<p>Greenhouse dryer (GHD) offers a promising and sustainable alternative to traditional drying methods for agricultural products. However, achieving true sustainability requires an environmentally and economically feasible drying solution. This study investigates the design, operation, economic advantages, and environmental benefits of drying bay leaves (<i>Laurus nobilis</i>) and neem leaves (<i>Azadirachta indica</i>) inside a single-slope greenhouse dryer operating in a humid subtropical climate. Results showed that both the crops dried significantly faster in the GHD (5.5–6.5 h) compared to open sun drying (OSD) (7.5–8 h). The GHD drying efficiency ranged from 22.44 to 25.75%. Energy efficiency varied within the GHD itself. The upper portion achieved 43.4% to 92.2% efficiency, while the lower portion ranged from 25.3 to 78.01%. Similarly, the energy utilization ratio varied significantly, from 8 to 83.2%. Environmental and economic parameters were also evaluated. The total embodied energy of the GHD was calculated to be 215.253 kWh. The payback period was 0.91 years, and the energy payback time was even faster at 0.37 years. Over a 15-year lifespan, the GHD is estimated to mitigate 17.10 tons of carbon dioxide (CO₂) emissions, with an initial CO₂ emission of 14.06 kg associated with its production. Finally, the quality of the dried bay leaves and neem leaves was also assessed, showing that the leaves inside the GHD were of superior quality than those dried using OSD.</p>