I thibk you mean apartment not department but anyway a suite is more for one or two people and has a small living room, bedroom, and kitchen. An apartment is more for a family and has at least two bedrooms

Are you asking about these in a business context? Suite can mean a small office (room) that a business rents from a larger building to operate from. Where a department is a section of a larger company. Examples: The payroll department is the part of Amazon that pays all the employees. The lawyer's office is located in suite 201 of the Sears Tower.

Suite is more often used to refer to short term living such as hotels and often doesnt have any more then the basics and an Apartment tends to refer to a complete long term living space that has a complete set of rooms. For example a bedroom bathroom livingroom kitchenette(sink fridge may have an oven and or stove or a microwave) would be a Suite but if it had a full kitchen it would be an Apartment.