This week was spent debugging the ray tracer, and adding the functions I need for simulating actual greenhouses. I did find a bug in the data saving function, so I have to redo the calibration. I don’t think it was that serious in these cases, since it agreed well with experiment, but better safe than sorry. I also ordered a spot light to provide intense even illumination for the experiments as I think the even illumination was the accuracy limiting variable. I tried jerry rigging my current lamp with reflectors etc but couldn’t get totally even illumination. When that arrives I can make some more heat maps that should be even closer to the simulation.
I now have code that can take a greenhouse model, ray trace all of the possible sun directions, and then save those results to file. Another program can take solcast like data of sun azimuth, sun zenith, direct sun flux, diffuse sun flux and compute quickly (1 sec) what the flux will be on every facet of the greenhouse. I also provide an estimate of the accuracy, which even for a quick test was generally good, about 1% error. This way I can simulate the greenhouse illumination over years of data quickly without having to ray trace separately for each day’s weather conditions.
For simulation, one of the remaining questions is how much light the plants absorb. I was trying to measure this with 3d scanning, but I just don’t have the budget for the quality of 3D scanner that could make that work. If anyone is interested in a lightly used revopoint 3D scanner let me know… I’ll sell it at half price.
Anyhow, Vanthoor assumed the plants were a block of green tinted glass and the darkness of the tint was related to LAI, or leaf area : floor area ratio. And then a correction factor in there of K=0.7. That’s a good start and a block of glass is definitely easy to do in the ray tracer, but I somehow doubt that 0.7 factor is constant under all conditions. I would like to directly measure the absorption, and measure K for myself. PAR sensors are pricey but I think I might be able to get by with 2$ lux sensors, which would mean lots of sensors for easy fitting to ray tracer data. I’m not sure I’ll pursue this immediately, but it’s on the todo list. My K might be also different depending on sun angle since all previous measurements have neglected the south wall effect.
Sun Aquasystems 