Tests of solar collectors are performed according to several international standards. Table 1 presents the procedures and standards currently in use. The collectors are divided in two categories related to their application: sanitary or swimming pool. The tests are also divided in two groups. The first group deals with minimum durability tests and the second with thermal behavior. The thermal efficiency test is performed after all group 1 tests have been finished.

Thermal efficiency tests are performed using an open-loop test configuration, according to ASHRAE 93-1986 specifications, with a constant head tank to maintain constant pressure through out the test. Figure 1 illustrates the collector testing facility, with one collector undergoing thermal efficiency tests, while two other collectors are subjected to the non­operational exposure test.

Once the tests are performed, the data is processed to generate the information for the label. The label for the collectors is similar to other labels used for appliances in Europe and Brazil. Figure 2 shows the version that has been in use since 2004. At the top, the label presents basic information including manufacturer, brand, model, maximum working pressure and application (sanitary or swimming pool). Then there is a classification in 7 different categories, from A to G. Below the graphic classification, the label presents the specific average monthly energy production (kWh/month. m2) and the average monthly energy production (kWh/month). Finally, the label sets out the gross collector area (m2) and the collector’s efficiency (%).

The efficiency is calculated using a standard linear efficiency equation derived from the test data and assuming the following operating point:

T — T

— a = 0,02 (1)

Gt

There was no attempt to create a number that would be closely related to the actual average energy production in different regions of the country, since the high diversity of climates makes it impossible to establish one single number that would be representative. A single number for the whole country was used in an attempt to keep the information presented to the consumer as simple as possible, while still providing a tool that would allow straightforward comparisons between different collectors. The use of a single number representing energy performance is used also for other products tested under the labeling program, e. g., refrigerators and air-conditioning units. These products are tested under a certain set of conditions, and their estimated energy consumption is stated for such conditions. Their actual energy consumption will vary depending on the operating conditions, as will the production of a solar collector.

There have been several efforts to educate consumers about the information on the label, and to make clear that average energy production values should not be used to size SWH systems.