Manual or Automatic Defrosting?

“It’s hard work, but someone has to do it.” We’ve all thought this when faced with those tedious chores we periodically have to do around the house, defrosting the freezer being one of them.

The vast majority of refrigerators in our homes need to be defrosted manually. On the other hand, for freezers and laboratory freezers, we have a choice: there are models with automatic defrosting and models with manual defrosting.

Let's see what the two practices consist of, what the differences are and finally the advantages and disadvantages.

What is Manual Defrosting?

In both laboratory freezers and conventional freezers, frost and ice tend to form inside the compartment. 

This is caused by repeated door openings , which allow warm air to enter, which contains more moisture than the same mass at a lower temperature. As the air cools, its volume decreases, and the moisture it contains condenses, but since it's inside a freezer, it turns to ice.

To manually defrost, first unplug the freezer. Then, leaving the door open, begin removing the easiest ice. The warm air will help melt the remaining ice, and you can use a sponge to collect the water that forms.

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What is Automatic Defrosting?

Some models of laboratory freezers implement a mechanism that automatically defrosts the freezer compartment and for this reason they are also called frost-free freezers.

In this type of freezer, defrosting occurs periodically via a mechanism that heats the cooling element (called the evaporator) for a certain period of time, in order to melt the ice that has formed on it. 

The resulting water is collected in a tray installed on the compressor, so that the heat it generates speeds up its evaporation.

Manual Defrosting vs. Automatic Defrosting

So, which one should you choose : a manual defrost freezer or an automatic defrost one?

It all depends on your needs.

On the other hand, the manual defrost freezer certainly has a price which is significantly lower than the automatic defrost freezers.

It also consumes less energy and is less noisy.

Modern self-defrosting freezers, on the other hand, require much less maintenance and are ideal for laboratories where the machinery must be constantly running and it might be inconvenient to have to empty it to defrost it.

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FDM Freezers with Manual and Automatic Defrosting

At FDM – Environment Makers we have been manufacturing climate chambers and laboratory instruments for over 70 years. Our freezer offering is varied and suitable for all needs. 

In fact, we have models with automatic defrosting (such as the NC/BC Series) and others with manual defrosting.

Don't hesitate to contact us to find out more.

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Reference Standards

• IEC 60068-2-1 — Environmental testing – Part 2-1: Tests – Test A: Cold. Reference for cold testing and ice buildup issues in climatic chambers.
• IEC 60068-3-5 — Confirmation of the performance of temperature chambers, which considers the effects of the defrost cycle on stability.
• ISO 23953-2 — Refrigerated display cabinets – Part 2: Classification, requirements and test conditions, includes specifications on defrost cycle.
• EN 441 — Refrigerated display cabinets – Test methods, including measurement of energy consumption during defrosting.
• ASHRAE Handbook – Refrigeration (current edition) — Chapter defrost methods (off-cycle, electric, hot-gas, reverse cycle).
• UNI EN ISO 23953-1 — Italian implementation of specific climate classes and defrost cycles.
• EU Regulation 2019/2019 — Ecodesign requirements for refrigerated appliances, including constraints on defrost system efficiency.

Authoritative Sources

• ASHRAE. American society, a world leader in HVAC-R, publishes the Refrigeration Handbook with chapters dedicated to defrost methods.
• IIR – International Institute of Refrigeration. Scientific and technical body for refrigeration with technical guides on defrost and performance.
• IEC – International Electrotechnical Commission. IEC 60068 series on environmental test chambers and their qualification.
• Eurovent Certification. European HVAC-R certification body that certifies the performance of refrigeration systems.

Frequently Asked Questions about Defrosting

What are the main types of defrosters and how do you choose them?

There are four main methods. Off-cycle (natural) defrost stops the compressor and allows the evaporator temperature to rise above 0°C. It has a slow cycle of 30–90 minutes and is suitable for chambers between +1°C and +10°C. Electric defrost uses heating elements on the evaporator. It has a 15–45 minute cycle and is commonly used in chambers down to −25°C. Hot-gas defrost sends hot refrigerant gas from the compressor outlet to the evaporator via a bypass valve. It has a rapid cycle of 8–20 minutes and is 30–50% more energy efficient than electric defrost. It is used in industrial systems >50 kW. Reverse-cycle defrost inverts the refrigerant flow (heat pump mode), which is common in heat pumps and frequently cycled cold chambers. The choice depends on the operating temperature, frequency of daily cycles, and energy budget and ecodesign.

How does defrost affect the stability of a climate chamber?

During defrost, the chamber temperature undergoes a transient overshoot typically of +2 to +8 °C compared to the setpoint for chambers < −20 °C, lasting 10-30 minutes. For critical environmental tests (IEC 60068 climate chambers) this represents an unacceptable deviation if the test requires cold continuity. Solutions: (1) double evaporator with alternating (while one defrosts, the other cools), overshoot reduced to ± 0.5 °C; (2) adaptive defrost that intervenes only when necessary (return air pressure or humidity sensor); (3) pre-cooling before defrost by lowering the setpoint by 3-5 °C; (4) software compensation of the test timeline. The IEC 60068-3-5 qualification must be performed including defrost cycles to represent real-life conditions of use.

How do you size a defrost cycle (time, frequency, termination)?

The critical parameters are frequency (cycles/day), duration (minutes), and termination logic. Typical settings for a −20°C chamber: 4-6 cycles/day, duration 25-35 minutes each, termination at evaporator temperature +15°C (contact sensor). To reduce energy consumption, adaptive logic is used: termination at differential pressure on the air filter (≥ 50 Pa), termination at return air humidity (< 60% indicates melted ice), and demand defrost with optical or ultrasonic sensors to detect ice layer. A poorly calibrated defrost cycle causes: (a) incomplete defrosting with progressive accumulation (COP efficiency -10-30% in 30 days); (b) excessive duration with temperature overshoot and energy waste. Sizing must consider ambient air humidity: at RH 80%, cycles can double compared to RH 40%.

What problems does manual defrosting cause in the laboratory?

The manual defrost requires operator intervention: turning off the unit, opening the door, removing ice with a plastic scraper (never a metal one, risk of perforating the evaporator), internal drying, restarting the refrigeration cycle. Main problems: (1) service interruption of 2-6 hours with the need to transfer samples to the backup refrigerator (GDP cold chain risk); (2) high energy consumption for setpoint recovery (+30-50% compared to the continuous cycle); (3) risk of contamination during prolonged opening (ingress of humidity, microorganisms); (4) not traceable in GMP audits without a dedicated SOP procedure and logbook. For 24/7 laboratories with GDP/GMP materials, the WHO PQS and EMA GDP regulations prefer auto-defrost with no-frost and double thermoregulation, maintaining continuous traceability of the parameters. The use of manual defrost is currently limited to low-cost refrigerators or non-critical applications.