The problem of energy storage is of central importance for and improved energy economy. Long term heat storage requires very low construction costs. Many underground storage alternatives can meet these requirements. In the big scale, hot water accumulation in rock chambers and in-ground hot water pools are competitive solutions. Direct storage of heat in soil masses is another alternative. The paper describes some new techniques for underground thermal storage. INTRODUTION The consumption of energy is closely related to external conditions like the daily activity pattern of the society and the weather fluctuations. When thermal energy for heating is produced by burning of fuels, then the production can be readily adjusted to the actual consumption level. The fuel itself is a good energy storage. In countries with cold climate, the energy required for heating of buildings is very large. In Sweden, for example, about half of the total energy consumptions used for heating. 90 % of this thermal production is based on oil. Measures for reducting the dependency on oil are discussed in many countries. Where the oil can be substituted with other fuels, like coal or biomasses, there will be no additional need for thermal storage in the system. However, other production methods for thermal energy also utilized or will be used in the near future. Examples of such methods are solar energy, industrial thermal waste and combined power and thermal production. Here the production and consumption patterns are very different on every time scale (daily, weekly, yearly) and thus thermal energy storage is required. Characteristics of thermal storages for heating purposes are low energy density (temperatures usually below 100° C) and low degree of utilization (once on a few times a year). Consequently the installation costs for these storages must be kept very low in order to make them economically competitive. The addition of a thermal storage to a combined power and heat production plant will enable the power production to be adjusted accord.ing to the consumption pattern of electrical energy. It will then not be necessary to waste any heat during peak power generation periods, just because there is not a concurrent thermal load in the system. In pure thermal, production units (central heating stations) a thermal storage has the benefit of reducing the required peak capacity of the heater (as well as of the redundant heater system). Maybe the most important advantage created by thermal, storages is that they permit the utilization of such thermal excess energy from the industry, that otherwise would have been wasted, and of thermal energy from solar collectors. This energy can only be produced during the warm season of the year, but will be consumed during the cold season. THE TWO SCALES OF THERMAL STORAGE Figure 1 shows the energy consumption for heating of buildings in a cold climate (Stockholm) during a year. This curve has variations on (at least) a daily, a weekly and a seasonal basis.

In the Osloregion (Oslo = Capital of Norway) many dual purpose rock installations are under construction. (1980) In peacetime they will be used as sports halls and swimming pools. In the event of war they can easily be converted into very good civil defense shelters. Five such installations are shortly described here. Norway is a relatively large country. It is approximately 50% larger than Western Germany. But while W. Germany has 62 mill. inhabitants, Norway has only 4 mill. 70% of the land is covered by rock. Installations in rock is therefore a Norwegian tradition. The activity in tunneling and rock blasting have several decades been very high. Planned tunnel length pro anno and pro million inhabitants for the period 1970–79 was 19 km compared to the average value for DECO-countries which was 3,2 km. Since 1916 nearly 150 hydro-power plants have been constructed in rock. This number is more than 50% of the total number in the world. It has given considerable experience to the designers as well as to the contractors. This has benefited planning, design and construction of a large number of other underground installations throughout the country ranging from caverns for storage purposes for different products such as oil, gas, ore, flour, paints, frozen food to drinking water reservoirs, sewage plants, parking lots, factories, telecommunication centers, swimming pools and sports halls. The defense and civil defense have also long traditions in rock installations. The first sports hall in rock was finished in 1972 in the small town Odda on the west coast. The main hall (fig. 2) is 25 by 60 m which makes it adequate for playing international handball games. The total volume of this installation is 25 000 m 3 •. The first swimming pool in rock was finished in 1975 situated in the small inland town Gjøvik. The installation contains a 25 m pool with 6 lanes, a smaller pool for beginners, a gym, saunas and ancillary areas. The total volume is 11.500 m 3 • Of special interest is the fact that the energy consumption for running this underground public bath and swimming pool has been cut down to 45% of what would have been necessary for a similar building on the surface. Fig. 3. The experience gained, both for the sports hall and swimming pools, is very good. Five such installations will be shortly described, but first some general comments. DUAL PURPOSE INSTALLATIONS Rock installations have a surprising resistance against weapon effects ranging from direct hit from conventional weapons to all the effects from nuclear weapons. Thus all these installations have a dual purpose: sports halls or swimming pools etc. in peacetime, civil defense shelters in wartime. The local community is by law responsible for building the installation, but approximately 2/3 of the cost is paid by the state government because it also can be used as a shelter. This makes it cheaper for the community to build in rock, compared to a construction in the open air.

In Norway, during the last decade, several dual purpose rock installations have been constructed. In time of peace they are serving as sports halls and swimming pools and in war events as public shelters. Running experiences have shown remarkable low energy consumption and maintance costs compared to conventional installations. A sports hall built in 1972 and a swimming-pool built in 1975 are referred to. INTRODUCTION Since the last World War, Norway has had ambious plans in building wartime shelters for greater part of the population. However, if the constructions cannot be given a reasonable application in time of peace, this would be a very expensive, if not impossible task. During the last decade, several large dual purpose rock installations have been erected. In 1972 a sport hall was taken into use in the western part of Norway, and in 1975 a swimming pool in the inland north of Oslo. For the swimming pool an extensive study was carried out to eludicate the energy aspects compared to a conventional indoor swimming pool. The calculations indicated very low energy consumption for the rock alternative. The running experiences have been very satisfactory, and have fully confirmed the theoretical estimates. In the following I will give a short summary of the theoretical and practical results and try to eludicate the reason why a rock installation is so favourable compared to a freestanding alternative. ENERGY BALANCE A conventional building is influenced by following main factors, determining the heating demand: -Heat transmission through building structures owing to the difference between inside and outside temperatures. -Heating of ventilation air volume. -Heating of infiltration air volume, owing to the leakages through building structures windows and doors. -Solar heat gain. -Electric illumination and motors. By meanse of modern insulation materials, it is possible to obtain very low heat tranmission through walls and roofs. The windows, however, will always be a tangible problem, especially where a high indoor air humidity is desirable, par example in a swimming pool. In a swimming pool, owing to high indoor air humidity and temperature in combination with low environmental temperatures during the winter, special attention has to be paid to the vapor barriere in walls and roof. Undesired ventilation owing to infiltration is practically propotional to wind velocity. In Norway, the highest wind velocities occure during the winter in combination with low ambient temperatures. The heat loss due to infiltration cannot be recovered. In theory it is not difficult to handle the infiltration problem. Most of the constructions suffer from unfortunate technical solutions and bad workmanship. And a present leakage has a tendenct to be constantly increasing as the time elapses. In building with high air humidity contents and temperatures, the leakage air transports large guaranties of vapour condensing into the insulation layer. Primarely this in causing reduction of the heat resistance of the structure, secondarely the building structure is damaged. The heat dissipation from electric illumination and motors are considered as integrated parts of the heating system.

In this first phase of the study, the heat losses of an earth-sheltered dwelling through transmission have been studied by means of a mathematical model. These results have been supplemented by approximate values for passive solar heating and other energy sources. The calculated energy demand of the studied house is 90 kWh/m2/year. A similar house, though not earth-sheltered, would demand some 110 kWh/m2/year. A number of other test projects on energy conservation also indicate energy demand in the region of 110 kWh/m2/year. The average Swedish detached house consumes 28 000 kWh/year, corresponding to 250 kWh/m2/year. It seems that improvements to the house studied are possible and that these would result in a further significant reduction in energy demand. INTRODUCTION The idea of earth-sheltered housing has met with considerable interest in the U.S. The Underground Space Center at the University of Minnesota has given itself the task ot studying the concept and of disseminating information about it. The Swedish Council for Building Research, in cooperation with the Underground Space Center, has awarded a research grant to VBB AB and Hagconsult AB, for a study project on the characteristics of earth-sheltered housing in Scandinavian climate and geology. EARTH-SHELTERING Earth-sheltering can vary between conventional houses with grass on their roofs to fully recessed houses which receive their daylight via an atrium. The Swedish study concerns a house on a sloping site, the roof and three walls of which are covered with at least So cm of earth. The exposed fourth wall faces south in order to receive maximum passive solar heating. This basic model is applied rather strictly - the effects of alterations may be studied in projects to come. The house, see Fig. 1, is a concrete structure with sufficient styro insulation to meet the requirements demanded by the Building Code. Where the earth shelter is greater than 3 metres, no insulation is necessary. CLIMATIC DATA In the Stockholm area, the monthly mean temperature varies between -3.2 and +17.5°C. Most of the earth around the house is only subject to minor variations in temperature, from +70C which is the average temperature over the year. The latitude of Stockholm is S90N, where the solar angle varies between 7 and 55 0. ENERGY AND POWER DEMAND Heat losses due to transmission through the earth have been calculated by means of a finite element model, as shown in Fig. 2. The two-dimensional heat flow is calculated for a section of the house. The effects at the two ends of the house are not included, but they will not, however, significantly affect the results obtained. The model must be extended 20 m outside the structure of the house itself. The heat losses depend on the geological conditions. For calculation purposes, they have been assumed to be as is shown in Fig. 3. At an indoor temperature of 200C and an outdoor temperature of 7°C (mean yearly temperature) transmission losses will be 70 W/m house.

Efficient utilization of solar energy and industrial waste heat requires heat storage facilities. Such facilities can be provided in groundwater aquifers. Two aquifer heat storage projects currently being carried out in Sweden are presented. INTRODUCTION Efficient utilization of solar energy and industrial waste heat presupposes the availability of short-term and seasonal heat storage facilities. Storage in natural groundwater aquifers is at present being studied in Sweden as one possibility. Various kinds of geological formation can be used, primarily in sedimentary rocks or Quaternary deposits. An ideal storage facility provides natural boundaries against water and heat flow from the facility. Methods are being developed to control this flow. Heat storage in aquifers could be used for internal heat storage in factories or as part of a district heating system. Low temperature storage can be used in combination with heat pumps. In this paper, two projects conserning heat storage in connection with district heating are presented. EXPERIMENTAL PROJECT ON STORAGE OF SOLAR ENERGY IN A SEDIMENTARY ROCK AQUIFER Background A pilot low energy housing project is being planned in Landskrona, in the south of Sweden. The basic concept of the project offers a range of possible energy-saving and energy-collecting installations. One example is a glass-covered street or arcade which functions as a giant solar collector for nine one-family houses, see Fig. 1. Aquifer storage system The low temperature heating system (40oC) will be built around heat-pumps which use groundwater (+5 to 20oC) for heat storage and extraction. The groundwater will be pumped up and injected by means of a two-well system, consisting of one "warm" well and one "cold" well. The system is primarily planned for short-term storage, for example, from sunny days to cloudy days. Experiments will be performed to find out if it is also possible to use the system for long-term storage, i.e. from summer to winter. The system is schematically illustrated in Fig. 2. On sunny days, the heat-pumps use warm air from the arcade to heat the cold groundwater being pumped up from the cold well. The temperature of the groundwater is raised from min +50C to max +20°C. It is then injected through the warm well into the aquifer. As a result, the temperature in the arcade will be kept at a comfortable level. On cloudy days, heated water will be taken from the warm well and used for heating. The whole pumping-system is closed and the groundwater is never in contact with the air. The maximum water flow has been calculated to be 200 m3/day. There is a suitable aquifer in the sedimentary rock about 30 m below the ground surface. The rock is more than 500 m thick and consists of Cretaceous limestone with banks of flintstone. The Quaternary layers covering the aquifer are mainly clay and clayey till. The aquifer is fracturous as well as porous and it is very extensive in area. The experimental siteis located near the sea and the natural hydraulic grandient is very small.

This paper discusses the current activity ann, in particular, the current research efforts in the area of earth sheltered building design, construction, and acceptance in the U.S. INTRODUCTION Interest in the use of earth sheltered buildings has expanded greatly in the past 6 years, and particularly in the last 2 years. Prior to 1973, there were only a few isolated earth sheltered houses and scattered commercial and institutional examples of underground buildings in the United States. These were mostly built for design aesthetics or environmental reasons. Since then the number of earth sheltered buildings and houses being built has increased very rapidly. Since earth sheltering is not yet a term that is universally understood, it would perhaps be well to further define the concept before embarking on a discussion of what research is currently underway in the field. In broad terms, earth sheltering uses the earth as a barrier and a moderator. The earth Moderates temperature extremes in the air, and moderates surface vibrations and airborne noise. It acts as a barrier to storm and wind effects, ultraviolet degradation, and an undesirable visual environment. It has a large thermal mass that can work well with an intermittent energy supply such as solar energy. The earth is also a natural element which supports vegetation and, hence, the other life processes on which we ultimately depend. Using the earth to shelter a house or building, then, is a means of providing a natural barrier to many undesirable climatic and man-made features of a particular area. The impact of the building on the surrounding environment will also be lessened, allowing more of the land's surface to remain in a natural state. Furthermore, and of particular importance at the present time, earth sheltering serves as a massive means of decreasing the dependence of the building on artificial methods of climate control derived from fossil fuel energy. Naturally, there are also some disadvantages to earth sheltered structures. These relate primarily to the heavier and stronger structure required, tile need for high quality waterproofing and insulation to combat exposure to ground moisture, and the need for a higher level of design and supervision in small scale construction. Although earth sheltered designs are not limited to any fixed definitions, it will perhaps be helpful to explain two of the basic layouts that are typical of earth sheltered construction. A typical design that is very appropriate for colder climates is the elevational design in which windows and openings are grouped on one side of the structure, with the remaining three sides and roof earth-covered. When the windows do face south, a maximum amount of passive solar heating can be achieved to combine with the low energy requirements of the structure. A courtyard or atrium design is quite common and is a very appropriate design for a flat site or a warm climate. The courtyard does not have to be totally enclosed. Using a U-shaped courtyard allows an easier transition and visual connection to the surrounding ground.

Storage of heated water in rock caverns is judged to be an interesting alternative for solving the storage problems connected to large-scale utilization of solar energy and surplus industrial heat. For verifying and demonstrating the technique, a test plant with a storage volume of 15 000 m 3 will be constructed, in which a comprehensive research programme will be carried through. The effects of various time/temperature cycles will be studied. Main items on the research programme are: heat losses, rock stability, heat exchange and material questions, water layer studies, and influence on the environment. INTRODUCTION The use of solar and wind energy as well as surplus or waste heat from industrial processes, power production, sewage water etc is judged to be an important way of reducing the very strong dependency on oil for heating purposes in Sweden. The increasing price on oil and the risk of disturbances of the supply together with the political decision on the limitation of use of nuclear power have lead to very strong efforts in Sweden to develop new techniques for the use of new energy sources and to reduce the need for energy. As the main part of solar and waste heat is normally available only during summer, this technique nessecitates seasonal storage. Extremely inexpensive methods will have to be used to make seasonal storage of low temperature energy economical. For large scale storage there are today few other choices available than storage in water or rock and soil. Since the "energy density" of such ·magazines is low, huge volumes will be needed to cover even a small part of the energy requirement for heating in Sweden. In particular storage of heated water in rock caverns or storage of heat direct in penetrated rock masses are judged to be most interesting due to common occurrence of suitable rock formations in Sweden and the possibilities this entails for optional localization of the storage close to the producer or user of the heat. The storage of heated oil in large rock caverns used in Sweden for many years has shown us that the use of rock caverns offers storage at low costs and that the energy consumption for heating the oil is small compared to the above ground alternatives. It was therefore natural to choose the same concept for the first heat storage facility in Sweden. The conditions for storing heated water in rock caverns have been studied in several R&D-projects in the 1970's. These investigations indicate that a large-scale storage in rock caverns can be advantageous from both technical, economical and environmental points of view compared to storage above ground. So far the technique has not been tested on a large scale. Research and demonstration plant For verifying the results of earlier investigations and for demonstrating the technique under realistic circumstances, full scale tests are necessary. For this purpose a test cavern, equipped with a comprehensive instrumentation for research, is now being designed.

Underground Pumped Hydroelectric Storage (UPHS) is a technique for supplying electric power to meet peak load requirements. Presently there are not any existing UPHS plants, either operating or under construction. Studies indicate that the UPHS concept is technically feasible and economically viable. This paper describes conceptual design parameters, plant layout, turbomachinery options, site-selection considerations, geological requirements, economics, and environmental concerns. Most elements of UPHS technology are sufficiently developed to enable plant construction. Advances in high head turbomachinery design and geotechnical excavation techniques are expected to enhance the economic attractiveness of UPHS. INTROPUCTION Underground Pumped Hydroelectric Storage (UPHS) is a technique for supplying electric.power to meet peak load requirements of electric utility systems. Its incorporates reversible pump-turbines or single function pumps and turbines in tandemand an underground reservoir mined from hard rock. During night and weekend off'-peak periods, low-cost power would be used to pump water from the underground reservoir to a surface reservoir located 1000 to 2000 meters higher (Fig. 1). During the subsequent daytime peak-load Periods the surface water would supply hydroelectric power over an 8 to 10 hour period, by refilling the lower reservoir through the turbines. This would eliminate the consumption of petroleum fuels by conventional peaking gas turbines. UPHS plants are not limited by the topographic siting difficulties of conventional pumped plants. A well designed UPHS plant could have a smaller adverse impact on the environmental than a conventional peaking plant. The underground pumped hydroelectric storage concept evolved because of the dwindling number of conventional pumped storage sites, decreasing public acceptance of large reservoirs, increased capacities at higher operating heads, and the feasibility of locating UPHS plants nearer load centers to reduce transmission capital and operating costs. The authors are not aware of any existing UPHS plant, either operating or under construction. The USSR has completed a feasibility study for a plant near Minsk and preliminary designs have also been developed for plants in the eastern and midwestern USA. A typical conceptual UPHS plant would have a capacity of 1000 to 3000 MW, an operating head of 1000 to 2000 meters, and a reservoir storage capability of 8 to 10 hours generation at full load. An upper reservoir capacity of about eight million cubic meters is contemplated. Its containment embankments could be economically constructed out of rock excavated from the subsurface shafts and caverns. Geologic conditions must be favorable for mining out the requisite volumes for the lower reservoir, powerhouse, access shafts, and interconnecting waterway tunnels. A competent and impervious geologic formation is required. Candidate rock types include granite/granodiorite, quartzite, massive gneiss, dolomite, limestone, and impermeable sandstone. TURBOMCHINERY The various types of pump-turbines considered for high-head pumped storage are briefly described (Blomquist, Frigo, and Tam, 1979; Rodrique, 1979). Single Stage Francis-Type Reversible Pump-Turbine (Fig. 2) This unit is widely used in the USA because of extensive design and operating experience in this country, least equipment cost, high unit capacity and speed regulation/load following capability with adjustable wicket gates.

The paper discusses the energy-saving potential of earth-sheltered buildings and the U.S. Department of Energy's research, development and demonstration activities and plans regarding their commercialization. INTRODUCTION The subject of my presentation--earth-sheltered buildings--involves a happy intersection of a problem and a potential. The problem is well recognized--the scarcity of energy and its rising price. The problem requires that we undertake effective energy conservation programs. In the United States, fully 37 percent of the nation's energy is used in the residential and commercial building sector. This underscores the importance of U.S. building energy conservation programs. The potential is not so broadly recognized. It is the potential of earth-sheltered designs to reduce by up to 30 to 60 percent or more the energy required for the heating and cooling of buildings. The U.S. Department of Energy regards earth-sheltered buildings as the promising alternative it is considering in its innovative structures program. The Department has monitored earth-sheltered building trends, supported research, identified barriers to commercialization, disseminated information, and is applying earth-sheltered designs to one of its own new buildings. HISTORY The term, earth-sheltered buildings, has not been captured by a formal definition. A good working definition applies the term to buildings with earth protection for 50 percent or more of the area of their roofs and exterior walls. Few of the buildings are entirely underground. but all use the earth to improve their energy performance. The current interest in earth-sheltered buildings is simply the latest chapter in man's continuing struggle to adapt to his environment. The first chapter was the caves inhabited at the dawn of human history. A more elegant version are the homes found in Ajanta, India, that date back to the 5th and 6th Centuries, A.D. A few centuries later, refugees from a crumbling Roman Empire, carved houses into soft, cone-shaped rocks in Cappadocia, Turkey. The Tunisian atrium houses through the century have provided protection from that area's extreme heat. The sod houses of the pioneers of the American prairie were another practical application of earth-sheltered design to cope with severe weather conditions where other building materials were not easily available. A rebirth of interest in earth-sheltered buildings has occurred in the United States during the past two decades. It has been nurtured by various themes. In the early phase, fear of atomic war led to habitable fallout shelters. In the later 1960's and 1970's, the environmental movement led architects to create earth-sheltered designs that were in harmony with the natural environment. The energy-saving benefits of earth-sheltered designs have fanned the rapidly spreading interest in the last half of the 1970's. As director of the Minnesota Energy Agency from 1975 to 1979 when I joined the U.S. Department of Energy, I participated in Minnesota's leadership in the support of earth-sheltered buildings. In the past few years, a state-sponsored guidebook, "Energy Sheltered Housing Design," (Underground Space Center, 1978) has become a best seller, selling more than 100,000 copies. A map of earthsheltered buildings is speckled with activity in all parts of the country with concentrations in Minnesota, Wisconsin and Oklahoma (Vadnais, 1980).

Within the national energy research and development programme the Swedish Council for Building Research is responsible for the programme of Energy use for Building a excl. industrial development support, which is administrated by the National Swedish Board for Technical Development. The Council is also responsible for energy prototype and demonstration activities in existing buildings and for experimental building activities. In its application for appropriations for the period of 1981–1984 the Council will present a proposal to a plan for its energy related activities during the current three-year period. The council has created a number of working-groups in order to work out the future action-programme, estimate the potential of different development strategies and propose activities as research, experiments and demonstration plants. This paper presented by one of these groups, deals with storage of waste heat and solar energy in soil, rocks, surface, and ground water and also bottom sediments in lakes and bays. The energy storage of solar heat is of great importance because the -energy has to be stored over a period of more than half a year. The energy storage is as a principle divided into Active systems, which are charged to a higher temperature range by a gaseous or liquid heat transfer medium and Passive systems, which are charged in a natural way by rainfall, atmosphere or solar energy during the summer. The active systems consist of stores in the underground or near the surface. the passive systems of stores in the surface, in lakes or in the ground water. Development potentials, ecological aspects, legal aspects and development resources are discussed. SUMMARY Description of subject area The subsurface storage of energy can be divided up into so-called active systems, where the storage facility is charged by solar collectors, heat pumps or waste heat, and passive systems, which are only heated by natural means. Active systems Theoretical calculations and small-scale pilot projects indicate that there are technical and economic grounds for storing heat under the ground. Storage on a relatively large scale is necessary with regard to heat loss, a factor which means that active energy storage systems are mainly of interest in connection with district heating and heat distribution centres serving groups of buildings. The field can be, divided into deep subsurface storage, aquifer storage and storage in water-filled rock caverns. Deep subsurface storage Deep subsurface storage is understood to comprise energy storage systems where charging and energy extraction occur via a closed circulation system in a vertical cavity. By utilizing thick layers of clay or rock from a depth of approx. 5 m down to about 200 m, heat can be stored on a seasonal basis in a fairly clearly defined volume of soil/rock. This storage technique is in principle dependent on the total absence of groundwater flows. Low storage temperatures ranging from between 10 to 15°C lead to a reduction of less favourable side effects in the facility such as heat convection and groundwater movements.