Experimental and Numerical Thermal Analysis of Joint Connection «Floor Slab – Balcony Slabe» with Integrated Thermal Break

Available online at www.sciencedirect.com

ScienceDirect Energy Procedia 85 (2016) 184 – 192

Sustainable Solutions for Energy and Environment, EENVIRO - YRC 2015, 18-20 November 2015, Bucharest, Romania

Experimental and numerical thermal analysis of joint connection «floor slab – balcony slabe» with integrated thermal break Kostiantyn Dikareva*, Anatoliy Berezyuka, Oleksandra Kuzmenkoa*, Al’ona Skokovaa a

Prydniprovska State Academy of Civil Engineering and Architecture, Chernyshevskogo str.24a, Dnipropetrovsk,49000, Ukraine

Abstract The present paper was concerned with study of concrete connection with thermal partitioning using reinforced thermal break. The results of a building diagnostics inspection with a thermal imaging camera are represented below. Thereby such building failures as thermal bridges were identified in the connection area between balcony and floor slab. The thermal behavior of a balcony board with integrated reinforced insulating elements is investigated by means of measurement as well as numerical analysis. For this reason a specimen consisting of an externally insulated brick wall and a part of a balcony is tested under a steady state temperature gradient of 34°C in an impermeable box. In accordance with the normative requirements temperature sensors are placed on critical sites within the construction and on its surface, prior to the pouring of cement. At the same time numerical analysis was realized using Fluent ANSYS workbench. Measured and calculated results are compared and degree of thermal break efficiency is explored. ©2015 TheAuthors. Authors. Published by Elsevier Ltd. is an open access article under the CC BY-NC-ND license © 2016 The Published by Elsevier Ltd. This Peer-review under responsibility of the organizing committee EENVIRO 2015. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee EENVIRO 2015 Keywords: Insulation; thermal partitioning; thermal imaging camera; insulating box; concrete

1. Introduction Currently the ideas of sustainable and energy efficient building design have become dominant in construction practice. Almost all the European countries continue to introduce strict requirements concerning envelope thermal performance of buildings. [1-4]

* Corresponding author. Tel.: +38-050-955-3900; Tel:+38-095-876-7729. E-mail address: [email protected], [email protected].

1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee EENVIRO 2015 doi:10.1016/j.egypro.2015.12.325

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These include requirements to increase thermal resistance of the walls, roofs and floors. Adding insulation to the building is one obvious way to do this, but insulation is not effective if there are easy heat flow paths around it. This is why codes and standards are progressively moving to requirements based on Effective Thermal Resistance, which requires identifying and minimizing thermal bridges in the building envelope. [5-7] A thermal bridge is a localised area of the building envelope where the heat flow is increased in comparison with adjacent areas. The connections of structural elements are typical structural thermal bridges. In practice, this connections often lead to additional heat losse and low surface temperatures in the room. Furthermore structural thermal bridges could provoke condensation and mold formation. [8] The problem of thermal bridging have fascinated many authors and some of them studied this phenomenon in their doctoral thesis [9-10]. Previous researches were focused on heat transfer through thermal break [11-12]. And other scientists explored effective solutions like load-bearing thermal insulation elements such as Schöck Isokorb [13]. Unfortunately, in Ukraine, only a small number of researchers are engaged in the problem of thermal bridging. [14] Furthermore innovative building products such as Halfen or Schöck Isokorb are not accepted in Ukraine. So scientific team of PSACEA elaborated own technical solutions in accordance with Ukrainian Building Codes [15] and basing on rich european experiance in eliminating of thermal bridges. Proposed thermal break solution is patented in Ukraine. [16] Thermal behavior of those construction details was investigated in cooperation with the Romanian colleagues in CAMBI Research centre, Technical University of Civil Engineering in Bucharest. 2. The results of a building diagnostics inspection in Dnipropetrovsk (Ukraine) and Bucharest (Romania) using a thermal imaging camera Testo. A thermal imaging camera records the intensity of radiation in the infrared part of the electromagnetic spectrum and converts it to a visible image. A building diagnostics inspection with a thermal imaging camera allowed us to identify and locate thermal bridges and also to visualize energy losses. The investigations were provided in accordance with [17]. The difference between the temperature indoors and the temperature outside was 14…35°ɋ. The results are presented in Table 1. Table 1. The results of a building diagnostics inspection in Dnipropetrovsk (Ukraine) and Bucharest (Romania) Dnipropetrovsk, Ukraine Photography

Thermal image

T, °ɋ

1 M1=-13,5 HS1=-0,1 HS2=-5,6

Bucharest, Romania 2 M1=7,9 Ɇ2=7,9 Ɇ3=7,2 HS1=9,4

Analyzing the results of inspection we can assume that concrete connection «floor slab – balcony slab» contain thermal bridge. This hypothesis proved by the temperature difference from 2,2 to 13,4°ɋ between main surface of construction and the area of balcony connection.

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3. Case study and general assumptions The fragment of concrete connection «floor slab – balcony slab» was selected for the analysis. Two types of this concrete connection were examined during the experiment. In the first case we investigated a model of a conventional balcony board connection with floor slab (a continuous steel reinforce concrete slab), as shown in Fig. 1(a). In the second case we studied a model of the same concrete connection interrupted by a thermal break, as shown in Fig. 1(b). Both samples were put into guarded boxes made of cellular polystyrene.

a)

b)

Fig. 1. (a) specimen including a model of the conventional balcony board connection with floor slab; (b) specimen including a model of the concrete connection interrupted by a thermal break

The both specimens used for the measurement in the guarded hot box were built in several stages. At a first stage a fragment of concrete beam was constructed. After that the insulating element was assembled within a wooden formwork (case with thermal break). Then the thermocouples were fixed with thermal transfer ribbon. Fig. 2 shows the thermal break, the reinforcement steel rods and some of the thermocouples. The latter were fixed on critical sites on both the cold and the warm side of the structure.

Fig. 2. Thermal break, the reinforcement steel rods and some of the thermocouples

An overview of the thermocouple positions is given in Fig. 3(a) and Fig. 3(b). Then, cement was poured into the formwork. Further a brick wall was built up. The dimensions are also indicated in Fig.3. A layer of 10 mm of external insulation (expanded polystyrene) was applied to the cold side of the brick wall. Other thermocouples were placed on the surface of the sample and between the brick wall and the insulation layer. In the case with conventional concrete connection thermal break is absent but the thermocouples are placed in the same points as in the specimen with insulating element (Fig. 3 (b)).

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Fig. 3. (a) dimentions of the sample with thermal break and disposition of the thermocouples; (b) dimentions of the sample without thermal break and disposition of the thermocouples

The whole sample with thermal break is represented in Fig. 4(a). Fig. 4(b) shows guarded insulating box which was used for the experiment.

Fig. 4 (a)whole sample with thermal break; (b) guarded insulating box which contain the sample

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4. Numerical thermal analysis of the specimen using Fluent ANSYS workbench The numerical analysis was carried out by Fluent ANSYS workbench, a program to calculate the threedimensional steady state temperature distribution and heat transfer. The numerical approach permitted also to verify required dimensions of the concrete samples in order to avoid distortion of the temperature field caused by edgeeffects during the experiment. Details of the model used to simulate the hot box measurement are given as well in Fig. 1 and in Fig. 2. The thermal conductivities of the materials are summarized in Table 2. With the purpose to obtain temperature difference of 34 °ɋ we imposed 11 °ɋ on the cold side and 45 °ɋ on the hot side. Heat transfer coefficient for interior surface is Įint=8,7 W/m2·Ûɋ and for exterior surface Įint=23 W/m2·Ûɋ. The calculations were done by choosing an appropriate grid [7] resulting in approximately 180,000 nodes for the three-dimensional and 7,000 nodes for the two-dimensional calculation. Table 2. Characteristics of materials Thermal conductivity Ȝ W/mǜK

Density kg/m3

Thermal capacity J/(kgǜɄ)

Concrete

2,04

2500

840

2

Masonry of ceramic brick

0,58

1400

880

3

Polystyrene of thermal break

0,039

30

1340

4

Reinforcement steel

58

7850

482

5

External insulation of polystyrene

0,039

30

1340

ʋ

Material

1

Symbolic representation

In order to compare the system of balcony including thermal break with conventional balconies the both systems were analyzed. The results are represented below in Table 3. Table 3. Results of numerical modeling on ANSYS workbench The model of concrete connection «floor slab – balcony slab» without thermal break 3D models

The model of concrete connection «floor slab – balcony slab» containing thermal break

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Section 1-1

Section 2-2

Distributions of temperature values in the section 2-2 (Fig.3) of the both models are represented in Fig.5(a) and in Fig.5(b). b)

a) Fig. 5(a) distributions of temperature values in the section 2-2 for conventional concrete connection; (b) distributions of temperature values in the section 2-2 for concrete connection with thermal break

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The additional thermal heat loss, in other words the coefficient of linear thermal transmittance kj due to the thermal bridges, was calculated according to ref. [15]. Thereby for conventional concrete connection kj = 0,58 W/(mǜk), while this value for concrete connection with thermal break is kj = 0,12 W/(mǜk). 5. Analysis of experimental results Experimental results are represented in Fig. 6(a) and Fig 6(b). Disposition of corresponding thermocouples is represented in Fig. 7 (a), (b) and Fig. 8 (a), (b).Temperature values on the hot side are lower in the case of conventional concrete connection in comparison with the specimen with thermal break. At the same time temperature values on cold side are higher in the case of conventional concrete connection «balcony slab-floor slab». This phenomenon prove that the thermal break reduce transmission losses via thermal bridges situated in the connection area between balcony and floor slab.

a)

b)

Fig. 6(a) distribution of the interior temperature values of the both specimens; (b) distribution of the superficial temperature values of the both specimens

a)

b)

Fig. 7(a) disposition of the interior thermocouples in the specimen of conventional concrete connection; (b) disposition of the superficial thermocouples on the specimen of conventional concrete connection

Kostiantyn Dikarev et al. / Energy Procedia 85 (2016) 184 – 192

a)

b)

Fig. 8(a) disposition of the interior thermocouples in the specimen with thermal break; (b) Disposition of the superficial thermocouples on the specimen with thermal break

The temperature difference between value of sensor ʋ 2 located on hot side of the thermal break and sensor ʋ 10 situated in the same point into the sample of conventional concrete connection reaches 8 °ɋ. In other words the presence of thermal break assure higher temperature on the hot side of concrete connection and protect this zone from heat losses. The energy saving effect of thermal break application proved by temperature values of sensors situated on cold side of both simples. Thereby the temperature values on cold side of the thermal break are lower then the values of sensors placed in the same points of the conventional concrete connection simple. 6. Conclusions The paper was dedicated to the experimental and numerical investigations of reinforced insulating element thermal behavior in comparison with conventional concrete connection. The results of numerical modeling were found to be sufficiently in good agreement with the experimental simulations. The obtained temperature values prove the advantage of reinforced insulating elements over conventional balcony boards from a thermal point of view. The present result is very promising and offers possibilities to develop in the future more detailed studies of thermal break in order to perfect mentioned technical solution. Acknowledgement Research carried out in the framework of the Scholarships Program "Eugen Ionescu" granted by Francophony University Agency (AUF BECO) and Ministry of Foreign Affairs of Romania. The authors acknowledge the support and advices of Professor Florin Baltaretu and Associate Professors Cristiana Croitoru, Illinca Nastase and Florin Bode of Building Services Engineering Faculty of Technical University of Civil Engineering . References [1]. Scientific and technical building centre. Ministry of ecology. France (2011). French standard: Method of calculations Th-BCE 2012. 1377 p. [2]. Public service of law distribution (2010) Réglamentation thermique 2012. Paris : Cahiers Techniques du Bâtiment n°300. [3]. Ministry of Transport, Constructions and Tourism. Romania. (2010) Modifications of the technical regulation «Thermotechnical calculation standard of constructive elements of building», indicative ɋ 107-2005. Bucharest: Government Publishing Service. [4]. Ministry of Regional Development and Construction. Ukraine. (2013) Order of the Ministry of Regional Development and Construction of Ukraine from March ʋ 82 «Changes No 1 DBN V.2.6-31 : 2006 « Thermal insulation of buildings». Kiev: Government Publishing Service. [5]. Scientific and technical building centre. (2013) Mise en oeuvre des rupteurs de ponts thermiques sous avis techniques. Guide en cadre de programme «Règles de l’Art Grenelle Environnement 2012». NEUF. [6]. Technical Committee ISO/TC 163. ISO 14683, Thermal bridges in building construction — Linear thermal transmittance — Simplified methods and default values. [7]. Technical Committee ISO/TC 163. ISO 10211:2007, Thermal bridges in building construction — Heat flows and surface temperatures — Detailed calculations [8]. Innovative building solutions. Schock. From: http://www.schock-us.com/

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[9]. ThiThanh Huyen NGUYEN. (2012). Analyses of the thermal breaks behavior under seismic loading. Doctoral dissertation, Ecole normale supérieure de Cachan, Cachan, France. [10]. Kaemmerlen Aurélie. (2009). Heat transfer through the building's thermal insulation. Doctoral dissertation, Henri Poincaré University, Nancy, France. [11]. Karim Ghazi Wakili, Hans Simmler, Thomas Frank. (2007). Experimental and numerical thermal analysis of a balcony board with integrated glass fibre reinforced polymer GFRP elements. Energy and Buildings 39, p 76–81. [12]. Kyriaki Goulouti, Julia de Castro, Anastasios P. Vassilopoulos, Thomas Keller. (2014). Thermal performance evaluation of fiber-reinforced polymer thermal breaks for balcony connections . Energy and Buildings 70, p 365-371. [13]. Umniakova, N.P., Egorova, T.S., Andreitseva, K.S. (2013). Innovative construction connection of balcony slab with floor slab and external wall. Moscow: Building materials, p 28-31 [14]. Kuznetsova, O.O. (2013). Simulation of thermal bridge influence on building envelope thermal resistance. Herald of the Kiev National University of Technology and Design, p 126-135. [15]. Ministry of Constructions and Architecture. Ukraine.(2006). Building standard of Ukraine. Thermal insulation of buildings. Kiev: Govenment Publishing Service. P 71. [16]. Berezyuk, A.M. , Dikarev, K.B., Skokova A. O., Kuzmenko, O.M. (2014). Ukraine. Patent No 95485. Kiev: Ukraine. State Service of Intellectual Property. [17]. EN 13187:1998 Thermal performance of buildings. Qualitative detection of thermal irregularities in building envelopes. Infrared method. Technical Standard