A ground source heat pump (GSHP) system has higher performance than air source heat pump system due to the use of more efficient ground heat source. However, the GSHP system performance depends on ground thermal properties and groundwater conditions. There are many studies on the improvement of GSHP system by developing ground heat exchanger (GHX) and heat exchange method. Several studies have suggested methods to improve heat exchange rate for the development of GHX. However, few real-scale experimental studies have quantitatively analyzed their performance using the same ground conditions. Therefore, the objective of this study was to evaluate the thermal performance of various pipe types of GHX by the thermal response test (TRT) under the same field and test conditions. Four kinds of GHX (HDPE type, HDPE-nano type, spiral fin type, and coaxial type) were constructed in the same site. Inlet and outlet temperatures of GHXs and effective thermal conductivity were measured through the TRT. In addition, the borehole thermal resistance was calculated to comparatively analyze the correlation of the heat exchange performance with each GHX. Result of the TRT revealed that averages effective thermal conductivities of HDPE type, HDPE-nano, spiral fin type, and coaxial type GHX were 2.25 W/m·K, 2.34 W/m·K, 2.55 W/m·K, and 2.16 W/m·K, respectively. In the result, it was found that the average borehole thermal resistance can be an important factor in TRT, but the effect of increased thermal conductivity of pipe material itself was not significant.

The electrical efficiency and durability of a photovoltaic (PV) cell degrades as its temperature increases. Accordingly, there have been continued efforts to control the cell temperature by cooling the PV module. Generally, passive PV cooling using heat sinks attached on the back of the PV module can improve the electrical efficiency. However, few experimental studies have evaluated the effect of the heat sink shape on PV cooling. Therefore, this study proposed a passive cooling technology using meshes made of iron and aluminum, and performed indoor tests using a solar simulator to analyze the cooling performance. The experimental results demonstrated that iron and aluminum meshes reduced the PV module temperature by approximately 4.35 °C and 6.56 °C, respectively. Additionally, numerical studies were performed using a computational fluid dynamics (CFD) simulation to compare the cooling fins and meshes. The numerical results showed that the cooling fins exhibited a better cooling performance than the metal mesh. However, meshes can be mass-produced and have a high structural stability against wind loads. Meshes are more likely be applied to PV systems than cooling fins if adhesion were improved.

The zero energy building (ZEB) is being introduced as a new energy policy in the building sector. Accordingly, to realize the ZEB, renewable energy systems that can produce energy are essential. Various hybrid systems are being proposed to develop a more efficient system than individual renewable energy systems, among which tri-generation systems are attracting attention. In this study, in order to find an economic solution of a tri-generation system for the realization of ZEB, the simulation model using the dynamic energy analysis code was constructed and a feasibility study was conducted. Moreover, the conventional design method and the design method for ZEB realization were proposed, and the return on investment (ROI) was calculated according to four local conditions and two design methods. As a result of energy analysis, the energy self-sufficiency (ES) in Seoul, Ulsan, Ottawa and Toronto were calculated as 62%, 65.1%, 57.7%, and 60.2%, respectively. Moreover, results of feasibility analysis compared to a conventional system showed that the payback period of the tri-generation system in South Korea was within 13 years, and Canada was within 10 years.

Abstract:A typical ground source heat pump (GSHP) system in South Korea has a ground heat exchanger (GHX) with a length of 100-150 m, which utilizes annually stable underground temperature to meet the loads of cooling, heating and hot water in buildings. However, most GSHP systems have been introduced in heating dominated areas because the system performance advantage is larger compared with air source heat pump system than that in cooling dominated areas. To effectively provide geothermal energy to the building in the limited urban area, it is necessary to install deep GHXs. Despite its large capacity, there are few studies on GSHP system with deep GHX over 300 m. In this study, to estimate the performance of the GSHP system with deep GHX and evaluate its feasibility, numerical simulation was conducted. To quantitatively analyze heat transfer between soil and GHX, the coupled model with GHX model and ground heat and groundwater transfer model was used. Furthermore, the heat exchange rate and the source temperature were calculated according to the operation modes, the length of GHX, and soil conditions such as geothermal gradient and thermal conductivity. As a result, the total heat exchange rate of GHX with a length of 300 m heat exchanger was 12.62 kW, 173% that of a length of 150 m. Finally, it was found that the GSHP system with deep GHX has realistic possibility in good condition of geothermal gradient.

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A ground source heat pump system is one of the high-efficient technologies for space heating and cooling since it uses stable underground temperature. However, in actual application, many situations cannot be achieved due to the unsuitable design of operation. In particular, the design characteristics of buildings with different building load patterns are not reflected by the conventional design method. Moreover, the design capacity of the heat pump can be reduced by designing less capacity than the peak load through the introduction of the heat storage tank, but there is no related quantitative design method. Therefore, in this study, the effect of the ground source heat pump system design factors such as shape, length of the ground heat exchanger, and the capacity of the heat storage tank on the system performance was analyzed. To quantify the effect of such factors on system performance, an experimental plant was constructed and case studies were conducted for each design factor.