PhD Thesis - Energy Systems Research Unit - University of Strathclyde

Both the high pressure inside the condenser-generator and the low pressure inside theevaporator-absorber vary linearly with change in hot water circuit inlet temperature.However, whereas the pressure inside the condenser-generator increases withincreasing temperature, the pressure inside the evaporator-absorber decreases withincreasing temperature.The high and low cycle pressure curves coefficients (a 0 , a 1 , b 0 and b 1 ) can thereforebe derived by varying the hot water circuit inlet temperature to the generator andrecording the resulting part-load cycle pressures. The relationships describing thebehaviour of the two system pressures with a corresponding change in T 11 , the hotwater circuit inlet temperature in °C, were then obtained using a linear regressionanalysis on the test data shown in Figure 3.6. A similar calibration exercise can berepeated to obtain the characteristics of any other chiller. Table 3.9 shows the generaland specific equations for the calibrated chiller together with the correspondingcorrelation coefficients.Table 3.9 - Relationships between hot water inlet temperature and the high and lowpressureGeneral equationformSpecific equation forcalibrated chillerCorrelationcoefficient withmeasured data (R)Low pressure insideEvaporator-Absorber(p low ) (kPa)High pressure insideCondenser-Generator(p high ) (kPa)a 0 +a 1 (T 11 ) (3.23) 0.0735(T 11 ) + 0.3429 0.9953b 0 +b 1 (T 11 ) (3.24) -0.0137(T 11 ) + 2.4019 0.99953.3.5.2 Calibration stage 2: Obtaining the chiller’s refrigerating power output as afunction of the water circuits’ inlet temperaturesThis part of the calibration process obtains an expression for the chiller’srefrigerating power output function (CH Power ) in terms of the three water circuits’inlet temperatures. It is this calculated power output which serves as the“performance map” described earlier in Section 3.3.3 and which in conjunction with119