This paper describes experiments studying the cooling of a greenhouse with a fan–pad system in Shanghai in a humid subtropical climate. Five working modes of cooling consisting of the combination of evaporative cooling with other methods (internal
thermal screens, external shading nets and circulation fans) were investigated. The results indicate that, with proper modes, the performance of the cooling system is acceptable, even under conditions of high temperature and high solar intensities. The main conclusions of the study are listed below:
1. Under high RH condition such as in Shanghai, air can be cooled to approximately 27–29 C after air flows through and is humidified by the evaporative cooling pads.
2. The indoor temperature and humidity of the greenhouse responds rapidly to the changing operation modes.
3. Solar irradiation is the key factor that influences the indoor temperature of the greenhouse. Shading is an effective way to partially isolate unwanted incoming solar energy so that the heat load inside the enclosed space can be reduced and the uniformity of the air temperature can be achieved. According to the experimental results, the internal air can be kept 2–3 C below the ambient temperature at a relative humidity of 80% using both evaporative cooling pad and shadings.
4. Circulation fans do not significantly improve the temperature in comparison to shadings when evaporative cooling pads are used.
5. When the evaporative cooling system is turned on, the greenhouse must be carefully closed/sealed to avoid disturbances from unnecessary air flows.
6. Although for a greenhouse in the subtropical climate, using evaporative cooling pan and fan system is not the most satisfactory way because it is not as efficient as it in the dry climate, it has the advantage of the energy-saving and easily-adjust over
the other alternatives, such as air conditioning and composite system. When the fan–pad alone is not sufficient, proper use of shadings is necessary and effective, as demonstrated by the experimental results. At the same time, to help the photosynthesis
process of the plants, we can adjust the strategy of shading-use based on the real situation, such as plant species and their growing conditions and real-time solar radiation values.In conclusion, the evaporative cooling pad system is an efficient
way to prevent greenhouse overheating in the summer which is worth being popularised.