# Impact of an Innovative Solution for the Interruption of 3-D Point Thermal Bridges in Buildings on Sustainability

^{1}

^{2}

^{*}

## Abstract

**:**

^{2}of wall area where 6 pieces of anchors per 1 m

^{2}are applied, the savings would be EUR 16,200. Such savings are already significant. The conclusion of this work is that these point thermal bridges have a significant impact on the overall transmission heat loss coefficient and therefore they have overall heat demand and energy demand.

## 1. Introduction

_{2}production [4]. One of the most important factors is the correct design of the external cladding compositions, which defines the heat-exchange of the building envelope. The perimeter shell includes various elements that form thermal bridges. The thermal bridge can be characterized as a part of the building structure, where the internal surface temperature changes significantly compared to the surrounding internal surfaces. This can be caused by a change in the thickness of the building structure, the various size of the inner surface that receives heat and the outer surface that transfers heat (for example: corners of walls, roofs, floors, etc.). If a thermal bridge is constructed in the structure of a heated building, then, in winter, its temperature on the inner surface will be lower than the temperature on other common interior surfaces. On the contrary, the temperature on the outer surface of the thermal bridge will again be more elevated than in an ordinary place. This is because in the place of the thermal bridge, the structure has a higher thermal conductivity than in another ordinary place of the building structure. The building envelope must protect the entire heated interior of the building so that the influence of thermal bridges is eliminated at all critical points, or at least sufficiently eliminated. Thermal bridges can be caused by modifying the material or the geometry of the structures. In addition to the fundamental types of the thermal bridges, modern types are also being created, using individual architectural modern designs. These are mainly anchoring elements that are part of a light perimeter cladding or ventilated façade. As it is shown, point thermal bridge effects in cladding systems can constitute a significant part of buildings’ thermal balance. Neglecting their presence can lead to significant underestimation of actual heat flows, which can account for 5% to almost 20% of total heat flows through the building envelope, depending mostly on the thermal transmittance of the load-bearing wall [5]. In the case of façade renovations, these systems have become a very attractive alternative to external thermal insulation composing systems (ETICS). Condensation issues in most varieties of such systems are very limited since an air cavity which allows “breathing” separates the insulation material from the external cover. These anchoring elements can be additionally used for the local attachment of the various elements such as railings, billboards, awnings, shelters, pergolas and the others. Therefore, it is necessary to devote significant attention to this issue, as it has an impact on the indoor environment but also on the overall heat loss and thus on the overall energy efficiency of buildings [6]. It should be pointed out that the use of different calculation methods of thermal bridges, provided in standards [7,8], can lead to different energy performance classes of a building and to percentage gaps on the energy requirements in the heating season, calculated to be more than 20% [9]. The Standard EN ISO 13786 [10] requires a dynamic calculation for the evaluation of building performance but refers to Standard EN ISO 10211 [11] to perform steady-state thermal bridges calculations. Martin et al. [12]. underline this contradiction. There are solutions to reduce losses through thermal bridges, but they are not always applied. To design these solutions, it is important to be able to estimate these losses correctly and the inertia. In 1989, HASSID proposed and simplified model to account for lateral heat transfers caused by thermal bridges for homogeneous walls [13] and multilayer walls [14]. The model is based on the integration of the two-dimensional conduction equation. It led to a simple expression to incorporate thermal bridge effects in steady-state calculation tools. There are many numerical tools to characterize the thermal behavior of 2-D or 3-D elements. Several mathematical methods are implemented to solve the equations that describe heat transfers: finite elements method, electric analogs border element method [15]. All the above facts lead to the confirmation of the importance of the analysis of individual anchoring elements, which form the local point 3-D thermal bridges on buildings. A simplified steady state calculation method is used for the given calculation. The dynamic method was not used. The computational part is mainly used for verification with the experimental model and determination of the thermal conductivity of the proposed anchor modification.

## 2. Thermal Bridges

^{2}. W/K is in the range from 1.5 to 1.6 m

^{2}. W/K. By including the frame structure, the thermal resistance is reduced by 35 to 40%. This would mean that houses built in this way would require approximately 10–12% more energy than those using a simplified calculation, without including frame structures [21]. Theodosiou et al. [5] carried out 3-D heat transfer simulations of cladding systems for building facades, showing that neglecting the point thermal bridge effect in these kinds of systems can lead to a significant underestimation (from 5% to 20%) of the actual heat flows. As can be seen, the problem of inhomogeneous constructions in the scientific field itself is elementally solved all over the world. When calculating the energy balance of a building, it is necessary, among other inputs, to know the thermal properties of building structures, which form the envelope of heated spaces. If the package includes an inhomogeneous structure, it must be taken into account when calculating the thermal resistance [22,23,24]. In addition to thermal bridges, the cladding also has an effect on heat losses [25,26].

#### Point Thermal Bridges

- q Heat flow in W/m
^{2}; - $U$ heat transfer coefficient in W/ (m
^{2}. K).

- q Heat flow in W/m
^{2}; - $\theta $ the inside or outside temperature in K;
- ${\theta}_{s}$ the temperature of the interior or exterior surface in K;
- ${R}_{s}$ the interior or exterior heat transfer resistance in m
^{2}. K/W.

- L
_{3D}is the linear thermal transmittance determined from the 3-D calculation of a 3-D building structure separating the two environments in W/K; - U
_{i}is the heat transfer coefficient of a 1D building structure separating two environments in W/ (m^{2}. K); - A
_{i}area over which the value applies Ui in m^{2}; - Ψ
_{j}linear loss coefficient W/(m. K); - l
_{j}the length of the geometric model over which the value applies Ψ_{j}in m; - N
_{j}number of 2D building structures; - N
_{i}number of 1D building structures.

## 3. Calculation Method for the Analysis of Point Thermal Bridges

#### 3.1. Description of Samples Used in the Calculation Method of Point Thermal Bridges

_{N}= 0.32 W/ (m

^{2}. K) according to our standard [31]. With the increasing demands on the energy efficiency of buildings, the requirements for the elimination of heat losses through the passage of heat through the heat exchange envelope also increased. Therefore, it was necessary to eliminate all the thermal bridges, whether the linear or the point thermal bridges. Due to the more demanding thermal engineering requirements after 2016, these anchoring brackets had to be modified to eliminate the point thermal bridges, which also increase heat losses due to heat transfer. The heat transfer coefficient after 2016 is U

_{N}= 0. 22 W/ (m

^{2}.K) according to our standard [31]. These anchor brackets were supplemented with polypropylene pads (Figure 4). This solution is economically less advantageous because it is another built-in element. In addition, with such a solution, there is also a more significant initial investment for the anchoring console.

_{i}= 23.05 °C, and the exterior temperature θ

_{e}= −15.22 °C. The resistance to heat transfer through the structure is R

_{si}= 0.13 m

^{2}. K/W a R

_{se}= 0.04 m

^{2}. K/W. These temperatures characterize the steady-state temperature during the measurement of the heat flux in the climate chamber (Figure 17). The thermal conductivity of a plastic-coated anchor is not easy to measure. Various devices from the Department of Materials Engineering at the Faculty of Civil Engineering in Bratislava were also used. To determine the thermal conductivity, it would be necessary to measure only the material itself in a climate chamber. The climate chamber was first used in the 1970s [32]. Homogeneous samples and later inhomogeneous constructions were solved first [33]. This author developed general rules for the construction of the chamber climate and also proposed a procedure for assessing heat loss. Among other things, the surface materials of the individual samples are also important [34]. In addition to the material used to plasticize the anchor, the thickness of the plastic applied to the anchor certainly has a significant effect. This will be the subject of further investigation. The description of individual variants is shown in Table 2.

#### 3.2. Calculation Analysis of Individual Variants

_{si}-values (linear thermal transmittance) and F

_{rsi}-values (temperature factor), producing a comprehensive report in accordance with the requirements of the international standards. The finite element mesh calculation is performed in accordance with EN ISO 10211 [8]. Boundary conditions according to BR497 and Passive House are available in the boundary condition tables.

#### 3.2.1. Hilti Anchor Analysis without Interrupting Point Thermal bridges

#### 3.2.2. Analysis of an Anchor from Hilti with the Break of Point Thermal Bridges—A Technical Solution from Hilti

#### 3.2.3. Analysis of an Anchor from the Hilti Company with Break of Point Thermal Bridges—Technical Solution of the Author of the Article (Patent)

#### 3.2.4. Comparison of Results for Individual Variants

#### 3.3. Influence of Point 3-D Thermal Bridges on Heat Losses through Heat Transfer for Different Variants of Ventilated Façade by Rockwool

^{2}. K) [31]. Even when using one anchor, the given perimeter wall does not meet the current thermal engineering requirements. One possible solution is to add a thicker insulation (Figure 10) or use anchors with thermal breaks. With a thermal insulation thickness of 140 mm and the use of one anchor, the heat transfer coefficient is from 0.26 W/ (m

^{2}. K) to 0.27 W/ (m

^{2}. K). For the given analysis of the influence of point thermal bridges on the total heat losses, a real administrative building with a ventilated façade was selected (Figure 11). The building was built of monolithic reinforced concrete with a thickness of 200 mm and insulated with mineral wool hr. 180 mm, which is part of the ventilated facade. The floor area of the administrative building is 335.8 m

^{2}, and the heated volume is 1074.56 m

^{3}(Table 5).

^{2}(Table 5). When applying three anchors, the saving is EUR 254.82. When applying six anchors per 1 m

^{2}, the saving is EUR 509.65. If we had a building with 10,000 m

^{2}of wall area where six pieces of anchors per 1 m

^{2}are applied, the savings would be EUR 16,200. Such savings are already significant. The savings are calculated using only a simple method without taking into account inflation, which is unfavorable this year. This would mean that the real savings would be much greater. These calculations can be applied to other buildings whose load-bearing structure is built of reinforced concrete and ventilated facade.

## 4. Experimental Method for the Analysis of Point Thermal Bridges

#### Experimental Measurements

^{2}at the moment when the plate emits 1 mV.

## 5. Discussion

## 6. Conclusions

^{2}. K). When using one anchor element, the thermal conductivity coefficient increases to 0.585 W/ (m

^{2}. K). If we use a plastic washer for a given anchoring element, we will increase the heat transfer coefficient to the value 0.543 W/ (m

^{2}. K). This means this is an increase of 26.57% compared to the composition of the circumferential shell without the anchoring element applied. This variant is divinely available, but as it uses other material and it is a plastic pad, its value increases as significantly as its impact on the environment. The last variant was a proposal (patent) that the anchoring element is only plastic-coated and thus its thermal engineering properties are improved, which is manifested mainly in heat conduction but also from the radiant point of view, as plasticizing the emissivity changes. Compared to the perimeter cladding without the application of an anchoring element, the heat loss increases by 29.37%. The difference between the anchoring element with a thermal insulation pad and the patented method is minimal. This is a 1.29% difference. This difference is negligible as the patented modification achieves a significant economic and technological effect. While the plastic pad costs about EUR 0.3 [3-D], the plastic coating represents a price of around EUR 0.03. These costs are directly related only to plastic coating without management and logistics. The service life of the plastic coating is guaranteed by the manufacturer for 53 years without damage, which means significant savings when using six pieces per square meter on major buildings with a significant area of the perimeter. Every innovation must be technically as well as economically advantageous. This innovative solution has positive results in the technical but also the economic field. The innovative solution saves the production of materials and at the same time saves energy in buildings. These features contribute to a sustainable architecture.

## 7. Patents

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Example of a ventilated façade concept. (

**a**) Anchoring a suspended façade; (

**b**) the principle of operation of a ventilated façade [11].

**Figure 2.**Example point thermal ventilation of the façade. (

**a**) Aluminum anchor with a plastic pad; (

**b**) method of attaching the tile [30].

**Figure 3.**Analyzed anchor HILTI MFT-MFI M. (

**a**) Application of the anchoring element to the perimeter wall; (

**b**) anchor dimensions in millimeters [30].

**Figure 4.**Analyzed anchor with polypropylene pad HILTI MFT-MFI M—the size of the anchor with pad in millimeters [30].

**Figure 5.**Analyzed HILTI MFT-MFI M anchor with surface plastic coating. (

**a**) Display of plastic-coated anchor; (

**b**) dimensions of the plastic anchor in millimeters [30].

**Figure 7.**Analyzed model with dimensions 0.5 × 0.5 m with anchor. (

**a**) Variant shown also with boundary conditions; (

**b**) Display of boundary conditions and anchors.

**Figure 8.**Analyzed model with dimensions 0.5 × 0.5 m with anchor. (

**a**) Variant shown also with boundary conditions; (

**b**) Display of a Variant 4 from an experimental measurement.

**Figure 9.**View of a 3-D model of load-bearing part with anchors. (

**a**) The structure; (

**b**) plastic pad for thermal bridge break and anchors from HILTI.

**Figure 10.**Dependence of the heat transfer coefficient of the structure for a thermal insulation thickness of 140 mm and 200 mm.

**Figure 13.**A climate chamber (Climatic Chamber) with the production name CLIMA TEMPERATUR SYSTEME (hereinafter referred to as CTS).

Material Number | Material Description | Thermal Conductivity λ in W/ (m. K) | Comment |
---|---|---|---|

1. | OSB board hr. 22 mm | 0.20 | Data were used from the material manufacturer. |

2. | Anchor—from HILTI | 160 | Data were used from the material manufacturer. |

3. | Pad thermal barrier—Hilti. | 0.117 | Data were used from the material manufacturer. |

4. | Polystyrene foam EPS F | 0.039 | Data were used from the material manufacturer. |

5. | Plastic coated anchor | 49 ^{1} | Patented application of the author of this work. |

^{1}Thermal conductivity was expressed from experimental measurements—Section 4.

Variant | Description | Variant Image | Comment |
---|---|---|---|

1. | Variant without the use of an anchoring element | No anchor was used in the given variant. | |

2. | Anchor without modifications to eliminate the thermal point 3-D bridge. | The anchor material is made of aluminum with high thermal conductivity. | |

3. | Anchor with modification to eliminate thermal point 3-D bridge. | The anchor material is made of aluminum with high thermal conductivity and with the interruption of the thermal bridge by means of a pad. | |

4. | Anchor with modification to eliminate thermal point 3-D bridge. | The anchor material is made of aluminum with high thermal conductivity and with interruption of the thermal bridge by means of plastic coating of the anchor. This proposal is the property of the author of the work. |

Variant | Heat Transfer Coefficient U in W/ (m ^{2}. K). | The Difference between the Simulated Values Relative to the Variant no. 1 in % | Comment |
---|---|---|---|

1. | 0.429 | 0 | - |

2. | 0.585 | 36.36% | This is a calculation of the increase from the value of the first variant (0.429–100% and 0.585–136.36%). Increase the heat transfer coefficient is 36.36% |

3. | 0.543 | 26.57% | This is a calculation of the increase from the value of the first variant (0.429–100% and 0.543–126.57%). Increase the heat transfer coefficient is 26.57% |

4. | 0.550 | 29.37% | This is a calculation of the increase from the value of the first variant (0.429–100% and 0.550–129.37%). Increase the heat transfer coefficient is 29.37% |

Variant | Description of the Supporting Structure | Thermal Insulation | Thermal Insulation Thickness in mm | Number of Anchors |
---|---|---|---|---|

1. | Reinforced concrete structure (λ = 1.58 W/ (m. K)) 200 mm | Thermal insulation (λ_{D} = 0.033 W/ (m. K)) | 140, 200 | 0, 1, 2, 3 |

2. | Reinforced concrete structure (λ = 1.58 W/ (m. K)) 200 mm | Thermal insulation (λ_{D} = 0.035 W/ (m. K)) | 140, 200 | 0, 1, 2, 3 |

Geometry of the Building | Values |
---|---|

Total floor area A in m^{2} | 335.8 |

Total built-up volume V in m^{3} | 1074.56 |

Construction height h in m | 3.2 |

Total heat exchange envelope in m^{2} | 693 |

Shape factor | 0.64 |

Area of wall in m^{2} | 314.6 |

Number of Anchors | Heat Loss in W/K | Percentage Increase to 0 Number of Anchors in% |
---|---|---|

0 | 54.74 | - |

1 | 70.16 | 28.16 |

2 | 87.46 | 59.77 |

3 | 100.67 | 83.90 |

Number of Anchors | Energy Need for Heating in kWh/ (m^{2}. a) | Percentage Increase to 0 Number of Anchors in% |
---|---|---|

0 | 34.81 | - |

1 | 39.48 | 13.41 |

2 | 43.53 | 25.05 |

3 | 46.64 | 33.98 |

Variant | Description of the Variants | Heat Flow q in W/m^{2} | Temperature Difference ΔT | Heat Transfer Coefficient U in W/ (m^{2}. K) |
---|---|---|---|---|

2. | Anchor without modification to eliminate thermal point 3-D bridge. | 2.32 | 38.616 | 0.578 |

3. | Anchor with modification to eliminate thermal point 3-D bridge. | 20.703 | 38.553 | 0.537 |

4. | Anchor with modification to eliminate thermal point 3-D bridge. | 21.052 | 38.744 | 0.543 |

Variant | Heat Transfer Coefficient U in W/ (m ^{2}. K). | The Difference between the Calculated Values Relative to the Variant n. 3 in% |
---|---|---|

2. | 0.578 | - |

3. | 0.537 | - |

4. | 0.543 | 1.117 * |

Variant | Heat Transfer Coefficient U in W/ (m ^{2}. K) from Experimental Measurement | Heat Transfer Coefficient U in W/ (m ^{2}. K) from 3-D Simulation | Increase the Heat Transfer Coefficient in% |
---|---|---|---|

3. | 0.537 | 0.543 | 1.117 * |

4. | 0.543 | 0.550 | 1.289 * |

Variant | Heat Transfer Coefficient U in W/ (m ^{2}. K). | The Difference between the Calculated Values Relative to the Variant n. 1 in% | The Difference between the Calculated Values Relative to the Variant n. 2 in% |
---|---|---|---|

1. | 0.429 | 0 | - |

2. | 0.585 | 36.36 * | - |

3. | 0.543 | 26.57 * | 7.73 * |

4. | 0.550 | 29.37 * | 6.36 * |

Variant | Heat Transfer Coefficient U in W/ (m ^{2}. K). | The Difference between the Calculated Values Relative to the Variant n. 1 in% | The Difference between the Calculated Values Relative to the Variant n. 3 in% |
---|---|---|---|

1. | 0.429 | 0 | - |

2. | 0.585 | 36.36 * | - |

3. | 0.543 | 26.57 * | - |

4. | 0.550 | 29.37 * | 1.29 * |

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**MDPI and ACS Style**

Ingeli, R.; Gašparík, J.; Paulovičová, L.
Impact of an Innovative Solution for the Interruption of 3-D Point Thermal Bridges in Buildings on Sustainability. *Sustainability* **2021**, *13*, 11561.
https://doi.org/10.3390/su132111561

**AMA Style**

Ingeli R, Gašparík J, Paulovičová L.
Impact of an Innovative Solution for the Interruption of 3-D Point Thermal Bridges in Buildings on Sustainability. *Sustainability*. 2021; 13(21):11561.
https://doi.org/10.3390/su132111561

**Chicago/Turabian Style**

Ingeli, Rastislav, Jozef Gašparík, and Lucia Paulovičová.
2021. "Impact of an Innovative Solution for the Interruption of 3-D Point Thermal Bridges in Buildings on Sustainability" *Sustainability* 13, no. 21: 11561.
https://doi.org/10.3390/su132111561