IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C2-A, November 9, 2009
Figure 2. External heat flows of simulated chiller response on 10K step in generator inlet temperature
without thermal mass
In Figure 1, graph 1 shows the temperatures in the generator which follow immediately the
step of the external inlet temperature, t 11 , because no thermal storage has been assumed.
Accordingly, the heat flow to the generator increases (Figure 2, top left graph). The strong
solution leaving the generator bundle follows immediately (x sG in graph 4 of Figure 1). The
strong solution leaving the generator sump follows in a damped fashion (x sA in graph 4)
because of the mass storage in the sump. The first change in mass fraction of the strong
solution reaches the absorber inlet two steps later. Three steps after the initial change the
mass fraction of the weak solution leaving the absorber bundle begins to change as well (x wA
in graph 4); the solution in the sump follows as well (x wG in graph 4) but this is hardly visible
due to the damping effect of the mass which is stored in the sump.
The flow of weak solution is kept constant (m sol,w in graph 7). The flow of strong solution
increases immediately (m sol,s in graph 7). This due to the rise in generator pressure (p G in
graph 5), which drives more solution through the expansion valve. The rise in pressure, in
turn is a consequence of the rise in the condenser heat flow (Figure 2, top right graph) due to
the rise of vapour mass flow to the condenser (m vG in graph 6). The flow of strong solution
from the generator bundle to the generator sump (m tbG in graph 8) decreases because the
inlet flow is constant and more vapour is being produced. Of course, also the mean
generator and condenser temperature (T G in graph 1 and T C in graph 2), and the condenser
cooling water outlet temperature (t 16 in graph 2) increases.
When the more concentrated solution reaches the absorber in step 204, the pressure
immediately falls (p A in graph 5). The absorber absorbs more vapour, the vapour flow from
evaporator to absorber increases (m vA in graph 6 of Figure 1), the flow from the absorber
bundle to the sump increases (m tbA in graph 8), and the absorber heat increases (Figure 2,
bottom right graph). Accordingly, the temperature of the cooling water leaving the absorber
increases (t 14 in graph 2). At the same time, the evaporator heat increases (Figure 2, bottom
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