In Controlled Environment Agriculture (CEA), the primary source of moisture is transpiration. This is the process where moisture supplied to a plant is carried from the roots to the leaves, where it is released as vapor. In plants that are actively growing, water is continuously evaporating from the surface of the leaves. Transpiration rates are dependent on a number of factors, including temperature, humidity, sunlight, soil type and airflow. In general, 97% – 99.5% of the water taken up by the roots is put back into the atmosphere.

In CEA Applications, moisture is removed from the space through infiltration, air conditioning, and mechanical dehumidification. Infiltration generally provides an insignificant impact on the total moisture load. Air conditioning will provide some dehumidification, but the primary design objective is to control the sensible load and as a result; high efficiency air conditioning systems are not designed to control the latent load. Mechanical dehumidification with a Model 1870 dehumidifier is designed to control the moisture load in a space.

The relative humidity requirement during cultivation is dependent on plant stage. In an open space, relative humidity varies with temperature and the temperature in the space varies with elevation (vertically) as well as proximity to outside walls. The Model 1870 dehumidifier, with a built in control and humidity sensor, will turn on its blower every hour to accurately measure and control the humidity in the space. Optionally, with an external humidity control placed at canopy height, the dehumidifier will react to and control the humidity level in close proximity with the plants in real time.

Refer to the CEA Sizing Guide to determine the number of dehumidifiers needed to control the moisture in the space. Because of the variation in irrigation types, plant growth stages, temperature and relative humidity required for growth stage and other environmental considerations, the CEA sizing guide uses a general rule of 20 pints/day per 1000 Watt light, 10 pints/day for lights less than 750 Watts, and 25 pints/day per LED light. Input the type of light, wattage (for incandescent), and number of lights, and the guide will output the number of Model 1870 dehumidifiers required for the application. The CEA Sizing Guide does not take into consideration the moisture removal provided by the air conditioning. As a result, the load calculation is conservative. In addition, in the case that one of the units needs service, an extra unit can be added to the total for additional redundancy.

There are two typical installation options, hanging and floor level. In all installations, the dehumidifiers should be spaced evenly throughout the area to be dehumidified with the following recommendations:

  1. Avoid an arrangement where the outlet of one dehumidifier is pointing toward the inlet of another.
  2. Account for handling dehumidifier condensate by considering drain or sump pump locations.
  3. Leave room on the drain outlet side for filter access and service.

The preferred method is hanging using the Model 5691 Hanging Kit. In this installation the on-board controls will be inaccessible and a Model 76 or Model 8840 is recommended as an External Control. Important Note: If using an external control and/or remote sensors, the humidity sensing device must be mounted in an area free from direct moisture sources.

The recommended dehumidifier positioning is around the perimeter of the room with the dehumidifier inlet pointing toward the wall and the outlet pointed to distribute the dry air over the canopy. This installation maximizes allowable plant space and works with the existing room fans to distribute air over the canopy.

An alternative to hanging is to install the dehumidifiers on the floor. In this case the dehumidifiers can be single level or stacked two high. Straps are recommended when stacking.

The Model 1870 dehumidifier comes with an on-board digital humidity (%RH) control. No additional wiring is required when using the on-board control. Every hour the on-board control will turn on the dehumidifier fan to sample the incoming air. Using the on-board sensor, the dehumidifier will accurately measure the relative humidity (%RH) of the incoming air. If the measured humidity is above the humidity setting the dehumidifier compressor will turn on, dehumidify the incoming air, and output dry air until the set humidity level has been achieved. The control requires manual access and therefore should only be used when the dehumidifier is in an accessible location.

When the dehumidifier is hung, a Model 8840 thermostat or Model 8840 thermostat with 8082 remote sensors, or a Model 76 external control can be mounted at canopy height. A Model 8840 with up to 4 remote sensors mounted at canopy height can be used to average the humidity measured by each remote sensor. An additional control option is to have a single Model 8840 or Model 76 controlling multiple dehumidifiers. The Model 76 control or 8840 Thermostat (or remote sensors) will measure the relative humidity where they are mounted, and turn the dehumidifier(s) on and off to control the humidity levels to the desired humidity setting. The humidity setting can be set and adjusted from the control and the display allows easy access and monitoring of the humidity level in the space.

The Model 8840 thermostat will allow you to set the desired %RH level for the space and can be used to turn the dehumidifier on or off. The feature benefit of the Model 8840 is the WiFi capability. Additionally, up to 4 remote sensors can be mounted near the canopy and connected to a single thermostat. The 4 humidity measurements are averaged and the thermostat will turn on dehumidification based on the averaged value. The UP/DOWN arrows on the thermostat are used to set the desired humidity setting. The humidity measurement is then made at the Thermostat or if applicable, at the remote sensors.

Reference the 8840 Installation Instructions and Owner’s Manual for set-up.

The Model 76 will allow you to set the desired humidity level for the space and can be used to turn the dehumidifier on or off. Pressing the ON button on the Model 76 will turn on the control. Use the UP/DOWN arrow buttons to set the desired humidity setting. When pressing the UP/DOWN arrows the Model 76 display will show the humidity setting. At all other times the display will show the humidity level being measured by the Model 76 on-board sensor.

Reference the Model 76 Installation Instructions and Owner’s Manual for set-up.

The preferred methods of installation are hanging, followed by floor level placement. If space requires the dehumidifier to be installed in a space outside the growing area, 10” ductwork and grilles can be used to duct the dehumidifier inlet and outlet to the space requiring the humidity control.

The dehumidifier also has the capability to run the fan using an Air Circulation feature. This feature can supplement the existing room fans to assist in air mixing. Air circulation time can be set from 0-60 minutes per hour. The Model 1870 will move 310 cfm of air when air circulating.

When actively dehumidifying the dehumidifier will draw approximately 8.3 amps at 80°F/60%RH. The dehumidifier is a 120 VAC device supplied with an 8’ grounded power cord. A 15 amp circuit is recommended. All applicable national and local codes must be followed.

The dehumidifier drain comes with a ¾” FNPT threaded outlet. A ¾” MNPT x ¾” PVC slip fitting with hard pipe and a clean out near the dehumidifier is the recommended method of draining. The dehumidifier comes with a ¾” MNPT x ¾” hose barb fitting for flexible drain tubing. When using either method, a constant downward slope of the drain tubing, and free of kinks when using flexible tubing, is necessary for proper draining. The condensate can flow to a floor drain or condensate pump.