Humidity ManagementHOW HUMIDITY WORKS AND POPULAR CONTROLS

Brought to you by:

Kurt ParbstDirector of Business DevelopmentEnvirotech Cultivation Solutions

Halle BrakeDirector of Upstart UniversityBright Agrotech

Kurt@agamgreenhouseusa.com halle@brightagrotech.com

Humidity - When is it a problem?

1) What is humidity, how does it work & what does it do?

2) Humidity measurement & management

3) Liquid Desiccants

4) More resources & support (stick around for a free downloadable resource!)

In this deck:

Humidity causes many problems, chief of which is promoting diseases and other pests.

But first, let’s learn the lingoHere are some important ideas and words to describe humidity and the effects that it has

(Plant) CanopyThe collective body of foliage in a grouping of crops.

TranspirationLoss of water vapor from stomates plays an important role in growth and development, ensuring the transport of nutrients from the soil (or solution) to the plant organs.

Relative humidityThe amount of water in air/water in saturated air (expressed as a percentage)

Humid

Saturated

Dew pointThe temperature of an object at which water vapor condenses on the surface of that object

PsychrometerA tool to measure humidity

Vapor pressure deficit (VPD)The ability (driving force) for water to evaporate from a surface

Where does humidity come from?

Evaporation & Transpiration(evapotranspiration)

Unmanaged humidity can cause:Disease outbreaks:• Botrytis• Powdery Mildew• Downy Mildew• Pythium• Phytopthora• Fusarium

How does humidity encourage disease?• Moisture promotes germination• Water film is pathway for infection• Dripping water can spread spores

• Significant damage common

• Catastrophic loss a threat

• Facilities become contaminated

Fungal Threat is serious

Botrytis

In addition, humidity can cause:-Hindered nutrient uptake-Insect pest outbreaks

So how can we dehumidify air?

Condensation is a key concept for farmers.

How does condensation happen?Sun increases transpiration and evaporation

Warm air holds more vapor

...How does condensation happen?

Temperature drops at night (esp. in fall and spring)

Condensation forms and water droplets form on cold surfaces like walls, and plants (shoot tips can be 2.5oC cooler)

*Temperature is key to humidity control

Relative humidity (RH) is temperature dependent-Alone, says little about plant’s ability to transpire

For every 10C increase in temperature, water holding capacity doubles (RH is halved)

When condensation doesn’t work...

RH measurements not always accurate

Coldest point not indicated on sensor for zone

Solid state humidity sensor not necessarily accurate

Growers can monitor VPD insteadMore accurate way of measuring ability of water to enter the air• VPD describes the ability (driving force) for water to evaporate from a surface

• VPD of zero means a plant cannot transpire as water will not leave the leaf, unless the leaf heats up

• High VPD: high temps, low RH

• Low VPD: low temps, high RH

dry air

water vapor

VPD Rates

.2 .3 .4 .5 .8 2.2

Best for seedlings

Disease

Best for mature Stress

RH vs. VPDWater holding capacity doubles with every increase of 20F

70% RH can approach lower and upper limit, depending on temp

Temperature, C RH, % VPD, kPa

16 70 .55

24 70 .90

32 70 1.45

RH vs. VPDWater holding capacity doubles with every increase of 20F

An RH ‘range’ is OK, at the right temperature

Temperature, C RH, % VPD, kPa

16 22 1.38

24 41 1.38

32 71 1.38

Let’s look at an exampleWhat does VPD and RH look like on a farm throughout a day?

VPD MonitoringGuatemala tomato farm: ‘beautiful’ weather. Unheated, natural ventilated greenhouse

Time Temp, F RH, % VPD, kPa0:00 61.2 89 0.20

2:00 59.4 91 0.16

4:00 58.1 95 0.08

6:00 58.3 95 0.08

8:00 74.8 82 0.53

10:00 91.4 31 3.5

12:00 89.4 28 3.43

14:00 86.7 41 2.58

16:00 76.1 69 0.96

18:00 68 87 0.31

20:00 63.9 94 0.12

22:00 61.7 95 0.09

Target: 0.3 to 1.5kPa

Low VPD stress 2x per day

Water stress midday

Poor quality, yields

Need: Heat & shade

What are the solutions to Humidity?

Goal:The key to suppression of disease is to keep the canopy dry from dusk til dawn.

3 main methods of control1. Ventilation (air exchange)2. Condensation (cold surfaces, AC)3. Desiccation (chemical absorption)

Option 1: Ventilation• Water vapor removal from aerial growing environment

• Ventilation: replace warm, high water vapor content inside air with cooler, drier outdoor air in intervals

Ventilation’s hidden costIndirect cost is heating/cooling new air

Option 2: CondensationCondensation: Single-glazed greenhouses typically have a good ability to dehumidify themselves satisfactorily (ventilation and condensation)

The problem for condensationModern greenhouses and other growing spaces don’t have the right materials for this

Double layer polyethylene - great for insulation, bad for

condensation

Glass - increasingly rare, bad for

insulation

What about thermal screens?

• Modern greenhouses utilize thermal screens for heat conservation. Greenhouses with double glazing and those with screens have a diminished ability for dehumidification.

• Screens in houses are typically gapped for humidity control. These leads to a loss of energy.

This can leave growers in a tough spot

• Ventilation introduces new heating costs, and condensation only works with some types of facility

A promising new solutions to humidity control: Dessicant systems

Dessicant systemsDessicants can be a solution• Keep air, walls and ceiling dry (less heat loss)• No ventilation is required (no wasted energy)• Condensing water releases energy (generates heat)

Agam Greenhouses is a company involved in making this solution accessible to greenhouse growersThey built a dessicant-based machine to deal with humidity challenges in spas, greenhouses for covered cherries, eggplants, and roses

They called it the VLHC• Liquid desiccant (salt solution) dehumidifier

• Primary heat source for growing environments

• Simultaneous dehumid. & direct air heating

• Airborne Fungal decontamination (Capture, Neutralize)

Learn more about VHLC here.

Ready to get empowered?