An integrated model of a desiccant cooling system with a hybrid photovoltaic thermal collector-solar air heater (PVT-SAH) was developed and coupled with a building model to enable a performance evaluation and optimisation of the system. A double pass PVT-SAH system that incorporates heat pipes was used to increase the air temperature of the PVT-SAH outlet in order to regenerate the desiccant in a desiccant wheel. The integrated model was then used to quantify the performance of the hybrid desiccant cooling system in terms of Solar Fraction (SF) and the Coefficient of Performance (COP) and its response to the various sizes of PVT-SAH systems. The model outputs showed that the selection of the PVT-SAH design parameters can be critical in improving the system's utilisation in a desiccant cooling process. For a commercial building case study in a hot and humid climate, the annual Solar Fraction and the electrical COP of the cooling system reached up to 96.6% and up to 19.8 respectively, when the design of the PVT-SAH was optimised. The optimal electrical COP was higher than those for non-optimal designs that ranged from 0.6 to 15.1. The minimum size of the PVT-SAH that is required for the hybrid desiccant cooling system to exceed a typical COP for commercial buildings (2.6–3.0) was found to be 0.35 m2 per m2 of the conditioned floor area.