The study carried out by John Maulbetsch for the DOE at Caithness touched this subject while searching for parameters.
If memory serves, there was not clear cut parameter or set of parameters that could be used to measure ACC performance as the ACC performance is dependant on a number of variables varying from anything from for for example, surface pollution of the bundles, temperatures, wind, air leakage between cells and from cells to the environment, excessive cooling cooling the condensate too much deceasing the HRSG efficiency etc…
As John put significant effort into this I would advise reaching out to him for advice.
My impression is that there is too much happening in the ACC to have a magic gauge showing efficiency per se, but a balanced verdict must be made based on several parameters
