Editing Earth shelter (section)

===Passive annual heat storage===
Passive annual heat storage is a building concept theorized to create a [[Seasonal thermal energy storage|year-round constant temperature]] in an earth shelter by means of direct gain passive solar heating and a thermal battery effect lasting several months. It is claimed that an earth shelter designed according to these principles would store the sun's heat in the summer and release it slowly over the winter months without need for other forms of heating. This method was first described by inventor and physicist John Hait in his 1983 book.<ref name=Hait2013>Passive annual heat storage: Improving the design of earth shelters. John Hait. 2013</ref> The main component of it is an insulated and waterproof "umbrella" which extends out from the earth shelter for several meters in all directions. Hence the term "umbrella house". The earth under this umbrella is kept warm and dry relative to surrounding earth, which is subject to constant daily and seasonal temperature changes. This creates a large heat storage area of earth, effectively a huge thermal mass. Heat is gained via passive solar in the earth shelter and transferred to the surrounding earth by conduction. Thus, when the temperature in the earth shelter dips below the temperature in the surrounding earth, heat will return to the earth shelter. After a time, a stable temperature is reached which is an average of annual heat changes in the external environment. Some criticize the technique (along with the earth sheltering technique as a whole), stating concerns including difficulty and expense of construction, moisture and lack of evidence.<ref>[https://www.greenbuildingadvisor.com/article/can-we-live-happily-underground][https://www.greenbuildingadvisor.com/question/new-earth-sheltered-pahs-construction Green Building Advisor: Can we live happlily underground?]</ref>