The physical size of the coldroom doesn't accurately determine its power requirements, you need the details of the condensing unit or even better you need to actually measure the current draw whilst it's operating. Refrigeration units can have wildly varying electrical loads depending on the ambient air temperature it's operating in. A fridge unit with a blocked condensor for example can easily draw 30% higher running current than when it's clean. Also when it's blocked it can also consume nearly double the power (units of electricity) to do the same refrigeration work than when it's clean. Same goes if the unit is under condensing for some other reason like poor design.

If you have equipment/appliances that only run intermittently you should be able to apply sensible diversity factors to the supply. If you just add up the current requirements for all the individual loads you're likely to end up paying for a supply that's much larger than you actually require because they're never all going to run at the same time.

Get a competent electrician to help you decide your supply requirements, it could save you a lot of unnecessary spending.