High insulation; how to control humidity Seminar 23 rd of October 2012, Gjennestad, Norwegen Frank Kempkes

Reduction of energy losses  Double covering materials ● High insulation = less convection losses ● Specific coatings = less radiation losses  Screening ● More screens are more effective as one single super screen  cavity-split standing air ● Up to three screens ● How to control ? But with increase of insulation humidity will increase as well

Reduction of energy losses Humidity:  Humidity is an increasing problem with increasing insulation  Decrease of condensation from 100l/m 2 /yr to about 10l/m 2 /yr  Search for alternative dehumidification system General: Worse humidity control results in non optimal use of energy savings Can we find an energy saving dehumidification system?

How can we dehumidify?  Condensation  Hygroscope materials (regeneration)  Ventilation

How can we dehumidify?  Condensation ● + reuse of water ● -- if mechanical sensible heat can be lost (up to 60%) & requires energy input  Hygroscope materials ● -- regeneration ● -- logistics ● - many materials have at least some toxicity  Ventilation ● + system is already available ● -- poor control with small flows ● -- with use of screen splits introduction of T differences

Energy flows  Removed moist has used energy to evaporate ● In summer  cooling of the greenhouse ++ ● In winter  often heating energy --  How to remove ● Out side air (“always” dryer as greenhouse air  abs. humidity) ● latent and sensible heat loss ● minimise sensible heat loss ● Cover ● condensation  cover temperature ● condensation heat remains in greenhouse ● Mechanical dehumidification ● condensation  cold surface ● what is source of this cold?  energy ● temperature below dew point but as well loss of sensible heat re- heating uses (lots of) energy

Energy, the bron Sun is a free energy source Energy input of a nice sunny or a dark day can differ more than 100 X Specific heat of water 4186 J/kg/K latent heat of vaporization water 2258 kJ/kg Specific heat of air 1000 J/kg/K 1 m 3 greenhouse air about 1.2 kg A sunny day give enough energy to (2223*10000)/(2258*1000) = 9.9 kg water evaporation Or (2223*10000)/(833)=26687 kg air 1 o C increased in T Or (2223*10000)/(4186)=5300 kg water 1 o C increased in T

Balance  Economic feasibility  Practical fit in (existing) greenhouses  Energy efficient  Ventilation

Ventilation for humidity control as now used  Controllability of ventilators (now the system follows and 1% today has different effect as 1% tomorrow)  Equal distribution  Often unintentional heat loss  Improvement of controllability  Mechanical ventilation!

Mechanical ventilation is: controlled movement of air  Complex in greenhouses: air is difficult to lead in the right direction (way of less resistance)  Influence on microclimate is not clear  In practice experience with several systems (mainly based on closed greenhouses) Distinguish: ● movement of air (MICROCLIMATE) ● Input of outside air (DEHUMIDIFICATION)  Movement of air (equal distributed en not to much) can help to create a “good” microclimate (what is good?)

 Introduction of fans ● Electricity use ● Avoid resistance or at least high pressure  On short distances it can help to level out temperature differences  Microclimate (mixing air, local) ● Capacity: movement of air of mm/s, cm/s, m/s and / or  Dehumidification (exchanging air between in and outside, transport & distribution) ● Capacity:m 3 /m 2 /hr. depended of crop transpiration Mechanical ventilation is: controlled movement of air

Dehumidification:  Capacity is balance between crop transpiration and difference of absolute humidity between in- and out-side air  Do we know crop transpiration? (radish or tomato)  Effect of soil in case of non soilless  How often we allow underperformance of the system  dehumidification by ventilators  Dehumidification system is not for cooling Dutch tomato crop capacity of 5- 7 m 3 /m 2 /hour  non soilless, single glass, lack of capacity in August/ September (warm nights  small Δx) Mechanical ventilation is: controlled movement of air

How did we start: principle Cold, dry outside air

Overview experimental plot Compartment 3 & 4 With system Compartment 1 & 2 control

About the system  System installed at 1.2 Ha  In total 18 fans installed in side walls  Maximum capacity of fans is 3000 m 3 /h  4.5 m 3 /m 2 /hour  Energy screen: LS10 Ultra Plus  Holes in tube directed to heating pipe (no pre heating of out-side air)  No “official” outlet; air percolates through gaps and holes

Fans in side walls

Air tube below the gutter And start running

Temperature along the tube T gh =15.5°C RH gh =88% AH gh =9.7 g kg -1 T air =16.1°C RH air =41% AH air =4.6 g kg -1 T outs =3.1°C RH outs =86% AH outs =4.1 g kg -1 T air =14.6°C RH air =44% AH air =4.5 g kg -1 T air =9.7°C RH air =63% AH air =4.7 g kg -1 T air =6.3°C RH air =76% AH air =4.5 g kg -1 air

Conclusions of first experiment  Horizontal temperature distribution in compartment with system is better than in control where humidity is controlled with screen splits  In experiment temperature of out coming air (because of non pre heating) not equal but in this case no problem ● condensation at tube specially at beginning beside side wall (makes growers nerves) ● grower likes preheating because of creating a “good feeling” (no condensation nearby the crop) but it’s a perfect dehumidifier)  Vertical profile as in reference

 Tube ● distribution works (bring temperature at greenhouse air temperature) ● heating of greenhouse by input of hot air at central point is not smart horizontal temperature distribution  Combined / mixing system including recirculation ● in mix system a fixed flow is distributed through the system. valves control outside air mixingd. − in practice often problems to control − pumping air ≠dehumidification − extra fans  energy − suck in of greenhouse air can create problems + regain of sensible (latent) heat possible Lessons learned this experiment and past

Recirculation an example Controlled ventilation of greenhouse air Recirculate inside air and / or distribute outside air

In practice: an example of dehumidification system Biological production (soil is in use) distribution system is lifted Combined with vertical fans for distribution in the crop Recirculate inside air and / or distribute outside air Controlled ventilation of greenhouse air

One tube each 6th span No pre-heating In practice: an example of dehumidification system

Tomato: temperature distribution with tube as heating system (close greenhouse) Temperature distribution in cooling mode ok Temperature distribution in cooling mode worse ● sidewalls to cold  to high RH ● return air flows along cold screen, cools down and drops before outlet is reached SidewallpathSidewall

Conclusions What to do?KIS  Keep It Simple  Heat air up to greenhouse air temperature to avoid horizontal temperature differences (and for feeling of grower)  Fixed airflow is better for distribution design knows small band of optimal control ● control by on of but ● control of pre-heating difficult ● time delay reaction time of measuring box Compromise is not yet crystallised out

 By increase of insulation an increase of humidity as well  Combination of screen use and screen-splits for dehumidification far from ideal  By ventilation lots of energy can be lost  good reason to control this as good as possible  Mechanical dehumidification with outside air can be a: ● simple system ● with or without pre heating ● with or without regain of sensible (latent) heat ● rather small capacity of m 3 /m 2 /hour necessary ● by keeping screen closed maximum energy savings of screen when in use ● more screening hours  extra energy saving For maximising energy savings dehumidification system essential So

Ready?  NO we need an energy efficient dehumidification  Balance ventilation can pre-heat the incoming air ● efficiency restricted because it mainly works on sensible heat (latent heat is lost) ● extra fan(s) is needed for the outgoing air ● easy and cheap heat exchanger is needed Balance between economics of extra investments and extra electricity use vs energy saving for pre-heating  Can we combine functionality of heating and dehumidification system? ● air heating means low water temperature  increase efficiency of boiler room or geothermal source

In Venlow energy: replacement of regain unit  Optimization of dehumidification system goals: ● reduction of electricity use ● improve regain efficiency ● low temperature heating system  increase efficiency of heat pump, boiler house, thermal energy master slave

Dehumidification & heating master slave

Temperature distribution (slab measurement)  Beneath slab slightly higher temperature  ΔT in-out 31 o C  ΔT inside ≈1 o C

Temperature of heating systems  3 heating systems ● Master ● Slave ● Pipe rail  Water temperature mainly < 45 o C Opening of screen

Heating system: water temperatures week 33 Venlow versus Practice ● Venlow (V) ● Practice (P) ● in Venlow no use of minimum pipe temperatures ● cyclemean is shown

Working of regain heat exchanger, may 5 th  Minimum fan capacity of 25% due to equal distribution inside the greenhouse ● T exhaust 17.8 o C ● T outside 8.2 o C } 82% sensible heat ● T mixed 16.1 o C } T gh box T exhaust T mixed Fans on T outside

How to save more energy?  Energy use is about m 3 /m 2 /week  Heat required between 02:00 tot 08:00  Nature (the sun) starts around 06:00 Always heat requirement

Ventilation week 23  Lots of heat are during evening released to create temperature drop

Energy saving compared to commercial farms Winter: double glazing Summer: growing concept+CO 2 Venlow concept compared to practice

Special thanks to my colleagues: Feije de Zwart, Jan Janse and Jouke Campen Takk skal du ha!

Verticale ventilatie (microklimaat) Slang ?

Conclusie: Lucht neemt weg van minste weerstand Bij hard blazen tussen tafels door in plaats van door tafel heen Uitdroging van potten wordt ongelijk Inhomogene verdeling door of zelfs langs de tafel Wat resultaten van andere systemen