Testing and computer simulation

• ISO 9459-4 is a procedure for characterizing annual system performance and uses measured component characteristics in the computer simulation program TRNSYS (described in Chapter 11, Section 11.5.1). The procedures for characterizing the performance of system components other than collectors are also presented in this part of ISO 9459. Procedures specified in ISO 9806-1 (see Chapter 4) are used to determine collector performance, whereas other tests are specified for characterizing the storage tank, heat exchangers (if used), and control system.

• ISO 9459-5 presents a procedure for the dynamic testing of complete systems to determine system parameters for use in a computer model. This model may be used with hourly values of local solar irradiation, ambient air temperature, and cold-water temperature data to predict annual system performance.

• ISO 9459-5 specifies a method for outdoor laboratory testing of solar domestic hot water systems. The method may also be applied for in-situ tests and indoor tests by specifying appropriate draw-off profiles and irradiance profiles for indoor measurements. The system performance is characterized by means of whole-system tests using a "black box" approach, i.e., no measurements on the system components or inside the system are necessary. Detailed instructions are given on the measurement procedure, processing and analysis of the measurement data, and presentation of the test report.

• The results of tests performed in accordance with ISO 9459-4 or ISO 9459-5 are directly comparable. These procedures permit performance predictions for a range of system loads and operating conditions. The disadvantage of these procedures is that a detailed computer simulation model of the system is required.

The procedures defined in ISO 9459-2, ISO 9459-3, ISO 9459-4, and ISO 9459-5 for predicting yearly performance allow the output of a system to be determined for a range of climatic conditions, whereas the results of tests performed in accordance with ISO 9459-1 provide a rating for a standard day.

Perhaps the most used is standard ISO 9459-2 (Part 2). This is because it requires the least investment in equipment and operator skills. In this standard, the system is pre-conditioned at the start of each test day and charged to the required temperature, Tc, then it is left to operate with no loads applied and the only measurements required are those of solar radiation and ambient temperature. Energy monitoring is required at the end of the day, during the single draw-off, and this can be achieved with either a simple manual temperature and volume measurements or a data acquisition system. The daily energy gain is determined for a range of clear and cloudy days with irradiation between 8 and 25 MJ/m2-d, with approximate the same (Ta-Tc) value for each day. The correlation parameter (Ta-Tc) is varied, however, by testing for a range of initial tank temperatures, Tc, for each day. The useful delivered energy at the end of the day, Qu, is correlated to the test results by

where a1, a2, and a3 = correlation coefficients.

The effects of thermal stratification and mixing in the storage tank are evaluated by a load calculation procedure using the temperature profiles measured during draw-off at the end of the day.

The long-term performance of the system is determined by a calculation procedure that accounts for the climatic conditions, energy carryover from day to day, and the load volume. Additionally, a 1 h time step procedure is specified for the determination of the nighttime heat loss and the energy carryover from day to day.

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