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.