In an office building, the internal heat and the skin load are both expected to change. Thus, this study is an initial step that searches for optimum replacement measures when a heat source system is replaced on an office building in Korea. The operation status of office buildings in Korea was investigated, and the heat source capacities at the retrofit and the design times were quantitatively studied to determine the optimum capacity during of a heat source during retrofit. For the four retrofit scenarios, the maximum cooling and heating loads were calculated to show that, when retrofit is performed, the maximum cooling and heating loads are decreased by 40%, while the heat source capacity is reduced by around 43%. This is believed to be because of the replacement of the window chassis, which are better sealed with higher heat insulation performance, due to the enhanced design criteria for exterior load designing, and an improved installation process. Concerning the air-conditioning load, the influence of the internal heat load turned out to be significant, indicating that such a factor should be considered when retrofit. Thus, if the heat source capacity at the initial design time is applied equivalently during the office building retrofit, it would lead to degradation in energy efficiency due to the excessive design. Thus, it is necessary to calculate a heat source capacity by reflecting the operational and current status of the load in an actual building at the time of a retrofit.

In a general building retrofit process, the reinforcement of insulation performance or air-tightness in walls and windows are conducted to reduce the maximum cooling and heating load of buildings. A heat source consists of heat-source equipment and water-pipe systems, which are replaced with high-efficient specification materials. Most of them are simply replaced with the same capacity as the previous heating equipment. This study aims to investigate matters required for decision making in a retrofit plan, such as conducting an investigation of the maximum load reduction in buildings obtained by the retrofit and the capacity of heat-source equipment that reflects the reduction, and the re-use or replacement of the water-pipe system, etc. in advance. This study verified that when the capacity of heat-source equipment was reduced, the pipe diameter of the water-pipe system was also decreased, but if existing pipes were re-used, the transportation power of the pump was reduced due to the reduction in flow velocity. The changes in maximum cooling and heating load through retrofit were quantitatively verified compared to that of the initial design of the building based on previous study results, and flow rates of cool and hot water were determined by re-calculating the capacity of the heat-source equipment. Using the results, the water-pipe system was re-designed, and the annual transportation power of the pump was calculated through simulations. The calculation results verified that the transportation power decreased by up to approximately 10% when oversized pipes were re-used from the existing water-pipe system. Additionally, when the capacity of the heat-source equipment was decreased, reasonable measures considering remodeling, construction duration, and cost were derived.

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