A wet surface three-fluid type heat exchanger for energy recovery in air-conditioning plants

The cooling performance of a recovery equipment for energy saving in air-conditioning processes is analyzed. The thermal behaviour of the system proposed, essentially consisting of a counterflow, three-fluid type, wet surface heat exchanger, where outside air is cooled simultaneously by humidified exhaust air and dehumidified supply air to be heated before its introduction into the ambient, is studied through a specifically developed finite-difference numerical model. Simulations are executed for different outdoor air and supply air psychrometric states relevant to typical summer climatic conditions, as well as for several values of the air-passage width, mean air velocity and heat exchanger length, whose influence on the cooling performance of the system discussed is pointed out. The numerical results obtained are expressed in terms of correlations among dimensionless parameters. Comparisons with the recovery efficiency of a three-fluid type, dry surface heat exchanger, as well as more traditional air-to-air recuperators for energy transfer between outdoor and exhaust airstreams, with both wet and dry heat transfer surfaces, are also reported.