IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration
Subtask A Report, Date:…
temperature. The influence of the ambient temperature can be seen in the Table 3 too. The
average values of the most important parameters of the chiller are presented for three
representative days in this table. It can be seen that the average generator power is similar
during the three days, but the deviations between the chilling capacities differ up to 19%.
This happens because at high values of the outdoor temperature, the capacity of the dry
cooler to reject the heat of the absorption cycle to the ambient decreases. Therefore, the
higher the outdoor temperature is, the lower the chilling capacity and the COP produced by
the absorption chiller are.
Date T dbo (ºC) T g,i (ºC) T ev,o (ºC) W ch (kW) W c (kW) W g (kW) COP
11/07/2008 35 94 12.4 4.02 12 7.9 0.48
29/07/2008 30.4 92.2 11.6 4.5 12.8 8.2 0.53
08/08/2008 29.4 91.9 9.5 4.8 13.3 8.7 0.53
Table 3.- Average values of three typical days.
5.3 Detailed Analysis
The steady state performance of the chiller was analyzed. In this way figure 4 shows the
influence of the outdoor temperature on the COP during 2007 and 2008 when the chiller
operated in the steady state period. The COP decreases when the sink temperature
increases. Both trends have the same slope, although the mean values of the year 2008 are
lower because the mean ambient temperature during 2008 was higher.
Fig. 4. – Influence of the outdoor temperature on the COP and in the chilling capacity
6 Experiences / Lessons Learned
As it was mentioned, during this first two years, the installation worked with a dry cooler
tower. The studies showed the great influence of the temperature of the heat rejection sink
on the machine performance. Therefore, the substitution of the initial heat rejection system
was proposed in order to improve the performance of the absorption chiller. Finally, it was
decided to use a geothermal system using a water well placed in the surroundings of the
solar cooling installation. With this modification the chiller operated with a constant
temperature in the heat rejection sink. This temperature, according to others water wells
placed near by was around 17 ºC. This water well supply water to a 25 m 3 water tank, in