KIEAE Journal

Nowadays, people have more interest in low-energy buildings due to worsened environmental pollution and thus increased value of ecological conditions. Accordingly, various policies and systems are being enforced to reduce energy load. Particularly for old buildings, attempts have been made to remodel them by replacing old system or using energy-efficient materials to reduce existing energy load and increase energy efficiency old buildings.

As for Korea, it has also made several efforts to activate green-remodeling market at the dimension of policy and system: information sharing through integrated energy DB of buildings (Korea Energy Economics Institute, 2015), setting greenremodeling guideline through demonstration or pilot projects and phased compulsory implementation, attraction to greenremodeling using private finance and interest preservation (Green- Remodeling Creation Center, http://www.green remodeling.or.kr/).

However, such problems as followings prevent from making preliminary feasibility decision, which is necessary to remodel existing old buildings. First, there is no systemized database of the elemental technology of green-remodeling by sector. Second, quantitative, qualitative, integrated comparison, and analysis system are absent for the evaluation of energy performance and cost of energy reduction. Last, since existing green-remodeling techniques heavily depend on expert's subjective judgement and expertise, non-experts have difficulty having access to them and it is also hard to obtain and derive objective and quantitative data out of them through objective and quantitative data analysis.

In this respect, this study developed a plan for qualitative and quantitative evaluation of old structure remodeling by element (exterior envelope, lighting, thermal source·air conditioning, new and renewable energy) and by use of existing building (large/small office facility, and apartment house) and Impact Table in which performance/cost database is provided by sector. In addition, this study developed preliminary study checklist and optimum combination dedication module (tool) in order to increase the usability of Impact Table and user's convenience.

And then Impact Table and optimum combination dedication module, which were developed in this study, were applied to 5 actual test models as pilot project to verify the usability and applicability of the proposed method. Last, the results from the evaluation of optimum combination dedication module were used to determine the suitability of preliminary business feasibility evaluation based on Impact Table for the decision making of green-remodeling project and limitations and the need of further study were pointed.

This study was conducted in the following order. First, Impact Table, preliminary study checklist for Impact Table, the components of optimum combination dedication module were analyzed. And then, 5 pilot project models (5 physical places) were chosen; a preliminary study checklist for each model was prepared; and the technological elements for green-remodeling were selected based on the checklist (using optimum combination dedication module ). Last, the performance and cost of the chosen technological elements were analyzed to find an optimum combination for green remodeling. Then, the optimum green remodel was evaluated and the results were analyzed and verified to determine the suitability of preliminary business feasibility evaluation based on Impact Table for the decision making of green-remodeling project. Limitations and the need of further study were pointed out. (Fig 1).

Fig. 1. 
Study process of optimum alternative for green-remodeling

Impact Table is the database of performance and cost of green remodeling project by sector (exterior envelope, lighting, thermal source·air conditioning, new and renewable). Therefore, it facilitates to review various alternatives in the stage of pre-design or schematic design of green remodeling project, and helps a client or a designer reduce trials and errors in the process of intial decision making.

Impact Table consists of Impact Table A where qualitative evaluation is carried out in pre-design stage and Impact Table B where quantitative evaluation is carried out in schematic design stage. In Impact Table A, energy efficiency, cost (disposal, production, construction, and so on), and performance of technological elements are compared by sector and classified into 3 classes (high, middle and low). Meanwhile, Impact Table B provides specific numbers (such as reduction ratio of energy, cost of energy reduction, construction cost) of technological elements by sector through the comparison with Reference Model¹⁾ (Table 1).

Criteria for alternative selection of green remodeling according to Impact Table are composed on the basis of five classification systems as below. The first classification system is separate implementation by construction type. The second classification system is by the scope of replacement. The third and fourth classification system are by construction classification and the scope of detailed construction. Last, the 5th classification system is selection of element technology and material by construction type. Figure 2 shows as example the alternative selection for exterior envelope according to 5 classification systems described above: then general low-e glass (low-emissivity coated glass) was selected as a technological element for partial replacement.

Fig. 2. 
Impact Table classification system (ex: exterior envelope)

After 5 steps of classification, Impact Table A (Figure 3) consists of constraints, applicable performance (qualitative), cost and constructability, and cost efficiency and Impact Table B (Figure 4) is composed of applicable performance (quantitative), energy consumption using reference model (qualitative), and cost.

Fig. 3. 
Composition of Impact Table A

Fig. 4. 
Composition of Impact Table B

Table 2 and Table 3 show the evaluation results of Impact Table A and Impact Table B composed by the selection of general low-e glass as partial replacement element in Figure 2 (based on total floor area 4,700m²).

As seen above, Impact Table A shows qualitative results of evaluation while Impact Table B shows quantitative results of evaluation on the technological elements a user chooses.

To perform reasonable selection of alternatives of existing building for green-remodeling based on Impact Table, it is necessary to examine the current status of target building for remodeling. Accordingly, this study made preliminary research checklists on exterior envelope, lighting, and thermal source·air conditioning of a target building. Each checklist is composed as seen in Figure 5. Figure 6 shows the checklists of lighting and thermal source·air conditioning sector as example.

Key input variables by sector include as follows: wall·roof·floor·window thermal transmittance, standard thermal transmittance, type of exterior and interior material and etc. for exterior envelope; lighting source type, lighting control type, control hour, control system, and etc. for lighting; and type and capacity of thermal source facility, air conditioning type, building operating hour, status of occupants, etc. for thermal source·air conditioning.

Fig. 5. 
Composition of check list

Fig. 6. 
Check list sample, Lighting(left), Thermal source/ Air conditioning(right) - partial omission

Impact Table A and B are made in Excel format. Since the classification systems are complicate and the data are bulky in size, however, it takes a long time to compare technological elements by sector one by one and choose an alternative. In addition, it is also not intuitive to do so. To tackle this issue, this study developed stand-alone softwares for Impact Table A and B: GRIS (Impact Table A in Figure 7) GRIT-OD (Impact Table B in Figure 8).

In addition, as for GRIS, a web version was developed to increase user's accessibility. The optimum combination dedication module of Impact Table has the following characteristics. It was designed to let a user select 5 stages of technological classification sequentiality using icons rather than exploring all the checklists, which is aimed to increase readability (visuality) and intuitiveness for non-experts. Second, comparison of alternatives are presented not in numbers alone but in graph and numbers together, so users can see the difference in performance/cost of alternative combinations. Third, optimum alternative dedication modules can be saved and printed out so database for green remodeling of a target building can be built and easily managed on regular base.

Fig. 7. 
Captured image in GRIS (based Impact Table A)

Fig. 8. 
Captured image in GRIT-OD (based Impact Table B)

To verify Impact Table A and B and optimum combination dedication modules, this study selected 5 office facilities as test model. Each test model is summarized in Table 4.

Name	Model A	Model B	Model C
Image
Location	Daejeon	Goyang	Seoul
Purpose	office	office	office
Floor	7F, BF1	5F, BF1	19F, BF2
Total floor	30,147.63 ㎡	6,477 ㎡	32,488.14 ㎡
Name	Model D	Model E
Image
Location	Mungyeong	Seoul
Purpose	office	office
Floor	4F, BF1	12F, BF3
Total floor	9,361 ㎡	11,880 ㎡

Table 5 shows the items of each building to check by sector through a preliminary research. Other items worth checking for aging are also described in the checklist. besides those items in Table 5, such as aging status index, operational and acceptancy status, contents of preliminary hearing. Followed are the findings from the preliminary research checklists.

Evaluation of Test Model A: as for exterior envelope, it turned out all of external wall, roof, bottom floor, thermal transmittance of window system did not meet the standard. Therefore, it is necessary to improve external wall and window thermal performance with thermal insulation boards and double pane window, and also to install wind-proof structure at the main entrance when remodeling it because wind-proof structure is absent. As for lighting, embedded louvers of fluorescent lights were applied to the building and they turned out bright enough as a whole. No damaged lighting equipment was found. As for thermal source·air conditioning, the building is equipped with gas boiler, package air-conditioner and EHP as heating and cooling source. Constant air volume conditioning units are used for cooling air conditioning. On the first floor, the building showed large cooling load due to frequency travels of people from outside (heavy influx of external air).

Evaluation of Test Model B: as for exterior envelope, it turned out that the state of external and interior wall finish was satisfactory, but thermal insulation boards were deteriorated by heat. Coated glass was used for windows (in aluminum frame) and the sealing state was so poor that the performance of thermal insulation and air-tightness of the boards were very low. Therefore, it is necessary to replace the deteriorated external thermal insulation boards and reinforce the sealing on the metal joints of the windows and ceiling to increase the performance of thermal insulation and air-tightness of the boards. As for lighting, it is open-embedded type with reflectors (plates). Therefore, it is necessary to add louvers to increase lighting efficiency. As for thermal source·air conditioning, it is necessary to check the working conditions of a hot water boiler and probe the causes for low thermal comfort. As occupants request ventilation, it is recommended to install a heat recovery ventilator during remodeling work. In addition, hot water pipes were not buried in some areas. Therefore, it is necessary to check the overall status of hot water piping.

Evaluation of Test Model C: as for exterior envelope, it was very difficult to diagnose the performance of thermal insulation boards of external walls thoroughly due to insufficient data. Therefore, general improvements are applied here (adding outside thermal insulation boards or inside thermal insulation boards to improve the performance of thermal insulation board of external walls). As for lighting, this building uses embedded louvers of fluorescent lights. It is necessary to review replacing them with LED fluorescent lights to improve lighting performance. Last, the thermal source·air conditioning of the building is short of load capacity and aged. Therefore, it is considered to replace facility system as a whole and increase load capacity. As for air conditioning, the building does not operate it now. Therefore, it is necessary to replace it in remodeling construction.

Evaluation of Test Model D: the preliminary research checklist found that Test Model D failed to meet all standards for exterior envelope (wall, roof, bottom floor, thermal transmittance of window system). Therefore, it is necessary to review replacing existing ceramic tile finish with stone-finished envelope and apply outside thermal insulation board system to improve exterior envelope performance. In addition, the performance of existing window thermal insulation boards needs improving by replacing them with low-e glass windows. For lighting, embedded and low-open fluorescent lights are applied to the building now and the brightness is evaluated to be generally satisfactory as a whole at bare-eye inspection. No damaged lighting equipment was found. Therefore, review for improvement is limited to only increasing lighting performance by louver installation. Lack of load capacity was found in thermal source·air conditioning. Therefore, it is necessary to increase load capacity by extending facility system. On the first floor, the building showed large cooling load due to frequency travels of people from outside (heavy influx of external air). Therefore, it is necessary to consider installing additional facility to increase load capacity.

Evaluation of Test Model E: exterior envelope turned out to be excellent in window performance. But the thermal transmittance of external wall, roof, and bottom floor failed to meet the standard . Therefore, it is necessary to improve the performance of thermal insulation boards of external walls by installing additional outside thermal insulation boards or inside thermal insulation boards. As for lighting, embedded louvers of fluorescent light are currently applied to the model. It is necessary to consider replacing them with LED fluorescent lights to improve lighting performance. As for thermal source·air conditioning, the efficiency of heating boilers was relatively low and it was found that air was supplied excessively due to inaccurate control of air volume for fuel volume. In addition, only one freezer was in use due to restriction of peak load to reduce the base rate of electricity, so the 1st cooling supply capacity was insufficient. Therefore, it is necessary to replace a whole system of heating source to improve thermal performance. For cooling source, installation of additional facility needs considering for increased load volume.

Using GRIS, which is the tool for the optimum combination module of Impact Table A, the alternative technological elements for remodeling of each test model were derived by sector (based on the elements derived by the preliminary research checklists in 4.2). And then, as seen in Figure 9, optimum alternative was selected by sector through qualitative comparison.

Fig. 9. 
Comparison of alternatives about light in GRIS (captured in optimum combination module of Impact Table A dedication tool)

Table 6 shows the final alternatives. In addition, Figure 10 lets us know the results of exterior envelope sector of Test Model A among the combinations derived by GRIS as example.

For exterior envelope (wall), reinforcement of outside thermal insulation boards, replacement of outside thermal insulation boards, reinforcement of inside thermal insulation boards were selected by test model. For exterior envelope (window), doubling of high thermal insulation glass, addition of high thermal insulation bar frame, and replacement with low-e glass were selected. For lighting, replacement with high-efficiency fluorescent lights, replacement with high-luminance reflectors (plates), and replacement with high-efficiency LED lamps were selected. As for thermal source, one-to-one exchange and addition of thermal source facility construction were selected as alternative technological elements for remodeling. Last, for air conditioning, one-to-one exchange of aged air conditioning system with constant air volume system unit and variable air volume system unit, respectively.

Fig. 10. 
Evaluation result of exterior envelop of Model A in GRIS (captured in optimum combination module of Impact Table A dedication tool)

To derive the quantitative evaluation figures of the optimum combination module of Impact Table A, this study entered technological elements selected in Table 5 into GRIT-OD, which is the tool for the optimum combination module of Impact Table B, and produced the graphs and tables like in Figure 11. Reduction ratio of energy, cost of energy reduction, and cost of initial investment of each test model were compared by sector (Table 7). And then the results of each sector were combined and years to take until recovering the cost of initial investment (payback period) were compared (Table 8). Test Model A was found most excellent in reduction ratio of energy and payback period of initial investment while and cost of energy reduction and initial investment were highest cost in Test Model C. Particularly, Test Model A showed excellent rate of energy reduction and payback period for cost of initial investment. Therefore, when technological elements selected in Table 6 are employed for green-remodeling, its effectiveness is expected to be high. On th contrary, Test Model C showed the lowest rate of energy reduction and the highest cost of initial investment. Therefore overall review is necessary for the selected technological elements of remodeling by sector.

Fig. 11. 
Evaluation result of Model A in GRIT-OD (captured in Impact Table B optimum combination dedication tool)

Figure 12 shows cost of initial investment and cost of energy reduction of Test Model C whose payback period for cost of initial investment rank on 5th on percentage base. Since it expresses the percentage of cost of initial investment and cost of energy reduction, it is very easy to catch technological elements that need reconsidering. As for Test Model C, lighting, exterior envelope, and cooling thermal source take higher cost of initial investment than other elements. On the other hand, Figure 13 shows the percentages of cost of initial investment and cost of energy reduction of Test Model B whose payback period for cost of initial investment rank on 4th among the test models. When the results of Test Model B (Figure 13) are compared with those of Test Model C (Figure 12), it is known that the former has lower percentage of cost of energy reduction for exterior envelope, but much higher percentage of cost of energy reduction for cooling thermal source than the latter. As a result, payback period for (cost of) initial investment is shortened.

Like this, since the evaluation of optimum combination tool based on Impact Table can propose percentage of cost of initial investment and cost reduction of remodeling elements by sector, it can show a direction and guideline to efficient green-remodeling business.

Fig. 12. 
Ratio of investment cost and energy reduction cost (Model C)

Fig. 13. 
Ratio of investment cost and energy reduction cost (Model B)