Performance evaluation of a novel compact humidification-dehumidification desalination system coupled with a heat pump for design and off-design conditions

•A novel heat pump coupled humidification-dehumidification system was proposed.•Heat pump evaporator was used as the air dehumidifier.•Sizes of the heat exchangers were obtained for fixed operational conditions.•System performance was balanced for fixed-size components at off-design conditions.•Characteristics method was utilized to study the system at off-design conditions. In this study, the theoretical investigation of a novel heat pump assisted humidification-dehumidification desalination system has been carried out. The conventional dehumidifier of the humidification-dehumidification system was removed and the evaporator of the heat pump was utilized for direct dehumidification of air. Besides, the heat pump condenser was used as the saline water heater of the humidification-dehumidification cycle. First, the sizes of the components were calculated at design conditions for fixed input operational conditions namely the ambient air temperature, relative humidity, and inlet saline water temperature. However, the input operating conditions vary at off-design conditions resulting in changes in heat pump performance. Since the performance of a heat pump is a function of its refrigerant saturation temperatures, to examine the performance of the designed system at off-design conditions, the system performance balancing was carried out through the method of characteristics for a given set of fixed-size components. It was observed that the gained output ratio and hourly yield of the proposed system reach 2.476 and 0.91 kg/h, respectively. The economic analysis indicated that the cost per liter of the proposed system is 0.014 $/L.