COST EFFICIENCY ANALYSIS OF DESIGN ELEMENTS FOR AN ENERGY EFFICIENT APARTMENT COMPLEX
Seung-yeong SONG Ph.D.1 Soo-jin LEE M.Eng. Course2
Jinu KIM Ph.D.3
1 Department of Architectural Engineering, Ewha University, Seoul, South Korea, [email protected]
2 Department of Architectural Engineering, Ewha University, Seoul, South Korea, [email protected]
3 Faculty of the Built Environment, University of New South Wales, Sydney, Australia, [email protected]
Keywords: apartment complex, energy, Building Energy Efficiency Rating System, cost efficiency
Summary
The demand for sustainability capable of coping with worldwide climate changes has been increasing.
Energy efficient buildings are essential for maintaining such sustainability. Buildings are responsible for over 25% of the energy consumption in Korea, and 68% of the total energy consumption in the building sector comes from residential use. This situation is not considered to be much different in almost every country.
Improvement of energy efficiency may lead to the rise of construction cost. If each design element can be prioritized according to its cost efficiency, energy efficient buildings can be designed more cost efficiently.
Thus, this study aims to analyze the cost efficiency of each item related to the energy efficiency of an apartment complex, which is the most common type of residential building in Korea. A baseline model apartment complex was set up, based on an actual apartment complex. Among all the assessment items in the Building Energy Efficiency Rating System of Korea, items that were appropriate for cost efficiency analysis and applicable to the baseline model apartment complex were selected as target items. Then, alternatives for each target item were set up, and then construction and energy costs of each alternative were estimated through actual price data and the assessment method of the Building Energy Efficiency Rating System. Finally, the results presented four kinds of cost efficiency index-the LCC, the NPV, the IRR and the payback period-and the order of priority of each alternative in accordance with each index.
1. Introduction
With the effectuation of the Kyoto Protocol, many countries in the world have been endeavoring to reduce their emissions of greenhouse gases in various fields of industry. In particular, it is anticipated that Korea will be confronted with much more international pressure to lower its emissions of greenhouse gases after 2013 when the second commitment period of the Kyoto Protocol goes into effect because Korea has been ranked 9th in carbon dioxide (CO2) emissions (IEA, CO2 Emissions from Fuel Combustion, 2004) and 10th in energy consumption (BP, Statistical Review of World Energy, 2006) in the world. Greenhouse gases are usually generated from energy consumption. Buildings are responsible for over 25% of the energy consumption in Korea, and 68% of the total energy consumption in the building sector comes from residential use (Korea Energy Economics Institute, 2005). This situation is not considered to be much different from in almost every country. Consequently, energy efficient residential buildings can play a key role in reducing greenhouse gas emissions and further solving environmental problems caused by the use of fossil fuels.
The energy efficiency of residential buildings are being enhanced by numerous systems or projects such as the Home Energy Rating System (HERS) and the Energy Star New Homes of the USA, the MNECH1997 of Canada, the Code for Sustainable Homes of the UK, the Passive House of European countries and so on. In Korea, the Building Energy Efficiency Rating System has been in force since 2001 in an attempt to improve the energy efficiency of the apartment complex, which is the most common type of residential building.
Improvement of the energy efficiency may bring about a rise of construction cost. If each design element can be prioritized according to its cost efficiency, energy efficient apartment complexes can be designed more cost efficiently. Thus, this study aims to analyze the cost efficiency of each item related to energy efficiency of the apartment complex by using the assessment method of the Building Energy Efficiency Rating System.
First, a baseline model apartment complex was set up, based on an actual apartment complex recently completed and regarded as the most common type. Among all the assessment items in the system, items which are suitable for analyzing the cost efficiencies were selected as target items. The lower and upper limit
values of each target item were determined. Then more alternatives whose values vary stepwise between the lower and upper limits were set up. And construction and energy costs of each alternative were estimated through actual price data and the assessment method of the Building Energy Efficiency Rating System. Finally, the LCC, the NPV, the IRR and the payback period of each alternative were obtained as indexes of cost efficiency, and then an order of priority of each index was given to all the alternatives.
2. Building Energy Efficiency Rating System and Passive House
Substantial numbers of systems or projects in the world are being implemented to improve the energy efficiency of residential buildings. HERS is a standard measurement of the home’s energy efficiency and Energy Star New Homes is a national mark given to the homes that meet guidelines for energy efficiency of USA. MNECH1997 and the Code for Sustainable Homes are national code of Canada and the UK, respectively, for energy efficient homes. The Passive House of the European countries, which is a voluntary project for very rigorous energy efficient buildings, is considered as a very strong project for energy efficient buildings in the world. And the Passive House, along with a domestic system, was selected for this study because it can provide criteria for a high performance energy efficient building.
2.1 Building Energy Efficiency Rating System
The System has been enforced by the Ministry of Commerce, Industry and Energy (MOCIE) and managed by Korea Energy Management Corporation (KEMCO). There are several regulations related to this system such as the Building Energy Efficiency Rating Regulation (MOCIE, Notification No.2005-10), Guidelines on the Funding of Energy Use Rationalization Work (MOCIE, Announcement No.2006-371) and the Building Energy Efficiency Rating System Management Regulation (also referred to as the Management Regulation hereinafter). An apartment complex with more than 18 units is qualified to apply for certification. Energy efficiency is determined by comparison of the energy demand reduction rate between the evaluated apartment complex and the standard apartment complex. The evaluated apartment complex is rated as 3 grades, as presented in Table 1. For the first or second grade, some incentives, such as loan at very cheap interest and so on, are given to the builder. The standard apartment complex, which is a hypothetical complex configured in accordance with the specifications mandated by the building codes currently in force, represents a complex with the minimum level of energy efficiency. The standard apartment complex is almost identical with the evaluated apartment complex except that each assessment item of the standard apartment complex has a value mandated by the building codes. Other physical conditions such as shape, size, structure, floor height, ceiling height, energy source, heating plant type and so on are the same as the evaluated apartment complex.
Table 1 Certification Grades of the Building Energy Efficiency Rating System1 Grade Energy demand reduction rate against the standard apartment complex
1 33.5% or more
2 23.5% - 33.5%
3 13.5% - 23.5%
The energy demand reduction rate of the evaluated apartment complex is calculated by using eqs. (1), (2) and (3). In eq. (1), HEDunit_std and HEDunit are calculated in the same manner as HERS, by using the variable heating degree day method and the 2-zone model2. Assessment items of the System are divided into two types, the basic and the extra. Basic items are required to calculate the HEDunit_std and HEDunit in eq. (1), which include items mandated by the building codes. Extra items are optional items, not mandated but recommended by the building codes. These are composed of one that is related to the heating, domestic hot water, electric power, lighting and so on.
Energy demand and energy cost of the evaluated apartment complex can be obtained by extending the way of assessment in the system. HEDapt_std and HECapt_std can be obtained using eqs. (4) and (5), respectively.
After calculating the REDapt using eqs. (1), (2) and (3), EDaptand ECapt can be obtained using eqs. (6) and (7), respectively.
In eqs. (6) and (7), the terms EDapt and ECapt are used instead of HEDapt and HECapt because REDapt includes the energy demand reduction rates for the extra items related to not only the heating but also to the domestic hot water, electric power, lighting and so on. In eqs. (1), (2) and (3), as well, both terms of heating energy and energy are used due to the same reason.
∑
+
− ×
= unit extra
std unit
unit std
unit unit RED
HED
HED
RED HED _
_
_ 100 (1)
∑
× +∑
= bldg extra
bldg unit
bldg unit RED
A A
RED (RED ) _ (2)
apt bldg
apt Abldg
A RED (RED × )
=
∑
(3)1 Building Energy Efficiency Rating Regulation (MOCIE, Notification No. 2005-10), Appendix 1.
2 Yu, K.H., 2006, A study on the energy efficiency rating and certification of apartment houses, Journal of AIK, Vol.22, No.12, pp. 322
HEDunit Heating energy demand of the unit in the evaluated apartment complex (GJ/year)
std
HEDunit_ Heating energy demand of the unit in the standard apartment complex (GJ/year)
REDunit Energy demand reduction rate of the unit in the evaluated apartment complex (%)
extra
REDunit_ Energy demand reduction rate by the extra item for unit, applied to the evaluated apartment complex (%)
REDbldg Energy demand reduction rate of the building in the evaluated apartment complex (%)
extra
REDbldg_ Energy demand reduction rate by the extra item for building, applied to the evaluated apartment complex (%)
REDapt Energy demand reduction rate of the evaluated apartment complex (%)
Aunit Floor area for private use of the unit in the evaluated apartment complex (m2)
Abldg Gross floor area for private use of the building in the evaluated apartment complex (m2)
Aapt Gross floor area for private use of the evaluated apartment complex (m2)
std unit std
apt HED
HED _ =Σ _
(4) HECapt_std =HEDapt_std×HER (5) 100
100
_ apt
std apt apt
HED RED
ED −
×
= (6)
100 100
_ apt
std apt apt
HEC RED
EC −
×
= (7)
std
HEDapt_ Heating energy demand of the standard apartment complex (GJ/year)
EDapt Energy demand of the evaluated apartment complex (GJ/year)
std
HECapt_ Heating energy cost of the standard apartment complex ( /year)₩
ECapt Energy cost of the evaluated apartment complex ( /year)₩
HER Heating energy rate per GJ ( /GJ)₩
2.2 Passive House
The Passive House refers to the concept of highly insulated and air-tight residential buildings that can keep indoor environmental conditions comfortable. In the Passive House, the heating energy demand is minimized by means of passive ways such as super insulation, heat recovery, solar gain and so on. The Passive House has a limited energy demand of around 15kWH/m2 for heating and around 120kWH/m2 for heating, domestic hot water and all other electrical equipments combined and it is reported to have less than one fifth of the heating energy demand mandated by the building regulations currently in force in the participating countries.
Promotion of European Passive Houses (PEP) provides technical solutions3 to achieve the Passive House level. It is a guideline about technologies applied in Passive Houses, and these technologies are composed of super insulation, heat recovery, passive solar gain, electric efficiency and on-site renewable. In addition, it provides the corresponding value range of each solution. Among the variable solutions, the one related to performance of the thermal envelope such as high insulation of walls, roofs, floors is selected for this study and the corresponding values are as follows: walls’ U-value ≤ 0.15W/m2K and roofs’ U-value ≤ 0.15W/m2K.
3. Baseline Model, Target Items and Alternatives for Cost Efficiency Analysis 3.1 Outline of the Studied Apartment Complex
In general, an apartment complex is divided into two types, the hall type and corridor type. Currently, the hall type is preferred because it offers privacy and more floor area for private use. The hall type “A” apartment complex, which was completed recently, has the unit of national housing size4, so it was selected for this study. “A” apartment complex has fourteen buildings with eight types of units whose floor areas for private use range from 85m2 to 273m2. Considering that it may be appropriate to give precedence to national housing, it is assumed that the floor area for private use of every unit is 85m2, while the gross floor area of the apartment complex is maintained. The analysis results of actual and reorganized apartment complexes are considered to show no difference because construction and energy costs of an apartment complex are mainly influenced by the gross floor area. Figure 1 and Table 2 show site plan and outline of the studied apartment complex, respectively.
3.2 Setting the Baseline Model
The baseline model is a unit building that has only 85m2 units, nineteen floors and two cores. On every floor,
3 Promotion of European Passive Houses (PEP), Passive House Solutions, 2006
4 National housing defined in the Housing Act of Korea is originated from the housing policy to relieve the housing shortage. It can be regarded as the most common and normal housing for ordinary people. Its floor area for private use should be 85m2 or below.
there are four units. The four units of the top floor have attics and there is a piloti at the right corner of the ground floor, so the baseline model has 75 units. The studied apartment complex was assumed to have only baseline model buildings. Figures 2 and 3 show a unit floor plan and a sectional plan of the baseline model, respectively, and Table 3 presents the outline of the baseline model.
Figure 1 Studied Apartment
Complex Site Plan Figure 2 Baseline Model
Unit Floor Plan Figure 3 Baseline Model Sectional Plan Table 2 Outline of the Studied Apartment Complex Table 3 Outline of the Baseline Model
Location Seoul Gross floor area 8,329.61m2
Gross floor area 192,451.98m2 Gross floor area 6,374.25m2 (Residence: 140,325.56m2, for private use
Car park: 52,126.42m2) Floor area of the 111.16m2 (floor area for The number of units Existing: 885 units unit private use: 84.99m2)
→ Converted: 1,263 units Floor height Top and ground floor: 3.0m,
Converted gross 107,384.40m2 Base floor: 2.9m
floor area for Insulation Wall:65mm, Side wall:90mm,
private use Roof:110mm, Ground floor:50mm
Heating plant District heating Glass 16mm Pair glass(5CL+6Air+5CL)
Orientation South Table 4 Target Items
No. Description No. Description
0 Balcony window U-value (W/m2K) 16 Energy efficient control systems of ventilation
1 Window U-value (W/m2K) fans of underground car park
2 Window area (m2) 17 Automatic control systems using computer, 3 Door and others (facing the outside) U-value networking or internet
(W/ m2K) 18 High efficiency induction motor (application rate, %) 4 Wall (facing the outside) U-value (W/ m2K) 19 Voltage drop of main power line (%)
5 Wall (facing the outside) Area (m2) 20 Bank configuration enables to control the 6 Roof U-value (W/ m2K) number of current transformers in operation 7 Ground floor U-value (W/ m2K) 21 Peak demand control system of electric power 8 Wall and door (facing the unheated space) 22 Automatic control systems of equipments for
U-value (W/ m2K) receiving and transforming the electricity 9 Awning coefficient factor. 23 Application of high intensity discharge lamp 10 Thermostat per each room or zone and automatic on/off control system of the 11 Electric circuit configuration which enables to outside lightings
break the main power outlet of the living room 24 Energy efficient control systems of service conveniently or installation of certified water pumps such as inverter control, etc.
energy efficient appliances 25 Automatic adjustment equipment of power 12 Windbreak space at the building’s entrance factor for power condenser installed in a group 13 Average efficiency of pumps for heating water, 26 Decentralized control system with open
service water, domestic hot water, etc. (%) protocol, which enables intensive control as 14 Equipments, pipe and duct insulation well as data compatibility with each control 15 Energy efficient control systems of heating system of mechanical and electrical
water pumps such as inverter control, etc. equipments
※ 0~9: basic items for heated space, 10~11: extra items for unit, 12~26: extra items for building
3.3 Setting the Target Items and Alternatives
Among all the assessment items in the Building Energy Efficiency Rating System, the items which are suitable for analysis of cost efficiencies and whose performance values are changeable in the baseline model were selected as target items. The selected 27 target items are presented in Table 4. The overall performance range of each target item was determined. In the case of the basic item, a lower limit value was set to the value of the baseline model. The upper limit value was set to the value to reflect the Passive House level and the Management Regulation. Then, more alternatives of which values vary stepwise between the lower and upper limits were set up. Performance values of the alternatives were determined by dividing the overall performance range into 5 steps while consideration was given to practical matters such as the specifications or dimensions of the products on the market. In the case of extra items, the Building Energy Efficiency Rating System just assesses whether they are applied or not, or provides step-by-step performance values. The performance value of each alternative was set with consideration of these criteria.
Table 5 shows the performance value of every alternative in the case of a typical.
Table 5 Alternatives for Each Target Item in the Case of Typical Floor
No. Units Low ◀ Performance range ▶ High No. Units Low ◀ Performance range ▶ High
0 W/m2K 3.3 3.1 2.9 2.6 2.4 2.2 11 - Not applied Applied
1 W/m2K 3.3 3.1 2.9 2.6 2.4 2.2 12 - Not applied Applied
2 m2 23.14(25.6%) 21.22(23.5%) 19.30(21.4%) 13 - 1.04Ebelow 1.04E-1.08E 1.08E-1.12E 1.12E-1.16E 1.16E more
3 W/m2K 2.4 1.6 14 - Not applied Applied
4-1 W/m2K 0.410 0.364 0.293 0.245 0.197 0.148 15 - Not applied Applied 4-2 W/m2K 0.418 0.370 0.297 0.248 0.198 0.149 16 - Not applied Applied 4-3 W/m2K 0.336 0.294 0.267 0.227 0.185 0.148 17 - Not applied Applied 4-4 W/m2K 0.401 0.353 0.285 0.240 0.193 0.146 18 % 50below 50-60 60-70 70-80 80more
5 m2 67.11 69.03 70.95 19 % 6.0more 5.0-6.0 4.0-5.0 3.5-4.0 3.5below
6 W/m2K 0.285 0.248 0.229 0.199 0.176 0.149 20 - Not applied Applied 7-1 W/m2K 0.262 0.247 0.212 0.198 0.175 0.149 21 - Not applied Applied 7-2 W/m2K 0.468 0.421 0.329 0.270 0.212 0.149 22 - Not applied Applied 8-1 W/m2K 0.574 0.511 0.437 0.338 0.238 0.151 23 - Not applied Applied
8-2 W/m2K 2.6 1.7 24 - Not applied Applied
9 - 0.520 0.507 0.485 25 - Not applied Applied
10 - Not applied Applied 26 - Not applied Applied
※ stands for the value of Baseline model apartment complex.
※ Actually, several extra items are applied to the studied apartment complex. However, this study assumes that extra items are not applied to the baseline model apartment complex because extra items themselves are the subject of cost efficiency analysis. In each case of No.13, No.18 and No.19, the value of REDextra_bldg of the baseline apartment complex is zero.
※ No.2: The window area of the unit in baseline model is 23.14m2, which is about 25.6% of total wall area. The window width is fixed for the day-lighting purpose, and the window heights of the living room and master bed room cannot be changed because they are entrance to the balcony. Window heights of the other 2 bed rooms are changed from 2.3m to 1.5m.
Therefore, there are 3 alternatives for No.2: one is the baseline model, another is the case of only one bed room of 1.5m in height, and the other is 2 bedrooms of 1.5m in height.
※ No.3: According to the Management Regulation, only the two values can be approved as alternatives.
※ No.4: 4-1 the front wall, 4-2 the back wall, 4-3 the corner side wall, 4-4 the side wall except for corner side wall.
※ No.5, 9: There are 3 alternatives because No5 and No.9 are dependent on No.2.
※ No.7: 7-1 floors facing the outside directly, 7-2: floors facing the outside indirectly.
In the baseline model, there are 3 units in the ground floor because there is a piloti. These 3 units face the outside indirectly (there are underground car park) and one unit above the piloti faces the outside directly.
※ No.8: 8-1 wall, 8-2 entrance door. According to the Management Regulation, only the two values can be approved as alternatives for No.8-2.
※ No. 13, 18, 19: According to the Management Regulation, five values can be approved as alternatives.
4. Cost Efficiency Analysis
The spatial range for this analysis was set as the baseline model apartment complex, which means whole studied apartment complex composed of only the baseline model. Specific information on the cost efficiency analysis of each alternative of the target items is as follows.
4.1 Construction Cost and Annual Energy Cost 4.1.1 Construction Cost
Based on the construction project supplied by the government, the construction cost of a baseline model apartment complex and the construction cost difference between each alternative and the baseline model apartment complex were estimated, including both material and labor costs. Material cost reflects the price in Feb. 2008 and labor cost reflects the Standard Labor Work Estimation prescribed by the government in Jan.
2008. Estimated construction cost of the baseline model apartment complex is ₩ 15,276,753,777 (₩ 1,000 is about USD 1.00) and the construction cost difference between each alternative and the baseline model apartment complex is shown in Table 7.
4.1.2 Annual Energy Cost
HEDapt_std calculated by eq. (4) is 55,905.52 GJ/year. Energy rate of the Korea District Heating Corp. (KDHC)
was applied to the value of HER in eq. (5). Monthly energy rate for the residential buildings of KDHC is presented in Table 6. HECapt_std calculated by eq. (5) is ₩813,843,820/year. The energy demand reduction rate of the baseline model apartment complex, calculated by eqs. (1), (2) and (3), is 23.74%. The energy cost of the baseline model apartment, calculated by eq. (7), is ₩ 620,637,297/year. The differences of both the energy demand reduction rate and energy cost between each alternative and the baseline model apartment complex are shown in Table 7.
Table 6 Monthly Energy Rate for Residential Buildings (KDHC, Mar. 2008, ₩ 1,000 is about USD 1.00)
Base Rate Energy Rate
₩ 42.02/m2 (exclusive residential floor area) ₩ 13,589/GJ
4.2 Cost Efficiency Index
4.2.1 Outline of the Cost Efficiency Index
There are various cost efficiency indexes such as NPV (Net Present Value), LCC (Life Cycle Cost) and IRR (Internal Rate of Return) which consider the time value of money, and the Payback Period which does not consider that. LCC is the sum of both the initial investment cost and operating costs during the lifetime. All operation costs are to be discounted to their present value prior to addition to the LCC total. LCC of both baseline model apartment complex and each alternative can be obtained by using eqs. (8) and (9). NPV is the sum of the present value of both investment and profits. NPV can be calculated by using eq. (10). The value of each alternative’s NPV means the difference of LCC between the baseline model apartment complex and each alternative. Therefore, a negative NPV, which means an alternative is in the condition of discounted cash outflow, should be rejected. IRR is any discount rate that makes an investment’s present value the same as the profits’ present value, that is, specific discount rate that results in a NPV of zero. The greater an alternative’s IRR, the better its rate of return. On the other hand, if an alternative’s IRR is less than the standard rate of return (e.g., standard value can be real interest rate. see eq. (11)), that alternative should be rejected. NPV expresses cost efficiency of an alternative as a sum of money (i.e., the unit is ₩, see eq. (10)) and IRR does as a percentage (i.e., the unit is %). Therefore, the IRR can be a more effectual standard of decision-making under limited investments, because the size of the investment hardly influences the IRR. The payback period, which refers to the period of time needed to repay an investment amount, can be obtained by dividing the profits by the investment amount. It can be calculated by using eq. (12).
EC PW CC
LCC = + × (8) ⎟
⎠
⎜ ⎞
⎝
⎛ −
+ +
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ ⎟ −
⎠
⎜ ⎞
⎝
⎛ +
× + +
= + 1
1 / 1 1 1
1 1
1
Ri Ri
Ri
PW n (9)
EC PW CC LCC
NPV =Δ =−Δ + ×Δ (10) 1 1
1 −
+
= + i
r R (11)
EC PP CC
Δ
=Δ (12) LCC Life cycle cost (₩) CC Construction cost (₩) PW Present worth coefficient
EC Energy cost (₩) i Price rise rate (%) R Interest rate (%)
n Lifetime (year) NPV Net Present Value (₩) r Real interest rate (%)
PP Payback period (year)
CC
Δ / ΔEC/ ΔLCC Difference of Construction Cost / Energy Cost / LCC between Alternative and Baseline Model Apartment Complex
4.2.2 Calculation of the Cost Efficiency Index
LCC of the baseline model apartment complex and the difference of LCC between each alternative and the baseline model apartment complex are calculated using eqs. (8), (9) and (10). In eq. (9), i was set to 3.2%5, which is the average consumer price index during the last ten years from 1998 to 2007. And R was set to 7.78%4, which is the average loan interest rate of the Bank of Korea during the last ten years from 1998 to 2007. The age of an apartment complex used to determine the qualification of reconstruction is prescribed in the City and Residential Environment Maintenance Act as 20 years after the completion, which implies the minimum value of economic lifetime. However, n was set to 30 years, considering the fact that the body of research on the lifetime of a Korean apartment complex suggests 30 years or so, and knowing that the LCC
5 Economic Statistics System of Bank of Korea, ecos.bok.or.kr
Table 7 Cost Efficiency Analysis Result
No. Case CC ΔCC RED ΔRED EC ΔEC LCC NPV(ΔLCC) IRR PP OP-1 OP-2
Baseline 15,276,753,777 - 23.74 - 620,637,297 - 25,460,421,604 - - - - -
0 1 15,432,114,144 155,360,367 24.49 0.75 614,533,469 6,103,829 25,515,627,882 -55,206,277 1.10 25.45 69 68 2 15,690,109,680 413,355,903 25.31 1.57 607,859,949 12,777,348 25,664,121,613 -203,700,009 -0.48 32.35 72 72 3 16,180,743,501 903,989,724 26.66 2.92 596,873,058 23,764,240 25,974,478,073 -514,056,469 -1.47 38.04 78 73 4 16,229,299,536 952,545,759 27.68 3.94 588,571,851 32,065,447 25,886,824,546 -426,402,942 0.06 29.71 75 71 5 16,434,711,330 1,157,957,553 28.80 5.06 579,456,800 41,180,497 25,942,672,900 -482,251,295 0.42 28.12 77 70 1 1 15,405,933,417 129,179,640 25.23 1.49 608,511,025 12,126,273 25,390,628,453 69,793,151 8.60 10.65 26 46 2 15,620,448,915 343,695,138 26.76 3.02 596,059,214 24,578,083 25,400,829,608 59,591,996 5.85 13.98 29 53 3 16,018,739,754 741,985,977 29.19 5.45 576,282,809 44,354,488 25,474,621,197 -14,199,593 4.28 16.73 64 58 4 16,068,773,499 792,019,722 30.88 7.14 562,528,849 58,108,449 25,298,974,394 161,447,211 6.09 13.63 16 52 5 16,239,568,989 962,815,212 32.63 8.89 548,286,582 72,350,716 25,236,077,008 224,344,596 6.32 13.31 9 50
2 1 15,144,786,999 -131,966,778 24.55 0.81 614,045,163 6,592,135 25,220,288,410 240,133,195 - - 8 2
2 15,012,820,221 -263,933,556 25.20 1.46 608,755,178 11,882,120 25,001,521,421 458,900,184 - - 2 1
3 1 15,390,613,227 113,859,450 26.21 2.47 600,535,355 20,101,942 25,244,440,253 215,981,352 17.52 5.66 12 32
4-1 1 15,288,668,697 11,914,920 24.31 0.57 615,998,388 4,638,910 25,396,219,416 64,202,188 38.93 2.57 27 13
2 15,322,008,271 45,254,494 25.18 1.44 608,917,946 11,719,351 25,313,380,246 147,041,358 25.87 3.86 17 22 3 15,355,366,347 78,612,570 25.77 2.03 604,116,268 16,521,030 25,267,950,439 192,471,166 20.95 4.76 14 27 4 15,405,394,210 128,640,433 26.36 2.62 599,314,589 21,322,708 25,239,190,418 221,231,187 16.40 6.03 10 34 5 15,488,761,647 212,007,870 26.96 3.22 594,431,526 26,205,771 25,242,434,583 217,987,021 11.94 8.09 11 39
4-2 1 15,295,722,204 18,968,427 24.55 0.81 614,045,163 6,592,135 25,371,223,615 89,197,990 34.75 2.88 24 15
2 15,348,970,508 72,216,731 25.79 2.05 603,953,499 16,683,798 25,258,883,824 201,537,780 23.06 4.33 13 25 3 15,402,220,307 125,466,530 26.62 2.88 597,198,595 23,438,702 25,201,296,430 259,125,174 18.57 5.35 7 31 4 15,482,094,258 205,340,481 27.46 3.72 590,362,307 30,274,990 25,168,997,801 291,423,803 14.49 6.78 4 38 5 15,615,216,513 338,462,736 28.28 4.54 583,688,788 36,948,509 25,192,618,251 267,803,353 10.35 9.16 6 42
4-3 1 15,308,537,758 31,783,981 24.20 0.46 616,893,616 3,743,682 25,430,777,744 29,643,861 11.30 8.49 38 41
2 15,340,763,185 64,009,408 24.48 0.74 614,614,853 6,022,444 25,425,612,311 34,809,294 8.62 10.63 37 45 3 15,405,214,037 128,460,260 24.92 1.18 611,033,940 9,603,357 25,431,306,097 29,115,508 6.27 13.38 41 51 4 15,501,890,315 225,136,538 25.36 1.62 607,453,028 13,184,270 25,469,225,309 -8,803,705 4.10 17.08 62 59 5 15,630,792,020 354,038,243 25.76 2.02 604,197,652 16,439,645 25,544,711,499 -84,289,895 2.29 21.54 70 65
4-4 1 15,290,495,014 13,741,237 24.20 0.46 616,893,616 3,743,682 25,412,735,000 47,686,605 27.22 3.67 34 19
2 15,325,242,933 48,489,156 24.86 1.12 611,522,247 9,115,051 25,359,347,320 101,074,284 18.69 5.32 21 30 3 15,359,990,852 83,237,075 25.29 1.55 608,022,718 12,614,579 25,336,673,561 123,748,043 14.92 6.60 19 36 4 15,412,112,730 135,358,953 25.74 2.00 604,360,421 16,276,876 25,328,702,985 131,718,619 11.58 8.32 18 40 5 15,498,982,527 222,228,750 26.20 2.46 600,616,739 20,020,558 25,354,144,941 106,276,664 8.15 11.10 20 47
6 1 15,285,255,461 8,501,684 23.83 0.09 619,904,838 732,459 25,456,904,798 3,516,807 7.68 11.61 52 48
2 15,292,307,994 15,554,217 23.87 0.13 619,579,301 1,057,997 25,458,615,779 1,805,825 5.40 14.70 53 54
3 15,306,413,061 29,659,284 23.94 0.20 619,009,610 1,627,688 25,463,373,131 -2,951,527 3.57 18.22 60 61 4 15,320,518,127 43,764,350 24.00 0.26 618,521,304 2,115,994 25,469,465,870 -9,044,266 2.59 20.68 63 63 5 15,341,675,727 64,921,950 24.06 0.32 618,032,997 2,604,300 25,482,611,143 -22,189,538 1.24 24.93 66 67
7-1 1 15,277,530,434 776,657 23.75 0.01 620,555,913 81,384 25,459,862,873 558,731 9.85 9.54 54 43
2 15,280,365,233 3,611,456 23.77 0.03 620,393,144 244,153 25,460,026,897 394,708 5.34 14.79 55 55
3 15,281,782,633 5,028,856 23.78 0.04 620,311,760 325,538 25,460,108,909 312,695 4.96 15.45 56 56
4 15,284,617,432 7,863,655 23.80 0.06 620,148,991 488,306 25,460,272,932 148,672 4.60 16.10 57 57
5 15,288,869,631 12,115,854 23.81 0.07 620,067,607 569,691 25,463,189,743 -2,768,139 2.38 21.27 59 64
7-2 1 15,277,661,978 908,201 23.82 0.08 619,986,222 651,075 25,450,646,702 9,774,902 71.69 1.39 50 8
2 15,280,976,912 4,223,135 23.99 0.25 618,602,688 2,034,610 25,431,260,043 29,161,562 48.18 2.08 40 11
3 15,284,291,845 7,538,068 24.10 0.36 617,707,460 2,929,838 25,419,885,709 40,535,895 38.87 2.57 35 14
4 15,289,264,246 12,510,469 24.20 0.46 616,893,616 3,743,682 25,411,504,232 48,917,373 29.91 3.34 33 16 5 15,294,304,761 17,550,984 24.31 0.57 615,998,388 4,638,910 25,401,855,480 58,566,124 26.41 3.78 31 21
8-1 1 15,278,046,321 1,292,544 24.46 0.72 614,777,622 5,859,676 25,365,566,222 94,855,382 453.34 0.22 23 4
2 15,305,005,104 28,251,327 25.33 1.59 607,697,181 12,940,117 25,276,346,261 184,075,343 45.80 2.18 15 12 3 15,358,922,670 82,168,893 26.53 2.79 597,931,055 22,706,243 25,170,017,284 290,404,320 27.62 3.62 5 18 4 15,466,757,803 190,004,026 27.85 4.11 587,188,316 33,448,981 25,101,581,219 358,840,385 17.46 5.68 3 33 5 15,491,500,795 214,747,018 28.91 5.17 578,561,572 42,075,726 24,984,773,098 475,648,506 19.50 5.10 1 29
8-2 1 15,365,163,777 88,410,000 24.81 1.07 611,929,169 8,708,129 25,405,945,103 54,476,501 9.13 10.15 32 44
10 1 15,675,230,277 398,476,500 24.49 0.75 614,533,469 6,103,829 25,758,744,015 -298,322,410 -4.43 65.28 74 76 11 1 15,402,927,477 126,173,700 23.99 0.25 618,602,688 2,034,610 25,553,210,608 -92,789,003 -4.16 62.01 71 75
12 1 15,311,500,239 34,746,462 23.99 0.25 618,602,688 2,034,610 25,461,783,370 -1,361,765 4.10 17.08 58 60
13 1 15,277,033,777 280,000 24.04 0.30 618,195,766 2,441,531 25,420,639,968 39,781,636 871.98 0.11 36 3
2 15,278,033,777 1,280,000 24.19 0.45 616,975,000 3,662,297 25,401,609,151 58,812,454 286.12 0.35 30 5
3 15,279,033,777 2,280,000 24.34 0.60 615,754,235 4,883,063 25,382,578,333 77,843,272 214.17 0.47 25 6
4 15,281,213,777 4,460,000 24.49 0.75 614,533,469 6,103,829 25,364,727,515 95,694,090 136.86 0.73 22 7
14 1 15,368,951,493 92,197,716 24.24 0.50 616,568,078 4,069,219 25,485,849,927 -25,428,323 1.92 22.66 67 66
15 1 15,283,483,777 6,730,000 24.24 0.50 616,568,078 4,069,219 25,400,382,211 60,039,393 60.46 1.65 28 9
16 1 15,285,903,777 9,150,000 23.99 0.25 618,602,688 2,034,610 25,436,186,908 24,234,697 22.18 4.50 43 26
17 1 15,301,733,777 24,980,000 23.99 0.25 618,602,688 2,034,610 25,452,016,908 8,404,697 7.11 12.28 51 49
18 1 15,279,963,777 3,210,000 23.84 0.10 619,823,454 813,844 25,450,277,726 10,143,879 25.32 3.94 49 23
2 15,281,123,777 4,370,000 23.89 0.15 619,416,532 1,220,766 25,444,760,786 15,660,818 27.92 3.58 48 17
3 15,283,223,777 6,470,000 23.94 0.20 619,009,610 1,627,688 25,440,183,847 20,237,757 25.13 3.97 45 24
4 15,284,223,777 7,470,000 23.99 0.25 618,602,688 2,034,610 25,434,506,908 25,914,697 27.22 3.67 42 20
19 1 15,522,950,777 246,197,000 23.84 0.10 619,823,454 813,844 25,693,264,726 -232,843,121 -11.15 302.51 73 77 2 15,769,148,777 492,395,000 23.89 0.15 619,416,532 1,220,766 25,932,785,786 -472,364,182 -12.25 403.35 76 78 3 16,015,346,777 738,593,000 23.94 0.20 619,009,610 1,627,688 26,172,306,847 -711,885,243 -12.69 453.77 79 79 4 16,258,676,777 981,923,000 23.99 0.25 618,602,688 2,034,610 26,408,959,908 -948,538,303 -12.91 482.61 80 80
20 1 15,286,753,777 10,000,000 23.99 0.25 618,602,688 2,034,610 25,437,036,908 23,384,697 20.27 4.91 44 28
21 1 15,290,329,777 13,576,000 23.99 0.25 618,602,688 2,034,610 25,440,612,908 19,808,697 14.74 6.67 47 37
22 1 15,332,214,777 55,461,000 23.99 0.25 618,602,688 2,034,610 25,482,497,908 -22,076,303 0.63 27.26 65 69
23 1 15,316,282,777 39,529,000 23.99 0.25 618,602,688 2,034,610 25,466,565,908 -6,144,303 3.07 19.43 61 62
24 1 15,280,753,777 4,000,000 23.99 0.25 618,602,688 2,034,610 25,431,036,908 29,384,697 50.87 1.97 39 10
25 1 15,289,977,777 13,224,000 23.99 0.25 618,602,688 2,034,610 25,440,260,908 20,160,697 15.16 6.50 46 35
26 1 15,361,753,777 85,000,000 23.99 0.25 618,602,688 2,034,610 25,512,036,908 -51,615,303 -2.02 41.78 68 74 CC: Construction Cost (₩), ΔCC: Construction Cost Difference between Alternative and Baseline Model Apartment Complex (₩), RED: Energy Demand Reduction Rate (%),
ΔRED: Energy Demand Reduction Rate Difference between alternative and baseline model apartment complex (%), EC: Energy Cost (₩/year), ΔEC: Energy Cost Difference between Alternative and Baseline Model Apartment Complex (₩/year), LCC: Life Cycle Cost (₩),
NPV: Net Present Value (₩) = ΔLCC(LCC Difference between Alternative and Baseline Model Apartment Complex), IRR: Internal Rate of Return (%), PP: Payback Period (year), OP-1: Order of Priority of LCC and NPV, OP-2: Order of Priority of IRR and PP
this alternative is rejected (NPV < 0 and IRR < real interest rate)
of an apartment complex for more than 30 years hardly affects the entire cost.6 As a result of the calculation, the LCC of the baseline model apartment complex is ₩ 25,460,421,604 and each alternative’s LCC is shown in Table 7. And the calculation results of NPV, IRR and the payback period of each alternative are also presented in Table 7.
4.3 Cost Efficiency Analysis Results of Each Alternative of Target Items
Table 7 shows the cost efficiency analysis result. In the case of No.2 (window area), both construction and energy costs of Alt1 and Alt2 are smaller than those of the baseline model apartment complex. This is because the construction cost is directly proportional to the window area. With respect the energy cost, the decrement of heat loss is more than that of solar heat gain through the window with the decrease of window area. The IRR and payback periods of Alt1 and Alt2 for No.2 cannot be calculated, and Alt2 of No.2 is given the first priority because of its more decrease in construction and energy costs.
Alternatives with negative NPV, No.0 (balcony window U-value), Alt3 of No.1 (window U-value), Alt4 and 5 of No.4-3 (corner side wall U-value), Alt 3, 4 and 5 of No.6 (roof U-value), Alt5 of No.7-1 (ground floor U-value facing the outside directly), No.10 (thermostat per each room or zone), No.11 (electric circuit configuration which enables to break the main power outlet of the living room conveniently or installation of certified energy efficient appliances), No.12(windbreak space at the building’s entrance), No.14 (equipment, pipe and duct insulation), No.19 (voltage drop of main power line), No.22 (automatic control systems of equipments for receiving and transforming the electricity), No.23 (application of high intensity discharge lamp and automatic on/off control system of the outside lightings) and No.26 (decentralized control system with open protocol, which enables intensive control as well as data compatibility with each control system of mechanical and electrical equipment) should be rejected. In addition, with respect to the IRR, these alternatives also proved to be cost-inefficient due to their IRR value being lower than the real interest rate, 4.44%, which is calculated applying the price increase rate, 3.2% and interest rate, 7.78%.
All but the rejected alternatives are arranged according to their NPV values. In case that if there are several alternatives for one target item, only one alternative having the best NPV value among them is selected. As a result, Alt5 of No.8-1 (wall U-value facing the unheated space), Alt2 of No.2 (window area), Alt4 of No.4-2 (back wall U-value) and Alt5 of No.1 (window U-value) are proven to be superior from the point of NPV. In the same manner, Alt2 of No.2 (window area), Alt1 of No.13 (average efficiency of pumps for heating water, service water, domestic hot water, etc), Alt1 of No.8-1 (wall U-value facing the unheated space) and Alt1 of No.7-2 (floor U-value facing the outside indirectly) are proven to be excellent with respect to IRR. Alt2 of No.2 (window area) is proven to be quite good regarding both NPV and IRR. And the order of priority of NPV shows the same as that of LCC, and IRR appears also the same as payback period.
5. Conclusion
This study analyzed the cost efficiency of each item related to the energy efficiency of an apartment complex by using the assessment method of the Building Energy Efficiency Rating System of Korea. The baseline model apartment complex was set up, based on an actual apartment complex. Among all the assessment items in the system, items that are suitable for analyzing cost efficiencies were selected as target items, and alternatives for each target item were set up. Construction and energy costs of both each alternative were estimated by using actual price data and the assessment method of the system. As a result, the LCC, the NPV, the IRR and the payback period as indexes of cost efficiency and the order of priority in accordance with each index were presented. In addition, very cost efficient alternatives with respect to the NPV and the IRR were suggested. The results of this study are expected to be the guideline for developing energy and cost efficient design models of an apartment complex.
Acknowledgements
This work was supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (The Regional Research Universities Program/Biohousing Research Institute).
This research was supported by a grant (06ConstructionCoreB02) from High-tech Urban Development Program (HUDP) funded by Ministry of Land, Transport and Maritime Affairs of Korea Government.
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