This lack of innovation is due to the difficult door design challenges facing the cold storage industry. Because product integrity is paramount, cold storage facilities focus on doors they believe will control temperature the best. Traditionally, that has meant heavy, well-insulated doors. The trade-off, however, is infiltration for insulation, because these doors are slow to open and close.

The other alternative, high-speed folding doors, open and close quickly to maximize productivity and help minimize air exchange. However, they have lower thermal resistance, R-value, require panel defrost systems, and are often energy-inefficient when shut.

Battle Against Losses
The design of a door comes down to a battle against losses – of energy, time, product, and people. Heat and humidity outside interact with cold inside, creating a set of challenges that any door must address.

Cold storage doors today come in several styles.

Hard-core doors. The most common doors found in cold storage facilities are hard-core doors. Made of rigid panels with high R-value insulation and designed to seal tightly around the perimeter, these doors will conserve energy caused by conduction, but do not accommodate rapid forklift traffic. Hard-core doors are typically slow operating, and their drive systems are not designed for a high number of cycles per day. They are also easily damaged by forklift impact, resulting in increased infiltration losses and costly repairs.
Many cold storage companies also use hard-core doors as backups for high-cycle doors. They are left open during production shifts and closed during shutdown periods to serve as a defense against conduction and infiltration costs.

Cold Storage Doors for high-cycle applications come in four basic configurations:

Strip curtains. These inexpensive doors consist of clear plastic strips suspended in the opening. Their appeal is that they are inexpensive, easily replaceable, and forklifts can pass through without delay. On the other hand, the R-value is low, so frost buildup is common. The door seal is marginal to begin with, and is further compromised with air pressure. In addition, scratches and frost buildup obscure forklift drivers' vision through the opening – a serious hazard, especially for pedestrians. Finally, because the door does not clear the opening, forklift drivers and product are constantly slapped by the strips as they pass through, causing quality concerns, discomfort and aggravation.


Air systems. Air systems create a vestibule where the relative humidity of the air inside the vestibule is manipulated. The vestibule system reduces the exchange of air and visibility is usually clear. Unfortunately, these complex systems are costly to install and do not seal the opening. They also have a large footprint that utilizes valuable floor space and consumes a great amount of electricity to maintain frost-free operation.

High-speed folding doors. These common systems are desirable because they open quickly, feature flexible panels that are impact-resistant and can provide good visibility with all-clear designs. Unfortunately, these doors do not provide an optimal seal around the door perimeter. And, because of their low R-value, they require panel defrost systems to minimize frost on the panels. In addition, several designs require a large footprint for installation that can occupy valuable floor space in the cooler or freezer. They also often require a backup door during shutdown periods for a better defense against conduction and infiltration costs.

Roll-up doors. These designs are common in industrial applications and have frequently been used in cold storage facilities because of their superior seal. They occupy little floor space and can have "breakaway" capability. However, like folding doors, they have low R-value and require defrosting. Though they open rapidly, overhead operations make them slower to clear the opening than bi-parting doors. Most designs require a sensing edge to reverse the door's travel in case it descends on an object or person, but these sensing edges have proven unreliable in harsh cold storage environments.

Advances in door technology now mean companies can come closer to having the best of both worlds. Today’s doors combine fast cycling with high efficiency insulation and effective perimeter sealing. They also resist damage and have low maintenance and operation costs. Recent innovations include:
• Thick yet flexible foam core panels that withstand impact and have sufficient R-value to make defrosting unnecessary.
• Fast, bi-parting action that clears the opening rapidly.
• Effective perimeter sealing, including insulated interlocking seals and a positive floor seal.
• Small footprint to maximize storage space and allow for operation behind racking.
• Automatic reversing without the use of sensing edges.


When these technologies are properly applied, the results are low long-term energy costs, high handling efficiency, and a safer environment for cold storage workers.


Selecting doors for any cold storage facility means looking in detail at the application and weighing both the front-end and long-term costs.


Key is Energy Efficiency


Front-end costs include not just the price of the door, but related costs for defrost systems and operating space. In cooler and freezer facilities, space is at a premium and is more productively used for product storage than for space-intensive door systems.


The key to low long-term costs is energy efficiency. A thorough energy analysis can predict with considerable accuracy which type of door system is the most economical choice. An energy analysis looks at a wide range of factors, such as:


• Temperature difference between cooler, freezer and outer room.
• Humidity difference between cooler/freezer and outer room.
• Size of the door opening.
• Number of work hours per day.
• Number of door cycles per hour.
• Door cycle time.
• Cost of electricity.
• Defrost system energy rating.


This data can be used to calculate infiltration losses (with the door both open and closed), conduction losses, and defrost system energy costs. The calculations are useful for showing energy-cost comparisons of all the door systems being considered. A complete cold storage door analysis also must factor in door maintenance and repair costs, employee safety and comfort, handling productivity and the quality of manufacturer service support and warranty.

Seek Advice


As door technology advances, cold storage facilities can lessen the compromise between handling productivity and energy efficiency. Facilities looking to upgrade cooler and freezer door performance can seek advice from an established door manufacturer's representative and ask for an energy analysis of their openings.