18 May 2017
The operational behavior of thermally driven heat pumps is characterized by flow and temperature measurements at the main heat exchangers. Non-intrusive ultrasonic clamp-on flow measurements and clamp-on temperature measurement are often the only option in field-installations with respect to process interruption or cost. However, the accuracy of these non-intrusive methods is sensitive to flow profile and piping geometry rendering them usually less accurate than intrusive methods.
A physical model is applied to allocate the effective measurement uncertainty according to the influences of temperature, flow velocity, piping geometry, fluid properties, and flow profile. The sensitivities of the important parameters and their impact on the deduced uncertainties in nominal and part-load operation are analyzed. As an example, data of an absorption heat pump designed at Technische Universität Berlin are analysed.
Results show that the relative uncertainty of heat flow measurement is highest in part load operation and has a large impact on the uncertainty of seasonal performance indicators. Acceptable uncertainties can be achieved by applying an expert system that optimizes the measurement configuration and corrects the influence of flow disturbances with a physical modelling approach.