insulation

[Sportsfan44]

hi my name is jordon and i need to have an interview with an expert to complete my science fair project. My topic is insulation and i have a few questions. 1) What is the most common type of insulation? 2) Where are common places in a house that contain insulation. 3) Can insulation be used to keep cold in and warm out. 4) What is the difference between thermal and electric insulation and 5) Does high quality insulation like fiberglass keep a house warmer compared to other unnatural objects like cotton or rags?

[rmarz]

Sportsfan44 - Jordan, the real help that Science Buddies experts give is assisting with some unknown aspects of projects or helping people get over some 'bumps' in the road in their experiments. There is a lot of research you should be doing to answer your own questions about insulation. Just to pique your interest in doing some research, I'll give you a hint as to what the most common thermal insulation material used in buildings is. The answer is "air". Now its time to do some research and try to answer "why".

Rick Marz

[Sportsfan44]

Thanks Rick I have already done all of my research but just need to ask an expert up to five questions for an interview it is half of the assignment. Do you know anyone who could help me.

[rmarz]

Jordan - I'm not specifically an expert on thermodynamics, but I think I could answer your questions fairly accurately. Others may update or correct a little. Here are my thoughts or my virtual 'interview':

1) What is the most common type of insulation? - As I originally mentioned, air is the most common form of thermal insulation. In the case of common fiberglass insulation, the fiberglass fibers simply prevent convection currents (stabilizing the movement of the air in the walls, for instance) minimizing heat loss. In the case of insulating Thermopane windows, the insulator in the space between the panes of glass is usually dry nitrogen or other gas (could be dry air). Again, an 'air' like material.

2) Where are common places in a house that contain insulation? - In a house, fiberglass or other insulation (rock wool, polystyrene or polyurethane foam, recycled paper base materials) are usually placed within external walls, in ceilings, roof rafters and beneath floors that are exposed to exterior temperatures. As mentioned above, windows can be a large source of heat loss. Multiple panes (Thermopane) or storm windows are used to limit that loss.

3) Can insulation be used to keep cold in and warm out? - Sounds like a trick question, like the joke about a Thermos bottle. It can keep cold liquid 'cold' and hot liquids 'hot'. How does it know? The answer is that insulation is a barrier to prevent heat flow between areas of different temperature. If you were building a 'cold' storage room, it might have the same insulation as you would build into a 'warm' storage room. The insulation is just limiting the passage of heat between the two temperature differential areas.

4) What is the difference between thermal and electric insulation? - In many cases good thermal insulators are also good electrical insulators. Again, air is sometimes utilized as an electrical insulator. Many of the materials that can be used for thermal insulation can be used as electrical insulators. Glass, fiberglass, plastics are common electrical insulators, but in most instances, materials that stand up to voltage stresses and remain stable are usually used. Everything from varnish on copper wire, thermoplastics, plastic films, rubber, paper, oil, fabric...the list goes on for materials that will not conduct electricity and remain stable over high voltage potentials. These same materials may not be cost effective in home insulation (or may propagate fire more easily) so aren't as good as some of the materials mentioned before.

5) Does high quality insulation like fiberglass keep a house warmer compared to other (unnatural?) objects like cotton or rags? - There is another aspect to insulation, thermal mass. That is the issue of a material to hold a quantity of heat. I mentioned that spun fiberglass insulation is really keeping a lot of air in place and motionless, but the glass itself has a relatively high thermal mass and is not a good thermal insulator in itself. The ratio of glass to air is really the secret to its good insulation properties. The insulating capability of plastic foam - again, is really the air content. Likewise of rock wool or other loose materials. They may even have lower thermal masses than fiberglass, and are better inherent insulators, so I can't tell you that fiberglass is superior to another material. How much air is being trapped by the rock wool or rag materials is part of the answer. Again, flammability is a real concern for home insulation. What fiberglass does provide is an economic insulator that is easy to install during the construction phase of a house. In many cases, 'blown in' insulators often used in attics is an appropriate choice because it is easy to install after construction. Another advantage of fiberglass is that it usually is manufactured with a metallic foil barrier. This reflects radiant heat and helps in the insulation properties. Up to now, the discussion above has focused on conduction and convection heat loss.

Hope this helps.

Rick Marz

[Sportsfan44]

thank you so much rick you interview answers were great and helped me finish my science fair project.

thanks again Jordon

[deleted-71588]

With respect to thermal insulation applications, vapor barriers are an important often overlooked aspect. Dry motionless air is an excellent insulator. Humid motionless air is a poor thermal insulator. Except for materials like solid cell foam that are intrinsic moisture vapor barriers, one has to be careful to keep condensation from entering an insulation system and reducing its insulation value and producing a place for mold spores to grow. The typical solution for insulation systems that are not an intrisic moisture barrier themselves is to put a vapor barrier on the hot side and ventilate the cold side. This means there really is a difference between which side is the hot and which side is the cold side for large temperature extremes for materials like fibreglass/air insulation.