Earth Tube Research Articles

アースチューブ併用自然換気システムの性能検証 : 第1報-自然換気解析とCFDの連成解析法の開発と再現性検証

アースチューブ併用自然換気システムの性能検証 : 第1報-自然換気解析とCFDの連成解析法の開発と再現性検証

B-25 クールチューブの必要本数に関する検討

B-25 クールチューブの必要本数に関する検討

THE THERMAL POTENTIAL OF AN EARTH TUBE HEAT EXCHANGER SYSTEM IN AIR TEMPERATURE MODERATING

The potential of earth tube heat exchangers in tempering ventilation air in delta region was studied experimentally by using two diffident systems. The two systems were installed at the research farm, faculty of agriculture, Kafrelsheikh University (31.07° N and 30.57° E), Kafrelsheikh governorate, Egypt. The first system (S1) consisted of one pipe with inner diameter of 10.85 cm. The second system (S2) consisted of two coaxial pipes the first pipe with inner diameter of 10.85 cm surrounded by the other one with inner diameter of 16.2 cm and the annular space between them filled by water and sealed. The length of both systems was 12 m and buried at a depth of 75 cm within two ditches 5 m apart and refilled with earth. The ambient air was blown by a 0.75 kW blower to pass through the two buried systems. The systems were operated during cooling and heating modes at four operating durations and five air velocities. It was found that, the maximum temperature reduction and rise were 12.65 °C at air velocity 1.8 m/s, 12 hours operating duration and 6.27 °C at velocity 3.7 m/s, 12 hours operating duration under cooling and heating modes for S1 respectively. Maximum thermal energy rate removed during cooling mode was 679.9 W for S2 at air velocity 9.7 m/s and 22 hours operating duration and the corresponding COP was 3.96. The maximum thermal energy rate added during heating mode was 629.7 W for S1 at air velocity 9.7 m/s, 12 hours operating duration and the corresponding COP was 3.67. Both systems contribute in air temperature control which declares in diminishing its amplitude. It was found that when the air velocity (mass flow rate) increase the thermal energy rate removed / added increases although the temperature reduction / rise decreases. This was because of the effect of increasing mass flow rate was predominant than the effect of temperature reduction/ rise in thermal energy rate exchanged evaluation. Key words: Earth tube, thermal potential, earth to air heat exchanger

A Design Strategy to Reach nZEB Standards Integrating Energy Efficiency Measures and Passive Energy Use

Abstract In this paper a design strategy is presented to integrate energy efficiency measures and passive energy use, in order to meet near Zero Energy Buildings requirements in European temperate climates. In particular, a hybrid system for the integration of natural and mechanical ventilation at different times of the year is proposed. ZEBs and nZEBs usually employ mechanical ventilation systems to provide air changes and energy saving. This common solution is in contrast with the principles of natural ventilation and adaptive comfort. It is well known that natural ventilation can significantly reduce the energy demand during the summer. The case study is represented by a social housing complex located in the periphery of Modena (Italy), dating back to 1980. The project consists in the deep energy renovation of some buildings of this complex to accomplish nZEB standards. The proposal envisages two different modes of operation for the buildings, one for the cold season and one the warm season. For the cold season, a mechanical ventilation system with earth tubes and heat recovery has been designed, together with airtightness, solar greenhouses and high thermal mass and insulation. For the warm season the design allows a free-running use: open trickle ventilators applied to windows which provide background ventilation, mass and insulation mitigate the heat loads, vertical ventilation shafts support natural ventilation and free night cooling. The ventilation shafts are designed with aerodynamic principles to provide each apartment with additional (and maximised) differences of pressure due to the stack effect. The ventilation shafts have an important role for the free cooling. The renovated buildings are also equipped with active systems to compensate the remaining energy demand: a Combined Heating Power System (CHP), PV panels and solar thermal collectors. The indoor comfort conditions in the warm season are evaluated according to the ASHRAE 55 adaptive model for free-running buildings. The internal comfort in the warm season is verified with a multizone dynamic simulation and a CFD analysis. The results of the study confirm that in the warm season acceptable indoor comfort conditions can be achieved in a free running nZEB.

Numerical analysis of earth air heat exchangers at operating conditions in arid climates

This paper presents the modeling and simulation of an earth air heat exchanger (EAHE), employed as an air-conditioning device for buildings in the climate conditions of the south of Algeria. The earth tubes buried in the ground can offer considerable advantages in terms of energy savings. The appropriate depth of the buried tubes was calculated taking into account the physical properties of the soil in the region under study and using a specific program developed by the authors. A parametric analysis was carried out taking into account the length and the radius of the pipe and the velocity of the air in the pipe. The results of performance and overall energy savings are presented. The maximum daily cooling capacity of the EAHE studied was 1.755 kWh. Results showed that a simple EAHE system can provide 246.815 kWh in a period of one year.

Field measurement of indoor air quality and airborne microbes in a near-zero energy house with an earth tube in the cold region of Japan

This study was conducted to evaluate the level of microbial contamination of indoor air during 3 years for two residences in one building equipped with heat recovery ventilation devices and located in Kimobetsu town of Hokkaido, Japan. This article documents a case study aimed at monitoring the microbes contaminations indoors for a safe use of energy saving ventilation devices and sanitary indoor air. This articles describes an investigative approach with three components. First, the authors evaluated the indoor air quality and microbial concentration by comparing the concentrations of particulate matter (PM10 and PM2.5), carbon dioxide, and airborne bacteria and fungi of indoor air and outdoor air during spring, summer and winter. Second, the microbial concentration inside an earth tube and a fixed sensible heat exchanger was evaluated by measuring the airborne microbial concentration of the supply air. Third, the authors assessed the possibility of microbial contamination inside the earth tube using the fungal index and by measuring temperature and relative humidity at the tube's outlet airflow. The results showed that the total concentration of airborne fungi was higher in summer than in spring or winter and that the fungal genera Cladosporium sp. and Penicillium sp. were dominant in the samples. Additionally, it was found that the environment inside the earth tube allowed easy growth of fungi from May to September with the highest fungal index measured in August. It was also confirmed that the earth tube did not affect the supply air for a building constructed 4 years ago.

Case Study of Trombe Wall Inducing Natural Ventilation through Cooled Basement Air to Meet Space Cooling Needs

AbstractUnderground spaces normally are at cooler air temperature than ambient air temperature because of earth-sheltered walls. This cooler air can be circulated to occupied spaces using a solar chimney effect to exhaust air from the basement to where it is needed. This work aims to study the viability of using natural ventilation induced by a Trombe wall to draw fresh air from underground basement floors for space cooling in the dry desert climate. Outdoor air is delivered to the basement through an earth tube. A numerical model integrating thermal models of the basement space and the occupied zone, and the Trombe wall is used to predict the air temperature variation with time in the occupied space air temperature and to predict thermal comfort. The feasibility of implementing the proposed system is assessed in a case study of a residence in the inland dry desert climate of Lebanon during the summer. It was found that the proposed system achieved thermally comfortable conditions at 80% acceptability for...

지중튜브시스템 주요 설계 변수의 성능 평가

지중튜브시스템 주요 설계 변수의 성능 평가

Assessment of Environment Control in Arid Area Green house coupled with Earth Tube Heat Exchanger

In hot arid regions, yields are low and unstable, growing season limited to one. Greenhouses can stabilize and improve yields and extend seasons. But their adoption is impeded by the requirement of large amount of water for (evaporative) cooling. Arid Area Greenhouse (AAG) is developed to reduce or eliminate this need by employing earth-tube-heat-exchanger (ETHE). ETHE was able to heat the greenhouse from 9°C to 22-23°C in 30 minutes in the cold winter nights. Static ventilation along with shading was effective for day time to control till early March. Subsequently ETHE was also operated. Yield of tomato in Arid Area Greenhouse was 1.5 to 2 times and water saving in AAG was 44% of that in open-field condition. ETHE and natural ventilation hold promise as environmental control devices for greenhouses in hot arid regions.

Evaluation of Passive Cooling Systems for Residential Buildings in the Kingdom of Saudi Arabia

In this paper, passive cooling strategies have been investigated to evaluate their effectiveness in reducing cooling thermal loads and air conditioning energy consumption for residential buildings in Kingdom of Saudi Arabia (KSA). Specifically, three passive cooling techniques have been evaluated including natural ventilation, downdraft evaporative cooling, and earth tube cooling. These passive cooling systems are applied to a prototypical KSA residential villa model with an improved building envelope. The analysis has been carried using detailed simulation tool for several cities representing different climate conditions throughout KSA. The impact of the passive cooling systems is evaluated on both energy consumption and electrical peak demand for residential villas with and without improved building envelope for five cities, representatives of various climate conditions in KSA. It is found that both natural ventilation and evaporative cooling provide a significant reduction in cooling energy use and electrical peak demand for the prototypical villa located in dry KSA climates such as that of Riyadh and Tabuk. Natural ventilation alone has reduced the cooling energy end-use by 22%, while the evaporative cooling system has resulted in 64% savings in cooling energy end-use. Moreover, the natural ventilation is found to have a high potential in all KSA climates, while evaporative cooling can be suitable only in hot and dry climates such as Riyadh and Tabuk. Finally, the analysis showed that natural ventilation provided the lowest electrical peak demand when applied into the improved envelope residential buildings in all five cities in KSA.

INVESTIGATION OF GROUND TEMPERATURE FOR HEAT SINK APPLICATION IN KUCHING, SARAWAK, MALAYSIA

Ground Air Heat Exchanger (GAHE) may be a solution to improve thermal comfort in buildings located in Sarawak but no ground survey specifically to examine the potential of GAHE has been done. Ground temperature prediction with computer program did not provide an accurate result for this region. In this study, a few sites with different soil profile in Kuching, Sarawak were selected to determine the soil temperature up to 4 meters depth. For peat soil area with high water table, the ground mean temperature is about 28 °C after 1m depth. For sandy clay type soil which is subjected to tidal activity, the daily soil temperature fluctuates greatly with the highest maximum temperature exceeding 32°C for all depth. This behavior is not really desirable if the ground were to be used as a steady heat sink source. Red podzolic soil gave an almost flat profile between 26°C to 27°C after the depth of 1m which is more desirable as a ground heat sink source. Therefore earth tube application in the state of Sarawak should consider the type of soil profile and optimum depth of to take advantage of the cool ground to provide building cooling.

Economic and energy consumption analysis of smart building – MEGA house

Energy efficiency and carbon reduction of new buildings are key objectives of policies that aim to decrease electric use nationwide, particularly during the summer, when electricity usage is at its highest. A case study was developed to test the energy-conservation performance and economic feasibility of the creative and intelligent open building “MEGA House”. MEGA House focuses on making improvements in four key areas: (a) Material, (b) Electronic, (c) Green Building, and (d) Automation. This paper focuses on applications in the areas of Electronic and Green Building. The economic analysis in this paper of electricity consumption and of the potential energy-savings is based on the use of energy conservation equipment such as earth tubes and solar chimneys, situation simulations, field measurements at four experimental stages, and economic calculations.According to the results of measurement and economic analysis, the MEGA House demonstrated optimal energy conservation performance. Using an earth tube (fan) and a solar chimney (exhaust fans) in the MEGA House lowered the indoor temperature about 1∼2 °C in summer, while using an earth tube (fan) instead of an electric heater increased the indoor temperature as much as 3–4 °C. In terms of economic benefits, the using the energy-conservation facilities installed in MEGA House reduced electricity expenditures by NT$8537.76 and decreased CO2 emissions by around 1288.83 kg per year.

Feasibility study on applications of solar chimney and earth tube systems for BEAM/LEED assessment

Feasibility study on applications of solar chimney and earth tube systems for BEAM/LEED assessment

Strategy for Cooling Green Buildings

Green building and its strategic areas for conservation or the rational use of material, energy and water resources. Fundamentals of cooling and basic strategies for cooling green building. Wide range of passive forms of building cooling based on the utilization of natural physical phenomena and renewable energy. Cooling by cross-ventilation. Cooling by stack ventilation. Earth tube cooling. Cooling by earth sheltering. Cooling by night ventilation with thermal mass. Cooling by sun shading system. Cooling through physical cavity of building. Cooling the building with energy from renewable sources – solar cooling systems, heat pumps using the energy of natural environment, well water direct cooling systems.

Review of Earth Tube Heat Exchanger

Review of Earth Tube Heat Exchanger

Evaluation of Thermal Comfort Level in Social Interest Housing with Earth Tubes for the Brazilian Bioclimatic Zones 1, 2 and 7

Evaluation of Thermal Comfort Level in Social Interest Housing with Earth Tubes for the Brazilian Bioclimatic Zones 1, 2 and 7

STUDYING SOME OF THE EARTH TUBE HEAT EXCHANGER AND SOILS PROPERTIES

In this paper the composition and thermal property of soil and pipe of earth tube heat exchanger are discussed. The main factors that impact the soil thermal properties and several commonly-used pipe materials are studied. The impact of soil thermal conductivity and pipe thermal conductivity on the soil temperature field around the buried pipe is very important. As an energy-saving and environment friendly air conditioning technology, earth tube heat exchanger has been utilized wildly for some years. It is necessary to study in detail soil properties and pipe materials for utilizing earth tube heat exchanger successfully. The thermal conductivity for sandy soil is higher than sandy clay loam soil and heat exchange rate between air in metal pipe and soil achieve more 5 time for PVC pipe and wet soil with 15% moisture achieve heat exchange rate to air in pipe by 5% more dry soil.

Theoretical assessment of the combined effects of building thermal mass and earth–air-tube ventilation on the indoor thermal environment

Both earth-tube systems and building thermal mass have the potential to provide desired performance levels for both indoor thermal comfort and energy saving; however, their coupling effects need to be further investigated. A model for evaluation of the combined effects of earth-tube ventilation systems and building thermal mass is proposed. Both the time-averaged indoor air temperatures and periodic temperature fluctuations are given as explicit formulas. Unlike the time lag induced by the separate use of building thermal mass, which is no longer than 6h, the combination with an earth-tube system could extend the time lag of indoor air temperature in an annual fluctuation period by tens of days and that of a daily period by a couple of hours. It is noticeable that the building thermal mass has significant impact on the effectiveness of earth-tube systems; therefore, a small heat transfer coefficient of external envelopes helps increase the annual time lag of indoor air temperature. Using a proper combination of building thermal mass and earth tubes, indoor thermal comfort can be achieved for a building located in a region with both hot summers and cold winters without any additional cooling or heating load.

A Proposed ‘Water Tube Heat Exchanger’ Space Cooling System Performance Analysis

Increasing energy demand for domestic space cooling in Kerala, India, necessitates innovations in the passive systems. Earth tube heat exchangers (ETHE) are gaining popularity in the architectural practice of the region. Owing to the higher specific heat of water and the other underlying principles of the ETHE, there is a possibility of developing a similar system by replacing earth with water as the heat exchange medium. A conceptual water tube heat exchanger (WTHE) system was designed, which consists of a 45 m long PVC pipe staggered in an underground reinforced concrete rain water harvesting tank connected to a house. Performance of the system was assessed using the 'Psychrometric Chart+Duct Calculator V4.3 simulation tool. Later, this system was developed on site and its performance was analysed. The simulation predicted a maximum difference of 4.7°C between the inlet and outlet air temperatures. However, a difference of 8.4°C was achieved by the proposed WTHE system built.

Cooling performance assessment of horizontal earth tube system and effect on planting in tropical greenhouse

The benefit of geothermal energy is used by the horizontal earth tube system (HETS); which is not prevalent in tropical climate. This study evaluated geothermal cooling ability and parameters studied in Thailand by mathematical model. The measurement of the effect on plant cultivation was carried out in two identical greenhouses with 30m2 of greenhouse volume. The HETS supplied cooled air to the model greenhouse (MGH), and the plant growth results were compared to the growth results of a conventional greenhouse (CGH). The prediction demonstrated that the coefficient of performance (COP) in clear sky day would be more than 2.0 while in the experiment it was found to be moderately lower. The parameters study could be useful for implementation of a system for maximum performance. Two plants Dahlias and head lettuce were grown satisfactory. The qualities of the plants with the HETS were better than the non-cooled plants. In addition, the quality of production was affected by variations of microclimate in the greenhouses and solar intensity throughout the cultivation period.