What is R-value and Why Does it Matter?
When you're shopping for commercial refrigeration, understanding the terms and measurements listed can help you feel confident in making the right decision for your business. One of the factors often listed on a piece of refrigeration is its R-value, which can have a significant impact on the life and operation of your cold storage equipment.
The R-value, also called the R-factor in some cases, is a way of quantifying the resistance (the R in the name) a material has to the transfer of heat in a specific application. The higher the R-value, the greater the resistance to temperature transfer. Because R-value takes the material being used and its thickness into account, the measurement refers to a specific usage, rather than the material itself. For example, a 2-inch-thick sheet of polyurethane would have a higher R-value than a 1-inch-thick sheet of polyurethane, so the material itself cannot have an R-value until its intended use is considered.
To determine R-value, we must know the material's thermal conductivity, also known as K-value or K-factor, as well as the thickness of the material. The K-factor is the ability of a material to conduct heat – the lower the number, the less heat it conducts and therefore the better an insulator it is. Most materials used as insulation have a K-value of less than one. To get the R-value, you would divide the thickness of the material (in inches) by its K-factor.
As an example, we will use an insulation material that has a K-value of 0.035. Using the formula of R-value = inches of thickness⁄0.035:
|Thickness:||0.5 in.||1 in.||1.5 in.||2 in.|
Importance in Refrigeration
R-value is typically more prominent in specs for walk-in coolers and freezers, referring to both the wall panels and the floor, but the R-value of a reach-in refrigerator or freezer is also often noted on the model's spec sheet or is available upon request. Knowing this figure can help you establish how well your equipment will maintain internal temperatures.
The higher the R-value of a refrigerator’s or freezer's insulation, the more it is capable of keeping ambient heat out of the box. This means that the compressor will not have to run as often in units that are able to better maintain internal temperature, which can affect both energy efficiency and the longevity of the unit. A refrigerator or freezer with a higher R-value can, over time, save you money in both maintenance and utility costs.
Types of Refrigerator Insulation
As with any other type of insulation, the material and thickness of the insulation in a refrigerator or freezer are used to determine each unit's R-value. Finding the best refrigerator insulation is all about balance - it must be affordable, lightweight, and have a low thermal conductivity so that a high R-value can be achieved without requiring an overly thick layer.
As a result, most modern commercial refrigeration uses foamed-in-place polyurethane. To create the expanding foam, a blowing agent must be used to create a chemical reaction. These blowing agents can also affect the final R-value of the insulation, as they help determine the density of the final foam product and can also leave gasses behind in bubbles in the foam that provide additional thermal resistance. However, these agents can also have a significant impact on the environment, and so recent EPA regulations have restricted the chemicals that can be used based on their Global Warming Potential (GWP) and Ozone Depletion Potential (ODP).1 Some common blowing agents used include Ecomate™2 and cyclopentane.
One place that this polyurethane insulation cannot be used is in glass doors, but even these can be treated to increase their R-values. Low-E glass has a thin coating that helps block ultraviolet light to help reduce the transfer of radiant heat.3 Some commercial refrigeration manufacturers also use argon gas as a filler between two or more panes of glass in a door. This gas is abundant, non-toxic, and clear, making it ideal as a glass insulator in refrigeration. Argon's thermal conductivity is about 33 percent less than that of air4, raising a glass door's R-value enough to save the operator a significant amount in energy costs over the life of the refrigerator or freezer.
- Federal Register: August 6, 2014. U.S. Government Publishing Office. Accessed May 2017.
- Rigid Polyurethanes. Ecomate. Accessed May 2017.
- What is Low-E Glass? Vitro. Accessed May 2017.
- Window Gas Fills. International Association of Certified Home Inspectors. Accessed May 2017.