Authors: Lemos-Marini, P. Flecher, J.
1. Use of a fluid as a heat sink (e.g. distilled water or oil) will enable cooling of the individual LED chips very efficiently and quickly without the need of expensive metal heat sinks
2. The use of heat transfer fluid will enable efficient transfer of heat between the lighting system and the growing solution (aquaculture and hydroponics solution)
3. The use of a non-conductive fluid will avoid the need to encase the LED reducing cost
4. The use a lay-flat tubing will enable a low cost solution for casing the led and to contain the thermal fluid.
5. The use of lay-flat tube will diffuse light in all directions without the need of optical lenses (preferred material is diffused ETFE lay-flat tubing due to the superior optical properties)
6. The use of the lay-flat tubing will enable easy disassembly when lighting isn't needed (e.g. summer)
7. White plastic beads suspended in the fluid could enhance scattering of the light even more if diffused plastic isn't sufficient.
A device to encase high power led chips for plant lighting avoiding the need of expensive metal heat sinks and with the added benefit of heat collection to use in other heat demanding processes is described.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 - Shows the image of one individual and complete system. In reality we would have several lay-flat sections connected to a circulation fluid grid on the top and one in the bottom. *The circulation grid would have only one (water to water) heat exchanger.
*The circulation grid has a pump to keep the fluid circulating (pump supplies energy lost due to resistance and turbulence in the fluid, although there will be no need to elevate water as entire system is connected and full of fluid)
Fig 2 - Shows ideal circulation in respect to the natural convection flow
Fig 3 - Shows the disposition of several lighting systems between plant growing towers. The height of the lighting system will depend on the height of the vertical growing system. We could have anything from a few meters up to few dozen of meters.
Fig 4 - Shows a schematic of inside the lay-flat with white matt plastic beads suspended in the fluid. Plastic beads will be present throughout all the fluid.
Their function is to increase light scattering and create the appearance of a fluorescent tube. Their size will likely be much smaller than seen in the drawing.
DETAILED DESCRIPTION OF THE PREFERRED MATERIALS
====Thermal fluid- Heat sink and heat transfer fluid=====
- Compatibility with the LED chip. (e.g Avoid the silicon coat damage and de-lamination problem)
- Low/no conductivity
- Available worldwide
- High Specific Thermal Capacity
- Environmentally sound to obtain and dispose
- Distilled water (e.g. rain water) - Free, available everywhere - Good Spectral Transmittance on the full PAR region
- Vegetable oil - Costly, poor Spectral transmittance on the blue region
--Considerations about the thermal fluid--
The challenges of immersing LED chips in a fluid are:
- Electrical conductivity of the fluid
- Compatibility with the silicone overcoat
- Electromagnetic Spectrum absorption of fluid - Spectral Transmittance profile
- Delamination of chip cause by moisture or other solvents
*Electrical conductivity trends to zero in distilled water. What could happen is that the left overs of industrial processes and solder flux may dissolve in water, so a few water exchanges may be needed to fully clean the electronics. (EC could be monitored to achieve it)
*Compatibility with the silicon overcoat should be compatible with pure water. Both chemical and VOC (Volatile organic compounds) should be considered as a silicon overcoat is normally gas permeable and could present discoloration and surface damage when exposed to VOC
*Water spectrum absorption is low for PAR (Photosynthetically active radiation) band.
*Delamination: Some of the new LED's have JEDEC Moisture Sensitivity Level 1 so they may survive full immersion in water for longer periods, even for a considerably longer period than the normative guarantee. If long time resistance is a problem an extra layer of silicon could be considered and if this is not viable the use of oil should be considered.
====Lay-flat Tubing material=====
The ideal material for the Lay-flat tubing is ETFE due to the excellent transmittance properties (this material is quickly becoming the standard for new greenhouse cover installations)
Diffused Lay-flat tubing should be used to scatter light. Different than most diffuse material, diffuse ETFE doesn't exhibit any light loss in precision experiments where measured. Check F-CLEAN diffused version.
====Micro Plastic beads for enhanced diffusion=====
No specific material have been considered. Material will need to be compatible with the thermal fluid.
====Micro Plastic beads for enhanced diffusion=====
No specific pumps have being considered.
*The pump will ideally be low power, high efficiency (it will only have to add the energy lost by resistance and fluid turbulence, there is no potential gravitational energy to be added or lost)
- It will have to be compatible with the size of the plastic beads if they are used
====LED Power Supply=====
A constant current power supply would be the ideal driver and LED would be connect in series. Respecting a limit of 60 V to class as safe voltage.
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====Copyright Aquaponics Lab 2014==== www.aquaponicslab.org
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