By Benjamin Brits
Insulation, and more specifically insulated panels – are considered critical in many aspects of the cold chain today, and several other industries too.
One may think that an insulated panel is the same from supplier to supplier and that the ‘material’ that they are made out of is all the same too. However, this is far from the reality as these essential components come in many configurations – and may deceive the eye when installed while at a glance you would need an intricate knowledge of this subject to know the difference.
Insulated panels, sandwich panels, composite panels, or also known as structural insulated panels were first a product of the built environment for homes and were invented in the 1930s. Wood chips were used as the insulating material. Their popularity gained traction for industrial applications from the 1970s when foam insulation was conceived, and with that, the use of chlorofluorocarbons (CFC) – which we know was harmful to the earth’s ozone layer. (Subsequently CFC use was replaced for foaming applications with hydrochlorofluorocarbons (HCFCs) and later hydrofluorocarbon (HFC). The use of these gasses too will be phased out in the near future and be replaced with one of the hydrocarbons (such as n-pentane, isopentane, or cyclopentane).
With the advancement of technology and the discovery of new and safer ways to manipulate and handle raw materials, as well as their properties under differing conditions, the world of insulation has taken great leaps since the early 2000s with designs and formulas to meet many requirements.
For applications in the cold chain, insulation material performs the function of keeping the temperatures inside and out of any space separated, thus requiring less work from the refrigeration system to maintain the temperature and so conserve energy. You could imagine trying to cool down a plain steel shed that is fully exposed to the peak heat of the day would not be very effective, or extremely difficult – not to mention the challenges one would experience at night or in erratic climatic conditions. It is therefore essential to manage the heat load factors – and insulated panels are the obvious answer.
For the most part, insulated panels are associated with storage rooms for produce, but their application in the cold chain extends further into cold and freezer rooms, food production facilities, display fridges, food preparation areas, abattoirs, medical rooms, growing environments, specialist applications, distribution and transportation services – any area where conditions for control are required in order to avoid premature decay of the product. This may include temperature as well as hygiene safety factors.
South Africa has, over the last few years, gained countless facilities – particularly cold stores and distribution centres directly related to the cold chain. This expansion has also seen several entries from international organisations and along with their investment has come high standards and requirements. This is of course good for the local manufacturing sector and especially for those providers who have kept up to speed with technology and global standards. New facilities are also pushing the boundaries of storage heights here locally with some sites now boasting 22m tall walls.
The transportation sector has also seen a boost over the last two years owing to the growing-ecommerce sector and has also been fuelled by the changing habits of the consumer. This is another very active sector that utilises these products with home delivery services of all kinds.
The how and what of insulated panels
The concept of the insulated panel construction is very simple – it is a material (the core) ‘sandwiched’ between two pieces of metal (also known as the skins). The production of these panels in South Africa is primarily through two methods – namely the use of pre-cut blocks bonded to the facings or through a process known as foam in place/injection – where the core material is blown into a cavity and expands to fill the void.
Now although a very simple product construction to understand, ‘the devil is in the detail’ as they say, and both the core and the skins that are available come in different forms – and of course these elements ultimately create different quality end-products. One such example is that profiles can come in a range from 25mm all the way through to 300mm in thickness, however the thickness of the product is not the only factor that needs to be considered – the profile density offers different thermal properties too.
Similarly, the skins could be a material that is anything from 0.25mm to a few mm in thickness and be a composite of several different combinations of metals, and, as another example – lower quality could result in premature corrosion or altering of structural limits. The skins not only protect the core insulation, they have other useful functions such as protection against weather (in the case of SA – the harsh sun), hygienic surfaces and a level of protection against fire or open flame. This is achieved via the various coatings that can be applied.
Fire risk rating has been covered extensively in previous issues of Cold Link Africa which can be referred to in terms of this subject matter. Also, several studies can be found online that offer insights into the optimum panel thickness and core choice for the categories of the cold chain based on application and geographical location.
Wall panels can be freestanding and interlocked using different joining techniques and can also be installed using a full frame support. They could further be used as wall cladding in the cases where a concrete structure already exists. Ceiling panels would be installed using the panel walls as the predominant supports with the addition of supporting hangars/steel cables. Both ceiling and wall panels can come in different span lengths and profiles, and the maximum production length is really only limited by the ability to transport the product. The longest panels (without a join) produced locally come in at 16.5m! Most reputable manufacturers will have guidelines as to appropriate and best installation practices for their respective products – be they for wall or ceiling applications.
A particular feature of these panels – which is supplier dependant – is the various methods of joining the panels together. This can be through a unique locking design, simple dovetail, direct insulation engagement with skin overlaps, or a separate extrusion system.
Insulated panels have a life expectancy of up to 30 years. The core material for the panels that is available in South Africa is listed as follows. Special formulations that are unique to some international suppliers are also available locally. As a highlight, the pros and cons of each material are available through various associations both locally and internationally. For example, some materials may degrade faster over time compared to others or permeability of liquids is more with one material over another, affecting performance.
Expanded polystyrene is produced by expanding polystyrene beads, which are then bonded together to form rigid boards. “Bead boards” as they are often referred to are manufactured in three densities. Polystyrene will “break down” if left exposed to sunlight for prolonged periods. This material must also be protected from solvents and only compatible adhesive and sealants can be used.
Phenolic foam is manufactured from phenol formaldehyde resin and is available as either an open or closed cell product. It should be protected from prolonged exposure to sunlight and water. It is suitable for wall sheathing, and for use on the interior, both above and below ground.
Polyisocyanurate and polyurethane insulation is manufactured by chemical reactions between poly-alcohols and isocyanurates creating or forming tiny air cells. The cells contain refrigerant gases instead of air. The boards must be protected from prolonged exposure to water and sunlight, and if used on the interior must be covered with a fire-resistant material.
Rockwool insulation refers to a type of material that is derived from actual rocks and minerals. It also goes by the names of stone wool insulation, mineral wool insulation, or slag wool insulation. A wide range of products can be made from rockwool due to its excellent ability to block sound as well as heat. This type of insulation is commonly used in applications that require the best resistance to fire risk. Although it is a product that can withstand 1000-degree heat, without a supporting structure to match, it is a brittle structural material.
Information about the technical differences between open and closed cell technology is available from manufacturers but in simple terms it involves weight, density and permeability properties of air/vapours which impact thermal resistance of insulation material that is manufactured using chemical reactions.
Insulation performance and measurements
The thermal performance of all components and systems, except windows and doors, is expressed in terms of an “R-value”. For windows and doors, performance is expressed in terms of U-value.
What is an R-value?
Insulation materials are rated for their performance in restricting heat transfer. This is expressed as the R-value, also known as thermal resistance. The R-value is a guide to performance as an insulator—the higher the R-value, the better the insulation or resistance to heat flow that the material provides. R-values are expressed using the metric unit’s m².K/W, where:
- M2 refers to one metre squared of the material of a specified thickness;
- K refers to a one-degree temperature difference (Kelvin or Celsius) across the material;
- W refers to the amount of heat flow across the material in watts.
- Use the nominal R-values as listed by the manufacturer to determine the performance.
Products which have the same R-value will provide exactly the same insulating effect, provided they are correctly installed. Products must be installed in accordance with the manufacturer’s specifications and guidelines.
Material R-values refer to the thermal resistance values of bulk/mass type insulation are measured on the product alone according to international standards. System R-values indicate the thermal resistance value of reflective insulation is calculated based on international standards and depend on the product being installed as specified in accordance to the manufacturer’s specifications. This is known as a system R-value which incorporates air spaces. Composite R-values are the thermal resistance values of composite insulation products are measured by testing the composite product as a unit according to international standards.
Direction of heat flow effect
R-values can differ depending on the direction of heat flow through the product. The difference is generally marginal for bulk insulation but can be pronounced for reflective insulation.
- Up R-values describe resistance to heat flow upwards (sometimes known as ‘winter’ R-values).
- Down R-values describe resistance to heat flow downwards (sometimes known as ‘summer’ R- values).
What is a U-value?
Sometimes insulation or systems are rated in terms of their thermal transmittance (U-value), rather than R-value. The U-value measures the transfer of heat through a material or a building element (thermal transmittance), whereas the R-value measures the resistance to heat transfer. U-values are often used in technical literature, especially to indicate the thermal properties of glass and to calculate heat losses and gains.
The U-value is the reciprocal of the R-value, R=1/U or U=1/R. For example, with an R-value of 2.0, the U-value is 1/2 or 0.5.
The U-value is expressed using the metric units (W/m².K) where:
- W refers to the amount of heat transmitted across the face or through the material in watts;
- m² refers to one metre squared of the material of a specified thickness; and
- K or ‘degree Kelvin’ refers to each °C temperature difference across the face of the materials or through the material.
A smaller U-value results in lower heat flow, and therefore less heat loss. Higher U-values mean greater heat loss.
What is an overall and total R-value?
The overall R-value is the total resistance of a building element or system combination. It takes into account resistance provided by construction materials used in a walls or ceilings, internal air spaces, thermal bridging, insulation materials and air films adjacent to solid materials. Each of these components has its own inherent R-value, the sum of which provides the overall R-value.
The intervention added R-value or added thermal resistance is the value of the insulating material alone. This is the term most used when buying thermal insulation. Some products will have a higher R-value for a specified thickness. For example, a 70 mm thick extruded polystyrene board and 100 mm thick glass wool blanket may have the same apparent R-value.
The R-value is the material thermal resistance, ie product only, whereas the total R-value describes the total thermal resistance of the system to heat flow provided by a roof and ceiling assembly (inclusive of all materials and air films), a wall or a floor. These values are calculated from the resistance of each component, including the insulation. Total R-values are the best indicator of performance, as they show how insulation performs within the envelope.
Thermal bridging is the transfer of heat across building elements, which have less thermal resistance than the added insulation. This decreases the overall R-value. Wall frames and ceiling beams are examples of thermal bridges, having a lower R-value than the insulating material placed between them. Because of this, the overall R-value of a typical ceiling and/or wall is reduced.
What elements form part of deciding on the right insulation product?
Having so many options of product to consider, you may wonder what aspects you need to keep in mind when doing your evaluations or generating the project specifications. As you would be aware, each room or facility for that matter usually involves customer or process-specific designs to suit. Some of the items that need to be included are:
- The size of the facility/rooms you need and the dependence on space needs and traffic.
- The type of product or process that will be stored or completed
- Volume of product entering and leaving
- Processing versus storage needs
- Temperature at which product is expected to enter or leave the process line
- The required storage temperatures (pull down, chill, freeze)
- Door sizes that will affect heat transfer
- Geographic location of the installation (not a universal solution)
Answering some of these questions will lead you to be able to consider some product specific elements, some of which have become more important today than ever, such as:
- Environmental impact
- Product stability (R-value range)
- Moisture resistance
- Service temperature range of the product (ie -40 to +120)
- Structural stability
- Performance tests in various scenarios
- Grade and density (eg 15kg/m3 to 80kg/m3)
- Complete product lifecycle and recyclability
- Local content and industry support
The conditions required around any facility will determine the product configurations. So, a company that for example extracts citrus oil from orange peels would require polyurethane insulated panels because this material type doesn’t disintegrate when exposed to the particular acid found in citrus oil. Also, as a closed cell material this means that the structure of the core doesn’t allow substances to easily penetrate it. The same conditions apply to the skins. Here if corrosion was likely such as the circumstances with working in an abattoir, the faces would need to be a certain grade of stainless steel. Rock wool insulation may be used to store high value products or used as a fire barrier in facilities owing to its flame and fire resistance.
Generally speaking, managing heat load in terms of insulation is the result of exposure time to an element (like the sun). To manage various heat loads and R-values for different zones at a facility or location, manufacturers produce different panel thicknesses. If you select a panel that is too thin, it is likely to result that an element (like the sun) will essentially overwhelm the insulation and start to transfer heat to the inside of the space – clearly not ideal as your cooling equipment now has to work excessively to keep that heat out. For these reasons, it is important to have very specific details around heat loads, not only considering the environmental influence but conditions within. This will further avoid premature plant failures.
Material choice also comes to the fore when for example you have a very confined space or small rooms to work with. Here selection of a polyurethane panel that is 60mm thick will provide the same thermal properties as a 100mm polystyrene panel, or 100mm polyurethane panel can replace a 150mm polystyrene panel, and so on. In a room that is only 1.2m wide, an 80mm space saving may be critical.
Moisture is another element that needs to get careful consideration when it comes to insulated panels. Resting moisture ingress opens up the door to the risk of toxic mould and bacterial growth. Now although some of the insulation materials have been formulated to have a low- to zero condition for these risks, no matter what core material you are working with, moisture will be a problem. Typically, moisture will have the greatest impact and affect at the joints in freezer rooms. Moisture means ice-formation and this can result in the core material breaking and compromising the room or facility. For this reason, coupled to insulated panels is the need for properly installed vapour barriers and correctly joined and sealed units.
Local manufacturing versus imported products
South African manufacturers in this space have come to compete with a large number of international companies from around the world (for example from China, UK, Central Europe, Russia, Poland) and these businesses have significant production facilities. Some suggest that the largest global supplier has the capacity to supply 20 times the volumes of the combined local production, which is of course a concern for the sector. This comes with several challenges in terms of pricing, research & development, and international recognition and accreditation.
“It is important to have very specific details around heat loads.”
The major barrier for entry into the global market space for local companies is the fact that testing and global accreditations can quickly accumulate to R2-million – which to say is prohibitive is really an understatement. However, the quality of production, production methods and various types of products produced are essentially on the same level as international companies in many respects. This then opens up the question of what can the industry do to work together to gain some form of international recognition, and is this even something to consider?
With the fast-growing sectors making use of these products, it would make sense for local manufacturers to bolster their status and the industry, keep the revenue within the country rather than companies being forced in supporting imported products, and then potentially sustain thousands of much-needed employment opportunities. Action such as this would ensure that foreign investors (who are heavily involved in SA expansions currently with some high-cost developments) could be and are willing and able to support local content.
South African manufacturing of insulated panels goes back probably more than 50 years, so hundreds of thousands of facilities already exist, and have existed for decades, and are satisfactorily performing to the facility requirements. Other than the recent rioting, looting and damages to the sector, very few incidents and problems have been reported – thus proving that locally we have the ability to produce quality and safe products. Naturally incidents do occur, but almost all of these involve external factors of human involvement and not the product itself.
A major hinderance for this sector locally is the subject of fire. This is something that gets spoken about very often related to insulated panels, and also often results in heated debates and opinions. One of the questions I asked during the process of putting this article together was: why can’t the industry develop a panel that doesn’t burn if this is such a big issue? We have access to such clever scientists and technologists! Unfortunately, the answer is not that simple!
The problem is not really a core or material itself but rather how a combination of elements that make up the final product will react. It is not to say that this cannot be done, however with repeated or continuous exposure to a flame, almost all components break down or have a change in properties – usually related to structural stability. Often a lot of emphasis is placed onto the panel itself when in a fire situation, and the core materials are not engineered to contribute to fire spread. The main problem comes in with the steel skins. Even as a rigid and sturdy material – under flame and heat conditions, steel also becomes unstable at a certain point. Because insulated panels in the cold chain form a major part of the structure, the building then becomes unstable. Naturally some materials handle heat and flame better than others, but if a fire reaches flashover point the construction materials become irrelevant – even for brick and mortar.
In several simple tests that Cold Link Africa witnessed, each material (1 imported product and 3 locally manufactured) reacted differently as expected – the materials were exposed to a flame for around 10 seconds and certain ones were still cold to the touch while others displayed properties that are not openly and accurately reported in terms of their reactions (not as bad). These simple tests are by no means a conclusive evaluation – but merely an indication of how each core product reacts. It must be noted that fire incidents must be considered from a holistic point of view and in this regard, no partial testing will produce the same result.
The point here really being that comparatively, South African-made products are as good as any other product available and react the same way as products produced anywhere else in the world. This speaks to the support of local industries that have been effectively providing for the sector for decades. It makes sense under these conditions to support and preserve local manufacturing.
Other applications of insulated panels
As a versatile product, insulation panels have been formulated into complex building components that have seen their deployment on a large scale into other sectors as an alternative construction product that is also being used as a modular system – designed and manufactured off-site and then transported to its destination and erected simply, effortlessly, and importantly – very quickly.
These applications include:
- Houses (high-end and low-cost solutions)
- Data centres
- Chemical storage areas
- Clean rooms
- General plant rooms
- Toilet and show facilities
- Portable facilities
- Flooring solutions
- Insulated panels have also been used extensively around the world for various building cladding or façades
As a critical element of the cold chain, insulated panels, as simple as they are, in fact have some very technical properties. Hopefully you have something more to think about when considering your next facility.
- Dalucon Refrigeration Products
- Panel World
- Precool Manufacturing
- Science Direct
- Thermal Insulation Products and Systems Association (TIPSASA)