# A Study on Variation of Thermal Characteristics of Insulation Materials for Buildings According to Actual Long-Term Annual Aging Variation

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## Abstract

Insulation materials used for buildings are broadly classified as organic insulation materials or inorganic insulation materials. Foam gas is used for producing organic insulation materials. The thermal conductivity of foam gas is generally lower than that of air. As a result, foam gas is discharged over time and replaced by outside air that has relatively less thermal resistance. The gas composition ratio in air bubbles inside the insulation materials changes rapidly, causing the performance degradation of insulation materials. Such performance degradation can be classified into different stages. Stage 1 appears to have a duration of 5 years, and Stage 2 takes a period of over 10 years. In this study, two insulation materials that are most frequently used in South Korea were analyzed, focusing on the changes thermal resistance for the period of over 5000 days. The measurement result indicated that the thermal resistance of expanded polystyrene fell below the KS performance standards after about 80–150 days from its production date. After about 5000 days, its thermal resistance decreased by 25.7 % to 42.7 % in comparison with the initial thermal resistance. In the case of rigid polyurethane, a pattern of rapid performance degradation appeared about 100 days post-production, and the thermal resistance fell below the KS performance standards after about 1000 days. The thermal resistance decreased by 22.5 % to 27.4 % in comparison with the initial thermal resistance after about 5000 days.

### Keywords

Actual long-term Aging variation Insulation materials Thermal resistance## 1 Introduction

The insulation materials used for a building directly affect its cooling and heating load, therefore significantly influencing energy bills throughout the building’s lifecycle. The Korean government has been strengthening the relevant systems or policies in order to improve energy efficiency of buildings, e.g., continuous improvement of energy-efficient building design standards used for new buildings, and making efforts to operate the improvement and management measures for the insulation performance of existing buildings [1]. Insulation is a fundamental method to reduce building energy consumption, as it directly affects the cooling/heating load and energy consumption of a building. The insulation performance of building envelope is largely determined by the thermal properties of building insulating materials. Those thermal properties include the density and thermal conductivity. Existing insulation materials are often replaced through renovation once a building has reached its life span or has been in use for a long period of time after its initial construction. In general, it is expected that the life span of a building is over 50 years, and the renovation of building skin and insulation material is carried out 20–25 years after the initial construction of the building. Therefore, the objective of this study is to investigate the thermal properties of building insulation materials according to long-term aging variation. The study presents the result of a longitudinal experiment on the thermal conductivity of insulation materials. Insulation materials’ performance data obtained throughout the study can be used as a basis of improving the competitiveness of insulation products in the market in the future. Thermal properties of different insulation materials due to long-term aging variation will be utilized to suggest the revision of the relevant standards and specifications of building insulation materials.

## 2 Aging Characteristics of Plastic Insulation Material

- (1)
Change in the 1st stage (primary stage): As the change according to rapid change of gas ratio in air bubbles inside the insulation material due to air penetration from the outside occurs, thermal drift occurs. (Generally, this change comes to an end within 5 years.)

- (2)
Change in the 2nd stage (secondary stage): Deterioration of thermal performance occurs due to slow release of gas penetrated into internal air bubbles to the outside, while air penetration from the outside is stopped. (This occurs for over 10 years and in some cases, over 100 years.)

## 3 Test Method

### 3.1 Specimen and Measurement Conditions

The specimens used in the experiment were Special Class and Class 1 expanded polystyrene foam, and 40 K and 50 K rigid polyurethane foam (specifications shown in Table 1) that were used as the insulation materials for buildings. These insulation materials were collected within 3 days from the production date and installed on the actual wall of the sample building as shown in Fig. 2. The experimental conditions include two cases: (1) installation of the specimen at the back of the class surface (1st floor) so that it is directly affected by the external condition, and (2) installation of the specimen inside the wall (2nd floor). The size of each insulation material specimen was 300 (W) \(\times \) 300 (H) \(\times \) 50 (D) mm and each specimen consisted of independent cells as shown in Fig. 2. Also, Fig. 2 shows the external view of the experiment setup and the cross section of the area where each insulation material specimen is installed.

Materials | Thermal conductivity [\(\hbox {W}\cdot \hbox {m}{^{-1}}\cdot \hbox {K}(\hbox {kcal}\cdot \hbox {m}{^{-1}}\cdot \hbox {h}\cdot {^\circ }\hbox {C})]\) | Density (\(\hbox {g}\cdot {\hbox {cm}^{{-3}}}\)) |
---|---|---|

| ||

Expandable polystyrene (EPS) | ||

1st | 0.036 (0.031) | \(\ge 30\) |

2nd | 0.037 (0.032) | \(\ge 25\) |

3rd | 0.040 (0.034) | \(\ge 20\) |

4th | 0.043 (0.037) | \(\ge 15\) |

Extruded polystyrene (XPS) | ||

Special | 0.027 (0.023) | – |

1st | 0.028 (0.024) | – |

2nd | 0.029 (0.025) | – |

3rd | 0.031 (0.027) | – |

| ||

1 class | ||

1st | 0.024 (0.021) | \(\ge 45\) |

2nd | 0.024 (0.021) | \(\ge 35\) |

3rd | 0.026 (0.022) | \(\ge 25\) |

2 class | ||

1st | 0.023 (0.020) | \(\ge 45\) |

2nd | 0.023 (0.020) | \(\ge 35\) |

3rd | 0.028 (0.024) | \(\ge 25\) |

### 3.2 Measurement Equipment

Netzsch’s Heat Flow Meters HFM 436 Lambda Series was used for thermal conductivity measurements in this study. Experiments were carried out in accordance with the measurement method specified in ASTM C 518 (standard test method for steady-state thermal transmission properties by means of the heat flow meter apparatus) and ISO 8301 (thermal insulation—determination of steady-state thermal resistance and related properties). The specification of the equipment and the diagram of measurement method are described in Table 2 and Fig. 3 respectively.

Outline of measurement equipment

Measuring range | 0.015–0.43 \(\hbox {W}\cdot \hbox {m}{^{-1}}\cdot \hbox {K}\) |

Size of specimens | \(300\times \,300\,\mathrm{mm}, \hbox {d}=5{-}100\,\mathrm{mm}\) |

Reproducibility | \(\pm \, 1\,\%\) |

## 4 Test Result

### 4.1 Expanded Polystyrene Type 1

### 4.2 Expanded Polystyrene Type 2

The initial thermal resistance of the Special Class expanded polystyrene insulation material type 2 specimen was 2.157 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\), and it decreased to 1.860 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\) after 100 days, showing thermal drift. It decreased to 1.694 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\) after about 1000 days and 1.575 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\) after about 5000 days. Also, the thermal performance falling below KS performance standards was shown after about 80 days from its production date.

The initial thermal resistance of the Class 2 expanded polystyrene insulation material type 2 specimen was 1.984 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\), and it decreased to 1.698 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\) after about 100 days, showing thermal drift. After that, it decreased to 1.566 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\) after about 1000 days and 1.472 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\) after about 5000 days, showing the pattern of continuous thermal drift. Also, the thermal performance falling below KS performance standards was shown after about 50 days from its production date.

### 4.3 Rigid Polyurethane

The initial thermal resistance of rigid polyurethane insulation material 40K specimen was 2.656 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\), and it decreased to 2.486 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\) after about 100 days, showing the pattern of thermal drift. It is about 6.3 % rate of change, showing lower thermal drift in comparison with the expanded polystyrene insulation material. However, the pattern of rapid thermal drift was shown after 100 days, and the thermal resistance decreased to 2.128 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\) after about 1000 days, falling below KS performance standards. It decreased to 1.929 \({\text {m}}^2\cdot \hbox {K}\cdot \hbox {W}^{-1}\) after 5000 days, showing thermal drift, and it is considered that thermal drift is still in progress.

Results of thermal resistance

Specimens | Thermal resistance ( \({\text {m}}^{2}\cdot \hbox {K}\cdot \hbox {W}{^{-1}}\)) | Density (\(\hbox {kg}\cdot {\text {m}}^{-3}\)) | Deterioration ratio (%) | |||||||
---|---|---|---|---|---|---|---|---|---|---|

Initial value | 100 days | 1000 days | 4000 days | 5000 days | ||||||

Window | Expanded polystyrene | Type 1 | Special | 2.485 | 1.965 | 1.493 | 1.469 | 1.424 | 35.4 | 42.7 |

1 class | 2.221 | 1.687 | 1.368 | 1.367 | 1.338 | 32.3 | 35.6 | |||

Type 2 | Special | 2.157 | 1.860 | 1.694 | 1.588 | 1.575 | 33.2 | 23.4 | ||

2 class | 1.984 | 1.698 | 1.566 | 1.471 | 1.472 | 30.5 | 20.6 | |||

Rigid polyurethane | 40 K | 2.656 | 2.486 | 2.128 | 1.992 | 1.929 | 36.3 | 29.3 | ||

50 K | 2.613 | 2.476 | 2.128 | 2.048 | 2.024 | 46.8 | 23.7 | |||

Wall | Expanded polystyrene | Type 1 | Special | 2.498 | 2.004 | 1.497 | 1.454 | 1.452 | 35.4 | 42.1 |

1 class | 2.222 | 1.725 | 1.370 | 1.346 | 1.322 | 32.3 | 36.2 | |||

Type 2 | Special | 2.158 | 1.825 | 1.486 | 1.535 | 1.535 | 33.2 | 25.1 | ||

2 class | 1.968 | 1.671 | 1.578 | 1.453 | 1.450 | 30.5 | 20.9 | |||

Rigid polyurethane | 40 K | 2.661 | 2.522 | 2.094 | 1.913 | 1.902 | 38.9 | 30.6 | ||

50 K | 2.579 | 2.445 | 2.044 | 1.903 | 1.897 | 49.4 | 27.5 |

## 5 Conclusion

- (1)
The initial thermal resistance of Special Class and Class 1 expanded polystyrene insulation material type 1 within 3 days from its production date met KS performance standards. However, the pattern of continuous thermal drift was observed, and the thermal resistance falling below KS performance standards was shown after about 50–150 days. After about 1000 days, the specimens entered into the steady state regarding aging variation, and the rate of change in comparison with the initial thermal resistance after about 5000 days was 39.8 % to 42.7 %.

- (2)
The initial thermal resistance of expanded polystyrene insulation material type 2 was lower than the initial thermal resistance of expanded polystyrene insulation material type 1. The range of the rate of change after about 5000 days was 25.8 % to 27.0 %. However, thermal resistance performance falling below KS performance standards was observed after about 80–110 days, showing the continuous aging variation.

- (3)
In the case of rigid polyurethane insulation material, while both specimens showed the gradual thermal drift after about 70–100 days, the rate of change increased afterward. The thermal drift below KS performance standards was shown after about 1000 days. The rate of change in comparison with the initial value after about 5000 days was 22.5 % to 27.4 %. It seems that the aging variation was continuously in progress.

- (4)
The specimens installed on the glass and the wall did not show a significant difference in aging variation, indicating that environmental conditions did not influence the release of foam gas in the insulation material.

### References

- 1.Ministry of Land, Infrastructure and Transport, 2013, Building energy saving design standardsGoogle Scholar
- 2.KS M ISO 11561:2009 Aging of thermal insulation materials: determination of the long-term change in thermal resistance of closed-cell plastics (accelerated laboratory test methods)Google Scholar
- 3.ASTM C518 (Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus)Google Scholar
- 4.KS M 3808:2011 Cellular polystyrene(PS) for thermal insulationGoogle Scholar
- 5.KS M 3809:2006 Rigid polyurethane foam for thermal insulationGoogle Scholar
- 6.KS L 9016:2010 Test methods for thermal transmission properties of thermal insulationsGoogle Scholar

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