Experimental study to investigate the effect of water impregnation on thermal performance of earth air tunnel heat exchanger for summer cooling in hot and arid climate

• Published in: Renewable energy 2018-05, Vol.120, p.255-265
• Main Authors: Agrawal, Kamal Kumar, Misra, Rohit, Yadav, Tejpal, Agrawal, Ghanshyam Das, Jamuwa, Doraj Kamal
• Format: Article
• Language: English
• Subjects: Knee point; Soil moisture content; Soil thermal saturation; Summer cooling; Water impregnation
• ISSN: 0960-1481; 1879-0682
• DOI: 10.1016/j.renene.2017.12.070

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. •Development of a novel experimental set up to evaluate the effect of soil moisture variation on thermal performance of dry and wet EATHE system.•Effect of soil moisture contents on thermal performance of EATHE system.•Determination of knee point position, heat transfer rate and COP of dry and wet EATHE systems.•Better thermal performance of EATHE due to enrichment of soil with moisture resulting in more air temperature drop at same pipe length.•Substantial saving in terms of excavation and backfilling cost, piping cost and labor cost due to improved heat transfer rate and COP.