heat transfer

  • How Aluminum Foil Insulates

    Many insulating materials come with a layer or multiple layers of aluminum foil. In fact a basic radiant barrier can function properly with a single layer of aluminum foil. Given that metals conduct heat rather well, especially aluminum, it might seem strange to use it as an insulating material. Here's how it works.

    Heat Transfer Basics

    Heat is really a measure of the energy of the atoms in a material. The more energy they have the higher the material's temperature. This energy is transferred in three ways: by conduction, convection, and radiation (and don't forget that heat always flows away from its source, from hot to cold.)

    Conduction happens when thermal energy is transferred through a material. When atoms are tightly packed, as they are in a solid metal, the energy moves easily.

    In a gas the atoms have more space, and the energy moves more slowly. That's why bubble materials are effective like down in a winter coat, which creates similar micro-air pockets - they slow the rate at which heat moves.

    Convection takes place when a liquid or gas expands. This makes it less dense and it rises, letting cooler fluid take it's place. That's why we say that heat rises.

    This leaves us with a puzzle: how does heat from the sun reach us through the vacuum of space?

    The answer is as light, both visible and invisible, or infrared. The sun radiates light, some of which passes through the earth's atmosphere to be absorbed by plants, soil, water, and so on.

    Absorbing Radiant Energy

    Some materials absorb light, and hence energy, better than others. A shiny material like aluminum tends to reflect a lot of heat while wood and concrete absorb a much higher proportion. That means aluminum is slow to warm up when exposed to radiant heat.

    Re-radiating, or emitting

    Everything that absorbs heat tends to give it off again. (Stand near a brick wall that's baked in midday sun and you'll feel the heat being radiated.) And just as some materials reflect better than others, some radiate heat better. This property of being a heat radiator is termed emissivity and it's given a value from 0 to 1.

    (Scientifically speaking, emissivity is the ratio between how much heat a material emits and the amount emitted by a 'perfect' emitter, otherwise known as a black body.)

    Iron and steel are quite good emitters and have emissivity numbers in the region of 0.5. (This is why they glow red hot when heated in a furnace or by a welding torch, they are radiating heat.)

    Aluminum has an emissivity of around 0.04. That means it radiates very little heat away from its surface, which is one reason why radiators aren't made from aluminum!

    Insulating with Foil

    Aluminum foil can be an effective insulating material because it doesn't radiate heat out into the environment. That's what makes it effective directly under a roof: although it will warm up through conduction from the shingles, it won't radiate that heat out into the attic space. In HVAC applications for example, the foil blocks heat from entering or escaping keeping the temperature where it is wanted inside the ducts. This same concept is used in many other residential and commercial applications.

    And that's how foil insulates.

  • Garage Door Insulation - Reflecting the Heat

    Garage Door Insulation TexasIs your garage insulated? If you are a typical homeowner, you've probably thought about insulating your garage to keep it warmer in cold weather (with the assistance of a small heater) but didn't want to spend the money or time on something you really only need a few months out of the year.

    Alternately, homeowners living in southern states have to cope with hot, stuffy garages all the time. Depending on the size of a garage, the cost of insulating the walls and ceiling could reach $1000 or more. Then you have the skin and respiratory irritations caused by fiberglass insulation, as well as the depressing thought of spending an entire weekend cooped up in a sweltering (or freezing) garage.

    Actually, It's the Garage Door's Fault

    Forget about insulating your garage walls and ceiling because it's not their fault your garage is uninhabitable--it's actually the garage door's fault for allowing most of the heat and cold into the garage. But the good news is you can insulate your garage door with an inexpensive, low-profile, easy to install type of insulation that is impervious to moisture and capable of repelling even the most intense UV rays.

    Reflective Insulation Will Make You Fall In Love With Your Garage Again

    In addition to allowing you to reclaim your garage, reflective insulation also provides these benefits:

    • Reduces energy bills in the home by keeping the garage temperature moderated (attached garages share a wall with the home)
    • Maximizes the efficiency of temperature-sensitive appliances in the garage (washers, dryers, refrigerators)
    • Makes the garage a more pleasant work environment (for vehicle repairs, big projects)
    • Reduces the level of outside noise
    • Contributes to a warmer garage in the winter and a cooler garage in the summer
    • Reflective insulation is quick to install and much easier on your wallet than fiberglass or "blown" insulation

    For homeowners living in steamy, southern climates, reflective insulation on garage doors not only keeps garages nice and cool but can help minimize infestations of insects or rodents seeking overly warm, dank conditions to raise more pests.

    Installing garage door insulation is the key to maintaining a comfortable temperature in your garage, regardless of the climate. Because reflective insulation has an aluminum layer on both sides, it works to prevent radiant heat from penetrating solid objects by powerfully reflecting it away from whatever it is insulating--specifically your garage door and garage.


  • Understanding Reflective Insulation: Conversing with a Customer

    We are always happy to speak with our customers. In doing so, we gain an insight into what questions they have regarding using our insulation in their applications.

    After enough conversations, a specific theme appears. For many, unfamiliar with heat transfer concepts, they want to understand exactly how this insulation will help them. Maybe a friend recommended the product or maybe they have found their way into reflective technology on their own. They know they have an application where insulation will help but they just don't know exactly how.

    This blog post is designed to outline the basic principles behind reflective insulation and how it can help you in your projects.

    First and most basic, reflective insulation blocks the transfer of radiant heat. Radiant heat is a primary source of heat transfer in a home. There are only three modes of heat transfer. Most insulation deals with slowing or trapping conductive or convective heat. Reflective insulation works in blocking the third type radiant heat. But what does this mean to you?

    It means there are inexpensive materials available that can help control the comfort in your home and save you money on your utility bills. How can reflective foil insulation do this?

    Remember, heat always flows from hot to cold. Here's an example of how to use a radiant barrier, a class of products primarily used in residential attics. Your home located in Las Vegas, Nevada gets extremely hot in the spring, summer, and fall months. Your home is older so there is not a radiant barrier installed. As the sun heats up the roof deck, this heat is radiated down (hot to cold) into the living space. The installation of a radiant barrier would reflect this heat back into the roof deck and outside not allowing your attic to heat up as much. This reduces the heat transfer to your living space. You in turn will be more comfortable.

    More importantly is when you choose to turn on your air conditioning. Now, you are spending money. Your air conditioning has to work harder to keep your home cool when your attic temperatures are high. There is more radiant heat transfer. Lowering your attic temperatures by installing a radiant barrier will decrease the amount of heat transfer and your air conditioning system will work less and you will save money.

    Here is another example from a cooler climate using foil bubble insulation, a different class of reflective products. Let's say your home is in Chicago and you have in-floor radiant heat between your floor joists with either a basement or crawlspace underneath. In the heating seasons, the heat is running almost continually. The heat emitted from the installed radiant system is transferring heat in all directions. Again, as heat goes to cold, a large majority of this heat will wind up in the basement or crawlspace. Installing foil insulation in between or on the bottom of the floor joists will reflect this heat back towards the floor where it is most effective for you. This causes your heating system to work less, saving you money.

    These two examples should help in understanding how our reflective insulation works for you in both comfort and energy savings. You will notice these examples showed two completely different climates. Once you understand how the product works you can apply this knowledge to your project which is always governed by your local climate. You will notice most southern climates use reflective insulation in attics to stop the sun's heat where northern climates utilize reflective technology in floors, under slabs, crawlspaces, walls, and ductwork to stop the loss of mechanical heat that you pay the heating company for.

    Hopefully this post helps you understand how heat is transferred and how you can control this process by utilizing the correct materials in an effort to save on your energy costs and increase your comfort within your home or building.

  • Insulation & Understanding Heat Transfer in the Home

    Many consumers don't really understand how heat transfer works and more specifically how it pertains to their home. A better understanding will certainly help in using the correct materials to lower energy costs. This short post helps to explain this.

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