I'm in the process of insulating our greenhouse with yard waste bags full of maple leaves, and some stuffed with hay. I'm wondering if anyone out there in permie land would know which is the better insulator? I have enough bags of maple leaves but don't have enough hay to line the entire surface of the walls so I'm wondering which one I should put at the top, which is where the best insulation is needed.
Location: Melbourne FL, USA - Pine and Palmetto Flatland, Sandy and Acidic
posted 7 years ago
There are three ways for thermal energy to travel:
Radiation (radiant heat) - electromagnetic radiation generated by the thermal motion of charged particles in matter (atomic particles vibrate when heated). In layman's terms, when you start a camp fire you are warming your hands with the thermal radiation produced. Place a thin sheet of aluminum foil in front of your hands and then you will notice the feeling of warmth greatly diminished because aluminum naturally reflects thermal radiation. The amount of thermal radiation produced when heated is directly related to the natural properties of the material. For example, iron when heated produces a lot of thermal radiation as compared to aluminum and you will notice this by placing your hand at equal distance apart and comparing the two. Radiant heating is based on this principle.
Convection - this requires a fluid movement (liquid or gas) where thermal energy travels by means of the movement of the particle carrying the thermal energy. For example, when you light a candle the air becomes less dense (less heavy) than the surrounding air and so it rises. When a fan in a fireplace blows hot air, the heat is traveling by means of convection.
Conduction - this is the transfer of heat energy by thermal diffusion (heat transfer rate between two or more particles) within a body due to a temperature gradient. Thermal conduction is another material property (unique to every material) where energy always travels towards the path of least resistance (hot to cold) and the resistance to this energy flow describes its conduction. So, copper is a highly conductive material which means thermal energy can travel relatively fast. Cellulose is an insulator so this means thermal energy does not travel very fast by means of diffusion. In a perfect vacuum (such as in space), thermal conduction is impossible because there is no mass to transfer the heat. Only radiant heat can travel in space.
Soooo, now I can explain assuming you read the boring part. Air is considered an insulator. Cellulose is a better insulator than glass (used in fiberglass) and the confusion about the trapped air explanation lies in the relation between the three methods of thermal energy traveling. I am not sure but I believe air may be a slightly better insulator than glass regarding thermal conduction so ideal strategy (and cheaper) is to fluff the fiberglass to slow the flow of air (which move heat by convection) preventing thermal energy moving. If Cellulose is a better insulator than air by means of thermal conduction (which I believe it is), than packing it tightly would be ideal. Be careful about thinking of loosely packing leaves and straw because it is not mechanically optimized to slow air so it will simply seep through cracks and heat/cool your home by convection.
As for maple leaf vs straw, it would be easy to test this by using two thermometers and two boxes. Get a bag of straw and leaves placing it in your house for a day or so making them the same temperature. Put the straw and leaves in separate boxes with the thermometer in the center in each and place the boxes outside for a period of time. Simply quickly open the box and check the temperature difference. You can also compare the tightly packed box vs the loose filled box as well.
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