This week I worked on the modelica simulation and got that working for a constant LAI (leaf area index). The error was in vanthoor actually, but the reference had it correctly for the internal transpiration resistance at low humidity. In case you’re following along, you need to consult Stanghellini 1987 for that one. I then setup a system to do ray traces for all the possible combinations of LAI and canopy height for each time period. This is very computationally intensive, so I may need to adjust that later. It seems like the simple way to do it for now though. I have this ouputing into a table where each column is the absorption for a .stl file of the greenhouse for a given LAI and canopy height.
The next step is to make a modelica function that takes that table and interpolates for the current LAI and canopy height. I may not get to that soon though because I want to make sure the greenhouse is ready for planting on July 1.
I started on the greenhouse controls, a lot of which I can reuse from the growth chamber. The heating loop (which hopefully will not be used), fan motor controls, humidity and co2 sensors are all the same. The switch to hydroponics means I need two pumps (one for each row in the greenhouse so I can time their irrigation independently).
The tricky parts are weighing the slabs and sealing the greenhouse vents when they are not in use. For this I plan on using a low pressure compressed air system. Seals can be inflatable plastic tubing that is pressurized when the vents are closed as a tight gasket, then vented to allow opening. For weighing the slabs, I plan on suspending them from a 50 kg load cell. Because the cheap load cells have a lot of drift with time, the cell can be periodically deloaded with an inflatable bag beneath the slab holder connected to the compressed air system. This will allow for automatic re-tare as needed. I’m hoping for 10 min cycles.
Sun Aquasystems 