Workshop onHumidity Control

Understanding greenhouse physics for improved growth control

March 10th 2015,

Stockbridge Technology Centre

Introduction

“Global player” with local partnersiSii

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SensorsSensors

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1 Digital climate control

2 Hydroponics

3 Plant sensors

4 Closed / semi closed greenhouse -> “The New Growing”, LED etc.

5 111111111..

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45 years of experience in Horticulture

How to get the optimum growing climate in any type of greenhouse? Every stage has its learning curve

Program of Workshop

○ Discussions about

● How to have better Humidity control on micro climate level

● How does evaporation work?

● How to have better transport of elements?

● How to save energy?

● What’s best to invest in ?

○ But first we need to know something very basic$.

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Translating the needs of the plant into Greenhouse physics to!

http://hnt.letsgrow.com/psychro : Hoogendoorn Psychro App explains Greenhouse Physics

Basic terms of humidity

Relative Humidity

Percentage water vapour to saturize air

RH =AH/MaxH * 100%

Humidity deficit

Deviation between Absolute Humidity

and Maximum Humidity (g/Kg air or g/m3 air)

Vapour Pressure Deficit (leaf-air)

Deficit between Vapour

pressure in plant and

greenhouse air (Kpa)

What is ideal RH or HD? Absolute Humidity: determines dewpoint

Example: AH on your climate computer

Balance : evaporation = export

Source: Peter Geelen Plantmonitoring.NL

Tomato example: AC perforated foil + Energy screen (LS10)

17Source: Peter Geelen Plantmonitoring.NL

Relative Humidity and Humidity Deficit

Source: Peter Geelen Plantmonitoring.NL

Effect of Temperature on humidity values

Source: Peter Geelen Plantmonitoring.NL

Background : humidity control and screening

Greenhouse 20 °C Greenhouse 20 °C

20 °C12 °C

Outside 10 °C

Absolute Humidty in- vs outside Export of humidity

1- By removing it away the micro climate around the plants

○ Maintaining air movement in all local spots where

humidity is being produced

2- By removing it from the Greenhouse air

○ By condensation

● Temperature difference between

air temperature under the screen and glass temperature

○ By ventilation

● Difference of AH in the glasshouse and outside the glasshouse

Working with a Pyrgeo / Irradiation sensor

Prevent: 'cold heads ‘ “goose bumbs”

Incoming vs outgoing radiation on a perfect day

Example Cloudy vs Clear sky

Cloudy sky Clear sky

Example pyrgeo measurement vs plant temperature

Condensation risk in canopy due to irradiation

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Example in Gerbera

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Flower Heart covered

Flower covered

Flower Uncovered

Greenhouse air

Close curtain earlier due to irradiation

Setting example:

How to prevent condensation and lower disease pressure?

○ Priority 1: a uniform climate● Try to have an equal climate everywhere horizontal and vertical

○ Reduce humidity when necessary

1. By condensation on glass/plastic roof

2. By venting or with gap in screen

3. Use fans to bring in outside air

4. By heating with minimum pipe

○ Control fruit temperature

● Heat up at max 1 degree/hour

● Start heating up before sunrise

● Use softsensors to rapidly lower humidity (AH) when needed

Overview of possibilities

○ Source: Presentation Aat Dijkshoorn, KAE , jan 2014

So what’s next?

Source: Presentation Aat Dijkshoorn, KAE, jan 2014

Try to stop using humidity cracks in screens and

Invest in a Measurement box above the screen !

How to start today? Measurement box above the screen.

Greenhouse temperature above curtain

Greenhouse temperature

Outside temperature

RH above curtain

Curtain position

Curtain: deviation above-below curtain

Adapt opening strategy regarding

deviation temperature above-below the screen.

Measurement box above the screen.

Setting example:○ When you just start using physics applied to your

greenhouse humidity controls you have a guaranteed

Return on investment within a day!

○ With small investments you can have a Return on

Investment within a month!

If you have any questions don’t hesitate to ask www.hoogendoorn.nl

Email: Rbe@hoogendoorn.nl

Summary