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4.3. Absorption Single Stage
4.3.1 Refrigerant cycle
The superheated refrigerant in point 51 is condensed in COND1 until
a condition of saturated liquid is reached (qu COND1,r,o = 0) in point 52.
The high pressure in the condenser is determined by the cooling water
temperature and the ∆T min of the condenser.
The evaporation temperature is given by the temperature of the
cooling circuit and ∆T min,COND1,r,o = 10 ◦ C 8 .
The refrigerant is led through expansion valve VA1 to point 53. The
low pressure in the evaporator (EVAP) is set so the temperature of the
chilled water obtains the desired temperature (T 49 = 6 ◦ C) for the given
closest approach temperature difference (between T 49 and T 53 ), which
is ∆T min,EV AP,r,i = 5 ◦ C. The temperature difference of the chilled water
leaving the evaporator (point 49) and the returned water in point 48
(∆T chill,EV AP ) is assumed to be 5 ◦ C 9 .
4.3.2 Solution cycle
When the refrigerant leaves the evaporator in point 54 as saturated
gas (qu EV AP,r,o = 1) it is absorbed by the strong LiBr solution (rich in
LiBr) entering at point 62 in the absorber. The heat is removed by the
cooling water entering at point 36 and leaving at point 37. Together
with the pressure, T 37 determines the concentration of the weak solution
which leaves at point 55, via the closest approach temperature difference
∆T min,ABSO,s,o = 5 ◦ C (Difference between T 55 and T 37 ).
The weak solution is pressurized by a canned pump (PUMP1) which
is assumed to have an efficiency of 0,5 (point 56). Next the solution
is preheated in SHEX1 before entering DES1 in point 57. The strong
solution leaving the desorber in point 59 transfers heat to the weak
solution in SHEX1 (point 60-61) and expands in VB1 before entering the
absorber.
8 EES has problems running if ∆T min,COND1,r,o is given explicitly, so in praxis
∆T min,COND1,r,o is given to 12,5 ◦ C in the standard parameter configuration, and
monitored and changed during investigations, so that ∆T min,COND1,r,o remains at 10 ◦ C
9 It is assumed that the water is sent to a cold water storage with a temperature of
10 ◦ C and that the air temperature for the air coming out of an air conditioning should
be about 15 ◦ C. Similar temperatures are used in [19] and [34].
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