How eutectic cold storage works
A eutectic solution is a mixture, often salts in water, that freezes and melts at a single, sharp temperature. That temperature can be designed to sit below zero, for example to suit ice cream or frozen food. When the refrigeration system runs, it freezes the solution in plates or tubes lining the cabinet. When the power goes, the solution slowly melts, soaking up heat at a near-constant temperature until it has fully thawed.
Melting absorbs a large amount of heat without changing temperature, which is why a modest volume of phase-change material can hold a cabinet cold far longer than cold air or the stock alone.
What hold-over time means
Hold-over time is how long the cabinet stays within its required temperature range after power is cut, with the lid or door closed, under stated test conditions. It depends on how much phase-change material there is, its melting temperature, the cabinet's insulation and the room temperature. A hold-over rating measured in a cool test room will be shorter in a 40 °C shop.
Vaccine refrigerators and freezers prequalified by WHO's PQS programme publish tested hold-over figures; for commercial units, ask suppliers what the hold-over time is and at what ambient.
Common types
| Type | How it works | Typical use |
|---|---|---|
| Eutectic plate freezer | Plates of eutectic solution in walls or lid | Ice-cream vending, frozen food in areas with outages |
| Ice-lined refrigerator | Water containers freeze and hold a chilled cabinet around 0 °C and above | Vaccine and medicine storage |
| Eutectic chiller | Phase-change material melting above 0 °C | Milk, beverages, chilled food |
| Portable eutectic cabinet | Charged overnight, used unplugged | Ice-cream carts, delivery, events |
When hold-over cabinets make sense
- Daily scheduled or frequent unscheduled power cuts of several hours.
- Sites where a generator or battery inverter is too costly or impractical.
- Mobile selling, such as ice-cream carts, where the cabinet must run unplugged.
- Products with a narrow safe range, where a short excursion means loss.
- Shops that close at night with power going off on a timer.
Trade-offs to understand
Phase-change material takes up space and adds weight, so a hold-over cabinet holds less stock than a standard cabinet of the same outer size. After a long outage, the material must be refrozen, which needs a long run of the compressor and adds to energy use at that time. The cabinet's recovery time after power returns matters as much as its hold-over time if your outages are daily.
Efficient design helps here too. Thick insulation and a well-sealed lid extend hold-over time without adding more phase-change material.
Using hold-over cabinets well
- Keep the lid or door closed during outages; every opening uses up stored cold.
- Load stock already frozen or chilled; warm stock eats into the reserve.
- Give the cabinet time to fully recharge after a long outage before heavy restocking.
- Use a thermometer or data logger to learn your real hold-over time on the hottest days.
- Keep condensers clean so recharge is quick when power returns.
Other ways to ride through power cuts
Hold-over cabinets are one option among several. Standard chest freezers already hold cold well because cold air stays in when the lid is shut, and a full freezer holds temperature longer than an empty one. Battery inverters and generators keep any cabinet running but cost more to install and maintain. For critical stock, temperature alarms that alert you by phone during an outage add a valuable layer of protection whatever approach you choose.
Frequently asked questions
- How long will a normal chest freezer stay frozen in a power cut?
- It varies with insulation, how full it is, the room temperature and whether the lid is opened. A full, closed chest freezer holds temperature much longer than an upright or half-empty one. Measure your own with a data logger rather than relying on a general figure.
- Do eutectic freezers use more electricity?
- They use energy to freeze the eutectic material, but that is stored cold that is later used. The overall effect depends on design; with good insulation, energy use can be similar to a standard cabinet.
- Can I add eutectic packs to my existing freezer?
- Frozen gel or ice packs in a freezer add some thermal mass and can help a little during outages. Do not block air vents or the evaporator, and keep packs clean and food-safe.
