Impact of External Insulation and Internal Thermal Density Upon Energy Consumption of Buildings in a Temperate Climate with Four

Renewable and Sustainable Energy Reviews xx (xxxx) xxxx–xxxx

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Renewable and Sustainable Energy Reviews

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Impact of external insulation and internal thermal density upon energy consumption of buildings in a temperate climate with four distinct seasons ⁎ Junghun Leea, Jeonggook Kima, Doosam Songa, , Jonghun Kimb, Cheolyong Jangb a Department of Architectural Engineering, Sungkyunkwan University, 2066 Sebu-ro, Suwon 16419 Gyunggi-do, Republic of Korea b Energy Saving Laboratory, Energy Eﬃciency Research Division, Korea Institute of Energy Research,152 Gajeong-ro, Daejeon 34129, Republic of Korea

ARTICLE INFO ABSTRACT

Keywords: Most of the building codes for energy saving are focused on strengthening the insulation and airtightness of the Envelope design standards building envelope. Insulation and air tightness of the building envelope reduces heat loss during the heating season, Insulation level but can lead to overheating in the cooling season according to the building types owing to the internal heat gain levels. Internal heat gain level This study reviewed the effect of strengthening the external insulation level on energy consumption for heating Energy savings and cooling in buildings with various internal heat gain levels. The reference building was located in a temperature climate with four distinct seasons in Seoul, South Korea. The variation of annual heating and cooling energy consumption was analyzed in regard to diverse internal heat gain levels and envelope properties using parametric simulation methods. Less total energy was required for heating and cooling by enforcing the insulation level in buildings with low internal heat gain levels, while more energy was required in large office buildings with high internal heat gain levels. The present prescriptive envelope design standards of Korea are ineffective in high internal heat gain buildings. Actually, the current U-value envelope standard may increase the annual energy consumption in commercial buildings in Korea. The standard for external thermal insulation should depend on whether the building is envelope-dominated or internally dominated to reduce the building heating and cooling energy demands.

1. Introduction 30]. Prescriptive codes, however, have several shortcomings [31–33]. First, the process of selecting items from the list does not ensure Buildings represent 32% of the total final energy consumption and maximum energy savings for the whole building. Second, prescriptive 40% of the primary energy consumption in the world [1–3].Inaddition, codes cannot ensure that the performance has not degraded with time. the building sector is often cited as one of the most cost-effective areas to The typical performance-based indices include the 2010 Energy reduce energy use [4,5]. The building envelope, the interface between the Performance of Buildings Directive, the 2012 Energy Efficiency interior of the building and the outdoor environment, serves as a thermal Directive, the Energy Cost Budget Method, the Total Building barrier and plays an important role in determining the energy demand to Performance Method, the Overall Thermal Transfer Value (OTTV), maintain a comfortable indoor environment [6–10].Mostcountries Perimeter Annual Load (PLA), and so on. The 2010 Energy began issuing building standards on insulation in the 1970s, and these Performance of Buildings Directive and the 2012 Energy Efficiency standards have been updated over the years with prescriptive or Directive are EU's main legislation when it comes to reducing the energy compulsory code and a performance-based index [11–20].Aperfor- consumption of newly constructed and existing buildings [11].The mance-based index allows designers greater flexibility than prescriptive Energy Cost Budget Method was introduced in ASHRAE 90.1–2013 code when selecting variables and tends to encourage more innovative [14]) and the Total Building Performance Method was presented in the building designs [21–24]. However, many countries are still adopting IECC 2012 [15], which are both used in the United States (US) as whole prescriptive codes rather than a performance-based index. Prescriptive building performance methods. The Overall Thermal Transfer Value codes are often considered easier to follow than performance-based (OTTV) is a measure of the average heat gain into a building through indices because they clearly describes what is acceptable and require the building envelope and was introduced in ASHRAE 90A-1980 [34,35]. little analysis by the building designer. Inspectors and code officials also Singapore was the first country to develop an OTTV standard [36] in Asia. prefer prescriptive codes because they can easily confirm compliance The standard for energy conservation in buildings and building services in with the codes during the design review phase and site inspections [25– Singapore was based on ASHRAE Standards 90-75 and 90-80 A with

⁎ Corresponding author. E-mail address: [email protected] (D. Song). http://dx.doi.org/10.1016/j.rser.2016.11.087

Please cite this article as: Lee, J., Renewable and Sustainable Energy Reviews (2016), http://dx.doi.org/10.1016/j.rser.2016.11.087 J. Lee et al. Renewable and Sustainable Energy Reviews xx (xxxx) xxxx–xxxx some refinements to suit the local climate and construction practices. In Table 1 the 1980s and early 1990s some countries in the Association of Southeast Analyzed building information and simulation conditions. Asian Nations (ASEAN), including Indonesia, Malaysia, Philippines and Building information Location Seoul, Korea Thailand, used Singapore's development as a reference model to develop Building type Large-scale office building their building energy standards [37–39].PLA,proposedbytheJapanese The number of floors 32 floors above ground and 6 government, is the total annual cooling and heating load in the perimeter floors underground of a building per unit floor area [40].Itincludesheatconductionthrough Building height About 150 m Floor area of a typical About 1200 m2, 2.8 m an envelope and is caused by indoor and outdoor temperature differences, plan and floor height solar radiation heat gain, fresh air load and indoor heat gain. The performance-based method is the most time consuming, and various Construction and -Wall: 0.25 W/(m2·K) manufacturer representatives and governmental agencies have developed materials -Window: 1.6 W/(m2·K), 0.4 software packages to determine compliance due to the complexity of the (SHGC), 0.744 (VT) -Interior wall: 2.761 W/(m2· performance-based method analysis. The appropriate use of a dynamic K) energy simulation tool requires a considerable degree of qualification and -Roof: 0.18 W/(m2·K) training. Therefore, they require the incorporation of additional resources -Floor: 0.8 W/(m2·K) to control the regulation and certification schemes, both for the building Window to wall ratio 70.8% Infiltration 0.1 ACH design team as well as for the administration [41]. However, these additional resources will most likely not be incorporated, resulting in Simulation Indoor set-point temp. Cooling: 26 °C, 50% RH, the simulator not being qualified. Thus, any energy analyses cannot be conditions and RH Heating: 20 °C, 40% RH trusted; this is the biggest issue with performance-based method analysis. Weather data Seoul, South Korea (EPW) In South Korea, the building envelope requirements in the Building Internal thermal loads -People: 0.2 person/m2 with Design Criteria for Energy Saving (BDCES) are mandatory for all new a metabolic rate of 130 W buildings,andthisstandardisspecified as a prescriptive building code. It -Lighting: 25 W/m2 statesthatthebuildingenvelopeshouldbedesignedwithpredefined -Equipment: 25 W/m2 thermal insulation and heat resistance levels, and either the U-value of the -Schedules: See Appendix Minimum fresh air 25 CMH building envelope component or the specific thicknesses of insulation fi materials are speci ed [20]. Here, the U-factor or U-value is the overall heat System Cooling system Type: Steam turbine transfer coefficient that describes how well a building element conducts Inlet and outlet temp. of heat or the transfer rate of heat (in watts) through one square meter of a chilled water: 13.4/5.6 °C structure divided by the difference in temperature across the structure. The Inlet and outlet temp. of condenser: 30/35 °C BDCES categorizes the U-factor values based on three geographical zones in Refrigerating capacity: 1000 South Korea, including central, south and Jeju Island. The Korean USRT government has increased the thermal resistance level of the building COP: 4.5 envelope to reduce the building energy consumption, and therefore the U- Heating system Type: Gas-fired value of the building envelope continues to drop in Korea. Capacity: 8 t/h Previous research has shown that a high thermal insulation in Max pressure: 16 kg/cm3 envelopes with high internal thermal loads exhibits low heat dissipation Efficiency: 92% through the envelope, thus increasing the energy consumption required – for cooling the building [42 44]. Likewise, inappropriate envelope building are shown in Table 1. For the simulation modeling, the interior design standards could increase the energy consumption of a building zone and perimeter zone were divided by virtual partitions; the adjacent rather than reduce it [45]. To design the optimum envelope thermal zones with the same thermal environment were merged into a single insulation level, the indoor thermal environment, including the internal zone [53,54]. The reference building equipped with Building Energy heat gain level, should be considered; this is because heat transfer of the Management System (BEMS) to assist the energy audits and identify the ff envelope occurs when there is a temperature di erence between the energy conservation opportunities [55]. The density of lighting, equip- – inside and outside of the building [46 52]. When designing an energy ment and schedules were obtained from the BEMS, described in ffi e cient building, both the internal heat gain level and the strength of the Appendices (a) to (c). The infiltration rate was set at 0.1 ACH [56,57]. envelope thermal insulation should be considered. However, the pre- The occupancy density and schedules were obtained via field measure- scriptive building codes for building envelopes in South Korea do not ment from 22 July to 26 July in 2014, and a metabolic rate of 130 W was take into account the dependency of internal heat gain when deciding the applied for people referenced by ASHRAE Handbook 2013 [58].Historic optimum thermal insulation level according to building type. Seoul weather data (IWEC) published by the Korean Solar Energy Theaimsofthisstudyaretoreviewthe prescriptive building codes for Society [59] were used for the energy simulation. Seoul corresponds to ff envelopes and determine if they can e ectively improve energy saving the 4 A climate region in the US [60]. The system operation hours are according to the internal heat gain levels in a building. A high-rise building described in Appendices (d) and (e). in a temperate climate with four distinct seasons in Seoul, Korea was also reviewed. The scope of this study includes investigating the energy consumption of alternative envelope properties, such as the U-value of 2.2. Simulation method building envelope and the Solar Heat Gain Coefficient (SHGC) of fenestra- tion, by using various different internal heat gain conditions. Finally, the The simulation modeling for analysis was based on the M & $2V limitations of prescriptive building codes will be discussed. guidelines of ASHRAE Guideline 14 [61]. There are four options in the M & $2V guidelines; option D was selected to calibrate the simulation. The 2. Case study actual energy consumption data of the reference building was obtained by the BEMS to conduct the calibrated simulation [62–65]. The mean bias 2.1. Reference building error (MBE) and the coefficient of variation of the root mean square error [Cv(RMSE)] were used as an error index to determine the accuracy of the The reference building used in our analyses was a large-scale office calibrated simulation results. This value represents the overall uncertainty building that is located in Seoul, South Korea. Other specifications of the of the simulation when predicting whole-building energy usage. The lower

2 J. Lee et al. Renewable and Sustainable Energy Reviews xx (xxxx) xxxx–xxxx the Cv(RMSE), the better the calibration [66].TheMBEwas&$2lt;±5%, Table 3 while the Cv(RMSE) was & $2lt;15% for the monthly error tolerance Input variables - envelope properties. according to ASHRAE Guideline 14. Variable Range The EnergyPlus building energy simulation software was used for the analysis [67]. In regard to cooling energy consumption, the MBE and Window U-value [W/m2K] 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 Cv(RMSE) for actual usage and the simulated value were 2% and 11.99%, SHGC [-] 0.2 0.3 0.4 0.5 0.6 0.7 0.8 respectively. In addition, the MBE and Cv(RMSE) for the heating energy Location Seoul, South Korea − fi WWR [%] 70.8 (Reference building value) consumption were 2% and 14.35%, respectively. These results con rm the Wall U-value [W/m2K] 0.25 (Reference building value) validity of the simulations. The variation of annual heating and cooling energy consumption was variation of the internal heat gain and envelope properties. Therefore, a analyzed in a diverse internal heat gain level combined with the envelope total of 252 unique cases were produced using different combinations properties. A parametric simulation method, EnergyPlus with jEPlus [68], of four internal heat gain values, nine window U-values and seven was used to calculate the yearly energy consumption of the building. jEPlus SHGC values, as shown in Table 4. allows users to specify various parameters and values, from which IDF files are automatically created and used to carry out the EnergyPlus simulations. The software is also useful in managing large and complex parametric 3. Results and discussion simulations and completing them in a reasonable amount of time [69–74]. The climate of Seoul features a wide seasonal temperature variation 2.3. Input data for the parametric simulations and has four distinct seasons. In the summer, the weather is hot and humid and the temperature can reach as high as 35 °C, while the 1) Internal heat gain temperature can drop as low as −20 °C in the winter. Internal heat gain was classified into three levels (Level 1, Level 2, Annual cooling energy consumption (kWh/m2) for various envelope Level 3) for a commercial building, and one level for a residential designs is shown in Fig. 1. The cooling energy consumption increased building (Level 4), which was lower than the lowest commercial level with an increase in internal heat gain level. Also, the cooling energy (Table 2). Level 1 represented the highest internal heat gain and consumption increased in accordance with thermal insulation perfor- Level 4 represented the lowest one. Level 1 (101 W/m2)corre- mance. This tendency was particularly strong when the internal heat gain sponded to a building in which the internal heat gain was very high, level and SHGC value were high. These results were opposite from what e.g., a department store, as referenced by MOTIE of Korea [75].Level was expected. The current building code in Korea encourages designs with 2(78W/m2) corresponded to a large office building with a high high insulation for the building envelope for the purpose of saving energy, occupancy density and high equipment usage, as referenced by the but these results demonstrate that this policy does not effectively improve HVAC design documents of the reference building. Level 3 (38.2 W/ cooling energy consumption. m2) corresponded to a small office building, as referenced by The energy consumption for heating (Fig. 2) was less than the cooling ASHRAE Fundamentals [58]. Level 4 (18.2 W/m2) corresponded to energy consumption. The energy consumption for heating decreased with a residential building, and this level was used as the residential the strength of the thermal insulation performance of the windows in all referencemodelbytheDOE[76]. The radiant fraction values of cases analyzed in this study. In addition, the heating energy consumption lighting and equipment were obtained from the ASHRAE Handbook decreased with increasing internal heat gain levels and increasing SHGC and were 0.46 and 0.8, respectively [58]. of the envelope. Thus, the current policy of strengthening the thermal 2) Envelope properties insulation performance of the building envelope to save energy is effective inthecaseofheatingthebuilding. Envelope properties were selected from a range of passive housing The annual energy consumption, including heating and cooling, is standards, including the Germany Passive House Institute [77,78], shown in Fig. 3. The annual energy consumption shows the 3 types of MOTIE [75], Energy-Saving Design Standards for Buildings [20] and profiles, including directly proportional, inversely proportional or a quadric the HVAC design documents of the reference building. The reference function, based on the internal heat gain and SHGC levels. When the U- building was finished with a curtain wall, so the influence of the SHGC value of the building envelope were small and the internal heat gain level and the U-value of the windows were large. Therefore, the window-to- waslessthan38.2W/m2, the energy consumption increased proportionally wall ratio (WWR) and the U-value of the walls of the reference building with the SHGC. These patterns could be found in the prior studies [79–81] were set at a fixed value (Table 3). The U-values of the windows ranged as well. The pattern of energy consumption had a quadric relationship from 0.4 W/m2K to 4.0 W/m2K in 0.4 W/m2K increments. The SHGC when the internal heat gain level was high, especially at 78 W/m2 and varied from 0.2 to 0.8 in 0.1 unit increments. The WWR was fixed at 101 W/m2. The minimum point of energy consumption was located at the 70.8% and the U-value of the walls was fixed at 0.25 W/m2K. middle of the heat transfer coefficient range. These results were similar to

2.4. Simulations Table 4 Total amount of simulation cases for the parametric models.

The purpose of the simulation analysis in this study was to assess Internal heat gain Building envelope U- Building envelope Total the energy consumption for the reference building based on the [W/m2] value [W/m2K] SHGC [ -] cases

101 0.8 0.2 78 1.2 0.3 Table 2 38.2 1.6 0.4 Input variables - internal heat gain. 18.2 2.0 0.5 Levels Variables Total internal 2.4 0.6 heat gain [W/ Lighting Equipment [W/ Occupancy m2] 2.8 0.7 [W/m2] m2] [person/m2] 3.2 0.8 1 33 33 0.25 101 2 25 25 0.2 78 3.6 3 12 10.8 0.11 38.2 4.0 4 5.8 8.2 0.03 18.2 4 9 7 252

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Fig. 1. Results of annual cooling energy consumption.

Fig. 2. Results of annual heating energy consumption.

Fig. 3. Results of annual heating and cooling energy consumption. the other results [82–84].Theenergyconsumption was inversely propor- heat gain (level 1), the minimum energy consumption point was tional to the U-value when internal heat gain was high (especially level 1, achieved with a relatively larger U-value and SHGC level, as shown 101 W/m2) and the SHGC was high (especially 0.8) [85,86]. Generally, the in Fig. 4(d). This is because the internal thermal load cannot dissipate annual energy consumption increased when the thermal insulation was to the outdoors when the heat transfer coefficient of the envelope is improved (lower U-values) and the SHGC value became larger when the small. The minimum point of energy consumption moved from right to internal heat gain was high (level 1). left (a lower U-value and greater strength of insulation) as the indoor The minimum energy consumption point was different depending heat gain rate decreased ((d) to (a)). on the internal heat gain level (Fig. 4). In the case of a higher internal The annual total energy consumption was affected more by the cooling

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Fig. 4. Minimum energy consumption point (shaded) according to the internal heat gain level.

Table 5 Results of annual energy consumption for an SHGC of 0.4.

SHGC [-] 0.4

Window 0.8 1.2 1.6 2.1a 2.4 2.8 3.2 3.6 4.0 U-value [W/ m2∙K]

Heating Level 1 2 3 4 6 7 9 10 12 13 energy (101 W/ consump- m2) tion [kWh/ Level 2 3468911131517 m2] (78 W/ m2) Level 3 7 1013161922252830 (38.2 W/ m2) Level 4 16 20 24 28 32 36 39 42 44 (18.2 W/ Fig. 5. Annual energy consumption according to the thermal insulation (U-value) and m2) internal heat gain level (level 1–4). Cooling Level 1 118 114 111 108 105 103 101 101 101 energy consumption when the internal heat gain level was high, while the energy Level 2 93 89 86 84 82 80 78 78 79 heating energy consumption was more dominant when the internal heat consump- Level 3 51 49 48 47 46 45 44 44 45 gain level was low. In buildings with low internal heat gain levels, such as tion [kWh/ Level 4 36 34 33 33 32 31 31 31 32 m2] residential buildings (level 4), envelope thermal insulation properties (e.g., the U-value) are more important when achieving a design with minimum Heating and Level 1 120 117 114 113 112 112 111b 112 114 heating and cooling energy consumption. Thus, policies for strengthening cooling Level 2 96 93 92 91 91 91 92 93 95 the thermal insulation properties of the building envelope are eﬀective for energy Level 3 59 60 61 63 65 67 70 72 75 consump- Level 4 52 55 58 61 64 67 70 73 76 conditions where the internal thermal load is low. These results indicate tion [kWh/ thattheprescriptivemethodasanenvelopedesignstandarddoesnot m2] always guarantee energy saving. The “Energy Saving Design Standards for Buildings” in South Korea are a Current U-value standard of exterior envelope b based on a prescriptive method and specify a U-value for each building The minimum energy consumption component. In the case of buildings with internal heat gains at Level 1 or 4. Conclusion Level 2, the required U-value for windows is less than 2.1 W/m2K. In addition, the current policy for the SHGC value in newly constructed The main objective of this study was to review the impact of external commercial buildings is 0.4. Fig. 5 and Table 5 show the annual energy insulation and internal thermal density on energy consumption of the 2 consumption for a U-value of 2.1 W/m K and an SHGC of 0.4. When the building in a temperate climate for four distinct seasons in Seoul, South internal heat gain level was high, less energy was required to heat and cool Korea. The limitations of prescriptive building envelope codes according to 2 the building when the U-value of the window was 3.2 W/m KatLevel1 building type were also discussed. The review was carried out using 2 and 2.8 W/m K at Level 2. These results indicate that the present parametric simulation methods and by varying the thermal insulation ﬀ prescriptive envelope design standards of Korea are ine ective in high properties of the exterior wall and the indoor thermal density. Finally, the internal heat gain (Level 1 and 2) buildings. In fact, the current U-value annual energy consumption for heating and cooling the building was 2 envelope standard, less than 2.1 W/m K, may actually increase the annual calculated. energy consumption in commercial buildings in Korea. The results showed that the annual cooling energy consumption

5 J. Lee et al. Renewable and Sustainable Energy Reviews xx (xxxx) xxxx–xxxx increased as the thermal insulation improved regardless of the indoor Actually, current envelope standardsofKoreathatrequireaU-valueless thermal density. This tendency was particularly strong in cases where the than 2.1 W/m2K may increase the annual energy consumption in high indoor thermal density and the SHGC of the envelope were high. Cooling internal heat gain buildings. Indeed, the minimum energy consumption energy consumption was greater than the heating energy consumption in point occurs where the U-value is around 2.8 or 3.2 W/m2Kinhighinternal all cases analyzed in this study. heat gain buildings. This result indicates that the prescriptive method as an As expected, the annual heating energy consumption decreased with envelope design standard does not always guarantee energy savings for increasing strength of the thermal insulation in all cases. Thus, the Seoul weather conditions. current policy of strengthening the thermal insulation of the envelope The prescriptive design guideline should be revised to consider the effectively improves the energy consumption when heating the building. internal heat gain, envelope properties and outdoor conditions. In The annual energy consumption for cooling and heating decreased addition, the performance-based design method should be urgently proportionally when the U-value of the building envelope was small applied for designing envelopes with maximal energy savings. and the internal heat gain was less than 38.2 W/m2. On the other hand, the annual energy consumption increased when the thermal insulation Acknowledgements was improved and both the internal heat gain and SHGC value were larger. Thus, the policy to strengthen the thermal insulation properties of This research was supported by a grant (15CTAP-C098308-01) from ff the envelope for energy saving is only e ective in conditions where the the Technology Advancement Research Program (TARP) funded by internal heat gain level is low. Importantly, the current building codes of Ministry of Land, Infrastructure and Transport of Korean government. Korea encourage high thermal insulation of the envelope to save energy are not effective when the internal heat gain and SHGC value are high. Appendix A Notably, the present prescriptive envelope design standards of Korea are ineffective in buildings with high internal heat gain, i.e., Levels 1 and 2. See Fig A1.

Fig. A.1. Hourly internal loads: (a) occupancy, (b) indoor lights and (c) equipment. System operation schedules: (d) heating and (e) cooling.

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