure being directly transferred by radiation to the objects within it  . . .  and this of course includes us humans.

We feel this radiant stable temperature (we call it 'coolth') on our skin  . . .  inside our houses its usually around 17 - 19 degrees C -  depending on your climatic region.

Now things start to get a bit more interesting . . . our epidermis can not only register the temperature of the air surrounding it, but as we've just seen, also the temperature of the radiant heat landing on it directly from the structure. 

Our brain silently identifies the two types of temperature signals, analyses them, make a choice, and advise us to either put more cloths on . . . take some off . . . or stay the way we are! 

In other words when you are inside an earth sheltered house you are being effected by two separate types of 'heat signals' both working together . . .  and it is quite probable that the air temperature is one thing and the radiant temperature is another . . . in which case the brain usually 'prefers' the radiant signal if they are not too far apart.  

It's what the meteorologists call "Feels Like".

The beauty of all this is that we don't have to adjust things . . . its working fine by itself . . .  mainly because our Australian climates are within the human comfort range.