Diagnostic method of solar thermal system based on the short time on-line measurements

•New short-time on-line diagnostics method of a solar heating system.•Short time on-line measurements for determination of static and dynamic properties.•Analysis of static and dynamic properties at different volumetric flow rates.•Impact analysis of flow rate on characteristic parameters of collector. This paper presents the method of a solar heating system diagnostics allowing determination of the following coefficients in operating conditions: heat loss coefficient ULK, collector efficiency factor F’ and heat removal factor FR related to the collector static properties, effective heat capacity (mc)e and time-constant Tz related to the collector dynamic properties. The proposed method is based on a comparison of two models: analytical and numerical. The analytical model was developed based on the collector energy balance and that combining characteristic parameters. The numerical model was developed based on the recorded operating data of the medium inlet and outlet temperature, and solar irradiance. The condition necessary to apply this method covers constant volume flow rate of the medium in the system during the experiment.