Less Space, Better Insulation
September 1, 2010
Small footprints, but better efficiency. Low thermal conductivity, but less insulation to allow for more storage capacity. Sound familiar?
In the past, these, and other laudable but disparate goals, would often force designers to make tradeoffs. Add insulation to a refrigerator/freezer, for example, and improve efficiency, but lose storage capacity. Or, use less insulation to save space, but negatively effect efficiency and thermal conductivity.
In that scenario, compressors, heat exchangers and other components would either have to work harder and cycle on and off more often, or the designer would have to specify larger and more powerful components.
Layered on top of that is the mission to design products with no harmful effects to the environment, meaning that it has little in the way of ozone depletion potential (ODP) or global warming potential. In addition, any upgrades should be accomplished with as little cost expenditure to the product or the production facilities as possible.
Of course, much of this activity stems from the industry’s forced conversion to more environmentally friendly blowing agents and refrigerants. First, via the Montreal Protocol, the industry migrated away from chlorofluorocarbons that worked well, but were banned because of ozone depletion. Many manufacturers then shifted to hydroclorofluorocarbons (HCFC) particularly HCFC 141b as a stop-gap material. That too worked well, but also had ozone issues and contributed to global warming.
Today, the debate continues between hydrofluorocarbons (HFCs) that are primarily used in the United States, and hydrocarbons (HCs) such as pentane that are used in Europe and other regions.
This might be changing, however, as companies such as GE Consumer and Industrial and Coca-Cola look to hydrocarbon-based materials. Whether this is a long-term migration is debatable.
The arguments between the two are ongoing:
What is known is that polyurethane rigid foam materials are often used in refrigeration and cooling technologies because they are effective. BASF’s polyurethanes division, Wyandotte, Mich., conducted a cold-chain analysis, following a frozen pizza from warehouse to truck to refrigerator, and found that if all of the facilities and equipment were insulated at an optimized thickness with polyurethane rigid foam, there would be an energy savings factor of 20:1, says Werner Wiegmann, BASF’s head of development for polyurethane insulation.
The energy saved would be 16 times greater than the amount needed to produce the insulation material itself. During the study, material thickness was also tested, which found big savings with small changes. For instance, a freezer with 50-mm thick insulation emits 23 kg of CO2 in seven days, whereas a model with 60-mm thick insulation emits only 15.5 kg over the same period.
So, while all of these environmental, economic and regulatory goals might seem incongruent, new insulation materials and production techniques are helping to make these goals a reality. As suppliers launch new and innovative products, their customers are finding new ways to use them.
In fact, in recent months, numerous manufacturers-primarily in the commercial and residential refrigeration industries-have developed cooling technologies that meet efficiency standards, customer specifications, environmental mandates and other desired wants and needs such as increased thermal conductivity, reduced footprints and enlarged, overall storage capacity.
According to several refrigerator manufacturers and OEMs, the push for better energy efficiency comes from their customers who are demanding a greener product.
Even more exciting than simply producing efficient equipment, is the fact that many of these manufacturers are using varied methods to achieve these goals. The efforts are not simply a swap out of one type of insulation for another. Some manufacturers are committed to hydrocarbon-based insulation or blowing agents. Some have chosen vegetable-based expansion agents. Others have chosen vacuum-insulated panels, and still others have concentrated on materials with high flow rates to create a better-insulated product.
Manufacturers' InnovationsJeremy Hall, managing director of U.K.-based Precision Refrigeration, says that his customers were concerned about the impact that their catering equipment had on the environment. Listening to the company’s customers was an impetus to convert its extensive line of commercial-catering, food-equipment products to an insulation material that is made, in large part, from vegetable oils such as rapeseed oil.
The insulation is called Envirofoam R2007 from IFS Chemicals Group, also based in the U.K. Its polyol component contains about 70% vegetable oil and it has a GWP of less than 1. The blowing agent falls within the “less than 5” GWP category. The non-flammable insulation exhibits a Lambda value of 0.020 wMk.
The insulation helps Precision Refrigeration manufacture the product with no extra cost and without the need for substantial plant upgrades, says Hall. Testing determined that thermal conductivity values were 20% lower than other insulation foams that were in use.
Another commercial refrigeration manufacturer has converted to a new insulation material, from an HCFC-based material. Delfield, a Manitowoc company based in Mt. Pleasant, Mich., has converted its entire line of cooling technologies to what it calls, “a more environmentally safe insulation material.” The company switched to Ecomate, a polyurethane foam developed by Foam Supplies of Earth City, Mo., that uses methyl formate blowing agents.
John Murphy, new product development manager at Foam Supplies, says that Ecomate is a non-ODP, non-GWP material that is also exempted from U.S. VOC regulations. The foam can be blended with a polyol or isocyanates, and handled in the same fashion as HCFC-141b, as they have almost identical properties, including boiling point, solubility and flammability.
One of the biggest appliance manufacturers in the world, GE Consumer and Industrial, Louisville, Ky., has gone the hydrocarbon (HC) route for its Monogram refrigerator. The company, which has filed a Significant New Alternatives Policy (SNAP) petition with the Environmental Protection Agency, chose cyclopentane for the insulation foam-blowing agent to replace commonly used HFC foam blowing agents. The decision was made, in part, because of GE’s global presence and the need to produce one technology for all markets.
Another large, international manufacturer that offers a low-ODP, low-GWP product is Sanyo, a part of the Panasonic group. The company offers a refrigerator cabinet that features the Sanyo V.I.P., a vacuum-insulated panel design that optimizes interior volume in the smallest footprint possible. (Panasonic offers the U-Vacua, vacuum-insulated panel for sale to OEMs, which is discussed later in this article.)
The Sanyo V.I.P. features a composite, thin-wall cellular construction that combines the vacuum panel insulation with polyurethane foam for structural stability and high-insulation values. It has a reflective barrier film for puncture protection, which also helps inhibit moisture accumulation that can lead to icing.
Samsung’s now two-year-old French door refrigerator, has one of the industry’s largest interior capacities, at 29 cubic feet, despite keeping an industry standard size. High-rate urethane insulation technology allowed the company to reduce the refrigerator walls from 2.04 in. to 1.38 in., resulting in an extra 3.5 cubic feet. The high-rate technology implies that it delivers the insulation material in a pour-in-place process at a sufficient flow rate to produce a fine cellular structure.
Cell StructureThere is an adage about cellular structure that still holds true: “the finer the cell, the better the insulation.”
The thermal conductivity of foam is affected by a number of factors including the blowing agent and the polyurethane matrix within the foam. Blowing agents are key tools to creating the fine cellular structure of the foam as they, in effect, carve out cells within the foam and become trapped within the cell. Blowing agents are also one of the materials most affected by environmental regulation changes.
For this reason, a number of suppliers are launching or developing new blowing agent materials. According to Ken Gayer, business director for Honeywell foam insulation blowing agents, these materials should feature a low-vapor thermal conductivity, be nonflammable, and remain liquid at room temperature-in other words, have a boiling point greater than 25 Deg. C.
A lower boiling point tends to keep the chemical in a vaporous state in the cell so that there is less degradation. They should feature low toxicity, zero ODP, low GWP, and chemical and thermal stability. They should be soluble in formulation, and have a low rate of diffusion. These too are important because the material must dissolve into the mixture, staying trapped in the cell when formed and cured.
Honeywell’s Enovate blowing agent is a hydrofluorocarbon (HFC-245fa, 1,1,1,3,3,) that was developed as a blowing agent for rigid insulating foams, says Gayer. It is a replacement for HCFC-141b and other fluorocarbon and non-fluorocarbon blowing agents. Enovate is a non-flammable liquid with a boiling point slightly below room temperature. It has a zero ODP, a low GWP, and is not considered a VOC in the United States. In several studies, Enovate was compared to a pentane-based material and was found to have a 10 to 15% lower thermal conductivity, according to Gayer.
Bayer MaterialScience, a German-based company with U.S. headquarters in Pittsburgh, is a supplier of materials for insulating refrigeration appliances. The company offers Baytherm rigid polyurethane foam systems, Mondur isocyanates, and Multrano and Arcol polyols.
The company also conducts extensive research on insulation materials to determine ways to make foams more economical by using less material. In a 2009 study, company researchers tested HFC 245fa and found that by increasing water levels to generate more CO2, as much as 68% less hydroflourocarbon was required. In this test, the average K-factor increased by only 11%.
Another strategy for reducing foam cost is supplementing reduced levels of HFC-245fa with HFC-134a. The need for insulation materials with improved energy efficiency and environmental profiles has led Arkema of Cary, N.C., to investigate a range of low-GWP blowing agents designed for most PUR applications. These fourth-generation blowing agents, the AFA series, are being developed in both liquid and gas formulations to replace HFCs such as 245fa and 134a. AFA-G1, and to a lesser extent AFA-G2. They have shown to potentially compete with HFC-134a in terms of solubility in polyol, dimensional stability and K-factor, although AFA-G1 doesn’t seem to perform as well at very cold temperatures. Additional versions such as the AFA-L1 displayed a similar blowing efficiency and dimensional stability and held a K-factor compared to hydrocarbons, according to Arkema.
DuPont Fluorocarbons has developed FEA-1100, a fourth-generation, foam expansion agent for polyurethane foams. It features zero ODP, and low GWP. Recent estimates indicate that FEA-1100 has a short atmospheric lifetime of approximately 16 days. FEA-1100 has low-vapor thermal conductivity and is a stable liquid at room temperature with a less than 25 Deg. C boiling point. This eliminates the handling and processing issues associated with the use of lower boiling materials such as HFC-245fa, allowing optimal FEA level in formulations to provide desired foam properties, according to DuPont.
Michigan-based Dow Chemical Co. has developed new foam systems using various blowing agents with a focus on hydrocarbons. Voratec SD 302 and the Voratec SD 308 are balanced for better flow rates, voids, demold and thermal conductivity. However, in order to address the need of the appliance industry to improve energy efficiency, further optimization of the insulation performance of these systems is required.
To enable the improvement of the Lambda values of the foam without compromising on other foam process properties such as demold or flow, Dow developed a base polyol for rigid-appliance foam systems called Polyol X. An improved Lambda value of between 2.5 and 3% was achieved, and no deterioration in other properties was observed.
Vacuum-Installed PanelsAside from new and improved blowing agents, there are other technologies in play such as vacuum-insulated panels. These panels, such as those used by Sanyo, attain a phenomenal R-value per inch, often exceeding 20 and more. The core material of vacuum insulation is micro-porous fumed silica, which is poured into a plastic membrane and formed into a board shape. The panel travels through a vacuum chamber where gas is evacuated and a sheet of metalized plastic barrier film is formed around the membrane and heat-sealed around the edges.
Vacuum-insulated panels, or VIPs, have very high-efficiency numbers, but they are susceptible to punctures. Suppliers are answering this problem with more durable, protective films.
Panasonic’s vacuum insulation panel is called U-Vacua. It performs about 20 times better than hard urethane foam, and 38 times better than glass wool, which enables high-insulation performance in a thin form. It achieved a thermal conductivity of 0.012 wMk at 24 Deg. C, with an applicable temperature range from -40 Deg. C to 105 Deg. C. In refrigerated applications, VIP is most commonly used in conjunction with standard foaming agents to assure the optimum combination for insulation value and maintaining cabinet rigidity. The panels are normally located between the inner liner and cabinet shell. The ultra-slim design enables manufacturers to increase the internal volume of the cabinet, while maximizing energy efficiency, says Jennifer Archibald, product manager - new business, Panasonic Industrial, Secaucus, N.J.
A newer twist on VIPs comes from Germany-based Va-Q-Tec. The core of the panel is made of inorganic oxides that are up to 80% fumed silica, IR opacifiers and a small amount of organic fibers. One of the company’s newest products is the Va-Q-Plus, which is produced with a new production technique that makes it possible to develop variant shapes and complex panels, such as cylinders and panels with holes, says Roland Caps, Ph.D., a physicist, and managing director of the company. It has a low-thermal conductivity of 0.0035 W/(mK).
Finally, Microtherm of Alcoa, Tenn., offers the Slimvac vacuum microporous insulation panels for refrigerators and freezers. The Microtherm panels feature a touch outer envelope, which the company says is impermeable. The outer envelope comprises multiple polymer layers, each chosen for their specific contribution toward maintaining a long working life without performance deterioration. The panels have a center panel thermal conductivity of 4.2, which is roughly five times lower than blown PU foam.
These panels, the improved blowing agents and other insulating materials discussed in this article are just some of the products that are on the market or planned for the near future. Numerous products are in the works, and each one of them might be the answer to a manufacturer’s need to improve efficiency and protect the environment.
For more information, visit: