Lighted cultivation fossil free through latent heat recovery

Latent heat recovery is the recovery of the energy required to evaporate water. The energy is recovered by condensing the moisture in the greenhouse in an air handling unit. Cold water, having the temperature of the dew point of the greenhouse air, heats up during the condensing of the greenhouse air in the air handling unit. The returned cooling water is

processed into cold and hot water. Part of that heat is used to return the cooled down greenhouse air back to 18°C. The rest of the heat is available for heating the entire greenhouse, for example by using tube rail heating.

Advantages in lighted cultivation

In a lighted greenhouse there is a lot of evaporation. Particularly in winter, when lots of heat is required, lighting is used and greenhouse growers can recover a lot of heat from the moist greenhouse air by means of latent heat recovery. Moreover, there is an important cultivation advantage. In the current lighted cultivation the grower has to ventilate heavily to drain the moisture. That also has to take place at undesirable moments because it is cold outside. The drainage is also hampered because the absolute moisture outside is almost as high as inside, for example during moist days in autumn. When using latent heat recovery, much less ventilation has to take place, saving on heat and CO2. It is also conceivable that dehumidification by the air handling unit requires much less minimum pipe temperature to keep the climate in order. The advantage is two sided.

Lighted cultivation and co-generation

For the most lighted companies generating their own electricity through co-generation is still the best economic option. It is still very well conceivable that through changed price structure in the future electricity will be less expensive when compared to gas, and the buying of electricity becomes economically viable. It is also very well possible that the heat of the co-generation will be much more viable in winter. Then it remains profitable to generate the electricity yourself when it is scarce, sell the heat to a neighbor or cluster, and heat their own lighted greenhouse with the recovered latent heat.

Difference latent co-generation and the (semi) closed greenhouse

The main difference between latent heat recovery and the heat recovery in a (semi)closed greenhouse is that latent heat recovery takes place in winter instead of the summer. This makes the seasonal storage in an aquifer unnecessary when using latent heat recovery. The required power for the heat pump and the capacity of the air handling unit to become fossil free is much lower in case of latent heat recovery than with a closed greenhouse.

Tests and demos
Application of latent heat recovery in lighted cultivation has consequences for the manner of cultivation. That is why there have been tests and demos organised through the Kas als Energiebron program, the innovation and action program by the ministry of agriculture, nature and food quality and LTO Glaskracht Nederland. Projects have started for the following projects.

• Perfect climate neutral chrysanthemum
• Perfect rose - next level
• Alstroemeria - cultivation of the future, up close
• Sustainable lighted tomato cultivation
• The Greenest cucumber

For more information:
LTO Glaskracht Nederland
www.ltoglaskrachtnederland.nl

Aat Dijkshoorn, Project leader Het Nieuwe Telen

adijkshoorn@ltoglaskracht.nl