Cold storage and a method of operating a cold storage

A method of operating a cold storage comprising a compartment, a first cooling unit arranged to cool the compartment, and a second cooling unit arranged to cool the compartment, the first cooling unit comprising a first circuit for circulating a first refrigerant between a first compressor unit, a first condenser and a first evaporator and the second cooling unit comprising a second circuit for circulating a second refrigerant between a second compressor unit, a second condenser, and a second evaporator, the second cooling unit further comprising a second fan, the cold storage further comprises a controller configured for operating the first cooling unit and the second cooling unit according to a first, a second, and a third mode of operation, the first mode providing use of only the first cooling unit, the second mode of operation providing use of the first cooling unit and the second fan of the second cooling unit, and the third mode of operation provides use of the first cooling unit and the second cooling unit, the method comprising:

• operating the cold storage in the first mode of operation;
• identifying a transition between a first temperature profile and a second temperature profile in the compartment, the transition being a result of a phase change of a substance stored in the compartment, and the phase change corresponding to a rate of temperature change between the first temperature profile and the second temperature profile;
• and
• determining a time for initiating the second mode of operation based on a point in time or a time interval where the transition occurs;
• wherein the transition between the first temperature profile and the second temperature profile in the compartment is identified by recording temperature in the compartment in respect of time;
• wherein the transition is identified by identifying the rate of temperature development.