Testing evacuated tube solar collectors using NI LabVIEW and FieldPoint

By Paul McEntee, Kingspan Renewables UK

Thermomax Ltd. manufactures equipment for efficient and economical conversion of solar radiation into thermal energy. Its evacuated-tube, solar collectors produce clean energy for domestic and industrial hot water, space heating and cooling, and seawater desalination.

The company engineers needed new equipment to test their solar devices at their Bangor facility in Northern Ireland. They chose to develop these testers with the aid of LabVIEW and FieldPoint systems from National Instruments, Austin Tex. The simulators are used in two test facilities, one that handles outside tests under real conditions and another specifically for indoor simulator. The new test equipment has cut the time and cost of product development as well as ongoing production quality assurance.

The two PC-based automated test systems use hardware based on FieldPoint PAC and software. Components include NI FP-1601 network modules, relay, counter/timer, analog input, output, and thermocouple modules, and NI LabVIEW DSC and LabVIEW software.

Six FP-1601 network modules on the outside test rig control and acquire data from 212 channels. Due to the high channel count, they used the LabVIEW DSC Module to reduce the development time for the control and data acquisition system and store the data in an easily accessible database. They can test up to four collector systems at any one time and subject them to one of nine text sequences.

An additional FP-1601 network module on the solar simulator acquires and controls 34 channels. The two-axis motion system is used to develop an irradiance map of the simulator lamp array prior to each test. A LabView program performs all the control, data acquisition, and analysis, automating  the efficiency tests on the collectors to  BS EN 12975 standards for test methods of solar collectors.

The engineers had to overcome several challenges at each test facility. On the outside test rig, they had a large number of channels to deal with and data had to be recorded over months and years. In addition, if the energy from the collectors was not used, it could result in thermal issues. So they developed alarms and safety interlocks into the system. The LabView DSC Module made the design and implementation of the control system relatively straightforward. They used the tag configuration editor to interface with the FieldPoint channels through Ethernet, which considerably reduced the amount of code writing. Through the tag configuration editor, they were also able to set up channel scaling, deadbanding, and alarms.

The Measurement and Automation Explore (MAX) software also proved to be useful. During commissioning, they used MAX for low-level control of the FieldPoint hardware without having to write code. When in operation, MAX delivers a simple way to view and export data from the citadel database using the historical viewer.

On the solar simulator, they had fewer channels, but the test requirement of BS EN 12975 demanded precise control of the temperature and mass flow rate of the system fluid. To achieve this control, they installed two Honeywell control valves, one to control the coolant flow to a heat exchanger for temperature control and the second to control the mass flow through the collector under test. They used the advanced PID VIs in LabView to generate the control signals to the valves through a FP-AO-V10 two-channel analog output module.

The next challenge was to develop a two-dimensional mapping system to precisely measure the incident irradiance on the collectors prior to each test. Initially, they attempted to acquire the map manually, but this required two operators and a lot of time. Therefore, they decided to install a two-axis motion system to move the pyranometer and record the irradiance. They used PCI-7342 motion controller and a UMI-7772 motion interface to control two step drives and motors. The system moved a Kipp and Zonen CM11 pyranometer, which is connected to an analog input channel on the FieldPoint bank and records data for the 200 point map.

The NI hardware and LabView software let the engineers develop an integrated system that could be constructed quickly and easily. The two test facilities are in use daily. Because the development time for new products had been considerably reduced, the engineers no longer need to send prototypes to European test institutes, which has reduced development costs.

National Instruments
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