Heating, Ventilating, and Cooling (HVAC) systems are designed to maintain optimal greenhouse growing conditions, which vary according to the crop grown, time of year, and local climate restrictions. The use of HVAC systems depends on the level of climate control desired by the greenhouse grower. Low-tech greenhouses may use shading and ventilation as the primary sources of climate control, whereas the medium-and high-tech greenhouses tend to use evaporative cooling and supplemental heating in addition to shading and ventilation. High-tech greenhouses may also opt for refrigerant-based heating and cooling systems, especially for recirculating air systems. Vertical farms, indoor gardens, and other closed plant production facilities typically use refrigerant-based HVAC systems to cool and dehumidify the production space.
The HVAC loads - the amount of heating, cooling, and humidification or dehumidification required to maintain optimal growing conditions - depends on several factors. The primary contributing factors to HVAC system design are local climate conditions, crop requirements, and facility type and construction. An engineering analysis can be performed to determine the HVAC loads and help inform the selection of systems that would work best for a given application. The following design criteria will inform this analysis:
1. Facility location
2. Facility description (type, size, construction)
3. Crop type(s)
4. Target temperature, relative humidity, and VPD.
5. Internal sources of heat gain (lights, people, equipment, etc.)
6. Internal sources of moisture (plant transpiration, evaporation from open irrigation systems)
7. What is the construction budget
There may be other design constraints and owner requirements that are unique to each operation. They may or may not impact the size of the HVAC equipment requirements, but they will most likely affect what type of system is selected, where it is located, and how it is operated. These desirable factors include everything from maximizing energy efficiency to limiting noise, as well as system redundancy and durability.
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