A heat exchanger combined with soil is an underground heat exchanger that can capture heat from and/or dispose of heat to the ground. They use a constant underground temperature on Earth to warm or cool air or other liquids for residential, agricultural or industrial use. If building air is blown through heat exchangers for heat recovery ventilation, they are called earth tubes (also known as earth cooling tubes or earth warming tubes) in Europe or air-geothermal exchangers (EAHE or EAHX) in North America. This system is known by several other names, including: air-to-ground heat exchanger, earth channel, earth channel, earth-air tunnel system, soil tube heat exchanger, hypocausts, underground heat exchangers, thermal mazes, underground air pipes, and others.
Earth tubes are often a viable and economical alternative or supplement to conventional central heating or air conditioning systems because there are no compressors, chemicals or burners and only blowers necessary to move air. It is used either for partial cooling or full and/or heating ventilation facilities. Its use can help buildings meet Passive Home standards or LEED certification.
Earth-air heat exchangers have been used in agricultural facilities (animal buildings) and horticultural facilities (greenhouses) in the United States for the last few decades and have been used together with solar chimneys in hot dry areas for thousands of years, possibly beginning in the Persian Empire. Implementation of this system in Austria, Denmark, Germany, and India has become fairly common since the mid-1990s, and is slowly adopted in North America.
The combined heat exchangers of the earth can also use water or antifreeze as a heat transfer fluid, often together with geothermal heat pumps. See, for example a downhole heat exchanger. The rest of this article mainly deals with geothermal exchangers or earth tubes.
Video Ground-coupled heat exchanger
Design
Earth-air heat exchangers can be analyzed for performance with some software applications using weather gauge data. These software applications include GAEA, AWADUKT Thermo, EnergyPlus, L-EWTSim, WKM, and others. However, many air-earth heat exchanger systems have been improperly designed and constructed, and fail to meet design expectations. Air-air heat exchangers appear to be best suited for air pretreatment rather than for heating or full cooling. Air pretreatment for air-fed heat pumps or heat source heat pumps often provides the best economic return on investment, with simple returns often achieved within one year of installation.
Most systems are usually made of 100 to 600 mm (3.9 to 23.6 inches) diameter, fine-walled (so they do not easily trap moisture and condensation molds), rigid or semi-rigid plastic, plastic-coated metal pipes or plastic pipes coated with an inner antimicrobial layer, buried 1.5 to 3 m (4.9 to 9.8 ft) underground where the earth's temperature is about 10 to 23 Â ° C (50 to 73 Â ° F) throughout the year in temperate climates where most humans live. Soil temperatures become more stable with depth. Smaller diameter tubes require more energy to move air and have less surface area contact with the ground. The larger tube allows slower airflow, which also results in a more efficient energy transfer and allows a much higher volume to be transferred, allowing more air exchange in shorter periods of time, when, for example, you want to clean the building from smells or unpleasant smoke, but suffer from worse heat transfer from wall pipe to air due to increased distance.
Some people think that it is more efficient to draw air through a long tube than to push it with a fan. The solar chimney can use natural convection (warm rising air) to create a vacuum to draw air passive cooling tubes filtered through the largest diameter cooling tubes. Natural convection may be slower than using a solar-powered fan. A 90 degree sharp angle should be avoided in the construction of the tube - two 45-degree bends produce a lower and turbulent airflow. While smooth-wall tubes are more efficient at moving the air, they are less efficient at transferring energy.
There are three configurations, a closed loop design, an open air system or a combination of:
- Closed loop system: The air from within the house or structure is blown through a U-shaped loop from the usual 30 to 150 m (98 to 492 ft) tubes (s) where it is moderated to near the earth temperature before returning for distribution through requiring channels throughout the house or structure. The closed-loop system can be more effective (during extreme temperatures) than open systems, because it cools and reuses the same air.
- Open system: External air extracted from filtered air intake (Minimum Efficiency Reporting Value, MERV 8 air filter recommended). The cooling tube is usually 30 m (98 ft) in length inside the house. Open systems combined with energy recovery ventilation can be almost as efficient (80-95%) as closed loops, and ensure that entering fresh air is filtered and forged.
- Combination system: It can be built with a silencer that allows closed or open operation, depending on the requirements of fresh air vents. Such designs, even in closed-loop mode, can attract a certain amount of fresh air when the decrease in air pressure is created by the sun chimney, clothing dryer, fireplace, kitchen or bathroom exhaust vent. It is better to draw air filtered passive cooling tubes rather than unconditioned outer air.
Single-pass earth air heat exchangers offer the potential for improved indoor air quality over conventional systems by providing an increased supply of outdoor air. In some single-pass system configurations, open air supply is constantly provided. This type of system will typically include one or more heat recovery ventilation units.
Thermal Labyrinth
The thermal labyrinth performs the same function as the earth tube, but is usually formed from larger volume chambers, sometimes inserted into the building's basement or below the ground floor, and which in turn is divided by many internal walls to form air paths labyrinth. Maximizing the length of the air path ensures a better heat transfer effect. Construction of maze walls, floors, and separating walls usually consist of cast concrete and high-reinforced concrete beams, with exterior walls and floors in direct contact with the surrounding earth.
Maps Ground-coupled heat exchanger
Security
If the moisture and colonization of associated fungi are not addressed in system design, occupants may face health risks. In some locations, the humidity in the earth tube can be controlled only by passive drainage if the surface is deep enough and the soil has a relatively high permeability. In situations where passive drainage is not feasible or needs to be added for further moisture reduction, the active system (dehumidifier) ​​or passive (desiccant) can treat airflow.
Formal research shows that air-earth heat exchangers reduce air pollution of building ventilation. Rabindra (2004) states, "Tunnels [air-geothermal exchangers] are found not to support bacterial and fungal growth but are found to reduce the number of bacteria and fungi that make the air safer for humans to inhale, so it is clear that the use of EAT [Earth Air Tunnel] not only helps conserve energy but also helps reduce air pollution by reducing bacteria and fungi. "Likewise, Flueckiger (1999) in a study of twelve different air-earth heat exchangers in design, plumbing, size and age, stated, "This study was conducted because of potential microbial growth concerns in buried ground-coupled air pipes. However, the results show, that no harmful growths occur and that the concentration of spores and bacteria that live in the air, with some exceptions, is even reduced after past the pipeline system ", and further stated," Based on this investigation of the operation of ground-coupled geothermal-to-air exchanger is acceptable during regular control and if appropriate cleaning facilities are available ".
Whether using an earth tube with or without an antimicrobial material, it is essential that the underground cooling tube has an excellent condensing conduit and is installed at a level of 2-3 degrees to ensure the constant removal of water condensed from the tube. When applying at home without a basement in a flat place, external condensing towers can be mounted at a lower depth than where the tube enters the house and at a point close to the entrance wall. Installing a condensing tower requires the additional use of a condensate pump to remove water from the tower. For in-house installation with basements, the pipe is graded so that the condensation drain inside the house is at the lowest point. In the second installation, the tube must continue to tilt toward the condensing tower or condensation conduit. The inner surface of the tube, including all joints should be smooth to aid the flow and discharge of the condensate. Choppy or ribbed tubes and coarse interior joints should not be used. Connections that connect the tube together must be tight enough to prevent water or gas infiltration. In certain geographical areas, it is important that the joints prevent the infiltration of Radon gas. Porous materials such as uncoated concrete tubes can not be used. Ideally, Earth Tubes with an inner antimicrobial coating should be used in the plant to inhibit the potential growth of fungi and bacteria in the tube.
Effectiveness
Implementation of air-earth heat exchangers for either partial or full cooling and/or air-heating ventilation facilities has been successfully blended. The literature, unfortunately, is filled with too much generalization about the application of this system - both pros and cons. A key aspect of the air-earth heat exchanger is the passive nature of the operation and the consideration of the wide variability of conditions in the natural system.
Earth-air heat exchangers can be very cost-effective both up front/capital costs as well as long-term operating and maintenance costs. However, this varies greatly depending on the location of latitude, altitude, ambient Earth temperature, climate temperature and extreme relative humidity, solar radiation, water table, soil type (thermal conductivity), groundwater content and building exterior efficiency. design envelope/isolation. Generally, dry-and-low soil with little or no soil shade will yield the least benefit, while dense wetlands with considerable shade should perform well. A slow drip watering system can improve thermal performance. The wet soil that comes into contact with the cooling tube warms faster than the dry ground.
The cooling tube of the earth is less effective in hot humid climates (like Florida) where the temperature of the Earth's environment is close to the human comfort temperature. The higher the temperature of the earth's environment, the less effective for cooling and dehumidification. However, the earth can be used to partially cool and reduce moisture replacement of fresh air intake for areas of passive solar thermal buffer zones such as laundry rooms, or solarium/greenhouses, especially those with hot tubs, swimming saunas or indoor pools at where warm humid air runs out in the summer, and cooler cooler air replacement supplies are desirable.
Not all regions and locations are suitable for air heat exchangers. Conditions that may inhibit or obstruct proper application include shallow rocks, high water tables, and insufficient space, among others. In some areas, only cooling or heating can be provided by an air-earth heat exchanger. In these areas, provisions for thermal soil replenishment should be considered. In dual function systems (both heating and cooling), warmer seasons provide soil thermal assimilation for the winter and winter provides geothermal replenishment for warmer seasons, although overtaxing the thermal reservoir should be considered even with dual function systems.
Renata Limited, a leading pharmaceutical company in Bangladesh, is trying a pilot project that tries to find out if they can use Earth Air Tunnel technology to complement conventional air conditioning systems. Concrete pipe with a total length of 60 feet (~ 18Ã,¼m), inside diameter 9Ã, inches, (~ 23 cm) outer diameter 11Ã, inch (~ 28cm) is placed at a depth of 9 feet (~ 2¾¾m) under ground and blower 1, 5 ¾ The kW power value is used. The underground temperature at that depth is found to be about 28 ° C. The average air velocity in the tunnel is about 5 m/s. The performance coefficient (COP) of underground heat exchangers is poorly designed starting from 1.5-3. The result convinces the authorities that in hot and humid climates, it is unwise to apply the concept of Earth-Air heat exchangers. The cooling medium (the earth itself) is at an approximate temperature that the surrounding environment happens to be the root cause of failure of these principles in hot, humid regions (parts of Southeast Asia, Florida in the US etc.). However, researchers from places like Britain and Turkey have reported strongly encouraging COP-well above 20. Underground temperatures seem to be of paramount importance when planning Earth-Air heat exchangers.
Environmental impact
In the context of increasingly depleted fossil fuel reserves, rising electricity costs, air pollution and global warming, well designed earth cooling tubes offer a sustainable alternative to reduce or eliminate the need for conventional compressor-based air conditioning systems, in non-tropical climates. They also provide the added benefit of a highly controlled, filtered, and temperate fresh air intake, which is invaluable in tight, risky, and efficient building envelopes.
Water to earth
An alternative to earth-to-air heat exchangers is "water" for geothermal exchangers. This is typically similar to a geothermal heat pump tube embedded horizontally on the ground (or it may be a vertical sonde) to the same depth of an earth-air heat exchanger. It uses about twice the length of the 35 mm diameter pipe, for example, about 80 m compared to the EAHX of 40 m. A heat exchanger coil is placed before the air intake of the heat recovery ventilator. Usually a brine fluid (very salty water) is used as a heat exchanger.
Many European installations now use this configuration because of the ease of installation. No drop point or drainage is necessary and safe because of reduced risk of fungus.
See also
- Passive cooling
- Solar air conditioning
- Solar chimney
- HVAC
- Renewable energy
- Geothermal power
- Geothermal heat pump
- Earth Shelter
- Seasonal thermal energy storage
- Aquifer heat storage energy
- Qanat
- Yakhch? l
- Stepwell
- Cistern
- Windcatcher
- Ab anbar
References
- International Energy Agency, Air Infiltration and Ventilation Center, Ventilation Information Paper no. 11, 2006, "Use of Earth to Air Heat Exchangers for Refrigeration"
External links
- Energy Saver: Earth Cooling Tubes (US Dept. of Energy)
- Single Pass Passant Exchanger Performance: An Experimental Study, Girja Sharan, Ratan Jadhav
- The small house system uses 4 "Earth air pipes - 7 years retrospectively: Vermont, USA
Source of the article : Wikipedia
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