WHAT IS AUTODEFROST 

The refrigeration products be it for +4ºC or +22ºC or freezers for -20ºC or -25ºC etc, all compulsorily employ auto defrost cycle, as an integral part of the system.  The auto defrost basically removes the ice formed in the refrigeration side especially the evaporator section, collection of which progressively decreases the efficiency of the cooling, and hence it becomes mandatory to remove the ice, so that the cooling efficiency is restored to the original level.

The auto defrost is generally achieved with a heater mechanism to melt the ice totally and a temperature sensor to control the cycle, either to evaporate the ice formed or drain it from the system in the form of water. This process is programmable in some machines and in some other systems, it is done manually. But however the whole process of auto defrosting takes anywhere between half an hour to one hour and repeated every 24 hours.

The auto defrost is a correction factor applied, after creating a problem due to deficiency in the basic design, and auto defrost could be obviated, if all the design characteristic aspects are taken into account, with respect to dynamics of air flow within the chamber in conjunction with the evaporator, fans and suction and circulation of air and so on, in toto.

SHORTCOMINGS OF AUTODEFROST :

• The auto defrost by the very design involves additional and wasteful power consumption and which can be significant over the life cycle of the machine.
• Process involves typically heater with 500 to 600 watts, and thermal fuse to prevent overheating, and the programmer for the auto defrost function, and all add up to the cost, even while lowering the overall efficiency of the system.
• The temperature of the contents inside the refrigeration cabinet raises significantly during the defrost cycles and more so, and if the load is less, this can cause “freeze burn” on items due to partial defrosting and refreezing !!
• The defrosting cycle may not be completed when the defrost timer is back to normal operation, and especially relevant under hot and humid conditions like in India and when door openings are frequent. This can lead to icing up, which interferes with the proper operation of the system or lead to continued heating even after complete removal of ice !.  On top of it, as the time duration for the defrost is fixed and there is no feedback mechanism which are all inherent weakness. So the mechanism in the absence of information to confirm completion of deicing, shall continue to heat or overheat ; on the other hand, system can also shut off earlier even if additional time frame is needed, for the completion process of deicing. In essence , the system with or without feedback mechanism does not really serve any real purpose !!.
• Auto defrost based systems are not ideal for storage of delicate biomaterial including blood, because the cycling time between set temperature and higher temperature attained during defrost repeated cycles, over a specified programmed time, over a long period can degrade the products. During the entire storage period of the products, this has significant adverse effect on stored material.
• The running cost is steep when the usage is high, and when the fan continues or starts to run whenever the door is open and more auto frost cycles are involved.
• In the case of auto defrost the duration of the defrost cycle is programmed and during such cycles, the product inside is elevated to a much higher temperature, till the completion of the cycle, till the product attains the set temperature. Hence repeated warming/heating  up of the products in chamber and lowering of the temperature and with repeated cycles, and over a period, product undergoes thermal shocks !
• If the temperature sensor or the defrost timer has a malfunction, making the system go through an erratic defrost cycle for much longer than necessary, thereby lowering temperature in the compartment, it can affect the blood or precious material stored.
• Fair amount of heat is released into the refrigerated storage compartment when the system is defrosting, resulting in significant increase of temperature inside and often above the alarm temperatures and going unnoticed !

Resultant damage : 

Wheecon right from the beginning recognised the major shortcomings with auto defrost function, which heats up the entire chamber much above the set storage temperature and often beyond alarm temperature  ! For example, when the blood bank refrigerator or bio refrigerator is set at 4ºC, during the auto defrost cycle the temperature with product can be as high as 10 to 12ºC or even higher. Ironically when the set temperature is 4ºC, the low temperature alarm is set at 2ºC and high ambient temperature at 6ºC conventionally.

So it should be clear that during the auto defrost cycle for a duration of anywhere between 30 to 60 minutes or even higher, every 24 hours,  the chamber is maintained far above even alarm temperature conditions, that is, beyond 8 or 10 or even 12ºC. This happens every day, at least once, and in some cases even twice, based on the other conditions including the humidity and so on. So it is easy to imagine the damage suffered by the biomaterial when every day for about an hour, the product is subject to “storage” temperatures under alarm condition ! Assuming that the storage of the product is for one month, product is outside the ideal storage temperature, for about 15 to 30 hours in total.

What we do:

Wheecon design the refrigeration including airflow system within the chamber ,in such a way and different from the existing design of the machines ,that it does not form ice. So no  need to remove the ice and hence no auto defrost mechanism needed.!! The air flow dynamics is such that,  the fresh air is drawn into the system and effectively spread across the evaporator coils with the assistance of  careful selection of three evaporator fans,  instead of the usual one used and with the judicious selection of the evaporator coil design and positioning with reference to the entire air flow involved, all go to avoid ice formation.

This unique design ensures that the fresh air every time, during the access of the product , is uniformly drawn across the chamber at appropriate critical speed of the fan and static pressure. The drawn fresh air is spread evenly across the evaporator section and smoothly flowing down the system for uniform recirculation. The whole design concept ensures that there is no need for auto defrost as no ice formation takes place  in the evaporator section and doing away with the major disadvantages of using auto defrost cycles as  part and parcel of refrigeration product, be it +4ºC, 22ºC or -20 ºC or -25ºC and so on.

IN SHORT, WE AVOID CREATING A PROBLEM AND THEN  FINDING A SOLUTION MORE DANGEROUS THAN THE PROBLEM ITSELF.  BEST WE AVOID IT IN THE DESIGN STAGE ITSELF !!