This is the second in a series of papers presenting the fundamentals of a simulation toolkit developed by ASHRAE TC 4.7. The modelling used in this toolkit is oriented toward simple solutions with a minimum number of parameters that are accurate enough for annual energy calculations of whole building systems. Quasi-static models, which are generally sufficient for such applications, allow the user to deal with the part-load regime. The chiller model is developed and documented on the basis of the following elements - an information flow diagram in which a selection of input and output variables and parameters is proposed, three conceptual schemas in which the main physical hypotheses are expressed, and a set of equations derived from the conceptual schemas. The actual refrigerant cycle is taken into account. Heat exchangers and reciprocating compressors are modelled with some realism. This approach is easy to understand for most engineers, and can be easily updated at any time. Practical possibilities of parameter identification (on the basis of catalogue data, for example) are provided, and some information about auxiliary consumption is given. Two alternatives are available for the compressor model - with and without the addition of a fictitious exhaust nozzle intended to produce an effect equivalent to valve pressure drops. Two alternatives are also proposed for parameter identification - looking to the compressor alone or to the whole chiller (i.e., including condenser and evaporator characteristics). Part-load is presumed to be realised by cylinder unloading and cycling between two unloading levels or between the ON and OFF regimes.

KEYWORDS: calculating, energy consumption, reciprocating compressors, chillers, condensers, evaporators, accuracy, part load, refrigerants, cyclic, fluid flow, flow rate, heat exchangers, models, heat transfer coefficient