## 3 Research Method  
In this study, the PMR is not a racking system supporting high loads but artificially integrates MEP elements supported by individual hangers. The construction drawings did not suggest a structural supporting system in which structural materials such as H beams are used but targeted MEP elements that collectively apply individual hangers. Pipes with a diameter of 100 mm or more, requiring a system channel of more than 50 mm, were excluded from the PMR integration to avoid lowering the ceiling height of the corridor. Although the MEP elements was bulky (similar to a duct), the elements that a 50 mm system channel could support were integrated into the PMR. In summary, the PMR of this study (1) deals with MEP elements supported by hangers, (2) excludes MEP elements requiring structural reinforcement, (3) targets corridors, and (4) includes MEP elements that can be supported by 50 mm channels. This study aims to identify an economical design for PMR structural frames among five designs. The data acquisition and comparison of economic feasibility for the five designs considered the following three factors:  
* Design cost: person-day input for the design phase per cubic meter. * Material cost: system channel input for manufacturing per cubic meter. * Manufacturing cost: person-day input for manufacturing phase per cubic meter. First, the basic designs of the PMR frames were prepared in the design stage, and the detailed coordination process for attachment was added for each type of frame. The increase in cost owing to this design process must be considered while applying the prefabrication method [18]. Second, the structural frame was assembled; the various construction members were combined and fixed in the form of a unit during transportation and construction. This step contributes the most to increasing the material cost. This study proposed PMR structural frame designs using lightweight system channels and calculated the cost of the system channel. Third, the labor input needed to produce the PMR units in the manufacturing stage was analyzed. The construction stage may be affected by the lifting equipment, construction method, and site conditions [29]. This study analyzed the material and labor costs required to produce PMR units up to the manufacturing stage. Studies on the structural framing of PMR have not been specifically reported; however, structural framing is one of the factors increasing the cost of PMR compared with traditional hanging systems [31]. Engineers and manufacturers were consulted to propose economic structural framings. The study aimed to reduce structural framing used for modularization. We identified five types of PMR structural frames through preliminary verification of constructability and economic feasibility and conducted mock-up tests on the five types. The five types of PMR modules were applied to different areas, and the input resources were calculated per cubic meter. This is because one cubic meter can be used to measure the density of an MEP system and the difficulty of coordinating the MEP system [32]. If the resources required for manufacturing PMR were calculated per square meter, calculating the effect would be difficult when the plenum space was low or high. Moreover, a PMR is a volumetric module that considers the modularization of space; hence, it was reasonable to calculate the amount of input resources per cubic meter. This study is based on a case study (Table 1). In Table 1, the length represents the length of the corridor to which the PMR is applied, and the length of the module was 6 m considering the ease of pipe assembly, processing, and movement. Accordingly, the number of modules was calculated. The area represents the horizontal area of the corridor to which the PMR was applied, and the volume represents the plenum space corresponding to the area to which the PMR was applied.