A study on utilization of ground source energy for space heating using a nanofluid as a heat carrier

Abstract

Ground source heat pump (GSHP) systems are well established as an energy‐efficient space conditioning device. However, for better utilization of the ground source, improvement in GSHP performance is desirable, which limits the small temperature difference between the ground and the circulating fluid. In this study, efforts have been made to investigate the performance of a ground heat exchanger (GHX) with a nanofluid as a heat carrier. Mathematical modeling is performed for the closed‐loop vertical U‐tube GHX with six different (Al2O3, CuO, graphite, multiwalled carbon nanotube, graphene, and Cu) water‐based nanofluids. The effect of different operating parameters on GHX length, fluid temperature, and pressure drop with nanofluids is determined. On the basis of the analytical results, it is found that the graphite particle‐based nanofluid plays a prominent role to enhance the performance of the GHX as compared with other nanoparticles. The maximum enhancement in the increase in outlet fluid temperature and reduction in pipe length with graphite particle‐based nanofluid are 68.3% and 63.3%, respectively, for an increase in temperature difference from 7°C to 15°C between the atmosphere and the ground. Also, with the graphite particle‐based nanofluid and the increase in pipe diameter from 20 to 50 mm, the fluid outlet temperature increases up to 11.2%, and the requirement in GHX length reduces up to 55%.

Application and Design Aspects of Ground Heat Exchangers

“…Investigation of ground heat exchangers includes numerical studies and experimental studies conducted in the field or a laboratory environment. Experimental parametric analysis of different design aspects is sometimes used for simpler configurations of GHE like earth-to-air heat exchangers [12,93] or when parameters that are easily controlled are investigated, like inlet temperature and velocity [94][95][96][97]. In most studies, an experimental investigation is used for validation of developed models and numerical or analytical modeling is used to assess design aspects of GHE [11,64,98,99].…”

“…Different configurations are commonly investigated based on fluid outlet temperature or exchanged heat rate [16,58,61,[100][101][102][103]. A temperature change of fluid flowing inside the GHE is also used [16,93,95], or difference between fluid and ground temperature [104]. Although the mentioned parameters indicate the better performing configuration, the initial and boundary conditions used in the analysis could shadow some of the conclusions made.…”

“…For example, the fluid temperature change is strongly related to pipe length, while total exchanged heat flux can be increased with length only until the temperature difference between fluid and undisturbed ground exists. The spatial temperature distribution or fluid temperature profile gives insight into possible limitations of heat exchange that occur due to exhausted temperature difference [95] or thermal short-circuiting inside GHE [26,33,37,95,105,106]. For EAHE and HGHE systems, fluid temperature profiles are not of great interest unless used for more detailed validation of the models or the investigation of the surrounding soil's influence on the GHE performance [10].…”

“…Cost analysis of investigated systems is given in a few studies, but usually for a single GHE layout [84,86] and where drilling costs are very high (DBHE, BHE) [118,123]. An example of a working substance that is thermally very good, but economically difficult to apply was given by Diglio et al [124] and Tarodiya et al [95] in the form of nanofluids containing silver or multiwalled carbon nanotubes.…”

“…They have the essential task of transferring heat from the ground to the heat pump system and vice versa. The most commonly used heat carrier in a BHE is water [95]. Its low price and relatively good thermal properties meet the set criteria in most cases.…”