ZEMCH 2015 - International Conference Proceedings | Page 690

Control strategy
The simulation model contains a number of differential controllers for temperature, modeled by
Type 2, which are used in order to control:
• the flow to the solar collectors: the controller allows the fluid to circulate in the internal heat
exchanger of the tank only when the difference between the temperature of the outlet fluid
from the collectors and the average temperature of storage tank is contained between a ΔT=
0.3°C and a ΔT= 5°C;
• the flow of the working fluid from collectors to an auxiliary cooling device, which has the purpose to reduce the temperature of the flow stream, removing energy from it at an user-designated rate (Qmax) whenever the temperature of the working fluid is higher than the user-designated one (Tset = 90°C);
• the operation of the auxiliary heater: this controller allows the gas heater to operate only when
the temperature of the fluid coming from the hot storage goes down 75ºC.
• The previous operation and the absorption chiller’s running take into consideration the presence of cooling demand from building, in fact they depend on a signal coming from a thermostat, modeled by the Type 108. The cooling stage is commanded when the room’s temperature
rises above 24°C.
Simulation results and discussion
With regard to the traditional water flat plate collectors system, temperature gets to a minimum
average value of 23°C and doesn’t overtake 100°C, the storage tank temperature shows, as expected, a lower range of values going from about 47°C to 79°C. In the figure 4.2 we can notice a general
increasing working fluid’s temperature by using nanofluid as working fluid.

Figure 4.1 Traditional water solar collectors temperatures (T_Coll) and hot storage tank temperatures
(T_TANKout) – TRNSYS Graph

688

ZEMCH 2015 | International Conference | Bari - Lecce, Italy