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.