LabVIEW based measurements and control system of a micro-ORC installation with Scroll Expander

City University of Applied Sciences Bremen, JRM Institute of Energy Engineering, Neustadtswall 30, Bremen, 28199, Germany

^* Corresponding author: Albrecht.Eicke@hs-bremen.de

Abstract

An innovative ORC-installation with a scroll engine as expansion device has been developed and designed at the City University of Applied Sciences in Bremen. This new transportable installation has the specific capability to be connected to an alternative power source, such as solar power. Pentafluoropropane (R245fa) has been selected as the working fluid because it is suitable for the required temperature ranges and exhibits some additional advantages related to this specific application. The details of the ORC-Cycle have been presented in another paper and are not the main topic of the presented work. The core matter of this paper is the measurement and control system of the installation, which enables the thermodynamic evaluation of the obtained experimental data, some back coupling, and control tasks. The data acquisition and matching procedure, connected with the operational measurement system, identifies the aggregate and operational states of working fluid in characteristic points of the thermodynamic cycle. The algorithm for searching for the points from the table of parameters take so much time, that the control loop cannot work correctly in time. This problem was solved with the producer-consumer architecture in LabVIEW. Data acquisition and quick response in the control loops are done in the producer-while loop. To reduce the number of values, data are written only every five seconds in a queue. From this queue the consumer-while loop reads values, if the computer has enough capacity. This technique ensures that no data are lost. The matching procedure searches in the parameter file for the thermal properties and displays the cycle in a T-s diagram. Some simple calculation procedures make it possible to evaluate the thermal efficiency and other cycle parameters while operating. At the end of this sequence, the data are saved in a file. In the next step, the producer-loop is executed directly in a Field Programmable Gate Array, so that the control can be executed stand-alone and the computer is only used for visualization.