PhD Thesis - Energy Systems Research Unit - University of Strathclyde

3.3.5.3 Calibration stage 3: Obtaining the total mass and the mass weightedaverage specific heat capacity of each individual nodeOnce the internal state points of the chiller have been defined, the third and final partof the calibration process is needed to calibrate the total mass (M node - M i , M j and M gin kg) and the mass weighted average specific heat capacity ( - , and inkJ/kgK) of the individual nodes. These define the dynamic characteristics of thechiller.There are two methods which can be used to calibrate the total mass and the massweighted average specific heat capacity. The first uses a ‘traditional’ approach andcan be used if enough information on the individual internal components is available.In this case the total mass (M node ) of each individual node can be considered as theaddition of all the masses (m 1 , m 2 ,…, m n ) represented by the node as shown inequation (3.26). The nodal mass weighted average specific heat capacity ( ) iscalculated using the specific heat values of the individual masses making up anindividual node (c 1 , c 2 ,…, c n ) as shown in equation (3.27).- (3.26)- (3.27)For this specific 10 kW th chiller, Kohlenbach in [38] gives a detailed breakdown ofthe masses and characteristics of the individual internal components from whichM node and can be calculated as shown in Table 3.11.Using such a method however suffers from two major limitations. As discussedpreviously, detailed data is required for the internal components of the chiller. Thisdata may not be available or require intrusive measurements to obtain. Secondly, insuch a complex system, made up of multiple parts, it is relatively difficult to clearlyidentify which mass may be associated with each node. The thermal capacitance of anode may be (even if partly) influenced by an internal component which is outside121