Most apartment buildings in South Korea use internal insulation systems to reduce building energy demand. However, thermal bridges such as balcony slabs in apartment buildings still lead to significant heat loss in winter, because the internal insulation system is not continuous in the balcony slab structure, and floor heating systems are commonly used in residential buildings. Therefore, this study investigates two types of thermal break elements, namely thermal break (TB) and thermal break-fiber glass reinforced polymer (TB-GFRP), to improve the thermal resistance of a balcony thermal bridge. To understand the effects of balcony thermal bridges with and without thermal break elements, the linear thermal transmittances of different balcony thermal bridges were analyzed using Physibel simulations. Then, the heating demand of a model apartment under varying thermal bridge conditions was evaluated using TRNSYS simulations. To understand the effect of insulation systems on heat loss through a balcony thermal bridge, apartments with internal and external insulation systems were studied. Whether the apartment was heating was also considered in the thermal transmittance analysis. Thus, the linear thermal transmittance of the thermal bridges with thermal break elements was reduced by more than 60%, and the heating energy demands were reduced by more than 8%.

This study investigated the impact of thermally improved spacers (TISs) on the condensation prevention and energy saving performances of residential windows. The temperature factor and total U-value were analyzed with the two-box model, by which the TISs are represented with the equivalent thermal conductivity. The results showed that the TISs could increase the temperature factor by up to 12%, and this significantly improved the condensation prevention performance. In addition, it was proved that the TIS enables the prevention of the condensation at an outdoor temperature that is 4.2 °C to 15.7 °C lower compared with the conventional spacer. Also, it was shown that the TISs reduce the total U-value by an amount from 0.07 W/m²K to 0.12 W/m²K, implying that the heat loss through the window is reduced by a rate from 2.8% to 8.2%. In addition, the results of the whole building energy simulation proved that the TISs can reduce the annual heating-energy consumption by a rate from 3.0% to 6.3%. The results were then used for the development of monographs to determine the equivalent thermal conductivity of a window spacer that can meet the performance criteria in terms of condensation prevention and energy saving.

Ground source heat pump (GSHP) can increase ground temperature and reduce system coefficient of performance (COP) during long term operation in the cooling season. This study proposed a GSHP cooling system combined with a hot water heat pump to improve the performance of the GSHP system. In the present study, the system was configured so that the condensation heat from GSHP could be used as the evaporative heat source for the hot water heat pump. This study analyzed the COP of the proposed combined system, a single cooling system and a single hot water system by TRNSYS 18 simulation. Simulation results showed that the COP of the proposed system was 37.27% higher in the cooling part and 14.40% higher in the hot water part, compared with the single heat pump system.

Light shelves provide a function to control direct sunlight and introduce daylight into indoor spaces. Also, chilled water flowing in the light shelf can mitigate local cooling demands in perimeter zones. Therefore, in this study, a thermally activated light shelf (TALS) system was proposed, and the TALS’s radiative cooling capacity was evaluated. To do this, a mock-up chamber was developed using prototypes of TALS systems based on panel configurations. It is included: ‘Insulated’ (INS), ‘Air layer’ (ARL), and ‘Air layer with fans’ (ARF), which were designed to increase thermal insulation, natural convection, and forced convection in the TALS panels, respectively. The experiment showed that the ARL and ARF increased cooling capacity by 29% and 57% compared to the INS. Natural convective heat transfer and fan-forced airflow in the TALS's air cavity contributed to improving cooling capacity. With the INS and ARL, the air temperature was recorded at 28.6°C, which requires additional space cooling. The ARF reduced air temperature up to 2.0°C because the TALS cavity fans expedited convective heat transfer and mixing air between the cavity and test chamber. The results of this study could be used to estimate TALS cooling capacity and propose an optimal design in buildings.