Since the discontinuous dynamics of adsorption/desorption cycle causes a variable cooling effect of the chiller, it is important to have a model that takes into account this transient behavior. The dynamic model proposed by Saha [5] has been implemented in INSEL. Given that only little information on the physical properties of the chiller and the nature of the silica-gel used is available, some modifications/simplifications in the model have been done. The silica-gel/water equilibrium model based on Henry’s law equation (1) developed by Ng and Chua [6] for the silica — gel Fuji-Davidson type RD was used to describe the adsorption/desorption process.

q* is amount of water adsorbed at equilibrium [kg/kg] (1)

Gat is the isosteric heat of adsorption (Gst=2510 kJ/kg)

KQ is a constant (if? = 2.1C-1S Pa"1)

P is the equilibrium pressure of the adsorbate in the gas phase [Pa]

The model was compared with measurement data (in 10 seconds time interval) of one chiller for different operating conditions of temperatures and volume flow rates. Figures 5 shows the simulated and measured temperature values of the 3 water circuits during 3 cycles for a heating temperature of 78-80 °C and a volume flow rate of

Figure 6 shows the measured and simulated temperatures for a heating temperature of 70-72°C and a volume flow rate of 90 m3/h.

The results for a hot water temperature of 70°C and a reduced hot water volume flow rate of 50 m3/h are shown in figure 7.

Figure 8 shows how the model behaves when the inlet cooling water temperature fluctuates, which happens often in reality when the cooling towers cannot cool down the water coming from the chillers.

2. Discussion

In this part, the results of the simulations of both the solar plant and the adsorption chillers are discussed and different ways of using the model for optimization of the system via online simulation will be proposed.