If you live in a colder climate, a lot of energy and money goes into keeping your home warm.
But you also need to keep that warmth in, which leads to a discussion of insulation.
Let’s talk about vacuum insulation. What is vacuum insulation anyway? A lot of people have become interested in it and wonder if they can use it in their homes.
If you’ve ever used a thermos or insulated water bottle, you may have had the technology in your hands without even knowing it. Because they are vacuum insulated.
A panel of vacuum insulation is comprised of a highly porous inner layer and a thin, tight outer layer or envelope. Air is evacuated and the envelope sealed, creating a vacuum within. This produces high thermal resistance, making heat transfer difficult by means of either conduction or convection.
Does that sound like you want to know more? Keep reading and I’ll cover all the vacuum insulation bases.
What is Vacuum Insulation Made Out Of?
Since we’ll eventually segue this conversation to if and how vacuum insulation can be used in the home, I’m going to talk about Vacuum Insulation Panels. I realize that’s not going to help you if you live in a giant thermos… and I’m sorry.
Vacuum Insulation Panels are used in a variety of places. Not just buildings, Here are a few other applications:
- Appliances where heat transfer is an issue such as dishwashers, fridges, freezers, and more
- Refrigerated transport
Vacuum Insulation Panels have evolved throughout the decades. The original panels were made in the 1930s and were composed of a layer of rubber wrapped around a porous material.
In the 1950s, the design was significantly upgraded, and a core made from glass was welded to a steel panel. The ‘60s saw the change to nanostructured materials with further advancement in the ‘90s when precipitated silica began to be used for the first time.
Clearly, the principles and design of this type of insulation have been around for a long time. However, with the advances and attention given to energy efficiency in the last few decades, there’s now a broader range of applications. Particularly in buildings and construction.
Since part of the process of vacuum insulation is the evacuation of whatever the interior material is made of, the core material is always made from something with an open-porous construction. The material also needs to be strong enough to survive the mechanical pressure load placed upon it.
These materials are typically microporous:
To guarantee the vacuum insulation panel’s optimum performance, the core material used should have the minimum possible thermal conductivity.
The microporous materials mentioned above are all able to absorb humidity, and the most commonly used options are glass fibers and fumed silica. However, in some cases, certain open-cell polymer foams are used. This would foam such as polyurethane or polystyrene.
The most important factor of the envelope material is that it’s impermeable to various forms of gas. Gas can’t pass through it.
It’s also important that it be impermeable to water vapor. If it’s not, it severely impacts the lifespan of the panel. Next, it needs to have low thermal conductivity. The last important criteria of the envelope material is that it has a high resistance to punctures.
To recap, the envelope material must be:
- Impermeable to various gases
- Impermeable to water vapor
- A composition of low thermal conductivity
- Highly puncture resistant
One of the most popular uses for vacuum insulation is in thermos bottles, and the envelope material used in them transitions nicely into insulation panels used in building too. This would be:
- Stainless steel
Any of these materials, when used in conjunction with the microporous core materials mention above—powders, fibers, and foams—can attain the high gas impermeability that is required for these panels.
Using any other combination exclusive of stainless steel, aluminum, glass, powders, fibers, and foams means a decrease in gas impermeability, which translates into a decrease in durability.
Most quality vacuum insulation panels will use an envelope of one of the following:
- Aluminum metalized high barrier plastic laminates
- Aluminum composite films
- Stainless steel films or sheets
If you’re looking to purchase panels and they don’t use these materials, chances are they are a sub-standard product, and won’t offer the type of heat transfer barrier you would get with a quality product.
How Does Vacuum Insulation Work?
There are three methods of heat transfer. Conduction, convection, and radiation.
Conduction occurs when molecules collide. Convection is a heat transfer that happens by the motion of air or water. The heated substance moves away from the heat source, carrying the energy with it. Radiation is the energy given off by a source, transmitted through air or water, and absorbed by something else.
In the first two of these methods—conduction and convection—a medium for heat transfer is required. Since the vacuum created by the core and the envelope of the panel eliminates the medium, it significantly reduces heat transfer.
However, radiation does not require such a medium, so in this case vacuum insulation isn’t as effective.
Vacuum Vs Traditional Home Insulation
Dow Corning has a product on the market that is 1 inch thick and has an insulating value of R-39 at the center of the panel and a unit R-value of R-30.
Sounds amazing, right? Yes, but remember this will only apply to conduction and convection heat. The sun beating down on your home and heating it up is radiant heat, and vacuum panels don’t work against radiation.
Secondly, at this point in time, these panels aren’t widely available on the consumer side of things.
In fact, while they are used in construction and building, it’s often only in green building initiatives, not typical construction projects.
Lastly, these panels are absurdly expensive—at least from a consumer point of view. Those designing and building green buildings are probably better able to swallow the price.
A quick search online found that a 1-inch thick panel will cost about $70 for a single square foot. Just as a comparison, Home Depot has 2-inch x 4 ft x 8 ft, R-13 rigid foam insulation panels for about $40.
The fact that these panels aren’t widely available and the cost or them really doesn’t make them favorable for the home market. For now, this type of insulation is most popular in thermos bottles, high-end refrigerators and freezers, and refrigerated transportation systems.
Maybe, if and when prices hit a sweet spot for consumers, they’ll become more popular. With an R-30 rating, I can see that happening.
The principles of vacuum insulation have been around for nearly a century. It’s most famously known for its usage in thermos and water bottles.
While it is used in the construction industry, it’s still somewhat limited to green or energy efficient projects. It has an incredibly high R-value so it’s a good choice,
Unfortunately, vacuum insulation isn’t widely available for homeowners, and the price can be restrictive even if the product can be sourced. Here’s hoping that at some point in the near future it’s an option more of us can choose.
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