For many businesses, the cold room is essential to keeping the operation running. As a storage space you cannot do without, it has to meet strict hygiene and safety standards. How it is fitted out, how it works and how it is maintained are all things you need to know if you want to use it properly. Do you know the difference between a positive and a negative cold room? This guide takes you inside a piece of equipment the cold chain cannot do without.
What is a positive cold room?
A cold room is a space designed to keep products at low temperature. Those spaces can hold all sorts of products: foodstuffs, medicines, vaccines, and even wooden furniture or works of art. Some materials, such as wood, have to be treated at low temperature. For works of art, the cold kills off any wood-boring insects that would damage the piece.
Every cold room has to meet one specific standard: AFNOR NF P75-401 - DTU 45.1. It covers building contracts for the thermal insulation of refrigerated buildings and climate-controlled spaces, and sets the rules on:
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- thermal insulation
- hygiene
- the materials to use (for the floor, the walls and ceilings, and so on)
What temperature should a positive cold room be set to?
Cold rooms fall into two categories:
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- Positive cold, which holds a temperature above 0°C.
- Negative cold, which keeps products at a temperature below 0°C.
The raw materials and finished products stored there have to be checked once or twice a day (unless temperature management is automatic).
Temperature readings: a guarantee of safety
Taking temperature readings is essential if you want to be sure food is being managed and kept properly in a cold room. Every reading must be archived, on a computer or in a logbook.
Several manual options are available for taking them:
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- by direct reading, from the real-time temperature display on equipment that produces both cold and heat.
- with an infrared or laser thermometer: this checks the air temperature inside a cold room.
- with an electronic probe, which checks the temperature of the products themselves. The probe has to be disinfected with clean water before and after use.
There are also automatic temperature logging systems, such as:
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- the USB temperature logger: a portable device that automatically records the temperature of your cold room throughout the day. It also has an alarm that goes off if the temperature rises above the level you programmed. To retrieve the readings, plug the USB port into your computer and you have all the temperature data.
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- the wireless temperature logger (over Wi-Fi): the same idea as the USB logger, but with a wireless Wi-Fi connection. Connect it to your computer over a Wi-Fi network and it sends all the data in real time. It has an alarm too, so you can receive alerts by email or SMS when there is a temperature problem in the cold room.
How do you manage temperature control across several cold rooms?
To monitor several cold rooms at once, install a centralised temperature logging and monitoring system. It lets you control all your cold room equipment remotely, and it records every reading in real time so you can keep your logs together.
What is the difference between a positive and a negative cold room?
As explained above, the main difference between positive and negative cold rooms is the temperature at which products are kept.
Negative cold rooms
The negative cold room has the advantage of anticipating and limiting the spread of bacteria. The cold air the system puts out is generally between -18 °C and -60 °C (deep freeze). Ideal for freezing food, this room uses negative cold to solidify the water contained in foodstuffs. That prevents the food’s cells from breaking down, and so preserves its nutritional qualities.
It is found in many professional kitchens in the restaurant trade, and in specialist food shops such as butchers and fishmongers. It is also used by the food and pharmaceutical industries.
Positive cold rooms
The positive cold room is widely used to keep fresh food. Unlike the negative cold room, it is not meant for storing foodstuffs over the long term. Because this cold space runs between 0 °C and 15 °C, it suits products such as fruit and vegetables and dairy.
You will usually find them in restaurant kitchens, in bakeries, butchers, caterers and patisseries, and in supermarkets and the medical sector.
How does a positive cold room work?
A cold room always includes a refrigeration unit that acts as the temperature regulator. Using refrigerants and a refrigeration cycle, it brings the temperature down. Fridges use the same system, in a less powerful form.
To understand how a cold room works, you need to know the parts that make up the refrigeration unit and the job each of them does in the cooling system:
The compressor
In the refrigeration cycle, the compressor takes in the refrigerant when temperature and pressure are low. It then raises the pressure and the temperature in order to push the gas towards the condenser.
The condenser
In the condenser, the refrigerant, which was in gaseous form, turns back into liquid. This is where sub-cooling by water or air takes place.
The drier
The refrigerant is stripped of its impurities and its moisture by being filtered in this part of the refrigeration unit.
The expansion valve
Here the temperature and the pressure are brought down again. This thermostatic component fills the evaporator with the sub-cooled liquid refrigerant.
The evaporator
This is where heat is exchanged between the cold room and the refrigeration unit. The component turns the refrigerant into vapour, and a ventilation system then spreads it evenly through the refrigerated space. A drainage system is also needed to remove the condensate.
Insulating a cold room
For a cold room to hold its internal temperature, a specific insulation system is essential. It needs at least two panels — aluminium, metal or laminate — each separated by polyurethane foam. When insulation materials are designed to measure, many businesses go straight to specialists. For insulation, CFCs and HCFCs are the best performers and also the most widely used.
Cold chain safety standards matter a great deal when goods are stored in the cold room. They matter just as much in transit, where keeping the chain intact is essential. Controlling it, and so guaranteeing the nutritional quality and the safety of food for the whole journey, takes expertise. Find out how to get delivery right and keep the cold chain intact.
