The problem of tuning single-loop controllers in heating, ventilating and air conditioning (HVAC) systems is explored. The HVAC process was described by a first-order-plus-dead-time (FOPDT) model. By using recursive least squares method, the model parameters were updated while the system remained in closed-loop. The Hinfinity loop-shaping tuning rules published in the literature were transformed to discrete-time tuning rules and were implemented in an adaptive PI control strategy. The methodology was applied to a discharge air temperature (DAT) control system. The output responses of adaptive PI controller were compared with a LQR optimal adaptive controller. Simulation results show that the adaptively tuned PI controller is able to track setpoint changes very well in the presence of changes in plant parameters, disturbances and external noise acting on the system. Copyright (C) 2004 John Wiley Sons, Ltd.