Experimental Investigation of Air Cooling and Humidification by a Wetted Porous-Clay-Duct Earth–Air Heat Exchanger in a Hot-Arid Greenhouse

A wetted porous-clay-duct earth–air heat exchanger (EAHE) supplied with outdoor air was tested in a 360 m2 experimental greenhouse in Al-Kharj, Saudi Arabia, during 22 July–11 August 2026. Over 21 days of continuous operation, the discharge air averaged 29.20 °C (range 24.3–36.0 °C; 96.2% of 30,117 one-minute records at or below 34 °C) with no upward drift, while the greenhouse centre averaged 40.53 °C and peaked at 64.6 °C. A partially shaded, unaspirated logger beside the supply fan read on average 10.57 K above the discharge, rising to 19.12 K above discharge during the daytime; comparison with airport records indicates that it may over-read by up to about 10 K at the daily peak. The discharge air carried about 4.4 g/kg more water than the intake-side air, day and night. Across scenarios combining 0–10 K intake bias with centreline-to-mean velocity ratios of 1.0–1.4, the daytime gross sensible rate was 5.38–15.79 kW and the moist-air enthalpy-decrease rate −1.52 to +6.84 kW, the upper values corresponding to no bias and a uniform velocity profile. At night, the discharge air gained enthalpy. Soil temperature and clay moisture were not measured, so the contribution of wetting cannot be isolated.