Design Blueprint: Night-Radiative Atmospheric Water Harvesting Unit (20 L per Night) — Build Specification Derived from the Psychrometric Bound on Atmospheric Water Harvesting

DESIGN BLUEPRINT — SIMULATED, NOT MEASURED — NOT BUILT. Build specification for the night-only, radiatively assisted condensation unit sized in Section 4.3 of the source paper, 'A Psychrometric Bound on Atmospheric Water Harvesting' (source paper: https://doi.org/10.5281/zenodo.24108587). The unit is a household atmospheric water harvester for humid coastal deserts, sized at its design point of 25 °C and 80% relative humidity (dew point 21.31 °C, cold surface 16.31 °C): it removes 4.54 g of water per cubic metre, processes 220.4 m³ of air per litre and 4,408 m³ per night for a target of 20.0 L per night, with a cooling load of 26.40 kWh of heat per night. A 20.0 m² radiator panel at a net 75 W/m² delivers 15.0 kWh over a 10-hour night (56.8% of the load); assisted electricity is 1.37 kWh per night, 0.0684 kWh per litre. The blueprint gives dimensions and layout (including a derived mean air flow of 440.8 m³/h and a minimum useful storage volume of 20.0 L), a bill of materials in generic specification classes, an assembly sequence, tolerances tied to the source figures, failure modes, and a maintenance schedule. Its operating envelope is a design feature: a controller inhibits operation below the assisted crossover humidity — 67.2% relative humidity at 25 °C against desalinated water delivered 500 km — with the crossover table given by temperature. All quantities are taken from the source paper or derived from its stated inputs in the deposited compute.py; nothing is measured and nothing has been built.