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A Multi-Objective (Energy, Economic and Environmental Performance) Life Cycle Analysis for Better Building Design

Sustainability 2014, 6(4), 1667-1685; doi:10.3390/su6041667

Article
Economic Feasibility Analysis of the Application of Geothermal Energy Facilities to Public Building Structures
Sangyong Kim 1, Young Jun Jang 2, Yoonseok Shin 2 and Gwang-Hee Kim 2,*
1
School of Construction Management and Engineering, University of Reading, Whiteknights, P.O. Box 219, Reading RG6 6AW, UK; E-Mail: rd026992@reading.ac.uk
2
Department of Plant/Architectural Engineering, Kyonggi University, Suwon-si, Gyeonggi-do 443-760; Korea; E-Mails: styx93@empas.com (Y.J.J.); shinys@kgu.ac.kr (Y.S.)
*
Author to whom correspondence should be addressed; E-Mail: ghkim@kyonggi.ac.kr; Tel.: +8-231-249-9757; Fax: +8-231-244-6300.
Received: 1 March 2014; in revised form: 13 March 2014 / Accepted: 18 March 2014 /
Published: 27 March 2014

Abstract

: This study aims to present an efficient plan for the application of a geothermal energy facility at the building structure planning phase. Energy consumption, energy cost and the primary energy consumption of buildings were calculated to enable a comparison of buildings prior to the application of a geothermal energy facility. The capacity for energy savings and the costs related to the installation of such a facility were estimated. To obtain more reliable criteria for economic feasibility, the lifecycle cost (LCC) analysis incorporated maintenance costs (reflecting repair and replacement cycles based on construction work specifications of a new renewable energy facility) and initial construction costs (calculated based on design drawings for its practical installation). It is expected that the findings of this study will help in the selection of an economically viable geothermal energy facility at the building construction planning phase.
Keywords:
economic analysis; geothermal energy; lifecycle cost; public building

1. Introduction

Demand for improvements in quality of life, as well as for various benefits necessitates the provision of a consumer-centred construction environment, even within the building sector. To satisfy consumer demands related to indoor and outdoor environments, a construction environment system should accommodate both natural and artificial controls. To accomplish this end, an optimal building structure should be built in composite harmony with construction plans, the latter including the facility system plan, the spatial plan and the structural plan. Interest in reducing greenhouse gas emissions arising from energy demand within building structures has gradually been increasing, this being a component of optimal building structure; however, there are technical limitations to the extent to which energy consumption can be reduced simply by maximizing the efficiency of fossil energy in conventional use. One of the approaches to addressing this problem is to reduce fossil fuel consumption using new renewable energy resources [1]. To fundamentally increase the efficiency of energy consumption, there is thus an urgent need to develop new technologies that can utilize these eco-friendly renewable energy resources [2].

The EU stipulates that all new building structures to be built from 2019 onwards must produce more energy than they consume; similarly, with a view toward achieving zero-energy buildings by 2025, compulsory regulations and obligatory expansion plans have been established in the U.S. [3]. Other advanced countries have likewise made efforts to expand new renewable energy facilities and increase the supply ratio. In line with this trend, Korea has also made efforts to increase the supply ratio of new renewable energy from the fairly low level of 1.6% in 2012. For these reasons, planning for energy consumption capacity and savings should start at the construction project planning phase.

Geothermal power is cost effective, reliable, sustainable and environmentally friendly. It is also available 24 hours/day which can be used as the base load. Historically, it has been limited to areas near tectonic plate boundaries. However, recent technological advances have dramatically expanded the range and size of this source, especially for applications, such as home heating, opening a potential for widespread exploitation, as has been described in this study. In this study, the geothermal system, a renewable energy facility applied to multiple building structures, was employed to analyse relative reductions in energy consumption and energy use cost and to determine the energy savings cost related to the use of this system in consideration of the lifecycle cost (LCC), which includes initial investment costs, repair and replacement cycles for major materials. The ultimate aim is that of proposing an effective plan for geothermal system selection at the construction project planning stage through economic feasibility analysis.

2. Methodology

This study is limited to the application of new renewable energy to a building structure with geothermal facilities, based on statistics and on previous studies. The target buildings selected for this research were three public buildings, within which the installation of a new renewable energy facility is compulsory. In all cases, the renewable energy facility, which varies in size across the three buildings, had already been designed. By analysing the design data of the buildings, the volume of new renewable energy was converted into that of the energy applied to the conventional energy facility, and the buildings were modelled with no application of the new renewable energy source. Using total energy consumption evaluation program (ECO2-OD), the compulsory supply volume of new renewable energy was calculated, and geothermal facility installation sizes in the proportions of 100% and 25% of compulsory supply volume, respectively, were set and applied in each case.

Energy consumption and primary energy consumption of the building structures were calculated to perform a comparative analysis of changes related to the application of the geothermal energy system and to determine the changes in the energy volume used. A comparative analysis of the economic feasibility of geothermal energy application was conducted between buildings with geothermal facilities and those without, based on reductions in energy cost. The initial construction cost was applied, together with the cost of the redesigned specification for buildings with geothermal facilities. Where the volume of the conventional energy facility was replaceable, the volume change of the conventional facility resulted from the application of the geothermal facility, and the removal of the facility was reviewed and reflected in the initial investment cost. The useful life was set at 40 years in the LCC analysis; the analysis cycle was set at 10 years, and the repair and replacement cycles of major materials were chosen to ensure the reliability of maintenance cost calculations.

3. Literature Review

Many studies on the application of new renewable energy facilities to building structures have been conducted, through which plans have also been proposed to improve the reliability and economy of such applications. Rezaie et al. [4] divided case buildings by usage to analyse the economy, efficiency and energy emission of geothermal, solar-powered, photovoltaic and hybrid power systems. Visa et al. [5] studied the energy state required before and after the installation of a photovoltaic energy system in terms of efficiency and economic feasibility and performed an analysis of the latter. Cucchiella et al. [6] conducted a performance evaluation of a photovoltaic energy system installed in building structures to analyse the time required to retrieve investment cost and the extent of influence of climate and the energy consumption behaviour of residents within the area of installation. Francisco and Batlles [7] conducted a comparative analysis between a cooling system that applied photovoltaic energy and a conventional system and predicted the rate of reduction in energy consumption capacity as an alternative to reducing energy consumption. Similarly, many studies have been actively conducted to examine the utilization of new renewable energy resources in different countries in order to reduce energy consumption. However, there are no clear-cut criteria for the selection and application of such renewable energy facilities at the building structure planning phase, and it is difficult to select a facility that will achieve effective energy savings and secure economic feasibility. Furthermore, the determination of a new renewable energy system for building structures should occur at the planning and design phases, and its applicability and characteristics need to be taken into account, because the energy source may vary depending on the appearance and use of a building structure.

Previous studies performed in Korea can be subdivided into two categories—those examining the current state and application of new renewable energy within building structures and energy production volume and economic feasibility analyses of new renewable energy sources. Jung et al. [8] proposed a process to integrate a new renewable energy system into a construction design factor to enable the application of new renewable energy; the authors analysed systems according to their characteristics to apply and analyse applicable new renewable energy systems depending on the design process. Kang et al. [9] analysed the building energy substitution rate for public buildings in which 5% of the total construction cost was invested into the installation of a new renewable energy facility and presented a plan for efficiency improvement with no additional cost, using such a facility. As a component of the fundamental data to develop plan criteria for the application of a new renewable energy system to building structures, Kim et al. [10] proposed a direction for domestic construction planning based on an analysis of building structures that apply new renewable energy in Korea and Germany, focusing on photovoltaic and geothermal energy. Yoon et al. [11] suggested an option for the development of a new renewable energy planning tool that reflects various requirements, including the supply ratio of new renewable energy, the selection of a system type, the time of application and the method. Seo et al. [12] derived an optimal application plan by researching the current state of new renewable energy penetration and reviewing alternatives for an efficiency improvement plan according to changes in the volume of conventional new renewable energy systems. In addition, reviews of energy production volume and economic feasibility relating to new renewable energy resources applied to building structures have been actively conducted. Kim and Kim [13] carried out economic feasibility evaluations of photovoltaic, wind, small hydro and bio-gas power systems and presented a new renewable energy application plan. Kim et al. [14] performed an LCC analysis of the application of new renewable energy to reduce energy consumption and to analyse the energy-saving effect resulting from the reduction in the energy consumption cost and the retrieval period of the initial investment cost upon application of the new facility; the authors also proposed a scheme for economic building structure planning. Lee et al. [15] conducted an analysis of energy intensity by building use based on an analysis of the actual state of energy use in public office facilities, with the enforcement of the law compelling the installation of new renewable energy facilities within public organizations. However, assessments conducted in previous studies have addressed the future applicability of new renewable energy sources at the level of fundamental data by exploring the current state of new renewable energy use, the actual state of management and its problems and user satisfaction; the limitation of these studies thus lies in the lack of understanding of a direction to improve the management of a new renewable energy system. In addition, there are no concrete analysis processes and criteria for the analysis of energy production volume and economic feasibility, and a cyclical analysis of the entire lifecycle of building structures has not been performed, resulting in many limitations to actual applications of resolutions. The summary of previous studies is listed in Table 1.

Table Table 1. The summary of previous studies. LCC, lifecycle cost.

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Table 1. The summary of previous studies. LCC, lifecycle cost.
AuthorsYearResearch Aim
Jung et al.2008Applying and analysis of a new renewable energy design process
Kim & Kim2008Presenting a new renewable energy application plan
Rezaie et al.2011Analysis of energy emission quantity based on renewable energy options
Kang et al.2011Analysis of renewable energy and building energy substitution rate
Kim et al.2011LCC analysis of the application of new renewable energy to reduce energy consumption
Cucchiella et al.2012Performance evaluations of integrated photovoltaic systems
Lee et al.2012Analysis of energy intensity by building use based on the actual state of energy use
Kim et al.2012Applying new renewable energy focusing on photovoltaic and geothermal energy
Francisco & Batlles2013Forecasting energy savings rate by applying solar energy
Yoon et al.2013Suggesting an option for the development of a new renewable energy planning tool
Seo et al.2013Improvement plan according to changes in volume of conventional new renewable energy
Visa et al.2014Economic analysis of the renewable energy mix in a building

4. The Geothermal System

A geothermal system uses geothermal heat to achieve an increase in temperature, with the latter maintained at a certain level deeper than 15 m below the surface of the Earth, regardless of atmospheric temperature. Geothermal energy can be largely subdivided into geothermal and land surface heat. Geothermal heat is heat energy continuously generated by the decay of radioactive isotopes in the core of the Earth, i.e., the energy that magma emits toward the surface of the Earth. Land surface heat can be classified as shallow or deep geothermal heat depending on depth below the surface of the Earth [16]. Shallow geothermal heat averages 5–20 °C at less than 15 m from the surface of the Earth. To use shallow geothermal heat, a 100- to 300-m-deep borehole is drilled to lay a geothermal heat exchanger, which provides energy to a building structure for heating and cooling using a heat pump and an air handling unit, as shown in Figure 1. In the case of deep geothermal heat, the Earth is excavated to 3 km below the ground to obtain steam with a temperature of 65 °C or higher to generate electricity through a steam turbine [17]. A geothermal system for cooling in summer operates as follows: the high temperature and high pressure cooling gas compressed by the compressor of a heat pump exchanges heat at the geothermal heat exchanger, with conversion into a moderate temperature and high pressure liquid, resulting in cooling effects when the liquid evaporates in the indoor evaporator at low temperature and in a low pressure state through expansion in the expander. On the other hand, in winter, the geothermal heat pump system works in the opposite direction, absorbing geothermal heat and supplying it to the inside of a building [18].

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Figure 1. The structure of a geothermal system.

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Figure 1. The structure of a geothermal system.
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Geothermal systems can be broadly categorized as either open or closed, depending on the circuit composition of the heat exchanger that collects the geothermal heat. An open loop system is one in which the pipe that carries water supplied from phreatic and underground sources is applied to locations within a basin with effluent water. A closed loop system is one in which water circulates within the pipe to collect (exchange) geothermal heat. Closed loop systems are classified as vertical or horizontal based on the loop type, as shown in Figure 2. The vertical type ranges from 100–150 m below ground, while the horizontal type ranges from 1.2–1.8 m below ground.

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Figure 2. Vertical (left) and horizontal (right) types of closed loop systems.

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Figure 2. Vertical (left) and horizontal (right) types of closed loop systems.
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5. Case Analysis of Energy Consumption Capacity by Building Structure

The following are to be determined for the analysis of energy consumption: (1) general information for each case and the major energy load factors for energy consumption calculation; (2) the total annual energy consumption for cases in which no new renewable energy facility is applied, the energy consumption cost and annual consumption by unit area, the consumption cost and primary energy consumption; (3) the total annual energy consumption for cases where a geothermal energy facility is applied; (4) a comparative analysis of energy consumption and consumption cost and the total annual energy consumption for each case, considering examples with and without a geothermal energy facility; and (5) the energy-saving effects and cost savings resulting from the application of a geothermal energy facility for all cases and the energy consumption and energy consumption cost by the scale of the building structure following the application of the geothermal facility.

As shown in Table 2, three public office buildings of a similar size, all of which are subject to compulsory installation of a new renewable energy facility, were selected as the target cases to be analysed. The location of all cases is a central city of South Korea. Energy consumption and energy consumption costs were analysed for each building; subsequently, the same parameters were measured following the application of a geothermal energy system, for use in calculating and analysing the LCC of the buildings.

Table Table 2. The description of an electric heat pump (EHP).

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Table 2. The description of an electric heat pump (EHP).
DescriptionCase 1Case 2Case 3
Type of casesPublic building
StructureReinforced concrete
Size of buildingNo. of floorsBasement floor = 1, Ground floors = 3
Building areas774.42 m21495 m22786.57 m2
Total areas1997.83 m24006.58 m212,690.79 m2
Heating and air-conditioning areas1421.58 m22699.4 m27292.16 m2
Outer wall area/window area20.45%18.81%32.67%
Type of casesPublic building
StructureReinforced concrete
Main energy facilitiesHeating (kW)EHP: 339.6EHP: 420.1EHP: 2358
Air-conditioningEHP: 301.6 kWEHP: 377 kWEHP: 2289.6 kW
Hot-water supply (kW)Gas boiler: 41.86Lamp oil boiler: 116.28Gas boiler: 244 kW × 2
Ventilation (kW)Exhaust fan lamp: 6.706Exhaust fan lamp: 5.47Air-conditioning equipment lamp: 35.72
Lighting6.64 W/m28.02 W/m28.00 W/m2

6. Analysis of Energy Consumption and Cost

Table 3 shows the total annual energy consumption and cost for each case, calculated using ECO2-OD. Total annual energy consumption and cost, which were compared across cases following the application of the geothermal energy facility, were calculated based on heating, cooling and hot-water supply calculated in consideration of cooling and heating areas and lighting and ventilation calculated in consideration of gross floor area and the sum total. In terms of consumption cost, the basic rate for contract electricity capacity applied to each building is fixed, and this was not included in the analysis of consumption cost. In the analysis of total annual energy consumption and consumption cost, the area to which individual energy load is applied was calculated by multiplying each cooling and heating area, while the lighting and ventilation load were calculated by multiplying gross floor area. There were therefore differences in total energy consumption capacity and consumption cost. For this reason, it was hard to set evaluation criteria for the comparison of each case, and this data was not utilized for comparisons; this aspect would, however, comprise a significant calculation variable for the application of a new renewable energy facility.

Table Table 3. Annual energy demand quantity and use of cases.

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Table 3. Annual energy demand quantity and use of cases.
DescriptionCase 1Case 2Case 3
Energy demand quantity (kWh/year)Heating68,981.18118,053.14365,861.47
Air-conditioning26,977.0160,118.07201,622.22
Hot-water supply18,091.8035,867.8066,520.70
Lighting31,160.8775,762.22238,485.33
Ventilation31,155.8612,350.45145,950.22
Total176,366.72302,151.681,018,439.93
Energy use cost (Won/year)Heating6,044,82111,415,73935,378,804
Air-conditioning2,363,9955,813,41719,496,869
Hot-water supply1,440,5184,040,6505,264,658
Lighting2,730,6277,326,20723,061,531
Ventilation2,730,1881,194,28914,113,386
Total15,310,14929,790,30297,315,248

The cost of the LCC of CO2 (LCCO2) emission can be estimated by multiplying the required material cost of a component with the CO2 emission basic units of the identified major construction materials. The multiplied cost should be converted into the current market-traded CO2 emission price. As mentioned earlier, there are various markets for trading emission rights with the intention of controlling air pollution in developed countries. Among various markets, the price of the EU Allowance (EUA), which is traded in the European telecommunication standards, is adopted to calculate the LCCO2, and the average price of CO2 emissions (from 2005 to 2009), as suggested by European climate exchange, is applied. The average price is 19.73 EURO/ton. In addition, the average Euro:Won exchange rate in 2009 is applied, which is the standard currency in the ECX.

7. Analysis of Energy Consumption Capacity and Cost in the Application of a Geothermal Energy Facility

Following the application of a geothermal energy facility, the energy capacity by facility was estimated based on calculations of geothermal energy production capacity equivalent to 11% of the expected energy consumption capacity of a building structure, with a compulsory supply rate for 2013 of 100% and 25% of geothermal system capacity. The calculation order of geothermal energy installation capacity was as follows: (1) the expected energy consumption capacity of the target building was calculated; (2) the geothermal energy production capacity was estimated by multiplying the compulsory supply rate by the expected energy consumption capacity; (3) the energy production capacity per unit capacity was estimated by multiplying unit energy production capacity by geothermal energy with the application of a modification factor; and (4) installation capacity was calculated by dividing the geothermal energy production capacity by the energy production capacity per unit capacity by geothermal energy. The geothermal energy production capacity is thus a modified value of energy capacity produced annually using a geothermal energy facility, and the expected energy consumption capacity is the expected annual energy consumption capacity.

The expected energy consumption and geothermal energy production capacities were estimated by applying 371.66 (kWh/m2/year) for unit energy consumption capacity and 1.73 for the modification factor by use. The applied locality coefficients were 0.99 in Case 1 (Gyeonggi region), one in Case 2 (Daejeon region) and 0.98 in Case 3 (Gyeongbuk region). The installation capacity actually selected based on the above process was applied to estimate expected energy consumption capacity, taking the dimensions and formations of each facility into account. Geothermal energy production capacity was calculated by applying 11% of the expected consumption capacity, the compulsory supply rate. The standard capacity represents the capacity of a geothermal energy facility required to satisfy the geothermal energy production capacity. Table 4 shows the application capacity of geothermal energy facilities by region.

Table Table 4. Geothermal energy application capacity of cases.

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Table 4. Geothermal energy application capacity of cases.
Case 1Anticipated energy usage1,271,703 kWh/year
Geothermal energy production139,887 kWh/year
Standard capacity99.00 kW
100% installation capacity of standard capacity105.80 kW
25% installation capacity of standard capacity25.65 kW
Case 2Anticipated energy usage2,524,596 kWh/year
Geothermal energy production277,706 kWh/year
Standard capacity194.00 kW
100% installation capacity of standard capacity208.38 kW
25% installation capacity of standard capacity53.80 kW
Case 3Anticipated energy usage8,159,820 kWh/year
Geothermal energy production897,580 kWh/year
Standard capacity628.00 kW
100% installation capacity of standard capacity658.80 kW
25% installation capacity of standard capacity167.20 kW

Case 1, which appeared to have the best average heat transmission value for the external wall of 0.619 W/m2 K (K: heat transmission coefficient) in the basic insulation standard, used electricity as the energy source, with the exception of hot-water facilities, which relied on an urban gas boiler. When applying 100% of the standard capacity, a higher level of cooling energy consumption was achieved compared to the application of 25% of the standard capacity. This may be because the power of the circulation pump for geothermal exchange is greater than that of other cooling load facilities, due to its relatively large size. For the total cooling capacity of the EHP, 191.4 kW was applied, with 3.75 kW for the consumption power of auxiliary devices, 105.8 kW for geothermal heat and 4.4 kW for the circulation pump. Table 5 shows the total annual energy consumption capacity and consumption cost of the geothermal energy facility by region, specifically for Case 1.

Table Table 5. Annual total energy demand quantity and use cost of Case 1.

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Table 5. Annual total energy demand quantity and use cost of Case 1.
Description100% application of standard capacity25% application of standard capacity
Energy usage
(kWh/year)
Heating59,109.3066,188.76
Air-conditioning25,062.4623,868.33
Hot-water supply18,096.7118,096.71
Lighting31,166.1531,166.15
Ventilation31,146.1731,146.17
Total164,580.78170,466.12
Energy use cost
(Won/year)
Heating5,179,7485,800,121
Air-conditioning2,196,2232,091,582
Hot-water supply1,440,9091,440,909
Lighting2,731,0902,731,090
Ventilation2,729,3392,729,339
Total14,277,30814,793,041

The reduction rate of the annual energy consumption capacity and the cost in the case of 100% compulsory installation capacity were shown to be 7.44% and 7.52%, respectively, when compared with cases where no geothermal energy facilities were present. The reduction rate in geothermal heat in the case of 25% compulsory installation capacity was shown to be 50% of the level of 100% compulsory installation capacity, indicating that when applying a geothermal system, differences may arise from different capacities of the geothermal circulation pump, which is known to be the primary cause of power consumption. The circulation pump in the geothermal system is running continuously, and its application capacity is determined depending on geothermal installation capacity. When a large capacity is loaded, the value increases, but the rate of increase is not proportionate to the installation capacity. The selection of an appropriate capacity for the circulation pump of a geothermal system is therefore considered to be a factor that can improve energy efficiency in the application of such a system.

The energy consumption per unit area is used as a criterion for the calculation of total energy consumption, but the gross floor area is used to calculate the lighting and ventilation load, while the cooling and heating areas are used to calculate the hot-water supply load. For this reason, the total energy consumption capacity may differ depending on the ratio of cooling and heating areas over the gross floor area. However, the consumption capacity per unit area shows the energy reduction effect of the applied geothermal energy facility regardless of the entire building structure and can be used as a good criterion for the evaluation of these facilities. Annual energy consumption capacity and cost per unit area are indicated in Table 6. Table 7 provides a comparison of the total annual energy consumption and cost.

Table Table 6. Annual energy demand quantity per unit area and use cost of cases.

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Table 6. Annual energy demand quantity per unit area and use cost of cases.
Description100% application of standard capacity25% application of standard capacity
Case 1Energy usageDoes not apply111.42
Apply103.13107.27
Reduction capacity8.29 kWh4.15 kWh
Reduction rate (%)7.443.72
Use costDoes not apply9662
Apply89359298
Reduction capacity727 Won364 Won
Reduction rate (%)7.523.77
Case 2Energy usageDoes not apply101.28
Apply91.1599.70
Reduction capacity10.13 kWh1.58 kWh
Reduction rate (%)10.001.56
Use costDoes not apply10,007
Apply9,0279,854
Reduction capacity980 Won153 Won
Reduction rate (%)9.791.53
Case 3Energy usageDoes not apply117.23
Apply108.68113.95
Reduction capacity8.55 kWh3.28 kWh
Reduction rate (%)7.292.80
Use costDoes not apply11,177
Apply10,34910,858
Reduction capacity828 Won319 Won
Reduction rate (%)7.412.85
Table Table 7. Annual energy demand quantity and use of cases.

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Table 7. Annual energy demand quantity and use of cases.
Description100% application of standard capacity25% application of standard capacity
Case 1Energy usageDoes not apply176,366.72
Apply164,580.78170,466.12
Reduction capacity11,785.94 kWh5,900.60 kWh
Reduction rate (%)6.683.35
Use costDoes not apply15,310,149
Apply14,277,30814,793,041
Reduction capacity1,032,841 Won517,108 Won
Reduction rate (%)6.753.38
Case 2Energy usageDoes not apply302,151.68
Apply274,793.40297,873.27
Reduction capacity27,358.28 kWh4,278.41 kWh
Reduction rate (%)9.051.42
Use costDoes not apply29,790,302
Apply27,144,84329,376,666
Reduction capacity2,645,459 Won413,636 Won
Reduction rate (%)8.881.39
Case 3Energy usageDoes not apply1,018,439.93
Apply956,066.67996,005.34
Reduction capacity62,373.26 kWh22,434.59 kWh
Reduction rate (%)6.122.20
Use costDoes not apply97,315,248
Apply91,283,75395,145,822
Reduction capacity6,031,495 Won2,169,426 Won
Reduction rate (%)6.202.23

Table 8 shows annual primary energy consumption per unit area by new renewable energy facility. Geothermal heat ranked higher in the category of annual primary energy consumption per unit area, which resulted from employing kerosene with an energy conversion factor of 1.1 for hot-water supply as the energy source.

Table Table 8. Annual primary energy demand quantity of cases.

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Table 8. Annual primary energy demand quantity of cases.
Description100% application of standard capacity25% application of standard capacity
Case 1Energy usageDoes not apply293.41
Apply270.61281.98
Reduction capacity22.80 kWh11.43 kWh
Reduction rate (%)7.773.90
Case 2Energy usageDoes not apply244.91
Apply212.60240.83
Reduction capacity32.31 kWh4.08 kWh
Reduction rate (%)13.201.67
Case 3Energy usageDoes not apply307.98
Apply284.46298.93
Reduction capacity23.52 kWh9.05 kWh
Reduction rate (%)7.642.94

The comparison of energy consumption and cost per unit area cannot be perfect, due to differences in equipment characteristics, such as the installation situation of the energy load facility and architectural characteristics, such as window area rate and the insulation performance of walls. However, it can be used as a reference for selecting an appropriate geothermal facility for a building structure, through a comparison of cases of different scales that are characterized as having similar energy consumption at a certain level and which do not require the application of cooling and heating areas. The effect of geothermal heat was shown to be best when applying 100% of the standard capacity. Apart from the installation size, geothermal heat effects are also determined by the energy consumption behaviour of the building structure itself, and the circulation pump of an auxiliary installation is a factor that cannot be ignored. Table 9 shows the energy consumption and cost characteristics for the application of a new renewable energy facility for each of the three cases.

Table Table 9. Annual energy demand per unit area of cases.

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Table 9. Annual energy demand per unit area of cases.
DescriptionCase 1Case 2Case 3
100% application of standard capacityDemand quantity reduction (%)6.6810.007.29
Use cost reduction (%)6.759.797.41
25% application of standard capacityDemand quantity reduction (%)3.351.562.80
Use cost reduction (%)3.381.532.85

When comparing primary energy consumption per unit area, which is the currently used criterion of energy efficiency rating for domestic building structures, a higher saving rate was found in Case 2, with 100% of the standard capacity, compared to Case 3, with 25% of the standard capacity. This is thought to be a result of the basic energy consumption of a building structure, i.e., the decrease in the window area rate of the external wall area resulted in a remarkable decrease in the required heating energy accompanied by the maximization of the effect of the geothermal heating facility and a greater decrease in the power consumption of the EHP system in accordance with reductions in the cooling and heating energy of the geothermal system. Table 10 shows the annual primary energy consumption per unit area for each application of a new renewable energy facility.

Table Table 10. Annual primary energy demand per unit area of cases.

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Table 10. Annual primary energy demand per unit area of cases.
DescriptionCase 1Case 2Case 3
100% application of standard capacityDemand quantity reduction (%)7.7713.207.64
25% application of standard capacityDemand quantity reduction (%)3.901.672.94

8. LCC Analysis by Geothermal Energy Facility

8.1. Repair and Replacement Cycle of the Applied Geothermal Energy Facility

In the LCC analysis conducted in this study, geothermal energy repair and replacement were based on an assumption of 40 durable years. To obtain more diverse results depending on the analysis period, the analysis was performed using a 10-year cycle. For items included in the specification, the rate and level of repair and repair and replacement cycles were applied, but when the items were not included in the specification, the durable years of items similarly categorized were applied. The LCC analysis used in this study was not for the entire building structure, but for the geothermal energy facility, and only the components of these facilities were analysed.

When calculating maintenance cost in terms of the repair cycle of the geothermal energy facility by primary process, the rate of repair level and the replacement rate of the geothermal heat pump were 10% at five years and 100% at 10 years. However, a replacement rate of 100% at 11 years was obtained for the expansion tank. When a new renewable energy facility is installed, a structure should be fitted to provide support for the fixation of a buttress and pump. A number of general processes usually applied to general facility work were also included, and the replacement rate of items was likewise analysed. The rate of repair level of the equipment of major components was identical to that of equipment and materials for general equipment work in which a heat pump was used, and there are many components with a short repair cycle; the repair cost was therefore shown to be high.

8.2. LCC Estimation of a Geothermal Energy Facility

LCC was calculated using the present value method. In the case of geothermal energy facility equipment for items that only have a replacement cycle, this was converted to nonrecurring cost for every repair cycle, while for items that have periodic repair and replacement cycles, this was converted to nonrecurring cost every repair cycle. Subsequently, all converted values and nonrecurring costs were summed to estimate maintenance cost. The discount rate applied to the estimation of maintenance cost was calculated using a real discount rate of 1.02%, obtained from the inflation and nominal discount rates based on the deposit interest rate for seven years.

The rate of increase of the average electricity fee between 2006 and 2012 was used to establish the inflation rate by referring to Monthly Energy Statistics issued in May, 2013; the value of 1.06% was used as the real discount rate obtained from the calculation of the rate of increase of a nominal discount to estimate energy savings cost. The initial investment cost was estimated by adding the costs of the applied geothermal energy facility calculation specification to variations in the amount accompanied by the replacement and dismantlement of the conventional facility. The construction cost of the wiring system installation for power was excluded, because it is not included in geothermal energy facility construction.

8.2.1. Calculation of Initial Investment Cost of a Geothermal Energy Facility

To calculate the initial investment cost of a geothermal system, the installed capacity of the existing facility should be changed. In Case 1, when 100% of the standard capacity was applied, a 116 kW outdoor equipment item was removed from the conventional EHP cooling and heating facilities and a new 23 kW outdoor equipment item was installed to preserve capacity. An indoor facility using the geothermal refrigerant method is compatible with the item of EHP outdoor equipment, and there was no influence on the construction cost of indoor facilities. The cost of the 116 kW outdoor equipment item was subtracted, and the cost of the 23 kW outdoor equipment item was added. When 25% of the standard capacity was applied, 75 kW outdoor equipment was removed and replaced with 52.2 kW outdoor equipment. In Case 2, when 100% of the standard capacity was applied, 52.2 kW, 71.8 kW and 78.4 kW EHPs were replaced, leading to a reduction in the initial investment cost. When 25% of the standard capacity was applied, with the substitution effect of a 52.2 kW EHP, the initial investment cost decreased. In Case 3, seven items of 46.4 kW EHP outdoor equipment and four items of 58 kW equipment, together with an item of 75.4 kW equipment were affected by the change. The construction costs of geothermal facilities have risen since the public announcement of the establishment of a base price in 2013. The design cost was calculated based on actual design drawings. In geothermal energy facility construction work, the drilling and installation costs of a geothermal exchanger were shown to be higher than the installation cost of geothermal equipment, along with the installation of a heat pump.

The capacity of the geothermal energy facility can be adjusted to be equivalent to the conventional cooling and heating facility; EHP equipment and installation costs that can be adjusted by case according to the application capacity were included in the initial investment cost of the geothermal system, but their value-added tax was not. The initial investment costs calculated with the construction cost for each geothermal energy type, as calculated based on the design drawings and adjustments in the capacity of the conventional load facilities, are provided in Table 11.

Table Table 11. Initial investment of geothermal energy facilities of cases.

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Table 11. Initial investment of geothermal energy facilities of cases.
Cases100% application of standard capacity25% application of standard capacity
Case 1177,413,21457,481,291
Case 2282,115,13587,934,371
Case 3684,896,176206,499,483

8.2.2. Calculation of Maintenance Cost of a Geothermal Energy Facility

The maintenance cost was obtained by adding replacement cost to repair cost. For items that only have a replacement cycle, this was converted to a nonrecurring cost for every replacement cycle, while for items that have periodic repair and replacement cycles, this was converted to a nonrecurring cost for every repair cycle. All costs were then added to the nonrecurring cost of the replacement cycle to estimate maintenance cost by analysis period. The maintenance cost of the geothermal system was determined to be higher when 100% of the standard capacity was applied. In the analysis of maintenance cost, it was found that with the exception of drilling work, most of the geothermal facility construction work in the three cases was similar to general cooling and heating construction work where a heat pump is applied; however, the maintenance cost was calculated as high due to a rise in repair and replacement costs resulting from the five-year repair cycle and from a 10-year replacement cycle for the heat pump.

8.2.3. LCC Calculation of a Geothermal Energy Facility

Based on the analysis of the initial investment and the maintenance costs of the geothermal energy facility in each case, the LCC was calculated for every 10-year analysis period. When 100% of the standard capacity was applied in all cases, the LCC of the geothermal energy facility increased as the analysis period increased. The LCC of the geothermal energy facility by analysis period for each case is shown in Table 12.

Table Table 12. The initial investment of geothermal energy facilities of cases.

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Table 12. The initial investment of geothermal energy facilities of cases.
CaseAnalysis yearApplication (%)Initial investmentMaintain costLCC
Case 110100177,413,21445,082,942222,495,156
2557,481,29122,929,86480,411,155
20100177,413,214114,814,736292,227,950
2557,481,29152,607,724110,089,015
30100177,413,214170,715,471348,128,685
2557,481,29178,901,211136,382,502
40100177,413,214182,417,96359,831,181
2557,481,29186,793,300144,274,591
Case 210100282,115,13578,591,384360,706,519
2587,934,37129,083,24389,533,243
20100282,115,135201,614,252483,729,387
2587,934,37170,780,448158,714,819
30100282,115,135303,539,695585,654,830
2587,934,371106,299,141194,233,512
40100282,115,135321,713,745603,828,880
2587,934,371114,652,882202,587,253
Case 310100684,896,176176,172,862861,069,038
25206,499,48364,219,177270,718,660
20100684,896,176447,156,0811,132,052,257
25206,499,957157,211,330363,710,813
30100684,896,176708,458,8551,393,355,031
25206,499,483236,056,719442,556,202
40100684,896,176743,348,8431,428,245,019
25206,499,483248,408,375454,907,858

8.2.4. A Comparative Analysis of the LCC of a Geothermal Energy Facility

In terms of geothermal energy, the cost savings effect did not appear to be in proportion to the application capacity, but differed in each case. Table 13 specifies the energy savings cost that accompanied the application of a geothermal energy facility in each case. The analysis showed that it is difficult to expect economic benefits from the application of a geothermal energy facility. Even though with the geothermal system the initial investment cost can be compensated for by adjusting the energy load capacity for the facility, this was not economically feasible, because of high initial investment and maintenance costs and low energy savings costs. This implies that the circulation pump required to operate the geothermal system consumes significant electricity, thus minimizing the energy-saving effect. Its initial investment cost is also high. To improve the economic feasibility of the geothermal energy system, less power-intensive circulation pumps and devices should therefore be selected and the initial investment cost should be reduced.

Table Table 13. Energy savings cost by applying the geothermal energy facilities of cases.

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Table 13. Energy savings cost by applying the geothermal energy facilities of cases.
CaseAnalysis year100%25%
Case 1109,750,9414,881,961
2018,526,0719,275,367
3026,423,04313,229,110
4033,529,73916,787,188
Case 21024,975,4933,905,093
2047,451,6037,419,390
3067,678,45010,581,999
4085,881,12713,428,114
Case 31056,942,69420,481,317
20108,186,93638,912,998
30154,302,99055,500,157
40195,804,05170,427,381

It was not effective to estimate the period required to recoup the initial investment with the analysed data, since the difference between energy savings and initial investment costs was high. The return rate of LCC input through energy savings cost was thus used. In Case 1, the return rate of LCC for a new renewable energy facility increased as the analysis period increased, which indicates that the increase in energy savings cost was greater than that in the LCC of a geothermal facility. Thus, if the initial investment and maintenance costs of the geothermal energy facility are improved, the economic effect will be greater. The LCC analysis of the geothermal energy facility applied to each case is provided in Table 14.

Table Table 14. Accumulated operation and maintenance cost (LCCO2 cost excluded).

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Table 14. Accumulated operation and maintenance cost (LCCO2 cost excluded).
CaseAnalysis yearDescription100%25%
Case 110LCC222,496,15680,411,155
Energy savings cost9,750,9414,881,961
LCC collection ratio4.38%6.07%
20LCC292,227,950110,089,015
Energy savings cost18,526,0719,275,367
LCC collection ratio6.36%8.43%
30LCC348,128,685136,382,502
Energy savings cost26,423,04313,229,110
LCC collection ratio7.59%9.70%
40LCC359,831,181144,274,591
Energy savings cost33,529,73916,787,188
LCC collection ratio9.32%11.64%
Case 210LCC360,706,519428,982,726
Energy savings cost24,975,4933,905,093
LCC collection ratio6.92%3.32%
20LCC483,729,387158,714,819
Energy savings cost47,451,6037,419,390
LCC collection ratio9.81%4.67%
30LCC585,654,830194,233,512
Energy savings cost67,678,45010,581,999
LCC collection ratio11.56%5.45%
40LCC603,828,880202,587,253
Energy savings cost85,881,12713,428,114
LCC collection ratio14.22%6.63%
Case 310LCC861,069,038270,718,660
Energy savings cost56,942,69420,481,317
LCC collection ratio6.61%7.57%
20LCC1,132,052,257363,710,813
Energy savings cost56,942,69420,481,317
LCC collection ratio6.61%7.57%
30LCC1,393,355,031442,556,202
Energy savings cost154,302,99055,500,157
LCC collection ratio11.07%12.54%
40LCC1,428,245,019454,907,858
Energy savings cost195,804,05170,427,381
LCC collection ratio13.71%15.48%

9. Conclusions

This study aimed to analyse energy consumption in the application of new renewable energy systems to a public office building based on compulsory application criteria. The study also sought to determine an effective plan for the selection of a new renewable energy facility that takes economic feasibility into account by performing a comparative analysis of LCCs of new renewable energy facilities and energy savings costs from their application. Two main research findings were obtained. First, energy consumption and costs related to the application of a geothermal energy facility were analysed in three cases, to arrive at effective data for the selection of geothermal energy facility types. Second, the energy cost reduction effect relating to the application of a geothermal energy facility was examined, and an effective plan for the selection of a geothermal energy facility was presented by calculating the LCC using the initial investment and maintenance costs of a geothermal energy facility, the latter obtained by applying repair and replacement rates based on the construction specifications of each facility. It is believed that the results of this study can be utilized as an effective plan for the selection of a geothermal energy facility based on economic feasibility. In addition, the energy-saving effects on energy consumption and primary energy consumption will also be utilized as fundamental data in the understanding and selection of geothermal energy facilities.

However, the capacity of a new renewable energy facility was not simply calculated based on its energy production capacity; to analyse energy efficiency and economic feasibility in a more practical way, the energy production capacity and use efficiency of each new renewable energy facility should be utilized. The energy production capacity should be calculated based on the characteristics of each facility, and the energy-saving capacity resulting from the application should also be considered. Future work should analyse the energy use and cost characteristics of building constructions with new renewable energy facilities, and the results should be compared with the energy use characteristics of buildings, evaluated based on design drawings, to secure reliability. A study should also be conducted to prepare selection criteria for an appropriate facility by use, size and characteristics based on the actual performance of each new renewable energy facility.

Author Contributions

In this paper, Sangyong Kim developed the research ideas and organized research flow; Young Jun Jang implemented research program and collected data; Yoonseok Shin participated analysis of case study part; Gwang-Hee Kim completed the writing work of corresponding parts.

Conflicts of Interest

The authors declare no conflict of interest.

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