GrowAire™ VPDsync™ Masters 4 Elements of CEA Control

September 2020


Desert Aire GrowAire™ VPDsync™ Controlled Environment Agriculture Matches the Needs of Plants for Better Results

GrowAire with VPDsync logo

An indoor plant environment has many factors that need to work together to achieve the optimal environment. There are four main elements that must be in sync in order to provide this indoor environmental control:

  • Light
  • Evapotranspiration
  • Vapor Pressure Deficit
  • Air Distribution

1. Light Energy

Light is the main driver for plant growth is light energy as it provides the energy to convert the carbon dioxide, water, and nutrients into organic compounds. Heat comes from the inefficiencies in generation of light by the lamp ballasts which create heat that warms the space. Infrared light contains a tremendous amount of heating energy. All of this heat energy needs to be offset with cooling during the photoperiod (lights on) to maintain an optimal space temperature.

2. Evapotranspiration

Watering creates moist soils, surfaces and, in some indoor plant environments, trays and troughs that hold water. This water evaporates constantly. Additionally, plants transpire water vapor during photosynthesis. The evaporation and transpiration together are called evapotranspiration and increase humidity in the space. This humidity load needs to be offset with dehumidification. Even during the dark period in an indoor plant environment, there is still a good deal of evapotranspiration that must be addressed. The amount of evapotranspiration is proportional to the size of the plants and their leaf density.

3. Vapor Pressure Deficit

Vapor Pressure Deficit

The process of transpiration occurs because the water vapor pressure in the plant foliage is higher than the surrounding air. This difference in the vapor pressure is the driving force for the transpiration process and is called the Vapor Pressure Deficit (VPD). The VPD has an optimal range for each stage of plant growth. Too low of a VPD slows transpiration and growth. Too high VPD creates issues where the plant cannot transport adequate water to the upper shoot and can stunt growth, or in extreme cases, damages the crop.

Air Distribution

4. Air Distribution

Within an indoor plant environment, it is critical that airflow is turbulent and well mixed. This avoids stratification that can cause unequal temperatures and areas of high humidity. Correct velocity ensures every plant is at the correct condition for optimal growth.

Creating a perfect condition in an indoor grow environment can be challenging. Heating, cooling, and dehumidification loads change rapidly during the shift from dark to photoperiod and vice versa. The amounts of dehumidification and cooling required shifts as the plants grow larger and have greater rates of transpiration. Environmental control units must be able to be flexible and accurate to maintain the perfect conditions. Only Desert Aire GrowAire units with VPDsync™ environmental control have the four dimensions of control to perfectly match the loads in an indoor plant environment.

Factors that impact HVAC performance


Due to the high intensity of lighting required for controlled environmental agriculture, most indoor plant environments have a high cooling load when plants are smaller and very limited dehumidification required.

As the plants grow and have more leaf area, the rate of transpiration increases. The water in the plant turns from liquid to vapor cooling plant, which in turn cools the room and offsets some of the heat load from the lights. Two things happen: the overall cooling load decreases and the dehumidification load increases.

The controls in a GrowAire unit with VPDsync™ commands the stages, airflow and valve positions to provide full modulation of the refrigerant system. This provides the optimal temperature from the machine at all times to maintain both temperature and humidity.

Through the use of a full-sized, fully modulating hot gas reheat coil, during the dark period, the GrowAire unit can provide air at not only a stable humidity, but a perfect temperature.

The GrowAire unit with VPDsync™ command environmental control technology has standard fully modulating variable speed fan control. The airflow varies throughout the growing cycle and periods and provides a shift in the unit’s cooling and dehumidification ratios.

The sensible heat ratio of an environmental control unit is a measure of how much cooling is taking place vs. the dehumidification.

Integrated system for indoor plant environment using VPDsync environmental control

Integrated System

The GrowAire unit with VPDsync™ command environmental control will modify the coil temperature to minimize the dehumidification. As the plants become larger the GrowAire will automatically and dynamically adjust the amount of dehumidification.

Typical air conditioners and dehumidifiers cannot adjust this ratio without impacting the capacity. Since the SHR from the machine is optimized, separate cooling and dehumidification equipment is unnecessary. Using a fully integrated system will yield a significant increase in energy efficiency and reduce the overall installed cost.

What GrowAire VPDsync™ means to the cultivator

Don’t make the mistake thinking equipment made for air conditioning office buildings or dehumidifying your basement are going to get you the yield and quality to be competitive in indoor agriculture market.

You need purposeful duty equipment that has been developed for the critical indoor growing environment.

VPDsync™ command environmental control:

  • Adjusts capacity to meet your grow room’s cooling requirements
  • Adjusts the amount of air delivered to your grow room to meet temperature and humidity requirements
  • Reduces or eliminates the over drying of a room during the startup of production or in rooms with early vegetation
  • Maintains tight, steady state temperature and humidity conditions for the perfect grow

GrowAire™ with VPDsync™ product information

View the VPDsync video to learn more about VPDsync environmental control with a detailed explanation of how and why it works to create the perfect day in an indoor growing environment.