The classical average method that was used at the beginning of the project of the full scaled PASSYS test cells (Vandaele, 1994) is based on steady state estimations; it has been applied as a first approach in this work. For this calculation the previously measured scaled cell data were used and the global properties of the overall heat loss coefficient, UA, and solar heat gain, gA, of the system were first calculated. Then these UA value and gA value were compared with the values calculated from the measurements of the solar irradiance, temperatures and electricity consumption for the small scale test cell, the classical average method was used to make a preliminary validation of the use of small scale test cell for the thermal evaluation of building components.

RESULTS

£ 0.0040 0.0035 0.0030 0.0025 0.0020

0.0015

21:50 pm

Figure 4. Measured solar radiation and instantaneous electricity consumption for the small scale test cells with three types of glazing.

Table 3 presents the overall heat loss coefficient, UA, and the solar heat gain, gA, of the small scale test cells for the clear glass, filter glass and reflective glass for concrete slab roof calculated from the measured results.

Figure 5 presents the measurements of the net heat loss divided by the temperature difference as a function of the incident solar radiation divided by the temperature difference using the classical averaging method. Linear regression technique was used, the intercept of the curve with the y-axis is the overall heat loss coefficient, UA, and the slope is the solar heat gain, gA. The least square equation is shown on the same figure.

Table 4 presents the comparison of UA and gA for the classical averaging method with the ones calculated from the measured results of Table 3.

The results of Table 4 show that the smaller percentage difference was 2.6% for UA for the filter glass and 2.8% for UA for the reflective glass, followed by 14.9% for gA for the clear glass and 16.9% for UA of the filter glass. The higher differences were 24.0% for UA of the clear glass and 72.2% for gA for the reflective glass. These results indicate that the classical averaging method had disadvantages; it does not give information on the dynamics of the system because it was based on steady state equations (Vandaele and Wouters, 1994). Thus, in order to have a more confidence results, it is necessary to compare the measurements with a dynamic method, which could give information about
the effect of the short term weather variations on the system properties. However, to compare the measurements by using dynamic methods, such as identification parameter method, it is necessary to increase the number of measurements from hours to days.

SUMMARY AND CONCLUSIONS

This paper presented a preliminary study to validate scaled solar test cells for solar thermal evaluation of building components. The scaled solar test cells were described and their measurements were presented. The comparison between the thermal performances of the scaled solar test cells with the real scale test cells Passys was carried out by the classical averaging method that was initially applied to the Passys cells to determine the UA and gA. The results indicated that such comparison should be taken as preliminary validation results due to the fact that some percentage differences were high for some tests. Thus, we concluded that, it is necessary to continue the validation tests increasing the period of the measurements and by using dynamic methods such as LORD 2.2