By John V. W. Howe, COO/CTO, Intelligent Thermal Solutions LLC
and Dwight Musgrave, President, Thermal Visions Inc.
Cold-chain packaging adds more mass to landfills than any other type of packaging. This is because the insulation required to keep the temperature-sensitive payload within the desired temperature range is extremely bulky. A simple corrugated box with no insulation occupies very little space in a landfill as compared with a foam insulated cold-chain container. Also, the corrugated box will decompose over time whereas foam insulation virtually lasts forever.
To reduce the growth of landfills owing to disposal of cold-chain packaging, we must design containers that use more-efficient insulation thus reducing the bulk of the insulation. The best solution to accomplish this is by using vacuum insulation panels (VIPs). The reason VIPs significantly reduce the volume of packing material in landfills is that they provide much more efficient insulation than other current solutions and require less bulk to provide the equivalent insulation.
A comparison of VIPs with other types of package insulation will show the advantages of using VIPs. We will use a measure called “R-Value,” which measures resistance to heat transmission in materials. Typical R-Value for vacuum panels is R-40 per in.¹ This is 9.5 times better than the R-Value of R-4.2 for expanded polystyrene (EPS) foam, the most common cold chain package insulation, and 5.88 times better than polyurethane (PUR) foam with R-Value of R-6.8.¹
Using the R-Value numbers, simple logic tells us that it will require 9.5 in. of EPS or 5.88 in. of PUR to achieve the same amount of insulation as one inch of an R-40 VIP.
This is true for a large flat surface like the wall in a house, but the amount of heat entering a shipping container is in direct relationship to the surface area of the container. For every inch added to the length, width, and height of the outside dimensions of the container, the outside area increases significantly. This added surface area of the container increases the amount of heat absorbed into the container.
One can see that this works against the EPS and PUR insulation since thicker walls are required to equal the thinner R-40 VIP, but as inches of insulation are added, the surface area increases, which in turn absorbs more heat.
To graphically illustrate the advantage of the VIP insulation, let’s design three equivalent containers with a payload space of one cubic foot (12 × 12 × 12 in.) using each type of material. Then we will compare the volume each will add to a landfill per 10,000 shipments.
When we use vacuum panel insulation, the outside dimensions for the container will be 14 × 14 × 14 in. This is derived by adding one inch of insulation on the six sides of the payload space. The resulting container occupies 1.588 cubic feet. This
is the base reference case for comparison to the other two types of insulation.
If we use the simple one dimensional relationship of R-values, the equivalent PUR foam box would seem to be 23.76 × 23.76 × 23.76 in. or 7.76 cubic feet.
However, when we analyze the PUR container by creating a 3-D model² of it and performing finite element heat flow analysis on the model using a sophisticated computer program,³ we find that the actual dimensions must be 36 × 36 × 36 in., owing to the heat absorption of the added surface area. This results in a PUR container with a volume of 27 cubic feet.
The EPS case is more remarkable. When we use the simple one dimensional relationship of R-value for EPS, the outside dimensions would seem to be 31 × 31 × 31 in. or 17.24 cubic feet.
However, when we use the 3-D model and finite element heat flow analysis program on this container, we find that even with a wall thickness of 84 inches on all sides (outside dimensions of 180 × 180 × 180 in. or 3375 cubic feet), the EPS container does not equal the performance of the VIP container.
The increase in wall thickness in the EPS container does not result in a linear decrease in heat flow as shown by Figure 1. The heat flow gradually decreases with increased wall thickness, but at a rate where the EPS container is not economically feasible. It appears from the graph that the condition exists where the heat flow line for EPS will approach the value of the VIP heat flow (4.06 BTU/Hr.), but will never equal it.
Assuming 10,000 shipments per year as the basis for our illustration and assuming none of the containers are reused, the waste from the VIP box will fill a football field 0.12 ft (1.47 in.) deep. The PUR foam box waste will fill the football field 5.42 feet deep. (See Figure 2.)
The EPS container, even with 84 inches of insulation, does not equal the performance of the VIP container, but if we use that container size for illustration, it will fill a football field 703 feet deep.
From these numbers, one can see the significant reduction in landfills by using vacuum insulation panels.
VIP containers provide another plus. Many times they are reused and usually make more than one trip before disposal or recycling. In order to achieve multiple trips with VIP insulated containers, the outer case must be solid and durable to protect the VIPs from damage. Each VIP container’s reuse further reduces the VIP contribution to landfills in relation to the other two types of insulation. Very few foam insulated boxes are reused.
An additional advantage of VIPs comes from the material used to make the panels. The core material for one type of panel is fumed silica, which is basically fine sand. This is about the same as adding dirt to a landfill.
Another type of core material is fiberglass. This core material can be reused by removing it from the old barrier film bag and inserting it into a new barrier film bag to make a new vacuum insulation panel so it can be kept out of the landfill.
If the fiberglass core material is not reused, it can be recycled as glass. The final core material is aerogel, which is a porous solid with very low density. Sending carbon aerogel to a landfill is like adding dirt to the landfill and with its very low mass, it contributes very little to the growth of landfills.
In summary, given the facts that vacuum insulation panels require much less mass than expanded polystyrene foam or polyurethane foam insulation and that vacuum panel core material can either be recycled or is made of sand or carbon, which are similar to dirt, vacuum panels contribute very little to the growth of landfills.
As well as being environmentally friendly, the superior insulation characteristics of vacuum panels significantly increase the thermal protection of the products that are shipped in vacuum panel insulated shipping containers. This technology is a win/win situation for mankind.
1. Wikipedia http://en.wikipedia.org/wiki/R-value_(insulation).
2. Solidworks 3-D CAD software.
3. ANSYS - engineering simulation software.