Paper Title (use style: paper title)

GSTF Journal of Engineering Technology (JET) Vol.4 No.3, August 2017

I.

PROBLEMS OF THE CONTACT WINDOW STRUCTURE AND BUILDING ENVELOPE

Dušan Katunský / Miloslav Bagoňa Department of Architecture and Building Structures Institute of Architectural Engineering, Faculty of Civil Engineering, Technical Universtity of Košice Košice, Slovakia [email protected], [email protected]

Martin Lopušniak Department of Building Physics Institute of Architectural Engineering Faculty of Civil Engineering, Technical University of Košice, Slovakia [email protected]

Abstract — Different behavior of the construction materials in dynamic boundary conditions causes deformations of thermal field of the window structure detail in envelope structure. Numerical thermal field analysis verified by the experimental measurement in experimental outdoor chambers is used for recognize the real heat-air-moisture behavior in the various structures. Window sill of brick walls is one of the most critical places in a connection of two envelope types objectively. If there are the transparent and opaque parts present together, the connection is much more complicated.

are suitable for comparison of experimentally obtained values with results of numerical experiments. Numerical analysis using computer simulation represents the effective method of exploration of window structure seating depth impact on degree of deformation of analysed thermal field.

Thermal field; numerical analysis; measuring; window sill; experimental chamber

II.

INTRODUCTION

The subject of transient numerical analysis and results of experimental measurement of temperature in the construction is the same construction detail of window and brick wall connection of window sill in the both cases. The detail selection is determined by its inhomogeneity – changing material properties and geometry of this place. Considered construction is a fragment of an envelope of the outdoor experimental chamber for in situ measurement. The objective is results comparison of temperature in construction gained by measurement and numerical calculation. Simulation and measurement are standard scientific methods to predict the thermal, physical performance of building elements [1]. It was compared to the northern and southern orientation to the cardinals of the chamber´s wall (Fig 1). The paper deals also with the effect of window structure depth in window lining on the deformation of thermal field. The contact of window structure with the wall (referred to as the connecting joint of window) represents a complicated thermal binding. The connection of different structural elements as to the materials and geometry causes significant deformation of thermal field.

3,2,1,chambers(No.3-left,No.2-middle,No.1-right)

Several papers [1, 2, 3] devote to problems of seating the window structure into the window opening. Results of panel research of the experimental wall structure with a window are presented in paper [4]. The numerical experiment has shown good conformity between measured and calculated values of surface temperatures on the connecting joint. Devices of the type of experimental internal and external chambers with adjustable environment, examples are given in papers [5, 6, 7],

Figure 1.

III.

The situation of experimental chambers.

WINDOW STRUCTURE AND EXTERNAL WALLS

Solved are two places (Fig. 5,6) in position of window sill. There is a heat flow deformation and thus decrease of inside

DOI: 10.5176/ 2251-3701_4.3.207 74

© The Author(s) 2017. This article is published with open access by the GSTF


surface temperature in detail of a window sill. Alternative depths of window structure seating are analysed by the numerical experiment using the computer simulation of thermal field. The objective of analysis is to optimize the window structure seating depth in the existing experimental wall. The effect of deformation amount of thermal field of analyzed contact on the course of surface temperatures and thermal coupling coefficient of the binding has also been analysed. From the point of view of building physics, the thermal bridge can be quantified by the change in heat flow (linear thermal transmittance) and change in inside surface temperature (fulfilment of hygienic criterion). Surface temperature (or temperature factor) is the only assessment parameter of thermal bridges in case of absence of requirements for the value of linear (point) thermal transmittance for design of building structures and buildings. Minimum temperature of inside surface of non-transparent (opaque) structures and their parts must be θsi [8]:

Figure 2.

temperature safety addition. Minimum surface temperature of transparent structures (frames, non-transparent and transparent opening panels) in areas with relative air humidity up to 50% must be θsi,w [8]: θsi,w > θsi,w,N = θdp

(2)

Where: θsi,w,N (°C) minimal required inside surface temperature value of transparent envelope parts, θdp (°C) dew point temperature, θsi,w (°C) inside surface temperature of transparent envelope part. The required normalized value of inside temperature of openings should be determined taking into account the average ambient temperature of the coolest month in the year for the locality of the On the contrary, the normalized value of inside surface temperature of non-transparent parts should be determined from the calculation temperature of ambient air in winter according to the locality of the building.

View and cut contact wall with window in chamber

Deformation of thermal field is manifested by formation of socalled thermal bridges in the building envelope.

Figure 3.

Floor plan contact wall with window

θsi ≥ θsi,N = θsi,80 + Δθsi

(1)

Where: θsi,N (°C) minimal inside surface temperature, θsi,80 (°C) critical mould growing risk temperature, Δθsi (K)

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Figure 4. Connection of window, building envelope fragments – window sill HELUZ, YTONG A – before thermal insulation B – after external insulation and plaster

Display of measured sensors in windows details in chamber I (southern orientation) and chamber II (northern orientation)

Figure 5.

However, in our case we will consider in both cases actually measured values of the temperature of ambient air during the monitored period. The surface temperature should be determined by calculation of thermal field of a critical detail. Calculation of heat flows and surface temperatures is carried out using models according to [10], simplified according to standard under determined conditions. Numerical calculation of thermal field can be carried out as simplified one (stationary) or accurate one (transient) [5]. For the correct use of dynamic – transient numerical model it is inevitable to know and to use correct boundary and initial conditions of calculation and declared verified material parameters. Optimizing of structural design – in this case the position of seating of the window structure at the point of sill of bricked wall – is one of numerous applications of transient numerical experiments.

Modification of the calculation model represents a simple method how to analyse suitability of distribution of temperature of alternative designs of the structure. Methods of seating window structure reflect the current state of the art. The optimum solution is to locate the window structure in the plane of inside edge of thermal insulation layer of the external wall. This solution minimizes heat flow. However, the precise position (even within the framework of thermal insulation layer) depends on the quantity of structural, thermal-technical, technological and material aspects of these elements of the envelope that can be very precisely taken into an account by the transient calculation [11]. A. Construction of connection wall and window It is a fragment of the building envelope construction of the experimental chamber wall. The experiment has been carried out on the detail of sill and external wall of envelope of experimental chamber. Composition of the brick wall construction is in Table 1. Measured sensors for humidity and temperatures can be seen at figures 5, 6. The objective of this analysis is to compare three alternative positions of the depth of window structure seating at the point of sill of bricked wall from the point of view of optimum solution of thermal field. But the numerical calculation was also carried out for the purpose of monitoring other aspects. First and foremost this is for the confirmation of correctness of seating in accordance with the current state of the art using the transient calculation. It is necessary to quantify the change in surface temperature at the point of connection of the window and bricked structures and to ascertain its significance for selected alternative solutions. Then it is necessary to localize a point with the lowest surface temperature based on solutions of thermal field. It is also necessary to confirm or to disprove the hypothesis that the aforementioned point is just the place of connection of the window and bricked structures. If it has been demonstrated that the point with the lowest surface temperature is different in this detail, it will be necessary to ascertain, whether alternative solutions of the window structure seating depth have any effect on surface temperature of this point within the thickness of the detail. B. Analysis of the numerical solution The solution includes a detail of connection of the window in the seating joint at the point of sill. Heat transfer in time (for homogeneous and isotropic structures) is described by the Fourier second partial differential equation for heat transmission: Composition of the brick wall construction is in Table 1 and Fig. 2. Computed thermal transmittance of the opaque wall part is U = 0.12 W/m2K. The window frames construction made by plastic composite material without frame reinforcement (Uf = 0.86 W/m2.K). Triple glass system of 4-124-12-4 Ar (Ug = 0.55 W/m2.K) is applied Transient calculation is made in Physibel software, module BISTRA.

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The energy balance method is used to set up a system of linear equations. The system is solved using a fast and accurate iteration procedure. Transient simulations are solved using the Crank-Nicolson finite difference method. This method meets the criteria of the standard STN EN ISO 10211 Annex A, for software computing method [11]. The experiment has been carried out on the detail of sill of AAC bricked envelope structure of an outer experimental chamber for measuring physical properties. This chamber is an integral part of laboratories of the Civil Engineering Faculty of Technical University in Košice. The brickwork is thermally insulated with the contact system on the basis of graphite polystyrene.

been carried out with the objective of obtaining and comparing values of inside surface temperature for assessed points A and B, Fig. 1. This is the point (A) in the corner with the connection of extension (base) frame section of window and brickwork and the point (B) in the corner with the connection of extension frame section to the window frame. Three alternatives of the window structure at the point of sill have been selected. Alternative 1 – seating in the plane of brickwork.

Alternative 2 – seating in the plane of thermal insulation (seating of the plane of inner edge of the extension frame Figure 6.

Solved places in connection of window sill and window structure.

TABLE I. COMPOSITION OF THE STRUCTURE (LAYERS ARE STATED IN THE DIRECTION FROM INTERIOR)

C. Measuring methodology Windows, brick walls and places of their connection (window sill, jamb) are monitored. The data in two measuring points of window sill of a two experimental chambers with different (northern and southern) orientation to the cardinals are monitored in this case. The points are A2/15 and A2/11 in chamber no.1 (southern orientation) and points A2/7 and A2/5 in chamber no.2 (northern orientation). The calculation has

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section into the plane of inner edge of the thermal insulation).

D. Numerical analysis The numerical calculation of transient two dimensional thermal field of window sill detail is realized to solve the temperature results of the points (A2/15, A2/11 and A2/7, A2/5). As the boundary conditions are used measured local climate and indoor data, Fig. 7. Transient calculation with solar radiation influence is made in Physibel software, module BISTRA. The energy balance method is used to set up a system of linear equations. The system is solved using a fast and accurate iteration procedure. Transient simulations are solved using the Crank-Nicolson finite difference method. This method meets the criteria of the standard STN EN ISO 10211 Annex A, for software computing methods. IV.

BOUNDARY CONDITIONS

In the analysis was chosen winter period, a week of January 2013 (01.01 - 08.01.2013) The winter season has been selected for demands of the calculation due to examination of fulfilment of requirement for the minimum inside surface temperature during the heating season according to the conditions. Hourly measured values of temperature of ambient air were used for the locality of Košice for the period from January 1, 2013 to January 8 2013. Ambient temperatures ranged from -6.5 to +7.1°C, the average temperature was -1.0 °C. The temperature measured in the experimental chamber during the monitored period was used as the inside temperature boundary condition. The average temperature of inside air in the chamber (northern orientation) is 19.1°C (Fig. 8). Temperature of inside air 20 °C and temperature of ambient air -13 °C are normalized conditions of the inside and ambient environment.

Alternative 3 – seating in the plane of thermal insulation with embedding by 27 mm (seating of the plane of inner edge of window frame into the plane of inner edge of thermal insulation).

in Fig . 8

Points of assesment A and B in the alternative details 1,2,3, of connection windows structure and window sill.

Figure 7.

Figure 8.

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in Fig . 9

Measured outside and inside boundary conditions in January 2013.



V.

RESULTS

A. Temperature results for chamber1 Course of the calculated and measured temperature at the time of assessment is almost identical results in both points (A2/15 and A2/11) Fig 12. Requirements for interior surface temperature at point “A” and at point “B” according to [11] have been met for all alternatives. Requirements were determined for the measured average interior air temperature (19.1°C) and for relative humidity of 50%. Fig. 12 and 13 illustrate courses of resulting values of interior surface temperature at assessed points “A” and “B” for selected alternative solutions with a hourly step. It follows for all alternatives from values at point “A” that Alternative 1 with the average temperature of 15.15 °C is the worst solution from the point of view of the surface temperature.

Figure 9. Course of temperature in the corner with connection of the extension (base) frame section and the brickwork (point “A” according to Fig. 7) for all alternatives of the window seating depth during the monitored period

Alternative 3 is more favourable, with the average temperature of 16.50 °C. Alternative 2 is the most optimum solution based on the selected criterion, i.e. seating the plane of inner edge of the extension frame section into the plane of inner edge of the thermal insulation. The average surface temperature at point “A” of this alternative solution achieves 17.37 °C. Results are of different nature at the second assessed point (“B”). First and foremost, it has been confirmed that there exists a point with lower value of surface temperature than the point “A”. This is at the point with connection of the window structure to the sill brickwork. The average temperature is lower here for all alternatives than in the previous case. It is interesting that differences for individual alternatives are minimal. The average temperatures are 14.96 °C for Alternative 1, 14.90 °C for Alternative 2 and 14.88 °C for Alternative 3. It follows, from presented results that the depth of seating has not any principal effect on the surface temperature at other points of the analysed detail. The effect of window seating depth is manifested mainly at the point with connection of the window structure to brickwork (“A”). The distribution of temperature in the assessed detail is closely related to the heat flow area density. It is obvious that at points with increased heat flow on the inside surface, the value of interior surface temperature will be low, Fig. 10.

Figure 10.

Distribution of thermal fields in alternatives 1,2,3.

B. Termal fields results The area thermal field from the transient calculation of presented solutions of analysed part 2.1 at 5 a.m., i.e. in time

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of the lowest recorded ambient air temperature during the monitored period that equals to -6.3 °C is given in Fig. 8. However, there exists a place with the lowest surface temperature at the corner with connection of the extension frame section to the window frame (“B”), but we will deal with the point “A”, i.e. with the point with connection of the window structure to the sill brickwork. Dependence between decreasing specific heat flow that is represented with the value of the linear thermal transmittance and the window seating depth has been shown a linear one in individual alternatives.

K. The computational model is thus significantly improved now.

This means that the closer the window is seated to the outer edge of non-transparent structure, the linear thermal transmittance is decreased at the point of connection of window to wall and the lower the value of heat flow through this point is. However, from the dependence between the window seating depth and the value of surface temperature it follows that the surface temperature is increased at this point only to a certain boundary. After exceeding this temperature, the geometry of detail causes that the surface temperature is decreased again, so additional shifting the window into exterior is not advantageous from this point of view [9]. Both dependences are depicted in Fig. 11.

Dependence between the linear thermal transmittance - X or surface temperature -Y and alternative solutions of window seating depth.

Figure 11.

The low value of interior surface temperature at points with increased heat flow on inside surface has been registered. The transient calculation has revealed that the increasing value of surface temperature has its peak depending on the decreasing value of linear thermal transmittance. The temperature is increased only up to a certain position of seating depth, and further decrease of heat flow represented by the decreasing value of linear thermal transmittance will not cause any additional improvement from the point of view of surface temperature, i.e. its increasing. The existence of such point creates a requirement for its accurate determination and finding of dependence between the thickness of structure or thermal insulation and specific heat flow and surface temperature. On the basis of the aforementioned dependence, it is possible to find the optimum depth of window seating. The seating of the window structure in the plane of zero isotherm is considered the optimum solution. From results of presented analysis it follows that such position of the window structure need not be optimum one from the point of view of surface temperatures. This is also conditioned by the overall geometry of structural detail. Both the effect of windows seating depth on surface temperature as well as heat flow is changed with the changing thickness of the external structure. It is necessary to analyse both quantitative and qualitative various details of external structures at the point of connection of windows, in order of creating a universal dependence between the window seating depth and the thickness of structure. The biggest difference between the measured (12,43 °C) and the calculated (14,44 °C) temperature of place A2/11 is 2,01 K on 06.01. at 0:16 am. At place A2/15 the biggest difference of measured (0,68 °C) and the calculated (3,40 °C) value is 2,72 K on 07.01. at 3:12 am. In recent work [2] has been the biggest difference of temperature in A2/15 even 7.81

Figure 12.

Measured and computed results for monitoring chamber 1.

Similarly as in chamber no.1 almost identical results in (A2/7 and A2/5) occur, Fig 13. Values are significantly different in the morning or when the daily temperature extremes, see Fig 8. Generally the biggest differences between the measured and calculated values occur on days with higher intensity of solar radiation.

Figure 13.

Measured and computed results for monitoring chamber 2.

Window in the chamber No 2 is oriented north - effect of a solar radiation is excluded. In place of A2/5 is the biggest difference between the measured (11,39 °C) and the calculated (12,34 °C) temperature 0,95 K on 05.01. at 12:00. Measured (1,15 ° C) and the calculated (2.22 °C) values with the biggest difference 3,37 K of A2/7 is on 07.01. at the 0:48 am, Fig 13.

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comparison of temperature results in construction shows regularity of simulation model, because of data compliance. Median is good quantitative parameter because is deprived of extremes. We have got the median differences of measured and calculated values from 0,2 K up to 1,0 K, in two different solved places in window sill construction of two different oriented experimental chamber´s walls. If we were not considered the solar radiation gains into an account, we will never get the correct results of southern oriented wall. We need to go far and improve the simulation model continuously to minimize or to avoid the differences. Errors and uncertainties in the calculation is caused by definition of material properties, initial material conditions, geometric subtlety, used boundary conditions and the uncertainty of numerical method. Advanced and verified simulation model allows us to solve different types of numerical experiments with a defined accuracy. The paper is related to knowledge published in [5, 6, 7]. It deals with looking for the optimum solution of seating the window structure into the wall. The original testing wall with a window [4] provided the information on validation of the simulation model that has become the base for optimizing. The optimizing is based on modification of the window structure seating depth in the existing testing wall structure with a window in the environment of simulation instrument. The numerical experiment allowed effective analysis of the window seating depth in the wall structure under real climatic conditions using the simulation instrument. The surface temperature and heat coupling coefficient at the point of seating joint and window according to scheme in Fig. 1 were considered criteria of optimizing [15]. It follows, from results of aforementioned analysis that the seating of the window structure in the plane of thermal insulation is correct. However, the precise position of seating depends on preferring the most favourable value of heat flow (linear thermal transmittance) or surface temperature. While heat flow is lower, if the window is seated closer to the exterior edge of sill brickwork, the surface temperature has the highest value in case of seating the plane of interior edge of extension frame section into the plane of interior edge of thermal insulation (Alternative 2). Alternative 2 represents the optimum solution by interaction of requirements for minimizing heat flow and maximizing the surface temperature. The aforementioned conclusion highlights complexness of problems of the optimum location of window structure in the building envelope, and extends possibilities of examination of problems with additional important factors affecting the quality of analysed detail. The geometry of interior sill, type and dimensions of interior sill board, position of heating device are additional aspects of the optimum position of the window structure. When using a suitable simulation instrument, it is possible to extend problems of optimizing the seating of window structures in building envelopes.

Measured results and comparison of Medians and Averages of computed and measured values in the points A2/15, A2/11, A2/5 and A2/7.

Figure 14.

Detailed analysis provides a comparison of medians and averages of measured and calculated values of temperature in the points, Fig. 14. In the averages and medians comparison can be seen that in both there is about the same differences in compared values. The best match (difference is 0,2 K) of the measured and calculated values is at point A2/5 (chamber no.2) The highest deviations (1,1 K) between these values are in point A2/7, paradoxically, in the same chamber. Variations of values in chamber no.1 are from 0,6 K (A2/15) to 0,9 K (A2/11). According to orientation to the cardinals of the experimental chamber's wall, we can recognize the higher compliance in chamber no.2. The mean of median differences of solved points is 0,6 K, while in chamber no.1 it is 0,75 K..Distribution of area thermal field in time of the lowest temperature of ambient air (on January 2, at 5 a.m.) and courses of isotherms of the lowest surface temperature (12,2°C) and dew point (8,4°C) of alternative solutions of the window structure seating depth at the place of sill. VI.

CONCLUSION

The facility used for in situ measurement allows results comparison of temperature in construction gained by numerical calculation. Verification and validation of computing simulation model is the key to resolve and predict the real hygrothermal (thermal) performance of building elements, details, constructions and its environment. The

ACKNOWLEDGMENT This contribution was created in accordance with the solution of the research project VEGA 1/0835/14 and VEGA

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Building Envelope Levels”, Advanced Materials Research, Vol. 649, 2013, p. 85-88 [5] D. Katunský, et al.. “Numerical Analysis and Measurement Results of a Window Sill”, Advanced Materials Research, Vol. 899, p. (2014) [6] M. Zozulák, “Creating a measuring procedure for monitoring physical parameters of packaging structures”, In: Young Scientist 2012: 4th PhD. Student Conference of Civil Engineering and Architecture: Košice, Slovakia, May, 2012. [7] D. Katunský, M. Vertaľ, M. Zozulák, “Experimentally Measured Boundary and Initial Conditions for Simulations”, Advanced Materials Research, 1041, 2014, pp. 293–296. [8] M. Vertaľ, D. Katunský, D. Buriková, “Moisture profile as initial condition for HAM analysis, Tepelná ochrana budov, 5/ 2012 pp. 13-16. [9] M. Zozulák, M. Vertaľ, D. Katunský, “Initial conditions determination for transient thermal field analysis”, In: CER Comparative European Research 2014: International Scientific Conference for Ph.D. Students of EU Countries : Proceedings : London : Sciemcee Publishing, 2014 pp. 74-78. [10] M. Zozulák, Temperature of the brick wall sill in dynamic conditions, Young Scientist 2013, Košice 2013 pp. 1-4. [11] Physibel Software – User Manual for Physibel, Maldegem, Belgium (2013)

2/0042/17 supported by Research Grant Agency of the Slovak Academy of Science and Ministry of Education of Slovak Republic. The authors appreciate Marek Zozulák, PhD., Martin Kamenský, PhD., Kristián Kondáš, PhD., Martin Labovský, PhD. and other former PhD-students at the TU Kosice for assisting in research projects and this work. REFERENCES [1]

[2]

[3]

[4]

M. Bagoňa, M. Lopušniak, and M. Vertaľ, “Numerical analysis of the hygrothermal performance of selected building structures in Slovak climatic conditions”, 12th Conference of International Building Performance Simulation Association, Sydney 2011, pp 2263-2268., M. Bagoňa, J. Šimíček, R. Baláž, “Solution of own window pane oscillation by subspace iteration method”, Applied Mechanics & Materials, Vol. 824, 2016 M. Bagoňa, D. Katunský, M. Lopušniak, and M. Vertaľ “Analysis of impact of selected glass units for energy consumption and the risk of overheating in the school building using simulation” In: Building Simulation 2011: proceedings of the 12th Conference of The International Building Performance Simulation Association: Sydney, Australia, November 14-16, - Sydney : IBPSA, 2011 P. 1392-1399. (2011) D. Katunský, M. Zozulák, M. Vertaľ, K. Kondáš, R. Baláž, “Measuring Methodology and Results of Heat-Air-Moisture Performances at

ABOUT THE AUTHORS

Dušan Katunský (prof. Ing. CSc.) Professor Katunský is a full-time professor at the Institute of architectural engineering at TU in Košice. He is the author of several book publications, a narrative and original scientific articles published in journals and conference proceedings. He is an authorized engineer and expert in building constructions and building physics. He is responsible for solving many domestic research tasks and foreign projects. He is a member of the scientific committees of international conferences, a member of editorial boards of journals and reviewer of many articles in domestic and foreign indexed magazines.

Miloslav Bagoňa (doc. Ing. PhD.) Associate professor Miloslav Bagoňa works as a professor at Department of architecture and building structures, Institute of Architectural Engineering. His professional career is focus on Transparent Building Design (windows, facades). He is familiar with Architectural Design of Buildings as Transparent structures analyzing. He is member of scientific comities for international and national conferences. He is a regular participant of international conferences in the field of Architecture an Civil engineering.

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Martin Lopušniak (doc. Ing. PhD.) Associate professor Martin Lopušniak works as a professor at TU Košice, Faculty of Civil Engineering. His professional career is focus on Advanced Building Design. He is familiar with Building simulations as well as Building performance analyzing. He is a member of Slovak Chamber of Civil Engineers (SKSI), IBPSA-SK and SSTP. He is member of scientific comities for international and national conferences. He is a regular participant of international conferences in the field of Architecture an Civil engineering.

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