1 GEOTHERMAL SYSTEMS AND TECHNOLOGIES 1. DIRECT USE OF GEOTHERMAL ENERGY
6. DIRECT USE OF GEOTHERMAL ENERGY 2 Geothermal resources have been utilized “directly” for centuries. Direct use means direct utilization of heat for heating – there are no energy heat for heating – there are no energy transformations in-between. Direct use resources are tapped for a variety of uses, such are: space heating, drying farm and timber products, aquaculture and industrial uses.
6.1. Introduction 3 The main utilization categories, known as “direct use”: � swimming, bathing and balneology; � swimming, bathing and balneology; � space heating and cooling, including district energy systems; � agricultural applications; � industrial applications; � GSHPs.
6.1. Introduction 4 The different applications for direct-use of GE vary according direct-use of GE vary according to temperature. Direct-use is typically associated with lower- temperature – < 150°C GRs. Examples of direct-use applications for geothermal energy (modified from Lindal, 1973)
6.1. Introduction 5 Economic, environmental and energy benefits: � � Lower heating costs Lower heating costs � Reduced emissions of CO 2 , NOx, SOx � Better use of resources � Domestic � Minimal ongoing costs after installation � Unlimited application of GSHPs
6.2. Technologies for direct use of geothermal energy 6 A chain of technologies involved: � Drilling technologies; � Well head completion; � Geothermal water treatment; Geothermal water treatment; � Heat exchanger complete; � Heat exchanger complete; � Pumping station; � Water transportation; � Heat distribution systems; � Regulation of heat supply; � Systems for collection of effluent geothermal water; � Re-injection.
6.2. Technologies for direct use of geothermal energy 7 The typical equipment for a direct-use system includes: � down hole and circulation pumps, � down hole and circulation pumps, � heat exchangers, � transmission and distribution lines, � heat extraction equipment, � peaking or back-up generators, and � water disposal systems. Typical direct use geothermal heating system configuration
6.2.1. Heat exchangers (direct or open loop system) 8 Normal heat carrier is the thermal water, taken from the well. Using of an open loop geothermal system is possible Using of an open loop geothermal system is possible only when the geothermal fluid is not corrosive and only when the geothermal fluid is not corrosive and with intention to scaling. Much more convenient are closed loop systems . The principal heat exchangers used in geothermal systems are: the plate , shell-and tube , and the down hole ones.
6.2.1. Heat exchangers (direct or open loop system) 9 Flows in plate heat exchanger Gasket plate- and-frame heat exchanger construction
6.2.1. Heat exchangers (direct or open loop system) 10 Shell-and-Tube Exchangers . The three most common types of shell-and-tube exchangers of shell-and-tube exchangers are: 1- fixed tube sheet design, 2- U-tube design, and 3- floating-head type. Shell-and-tube exchanger with one shell pass and one tube pass
11 Typical down-hole heat exchanger (DHE) system (Klamath Falls, OR).
6.2.2. Heat distribution and piping 12 Usually the geothermal well is located some distance away from the user. Therefore, a transmission pipeline is required to transport the geothermal fluid. the geothermal fluid. The cost of transmission lines and the distribution networks in direct use projects is significant. Both metallic and nonmetallic piping can be considered for geothermal applications.
6.2.2. Heat distribution and piping 13 Carbon steel is now the most widely used material for geothermal transmission lines and distribution networks. Corrosion is a major concern with steel piping. Galvanized steel has been employed with mixed success in geothermal applications. Galvanized steel has been employed with mixed success in geothermal applications. Buried pre-insulated pipes for Geothermal district heating, Xian Yang – China Aboveground geothermal pipes to the Nesjavellir geothermal power plant
6.3. Types of direct use of geothermal energy 14 Spas and Pools The word spa derives from a natural hot spring of iron-bearing water in Belgium that was used starting in 1326 to cure that was used starting in 1326 to cure ailments. The hot water from the earth, containing certain minerals can give the spa meaning from a religious, symbolic, aesthetic, philosophical, or medical context.
6.3.1. Spas and pools 15 Typical temperature for a swimming pool is 27 o C, therefore in a geothermal heated pool, the hot water must often be cooled by mixing the hot water must often be cooled by mixing with cooler water, aeration, or in a holding pond. Geothermally heated swimming pools have alternative energy sources if the geothermal water is not used directly in the pool.
6.3.2. Domestic water heating 16 The various uses for domestic hot water include dish washing, laundry, bathing and hand hand washing. washing. Hot Hot water water consumption consumption depends on uses and application temperature. Domestic hot water heating often requires water higher temperatures than space heating does.
17 The storage recharge method for DHW heating Instantaneous method for DHW heating 6.3.2. Domestic hot water heating
6.3.3. Swimming pool heating 18 The size of a swimming pool is important item in the pool design; it is a basic factor for design; it is a basic factor for determining the pool’s ser- vice, water value, selection of equipment etc. Swimming pool heating with geothermal water
6.3.3. Swimming pool heating 19 Heat loss from outdoor pools is mainly due to: convection, evaporation, radiation, conduction and rain. With geothermal heat pump systems . Heating swimming pool with geothermal With geothermal heat pump systems . Heating swimming pool with geothermal heat pump depends on the climate. In northern climates, more heat is generally extracted from the ground than is rejected during the year. In southern climates, the opposite occurs and more heat is generally rejected to the ground than is extracted during the year.
6.3.3. Swimming pool heating 20 Figure illustrates the system for Southern climates. The for Southern climates. The vertical bore ground loop was used for the combined loads of the house and pool. Swimming pool heating with geothermal heat pump
6.3.4. Space heating and cooling (air conditioning) 21 Under the expression "space air conditioning" both heating and cooling of rooms is understood. Space conditioning includes both heating and cooling. Absorption space cooling with geothermal energy has not been popular because Absorption space cooling with geothermal energy has not been popular because of the high temperature requirements and low efficiency. District heating involves the distribution of heat from a central location, through a network of pipes to individual houses or blocks of buildings. The distinction between a district heating and space heating system is that space heating usually involves one geothermal well per structure.
6.3.4. Space heating and cooling (air conditioning) 22 Thermal load density or heat demand. High heat density is recommended. Geothermal can usually meet 50% of the load 80 to 90% of the time, thus improving the efficiency and economics of the system. Fossil fuel peaking usually applied. applied. Geothermal district heating systems are capital intensive. The typical savings to consumers range from approximately 30 to 50% per year of the cost of natural gas. Heating of individual rooms and buildings is achieved by passing geothermal water (or secondary fluid) through heat convectors (or emitters). The method is similar to the one used in conventional space heating systems.
6.3.4. Space heating and cooling (air conditioning) 23 Three major types of heat convectors are used for space heating: 1. forced convection systems 2. natural convection systems 3. 3. radiant panels radiant panels Forced convection air systems are based on the use of a water/air heat exchanger through which the air is blown by a fan. Main characteristics of space heating: � Preferred water temperatures 60-90 ° C. Common return water temp. is 25-40 ° C. � Chemical composition of the water is important. � Radiators or floor heating systems and air heating systems. � GHP can be used if the temp. of the resource is too low for direct application.
6.3.4. Space heating and cooling (air conditioning) 24 The supply temperatures required for a range of domestic heating distribution systems: Delivery Distribution system temp. °C Under floor heating Under floor heating 30-45 30-45 Low temperature radiators 45-55 Conventional radiators 60-90 Air 30-50 GSHP systems may not be suitable for direct replacement of conventional water-based central heating systems.
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