Testing of controllers for thermal solar systems

One standardised way to determine the performance of thermal solar systems is based on component testing and system simulation. The approach is to test the solar collector, the store, the controller and other selected components separately and to carry out system simulations using the determined parameters. Due to increasingly complex control strategies, particularly implemented within so-called multi-function controllers for solar combisystems, the available test method for controllers – for the time being defined in ENV 12977-2, Annex B – has to be extended. In order to substitute temperature sensors by variable resistors and to document the response of a tested controller, a computer based test facility featuring an input/output-emulator between the controller and a PC has been developed. The emulator generates varying resistance values as input signals for the controller and records the status of the different outputs as its response. Both, manual adjustment and programmed temperature profiles provided by the PC are possible. All transmitted inputs as well as the response of the controller are stored in a data file. Experience gained from testing controllers used in thermal solar systems for combined hot water preparation and space heating, commonly called combisystems shows that alleged advanced control algorithms or fancy features do not inevitably result in an improvement of system performance or increased reliability. The extended test method and the set-up of the test facility described in this paper enable detailed investigations of nearly all kinds of controllers. Particularly with respect to multi-function controller testing, the introduced test method will be one basis for the upcoming standard prCEN/TS 12977-5, replacing ENV 12977-2, Annex B.