CO2 and ammonia in practice — natural refrigerants in supermarket and industry

While much of the development in the cooling industry has historically been about finding new synthetic refrigerants, the future is now pointing back to two substances that have been known for over a hundred years: carbon dioxide and ammonia. Both are natural refrigerants with a GWP close to or equal to zero, but they are used for different purposes and each requires their own handling.

§CO2 (R744) — supermarket cooling's new standard

CO2 is not toxic and not flammable (safety class A1) but it operates at much higher pressures than traditional refrigerants and it has a critical temperature of only about 31 degrees — that is a temperature which a system's condensing side can easily reach on a hot summer day. When it happens the system goes into transcritical operation: the refrigerant no longer condenses to liquid on the high-pressure side but remains in a state where pressure and temperature must be carefully controlled by the regulator to keep the system efficient. This requires components and controls built specifically for CO2 and significantly higher pressure ratings than traditional refrigerants.

§Denmark as a major player

Danish companies have played a leading role in developing transcritical CO2 systems for supermarkets, and transcritical CO2 now accounts for nearly the entire market for new supermarket refrigeration installations in Denmark. This is due to a combination of tighter taxes and regulations on HFC refrigerants, falling prices on CO2 components, and a mature supply of compressors, valves and controllers built specifically for the purpose. For you as an aspiring refrigeration technician, this means CO2 systems with booster circuits and parallel compression are not a niche — they are the mainstream in commercial refrigeration here at home.

§Ammonia (R717) – industrial cooling with respect

Ammonia has excellent thermodynamic properties and has been used in industrial cooling for over a hundred years – from cold storage facilities to dairies and breweries. Unlike CO2, ammonia is classified B2L: it is toxic upon inhalation and low flammability. Even relatively low concentrations in air are harmful to health, and the smell is so sharp that you can usually smell a leak long before the concentration becomes dangerous – but this must never stand alone as a safety measure.

§Special requirements for ammonia systems

• 01Gas detectors and alarms that warn long before dangerous concentrations are reached.
• 02Clear procedures for alarm and evacuation in case of spill accident.
• 03Requirements for appropriate ventilation in machine rooms where ammonia is handled.
• 04Work with ammonia in certain facility sizes falls under an extended certificate (Type II) that requires prior documented experience with the substance.
• 05The risk ordinance sets a special, low threshold quantity for ammonia, which triggers stricter requirements for companies storing it on an industrial scale.

§Two refrigerants, two realities

It is easy to think of 'natural refrigerants' as one category, but CO2 and ammonia place very different demands on you. With CO2, the main challenge is the high pressure and transcritical operation; with ammonia, the main challenge is toxicity and the responsibility that comes with working with a substance that can seriously harm people in an accident. Both require you to know the system, know the refrigerant and follow the procedure — neither tolerates a technician who cuts corners.

“Ammonia smells long before it is dangerous. CO2 does not smell at all – and that is precisely why you should rely on your instruments, not your nose.”