Study of thermal performance enhancement of geothermal energy pile using PCM

Abstract

The expected demand for space heating/cooling due to increase in population and living standards worldwide is intensifying the search for renewable energy sources. The use of geothermal energy pile (GEP) offers a promising and sustainable way of generating energy needed for space heating and cooling via underground structures such as pile foundations. Shallow concrete GEPs have been used successfully to extract heat from the ground for space heating and cooling. However, there are some constraints facing its acceptability and this includes its inability to generate enough energy as a result of shorter length of the pile. Moreover, limited research data is available on the experimental and sustainable means of enhancing the quantity of the energy that can be generated for space heating /cooling through concrete GEP. Therefore, this study presents an experimental investigation of the thermal performance enhancement of concrete GEPs modified with bio-based phase change material (PCM) impregnated concrete made up of glass aggregates (GAs) and fly ash aggregates (FAs) sourced from waste materials. For the first time, aggregates made up of recycled GAs and FAs were used to host bio-based PCM. In addition, a PCM leak free thermal energy storage lightweight aggregate GAs and FAs were developed. Moreover, the developed thermal energy storage GAs and FAs remained stable under the influence of abrasive forces which make it a good material in concrete production. The ease of flow and workability of the concrete are greatly affected depending on the percentage substitution of normal aggregates with PCM impregnated GAs/or FAs. However, the compressive strength of the concretes was greater than the minimum conventional concrete strength required (i.e. 15 MPa) for any structural application. Heat storage capacity of concrete GEP increased with an increase in PCM incorporated. Furthermore, GEPs expanded/contracted during the test and returned to its initial strain value after test. Surrounding soil temperature ranges between 14°C and 22°C during the test. On the life cycle assessment point of view of the PCM modified GEP, incorporating PCM in GEPs reduce the manufacturing /production process impact of the pile. Finally, it can be concluded that incorporating bio-based PCM in GEP is a promising and sustainable way of enhancing its thermal performance.