Studies of Parameters on Heat Transfer through Glazing System using Guarded Hot Plate Apparatus

Review Article

Studies of Parameters on Heat Transfer through Glazing System using Guarded Hot Plate Apparatus Sunny Kumar1, Anuranjan Sharda2

Abstract Heat transfer through different modes from outside environment to inside occur by conduction, convection and thermal radiation. Inclusion of automatic-advance-generation-software; ‘WINDOW 6.3’ makes possible the detailed true picture of the impact of glazed material and its thickness/ pane spacing on its Thermal Transmittance.. This technique makes the user easy to understand thermal performance of glazing system without extensive knowledge of numerical methods of heat transfer. The U-value and solar heat gain coefficient are the key parameters to analyze heat transfer through window 6.3. Therefore, an attempt has been made to carry out the study to calculate U-value, solar heat gain coefficient of different glazing systems with varying thickness/pane spacing in prevailing seasons. Composite climate of Una persisting in different season was well defined. The U-value obtained from simulation were validated using the guarded hot plate apparatus After analysis the experimental results, it was concluded that the Uvalue and Solar Heat gain coefficient was noted maximum in single glazed window consists of 3mm thickness during the hot dry weather. The authors finally recommended Double-glazed windows with 19mm pane spacing to be preferably used in Una region.

Keywords: Glazing, U-value, Window 6.3 Introduction Heat transfer through a single/double - Glazed Window take place through three modes of heat transfer i.e. conduction, convection and radiation. Conduction occurs in window panes and convection in fluid and radiation through electromagnetic waves. Hence convection/radiation occurs in cavity and at the indoor and outdoor faces of window. Window with both good looks and desired control for heat flow requires a thorough understanding of mechanism of how glass responds to solar gain and thereafter measures needs to be taken to control that heat transfer. Normal clear glass is almost transparent to high frequency solar radiation, but is a difficult to low frequency or long wave radiation. The solar heat energy passing through the glazing warms up the various surrounding surface by absorption and these surrounding surface then become heat radiators of low frequency re-emitted heat which is trapped inside causing the temperature to rise.

1

Department of Mechanical Engineering, Sri Sukhmani Institute of Engineering and Technology, Dera Bassi, Chandigarh, India.

Faculty of Engineering and Technology, GNA University, Phagwara, Punjab, India.

2

Correspondence: Mr. Sunny Kumar, Sri Sukhmani Institute of Engineering and Technology, Dera Bassi, Chandigarh, India.

E-mail Id: er.sunnykumar@gmail.com Orcid Id: http://orcid.org/0000-0001-9186-5664 How to cite this article: Kumar S, Sharda A. Studies of Parameters on Heat Transfer through Glazing System using Guarded Hot Plate Apparatus.. J Adv Res Glass Leath Plast Tech 2017; 2(1&2): 12-17.

© ADR Journals 2017. All Rights Reserved.

J. Adv. Res. Glass Leath. Plast. Tech. 2017; 2(1&2)

Kumar S et al.

Previously, shading coefficient was used to represent the heat flowing through the window and was defined as the solar gain through a given fenestration compared, to what the solar gain would have been through an opening of the same size and orientation glazed with a standard single pane of 1/8� double strength clear glass.

Measurement Technique through Guarded Heater Apparatus

However complexity of modern glazing systems could not be properly evaluated by single shading coefficient. However, ASHRAE devised an alternate method for determining this heat and presently in order to calculate the U-value and solar heat gain coefficient through windows, windows 6.3 software can be used.

Heater Design

Need for Present Work From the literature review it was clear that no systematic study has been carried out so far on the guarded heater plate method with temperature of hot and cold plate in conjunction with Indian climate. In the developing country like India, there is huge scarcity of energy sources. We have to focus on the alternatives, which not only conserve the energy but also help in maximum use of renewable source of energy. Therefore an attempt was made to study the energy conservation with double glazed window with the help of guarded heater plate method. This apparatus has been used over the last several years to perform U-value measurement on a variety of prototypical glazing system. The primary objective of this system is to control the heat flow through it from inside to outside in winter and from outside to inside in summer.

The apparatus consists of heaters i.e. main and guard heaters, cold plate, heat plate, baths, power supply system and other accessories. Cold plate which act as the heat sinks, hot plate which act as heat source.

The heater used consists baths, power supply system and instrumentation for ensuring measurements of two main parts 1. Main heater 2. Guard heater The cold and hot plates are maintained at constant temperature separately by passing the heated fluid through copper tubes, which are brazed in a rectangular spiral pattern at the backsides of each of these plates. Three recesses (arranged as top, middle and bottom) are made symmetrically on the hot plate within three copper heater plates, each of an overall thickness of 6 mm thick and of surface area 200x200 mm, are positioned.

The middle heater is used to apply a unidirectional heat flux through Glazing-unit sample while the guard heaters are maintained at the same temperature as that of the main heater so that the entire heat is transferred through the sample thereby minimizing the heat losses. The heating material used is copper due to its high thermal conductivity aiding in achieving a constant plate temperature.

Figure 1.Schematic of Experimental Setup

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J. Adv. Res. Glass Leath. Plast. Tech. 2017; 2(1&2)

In order to measures the voltage current from the exposed surface of the guarded heater plate, it is necessary to measure the rate at which electrical energy is supplied to heater plates. The electrical supplied to the heater plate is simply.

Vh = Qe / Ih …

Window program has roots in a paper detailing a method for calculating the heat transfer through windows. The various operating system of window 6.3 software configuration as follows:

Main Screen

(1)

Where Ih = Current measured through the heater wire; Vh = Voltage drop through the heater wire

Main screen is helpful in calculating the window properties, these properties includes U-value, Shading Coefficient, Solar Heat Gain coefficient.

When the experiments are performed to determine the glazing system U values, Ih is measured directly using a digital multimeter. This method simplifies the experimental procedures used for data reduction. We are providing D.C electrical power supply.

Window Library

A U-value based on measurement for the glazing system can be found by using suitable indoor and outdoor side thermal conductance’s (hi and h0, respectively).

Glass Library

U =[C-1 + hi-1 + h0-1] -1 …

(2)

Simulation through Window 6.3 Software Window 6.3 is a publicly available LBNL Window LBM PC compatible computer program developed by the building technologies group at the Lawrence Berkeley Laboratory for calculating the thermal and optical properties necessary for heat transfer analyses of fenestration products. All the calculations are discussed in the International System of units (SI).

Window 6.3 is the latest in a series of programs released by the Lawrence Berkeley Laboratory. The

Window Library is used to window properties, which are created on MAIN SCREEN. NO calculations are associated with this screen.

Glass Library includes glazing layer properties weighted average optical properties are obtained by integrating these properties over the various wavelength ranges, if spectral values of transmittance and reflectance are available. In the present study clear that glass were used as the pane spacing.

Gas Library contains two different mixtures of gases.

For the present study only pure air is considered whose thermo-physical properties are listed below:

Software Parameters for Current Simulation Studies Gas Used For the present study only pure air is considered whose thermo-physical properties are listed below:

Table 1.Thermo-physical Properties

ID 1

Name Air

Type Pure

Conductivity W/m-K 10.024069

Viscosity g/m-s 0.000017

Type of Glazing System Used and Pane Spacing Glazing System The glazing units can be categorized into single with multiple glazing layers are often called insulating Glazing Units IGUs are double glazing, triple glazing,

Cp J/kg-K 1006.103271

Density kg/m3 1.292171

Prandtl 0.7197

and quadruple glazing. The glass pane can be clear, tinted, or coated with reflective units were investigated, as listed in Table glass with thermal conductivity of 1 W/ (m.K). For the present study, a double glazed window with clear glass was selected for the analysis of U-value, Shgc and Rhg (ZHOU XU 2011).

Table 2.Description of Selected Glazing Library

S. No 1 2 3 4 5 6

Name Single glazing Double glazing Double glazing Double glazing Double glazing Double glazing

Layer 1 4mm glass 4mm glass 4mm glass 4mm glass 4mm glass 4mm glass

Layers Layer 2

Layer 3

10mm air gap 13mm air gap 16mm air gap 19mm air gap 25mm air gap

4mm glass 4mm glass 4mm glass 4mm glass 4mm glass

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Though there have been studies explain the use of double glazed windows in the west, very in research has been done in this area in Indian climate conditions. For the purpose this study has considered the following glazing units to analyze their effect as per composite climate of northern India.

Glazing Pane In the present study clear-dat glass of 3mm thickness from generic glass manufacture. The various solar and optical properties of this glass shown in table from Gen were used as the pane spacing. Glass consists fellow:-

Table 3.Glass Properties

Thickness 3.048

Tsol 0.834

Rsol1 0.075

Rsol2 0.075

Tvis 0.899

Rvis1 0.083

Rvis2 0.083

Tir 0.000

Emis1 0.840

Emis2 0.840

monsoon season and brings slightly lower temperature with the majority of all rainfall for the year and large cloud cover; the final season lasts from October to February, with temperatures getting colder, but with little to no precipitation (ISHRAE 2005). Based on these three seasons the climate data for the year 2012 was consider to define wind speed (http://m.accuweater. com/) and solar radiations. The peak temperatures of each of the seasons were chosen as the summers are more prom ante choring and max temp. Difference between the extreme outside condition and conditioned room space is 180C only. The inside conditions are always considered to be designed values for conditioned space is 250C as below.

Environmental Conditions Library The environmental condition parameters important to U-value calculation are temperature and airflow velocity. For the present study, the composite climate of Una was selected. The composite climate zone, defined by 2005 National Building Code, contains aspects of all other climates zones, and changes greatly over the course of the year.

On an annual basic, temperature, relative humidity and average rainfall data indicates three distinct seasons with transitional periods in-between. The first seasons is roughly from March to June and is characterized by hot temperature and little to no precipitation. The second season is known as the

Table 4.Composite Climate Condition for Una Location

S. No 1 2 3

Composite climate condition Hot and dry Hot and humid Cold and dry

Tout (0C) 43.0 34.0 5

Tin (0C) 25.0 25.0 25

Solar radiation W/m2 6570 5470 3948

Wind speed m/s 4.815 4.02 3.95

Season: Hot and Dry, Hot and Humid, Cold and Dry simulation value

Convection Force Used There are so many wind directions, but according to the Indian point of view, particularly this direction is used.

Table 5.Effect of Glazing and its Thickness on U-Value (w/m2K) in Different Season (Predicated and Simulated Readings for Hot and Dry)

Season - Glazing and its thickness/spacing Single glazed 3MM Double glazed 10MM Pane Spacing Double glazed 13MM Pane Spacing Double glazed 16MM Pane Spacing Double glazed 19MM Pane Spacing Double glazed 25MM Pane Spacing

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Hot and dry predicated 5.62 2.98 2.68 2.87 2.86 2.73

Hot and dry simulated (Software) 6.46 3.35 3.20 3.13 3.08 3.07

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Table 6.Effect of Glazing and its Thickness on U-Value (w/m2K) in Different Season (Predicated and Simulated Readings for Hot and Humid)

Season - Glazing and its thickness/ spacing Single glazed 3MM Double glazed 10MM Pane Spacing Double glazed 13MM Pane Spacing Double glazed 16MM Pane Spacing Double glazed 19MM Pane Spacing Double glazed 25MM Pane Spacing

Hot and humid predicated 5.11 2.8 2.68 2.7 2.67 2.5

Hot and humid simulated (Software) 5.88 3.15 3.02 2.94 2.88 2.82

Table 7.Effect of Glazing and its Thickness on U-Value (w/m2K) in Different Season (Predicated and Simulated Readings for Cold and Dry)

Season - Glazing and its thickness/spacing Single glazed 3MM Double glazed 10MM Pane Spacing Double glazed 13MM Pane Spacing Double glazed 16MM Pane Spacing Double glazed 19MM Pane Spacing Double glazed 25MM Pane Spacing

Cold and dry predicated 5.06 2.59 2.48 2.53 2.53 2.44

Results and Discussions U-Value Software & U-Value Experimental A perusal data represented in the Table 5, 6 and 7 shows the significant variation in the U-value due to all the three factors i.e. season, type of glazing system and pane spacing (for Double glazed windows). With regard to the type of glazing system in the hot and dry season the highest U-value was found in single glazed window having 3mm thickness i.e. 6.46 (w/m2K).

Lowest U-value was noted in double glazed window having 25mm pane spacing i.e. 3.07 (w/m2K). In another case of hot and humid season U-value with respect to glazing and its thickness was found highest (5.88) in single glazed window having thickness 3mm, whereas, lowest (2.82) was found in double glazed window having 25mm pane spacing. As in the case of cool and dry weather conditions, U-value ranged from 2.73 to 5.82 with respect to glazing and its thickness.

However highest value was recorded in single glazed window having 3mm thickness and lowest was recorded in double glazed window having thickness 19mm. In the interaction effect of both glazing and its thickness/pane spacing and seasons, the maximum Uvalue was recorded in the single glazed window having thickness 3mm during the hot and humid weather condition. The minimum U-value was recorded in double glazed window having 19mm thickness during the cool and dry season. As the pictorial representation of data recorded shown in Fig. 1, 2 and 3 indicated that there is gradual decrease in the U-value from single glazed window to double glazed window with the increase in thickness/pane

Cold and dry simulated (Software) 5.82 2.92 2.79 2.75 2.73 2.75

spacing. The possible reason for the increased U-value in single glazed system than double glazed is that there is higher heat conduction through single pane than double pane with air in the gap. Moreover the resistance offered by the air gap increases with increase in pane spacing and hence the U-value decreases. Present finding is also supported by Wright JL, Sullivan HF.2 In relation to the U-value with all the seasons, the U-value is found lowest in cool and dry season and vice - versa. This may be due the fact that in cold and dry climate there is less incidence of solar radiation which allows for a lesser temperature rise of the outer pane of window and hence the lesser thermal transmittance.1 Similar findings have also been reported by Wright JL, Sullivan HF; Curcja D, Goss WP; Reilly S.2-4

Conclusion From the present investigation it can be concluded that the U-value was highest in single glazed window with lowest thickness in hot and dry weather condition in Una city. U-values become the deciding factor in choosing windows for composite climate.

Though Double Glazed windows with 19mm Pane spacing, gives us the lowest value of U-factor i.e. 2.73 in cold and dry season, still it is not recommended for use in Una region. This is so because in composite climate summers are comparatively longer and preference needs to be given to Double glazed windows with 25mm pane spacing having lowest Uvalues of summer season i.e. 3.07 and 2.82 for HotDry and Hot-Humid season respectively. Thus the use of Double glazed windows with 25mm pane spacing is

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recommended for the composite climate of Una. However if there is a constraint of cost or of space occupied, Double glazed windows with 19mm pane spacing must be used. By using the GHP apparatus, we are able to decrease the U-value and the difference between experimental and software value is 0.07%.

References 1. Singh I, Bansal NK. Thermal and optical parameters for different window system in India.

International Journal of Ambient Energy 2002;

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23(4): 201-11.

2. Wright JL, Sullivan HF. A 2-D numerical model for glazing system thermal analysis. ASHRAE Transactions 1995; 101(1): 819-31.

3. Curcja D, Goss WP. Two dimensional finite element model of heat transfer in complete fenestration systems. ASHRAE Transactions 1994; 100(1): 1207-21.

4. Reilly S. Spacer effects on the edge of glass and frame heat transfer. ASHRAE Transactions 1994; 100(1): 1718-23.