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Sunlight and Glass

Objectives:

  • To understand the science behind solar energy and heat transfer
  • To use solar energy and heat transfer principles in explaining how window film works to  prospective customers

What we will cover:

  • Benefits of solar control window film
  • Types of solar energy
  • Wavelengths
  • The solar spectrum
  • Heat transfer
  • The relationship of solar energy and heat transfer to window film
  • The effect of sunlight on window glass
  • Measures of effectiveness and insulation for window film

Start With the Problem

  • Principles of solar energy and heat transfer are the science behind window film.
  • These are the same principles your 6th grade science teacher tried to teach you.
  • We will try to help you understand how you can use these principles to elevate both the credibility of your product, your business as well as you as a solar control specialist.

Know Solar Energy Science

  • And you will know
    • How solar control film works
    • How to sell film to upscale homeowners, engineers and architects
  • The window film industry is all about the control of energy from the sun.
  • Knowledge of solar energy is the basis for understanding the window film industry, product, and how to position and sell window film within the architectural glass market.

Energy From the Sun

  • Sun constantly sends energy to earth.
  • Travels In the form of electromagnetic radiation – waves.
  • The sun constantly sends energy through space towards earth
  • This energy leaves the sun in the form of electromagnetic radiation or waves, referred to as radiant energy.
  • This energy Is also known as solar energy.

Types of Solar Energy

  • Infrared Light
  • Visible Light
  • Ultraviolet Light
  • These waves, while invisible, are one of the major factors that sustain life on earth.
  • The waves travel in a straight line out from the sun. Think of a rock thrown into the water and how the waves go out in all directions.
  • The earth only receives a tiny fraction of the energy that leaves the sun.

About Energy Waves

  • Electromagnetic Waves

–  travel in straight lines from the sun
– are in constant motion
– shaped in an up and down curve called a cycle
– full cycle is a wavelength

  • During the entire journey from the sun, the waves are in constant motion.
  • The motion of the wave, just like the ripples in the water is an up-curve and a down-curve with this cycle repeating itself all the way from the sun.
  • The full cycle of the wavy motion is called the wavelength.

Wavelength

  • Measured In Nanometers.
  • The wavelength is characterized by an up-curve and a down-curve. Remember this cycle  repeats itself all the way from its point of origin.
  • The full cycle of the wavy motion is called the wavelength
  • The unit of measure is the nanometer. A nanometer equals one billionth of a meter.
  • Each type of electromagnetic wave has its own specific wavelength.

Electromagnetic Waves

  • Electromagnetic waves from the sun are known as solar energy or solar radiant energy
  • We are surrounded by other types of electromagnetic waves.
  • Each type of wave has Its own wave length.
  • There are other types of energy that travel in waves that surround us everyday.
  • Each of these other types of energy travel in waves that in turn have their own characteristic wavelength.
  • The electromagnetic spectrum is a diagram that illustrates wavelengths of energy and puts them in order by the length of their wave.
  • Within the entire electromagnetic spectrum, solar radiation waves range from 100 to 2500 nanometers In length.
  • One hundred percent of the solar radiation reaching the earth is made up of three types of energy you have head about: ultraviolet, visible light and near infrared.

The Solar Spectrum

  • Ultraviolet  ( 100 – 400 Nanometers )
  • Visible Light ( 380 – 770 Nanometers )
  • Infrared  ( 700 – 2400 Nanometers )
  • This illustrates the portion of the electromagnetic spectrum that represents the energy from  the sun.
  • There are other types of electromagnetic waves that would be on either side of this spectrum.
    • On the far right you would find x-rays.
    • On the left you would find things like radio waves, waves carrying cell phone transmissions  and microwaves.
    • Again each of these other types of waves have their own characteristic wave length.

Sun’s Electromagnetic Waves

  • Of all the waves

–  3% Ultraviolet Light
– 44% Visible Light
–  53% Solar Heat (Infrared)
3 + 44 + 53 = 100% Energy from Sun

  • The ultraviolet light band of the electromagnetic spectrum comprises 3% of the energy that reaches the earth form the sun.
  • The visible light band of the electromagnetic spectrum comprises 44% of the solar spectrum or energy from the sun.
  •  The infrared portion is 53%
  • There three types of energy comprise 100% of the solar energy that reaches the earth from the sun.

Ultraviolet

  • The shortest of sun’s energy waves

– UV-C, little reaches the earth
– UV-B, causes skin cancer
– UV-A, causes wrinkles
– Both UV-B and UV-A causes tanning

  • Film blocks up to 99% of UV
  • Ultraviolet energy is made up of the shortest energy waves from the sun.
  • As all waves, ultraviolet energy is invisible and is broken into three categories:
    • UV-C (100-280 nanometers),
    • UB-B (280 to 320 nanometers), and
    • UV-A (320 to 380 nanometers).
  • UV-A is the weakest form of ultraviolet energy.. It causes skin aging, wrinkles and can also damage outdoor plastics and paint.
  • UV-B, which is stronger than UV-A, is the most harmful to us and other life forms. UV-B causes skin cancer and cataracts.
  • Both UV-B and UV-A cause suntans and sunburns.
  • UV-C, which is even stronger than UV-B, never reaches the earth’s surface because it is filtered out by the atmosphere.

Visible Light

  • Makes vision possible
  • No light – can’t see
  • With light from the sun comes color
  • 44 % of the energy from the sun is made up of visible light
  • Light is the form of solar energy that makes vision possible.
  • The ability to see and distinguish objects depends on light reflecting from the object. That is why you cannot see in the dark. In the dark, no light reflects from an object that may be just in front of you.
  • With light from the sun, comes color.

Visible Light and Color

  • Each color has its own wavelength, therefore Its own place In the electromagnetic spectrum.

– Violet is the shortest, red the longest

  • Ultraviolet waves the shortest
  • Infrared waves the longest
  • Violet is the first color by wavelength order, and is just a little longer than ultraviolet in wavelength.
  • Red is the last color in wavelength order and is just shorter than infrared in wavelength
  • The order of the colors in the visible light spectrum is the same as the order of the colors of the rainbow. Ain’t nature grand!

The Solar Spectrum

  • Ultraviolet ( 100 – 400 Nanometers )
  • Visible Light ( 380 – 770 Nanometers )
  • Infrared ( 700 – 2400 Nanometers )
  • This illustrates the portion of the electromagnetic spectrum that represents the energy from the sun.
  • There are other types of electromagnetic waves that would be on either side of this spectrum.
    • On the far right you would find x-rays.
    • On the left you would find things like radio waves, waves carrying cell phone transmissions and microwaves.
    • Again each of these other types of waves have their own characteristic wave length.

Visible Light

  • Is measured in lumens or candle power
  • Is responsible for glare
  • Window film is used to control glare
  • Light is measured with a light meter that reports the amount of light in lumens or foot candles.
  • Glare in a room is a function of:
    • amount of light at its source
    • the contrast between the source and the room
    •  the types of surfaces the light falls on
  • Window film can be used to cut the amount of light at its source (if the source is a window).

Infrared Energy

  • Infrared energy is the heat from the sun
  • Called near Infrared energy
  • Measured In BTUs
  • Window film is used to control the infrared energy at the window
  • Infrared energy is the heat energy that comes from the sun. This energy ranges from 780 to 2500 nanometers.
  • Energy in this range of wavelengths is referred to as near infrared energy.
  • This type of energy is measured in BTU’s.
  • BTU = British Thermal Unit.
  • BTU = the amount of heat necessary to raise the temperature of one pound of water by one degree Fahrenheit.
  • This is the type of energy that the metal in window film reflects away.
  • Window film’s ability to reflect this type of energy is the whole basis for the energy saving benefits of film.

You Can’t See or Feel Infrared Energy

  • The energy is only converted to heat when it strikes an object
  • Campfires and hot cars
  • The earth heats from radiant energy striking our surroundings
  • You can’t see or feel its heat as it travels through the air.
  • A person only feels the heat energy of infrared when the waves strike an object.
    •  An example of heat carried by radiant energy is heat from a campfire. When you are sitting facing a fire on a cool night your skin or clothing becomes very warm while your back can be cold. While there is little, if any difference, in air temperature between your front and back, you are feeling the radiant energy that hits the front of your body. The radiant energy is not actually converted to heat until your body absorbs the infrared waves.
  • The earth is not warmed by the energy from the sun until the infrared waves hit a body. That body can be the earth’s atmosphere, the ground, or any number of things. Once the infrared energy is converted to heat, the heat reflected from those bodies warms our environment.

Solar films are designed to reflect and/or absorb near infrared and visible light waves and block most of the ultraviolet energy that strikes a window.

So how do solar control films do anything about the energy from the sun?

  • Film reflects and/or absorbs visible light
  • Film absorbs almost all of the ultraviolet light

Heat Transfer

  • The movement of heat from one place to another Is called heat transfer
  • The transfer of heat is always from

– High Temperature Body
– Low Temperature Body

  • Understanding solar radiation or energy from the sun is critically important to becoming successful in the window film industry.
  • Equally important to your knowledge of how window film works, is understanding how heat moves from one object to another once it get to the earth.
  • The movement or transfer of heat from a region of higher temperature to one of cooler temperature is called heat transfer.
  • The transfer of heat is always directional, from hot to cold.
  • No heat will transfer if there is no difference in temperature.

Methods of Heat Transfer

  • Radiation
  • Conduction
  • Convection
  • NO temperature difference…
    • NO heat transfer!

There are three methods of heat transfer

  • Radiation
  • Conduction
  • Convection

What does any of this have to do with selling film?

  • Understanding heat transfer will help you understand how to use performance results

– R-value
– U-value
– Emissivity

  • The principles of heat transfer are put to use when you start explaining how window film works.
  • The terms are used to describe the benefits of using film or the differences between types of film.

Conduction

  • Heat transfer through a solid
  • Conduction takes place through a window when there is a temperature difference between inside and outside
  • Conduction is heat transfer through a solid such as metal
  • If one end of a silver spoon is put into hot coffee, the heat transfers up the spoon to your hand.
  • Conduction takes place through a window when there is a temperature difference between outside and inside air.

What does conduction have to do with film?

  • The transfer of heat from the outside (warm) of the window to the inside (air-conditioned) takes place through the window by conduction.

HOT → COLD

Film doesn’t stop conduction

  • Conduction of heat occurs through a window
  • In the summer heat conducts from the outside to an air-conditioned inside.
  • In the winter heat conducts from the cold outside to the heated space.
  • Remember the heat is going hot to cold.
  • The energy you put into the room to heat or cool conducts through the window.
  • Window film does very little to stop conduction.

Convection

  • Transfer of heat between a warm gas or liquid and a cooler solid body based on the movement of that gas or liquid
  • Convection is the transmission of energy between a warm gas or liquid and a cooler solid body based on the movement of the gas or liquid.
  • Example
    • A potato cooks from the movement of hot water in the pan. The water circulates around the potato carrying heat to the cooler surface of the potato. The cooler temperature of the potato causes heat transfer from the convected water currents to the cool potato. The potato, being a solid heats from the surface inward by conduction.
  • Wind against a window either carries heat to a window on a hot day or away from a window on a cool day.
  • Window film doesn’t really affect this type of heat transfer.

What does convection have to do with film?

  • Winter wind  carries away heat as It blows across the outside 11 surface of a window.

Film doesn’t stop convection

  • On a cold day, the wind blows across the window surface carrying the room’s heat away.
  • Window film will not stop convection.

Radiation

  • The method of heat transfer that moves infrared waves
  • Energy through a window is transferred or transmitted by infrared waves
  • Radiant energy is converted to heat when it strikes people or objects
  • Radiation as we learned is the transfer of energy by infrared waves. This is why we refer to solar energy as solar radiation.
  • Radiation transfers the heat from a hot body like the sun or a fire to a cooler body or object.
  • It can’t be felt in the air but a rise in temperature is noticed once the infrared waves hit an object.

What does Radiant heat transfer have to do with film?

  • The heat comes through a window as Infrared waves.
  • The method of moving infrared waves is radiant heat transfer.
  • Keep out infrared and you keep out heat.
  • The energy coming through windows is transferred or transmitted through the glass by radiation of infrared waves. It is converted to heat when it strikes people or things on the other side of the glass.
  • If you block the transfer of this energy you keep it from turning into heat because it never strikes an object.
  • Window film interrupts the transfer of this energy by reflecting the energy back.

Heat Transfer and Windows

  • Convection
  • Conduction
  • Radiation

In review

  • Windows are greatly affected by heat transfer
  • Convection wipes cold or hot air across window surfaces
  • Conduction is the heat that transfers through the solid material of the glass
  • Radiation is the movement of the heat that the sun carries. Block this and you stop the majority of heat gain into a space.

Solar Energy and Windows

  • Solar energy striking a window is made up of:

– Ultraviolet
– Visible light
– Infrared energy

  • What happens when sunlight strikes glass and why film makes the situation better depends on the type of glass and the particular film applied to the glass.
  • Each film offered by Tint Depot differs and is designed to address diverse customer requirements.
  • To help a customer choose a film, you need to know the properties of the films and the concepts that describe those differences.
  • The radiant energy that strikes a window is referred to as solar energy. This energy is made up of ultraviolet, visible light and infrared energy.

When solar energy strikes glass, it will do one or all:

  • Pass through the glass (transmittance)
  • Reflect energy away (reflectance)
  • Absorb energy Into glass (absorbance)
  • When solar energy strikes a pane of glass three things happen.
  • The majority of the energy from the sun goes right on through and into the room side of the window.
  • Of all the energy (=100%) from the sun, some is
    • Reflected
    • Absorbed
    • Transmitted
  • Energy that is reflected is like what happens with a mirror – bounces the energy right back.
  • Energy that is absorbed goes into the glass and is stored as heat. Eventually it moves from the glass by conduction or convection to the cooler side of the window.
  • Energy that is transmitted passes directly thought the window as radiant energy to make heat once it strikes an object.

Distribution of Solar Energy

  • Total energy = 100%
  • Distribution of the 100% changes based on film and window type.
  • Our industry exists because of the ability to redistribute solar energy with reflective film.
  • The amount of solar energy reflected, absorbed or transmitted into a room will change based on type of glass but the solar film industry really exists because of how you can re-distribute this energy with film.

REMEMBER: There are 3 types of energy from the sun that film affects.

Note: Infrared is reported within Total Solar Energy

Solar Energy

  • When solar energy strikes a pane of 1/8″ clear glass, the glass:

– Transmits – 87% (most of the energy)
– Reflects – 8%
– Absorbs – 5%

  • The total = 100%
  • When solar energy strikes a pane of 1/8″ clear glass, the glass:

– Transmits – 87% (most of the energy)
– Reflects – 8%
– Absorbs – 5%

  • The sum of reflectance, absorptance and transmittance totals 100%.

Solar Energy and Glass

  • Glass without Film
    • Solar Energy 100%
    • Transmitted 87%
    • Reflected 8%
    • Absorbed 5%
  • If we look at what happens when sunlight strikes a window, we see the majority of the energy (87%) from the sun goes right on through or is transmitted into the space.

Solar Energy…Film Added

  • Tint depot Silver Reflective 15 %, the same glass:

– Reflects – 50% (away from the room)
– Transmits – 10% (into the room)
– Absorbs – 40%
– The total solar energy kept from the room = almost 81%

  • Installing Silver reflective 15% on the same pane of 1/8″ clear glass makes a dramatic difference
  • There is a dramatic increase in reflectance and absorbtance resulting in a sizable reduction in infrared energy transmittance.
  • The sum of reflectance, absorbtance and transmittance still totals 100%.
  • You can see that clear glass transmits a very high percentage of solar energy through it and into the room. Similarly, it does not reflect much solar energy.
  • Note the difference between the amount of energy transmitted into the room before and after film. This explains why west-facing rooms get so hot and why comfort increases after the installation of film.

Solar Energy and Window Film

  • Glass with Silver 20 Window Film
    • Solar Energy 100%
    • Transmitted 12%
    • Reflected 50%
    • Absorbed 38%
  • Look at the re-distribution of solar energy with reflective film
  • Reflective solar film on the window dramatically redistributes the amount of energy that goes on into the room
  • This is the major property of window film that provides the benefits we will be discussing through this course.

Measures of Effectiveness

  • A number of measures help us compare one film to another for a given application.
  • Helping the consumer choose among films is the function of the solar control specialist.
  • Different films redistribute solar energy differently
  • Learning to use the measures of effectiveness will help you understand the differences between various films.

Where to’Find Measures of Effectiveness

  • The Performance Results sheet documents how film and glass combination redistributes energy – and the effectiveness of a particular film.
  • Later we will go into detail how these numbers are determined. For now know theses are the same performance characteristics that are reported on other glass and glazing material and that the entire glass and glazing industry used the same methodology to determine these numbers.
  • Instructor pass out performance sheets. Go over:
    • Total Solar energy numbers – Silver vs. SS
    • Visible Light – Silver vs. SS
    • UV Light T%

Shading Coefficient

  • Measures effectiveness of a film In rejecting solar energy.
  • Rates the solar heat gain of a window with film compared to that window without film.
  • Plywood over glass SO = 0
  • Lower shading coefficients reject more heat.
  • Shading coefficient is the terms commonly used to describe effectiveness of window film in rejecting heat.
  • The shading coefficient is the ration of solar heat gain through a window with film, to the solar heat gain that would occur in the window if it were made of clear glass.
  • As a baseline think of plywood over a window as having a shading coefficient of 0.
  • The lower the shading coefficient the better.
  • SO WHAT!
    • This rates a glass window with film compared to that same glass without film. Examination of shading coefficient numbers reveal which films reject more heat from a room.
  • Instructor – Compare the SO for high performing and lower performing films.

Solar Heat Gain Coefficient

  • Measures the heat coming in the window,

–   Transmitted + absorbed and re-radiated energy.

  • Used by engineers and architects.
  • Lower solar heat gain coefficients reject more heat.
  • Engineers or architects use solar heat gain coefficient to look at the same concept. This is a term used in the construction industry to measure the effectiveness of both glass and the framing system together.
  • It measures the percentage of solar energy directly transmitted or absorbed and then re-radiated to the building.
  • Absorbed and re-radiated to the building means that once the temperature of the glass rises, the glass can become the warmer body and release heat into the cooler room.
  • This term is used almost exclusively in the heating and cooling industry and will be requested for a calculation of reducing air-conditioning requirements with film.
  • The lower the solar heat gain coefficient for a film or coating the better
  • So What! Solar Heat Gain reveals how much a film will save on air-conditioning load
  • Instructor – compare SC and SHGC between SS and Silver film.

Total Solar Energy Rejection

  • Referred to as TSER
  • Percent of total solar energy rejected.
  • Total solar energy rejection (TSER) measures a film’s ability to reject solar energy.
  • Visible light and infrared radiation energy are combined in this measurement.
  • TSER equals the solar reflectance plus the part of solar absorption that was absorbed by the glass and radiates back into the room.
  • SO WHAT! This number is a good was to compare performance of one film to another
  • The higher the TSER the better.
  • Instructor’s Note: The rule of thumb on TSER is that about 10% or the heat absorbed by the glass radiates into the room. But if there is a breeze of as little as 7.5 mph outdoors the convective currents will carry away any built up heat, thus reducing the effect of absorbed heat being reradiated into the room
  • Instructor – compare TSER with SC and SHGC for various film.

Emissivity

  • Ability of a material to absorb heat and to reflect it back out (long wave infrared).
  • For windows or film, refers to heat reflected back to room.
  • Low emissivity, more heat reflected back to the room.
  • Emissivity is the ability of a surface to absorb heat and to “emit” it or reflect is back out.
  • Emissivity is important in cold climates because it affects the room heat being reflected back from the inside surface of the window, back into the room.
  • The lower the emissivity of the film, the more effective it will be in reflecting heat back into the room.
  • Instructor – look at Silver AG 25 Low-E performance numbers and examine a sample.

Emissivity Ratings

Gold, polished                                      .02
Aluminum,                                           .05
polished
Low-E films                                         .29 to .45
Standard reflective                            .65 to .89
films
Normal glass                                       .84
Wood                                                     .91
White enamel                                    .91
Flat black lacquer                              .96

  • To get a better understanding , it is helpful to look at the emissivity ratings of various materials.
  • The emissivity rating of polished gold Indicates a material that absorbs very little energy. It Is a very good reflector.
  • The emissivity rating of flat black pain on the other hand indicates a material that absorbs energy. These surfaces cannot reflect much energy away from the surface.
  • A rule of thumb for film Is that the more reflective on the room side of the window, the lower the Emissivity rating.
  • SO WHAT!
    • Low-e film Is the film Industries effort to retrofit windows to low-e performance
    • Emissivlty becomes important in cooler climates where low-e film Is an important option for consumers.
    • Silver AG 25 Low-e has a very low emissivity
    • In building energy analysis this film is found to contribute to energy savings as far south as Miami!

Interior Reflectivity

  • Refers to visible light reflected back into room.
  • To reduce reflectivity into an interior, a low reflectance film or dyed film is laminated to the room side of a metallized , high performance film.

Measures of Insulation

  • The measure of heat that passes through a medium.

– U-Value (glass only)
– R-Value

  • Always a function of temperature difference.
  • In addition to heat entering a room through a window, heat loss through windows is also important.
  • The measurements are referred to a U-value and R -value. This is the transfer of heat through a material.
  • Without a temperature difference there is no transfer of heat.

U-Value

  • Used to describe the heat transfer through glass.
  • The lower the U-Value the less heat transfers.
  • Term unique to the glass and glazing industry.
  • There are summer and winter U-values.
  • U-value is a measurement of heat transmission due to temperature difference.
  • It is used almost exclusively to describe the heat that is lost through glass.
  • The lower the U-Value, the less heat transfers.
  • U-Value is most often used in the glass and glazing industry
  • If you need to know- U-Value is expressed in BTUs per square foot/hour/degree temperature difference.

R-Value

  • Used by architects and engineers.
  • Describes a material’s ability to prevent heat flow or act as an insulator.
  • The higher the R-Value, the less heat transfer.
  • U .03 = R 30
  • R-Value describes a material’s ability to act as an insulator or retard heat flow.
  • This terms is used by engineers and architects rather than the film industry.
  • R-Value is commonly used to describe wall and ceiling insulation. The higher the R-Value, the less heat transfers.
  • If you need to know: R-Value is the reciprocal of the U+Value, so R=1/U. A window with a U-Value of .25 has a R-Value of 4.0 or 1 divided by .25.
  • SO WHAT!
    • Insulation measures The U-Value of glass isn’t really changed by film. If some one is looking for a way to reduce heat loss, look at Low-E film/
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