Ever feel heat on the floor as you walk by your kitchen refrigerator? That’s the result of your refrigerator extracting heat from its interior (and anything stored there) and transferring it to the outside.  This same principle of heat removal is at work in a walk-in cooler or freezer.

 

 

Removing heat from inside a walk-in is somewhat like sponging water from the bottom of a dinghy: You soak the water up, squeeze it out over the side, and keep on doing it until the dinghy’s dry and the water’s back in the lake, where it belongs.

 

With a walk-in, it’s heat that’s transferred, not water. Heat is absorbed by liquid refrigerant in an evaporator, and as it’s absorbed, it turns the refrigerant into a low-pressure, low-temperature vapor. This vapor, then, is pumped into a compressor, where it’s compressed into a high-pressure, high-temperature vapor and discharged into a condensing unit outside the walk-in.

 

What happens, essentially, is that the condenser “squeezes out” the heat and condenses the vapor back into a liquid. This re-liquified refrigerant next travels through a metering device, experiences a drop in pressure and temperature, reenters the evaporator, and re-vaporizes, ready to begin the cycle again. It’s a cycle that repeats until the desired level of “cold” is reached inside the walk-in.

Food Preservation

 

Food, especially, needs cold if it’s to be preserved, because virtually all food contains spoilage-inducing bacteria, and cold slows bacterial growth. The longer you can keep bacteria from increasing, the longer food remains edible. The trick is in achieving the right level of cold. (Or “heat removal.” Remember?)

 

Since most foods contain a great deal of water, they’re best kept at temperatures slightly above freezing. Standard walk-in coolers are designed to maintain food temperature at 35° F. For this purpose, Polar Leasing walk-ins employ Copeland condensing units and Larkin evaporators, the finest available.  We do, of course, adjust our walk-ins to the customer’s specific temperature requirements, if they differ from the norm.

 

Then, there’s the matter of freezing food.
 
Freeze it slowly (to the freezing point of water, or close to it), and large ice crystals form within the structure of the food, breaking it down. That not only compromises the appearance and taste of the food when you defrost it, but it also causes the defrosted food to spoil quickly.

 

A good solution is to fast-freeze food to temperatures of 0° F to -15° F. This inhibits ice formation, producing much smaller, less destructive ice crystals.

 

 

Okay. So the whole idea of refrigeration is to remove heat. But where exactly does this heat that has to be removed come from? Most commonly from the food itself, depending on how much of it is loaded into the unit.  And from the warmer air outside that gets inside whenever the walk-in door is opened.

 

It’s a good idea to keep door openings and closings to a minimum—to conserve energy. Also, whenever you can, leave the door shut while you’re working inside the cooler. A reputable walk-in manufacturer will include a standard inside safety release so you can get out easily. It’s still a “best practice,” though, to let someone know beforehand that you’ll be entering a walk-in.

 

An automatic door closer is also recommended for every walk-in door. This small device finishes sealing the door as it shuts past the latch. A tighter seal helps you cut refrigeration run time and electrical costs.

 

 

The use of strip doors, or door curtains, is another way to maintain cold walk-in temperatures efficiently—and reduce electrical consumption. Many customers order such doors with their units; others order them separately, later.

 

You’ll find strip doors most often used in freezers and in warmer climates where the freezer or cooler sits outdoors and you enter it from the outside.  Of course, a lot of customers specify that  a walk-in be attached directly to their kitchen. 
Whatever the application, strip doors provide an excellent barrier not only against heat but also against critters, dust, drafts, and noise when the walk-in door is left open. The ultimate benefits are reduced energy consumption and reduced maintenance costs for compressors.

 

 

Polar Leasing coolers and freezers, which are built by Polar King, include a seamless fiberglass exterior, so they don’t require a roof cap. But if you have another brand, particularly an older unit, you might be surprised to see how quickly a flat-membrane roof cap can fail.  When it does, you end up with moisture leaks and a reduction in operating efficiency.

 

For best results, make sure the membrane material (typically a polyester fabric with a thermoplastic coating) is intact. If it’s torn or dry-rotted, or if it’s pulled away from the roof of the cooler or freezer, have it repaired or replaced immediately.

 

 

As mentioned earlier, the primary source of heat in your walk-in freezer or cooler is the food (or whatever product) you load into it. The more you load, and the higher its temperature when you load it, the harder your unit will have to work to remove the heat.

 

For example, if you load your walk-in with 1,500 pounds of product at 0° F, very little heat will have to be removed to obtain a temperature of, say, -10°F. But if the same 1,500 pounds is delivered from your supplier at 25° F, you’ll pay a lot more running your refrigeration system to remove the additional heat and get down to that same -10°.

 

The “moral” of this story? Don’t remove heat from the product yourself. Let your supplier do it first. Your utility bills will be a whole lot smaller.

 

Want to learn more energy-saving, money-saving tips? Contact your Polar Leasing representative. You’ll pick up a few more “refrigeration basics” and discover how beautifully and efficiently Polar Leasing walk-ins can put them to work for you.