Control Strategy Based on Artificial Intelligence for a Double-Stage Absorption Heat Transformer

Thermal energy recovery systems have different candidates to mitigate CO2 emissions as recommended by the UN in its list of SDGs. One of these promising systems is thermal absorption transformers, which generally use lithium-water bromide as the working fluid. A Double Stage Heat Transformer (DSHT) is a thermal machine that allows the recovery of thermal energy at a higher temperature than it is supplied through the effect of steam absorption in a concentrated solution of lithium bromide. There are very precise thermodynamic models which allow us to calculate all the possible operating conditions of the DSHT. To perform the control of these systems, the use of Artificial Intelligence (AI) is proposed with two computational techniques-Fuzzy Logic (FL) and Artificial Neural Network (ANN)-to calculate in real-time the set of variables that maximize the product's Gross Temperature Lift (GTL) and Coefficient of Performance (COP) in a DSHT. The values for Coefficient of Determination (R-2), Mean Square Error Root (MRSE), and Mean Error Bias (MBE) for the two types of computational techniques were analyzed and compared with the purpose of identifying which of them may be more accurate to calculate the operating conditions (temperatures, pressures, concentration and flows) with the highest COP for an interval of the value of the temperature absorption entered by the user. The result of the analysis of the evaluated techniques concluded that the control strategy of a DSHT in real-time will be based on the precise calculation of the refrigerant flow in the second evaporator with a Neural Network of 30 neurons, 300 weights and 40 bias, as it is more accurate than the Fuzzy Logic technique. The goodness-of-fit for two computational techniques was evaluated as having an R-2 higher than 0.98 for the provided data. Future AI controllers must be based on evaporator flow values with evaporator power at 3.9(-04) kg/KJ.

Automated summary

Thermal energy recovery systems, including thermal absorption transformers, have the potential to mitigate CO2 emissions. These systems use lithium-water bromide as the working fluid. The Double Stage Heat Transformer (DSHT) is a thermal machine that recovers thermal energy at a higher temperature through the absorption of steam in a concentrated lithium bromide solution. Precise thermodynamic models are used to calculate the operating conditions of the DSHT.