5 Things You Must Know Before Buying Radiant Barrier
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Consumer Report: 5 Things You Must Know Before Buying Radiant Barrier 1 INDEX I: How Do Radiant Barriers Really ork pg 3 A: Understanding Heat Transfer pg 333 B: How Radiant Barriers Stop the Heat pg 444 II: hat Type of Savings Can I Expect pg 555 III: How, hen and here to Install Radiant Barrier pg 777 A: Perforated or Non,Perforated pgpgpg 777 B: Re-uired Installation Tools pgpgpg 888 C: here to Install Radiant Barrier pgpgpg 999 I.: Radiant Barrier Myths/ Busted pg 101010 A: Radiant Barrier Paint vs. Rolls pg 10 B: Radiant Barrier 1 Roof Shingles pg 101010 .: Not All Radiant Barriers Are Made the Same pg 111111 2 I: How Do Radiant Barriers Really ork2 To help you to understand how a radiant arrier works, let me first start y explaining a little a out heat transfer. When talking a out radiant arriers, insulation, ()AC systems and energy efficiency, it is important that we recogni-e that all of these things are a out controlling heat. A. /nd/nderstandingerstanding (eat Transfer (eat transfer happens in homes and uilding in three distinct ways. * Conductive heat transfer (conduction) * Convective heat transfer (convection) * Radiant heat transfer (thermal radiation) Conduction is the least efficient method of transferring heat, and in a kitchen analogy, that would e an e0ui1alent of oiling water in a pot o1er a sto1e. The fire heats the pot and the pot transfers its heat to the water and the water e1entually comes to a oil. The key point here is that conduction is the transfer of heat through direct physical contact. Con1ection is more efficient than conduction, and in our kitchen analogy, con1ection would e the use of an o1en to heat food. Con1ection heat transfer is the process y which heat is circulated in an area through the air and2or fluid. The key point here is that heat is transferred through air circulation. 3adiant heat otherwise known as thermal radiation is the most efficient type of heat transfer and the est example in our kitchen analogy would e the use of a microwa1e. 3adiant heat is generated when heat from the mo1ement of charged particles within atoms is con1erted to electromagnetic radiation. In a home or uilding, radiant heat refers to heat radiated from o 4ects and materials, such as incandescent lights, concrete flooring and the sun. It is also important to note that radiant heat mo1es through the air without heating the air, instead it will heat the first surface that it touches, and this surface will then re5radiate that heat in the space making it feel warmer when you are in that space. In general, heat transfer etween the interior and exterior of a home or uilding is ad and decreases the efficiency of the heating and cooling system. There are some special conditions where heat transfer is used to increase the efficiency, such as traum walls, thermal masses, and other natural heating and cooling techni0ues. 6ut for the most part, in a typical home or uilding which relies on mechanical means of heating and cooling, heat transfer is the enemy. 3 So, it makes sense to stop as much heat transfer as possi le. This is why insulation is used in all structures. Insulation is great at reducing con1ecti1e heat transfer, while also reducing some radiant and conducti1e heat transfer as well. (owe1er, the typical amount of insulation in a home or uilding 8anything elow 3399 is simply not enough to stop the ma4ority of radiant heat from infiltrating the structure. 6. (ow 3adiant 6arriers Stop the (eat A radiant arrier is a material with a 1ery low emissi1ity and high reflecti1ity gi1ing it the a ility to 1irtually stop the transfer of radiant heat or thermal conducti1ity. This allows the radiant arrier to reduce heat gain in the summer and heat loss in the winter, thus reducing the net heating and cooling needs of the structure. There are two key 1alues that determine the effecti1eness of a radiant arrier, and those are its reflecti1ity 8higher is etter9 and emissi1ity 8lower is etter9 1alues. The reflecti1ity 1alue of a radiant arrier is pretty easy to understand, the higher the reflecti1ity 1alue, the more light energy 8heat9 the radiant arrier is a le to reflect. 3eflecti1ity 1alues are expressed as a percentage num er 8:9, which asically descri es how much light energy the surface will reflect. The emissi1ity 1alue is asically the ratio of heat energy radiated y a material to the heat energy radiated y a true lack ody at the same temperature. This may sound a it confusing, so let’s talk in layman’s terms. 6asically, if we were to take a pure lack o 4ect 8theoretical9 which reflects no light energy and a sor s all light energy that touches it, it would ha1e an emissi1ity 1alue of one 8 = 19. Any real o 4ect, weather it is lack or not would ha1e an emissi1ity 1alue of less than 1. So, what this definition is really saying is that the darker an o 4ect is, the more light energy it will a sor ed and re5radiated. And su se0uently, the lighter and more reflecti1e a material is, the less light energy it will a sor ed and re5radiated. 3adiant arriers, e1en though they ha1e little or no “insulation” properties can effecti1ely lock most of the heat coming in or lea1ing a structure. This is ecause radiant heat is the most efficient type of heat transfer, and stopping radiant heat transfer is the most effecti1e way to decreasing your heating and cooling needs. In the summer, less radiant heat entering your attic makes your AC system run more efficiently, and in the winter, less heat energy eing lost through the roof makes your heater more efficient. 4 II: hat Type of Savings Can I Expect Many indi1iduals want a hard num er or percentage of estimated sa1ings from a radiant arrier, it really is impossi le to predict, ecause there are so many different factors which contri ute to its effecti1eness or ineffecti1eness. (owe1er, according to studies done y the /.S. Department Of Energy, it is generally accepted that installing radiant arrier in the attic will reduce heat gain through the ceiling y 40: typically leading up to a 17: reduction on heating and cooling utility ills. While this 17: figure may hold true for many climates and a typical installation, it will 1ary from place to place. Many independent studies and radiant arrier users ha1e tested their results and reported energy sa1ings 1arying from as low as 12: up to as high as 39:. The graph elow shows the attic temperature difference etween two similar attics spaces, one with a radiant arrier installed and the other without. As you can see, the attic with the radiant arrier8 lue9 stayed much cooler throughout the day. This report is not meant to gi1e hard figures, rather it is meant to gi1e the potential radiant arrier user2installer the proper information to make the most informed decision possi le. With that eing said, the section elow will list and descri e some of the main factors which will affect the performance of a radiant arrier installation. 5 MMMainMain FFFactorsFactors DDDeterminDeterminetermininginginging 3adiant 6arrier EEffecti1eness.ffecti1eness. • Attic Ductwork C If ductwork or air handlers are located in the attic, the temperature of the attic area will affect the efficiency of the ()AC system. /sing a 3adiant 6arrier to control attic temperatures will increase ()AC system efficiency, thus reducing energy costs. • Existing IIInsulationInsulation C If existing attic insulation is less than a 339, a 3adiant 6arrier installation will help to stop excess radiant heat. (omes with a 339 or higher ceiling5insulation, and ha1e no ductwork in the attic will not achie1e much energy sa1ings from a 3adiant 6arrier installation. • Cold Climates C In climates where the ma4ority of annual energy usage goes towards heating the structure, a radiant arrier on the floor of the attic, a o1e the insulation and ductwork will pro1ide su stantial energy sa1ings. • Hot Climates C In climates where the ma4ority of annual energy usage goes towards cooling the structure, a radiant arrier stapled to the ottom of the roof rafters will pro1ide maximum energy sa1ings. • ild Climates C In more mild climates where neither heating nor cooling is used much, a radiant arrier installation will not create massi1e energy sa1ings. (owe1er, the 3adiant 6arrier can increase the o1erall comfort of the structure while pro1iding small to moderate energy sa1ings. 6 III: How, hen and here to Install Radiant Barrier A 3adiant 6arrier installation can e a 1ery daunting task. 6ut with a little know how and the proper tools, any handy man 8or woman9 can definitely do the 4o . A radiant arrier installation is est done when the outside temperature is mild so as to minimi-e installer discomfort. Spring or fall are the est seasons to install radiant arrier, howe1er if you must install radiant arrier during summer or winter months, early mornings and e1enings are the est times to work, as the attic is cooler. There are a 1ariety of different installation procedures and locations, which depend on a num er of different factors. 6elow, we will address all of the most common factors and their subse0uent installation applications. AAA.A. Perforated or NonNon5555perforatedperforated The type of radiant arrier you choose will depend on your local climate and humidity. Eou will find that radiant arriers come in two main fla1ors, Perforated or Non5Perforated 8aka. )apor 6arrier9. It is 1ery important to understand when, where and if a non5perforated 8)apor 6arrier9 radiant arrier is needed.