Cold Storage Door Systems

Attention to detail is required to achieve effective thermal performance

Cold storage is a large and growing industry in the U.S. and other developed nations around the world. Primarily used for storing and distributing perishable food items such as meat, dairy products, poultry products, fruits, nuts, and vegetables, these facilities have become essential to the availability of these foods. Currently estimated at over 16 billion cubic feet worldwide, they take the form of public, private, and semi-private refrigerated warehouses.

Cold storage facilities are also found as an integrated part of many building types including supermarkets, retail locations, restaurants, food processing plants, institutional facilities, cold storage warehouses, food service operations, prisons/correctional compounds, and warehouse distribution centers. The construction of these facilities is fairly straightforward, relying on thickly insulated walls and appropriately sized cooling systems to deliver the required refrigerated temperatures. From an architectural standpoint, the flow of people and equipment into and out of these cold storage rooms or buildings becomes the key design issue. Central to that issue is an understanding of the options for doors and their construction in these cold storage locations.

Cold Storage Overview

Keeping things cold while in storage has been a design challenge since the 1800s in this country. Without any modern day refrigeration, ice was the main source of cooling and was harvested during winter for use year round. For it to last, it was stored underground or in enclosures filled with things like sawdust for insulation. The emergence of the household “ice-box” and the selling of blocks of ice by truck in cities meant that perishable food could be kept cool, although not particularly well controlled in homes. It also created a demand for more perishable food and for stores and warehouses to have the same capacity to keep larger quantities cool.

Trade Associations

The wave of inventiveness and creativity touched off by the Industrial Revolution included the development of mechanical means to cool a defined space or box. This became popular enough that by 1904 the American Society of Refrigeration Engineers (ASRE) was founded initially for the purpose of promoting the technology of refrigeration for appliances, railroad cars, trucks, etc. In 1959 they merged with the American Society of Heating and Air-Conditioning Engineers (ASHAE) which was actually founded in 1894—10 years earlier than ASRE—to form the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). We know ASHRAE today as a large, international organization with a mission to advance the arts and sciences of heating, ventilating, air-conditioning, and refrigeration. While we may think of them only for the HVAC systems in buildings, the “R” for refrigeration has clearly long been a core part of what these engineers and other members do. In fact their core publications include the 2010 ASHRAE Handbook: Refrigeration, which covers the design of refrigeration equipment and systems for applications other than human comfort including cooling, freezing, and storing food; industrial applications of refrigeration; and low-temperature refrigeration.

Not surprisingly, other organizations were created and grew during the same timeframe as ASHRAE. The International Association of Refrigerated Warehouses (IARW) came into existence in 1891 when a number of conventional warehousemen began storing perishable food to meet market demand. They soon realized the increased challenge and complexity of operating temperature-controlled storage facilities compared to typical warehouses without temperature control. This organization has grown to the point where today, IARW aggressively promotes best practices in temperature-controlled warehousing. As an organization they promote relevant research, industry benchmarking, member networking, and education for members and the public. They are politically active in that they also advise members of legislation and regulations affecting the food industry while assisting members in complying with U.S. and international regulations. In recent times, they have also become quite focused on l ogistics in terms of moving, shipping, or distributing the goods that they are storing into and out of those warehouses.

As the design and construction of cold storage facilities became more focused on how to best insulate and construct these facilities, those involved in that work saw the need to come together as well. In 1978, a small group of insulation contractors began to discuss creating an association representing contractors who serve the specific needs of the cold storage industry. Within a year, the National Association of Cold Storage Insulation Contractors was incorporated, its founding Board of Directors was named, and its purpose and objectives were defined. In 1987, the name was changed to the International Association of Cold Storage Contractors as they expanded to include members from the UK and elsewhere. In 2002, another name change was made to create the current International Association for Cold Storage Construction (IACSC) in order to invite a broader membership base while providing equal status for all. Today, they are made up of general contractors, cold storage construction contractors, and suppliers all focused on the best means for constructed refrigerated facilities.

In 2005 the IARW and IACSC began to see the benefit of working with other related trade organizations. These included The World Food Logistics Organization (WFLO) whose members were focused on the logistics portion of cold storage and distribution. Together, they also recognized the benefit of teaming with the International Refrigerated Transportation Association (IRTA) that provided refrigerated trucking and other shipping means. By the close of 2006, the boards of all four of these organizations created the Global Cold Chain Alliance (GCCA), an umbrella organization creating partnerships among associations, governments, institutions, and private companies spanning each link of the cold food storage and distribution chain. GCCA officially launched in April 2007 and now acts as the platform for communication, networking, and education, serving as the focused voice of the cold chain industry. Many members of any one of these four organizations under the GCCA umbrella also enjoy joint membership with one or more of the others.

Modern Cold Storage Facilities

Designing cold storage facilities today involves a distinction between general building construction and cold storage construction. A building may contain some cold storage inside it which typically means that the cold storage enclosure is made from pre-fabricated sandwich panels with spray foam between metal faces. These panels then determine the size, height, and thermal performance of the cold storage system with the surrounding building which is fulfilling other purposes. In cases where the entire building is the cold storage facility, it may well be that the walls, roof, and floor of most or even all of the building are the critical enclosing components and they must be designed and specified accordingly.

Beyond the distinction of using a freestanding internal enclosure or a building enclosure, cold storage in general falls into two overall categories identified by size. A small facility is defined as one under 3,000 square feet even though this is equivalent to the size of a house. In practice these small enclosures range in size from a walk-in refrigerator or freezer of a few hundred square feet typically found in restaurants up to larger-capacity units found in supermarkets or institutions with a large food preparation operation. From a regulatory standpoint, these smaller walk-in facilities are subject to the Energy Independence and Security Act of 2007 (EISA). This comprehensive legislation added to and amended the previous Energy Policy and Conservation Act (EPACT) first passed in 1975 and revised several times through 2005. Part of the provisions of these current regulations include a definition of the terms “walk-in cooler” and “walk-in freezer” which mean “an enclosed storage space refrigerated to temperatures, respectively, above, and at or below 32 degrees Fahrenheit that can be walked into, and has a total chilled storage area of less than 3,000 square feet.”

The EISA legislation goes on to address some very specific aspects regarding the construction of any walk-in cooler or walk-in freezer manufactured on or after January 1, 2009. First they must have automatic door closers that firmly close all walk-in doors although there is an exception for doors wider than 3 feet 9 inches or taller than 7 feet. Second, they must have strip doors, spring hinged doors, or another method of minimizing infiltration when doors are open. When it comes to the construction of the units, they must contain wall, ceiling, and door insulation of at least R-25 for coolers and R-32 for freezers, except for glazed portions of doors or structural members. Floors of freezers must be insulated to at least R-28. There are also specific provisions for the refrigeration equipment types, and efficiency in the interest of saving or reducing electrical energy used. Nonetheless, the legislation clearly recognizes the significance of the basic construction of the enclosure and attention to detail at the doors in terms of conserving energy.

Large facilities over 3,000 square feet are not covered by the provisions above, but they are subject to energy efficiency standards for buildings when they comprise most or all of a warehouse or similar building. This is particularly important when you consider that refrigerated spaces are being controlled to an interior temperature of 34-36 degrees Fahrenheit while freezer storage is controlled to 0 to 20 degrees Fahrenheit. That means as a practical matter, these larger facilities likely want to meet the same or better R-values as stated above to create efficiency in energy use and to control operational costs. It is common for these large facilities to bump up the R-values to R-32 for refrigerated storage and R-48 for freezers. It is also likely that a large facility will require multiple doors that are larger in size to allow not only walk-in operation but drive-in operation of forklifts or other equipment. The best rule of thumb in this case is that these doors should be made to match the thickness and performance of the walls (e.g. R-32 and R-48). Beyond that, since these doors are the only source of thermal interruption and usually the only operable item, it is worth spending time to focus on the details of the options, types, and fabrication of these doors.

Swinging Doors

Single- and double-panel swing doors are commonly used for walk-in applications where strong environmental control is necessary. Swinging cooler and freezer doors provide time-proven performance for new or existing applications and are suitable for both interior and exterior applications. Typically they are used for personnel walk-in doors and are sized accordingly, but much larger swinging doors are possible that can allow machinery or equipment to pass through as well. Because the door swings out into the path of travel, the facility design needs to account for both this door swing and the travel clearances required for people or equipment when entering/exiting.

While swinging doors in general are commonly used for many building applications, it is the details of these cold storage swinging doors that make them different. This is particularly true when it comes to the air and temperature sealing the perimeter of the door. The type of gasket used in particular is extremely important not only to comply with EISA regulations but to minimize the energy loss overall. Magnetic gaskets with a push in flexibility are one option that provides superior positive sealing since they can accommodate “out of square” or irregular conditions more readily than traditional compression gaskets. Similarly, a sweep sill gasket will prevent thermal infiltration along the bottom of the door. In cases where the door frame is installed flush with the floor line, there can be no need to embed a sill in a concrete floor. Further, if cam lift hinges are used that raise the door when opened, it provides reduced friction on the floor seal and eliminates the need for sloped floors.

In addition to these details there are some other things to be aware of that are options for a swinging cold storage door. First is the use of electric heating in the door or the sill to prevent the build-up of condensation or ice around the perimeter of the door. Such heating needs to be very low wattage and be regulated so that it uses just enough energy to be useful but no more than is needed. If a window is included in the door as an option, there may also be a need to provide some electrification there to prevent condensation or moisture buildup. In regards to hardware, there are choices in types of hinges depending on the size and operation of the door to consider. There are also options on the release latch including some that can be released from the inside even if the door is padlocked on the outside. And of course there are options for finishes. Most doors are finished with metal to comply with sanitation requirements as well as provide a solid measure of durability. These include stainless steel, aluminum, or galvanized steel in a textured or smooth finish.

Sliding Doors

The common alternative to swinging doors is the use of single or double sliding doors that hang on a track in front of the cold storage enclosure. Horizontal sliding doors are best suited for high-use and heavy-duty applications particularly where forklifts and other equipment are used. They are usually designed for high cycle, abusive applications and are considered a true “workhorse” door. From a design standpoint, the horizontal sliding function of the door means that a door swing area does not need to be factored in. However the external wall area adjacent to the door opening obviously needs to be kept clear so that the door can operate properly—it does not recess into the wall since that would compromise the thermal performance of the enclosure. A single sliding door would need to have the wall clearance the full width of the door on the side that it slides toward. If bi-parting doors are selected, then half the width of the door needs to be kept clear on each side of the opening.

In terms of sealing sliding doors when closed, most major cold storage door manufacturers utilize a balloon type seal that is either attached to the jamb casing or the door panel. When the door slides over it, it simply compresses against this seal to restrict air exchange, but doing so makes this type of seal is subject to wear and tear during normal operation and is easily damaged. An innovative seal used by at least one manufacturer utilizes a two-ply, fabric reinforced blade seal against the top and side edges of the door panel. This solves a number of issues including frequent replacement of worn out seals, wear and tear on sealing surfaces and gasket damage from impact. It also minimizes air infiltration and moisture problems common to traditional cold storage doors.

The track that the sliding door hangs on is obviously an important component that can make a difference in the long-term proper operation of the door. Standard duty tracks are typically designed for smaller to midsize doors (6 feet wide or less) while heavy duty tracks are intended for larger doors or those in an abusive environment. Rather than keeping the track and roller system exposed, an optional protective hood system is available from manufacturers. The roller assembly sits on the track allowing for the smooth motion of the door and is available with an anti-lift device to retain its adjustment even when the door is bumped, eliminating the need for secondary adjustments. There is also the option of an adjustable track mounted hold close bracket which prevents “bounce back” on manually operated doors. The combination of the track/roller assembly plus the gasket system impacts the detailed operation of the door. The traditional operation relies on a “down and in” closing motion that pulls the door panel down and in towards the gasket when closed. While this ensures a positive seal, it can make the door difficult to open. Alternatives that use a different gasket system that is coordinated with a properly designed and selected track system can eliminate the need for the down and in motion, making the door easier to operate.

To complement the assembly at the top of the door, some cold storage doors incorporate an adjustable floor guide system that installs under the door panel. This concealed design is an alternative to exposed floor rollers that many cold storage doors require. The under panel guide is easy to install, can be adjusted for a perfect seal, and has a much cleaner look than bulky rollers that are prone to being hit by loads passing through the opening.

Like swinging doors, the perimeters swinging doors are typically heated to prevent condensation and ice buildup and other options such as windows and finish materials are available consistent with those for swinging doors. There is even the possibility of adding a smaller, swinging personnel door within the larger sliding door for cases where people walking are using the door as often as larger equipment thus minimizing the door opening impact on cooling. The biggest option in sliding doors, however is whether to use manual or electric operation. In lower use areas, the process of a forklift operator stopping, getting off the forklift and manually opening the door, driving through, stopping, and then closing the door all may be acceptable. But it is clearly not efficient and is prone to having the door open longer than it needs to be. A much smoother operation is to use an electric door opener with an automatic sensor that allows the forklift to approach the door causing it to open for clear passage and then closing behind the forklift once it is inside. The workflow is not interrupted in this way and more goods can be moved in and out of the cold storage area as a result. In order to minimize the opening and closing time, bi-fold doors can be used which will move both panels in half the time it takes for one larger single panel to move. Hence it is common to find single slide doors opening at 18 inches per second and bi-fold doors at 36 inches per second. The electric motor size and type and the associated controls and wiring that go along with it can vary by installation and by the specific manufactured product selected.

Vertical Lift Doors

In locations where sidewalls are less available than overhead height and multiple doors are needed, vertical lift doors are a possibility. This type of door is common in general for warehouse loading dock applications and they can be manufactured to have all of the insulating and gasket sealing properties needed when the loading dock opens directly into a cold storage area. While they are appropriate for the potentially heavy-duty usage in these locations, they are considered best for locations that don't require a lot of opening and closing, say on the order of five times a day or less.

Vertical lift cooler doors and vertical lift freezer doors are both available with electric and manual operators just like horizontal sliding doors. They typically come with heavy-duty side tracks and hardware that can include a counterbalance weight system if desired. The gasket system covers the casing area that the vertical door closes down against and a continuous gasket along the door bottom seals that area. Freezer doors have perimeter heating and can also have heated pull cords in the freezer area to prevent them from freezing and binding up.

Code-Related Issues

Regardless of the door type selected, there are obviously code concerns anytime doors are used in buildings, particularly since these may be the only doors into or out of the enclosed cold storage areas. Hence, meeting code egress requirements is paramount so that there is no chance of anyone being stuck or stranded inside these spaces. The door size will need to be determined according to code just as with any other occupied space and the requisite egress hardware will need to be provided to allow proper and unfettered exiting. In the interest of avoiding “entrapment” door hardware that allows emergency escape or exiting, even if locked from the outside, can be critical and is commonly available.

If the door is part of a fire-rated enclosure, then obviously that door, frame, and related details need to be fire rated. This is not generally available for cold storage doors and may or may not be an issue. In cases where fire ratings are needed, it may be best addressed by constructing a conventional fire separation and door outside of the cold storage enclosure portion of the building with appropriate passage areas in between. Similarly, if the cold storage portion of the building needs to be handicapped accessible per building codes or the Americans with Disabilities Act (ADA), then all of the issues related to doors will apply. Size and operation are often not a problem given the range of choices and in some cases a sill or threshold can be avoided altogether depending on the door and frame construction type chosen. One solution that is not handicapped accessible however, is to add a personnel door within a larger sliding or vertical lift door. The bottom of the larger door will require a continuous member across the bottom that will be too high to meet handicapped accessibility requirements. If the entire door is automatically operated and can otherwise be accessible, then that limitation becomes unimportant.

Cold Storage Door and System Fabrication

The construction of door panels for cold storage doors has come a long way since the 1800s. Because of its low cost and availability, wood has been a traditional material of choice for cold storage door manufacturers. However, its tendency to warp, swell, and rot because of the high moisture environment it is subjected to created numerous problems for maintaining a good perimeter seal. Further these conditions encourage wood to harbor bacteria, mold, and fungus, meaning it is no longer acceptable to most health inspection agencies. Pressure treated wood solved the rotting problem for a while but unfortunately it warps even more than untreated wood.

As manufacturers began to look for a strong, non-wood door at a competitive price, they looked for a better material to make a better product. After considerable research and development, a popular and effective option emerged which replaced wood framing materials with fiberglass reinforced pultrusions (FRP). The well-known mechanical properties of fiberglass offer some tremendous advantages in cold storage applications not the least of which is its extremely low thermal conductivity. Compared to other structural materials, this meant that thermal performance of the door did not need to be unduly compromised by the presence of internal framing for the door panel. Fiberglass is also well known to be as strong as steel but 30 percent lighter in weight which helps in the operation of the door. It is impervious to water and moisture so it will never swell or rot and it is easy to clean. It also maintains its shape over a wide range of temperature differentials and will maintain all of its properties even in extremely cold conditions. Following all the way through on this approach, internal blocking for securely attaching hinges, handles, and other hardware reinforcements has also been replaced with an in-organic polymer material instead of the traditional wood.

The FRP framing is supplemented with spray foam insulation which provides the full thermal performance of the door. Some of the best designs use many ribbed cavities that capture and hold foamed-in-place polyurethane insulation. This produces an incredibly strong panel that has high impact resistance yet weighs notably less than traditional wood frame designs. And in the interest of maintaining an environmentally friendly product, the spray foam used is increasingly free of chlorofluorocarbons (CFCs).

As noted earlier, the inner and outer surfaces of the door panels are covered with a choice of metals including stainless steel, aluminum, or galvanized steel in smooth or textured finishes. It is also common to add a large kick plate to the lower portion of the door for added protection from day-to-day abuse. All fasteners used to create the frame, face sheets, and hinge or track hardware on the door are commonly stainless steel for the best long-term durability and rust resistance. By contrast, on swinging doors, heavy-duty chrome plated hinges and latches are common with nickel plated strap hinges fairly standard on larger doors.

Similar to the door, door frames and casings have advanced over time. Wood has again been commonly replaced by extruded polymer that is designed to work with the door gasketing system. The overall door frame design has even been optimized by some manufacturers to include a thermal break, in much the same way windows include thermal breaks, to minimize any heat or cold transfer that may occur through the framing members. There are several options in the type and use of casings. A “Casing Mounted” Door System is a door that includes a frame or set of casings or frames that mount to the wall of the cold storage enclosure. All of the door system components including the track, operator, and gasketing mounts to the casings, with the exception of the swing door. Virtually all sliding cold storage doors and many swing doors are casing mounted. Since the “wall” that is being mounted to frequently consist of non-structural foam panels, there is no internal wall structure to attach the door to. So called mirror casings are used to support the door system on the interior of the cooler box or freezer box, getting their name from “mirroring” the external casing. A jamb wrap can also be added to cover the jamb area between the casing and mirror casing to finish out the door frame. In applications where the cold storage door is installed in a rough opening, thru-wall casings can be used to finish the opening. This type of casing wraps around the frame to create a finished opening on both sides of the wall, as well as the jamb.

Cold Storage Door Installation

One of the advantages of cold storage doors is that they are commonly custom manufactured to suit a particular building application and installation. Therefore, when it comes to their proper installation, it is always best to refer to the manufacturers' instructions and recommendations since details often vary between manufacturers. Nonetheless, we can look at some general guidelines for each type of door.

Swinging doors are dependent on the frame and casing to support the door, so the proper installation of these components is very important. Some consultation with the manufacturer of the cold storage enclosure may be appropriate to determine whether or not the frame needs to bear the entire load of the door or if the wall panel has some reinforcing for that purpose. The details of the frame installation will be based on the option selected such as whether or not mirror casings or thru casings are used. One or both may be required if the enclosure panels don't provide any other attachment option. From there, the door hinges can be installed so the door can be hung and set in place. Door gaskets are likely already installed at the factory, but should be checked and adjusted as appropriate and as recommended. If there are any heated elements in the door such as the perimeter or the glazing, then the electrical connections will need to be made.

Sliding doors will also require some casing arrangement for the door to rest against, but the critical element here will be the installation of the track which the sliding door hangs from. Placing the track on the outside of the enclosure means that it is isolated from the cold side eliminating any possibility of transfer there. It also means that the installation can take place primarily outside of the enclosure. The track length and location will depend on whether the door is a bi-parting design or a single sliding design and adequate clearances will be needed in either case. Once the track is secured, then the door can be hung and door operator hardware installed. If the sliding door is electrically operated, then the operator will need to be installed and the electrical connections made. Separate electrical connections will be needed if perimeter door or threshold heating is required.

Vertical track door installation may require lifts or scaffolding to reach the heights of the open door and track. The track must be secured to the building and aligned to the opening properly so that the door operation does not interfere with anything else and will seal correctly when closed. Once in place, the door panel can be installed aligning the operating hardware with the track openings. Gaskets need to be checked and all operating and latching hardware needs to be finalized. Then, any electrical items such as openers or heating need to be connected.

Regardless of the type of door, the final installation steps include final cleaning and testing. The door should operate smoothly and close securely in all cases. The seals should engage and prevent air leakage between inside and outside of the cold storage enclosure. From a maintenance standpoint, the doors should be routinely checked to be sure they continue to perform as installed over time. If not, they should be repaired promptly by qualified personnel to prevent energy loss or productivity slow-downs. If there is a concern about protection of the doors during use, then bollards, railings, guard rails, or similar protective measures should be installed adjacent to or around the door openings and side areas.

Conclusion

Cold storage design is a specialty type of building use that requires specialty doors to provide successful design solutions. The current technology of cold storage doors allows for higher thermal performance and better operation but the overall layout and work flow of the facility must be taken into account when determining the type of door to use. Swinging, horizontal sliding, and vertical track doors are each suitable to certain uses and applications. By understanding the differences in the doors, their make-up, and their operation, architects can assure that large or small cold storage designs can be successful, compliant, and functional over the long haul of the building's operation.

Peter J. Arsenault, FAIA, NCARB, LEED AP, practices architecture, consults on green and sustainable design, writes on technical topics, and presents nationwide on all of the above. www.linkedin.com/in/pjaarch

 

Founded in 1932, Chase Doors is the global leader and most recognized manufacturer of high-quality, made-to-order specialty doors systems including cold storage doors, corrosion-resistant doors, fiberglass doors, sliding fire doors, pharmaceutical doors, and impact traffic doors. www.chasedoors.com