Journal · 2026.07 · 10 min

Improving Thermal Performance in Hot and Humid Climates

In Taiwan the greenhouse thermal problem is the opposite of temperate countries — the point is not to keep heat in, but to keep the sun’s heat out and vent the heat that does get in. Get the direction wrong and the house becomes a steamer. This piece covers covering, shading, ventilation, and evaporative cooling for hot, humid climates.

Temperate countries talk about “insulation” mostly to keep heating indoors in winter; but in a hot, subtropical climate like Taiwan the real enemy is summer heat and intense sunlight. Here, thermal performance means a whole strategy of blocking incoming heat, venting indoor heat fast, and managing humidity at the same time. Get the direction backwards — say, piling on thicker covering for insulation — and the house becomes an unworkable steamer in summer.

How to block heat, how to vent it, and how to hold humidity down — the answers live in the optical properties of the covering, the shade factor, the ventilation rate, and mechanical capacity. Below, the essentials are organised into three layers — block heat, exhaust heat, cool down — with references from U.S. extension centres and international research.

Most heat entering a greenhouse comes from solar radiation. The optical properties of the covering decide how much of it is carried straight inside. In hot climates, choosing a covering that reflects or blocks near-infrared (NIR) while keeping enough visible light is the first line of defence — letting in the light the crop needs while keeping excess heat out.

• Selective coverings: films and coatings that reflect or scatter near-infrared (NIR) cut heat load without markedly sacrificing photosynthesis.
• Diffusing coverings: diffusion films even out light, reduce local hot spots and leaf scorch, and lessen inter-plant shading.
• Exterior whitewash: spraying a reflective shading compound on the roof in summer is one of the lowest-cost ways to block heat, washed off when autumn cools.
• Use double glazing with care: double covering insulates well, but in Taiwan’s summer it hampers heat rejection and must be paired with openable ventilation and shading.

Shade screens block heat in the simplest way: they keep excess sun out. International research shows that in humid tropical and subtropical coastal regions, combining shade screens with pad-and-fan systems cuts a further 5–8°C beyond pad-fan alone — in trials near New Delhi, shaded houses ran markedly cooler than unshaded ones in May. A retractable curtain balances summer shading with light needs in other seasons.

After blocking some heat, the rest must be vented out. Natural ventilation (roof plus side vents) is the most energy-efficient first step; only when that is insufficient do you move to mechanical ventilation and evaporative cooling. UMass notes evaporative cooling can drop indoor temperature 10–20°F (about 6–11°C) below outdoor air in suitable conditions, but its efficiency depends on the wet-bulb depression — the more humid the air, the less room there is to cool.

“Evaporative cooling is most effective in dry climates, but it has limitations in our hot, humid climate.”

— University of Florida / IFAS Extension

This is exactly Taiwan’s core challenge: UF/IFAS states plainly that pad-and-fan evaporative cooling is limited in hot, humid climates, especially when night humidity is high. So in Taiwan you can’t rely on pads alone but must layer “shade first, then ventilate, then evaporative cooling,” while managing the rising humidity with dehumidification and air circulation to avoid disease. Design must also keep pad-to-fan distance reasonable (generally under 40 m), or the crop near the pad runs too cool while the crop near the fans runs too hot.

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