Virtually every high-volume foodservice kitchen has a walk-in freezer, from small 6-ft. x 4-ft. prefabricated units to huge, custom-made boxes. Their value lies in providing longer-term storage than a refrigerated walk-in for either bulk purchases to take advantage of pricing or bulk production runs of soups, sauces or other foods. You’ll know you need a walk-in freezer when your kitchen staff accesses a reach-in freezer multiple times a day or orders frozen food deliveries more often.
A few calculations will help you determine what size to spec. As a general rule of thumb, figure on about half a cubic foot of frozen storage for every meal per day you serve. Every cubic foot of space holds about 28 lb. of food, so a 50-lb. batch of chili, for example, will take up about 1.8 cubic feet of space.
Also take into account ceiling height in your kitchens, and the space you have available for storage. Those factors determine which type of walk-in freezer to purchase—a prefabricated model or a custom unit assembled on site. Pre-fab models come in a variety of standard square or rectangular sizes with a choice of a couple of standard heights. If your available space is oddly shaped or has high ceilings, walk-in manufacturers will custom-build the components and assemble and install them on site.
A Solid Base
Walk-in freezers comprise four basic components—floor, wall panels, door and refrigeration system. The floor is in many cases the most important place to start. First, as the foundation for the rest of the walk-in, floors must be plumb and level with tight, clean corners (no matter what the angle). If not, the rest of the pieces of the walk-in— walls, door and ceiling—won’t fit together properly or seal tightly.
Second, the Department of Energy requires that walk-in freezers have insulated floors. If your walk-in will be installed at grade, a concrete pad is best. If new construction, the pad must be insulated from below. If you’re dealing with an existing pad, you can use a manufacturer’s insulated floor panels on top. You can build walk-in floors on above-grade locations with insulated floor panels. In all cases, make sure the insulation is adequate to prevent condensation from forming—that not only can make the inside floor of the walk-in icy, slippery and unsafe, but also makes the compressor work harder.
Whether an insulated concrete pad or manufactured panels, the floor should have a thermal break around the perimeter where the walls will be erected. Most installers use redwood, for example, when pouring a concrete floor, but other materials that don’t conduct cold may be used. The break prevents the cold temperatures from spreading beyond the walk-in walls where warmer ambient temps could cause condensation.
Walk-in access is important. Installing a walk-in on an existing floor is the simplest, but creates a step up that could limit access to foot traffic only. You may need exterior or interior ramps for carts or rolling racks. Both can have drawbacks: outside ramps can jut into kitchen gangways and present tripping hazards; interior ramps diminish the floor space available for storage. But if you need to roll in product, you’ll need a ramp if the entry is a step up.
You Gotta Carry That Load
Along with what you plan to use to move food in and out of the walk-in, you need to think about how much product you plan to store, and on what type of shelving. The floor itself has to be strong enough to bear the weight of the product, so you need to know both the rolling load weight and point load weight (that a shelving leg will put on the flooring, for example).
Standard floor panels are usually .080-in. or .100-in. aluminum, which in most circumstances can handle between 600 lb. and 800 lb. per square foot of stationary load. Rolling product in and out of the walk-in in heavier loads eventually delaminates the panels. Heavier loads require reinforced floor panels. One way manufacturers do this is by laying plywood on the panel frame before adding insulation and the metal skin. Usually walk-in makers also increase the thickness of the skin to 3/16 in. Even heavier loads more typical of a warehouse freezer may require a structural floor with support members built into the panels.
One manufacturer has a new, patented floor bracket that prevents delamination and the requirement for a plywood underlay. The company’s standard floor can handle loads of up to 1,000 lb./sq. ft. for foot traffic and rolling carts. Its structural floor with the new bracket will take loads of up to 5,000 lb./sq. ft.
Finally, flooring is available in a number of surfaces. Walk-in freezers can install floorless directly on top of an insulated concrete slab. Metal floors can be aluminum or stainless, but not galvanized stainless (it can rust over wear and time) and they either have to be smooth or diamond tread. Quarry tile, poured epoxy and rubberized flooring are other options, usually installed after the walk-in is installed. Some operators install slip-resistant finishes only on ramps and walkways inside the box. One maker even offers an antimicrobial steel floor.
An Open And Shut Case
Next to floors, doors are the other walk-in component that will take the most abuse. They should be built solidly enough to hang plumb for the life of the walk-in and tough enough to withstand not only multiple openings and closings each day, but bumps and bruises from carts, pallet jacks and even the occasional well-placed shoe.
Constructed in much the same way wall, ceiling and floor panels are, doors are thoroughly insulated with foamed-in-place polyurethane (FIP) or extruded polystyrene (XPS). Usually, they’re built in the same manner a manufacturer uses to make panels, but doors are sometimes built within a frame to make them stronger and more rigid. Makers typically use ABS plastic or steel for door frames. Steel is less prone to break under stress, and adds strength to the door. ABS plastic, however, is a good insulator and usually is less expensive.
Both types of frames are formed in such a way (often U-shaped) that they create channels in which all door wiring fits. The wiring includes heated wires to prevent condensation around the door from forming and freezing the door shut; and electric service to interior lights. Manufacturers who use ABS plastic frames say their insulating properties enable them to use lower wattage heater wires in the door. In either case, heater wires attach to thermostatic controls to prevent overheating.
Door wiring also may service an interior light switch. As a safety feature, some models have a motion detector switch to turn on interior lights, and one maker has a low-watt nightlight incorporated into the light fixture that can guide employees to the door and light switch if they’re accidentally turned off. Wiring also may service a digital thermometer mounted next to the door, and/or a control panel.
Door hardware is typically mounted to steel backup plates that are foamed-in-place when insulation is blown into the door. Hardware may be different materials depending on the manufacturer. Some use chrome, others may offer polished or satin aluminum. Handles usually come with cylinder locks standard, and they all come with an interior safety release. Some can be fitted to accommodate a padlock if desired.
Door closers are built into all doors. Some manufacturers use either a spring-loaded or hydraulic mechanism attached to the top of the door. Others spring-load one of the cam lift strap hinges most commonly used on walk-in doors. Hinges are usually adjustable to give field installers a little leeway when getting a door plumb. Some doors have three hinges, which proponents say are longer lasting and better at keeping the door working well for a long time. Others install only two.
Doors are available in a variety of widths, and a “standard” door varies in width from one maker to another. Most manufacturers, however, offer widths such as 26 in., 30 in., 34 in., 36 in., 42 in. and 48 in. and at least two door heights (some offer as many as four standard heights). Since most makers custom-build walk-ins of any size and shape, you can get doors made to your specs, too, including sliders instead of hinged doors. (One manufacturer built a custom cooler for Tesla Motors with sliding doors covering an opening 20-ft. wide so cars could be driven in and out to test them and their batteries in cold conditions.)
Usually flush-mounted in the frame, doors come with magnetic gaskets, and often vinyl, wiper-style strips on the bottom, to keep cold air in and warm air out. A couple of lines have a stepped-hinge profile door design, which the makers claim provides an even better barrier against air flow.
Many makers also offer kick plates as standard equipment to help protect doors from dings. And some even offer insulated and heated glass windows.
R You Insulated?
Walk-in wall panels are a little different than the paneling in the den you remember from when you were a kid. Panels for walls and ceilings have to provide excellent insulation (an R-value of at least 32, according to the DOE) and structural strength. (The same type of panels, by the way, usually make up the floor, but they’re required to have an R-value of only 28.)
Panels are typically 4-in. or 5-in. thick, with metal skins on both sides, and usually constructed in 12-in. increments. Walk-ins with 6-in.-thick panels are not uncommon when located outdoors in cold climates. Manufacturers offer a wide variety of finishes for the metal skins, both inside and out.
R-value, of course, is a measure of an insulating material’s resistance to heat transfer. To calculate it, you also need to know either a material’s K-factor (a measure of its thermal conductivity) or its C-factor (the rate of its thermal conductance). For purposes of simplicity, the higher the R-value, the better the insulating properties.
Makers use a couple of different insulation materials and a couple of manufacturing techniques to build panels. By far, the most common insulation manufacturers use is FIP because it’s easy to work with and has a very high R-value, especially initially (all units lose R-value over time).
XPS insulation is manufactured through an extrusion process that melts together the plastic resin and other ingredients. The liquid formed is then continuously extruded through a die and expands during the cooling process. This produces a closed-cell rigid insulation (FIP too ends up as a closed-cell insulation). XPS should not be confused with expanded polystyrene (coffee cups) which is formed under a completely different process that fuses beads and does not have a closed-cell makeup. XPS is milled to the precise dimensions and thickness desired for each panel before being sandwiched and glued between metal skins.
Depending on the manufacturer, you will hear competing arguments about the superiority of FIP over XPS and vice versa. FIP proponents tout the insulation’s efficiency, the fact that FIP anchors components within the foam, adheres to metal skins, and can be foamed edge to edge filling all gaps (depending on the maker; shoddy FIP by a less professional maker can leave gaps and bubbles).
XPS proponents say the polystyrene is less permeable to moisture, which compromises insulation’s effectiveness, retains its R-value better over time because of it and is therefore longer lasting. XPS has less moisture permeability than polyurethane, according to the DOE, but there are reputable and less reputable makers of XPS, too. A manufacturer should be eager to show you facts about the brand of XPS it uses. Also, as mentioned, some FIP walk-in manufacturers are better than others, and can guarantee their panel construction to be sealed tight and moisture-proof, rendering absorption risks moot.
Your best bet is to ask about the manufacturing process in detail, ask for the R-values, do’s and don’ts of walk-in freezer installation based on site and climate, and ask for references (especially of operators with older units). Most importantly, ask for warranty information. A maker with a long warranty is making a statement about its product.
Baby, It’s Cold Inside
You have three options when it comes to refrigeration systems—top-mounted, side-mounted and remote. Which you choose depends on the size of your walk-in and where it’s located. Smaller walk-ins located indoors often have top-mounted refrigeration units if there’s enough ceiling space above, or side-mounted units if there isn’t. Top-and side-mounted units also are used on walk-ins located outside. Larger walk-ins typically have remote units mounted on the roof of the building.
Both types of “self-contained” walk-in refrigeration units located indoors need adequate ventilation. Remember, too, that they’ll put an additional load on your HVAC system, which remote units don’t.
Whether you spec a standard size or custom-designed walk-in, the manufacturer will match it with a balanced refrigeration system designed for the cubic volume of the walk-in itself. Some makers claim to oversize their systems somewhat so they don’t work as hard at pulling down product temps when new deliveries come in or chefs place product in the walk-in to cool down or freeze.
Ambient conditions strongly affect walk-in performance. The refrigeration system for a freezer in a Southern California kitchen should be spec’d differently than one for a restaurant in Vermont. And a unit in the humid conditions of Houston should be sized differently than one in a drier climate.
In recent years, manufacturers have added a number of features that maximize performance and energy savings and minimize impact on the environment. To reduce the refrigerant charge needed for its walk-ins, for example, one manufacturer has designed a “microchannel” condenser. Made of brazed aluminum, the condenser’s fins are set between flat microchannel tubes, which are then joined to a pair of refrigerant manifolds. The resulting condenser, the maker claims, performs better, resists corrosion, and is structurally stronger despite its lighter weight than traditional condensers.
Compressors, too, are working less hard and saving energy while delivering comparable performance to older models. Low-temperature walk-ins using R448a or R449a refrigerants that replace R404a typically use scroll compressors now. And one manufacturer has added two-speed fan motors to both its evaporator and condenser fans saving even more energy when the system isn’t working as hard. The evaporator fan switches to low when the compressor cycles off, and the condenser fan does the same when the ambient temperature drops below 60°F.
Controls, too, have grown more sophisticated as manufacturers find more ways to use electronics to monitor and fine-tune the refrigeration system’s performance. Several makers now have “smart” controllers that more accurately adjust temperature inside the freezer, monitor icing on the evaporator and initiate defrost cycles only when and as long as needed. The controllers also eliminate a lot of cross-wiring making them easier to install, and offer self-diagnostics to speed service.
Temperature monitoring and alarm systems can be added on to some of these control units that alert staff if the door is left ajar or the walk-in temperature is outside set parameters. Some let you choose how to receive alerts—via text or Wi-Fi to a PC, for example. HACCP data collection is available with these monitors as well.
You can get additional energy savings by selecting LED or fluorescent lights instead of incandescent bulbs with a vapor shield. Controllers that automatically shut off lights after a certain amount of time also save you money.
Again, as always, check warranties and service networks before you buy.
The Nose Knows
Most walk-in manufacturers use a tongue-and-groove design with cam locks to connect insulated panels. Depending on their design, you may hear manufacturers describe their panels as having a “soft” or “hard” nose. A hard nose is when the panel is built using a “high-density” wood, metal or some other rigid but non-insulating material frame to shape the panel and the foam is blown within the frame. A panel made with the soft-nose technique is framed with a removable jig. The jig creates a temporary barrier while the panel is foamed in place, providing full insulation edge to edge.
Fanning The Future
Efficient electronically commutated motors (ECMs) that power fans and are required equipment now on walk-ins may soon have competition.
It’s estimated that 65% of the walk-ins still in use have old shaded-pole fan motors that are only about 20% efficient. ECMs eliminated the brushes in shaded-pole electric motors, using electronically controlled pulses to build the magnetic field that causes the rotor inside a ring of magnets to turn. ECMs are about 60% efficient.
A new motor called “Q-Sync” could eventually replace ECMs. In this synchronous motor, the rotor is synchronized with the frequency of the supplied current. Instead of using the electronics to convert AC to DC to drive the motor, the Q-Sync electronics get the motor up to the desired speed then shift the motor to AC power directly from the grid. Tests so far show that Q-Sync motors are about 73% efficient; they cut energy use by 30% compared with ECMs.
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