Door Fogging: Whenever the weather gets humid, and especially on warm and muggy summer days, many walk-in coolers will experience condensation, in the form of sweat or fog, on the frames and glass of reach-in glass doors. This happens because these surfaces, especially on older walk-ins in stores without air conditioning, are colder than the dewpoint of the moisture-laden air.

Some modern glass doors overcome this problem by better insulation and thermal breaks in the frames. Although more expensive to purchase, this is the preferred solution since no energy need be used at all from the time of installation on. Installing electric heaters in the doorframes and glass is the most common solution, however, usually with a manual switch on each door. This requires someone remembering to switch the heaters on and off as needed. The reality is that the door heater switch positions aren't usually in the top thousand favorite things a store manager has to keep track of, so he or she will simply leave them on all the time, since they won't cause problems that way. No problems, that is, except for problems with the electric bill. The heaters often don't have to be on more than a couple of weeks a year, in some cases. The rest of time the electricity is completely wasted. Make that more than completely wasted, since having the heaters on makes the walk-in warmer and the compressor work harder.

The hundreds or even thousand of dollars wasted on electricity to heat a store's reach-in doors each year is easily saved by using a Freeaire Cooler Controllertm to control the door heater operation. Simply position the Freeaire's humidistat (item # 550) near the doors and set it at the relative humidity setting at which condensation starts to become a problem. That's it. Set it and forget it. The heaters will be on when they're needed and off when they aren't, and the only loser will be the power company.

Evaporator Icing: The same kind of weather that causes condensation on doors causes icing or frosting of the evaporator coils. When the compressor is operating, moisture condenses on the cold evaporator coils or fins and then freezes. The more the compressor runs and the more humidity in the air the faster the ice builds up. If the ice builds up until it clogs the air spaces between the fins, the heat transfer efficiency of the evaporator declines. This leads to a downward spiral of increasing compressor operation, increasing icing, and decreasing efficiency, leading to eventual loss of refrigeration to the walk-in, and possible damage to the equipment.

The solution to this problem is to have periodic defrost cycles to remove ice from the evaporator coils while the compressor stays off. In general, most walk-in freezers use electric heaters for defrosting the evaporators, while walk-in coolers usually use "air defrost." Air defrost means that the evaporator fans operate while the compressor does not. Above-freezing air passes over the coils, which gradually warm to above freezing and the ice melts. Once all condensate is drained to outside the walk-in the defrost period can safely end. Air-defrost compressor systems are supposed to be sized large enough that even during the hottest, most humid weather with the largest likely cooling load the compressor can cool the walk-in to the desired temperature while operating only 3/4 of the time. This is because the evaporators may need up to 6 hours per day of air defrosting to stay free of ice and out of the downward spiral mentioned before.

To make sure that a walk-in gets enough defrost time, most evaporator fans operate 24 hours a day and mechanical time clocks are used to schedule a defrost period for a walk-in cooler once or twice a day, just in case more defrosting is necessary. A walk-in freezer may have six 20-minute defrost periods of electric heater operation a day. Most of the year, that much defrost time isn't necessary, but a simple timer can't know that, so it has the same defrost cycles everyday. What is adequate in July is overkill in January, when all that unnecessary evaporator fan operation is just wear and tear on the fan motors and money wasted on electricity. Evaporator fans usually need to operate only about 40% of the time to deliver cooling to the walk-in and to air defrost the coils. The other 60% of the time they are simply greatly overpowered circulation devices. The energy waste is compounded in a walk-in cooler by another 40% (60% in a freezer) because all the electricity used to operate the evaporator fans (and the electric defrost heaters in freezers) turns into heat which must then be removed by the compressor.

A Freeaire refrigeration system's Cooler Controller solves these problems in walk-in coolers or freezers by eliminating unnecessary evaporator fan operation and supplying defrost on demand. Evaporator fans run only the 6 to 12 hours a day they are needed, thus saving money on electricity for the fans as well as the condensing unit. A super-efficient (only 36 watts!) Circtm circulating fan provides the needed air movement to prevent stratification inside the walk-in whenever the evaporator fans are off. Open-ended defrost cycles occur after a set period (usually 6 hours for a cooler or 4 hours for a freezer) of accumulated compressor runtime and last as long, but only as long, as needed. A temperature sensor mounted in the evaporator coils keeps track of ice and knows when to end a defrost cycle. The refrigeration system always operates at peak efficiency because the evaporator coils are regularly kept clear of ice. Less evaporator fan and compressor operation makes them last longer and saves money on replacement as well as operating costs.

If the Freeaire's optional Cool Breezetm Outside Air Package is used to bring outside air into a cooler the Cooler Controller's defrost strategy automatically compensates for varying levels of humidity. If 32°F outside air at 100% humidity is brought into the cooler and the compressor is operating to share the load, the defrost cycle is unchanged, other than to last longer than if the outside air were dry.

Condensation on Product: Sometimes infiltration of warm, humid air can cause moisture to condense on cold surfaces within a walk-in cooler. Cardboard or boxboard packaging can become soggy and fall apart, sometimes halfway to the cash register! Some beer distributors store their bottled and canned beer at warmer temperatures in the summer than in the winter to avoid these problems. Using the optional Cool Breeze Outside Air fans doesn't affect this problem at all. Because the outside air being brought in is always cooler than the air inside the walk-in, and because warm air can hold more moisture than cool, there is no tendency for condensation to occur anywhere but on the evaporator coils. This condensation is easily removed by the defrost cycle.

Product Drying: Although dry packaging is always good, the air inside any walk-in cooler may sometimes gets too dry, especially in the winter. Because moisture condenses on the evaporator coils and is drained to the outside during defrost cycles, the air's relative humidity can gradually drop if more moisture is not constantly brought in. This can be a problem for produce or any product whose moisture content should not be changed. That's why it is always recommended that airtight containers be used in walk-in coolers to prevent product drying. The Freeaire's Cool Breeze Outside Air fans can bring in extremely dry air during frigid winter weather, so the need for airtight packaging remains.