Input-Output Controller (IOC)
The Input-Output Controller is a simulation based failure detection method available on the market since 2007. The first variant of the method monitors only the energy yields in the solar circuit. Furthermore, two temperature values in the storage are used as input for the simulation. A second approach also includes the buffer storage discharging. The IOC compares the daily measured and expected energy yields in the solar loop. The standard uncertainty (o) of the IOC-procedure, including measurements and yield calculation, is about 7 % (o). If the difference between measured and simulated yield is larger than 20 % (3 o) a fault is detected. This leads to a 99 % reliability for a correct fault prediction. Below a yield of 1.5 kWh/m2d the uncertainty margins are higher. There is a failure tree to establish if the fault occurred inside or outside the solar loop, and if it is for example the control or the solar station which causes the problems. The IOC is sold for 1190 € inclusive temperature and irradiance sensors, but without volume flow measurements. To be able to check the performance from home an extra data logger is necessary [9; 10].
3.3. Kassel University method (KU)
At Kassel University a failure detection method was developed, that combines a static algorithm based function control with dynamic simulation based failure detection [11]. The method consists of three steps. In the first step it is checked if too much data is missing due to data gaps and sensor defects. A minimum of 95 % of data points should be available to continue with the failure detection. In a second step a plausibility check is carried out, in which the correct operating of individual components is checked, similar to the approach used in [3]. The third step is a simulation based step in which the system is modelled with TRNSYS. Measured and simulated energy gains are compared at the heat exchanger for charging and or discharging the storage unit. If the difference is larger than the uncertainty margins on both sides an error is reported [12; 11].
Several failures were detected and partially identified. These were for example air in the collector field and a calcified heat exchanger. This approach is being further developed.
3.4. Guaranteed Solar Results (GRS)
In Guaranteed Result of Solar Thermal Systems the energy yield is guaranteed by the seller/builder of the system. Sophisticated measurement equipment is installed and monitors the system, costs for the measurement equipment and one year of operation are in the range of 10 k€. Daily averaged and monthly measured values are sent. Measured yearly energy yields are compared to simulations with f - chart, a simple simulation program, although also other simulation programs could be used. A comparison on a shorter basis is not possible, due to limitation of the simulation program. Large failures on a yearly basis can be detected; however failure analysis is not possible [13; 14].
