Model-based control of absorption heat pumping systems

×

Figure 1: Testbench setup for both AHPS (H2O/LiBr and NH3/H2O machine) © Institute of Thermal Engineering, University of Technology Graz

Figure 2: Comparison of the results of the controller design model with measurement data for stepwise changes of the hot water inlet temperature (H2O/LiBr machine)

Figure 3: Schematic representation of the intended model-based control strategy for AHPS

❮ ❯

Absorption heat pumping systems (AHPS, comprising heat pumps and chillers) use thermal instead of mechanical energy as driving power and are therefore considered a promising way to increase the share of renewable energies in the heating and cooling sector. Historically, AHPS have typically been operated at rather constant, steady state operating conditions - in the course of growing environmental awareness, however, AHPS now start to become attractive also for other applications, where operating conditions can be significantly more dynamic.

The currently used control strategies are often not able to meet the requirements for these dynamic operating conditions. Therefore, this project aims at improving the control of AHPS. It should be capable to explicitly consider and compensate the coupled and partly non-linear correlations between the different process variables, as well as fluctuations of external disturbances like varying inlet temperatures. This shall be achieved by developing a model-based control strategy for AHPS.

The project is currently in the third and final project year. Over the first two project years, a test stand with extensive measurement and actuator technology for two AHPS (one H2O/LiBr and one NH3/H2O machine) was planned and built, and numerous tests were carried out to investigate their static and dynamic behavior. Then, two types of models were developed to describe their dynamic behavior, where each of them serves different purposes: The first model type (simulation model) describes the plant behavior in great detail and has the purpose of serving as a virtual test bench. This allows, for example, the investigation of partial load behavior and operating point changes, and the testing of new control strategies to be carried out cost-efficiently, quickly and reliably in the simulation. The second type of model (controller design model) describes the most important elements of the plant behavior by means of mathematical relationships that are as simple as possible and has the purpose of being used directly when designing the model-based control strategy to explicitly consider the plant behavior.

In the third project year, the model-based control strategy for AWPA is designed through iterative development and validation in simulation and at the real test bench. In the end, the new model-based control strategy is expected to increase the reliability and efficiency of AHPS, improve their dynamic behavior and thus enable their use also for applications with highly dynamic operating conditions.

Projektvolumen

Start of project

Supported by

Projektpartner

Publications