15.07.2015   EuroSun2008-3

Thermal performance

Using linear adjustments, the hybrid optical efficiency p0(-) and the thermal losses coefficient U(W/m2°C) were calculated. The thermal losses coefficient is the slope of the thermal efficiency estimated linear behaviour while the optical efficiency is the interception of that line with the yy axis (Fig. 3 and Table 1). The optical efficiency represents the thermal efficiency when there are no thermal losses since the ambient temperature is the same as the average temperature in the thermal receiver.

Подпись: ♦ Thermal efficiency per active glazed area ■ Thermal efficiency per total glazed area Fig. 3. Assumed linear thermal behaviour based on thermal efficiency measurements calculated per active glazed area and total glazed area. The efficiency was estimated based on measurements for global irradiation values higher than 900W/m2. (A^ thermal=3.7m2 Atotal=4.6m2)

Thermal Efficiency G>900W/m2

Thermal parameters

Per active glazed area

(Aactive thermal=3.7m )

Per total glazed area (Atotal=4.6m2)

По(-)

0.64

0.52

U(W/m2°C)

3.1

2.5

Table 1. Measured optical efficiency no(-) and thermal losses coefficient U(W/m2°C).