KIEAE Journal

With the recent increase in awareness of environmental protection and energy conservation in South Korea, various construction technologies utilizing renewable energy are being applied to the building sector, which accounts for approximately 20% of the total energy consumption¹⁾. The use of renewable energies such as photovoltaic power, solar energy, wind power, and geothermal energy, has been recognized as optimal solution for solving the global energy and environmental issues, and the current state of research and policy has been focusing on the utilization and distribution of renewable energy²⁾. Of these renewable energies, the photovoltaic energy has been in the limelight as alternative energy source because it can provide a limitless amount of clean green energy, and it is appraised as energy source with the highest potential³⁾.

As public building, the school facility is an ideal place for installation and distribution of renewable energy, for it will be highly educational and effective in raising public interest, and its relatively wide roof area and modularized configuration space make schools an optimal building for installing solar power systems. Also, according to the Industry and Energy Affairs Notice No. 2012-18 ｢Regulation on Promoting Rationalized Energy Use in Public Institutions｣, it is mandatory for school facilities in South Korea to install renewable energy systems. The government began by passing law, which obligated 5% of the total construction cost to be invested in the installation of renewable energy facilities in the construction of newly-built public facilities with a total floor area of over 3,000m² and currently, all newly-built or renovated buildings with a total floor area of over 1,000m² are required to invest and install a renewable energy source that can account for over 12% of the expected energy use⁴⁾.

With over 74% of the country’s buildings being built over 15 years ago, before the insulation standards were reinforced, remodeling deteriorated buildings for energy efficiency is essential and thus the 「Green Remodeling Activation Plan」 was finalized in the Minister of Economic Relations Conference in July 2013. It indicates the need to increase the proportion of energy-saving buildings by the reinforcement of regulations on various energy standards on newly built buildings, but it also suggests the importance of remodeling deteriorated buildings into a more energy efficient design.

In particular, deteriorated school facilities over the typical building lifespan of 25 years account for 50% of all schools ⁵⁾, the installation of renewable energy systems is being promoted as part of the energy-efficiency remodeling project and the Green School Project, which is the core project of the government’s Green New Deal Project.

Previous studies on the Green School Project ⁶⁾ has analyzed that regarding application of renewable energy, the Photovoltaic (PV) system accounts for the largest part of the budget. However, because the PV system highly depends on the natural environment, the supply pattern is inconsistent and unpredictable, and as a result, if the system capacity is determined by the total power demand of the building, it may lead to excess energy due to overproduction. In other words, it may lead to unnecessary investment in renewable energy systems. Therefore, in order to determine the optimal installation capacity of PV systems, the annual electricity consumption patterns of the building must be analyzed, and a strategy for efficient use of power must be implemented.

The objective of this study is to determine the optimal capacity for fixed PV systems based on the conformity degree of demand/supply patterns of renewable energy systems and the annual electricity demands of deteriorated elementary, middle, and high school buildings.

This study analyzed the demand/supply patterns of standard school models of deteriorated schools derived from previous studies ⁷⁾⁸⁾⁹⁾ and the input elements of the Visual DOE energy simulation standards applied to standard schools using the Merit program. Based on the results, the optimal installation capacity of PV systems for each school level was determined, and the energy savings effect compared to the deteriorated schools’ average annual energy consumption was analyzed.

In the previous study, a virtual school was set as standard to evaluate energy performance in deteriorated elementary, middle and high schools. Based on the ｢School Facility Standard Design｣ in 1980 and S-elementary school in Kyunggi-Do selected on time, physical, performance, and operational standards, the establishment year of the virtual school was set in the 1980s, the building structure was set as reinforced concrete structure, and it was set as a four-story building with an area of 1,333m². Furthermore, the cooling method was set as package air conditioning, heating systems were designated as gas heaters, the exterior wall insulation was set as T50, roof thermal insulation was T100, flooring was artificial stone floor finishing, and the windows and doors were set as double glazed. Table 1 and Fig. 1 show an overview of the standard school and the typical floor plan.

Fig. 1 
Typical Floor Plan of Standard School

On the dynamic simulation program of the Visual DOE, zoning was performed with respect to rooms with identical air conditioning when determining simulation analysis models for energy analysis simulations for each school level. In addition, energy consumption calculation for non air-conditioned rooms were included, and input data for standard school energy analysis model such as schedule, infiltration schedule, physical properties for each material, and HVAC system variables of air-conditioned and non air-conditioned rooms were set based on the ｢School Facility Standard Design｣ and the blueprint for S-elementary school. However, schedules including actual use time, indoor time, density, and air-conditioning time, which are the biggest factors in assessing energy performance in school facilities, were set differently for each school level.

Fig. 2 
Energy Simulation Modeling for Standard School

In addition, based on insulation, windows and doors (SHGC), natural light (south shades), control (system efficiency and indoor set temperature), and others (infiltration, natural ventilation, and artificial lighting), which are important factors for energy efficiency remodeling at deteriorated school facilities, energy simulation was performed according to the application of the above mentioned technologies in the standard school model. The baseline input data used for standard school energy analysis were based on the「School Facility Standard Design」, blueprint of the standard school, school health regulations (indoor set temperature and natural ventilation), and previous studies¹⁰⁾ (infiltration level), and the details are listed on Tables 2 and 3.

The annual energy consumption was analyzed according to each school level by the energy analysis model, which applied the baseline settings for standard schools, and the results are listed in Table 4. The results indicated that the average annual energy consumption was 123,719kWh/yr at elementary school, 144,080kWh/yr at middle school, and 199,982kWh/yr at high school. The total annual energy consumption at high school was 61% higher compared to elementary school, and 23% higher compared to middle school, and the total energy consumption at middle school was 32% higher compared to elementary school.

In detail, the annual electric energy consumption was 51,468kWh/yr at elementary school, 58,315kWh/yr at middle school, and 88,268kWh/yr at high school. The annual heating energy consumption was 27,277kWh/yr at elementary school, 32,508kWh/yr at middle school, and 39,342kWh/yr at high school, and as for air-conditioning energy, it was 44,974kWh/yr at elementary school, 53,257kWh/yr at middle school, and 72,372kWh/yr at high school.

The Merit program was used to analyze the power supply/demand patterns. The Merit is a program used to establish energy plans for building or neighborhoods, developed by the ESRU (Energy Systems Research Unit) of Strathclyde University in Scotland. The program is used as a tool to evaluate the suitability of a given energy supply system by assessing the user’s demands through matching analysis. As an input condition for simulation analysis, each school level’s energy demands were set hourly for a total 8,760 hours per year by utilizing the Hourly Data Output feature of the Visual DOE program used for energy simulation. The PV installation capacity was divided into six stages from 20kWp to 120kWp, and analyzed (Refer to Fig. 3). Because the availability of the standard school roof area is about 1,200㎡, considering the area required for copper shades and maintenance, the maximum PV installation capacity was set as 120kWp, which is the total required floor area for crystalline solar cells, the most commonly distributed PV system, that needs floor area of approximate 10㎡/kWp per unit. The supply target for the power generated by the PV system was based on the demand of the lights and equipment during the time when the heat source system is not operating, which reflects the fact that the energy sources may be measured differently depending on the type of the heat source system and that operation may be limited, and depending on the operating systems of each school, such as the vacation period, measurements may be low even though it is during the peak usage period.

Fig. 3 
Annual Electricity Power Demand Pattern and Production

Type	Appropriate capacity	Surplus capacity
Elementary school
	Capacity : 40kWp	Capacity : 60kWp
Middle school
	Capacity : 60kWp	Capacity : 80kWp
High school
	Capacity : 60kWp	Capacity : 80kWp

Table 5 shows the supply/demand patterns for each school level attained through simulation. As shown in the analysis results, the appropriate capacity of the PV system was 40kWp for elementary school and 60kWp for middle and high schools on the standard school, and the analysis indicates that if the installation capacity is increased by 20kWp from the appropriate installation capacity for each school level, energy production appears to be greater compared to the interim peak hourly demand, leading to oversupply. Based on the analysis results, energy savings depending on PV system installation was reflected in energy analysis, and for the standardization of the appropriate installation capacity for the PV system, the appropriate installation capacity for each school level was proposed in Table 6. The appropriate capacity of PV systems for each school level was indicated as 1.4 times the number of classrooms at elementary school, and 2.0 times the number of classrooms at middle and high schools.

In order to calculate the energy savings of school levels following the PV installation on the roof, appropriate alternatives for each school level were selected and compared with the standard energy use for each different purpose. As an alternative for the PV installation, solar power systems of 40kWp were installed at elementary school, and solar power systems of 60kWp were installed at middle and high schools. Examination of the blueprint of the standard school showed that the fixed PV system could be installed in 1,200m², thus approximately 10m² of roof area was required per 1kWp of PV capacity. Table 7 indicates the annual production (power generation) and consumption (supply) of the standard school following the installation of the solar power system. For example, if a solar power system of 40kWp is installed, annual energy consumption is 19,820kWp/yr and the annual energy production is 35,610 kWp/yr, which makes the annual excess energy 15,790kWh/yr. Therefore, as shown in Tables 8, 9, and 10, the installation of the appropriate capacity of solar power system reduced the annual energy consumption by 20.2% at elementary school, 26.9% at middle school, and 21.0% at high school, with the largest annual energy saving at middle school building.