On the Suitability of Test Method of GB/T 18708 for Water-in-Glass Evacuated Tube Solar Water Heaters

Abstract

The thermal performance of water-in-glass evacuated tube solar water heaters is evaluated based on the daily radiation on the collector surface instead of the daily radiation actually received by a solar tube array, as described by test method of GB/T 18708 (eqv. ISO 9459-2). However, the daily radiation actually received by a solar tube array is quite different from that on the collector surface and strongly dependent on its structural and installing parameters. To assess the suitablity of the said test standard, a sensitivity analysis on the ratio of daily beam radiation actually received by a south-north oriented solar tube array to that by the collector surface, R b,t-s , was performed based on the radiation predicted under clear sky condition. Results show that R b,t-s , is strongly dependent on the distance between two adjacent tubes, implying that the testing result of thermal performance based on the test standard of GB/T 18708 is not of comparability for water-in-glass evacuated tube solar water heaters with different tube distance, and a further modification is necessary to essure test results comparable. Results also indicate that R b,t-s is less sensitive on the tilt and azimuth angles of the collector for the case of o 10 ≤ − λ β and o 20 ≤ φ .

The relationship between iodine nutrition and thyroid disease in lactating women with different iodine intakes

“…The I content in table salt from households of lactating participants was determined using the general test method of the salt industry ( 12 ) . Each participant provided a table salt sample of at least 50 g. The standard salt I content in Guangxi province and Shanxi province is 25 mg/kg.…”

Performance of Horizontal Water-in-Glass Evacuated Tube Solar Collectors

“…As described in the ISO 9459-2 standard 5 , the collector heat output is correlated to the total incident radiation, H, and the difference between the ambient temperature, T amb , and collector inlet temperature, T in , using the following relation: Q = a 1 H + a 2 (T amb − T in ) + a 3 (1)…”

“…Performance testing of water-in-glass evacuated tube collectors is covered by Chinese standard GB/T 18708, a test of total daily heat output, similar to ISO 9459-2 [3][4][5] . Although the H-type collector type is a pump-though collector, obtaining steady-state thermal performance, such as defined in ISO 9806, is complicated by the large internal volume.…”