Dome Science: How Air Structures Stay Warm, Part 1
Winter is back, which means The Farley Group is winding down from a busy dome-inflating season. Bubbles across the country are ready to keep games going until the snow and cold recedes for the spring. But with the dropping temperature, a common question we hear is, “With fabric walls, how does it stay so warm?”
This is a question with two real answers: 1) high quality heaters, and 2) insulation science!
Before getting into dome heaters, it’s important to understand the science of insulation. After all, you could have the warmest, most efficient heaters around but if that heat just floats away, those expensive heating units are useless. To follow up on our article about the science of air and air pressure, let’s talk about the science of heat.
What is heat?
To first dig into the subject, we need to understand, what is heat? Heat is a form of energy and energy can neither be created, nor destroyed—it can only switch from one form to another. To create heat, you are actually transferring a form of energy (like electricity or fuel) to a medium, which in this instance is the air. Giving this energy to the air molecules, makes them move faster and that is what we feel when air is warm.
For the air to lose this energy and become less warm, it needs to transfer it to something else. This is why everything in a room will equalize in temperature to the ambient air.
You may remember learning this early on in science class, but heat can transfer in three different ways: conduction, convection, and radiation. Convection involves fluids so, unless your bubble is full of water, we don’t really need to worry about.
Conduction involves directly transferring heat from one medium to another. For example, when you touch a cold piece of metal, the heat in your hand transfers into the metal making your hand cold. Conduction is also the process described earlier when air passes it’s energy to whatever it is touching. Air does this much less efficiently than dense materials like metal though.
In general, the more dense something is (the closer packed the molecules are) the more heat conductive the material. Metal, bricks, glass. These are all great examples of materials that conduct heat exceptionally well, which is why windows, bare walls, and metal trim are always cold in the winter when directly exposed to the outside.
A Fabric Misconception
A common belief is that for something to retain heat, it needs to be thick. Intuitively, a thick blanket is warmer than a thin blanket, right? So a thick, brick wall must hold in more heat than a thin piece of fabric? This might seem a logical conclusion to make, but there’s a lot more science to it than that.
The first thing to consider is whether you are stopping the flow of air. An air-structure is already mostly airtight or it would collapse to the ground. Check. The next thing is to stop conduction through the wall.
Now we know that air is actually a terrible conductor of heat, but this is what makes it an incredible insulator. Most insulators work not because they are thick, but because they are able to trap air in one place, which then makes it very difficult for any heat to transfer via conduction. The fluffier something is, the more air it has trapped in it and that’s why your big, fluffy blanket keeps you so warm!
Farley air structures use this same principle. Because there are multiple layers to the dome fabric, there is a layer of air in between the two fabric surfaces. This air keeps the cold out and the warm in.
Of course, some heat still escapes and this is why Farley uses unique insulation to add more protection from the cold. This insulation helps to slow down conductive heat transfer, but it also protects against another source of heat loss, radiation. Radiative heat loss is another fun topic and we’ll get into that in part two of this article!