A HDD system based on psychrometric energy process desalination (PEPD) is constructed and tested. A purposely designed medium temperature solar collector will be used to heat up and spray seawater to humidify an incoming air in the humidification chamber. The humidified air enters the dehumidification chamber and is cooled by the incoming seawater, in the meantime the seawater is pre-heated to recover heat. The moisture is condensed out and the pure water is accumulated at the base of the chamber, and the dehumidified air is discharged to the outside or re-circulated. Several tests on the solar collector and desalination unit were carried out and an economic estimation of cost and carbon savings are also given.