High insulation; how to control humidity

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

2. 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

3. Reduction of energy losses Humidity: • Humidity is an increasing problem with increasing insulation • Decrease of condensation from 100l/m2/yrto about 10l/m2/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?

4. 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

5. Balance • Economic feasibility • Practical fit in (existing) greenhouses • Energy efficient  Ventilation

6. 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!

7. 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?)

8. Mechanical ventilation is: controlled movement of air • 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: m3/m2/hr. depended of crop transpiration

9. 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 m3/m2/hour  non soilless, single glass, lack of capacity in August/ September (warm nights  small Δx)

10. How did we start: principle Cold, dry outside air

11. About the system • System installed at 1.2 Ha • In total 18 fans installed in side walls • Maximum capacity of fans is 3000 m3/h  4.5 m3/m2/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

12. Fans in side walls

13. Air tube below the gutter And start running

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

15. 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

16. Lessons learned this experiment and past • 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

17. 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 Controlled ventilation of greenhouse air Recirculate inside air and / or distribute outside air

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

19. So • 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 5 - 6 m3/m2/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

20. 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

21. 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

22. Dehumidification & heating slave master

23. Temperature of heating systems • 3 heating systems • Master • Slave • Pipe rail • Water temperaturemainly < 45 oC Opening of screen

24. Working of regain heat exchanger, may 5th • Minimum fan capacity of 25% due to equal distribution inside the greenhouse • T exhaust17.8 oC • T outside 8.2 oC }82% sensible heat • T mixed 16.1 oC } T gh box T exhaust T mixed Fans on T outside

25. How to save more energy? • Energy use is about 0.1-0.2 m3/m2/week • Heat required between 02:00 tot 08:00 • Nature (the sun) starts around 06:00 Always heat requirement

26. Energy savingcomparedto commercial farms Venlow concept compared to practice Summer: growing concept+CO2 Winter: double glazing

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