Building Envelope Insulation and Cost Efficiency in Taiwan · Building Envelope Insulation and Cost Efficiency in ... correct energy consumption and annual thermal loading. Since

Building Envelope Insulation and Cost Efficiency in Taiwan

(1) J.C. Fu, Ms (2) P.Y. Kuo, Ass. Prof.

(1)[email protected] (2)[email protected] Chaoyang University of Technology, Graduate School of Architecture and Urban Design 168 Jifong E. Rd., Wufong Township, Taichung County, Taiwan, R.O.C.

Abstract

The study investigated the relationship among insulation performance, air-conditioning energy consumption, and cost-efficiency that was seldom discussed in previous studies in Taiwan. By opening ratio and structure insulation control, the annual thermal loading was calculated with the architectural energy simulation software PowerDOE. Common insulation materials were then combined with the hope to achieve the same (U value = 1.2) or better (U value = 1.0) roof insulation while cut down the cost. The study thus provides a rapid reference for designers to carry out the insulation design of roof structure.

Simulation results showed that, when the opening ratio of external wall was controlled at 40% and the U value of external wall insulation was fixed, the annual thermal loading decreased by 1.1-1.3% whenever the U value of roof insulation decreased by 0.1; when the U value of roof insulation was fixed, the annual thermal loading decreased by 0.4-0.5% whenever the U value of external wall insulation decreased by 0.1; when the U values of both external wall insulation and roof insulation decreased by 0.1, the annual thermal loading decreased by 1.5-1.9%. Furthermore, based on a reinforced concrete structure with a 1.2 U value of roof insulation and a 3.5 U value of external wall insulation, when polystyrene board was applied as the main insulation material, the U value of roof insulation decreased to 0.8, reducing the annual thermal loading by 2,870.2 kcal (-5.7%) while increasing the insulation cost per square meter by NT$589/m2.

Keywords Green building, Envelope insulation, Architectural energy simulation, Cost efficiency

Session E. Green Building – Energy and Resource

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1. Introduction

Since 2004, the U values of structure heat transmission coefficient for “residences, schools, large spaces and other constructions” have been regulated by detailed specification in the Green Building Standards section of the Building Technical Regulations in Taiwan as 1.2 for roof insulation and 3.5 for external wall insulation. To facilitate energy conservation and carbon reduction in practice, the U value of roof insulation was reduced to 1.0 in July 2009. However, consumers still have little understanding of the principles of roof insulation and consider insulation materials to be very expensive. In order to implement the policy and achieve the goals of energy conservation and carbon reduction, it is necessary to illustrate the principles and use of insulation materials to consumers with correct computer simulation and reasonable cost accounting.

In this study, the simulation of energy consumption was carried out by globally recognized architectural energy simulation software (PowerDOE) to investigate the structure insulation types and energy consumption with the vast and fast computing features of computer simulation. The top-floor classroom space of school buildings, which covers a wide scope and has a far-reaching impact, was chosen as the object of simulation to look into the annual thermal loading produced by different forms of roof insulation. With the simulation data, it was expected to prove that appropriate forms of roof insulation could reduce the indoor thermal loading and energy consumption.

Furthermore, an analysis of cost efficiency that was seldom discussed in previous studies was also performed in the research. From current structural materials in Taiwan, several common materials were selected with different thickness for cost accounting. After the cross-analysis of building energy consumption and cost efficiency, it was expected to reach the same or better insulation standards while taking cost control into consideration. The study thus can provide a rapid reference for designers to carry out the insulation design of roof and external wall structures.

2. Research methods 2-1 Architectural dynamic energy analysis 2-1-1 Simulation model It was concluded that the area of each classroom was 112.5 m2 (9×12.5×4m) based


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on the assumption that the standard area was 2.5 m2 for each person and there were 45 persons in each classroom. In order to make the result of energy consumption simulation more accurate and closer to the actual situation, an architectural massing model (Figure 1, Figure 2) of three ordinary classrooms and two subsidiary spaces was established to carry out the analysis of dynamic energy. With the opening ratio of external wall set as 40% and the external shade depth as 0.4 m, the middle classroom was selected as the main object of simulation analysis. Other than the architectural energy consumption of a single classroom, the overall architectural energy consumption was also observed.

Figure 1 Model Plan (gray for the main simulation classroom) Unit: cm

Figure 2 PowerDOE simulation model—three-dimensional diagram of

the building with windows facing west 2-1-2 Simulation parameter setting In this study, the weather database TMY2 of Taichung area, Taiwan from previous studies was adopted as a reliable basis of software climate setting for the simulation software PowerDOE. In addition, parameters such as indoor lighting density, heat dissipation of human body, heat dissipation of equipment (Table 1), the system loop of chilled water and heated water, the chiller, the loop system, and the air-conditioning system, etc. were all set in detail.


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Moreover, an annual schedule (Figure 3) was established based on the starting time of indoor lighting, staff, machinery, cooling, heating, etc. in the building so that the simulation software could follow the use time of the building to calculate the correct energy consumption and annual thermal loading. Since the simulation model is a classroom unit, the annual calendar of a school was chosen as the basis for schedule establishment.

2-2 Cost efficiency analysis The two major types of roof insulation for school buildings in Taiwan, reinforced concrete and the steel deck, are different to some degree in their constructions and costs. In this study, these two basic types were combined with common insulation materials (Table 2) to provide roof insulation constructions with five different U values (1.2-0.8) for reinforced concrete and steel deck respectively. On the basis of construction prices, published by Taiwan Construction Research Institute Foundation in March 2008 and updated every two months, the cost of roof insulation was calculated in hope of striking a balance between roof insulation and costs so as to promote the benefits of roof insulation of green buildings.

Table 1 The simulation parameter setting of PowerDOE Item Range

Location Taichung Azimuth 270 ℃ Area 112.5 m2 (9 m * 12.5 m * 4 m) Number of people 45 Area / Person 2.5 m2 Opening ratio 40 ％ Window overhang 0.4 m U-value of Roof 1.2 ~ 0.8 (U-value input) U-value of Wall 3.5 ~ 3.1 (U-value input) Glass Default Glass GTC1000

Center glass U-value: 6.31, Solar transmittance: 0.83, Desc: single clear 3 mm, Solar reflectance: 0.136 (from the inside)

Lighting 21 w/m2 Equipment 7.5 w/m2 Heat gain Male: 198 Btu/h-person, Female: 254 Btu/h-person


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Figure 3 Annual schedule for the energy consumption simulation parameters

of PowerDOE

Table 2 Introduction list of roof insulation materials used in this study

Material Thickness (m)

Thermal conductivity [W/(m．K)] Price

Reinforced concrete 0.15 1.4

Steel bar, NT. 25,700 per ton 3,000psi Concrete, NT. 2,100 per m3

Heat-Shield-Brick 0.029 1.5 30cm*30cm, NT. 8 per piece Foam concrete 0.100 0.8 NT. 2,800 per m3 Rockwool 0.02 0.051 NT. 180 per m2

Polystyrene 0.025 0.028 90cm*180cm, NT. 170 per piece

Polyethylene 0.001 0.038 NT. 160 per m2 2 mm Polyurethane 0.002 0.050 NT. 430 per m2

6 mm Polyurethane 0.006 0.050 NT. 770 per m2

3. Results and discussion

3-1 Architectural dynamic energy analysis Based on the roof insulation U value 1.2 and the external wall insulation U value 3.5, the result of the simulation showed that (Table 3) the annual thermal loading of a single classroom space was 50,173.3 kcal. In addition, the body shell structure which produced the highest annual thermal loading was the simulation sample of roof


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insulation U value 3.2 (composed of reinforced concrete 15cm as the main body and cement mortar 1.5cm for the inner and outer surface) and external wall insulation U value 3.5, which produced the annual thermal loading as high as 62,553.41 kcal, increased by approximately 13,796.8 kcal (24.7%). If the simulation was carried out on the basis of roof insulation U value 1.0 and external wall insulation U value 3.5 according to the current regulations, the annual thermal loading was 48,756.6 kcal, decreased by approximately 1,416.7 kcal (-2.8%). If the roof insulation U value was further reduced to 0.6, the annual thermal loading was 45,811.5 kcal, decreased by approximately 4,361.8 kcal (-8.7%).

From Table 3, it was also shown that when the U value of external wall insulation was fixed, the annual thermal loading decreased by 1.1-1.3% whenever the U value of roof insulation decreased by 0.1; when the U value of roof insulation was fixed, the annual thermal loading decreased by 0.4-0.5% whenever the U value of external wall insulation decreased by 0.1; when the U values of both external wall insulation and roof insulation decreased by 0.1, the annual thermal loading decreased by 1.5-1.9%. Though the above-mentioned change of annual thermal loading was not resulted from calculation over a long period or from multiple samples, it could still serve as a fast and convenient reference for designers to build or improve the roof insulation of school building classrooms.

Table 3 Annual thermal loading of a single classroom facing west with various U values Units: kcal

U=3.5 U=3.4 U=3.3 U=3.2 U=3.1 Wall

Roof Thermal loading

% Thermal loading

% Thermal loading

% Thermal loading

% Thermal loading

%

U=3.2 62553.4 24.7 62356.1 24.3 62155.2 23.9 61951.9 23.5 61745.7 23.1U=3.1 62003.0 23.6 61805.2 23.2 61604.9 22.8 61400.7 22.4 61195.1 22.0U=3.0 61446.1 22.5 61248.3 22.1 61047.9 21.7 60844.6 21.3 60638.2 20.9U=2.9 60881.9 21.3 60684.3 20.9 60484.0 20.6 60280.1 20.1 60075.2 19.7U=2.8 60312.1 20.2 60114.3 19.8 59913.5 19.4 59710.4 19.0 59504.7 18.6U=2.7 59735.3 19.1 59537.0 18.7 59336.6 18.3 59133.0 17.9 58927.7 17.4U=2.6 59150.7 17.9 58953.1 17.5 58752.0 17.1 58549.7 16.7 58343.0 16.3U=2.5 58559.7 16.7 58361.9 16.3 58161.3 15.9 57958.0 15.5 57753.1 15.1U=2.4 57961.0 15.5 57763.9 15.1 57562.8 14.7 57360.2 14.3 57154.1 13.9U=2.3 57355.7 14.3 57157.9 13.9 56957.5 13.5 56754.9 13.1 56548.8 12.7U=2.2 56743.1 13.1 56545.3 12.7 56345.5 12.3 56142.1 11.9 55937.2 11.5U=2.1 56122.7 11.9 55924.6 11.5 55724.5 11.1 55521.9 10.7 55316.6 10.3


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U=2.0 55494.2 10.6 55296.6 10.2 55096.3 9.8 54894.0 9.4 54688.1 9.0U=1.9 54857.9 9.3 54660.9 8.9 54461.0 8.5 54258.2 8.1 54052.8 7.7U=1.8 54213.8 8.1 54016.8 7.7 53816.4 7.3 53613.8 6.9 53408.7 6.4U=1.7 53561.4 6.8 53364.3 6.4 53164.3 6.0 52962.4 5.6 52756.8 5.1U=1.6 52901.2 5.4 52704.1 5.0 52503.8 4.6 52301.9 4.2 52096.8 3.8U=1.5 52231.9 4.1 52035.3 3.7 51835.2 3.3 51633.1 2.9 51427.8 2.5U=1.4 51554.5 2.8 51357.7 2.4 51157.6 2.0 50955.5 1.6 50751.1 1.2U=1.3 50868.8 1.4 50671.8 1.0 50471.9 0.6 50269.8 0.2 50065.5 -0.2U=1.2 50173.3 - 49976.5 -0.4 49777.2 -0.8 49575.3 -1.2 49370.2 -1.6U=1.1 49469.7 -1.4 49272.7 -1.8 49073.6 -2.2 48871.5 -2.6 48666.4 -3.0U=1.0 48756.6 -2.8 48559.8 -3.2 48361.2 -3.6 48159.4 -4.0 47954.5 -4.4U=0.9 48034.4 -4.3 47838.1 -4.7 47639.0 -5.1 47437.4 -5.5 47233.5 -5.9U=0.8 47303.1 -5.7 47106.5 -6.1 46907.5 -6.5 46706.9 -6.9 46502.5 -7.3U=0.7 46562.0 -7.2 46365.9 -7.6 46167.6 -8.0 45966.2 -8.4 45762.6 -8.8U=0.6 45811.5 -8.7 45616.2 -9.1 45417.7 -9.5 45216.6 -9.9 45012.9 -10.3

Note: The black background represents the insulation value set in this study The gray background represents the insulation value currently stipulated in the “Building Technique Regulation” in Taiwan

3-2 Analysis of cost efficiency To reach the set U values, roof structures including reinforced concrete and steel deck were combined with the pre-selected insulation materials (Table 1) and the cost per square meter was then calculated. Five basic types of roof insulation and their costs were sorted out for each of the two roof structures in Table 4 and Table 5. In addition, the insulation performance and material cost of the two roof structures alone without any insulation materials were also provided to illustrate that the insulation standards could still be met with simple insulation materials at a low cost.

As shown in Table 4, the reinforced concrete roof was based on the insulation U value 1.2, which was composed of reinforced concrete 15cm as the main body, cement mortar 1.5cm for the inner and outer surface, and insulation bricks, with a material cost of NT$4,823 per square meter. The rest of the reinforced concrete insulation structures were formed by increasing, reducing, or replacing materials on the basis of this type for comparison.

As shown in Table 5, the steel deck roof was based on the insulation U value 1.2, which was composed of reinforced concrete 15cm as the main body, galvanized steel deck on the inner surface, cement mortar 1.5cm for the outer surface, PU 0.002 m, and insulation bricks, with a material cost of NT$5196.5 per square meter. The rest of


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the steel deck insulation structures were formed by increasing, reducing, or replacing materials on the basis of this type for comparison.

From Table 4 and Table 5, it was concluded that using synthetic resin materials with lower thermal conductivity such as PU, PE, styrofoam, etc. could easily achieve a U value 1.2-1.0 for insulation design with a relatively low cost per square meter.

Table 4 Form table of insulation U values, materials, and costs of reinforced

concrete roofs

Note : The value in the brackets represents the cost increased with the change of insulation materials

as compared to roof structures of U=1.2. The gray background represents the material increased to reach the set insulation value as compared to roof structures of U=1.2.


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Table 5 Form table of insulation U values, materials, and costs of steel deck roofs

Note : The value in the brackets represents the cost increased with the change of insulation materials

as compared to roof structures of U=1.2. The gray background represents the material increased to reach the set insulation value as compared to roof structures of U=1.2.

However, with the replacement of various materials one by one, it was found that when the U value was to reduce to 0.9 or 0.8, the cost of the thin forming synthetic resin materials increased with the thickness, along with the composite levels required and the difficulty of construction. Therefore, changing materials should be another feasible way to decrease the insulation U value of roof below 1.0.

In Table 4 and Table 5, the roof insulation types with U value 0.9 of reinforced concrete and steel deck both adopted the light-weighted concrete, which was mostly used in school buildings approved by green building regulations. The cost of this material was 1.65 times that of ordinary concrete with a low 75% thermal


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conductivity. The high price caused the cost of roof insulation using light-weighted concrete to rise. In consideration of the cost, other popular alternative materials with similar thermal conductivity could be used to reduce the insulation cost.

In this study, roofs with the last level of insulation U value 0.8 were discussed. For these roofs, polystyrene board and rockwool insulation were adopted by reinforced concrete and steel deck structures respectively. The two materials had a low thermal conductivity and their costs were not as expensive as that of light-weighted concrete. They were commonly used to greatly reduce the indoor thermal loading in the improvement project of roof insulation. If they were matched with other synthetic resin materials, the U value of roof insulation could reach 0.6-0.7. Therefore, with the combination of different insulation materials, the U value 1.0 for roof insulation stipulated by current regulations could still be easily reached, or even surpassed to 0.8.

4. Conclusions

1. Relationship between roof insulation capacity and cost efficiency

For roof insulation, on the basis of the reinforced concrete with roof insulation U value 1.2 and external wall insulation U value 3.5, the relationship between the annual thermal loading and the cost of insulation was shown in Table 6. Compared to spaces with roof insulation U value 3.2, the cost per square meter was decreased by NT$96 and the annual thermal loading was increased by 12380.1 kcal (24.7%). If the roof insulation U value was decreased to 1.0, as stipulated by current regulations, the cost per square meter was increased by NT$920 and the annual thermal loading was decreased by approximately 1,416.7 kcal (-2.8%). If the roof insulation U value was decreased to 0.8, the cost per square meter was increased by NT$589 and the annual thermal loading was decreased by 2870.2 kcal. However, when the roof insulation U value was decreased to 0.9, the annual thermal loading was decreased by 2138.8 kcal while the cost per square meter was increased dramatically by NT$1,267, much higher than the cost of roof insulation U value 0.8. The main reason of this was the use of light-weighted concrete. It was also why light-weighted concrete was less recommended for roof insulation in this study.

In addition, in Table 6, to decrease the roof insulation U value from 1.2 to 1.0, the reinforced concrete layer were made thicker for comparison alone without other


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insulation materials. According to the result of calculation, the thickness of the reinforced concrete had to be increased from 0.15 m to 0.38 m to reach the standard of insulation value 1.0. Though the cost was increased only by NT$483, less than the cost of 0.6 mm PU, the weight per square meter was increased by approximately 552 kg, resulting in the significant increase of architectural load that was adverse to structural stability. Therefore, it was not recommended to simply increase the thickness of reinforced concrete for insulation.

Table 6 Relationship between the roof insulation capacity and cost efficiency of a single reinforced concrete classroom

Roof U value

Annual thermal loading (kcal)

Insulation cost (NT/m2)

Main insulation materials

U=3.2 62553.4 24.7% -96 - U=1.2 50173.3 - - Heat-Shield-Brick U=1.1 49469.7 -1.4% +580 0.2 mm Polyurethane

+920 0.6 mm Polyurethane U=1.0 48756.6 -2.8% +483 0.38m Reinforced

Concrete U=0.9 48034.4 -4.3% +1,267 Foam Concrete U=0.8 47303.1 -5.7% +589 Polystyrene

Note: the external wall insulation U value is 3.5 2. Avoid using materials with high thermal conductivity and high cost

It was shown in this study that to reduce the building envelope insulation U value, one could increase or decrease the thickness of the material or replace the material. Among them, reinforced concrete with polystyrene board and steel deck sprayed with rockwool had the best insulation effect with the least cost. Materials with high thermal conductivity and high cost such as light-weighted concrete should be avoided to easily reach a balance between insulation and cost.

3. For building envelope insulation, roof insulation should prevail the external

wall insulation The energy consumption simulation and cost calculation of insulation materials were performed in this study. The effect was not remarkable from the result of the simulation since when the roof insulation U value was fixed, the annual thermal loading was only decreased by 0.4-0.5% whenever the external wall insulation U value was decreased by 0.1. In particular, using too many insulation materials on the external wall would thicken the wall and reduce the valuable interior are. Therefore, for building envelope insulation, roof insulation should still be the primary goal.


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Reference

1. T.M.I. Mahlia, B.N. Taufiq, Ismail, H.H. Masjuki, (2007) “Correlation between

thermal conductivity and the thickness of selected insulation materials for building wall”, Energy and Buildings, Malaysia, Vol：39, Issue：2, pp182 ~ 187.

2. C.A. Balaras, A.A. Argiriou, (2002) “Infrared thermography for building diagnostics”, Energy and Buildings, Greece, Vol：34, Issue：2, pp171 ~ 183.

3. Takakura T., Kitade S. & Goto E., (2000) “Cooling effect of greenery cover over a building”, Energy and Buildings, Japan, Vol：31, Issue：1, pp1 ~ 6.

4. Hongxing Yang., Zuojin Zhu., John Burnett., (2000) “Simulation of the behaviour of transparent insulation materials in buildings in northern China”, Applied Energy, Hong Kong, Vol：67, Issue：3, pp293 ~ 306.

5. M.T. Wang, (2008) Construction Cost Data, Taipei. 6. Construction Magazine Company, (2007) Building Technique Regulation, Taipei.

Presentation of Author

Educational background 2008 Master in Architecture and Urban Design, Graduated from Graduate School of Architecture and Urban Design, Chaoyang University of Technology. 2005 Bachelor in Architecture, Graduated from Department of Architecture, Chaoyang University of Technology. Paper 2008 “A Research to Intensify the Building Envelope Insulation Standard and Cost Effective”, Master’s thesis, Chaoyang University of Technology, Taichung.

Jen-Chi Fu. Nov 16, 1982


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Building Envelope Insulation and Cost Efficiency in Taiwan · Building Envelope Insulation and Cost Efficiency in ... correct energy consumption and annual thermal loading. Since

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