Reevaluating the energy performance after considering thermal pollution treatment in humidification-dehumidification desalination

The humidification-dehumidification (HDH) desalination cycle is often celebrated for its potential sustainability. However, thermal pollution from the discharge of hot brine has been largely overlooked when assessing its energy consumption, which is a critical environmental drawback. This study reevaluates the energy performance of HDH desalination by accounting for the substantial energy penalty required to mitigate this thermal pollution. Specifically, three system configurations are proposed and thermodynamically analyzed: a baseline system with an add-on cooler (System 1), a system with internal waste heat recovery (System 2), and an integrated system using a heat pump for simultaneous cooling and heating (System 3). The results demonstrate that in a conventional system operating at 65 °C, the cooling load can reach up to 60 % of the original heat input. System 2 effectively reduces the cooling load by over 60 % and the total SEC by ∼30 % through waste heat recovery, with an internal heat exchanger effectiveness of 0.875 identified as a reasonable trade-off. System 3 offers an elegant, all-electric solution with a low electrical SEC of ∼150 kWh/m³, albeit at a more moderate operating temperature. This work shows that thermal pollution mitigation is not a peripheral concern but a central factor in HDH design, drastically altering energy performance metrics and determining the technology's environmental sustainability.