Heat load and capacity planning
Cold room sizing starts from the load, not from the room dimensions. List what enters the room each day, at what temperature, and how long it stays; product load is usually the dominant component and it changes with turnover and season. Then add the other components: transmission through panels, door openings and the air exchanged each time, people working inside, lighting, and any evaporator fan heat. Confirm the room ambient outside the panels, because a room built into a hot kitchen or an unshaded yard faces a different load from one inside an air conditioned store. State the internal dimensions, the clear height under the ceiling and the racking or shelving plan, since usable volume depends on how the room is filled. If the room will be expanded later, say so at the planning stage, because panel layout and system capacity are easier to allow for at the start than to change afterwards.