Advances In Glazing Materials Essay Research Paper

Advances In Glazing Materials Essay, Research Paper

Table of Contents

Section Page

List of Figures 2

Introduction 3

Definitions 4

Current Options In Widow s Energy Efficiency 5

Understanding How Energy Moves Through Windows 5

Different ways Energy Travels 5

How is Energy in Windows Measured 6

R-values / U-values 6

Types Of Glazings In Windows 6

Low-e Glazing 7

Spectrally Selective Coatings 7

Heat-Absorbing Glazings 8

Reflective Coatings 8

Tomorrow s Options for More Efficient Windows 8

Superwindows 8

Summary/Conclusions 10

Recommendations 11

References Cited 12

List of Figures

Figure Page

1. How energy flows through windows: Radiation 6

2. How energy flows through windows: Convection … .6

3. How energy flows through windows: Conduction .7

4. Three Routes to Switchable Windows. 10

Introduction

Until recently, clear glass was the primary glazing material used in windows. Although

glass is durable and allows a high percentage of sunlight to enter buildings, it has very little

resistance to heat flow. During the past two decades, though, glazing technology has

changed greatly.

Research and development into types of glazing have created a new generation of materials

that offer improved window efficiency and performance for consumers. While this new

generation of glazing materials quickly gains acceptance in the marketplace, the research

and development of even more efficient technologies continues.

Definitions

Gas Fill A heavier-than-air gas such as argon or krypton is used to fill the space between panes to slow heat transfer.

Glazing The glass and/or plastic in a window unit that provides visibility yet blocks air leakage and some of the heat flow.

Infrared Radiation Invisible radiation that humans perceived as heat.

Low-e Coating Low-emissivity (low-e) coatings on glass surfaces reflect heat energy, but transmit visible light.

Pyrolytic (Hard Coat) Low-e Durable metal oxides that are fused into the surface of window glass.

Sputtered (Soft Coat) Low-e A coating on the inside pane of window glass in a sealed unit. It is made of reflective metal deposited in a vacuum.

R-Value A measure of a window s resistance to heat flow.

Total Solar Transmittance The total amount of all light spectra that is admitted by the window glazing.

U-Value The amount of heat transmitted by the window.

Center Of Glass R-Value/U-Value Performance of a window measured through the center of the glass only; not the entire unit.

Unit R-Value/U-Value A measure of thermal resistance/ heat transmittance for an entire window, including the frame.

Visible Light Transmittance A measure of the amount of that portion of the total solar radiation visible to the human eye.

Understanding How Is Energy Moves Through Windows

Different Ways Energy Travels

Understanding how windows work and how energy travels through them is the first step necessary to comprehend this concept of windows and energy. Windows start with the glass, or glazing. According to Krahn glazings do three basic things: They light in, they let you look out, and they isolate indoor environment from outdoors. (Wilson, p.94). Glass is transparent to sunlight, in other words short wavelength radiation. Glass absorbs radiant heat, or long wavelength infrared radiation, warming up in the process. (Wilson, p.94). The glass radiates this heat both inside and outside.

Figure 1. How Energy flows through windows: Radiation.

Figure 2. How Energy flows through windows: Radiation.

Figure 3. How Energy flows through windows: Conduction.

How is Energy in Windows Measured

R-Value / U-Value

Manufacturers usually represent the energy efficiency of windows in terms of their U-

values (conductance of heat) or their R-values (resistance to heat flow). If a window’s R-

value is high, it will lose less heat than one with a lower R-value. Conversely, if a window’s

U-value is low, it will lose less heat than one with a higher U-value. In other words, U-

values are the reciprocals of R-values (U-value = l/R-value).

Usually, window R-values range from 0.9 to 3.0 (and U-values range from 1.1 to 0.3), but

some highly energy-efficient exceptions also exist. When comparing different windows,

you should ensure that all U- or R-values listed by manufacturers: (1) are based on current

standards set by the American Society of Heating, Refrigerating, and Air-Conditioning

Engineers (ASHRAE), (2) are calculated for the entire window, including the frame, and

not just for the center of the glass, and (3) represent the same size and style of window.

Types of Glazings In Windows

Today, several types of advanced glazing systems are available to help control heat loss or

gain. The advanced glazings include double-and triple-pane windows with such coatings as

low-emissivity (low-e), spectrally selective, heat-absorbing(t

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