Case 4: Cooling in a warm and humid climate

In a hot and humid climate, heating is hardly an issue. Also water availability is mostly not an issue as humid tropical climates normally have periods of heavy rain fall. If managed well, rain water can be used to replenish water reserves.
Cooling, however, is very difficult in such conditions. Taking the typical weather in Singapore as an example, the scenarios below show that greenhouses with natural ventilation, but also greenhouses with pad and fan cooling cannot be cooled sufficiently to grow common greenhouse crops like tomato or lettuce. Only air conditioned greenhouses provide temperatures low enough to grow the typical greenhouse crops. And, just like in the dry hot climates, the performance of these air conditioned greenhouses improves a lot when CO2 dosing is applied.

In this case heating scenarios are reviewed for a Dutch greenhouse using different heat sources. The following scenarios are compared:

Natural ventilation
Pad and fan
Mechanical cooling without CO₂fertilisation
Mechanical cooling with CO₂fertilisation

With the following assumptions:

Non illuminated tomato cultivation in a modern glass greenhouse in Shanghai
As light-conditions are equal in all scenarios, the temperatures to be achieved in the greenhouse are equal in all scenarios (a consequence of RTR-based temperature control)
Because of low temperatures in winter, a boiler on LPG in combination with a thermal screen is used

The configuration differences between the scenarios are shown in the table below.

Performance

The simulation results are grouped into realised climate, CO2, electricity and heat. Expand each topic for detailed results.

Greenhouse climate

First, let’s look at the realized greenhouse climate. It is clear that evaporative cooling with the pad and fan system is not an option here because of the humid climate.