Determination of the Degree of Mixing
Before the start of test, mix the water in the storage tank by using a small pump to circulate the water from the top to the bottom of the store. The water in the store is assumed to be at a uniform temperature when the temperature of the water at the outlet of the store varies by less than 1 K for a period of 15 min. Draw off water from the store at a constant flow rate of 600 lit/hr. The cold water
entering the store shall be at a constant temperature of less than 30 °С, shall not fluctuate by more than
±0.25 K and shall not drift by more than ±0.2 K during the draw-off period. Measure the temperature
at least every 15 s and record an average value at least every time a tenth of the tank volume is drawn off. Fig. 8 shows that a mixing draw-off temperature and water flow rate trend and relationship change with draw-off time.
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Fig.8 Mixing raw-off temperature and flow rate graph 4.3. Determination of storage tank heat losses Before the start of the test, mix the preconditioned water in the store by using a pump to circulate the water from the top to the bottom of the store. The water in the store is assumed to be at a uniform temperature when the temperature of the water at the outlet of the store varies by less than 1 K for a |
period of 15 min. The average temperature over these 15 min is to be taken as the initial temperature of the tank. After cooling the tank for a period of between 12 h and 24 h, the water should be recirculated in the storage tank so that it reaches a uniform temperature. The temperature is assumed to be uniform when the temperature at the outlet of the tank varies by less than 1 K for a period of 15 min. The average temperature during this 15 min period shall be taken as the final temperature of the tank.
In this paper, automatic control system for domestic water heating test system has been studied and developed. Test procedure according to ISO 9459-2 is a series of complicated work and the whole process is a high cost test for water heating system. By the use of Labview a set of automatic control system can operate the test system, collect and record the corresponding data, and manipulate all sorts of equipments. In this case, it is easier and lower cost than has ever been before.
[1] ISO9459-1(1993). Solar heating—Domestic water heating systems--Part 1: Performance rating procedure using indoor test methods.
[2] ISO9459-2(1995). Solar heating—Domestic water heating systems--Part 2: Outdoor test methods performance characterization and yearly performance prediction of solar-only systems.
[3] ISO9459-3(1997). Solar heating—Domestic water heating systems--Part 3: Performance test for solar plus supplementary systems.
[4] ISO9459-4. Solar heating—Domestic water heating systems--Part 4: System performance characterization by means of components tests and computer simulation.
[5] ISO9459-5. Solar heating—Domestic water heating systems--Part 5: System performance characterization by means of whole system tests and computer simulation.
