Maldives Lettuce Greenhouse HVAC Solution

Project Location



Condensing unit, Vertical AHU,  Air-cooled water chiller, ERV


Lettuce cultivation

Key requirement for lettuce cultivation HVAC:

Greenhouse can protect crops from adverse weather conditions allowing year-round production and have better protection control over pests and diseases, and still benefiting from the sun’s natural light. The ideal climate condition for lettuce cultivation should maintain constant temperature and humidity for 21℃ and 50~70%. Indoor temperature, humidity, carbon dioxide control and adequate irragation are the most essential factors for lettuce cultivation.

Local temperature & humidity: 28~30℃/70~77%

Indoor HVAC Design: 21℃/50~70%. Day time: constant temperature & humidity; Night time: constant temperature.

Project solution:

1. HVAC Design: Indoor temperature and humidity solution

1. Two pieces of condensing outdoor units(Cooling capacity:75KW*2)

2. One piece of vertical air handling unit (Cooling capacity:150KW, electric heating capacity:30KW)

3. One piece of PLC constant temperature and humidity controller

Sufficient ventilation is very important for optimal plant growth, especially in the case of high outside temperatures and solar radiation. Heat must constantly be removed from the greenhouse. Compare to natural ventilation, AHU with PLC control can precisely obtaining the required climate conditions; it can further reduce the temperature, especially under high ambient temperatures or high radiation levels. With high cooling capacity it can keep the greenhouse completely closed, even at maximum radiation levels. AHU can also provide an energy-efficient dehumidify solution to avoid the condensation during daytime and particularly few hours after sunset.

2. HVAC Design: Indoor CO2 control solution

1. One piece of energy recovery ventilator (3000m3/h, one time air change per hours)

2. One piece of CO2 sensor

CO2 enrichment is essential to increase quality of produce. In the absence of artificial supplies, greenhouses have to be ventilated during a large part of the day makes it uneconomical to maintain a high CO2 concentration. The concentration of CO2 within the greenhouse must be lower than outside in order to obtain inward flow. It implies a trade-off between ensuring inflow of CO2 and maintaining an adequate temperature within the greenhouse, particularly during sunny days.

The energy recovery ventilator with CO2 sensor provides an optimal CO2 enrichment solution. CO2 sensor real-time monitor indoor concentration level and precisely adjust extract and supply airflow to achieve CO2 enrichment.

3. Irrigation

We suggest to use one water chiller and thermal insulation water tank. Water chiller cooling capacity:20KW (with outlet chilled water of 20℃@ambient of 32℃)

Post time: Mar-26-2021

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