Chillers should be defined in priority order. Often it is the case that there are multiple identical chillers that rotate priority order. Smaller ‘pony’ chillers that run during low-load conditions should be given top priority. The chiller capacity (tons) and chiller type (Constant speed versus variable speed; air-cooled versus water-cooled) are required inputs. Optional inputs (with typical defaults available) include the chiller efficiency, the chiller minimum part load ratio and the staging scheme (part load ratio associated with chiller stage-up and stage-down). Chiller efficiency can be input in terms of kW/ton or in terms of COP. Different defaults are available for air-cooled versus water-cooled chillers.