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Ground-source heat pump (GSHP) systems coupled with borehole heat exchangers (BHEs) are widely used as a renewable energy source. However, the high initial costs to install the BHEs still acts as an obstacle in the expansion of these renewable energy source systems. Specifically, in South Korea, a typical residential type corresponds to an apartment building with a high building-to-land ratio for land efficiency, and thus the space to install the BHEs is usually insufficient. Furthermore, the high initial cost issue of BHEs makes it difficult to ensure the feasibility of GSHP projects in this type of a situation. This study proposes a novel BHE sizing method to support the process of sizing energy sources in the design development phase of a construction project. Life cycle cost (LCC) analysis was combined with a tool to optimize BHE sizing by considering various economic aspects. Entering water temperatures (EWT) to heat pumps in conjunction with the LCC were used to define objective functions. Consequently, Pareto optimal solutions were obtained on the EWT-LCC plot. A group of Pareto optimal solutions forms a Pareto-curve, and each point on the curve indicates a possible sizing scenario or alternative. Finally, it is possible for decision makers to compare the solutions that include both technical and economic information. The Pareto optimal solutions are expected to support proper decision making in the early design phase.

The appropriate capacity of a ventilation system based on the air infiltration rate in Korean classrooms is investigated to obtain optimal design conditions for ventilation systems. Theoretical and the experimental analyses are performed to estimate the proper ventilation capacity with a consideration of the air infiltration, the indoor air quality, and the ventilation rate. The air infiltration rate of the classroom is measured within the range of 0.5-1.5 1/h, and the required ventilation rate should be decided not by the contaminants (Formaldehyde and TVOC) emitted from the construction materials but by the carbon dioxide (CO 2 ) emitted from human breath. The appropriate capacity of the ventilation system based on the air infiltration rate of the classroom for elementary schools is 500CMH and for middle and high schools is 800 CMH. The measured and the estimated values of CO 2 concentrations are very similar and the modeling equation of CO 2 concentration can be used as a reference for the proper estimation of ventilation rate in Korean schools.

This study proposes a simple ground heat exchanger design capacity that is applicable in the schematic-design stage for several configurations used for borehole heat exchangers (BHEs). Three configurations—single, compact, and irregular types—were selected, and the heat transfer rate per unit BHE was calculated considering heat interference. In a case study with a typical configuration and general range of ground thermal conductivity, the BHE heat transfer rate of the compact configuration decreased owing to heat interference as the number of BHEs increased. However, with respect to the irregular configuration, the heat transfer rate increased as the same number increased. This was attributed to the relatively large increment rate of the distance between the boreholes in the irregular configurations, making the heat recovery factor more dominant than the heat interference. The results show that the average heat transfer rate values per BHE applicable to each configuration type in the schematic-design stage were 12.1 kW for the single configuration, 5.8 kW for the compact type, and 10.3 kW for the irregular configuration. However, owing to the large range of results for each case study, the error needs to be reduced by maximally utilizing the information available at the schematic-design stage.