The recent increase in global energy consumption has led to a phenomenon called global warming and related climate problems, resulting in a growing interest in developing various technologies that aim to reduce energy consumption, including passive designs, which can reduce the energy load of a building [1
]. Though unrelated to various efforts in reducing energy consumption, the ratio of glazing in building façades has also increased for aesthetic purposes. As a result, direct solar radiation inside the building rose, causing thermal issues as well as increased heating and cooling energy consumption. Particularly, in hot climate regions, the energy cost attributed to the increase in cooling energy consumption significantly increased [3
]. To solve these issues, various energy saving techniques have been introduced to block direct solar radiation, such as tinted glass, colored glass and phase changing materials. In particular, there is a growing interest in the double skin façade (DSF), which can be implemented in buildings with a high glazing ratio [7
A DSF consists of the external and inner skins, as well as the cavity existing between the two skins. Since the heat transfer on DSF occurs due to the temperature differences among the external skin, cavity, and the inner skin of a building, managing the heat in the cavity in the summer and in the winter is a key issue. Thus, research on: (i) the shading and the airflow operating methods in the cavity and (ii) the thermal insulation of the glass and the inner skin in the cavity have been conducted. Research on thermal management in the cavity of DSF can be categorized into two types: (i) heating and cooling energy reduction by implementing airflow operating methods; and (ii) thermal bridge effect reduction by improving thermal insulation.
First, several studies have focused on the airflow operating methods by opening and shutting the openings in the cavity of DSF. In winter, the heat in the cavity can considerably reduce the heating load of a building in terms of thermal comfort. Particularly, in winter, conducting the heat in the cavity to the building's interior can be maximized by using a static air buffer as an airflow operating method, which seals the heat in the cavity [9
]. The Telus Headquarters building in Toronto and the Occidental Chemical buildings in Niagara Falls and in New York use a static air buffer as an airflow operating method to reduce heating energy consumption in winter [13
]. Additionally, Xu et al.
] analyzed that 20% to 30% of heating energy consumption can be reduced by using a static air buffer in applying DSF to buildings in Japan. Gracia et al.
] also showed that the static air buffer could save up to 26% of heating energy consumption in winter. Next, the cooling load on a building can increase in the summer because of the heated air in the cavity [16
]. Accordingly, in terms of thermal comfort, management of heated air in the cavity in summer is an important issue. Various studies have been conducted on the airflow operating methods in implemented during summertime. It has been shown that the external air curtain as an airflow operating method that opens the openings in the cavity (i.e.
, allowing the heat in the cavity to travel freely outside) would save cooling energy consumption during summer because the heated air in the cavity due to solar radiation could be removed in advance before being transmitted to a building [9
]. To discharge the heated air in the cavity and the building to outside the building, natural ventilation, as well as the external air curtain, are also considered important [7
]. Gratia et al.
] mentioned the significance of natural ventilation after sunset in addition to the duration of sunshine through solar radiation in summer. By emitting the heat inside the building through natural ventilation, 25.5% of cooling energy consumption was saved [7
]. Based on the previous studies related to the airflow operating methods, there was little research that simultaneously applies the airflow operating methods and natural ventilation with the consideration of the climate differences between summer and winter. Therefore, this study focused on the facilities located in the regions with the hot summer and cold winter, simultaneously. The East Asian monsoon climate is divided into a hot and wet summer monsoon and a cold and dry winter monsoon, resulting from the monsoonal flow that carries moist air from the Indian Ocean and Pacific Ocean to East Asia. It is driven by the temperature differences between the Asian continent and the Pacific Ocean. Although the East Asian monsoon climate region (e.g., Seoul) has four seasons including spring and fall, spring and fall only last for a short period in this climate region [22
], therefore, this study only focused on the climatic characteristics in summer and winter.
Second, as a method of controlling heat in the cavity of DSF, various studies have focused on reducing the thermal bridge effect by improving the thermal insulation of the inner skin. It has been shown that the method was effective in both summer and winter. In terms of the thermal bridge effect, Manz [26
] and Perez-Grande et al.
] conducted studies on reducing heating and cooling loads by improving the thermal insulation of the inner skin glazing. Other studies have also shown that improvement in the thermal insulation of the inner wall reduces the thermal bridge effect [16
]. Feist [30
] has shown that heating and cooling energy consumption increases due to the unnecessary heat transfer caused by the thermal bridge effect on the wall in addition to the window. Evola et al.
] determined that there is about 3.5% of the increase in cooling energy consumption due to the thermal bridge effect of the building skin during summer.
Other studies have focused on reducing the thermal bridge effect by implementing a green wall (GW) on a single skin façade (SSF) [32
]. Studies showed that installing a GW on the facades of a two-story building could reduce the cooling load on a clear summer day by 28% [33
]. Akbari et al.
] has shown that the installation of a GW would reduce heat transfer by 0.24 kWh/m2
. Likewise, other researchers have shown that the use of plants as shading devices in warm or tropical regions would reduce the cooling load in summer as they helped create a sun-blocking effect [35
]. These previous studies on thermal bridge effect have concentrated mainly on SSF buildings, while only a few considered DSF buildings. Therefore, this study focused on reducing the thermal bridge effect by implementing GW as the seasonal energy efficiency strategies of a DSF.
In conclusion, it has been shown that in implementing DSF, the management of heat in the cavity is a very important control factor in cooling and heating energy consumption reduction. Therefore, this study aimed to establish seasonal energy efficiency strategies, and evaluate the effect of these strategies to efficiently manage heat in the cavity of DSF. Furthermore, it aimed to implement these seasonal energy efficiency strategies to four types of DSF, and select an optimal DSF after conducting life cycle cost (LCC) and life cycle CO2 (LCCO2) analyses.
This study was conducted in four steps: (i) establishment of seasonal energy efficiency strategies; (ii) application of seasonal energy efficiency strategies; (iii) analysis of energy saving effect by season by applying seasonal energy efficiency strategies; and (iv) LCC and LCCO2
analyses for selecting an optimal DSF. The scope of this study included library facilities located in Seoul, South Korea, which is part of the East Asian monsoon climate region. As mentioned spring and fall only last for a short period in this climate region, therefore, this study only considered winter and summer characteristics to establish seasonal energy efficiency strategies (Figure 1
To improve the effect of the DSF implementation, this study established seasonal energy efficiency strategies and analyzed the effect of these strategies through a case study. It aimed to select an optimal DSF in terms of SIR. The university facilities were statistically significant in terms of energy consumption. It was determined that the energy consumption of the university facilities in 2010 was 295 thousand TOE, which is ranked second among all types of buildings in South Korea (refer to Table A2
). Especially, the library facility is the main factor of energy consumption and exists in all the university. Therefore, the university library facility could have a great effect on the whole energy consumption of South Korea.
The seasonal energy efficiency strategies were established in summer and in winter. First, to establish winter-energy-efficient strategies, a combination of two methods was considered: (i) static air buffer (Method_A1) as an airflow operating method; and (ii) GW (Method_B) for improving thermal insulation. Next, to establish summer-energy-efficient strategies, a combination of the following three methods was considered: (i) external air curtain (Method_A2) as an airflow operating method; (ii) natural ventilation (Method_A3) as an airflow operating method; and (iii) GW (Method_B) for improving thermal insulation (refer to Table 3
The energy consumption analysis on the energy models showed that the seasonal energy efficiency strategies were effective during both summer and winter seasons. First, in terms of winter-energy-efficiency strategies, the implementation of the static air buffer (Method_A1) as an airflow operating method to EMS #1 (shaft box DSF) resulted in 644,507 kWh, with a reduction rate of up to 3.97% in heating energy consumption. Also, to reduce the thermal bridge effect, the use of GW as a method for improving thermal insulation showed that EMS #3 (shaft box DSF and GW) was 643,399 kWh with a reduction ratio of up to 4.13% in heating energy consumption.
Next, in terms of summer-energy-efficiency strategies, the implementation of the airflow operating methods including natural ventilation showed that the cooling energy consumption of EMS #4 (multistory DSF) was 868,302 kWh, with a reduction rate of up to 12.62%. Also, to reduce the thermal bridge effect, the use of GW as a method for improving thermal insulation showed that the cooling energy consumption of EMS #5 (multistory DSF and GW) was 867,844 kWh with a reduction rate of up to 12.67%.
Finally, to maximize SIR40 and minimize BEP40 through the LCC and LCCO2 analyses, this study selected an optimal DSF with seasonal energy efficiency strategies, which was the multistory DSF with SIR40 (3.20) and BEP40 (nine years). The analysis showed that this optimal DSF resulted in smaller investment cost (additional initial cost: $190,743; additional replacement cost: $113,395) and higher savings with benefits (LCES benefit: $958,399; KCER income: $15,748).
The results of this study can be used in making decisions regarding: (i) seasonal energy efficiency strategies to save heating and cooling energy consumption in the East Asian monsoon climate region with a high temperature gap in summer and in winter; and (ii) application not only to existing buildings but also for new buildings.
The research team plans to conduct the following future research: (i) an optimal design according to the types of DSFs in terms of energy performance based on cavity depth, the size of an opening, and the position of the shading device of a DSF; (ii) airflow operating methods by season as well as optimal airflow operating methods that change in real-time, depending on the change in temperature inside and outside the building; (iii) thermal bridge effect reduction through thermal insulation of the applied GW, as well as the effects of sunblock and air purification of the applied GW; and (iv) decision support system for the sustainable design and management of buildings based on the long term validation with consideration of the deterioration process.