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In the present experimental work, two identical real field experimental setups (with dry soil and wet soil) of ground-air heat exchanger (GAHE) have been developed in order to evaluate the influence of change in inlet air temperature, airflow velocity, diameter of pipe and soil moisture content on the thermal performance of GAHE system. Influence of these parameters on the required pipe length to produce a specified drop in air temperature has also been investigated. Results reveal that the drop in air temperature achieved from GAHE having dry soil is 11.2 °C at 60 m pipe length, whereas, for GAHE with wet soil having 20% moisture, the same amount of drop in air temperature is obtained at a pipe length of 28 m only. Moreover, upon increasing the airflow velocity from 2 m/s to 10 m/s, cooling capacity of GAHE with dry soil, wet soil with 5% moisture and wet soil with 20% moisture increases by 122%, 185% and 220%, respectively, after 6 h of operation, but the effectiveness of the GAHE system with dry soil, wet soil with 5% moisture and wet soil with 20% moisture decreases by 55.4%, 42.5% and 36.2%, respectively. • Development of an outfield experimental set up for GAHE system with dry and wet soil. • 53% length of GAHE pipe can be reduced by using wet soil with 20% moisture. • By increasing air flow velocity 2 m/s to 10 m/s, cooling capacity increases 220% in wet soil. • By increasing air flow velocity 2 m/s to 10 m/s, effectiveness decreases 36.2% in wet soil. • Required length of GAHE pipe highly depends on soil moisture, air velocity and pipe diameter. [ABSTRACT FROM AUTHOR]

Thermal performance of ground-air heat exchanger (GAHE) depends on the rate of heat transfer between air and soil, which is governed by thermal properties of soil surrounding the GAHE pipe. Soil thermal properties around GAHE pipe can be improved either by increasing its moisture contents or by using some thermally enhanced backfilling materials. In the present study experimentally investigates the thermal performance of ground-air heat exchanger system using a sand-bentonite mixture (dry as well as wet) and compare their performance with the ground air heat exchanger system having native soil (dry as well as wet) as backfilling material. The study acknowledges the highest cooling capacity (125 W) for GAHE with wet sand-bentonite as backfilling material, and after 6 h of continuous operation, it is 38.4%, 18.4% and 11.1% higher than that obtained with dry native soil, dry sand-bentonite and wet native soil, respectively. The study also revealed that thermal performance deterioration factor (TPDF) increases with the duration of the operation. At airflow velocity of 5 m/s, after 6 h of continuous operation highest TPDF is noticed for ground-air heat exchanger with dry soil (0.22); whereas, lowest TPDF is observed for ground-air heat exchanger system with wet sand-bentonite (0.07). Schematic of laboratory experimental setup of GAHE system. Image 1 • Development of a laboratory scale experimental set up for GAHE system. • To evaluate the effect of sand-bentonite backfilling material (dry as well as wet) on performance of GAHE system. • Maintaining a certain level of moisture into the soil in the close vicinity of GAHE pipe. • Better thermal performance of GAHE due to BFM resulting reduction in required pipe length. [ABSTRACT FROM AUTHOR]

• Earth air heat exchanger system is one of the promising passive techniques for building heating and cooling application. • Efficiency and utility of the EAHE system increase by coupling it with other active/passive systems. • EAHE system may be a good option for pre-heating and pre-cooling of air in industrial applications. • Large land area required to install EAHE is a major constraint for the adaptability of EAHE system in urban areas. • The required pipe length of EAHE can also be reduced by using soil of high thermal conductivity at the vicinity of the pipe. Earth air heat exchager (EAHE) is a promising passive technique that utilises the constant temperature of the underground soil for heating/cooling of air. The EAHE system possesses several advantages and can be used stand-alone as well as in hybrid mode for heating/cooling of air for building and commercial/ industrial applications. This article reviews the available literature pertaining to technology integration and applications of earth air heat exchanger system in the last four decades and also account for the recent significant developments in EAHE to indicate the emerging trends in the domain. The comprehensive review of the literature suggests that a standalone EAHE system can does not cater the requirements of thermal loads entirely and therefore has not grown much popular and still vying for commercial/ industrial applications, worldwide. The requirement of auxiliary devices so as to supplement the standalone EAHE system to achieve thermal comfort conditions entailing huge expenses conflicts the economics of the hybrid EAHE systems. The exorbitantly increasing costs of pipes, land and labour necessitate the paradigm-shift in the major thrust of the research associated with thermal comfort so as to incorporate the economics of system as a whole to enhance the acceptability of EAHE system. [ABSTRACT FROM AUTHOR]

Highlights • Fabrication of a unique sub-soil water trickling system (SWTS) integrated with EAPHE system. • Three soil moisture content values viz. 5%, 10%, and 15% have been considered for wet EAPHE system. • Investigation of the effect of soil moisture variation on thermal performance of EAPHE system. • Comparison of thermal performance of dry and wet EAPHE system for winter heating. • Estimation of heat transfer rate, COP and knee point position for dry and wet EAPHE systems. Abstract Earth-air-pipe heat exchanger (EAPHE) system is a passive system but requires long pipes for heat transfer and its performance also gets deteriorated during continuous operation. In this study, the moisture content of sub-soil is increased in the close vicinity of EAPHE pipe and its influence on thermal performance and pipe length requisite for certain temperature rise in winter season have been determined. The system comprises of two identical set-ups of EAPHE system buried at a depth of 3.7 m (one for dry soil, other for wet soil). A unique water impregnation system is presented to maintain different soil moisture content levels in the close vicinity of EAPHE pipe. The knee point for dry EAPHE system is obtained at a pipe length of 40 m from inlet section while in wet EAPHE system knee point is obtained at 28 m, 27 m and 26 m with 5%, 10%, and 15% soil moisture levels respectively, after 12 h of continuous operation. The average heat transfer rate and coefficient of performance increase up to 26.0% and 26.1% respectively, for 15% moisture content at 30 m length of EAPHE pipe as compared to dry system. [ABSTRACT FROM AUTHOR]

An EATHE system performs well for short periods but its thermal performance gets deteriorated during long continuous operation due to sub-soil thermal saturation in the vicinity of buried pipe. Effect of soil thermal saturation can be reduced to some extent in longer EATHE pipe but it is uneconomical. In the present study sub-soil moisture content is increased to enhance soil thermal properties and its effect on EATHE thermal performance and pipe length requirement for certain temperature drop has been investigated experimentally for summer cooling in hot and arid climate. In the study, two identical experimental set-ups have been developed at Ajmer city (India). A water impregnation system has been introduced to maintain different soil moisture contents in the close proximity of EATHE pipe. Knee point is obtained at a length of 29 m, 28 m, 27 m and 26 m from pipe inlet section with 5%, 10%, 15% and 20% moisture in sub-soil respectively, as compared to 41 m length in dry soil, after 10 h of continuous operation. The average heat transfer rate and COP increased by 24.1% and 24.0% respectively for 20% moisture content at 30 m EATHE pipe length as compared to dry system. [ABSTRACT FROM AUTHOR]

• Evaluated economic feasibility of backfilling materials for GAHE system. • Developed a CFD simulation model for GAHE system with backfilling materials. • Use of backfilling materials to improve the overall economics of GAHE system. • Required length of GAHE pipe is determined with different BFMs. The ground-air heat exchanger (GAHE) system is an energy-efficient system for building cooling/ heating, but its initial cost is higher due to the requirement of longer pipes to achieve the desired heat exchange between air and soil. To reduce required pipe length, secondary soil (i.e. soil of high thermal conductivity) can be used as backfilling material in the vicinity of GAHE pipe. However, due to the use of secondary soil, the installation cost of the GAHE system may increase. Therefore, the key objective of this study is to explore the economic feasibility of using backfilling materials in the vicinity of GAHE pipe. For this, a three-dimensional CFD simulation model of GAHE system with backfilling material has been developed using FLUENT 15.0, and the required length of GAHE pipe to achieve a specified drop in air temperature with backfilling materials has been determined. Based on this, the initial installation cost of the GAHE system (i.e. pipe cost, trench excavation cost, backfilling material cost) has been estimated. The study revealed that the initial installation cost of a GAHE system could be reduced by 25.7%, 32%, and 38% using dry sand-bentonite, wet sand-bentonite, and wet native soil respectively, as backfilling materials in place of dry native soil. [ABSTRACT FROM AUTHOR]

• Development of a laboratory scale experimental set up with slinky-coil pipe layout. • Use of sand–bentonite mixture as backfilling material for GAHE system. • Required length of the trench is reduced by using slinky-coil pipe layout. • Substantial saving in terms of excavation cost and piping cost. The ground-air heat exchanger (GAHE) is the promising passive technique for building heating/cooling, but due to its high installation cost (mainly pipe cost and excavation cost), it could not become popular. The required length of pipe can be reduced by using thermally enhanced backfilling material (BFM), while, the length of the trench can be reduced by using slinky-coil pipe layout. In the present study, an experimental laboratory setup of GAHE system has been developed with a slinky-coil pipe layout and sand-bentonite as BFM. For this, a flexible PVC pipe of 75 mm diameter and 30 m length, has been arranged in slinky-coil pattern and installed horizontally in a soil box of 10.2 m length. For the study, variation in soil temperature (23 °C–27 °C), inlet air temperature (38 °C–46 °C), air flow velocity (5 m/s–20 m/s) and soil conditions (dry and wet), have been considered. Study reveals that a drop-in air temperature as high as 18.7 °C at 30 m pipe length (trench length of 10.2 m) can be achieved with soil at a temperature of 27 °C and inlet air temperature of 46 °C. The study also revealed that the pipe length could be reduced by 20% with wet sand-bentonite as compared to dry sand-bentonite. [ABSTRACT FROM AUTHOR]

Abstract: The non-response to hepatitis B vaccine in health care workers (HCWs) is reported to vary between 5 and 40%. The underlying cellular and molecular events for unresponsiveness to HBV vaccine have not yet been characterized at any great extent. In the current study, we examined the CD150 surface expression levels and its association with polyclonally activated and HBV specific stimulated cellular proliferations in responders and non-responders. CD150 was identified as upregulated expression marker with suppressive regulatory cell function on all activated T cells by gene chip analysis. We found the overall weak cellular proliferation in response to specific and non-specific agents in non-responders. This is significantly associated with enhanced surface expression of CD150 in the non-responders. A strong expression of CD150 with weak cellular proliferation could be used as a predictive marker for non-responsiveness. [Copyright &y& Elsevier]