As an example of the results that can be obtained from the simplified model, a real ther­mosyphon system has been modelled exposed to real weather data during 24 hours without draw-off. The system consists of 2 collectors of about 2 m2 of absorber area connected to a horizontal cylindrical tank of about 300 l of capacity (diameter=0.42 m and length=2.08 m).

Some of the information that can be obtained from this kind of simulations is shown in figure 1. The figure shows the time evolution of the ambient temperature, Ta the average temperature of the water in the tank, TOT, and of the integrated terms of the global energy balance during the test: total solar irradiance over collector plane, СЙ, reflected solar irradi — ance, Gtref, accumulated energy at the store £M, and heat losses at the collector, at the

pipes and at the tank, which respectively axeQc, Qp and Q,.

Figure 1: Numerical results with the simplified model. Modelling of a real thermosyphon system during 24 hours of exposure to outdoor conditions and without draw off. a) Evolution of the ambient temperature, , and of the average temperature of the water at the store,

, during the testing period. b) Evolution of the terms of the global energy balance during the testing period: solar irradiance over collector plane, , reflected solar irradiance, , accumulated energy at the store, Eas, heat losses at the store, Qs, at the pipes and at the collector, . The values of the terms of the energy balance are integrated in time from

the initial of the test, and are given in % with respect to the total incident daily radiation.