sustainability Article Optimal Combination of External Wall Insulation Thickness and Surface Solar Reflectivity of Non-Residential Buildings in the Korean Peninsula Jung Ho Kim 1 and Young Il Kim 2,* 1 Department of Architectural Engineering, Graduate School, Seoul National University of Science and Technology, Seoul 01811, Korea; [email protected] 2 School of Architecture, Seoul National University of Science and Technology, Seoul 01811, Korea * Correspondence: [email protected] Abstract: To delay fossil energy depletion and implement the Paris Climate Change Accord, the South Korean government is attempting to reduce greenhouse gas emissions with the establishment of the 2030 Roadmap. The insulation performance of external walls is being continuously enhanced in the architectural domain. However, Korea’s policy and construction market focuses only on the heat resistance of buildings’ external walls to enhance the insulation performance, leading to an increased thickness of the insulation materials. In this study, the relationship between the surface reflectivity and insulation thickness of external walls was examined to formulate an effective insulation strategy for buildings in Korea. Office buildings of 12 regions in the Korean Peninsula were considered. The dynamic energy simulation program EnergyPlus was used to perform the heating and cooling load analyses. The present worth method was adopted to perform the economic analysis. The analysis of the cooling and heating loads indicated that a change occurred not only in terms of the latitude but also between the Eastern and Western regions. The energy consumption could be reduced by Citation: Kim, J.H.; Kim, Y.I. increasing the reflectivity in the Southern region and lowering the reflectivity in the Northern region, Optimal Combination of External based on the total load. In addition, a higher latitude corresponded to a higher energy saving effect Wall Insulation Thickness and Surface owing to the increased insulation thickness. In the case of Jeju Island and Busan, regions with a Solar Reflectivity of Non-Residential Buildings in the Korean Peninsula. relatively large cooling load and small heating load, the total load is little affected by insulation Sustainability 2021, 13, 3205. https:// thickness at high reflectivity. If the external skin was considered to have the optimal reflectivity, doi.org/10.3390/su13063205 the regions for optimal insulation thickness could be divided into three categories: north, central and south. Academic Editor: Dong Hwa Kang Keywords: EnergyPlus; heating and cooling loads; insulation thickness; present worth method; reflectivity Received: 2 February 2021 Accepted: 11 March 2021 Published: 15 March 2021 1. Introduction Publisher’s Note: MDPI stays neutral Among OECD countries, South Korea ranks first in terms of the increase in greenhouse with regard to jurisdictional claims in gas emissions [1] (increase of 113% since 1990). To prevent energy depletion and implement published maps and institutional affil- the Paris Climate Change Accord, the National Greenhouse Gas Reduction Goals 2030 iations. Roadmap was formulated by the government of the Republic of Korea in 2016. The objective is to reduce 37% (domestic 32.5%, overseas 4.5%) of the emissions compared to those in business as usual (BAU) conditions in the industry, home, commerce, public, and transportation domains. According to the roadmap, the industrial domain requires Copyright: © 2021 by the authors. the highest reduction in the emissions (from 481.0 to 382.4 million tons of CO2), with a Licensee MDPI, Basel, Switzerland. reduction rate of 20.5%. Nevertheless, the architectural domain requires the highest rate This article is an open access article of reduction (from 197.2 to 132.7 million tons, 32.7%) compared to the BAU conditions [2] distributed under the terms and to minimize the impact on the social economy. Moreover, only limited approaches are conditions of the Creative Commons available to enhance the energy efficiency after construction, and most buildings have a Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ long life span. Therefore, the formation of buildings with a high energy efficiency has 4.0/). become a key administrative purpose for the nation [3]. Sustainability 2021, 13, 3205. https://doi.org/10.3390/su13063205 https://www.mdpi.com/journal/sustainability Sustainability 2021, 13, x FOR PEER REVIEW 2 of 25 Sustainability 2021, 13, 3205 long life span. Therefore, the formation of buildings with a high energy efficiency2 ofhas 24 become a key administrative purpose for the nation [3]. Since September 2013, the Korean government has expanded the scope of the energy savingSince plan September submission. 2013, It is the mandatory Korean government to submit an has application expanded to the obtain scope a building of the energy per- mitsaving with plan a floor submission. area of 500 It ism mandatory2 or more, to change submit anthe applicationuse or report, to obtainor to change a building the contentspermit with of the a floorbuilding area register. of 500 m The2 or energy more, to saving change plan the of use a building or report, consisted or to change of man- the datorycontents (21 of items the building in the architectural, register. The mechanical energy saving and plan electrical of a building sectors) consisted and recommenda- of manda- tiontory aspects, (21 items along in the with architectural, the energy mechanical performance and index electrical (EPI) sectors)(40 items and in the recommendation architectural, mechanical,aspects, along electrical with the and energy renewable performance sectors). index All the (EPI) mandates (40 items were in the require architectural,d to be met, me- andchanical, the recommendations electrical and renewable required sectors). a score All of the 65 mandatesor higher were(74 for required public tobuildings) be met, and to obtainthe recommendations the approval of required a building. a score Especially, of 65 or higherinsulation (74 for(one public of different buildings) mandatory to obtain en- the ergyapproval saving of plans) a building. has been Especially, strengthened insulation the (onemost ofso differentfar because mandatory appropriate energy insulation saving canplans) reduce has beenthe energy strengthened consumption the most by approximately so far because 40% appropriate to 70% compared insulation to can non reduce-insu- lationthe energy cases, consumption depending on by the approximately region and 40%climate to 70% [4,5]. compared The basic to points non-insulation (21–34) of cases, the averagedepending thermal on the transmittance region and climate of the wall [4,5]. were The allocated basic points the (21–34) largest ofproportion the average of the thermal total pointstransmittance in the recommendation of the wall were section. allocated Thus, the the largest applicant proportion was encouraged of the total to points maintain in the a highrecommendation insulation performance. section. Thus, The the standard applicant for was the encouraged heat transmission to maintain rate aof high building insulation sites byperformance. region was Thedivided standard into forfour the climates heat transmission and applied rate accordingly of building (the sites divisions by region for wasthe climatedivided were into increased four climates from and three applied to four accordingly in September (the 2018). divisions Buildings for the in climatea higher were lati- tudeincreased required from a threehigher to insulation four in September performance. 2018). Figure Buildings 1 represents in a higher the latitude insulation required criteria a forhigher the external insulation wall performance.s of non-residentia Figure1l representsbuildings in the the insulation Korean Peninsula, criteria for in the the external central region.walls of The non-residential x-axis indicates buildings the revision in the year, Korean and Peninsula, the y-axis in shows the central the legal region. thermal The trans-x-axis mittanceindicates criteria. the revision The heat year, insulation and the y -axiscriteria shows have thebecome legal more thermal stringent transmittance with time. criteria. Cur- rently,The heat Korea insulation’s standar criteriad for thermal have become transmittance more stringent has been with revised time. to the Currently, level of Korea’spassive house.standard for thermal transmittance has been revised to the level of passive house. 2.500 2.093 2.000 K] ㎡ 1.500 1.000 0.581 0.581 0.581 0.470 K [W/ K 0.360 0.500 0.270 0.270 0.260 0.170 0.000 Sep-79 Dec-80 Dec-84 Jul-87 Jul-08 Nov-10 Mar-13 Oct-13 Dec-15 Dec-17 Figure 1. Changes in the insulation criteria of Korea: Central, non-residential, external wall (Source: Specification for en- Figure 1. Changes in the insulation criteria of Korea: Central, non-residential, external wall (Source: Specification for ergy-saving design of buildings, Ministry of Land, Infrastructure and Transport Notice, 2017-881). energy-saving design of buildings, Ministry of Land, Infrastructure and Transport Notice, 2017-881). TheThe status status of of z zero-energyero-energy building h hasas become mandatory for public buildings since 20202020 in in Korea. Specifically, Specifically, the primary energy output and primary energy consumption ofof the the buildings buildings are are evaluated, evaluated, and and the the bu buildingsildings are are assigned assigned five five grades grades according according to the to energythe energy independence independence ratio.