Dynamics and control of solution levels in a high temperature generator for an absorption chiller

It is desired to keep the level of a high temperature generator (HTG) solution constant for the purpose of linear controllability and solution economy. Level switches are used to control the solution level. The control of the solution level requires a good flow rate prediction model. It is found that the model can be approximated as a function of HTG solution temperature and coolant inlet temperature. This study identified two aspects of the control strategy for a solution pump inverter that are practiced in the industry. (1) A cut-off frequency of 27 Hz is set up to supply more solution than expected at low HTG temperatures against any possible depletion of solution and (2) at high HTG temperatures, the sensitivity of the inverter frequency to the cooling water inlet temperature is set to a minimum to reduce solution level fluctuations. This study suggests an improved control algorithm that is proven to have high control performance.

► Solution level should be constant for controllability and solution economy.
► Level switches are used to control the solution level.
► The level control requires a good flow rate prediction model.
► Control strategy of a solution pump inverter practiced in the industry was identified.
► Control algorithm based on 4 level switches shows improved control performance.