IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C2-A, November 9, 2009
T C,
i − T C,
i−1
( r + c ⋅ ( T G,
i − T C,
i
) + ( M ⋅ c ) ⋅
= ( UA) ⋅ ( T T )
& (29)
∆t
m
v, G,
i
⋅
( pc)
p,
v
p C,int
C,int
C,
i
−
C,
i
m&
v,
A,
i
⋅
( r + l − c ⋅ ( T G,
i − T E,
i ) + c ⋅ ( T G,
i − T A,
i
)
( pc)
T A,
i − T A,
i−1
( M ⋅ c ) ⋅
= ( UA) ⋅ ( T − T )
p A,int
( pc)
∆t
p,
v
A,int
p,
w
A,
i
A,
i
+ Q&
SHX , i
+
(30)
Equations (27) and (28) describe the internal heat transfer in evaporator and generator,
respectively. There, the heat which is given off by the heat exchanger (right-hand side) partly
heats up the internal parts of the vessel (second term on left-hand side) and partly is used for
the heating of solution and refrigerant (first term on left-hand side). In analogy, equations (29)
and (30) describe condenser and absorber, respectively. There, the heat which is given off
by the solution and refrigerant (first term on left-hand side) is used partly to heat the internal
parts of the heat exchanger (second term on left-hand side) and partly to heat the cooling
water (right-hand side).
The equation system is being solved in MATLAB using a Newton-Raphson procedure with
finite-difference Jacobian approximation [6].
Experimental Verification
The agreement between simulated and experimental data has been tested using an
experimentally measured hot water input step from 75 to 85 °C. The results of the simulation
using these input data are shown in Figure 5. The hot water inlet and outlet temperatures in
Figure 5 are taken from experimental measurements of the Phoenix absorption chiller. They
show the transient behaviour of the chiller for a 10K step in hot water inlet temperature.
Cooling and chilled water inlet temperatures as well as all external mass flow rates were kept
constant during the step. It can be seen that it takes approx. 600s or 10 minutes to achieve a
new steady-state in hot water inlet temperature after the step. This is shorter than the 15
minutes it takes for all parameters to achieve steady-state again. The simulation was
performed using the measured data as inputs in the model and comparing simulated and
measured hot water outlet temperatures.
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