A seasonal thermal store (also known as a seasonal heat store or inter-seasonal thermal store) is a store designed to retain heat deposited during the hot summer months for use during colder winter weather. The heat is typically captured using solar collectors, although other energy sources are sometime used separately or in parallel. A solar collector is a device for extracting the Energy of the Sun not indirectly into a more usable or storable form
Seasonal (or "annualized") thermal storage can be divided into two broad categories:
In both cases, very effective above-ground insulation / superinsulation of the building structure is required to minimize heat-loss from the building, and hence the amount of heat that needs to be stored and used for space heating. The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer Superinsulation is an approach to building design construction and retrofitting
Despite the differences in design that they involve, low-temperature systems tend to offer simple and relatively inexpensive implementations which are less vulnerable to equipment failure. They do, however, require the site of the building to be clear of the water table, bedrock and existing buildings, and are limited to temperate (or warmer) climate zones and to space heating only. The water table is the level at which the ground water pressure is equal to Atmospheric pressure. Bedrock is the native consolidated rock underlying the surface of a terrestrial planet usually the Earth. The Köppen climate classification is one of the most widely used climate classification systems It was developed by Wladimir Köppen, a German climatologist High-temperature systems share the same vulnerabilities as conventional space and water heating systems due to their 'active' mechanical and electrical components, as well as their advantage of enabling greater control. They can also be employed in colder climates.
One of the original motivations of early man's movement into caves was probably the ability of the earth to naturally even out variations in temperature. A cave is a natural underground void large enough for a human to enter At depths of about 20 feet (6m) temperature is naturally “annualised” at a stable year-round temperature.
With the development of modern passive solar building design, during the 1970s and 1980s a number of techniques were developed in the US that enabled thermally and moisture-protected soil to be used as an effective seasonal storage medium for space heating, with direct conduction as the heat return method. Passive solar buildings aim to maintain interior Thermal comfort throughout the sun's daily and annual cycles whilst reducing the requirement for active heating and cooling Space heating is the Heating of a space usually enclosed such as a house or room Heat conduction or thermal conduction is the spontaneous transfer of thermal energy through matter from a region of higher Temperature to a region of lower
Two basic techniques can be employed:
These concepts are compared in greater detail at: www.greenershelter.org.
High-temperature seasonal thermal stores are found on a variety of scales, from those installed in individual houses to those serving neighbourhoods via district heating. District heating (less commonly called teleheating) is a system for distributing heat generated in a centralized location for residential and commercial heating requirements
Although the use of high-temperature seasonal thermal stores within individual buildings dates back to at least 1939 (MIT Solar House #1), the United States, Switzerland and Germany have all been notable pioneers in this field. The following buildings have been recognised as being of international significance in pioneering the use of modern engineered solar building design: MIT Solar House #1 The United States of America —commonly referred to as the Switzerland (English pronunciation; Schweiz Swiss German: Schwyz or Schwiiz Suisse Svizzera Svizra officially the Swiss Confederation Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe.
Perhaps the best known international example of this active approach is the experimental “Jenni-Haus” built in 1989 in Oberburg, Switzerland. Oberburg is a municipality in the district of Burgdorf in the canton of Bern in Switzerland. Switzerland (English pronunciation; Schweiz Swiss German: Schwyz or Schwiiz Suisse Svizzera Svizra officially the Swiss Confederation This has 3 tanks storing a total of 118m³ (4,100 cubic feet)  providing far more heat than is required to heat the building.
The more recent “Zero Heating Energy House”, completed in 1997 in Berlin as part of the IEA Task 13 low energy housing demonstration project, stores water at temperatures up to 90 °C (195 °F) inside a 20m³ (700 cubic feet) tank in the basement , and is now one of a growing number of similar properties. Berlin is the capital city and one of sixteen states of Germany. IEA Solar Heating & Cooling Implementing Agreement - Task 13 (Solar Low Energy Buildings was an international effort organised by one of the International Energy Agency 's Implementing The Celsius Temperature scale was previously known as the centigrade scale. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 A basement is one or more floors of a building that are either completely or partially below the Ground floor.
At the neighbourhood level, the Wiggenhausen-Süd solar development at Friedrichshafen has received international attention. Friedrichshafen is a town on the northern side of Lake Constance ( Bodensee) in southern Germany, near the borders with Switzerland and Austria This features a 12,000 m³ (424,000 cubic feet) reinforced concrete thermal store linked to 4,300m² (46,000 square feet) of solar collectors, which will supply the 570 houses with around 50% of their heating and hot water . Reinforced concrete is Concrete in which reinforcement bars (" Rebars quot or fibers have been incorporated to strengthen a material that would otherwise be
A different approach is illustrated by the Drake Landing Solar Community development in Okotoks, Alberta. Okotoks is a town situated on the Sheep River, south of Calgary Alberta, Canada. Alberta (ælˈbɝtə is one of Canada's prairie provinces. It became a province on September 1 1905 Here the store is created from the ground itself, with solar heated water pumped into a Borehole Thermal Energy Storage (BTES) system. This consists of 144 boreholes, each 37m (121 ft) deep, which heat the ground to a maximum of around 90 °C (195 °F) . A borehole is the generalised term for any narrow shaft drilled in the ground either vertically or horizontally The Celsius Temperature scale was previously known as the centigrade scale. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724
Thermal storage (sometimes referred to as heat and cold storage) is also used extensively for applications as the heating of greenhouses.  In summer, the greenhouse is cooled with ground water, pumped from a aquifer, which is the cold source. An aquifer is an underground layer of Water -bearing Permeable rock or unconsolidated materials ( Gravel, Sand, Silt, or Clay This heats the water, which is then stored by the system in a warm source. In winter, the warm water is pumped up to supply heat. The now cooled water is returned to the cold source.
 The combination of cold and heat storage with heat pumps has an additional benefit for greenhouses, as it may be combined with humidification. In the (closed circuit) system, the hot water is stored in one aquifer, while the cold water is stored in another. The water is used to heat or cool the air, which is moved by fans.  Such a system can be completely automated.