Understanding & working with the physical properties of heat.
(Published in 2 parts in Maximum Yield Magazine, 2009)
I am the rhythm, the glow, the darkness & the light. Everywhere, nowhere, the eternal flow, felt and seen but never touched. I give life and I take it back. Some worship me and others call me “the Devil” but come, let’s dance for a bit…. trust me… my name is HEAT…. ?
Hello readers !
“HEAT” is a mysterious concept, that’s why I chose to lead into this article with a poem. There’s something abstract about it, something that scientific explanations fail to capture. I mean, have you ever really stopped & thought deeply about heat ? What it is, what it can do and what its limits might be ?
My name is Paul Cronk & I am the inventor of the reflector products known as Adjust a Wings and Super Spreaders. I have a bachelor of science degree & hold 3 international patents in the field of light / heat manipulation.
I have been designing horticultural reflectors for more than 15 years and over that period I have spent significant effort maximising the efficiency of lighting systems and improving their energy consumption. This line of work has brought me into close & consistent contact with heat and over time my opinion of this elusive entity has evolved from spectre to adversary to friend.
In the passages that follow I will endeavour to describe heat as I understand it and share with you some of its’ lesser known traits & how I work with these characteristics to achieve innovative solutions for indoor gardening applications.
What is Heat ?
When you look closely at heat it is not a definable substance, it is simply a condition related to the absorption of energy by a substance. A substance is said to “possess” heat and does so only by the vibration of its molecular constituents (atoms etc). Heat is energy in transit and constantly proceeds in the direction from high temperature towards low.
How does Heat move ?
Conduction, convection & radiation are heat’s only known modes of transport.
Conduction is the movement of energy through a substance from one atom to the next. It is most effective when the substance is dense (solid materials), it is less effective in medium density substances (liquids) and not very effective in low density substances (gasses). Conduction is more efficient in metals than in non-metals and this is because metal atoms “swim in a sea of electrons” allowing energy to flow rapidly between them.
Convection as a rule, only takes place in liquids and gasses. It takes place due to the combined effects of conduction and fluid movement. For example, if heat is applied to a portion of a column of gas, the heated gas will rise and transfer some of its energy (heat) to the cooler portion of gas above it. The rising is caused by a decrease in density & the heat is transferred by conduction. This heat transfer, from low in the gas column to higher up, is said to be the result of convection.
Radiation is produced by movement of the atoms within a substance. Atoms contain charged particles (protons & electrons) and their temperature driven vibrations result in the emission of electromagnetic waves. These waves transport energy / heat away from the surface of the substance and we call this process electromagnetic radiation (EMR).
If a substance is warm, its particles vibrate at a moderate rate and it will emit radiation of a moderate frequency. If a substance is hot, its particles vibrate quickly and it will emit high frequency radiation. Further, if a substance is extremely hot it will “glow” or emit light. Therefore, in simple terms, light can be described as extremely high frequency EMR.... Yes, radiant heat & light are very closely related, some might even suggest “alter egos of the same effigy ” ?
Heat in the Grow Room,
Ok, now we understand a bit about heat & how it gets around, so let’s move on to an indoor grow room situation and look at heat in the context of that environment.
First of all we need to identify the major heat sources.
Lighting systems consume most of the power in the grow room and consequently they create most of the heat. All the other equipment combined (fans, pumps, timers etc) produce negligible amounts of heat when compared to the lighting system.
The most common form of lighting used in horticulture today is High Intensity Discharge (HID) and for sake of practicality I will limit my discussions on lighting to HID.
HID lights require a ballast and a lamp for operation and as a result they produce heat from two sources.
The HID ballast transforms mains power to the appropriate current and voltage to run the HID lamp. It is an important piece of equipment because it starts the lamp and ensures that it produces consistent output. A gardeners’ main concern with ballasts is that they are inefficient devices that produce significant amounts of heat. Fortunately, HID ballasts can be operated at remote distances from their lamp partners and it is common practise to locate them outside the grow room to physically remove the associated heat.... Get outside ballast, and stay outside !
HID lamps and consequently the heat that they create cannot be physically removed from the grow room, for obvious reasons, so let’s have a look at what HID lamps produce and ponder the consequences.
Heat from the Lamp,
H.I.D. lamps contain a ceramic cylinder (the arc tube) that encapsulates a small amount of metal under strong vacuum. When the lamp is connected to the ballast and current is allowed to flow, the metal inside the arc tube reaches extreme temperatures and becomes a conductive vapour. Under these conditions the metal atoms vibrate at extreme rates and produce a spectrum of high frequency electromagnetic radiant emissions…. Predominantly light.
The reaction within the arc tube is highly efficient in producing light, however the lamp as a complete unit is not. The lamps structural components restrict and transform its rudimentary emissions and allow heat to accumulate. ie) Some of the radiation emitted by the metal vapour is restricted by the ceramic walls of the arc tube causing it to become hot and in turn some of the emissions from the arc tube are restricted by the lamps protective glass envelope causing it to become hot. In total the Lamp emits 3 streams of radiation, one from the metal vapour, one from the ceramic tube and one from the glass envelope.
The metal vapours inside the arc tube reach temperatures between 1100 - 1500 C and emit radiation that is predominantly in the Visible light Spectrum (350 to 750 nm).
The ceramic walls of the arc tube reach temperatures between 500 - 700 C and emit radiation that is predominantly in the Near to Mid Infra Red spectrum (750 to 3500 nm)
The glass envelope reaches temperatures from 200 to 300 C and emits radiation predominantly in the Mid to Far Infra Red range (3500 to 6000 + nm).
These 3 emissions are the raw produce of horticultural lighting and to be successful in the fields of energy efficiency and heat reduction one must dance intuitively with all 3.
Figure. 1) Waves in the electromagnetic spectrum vary in size from very long radio waves the size of a city block, to very short gamma-rays smaller than the size of the nucleus of an atom. Waves in the visible light spectrum (350 to 750 nm) are approximately the length of a virus and waves in the Infrared spectrum (750 to 10 000 nm) may reach the size of a single cell or larger.
Dancing with Light, (EMR 10 – 750 nm)
After escaping the lamp, light waves in the grow room will either,
i) strike reflective surfaces or
ii) pass through transparent heat barriers or
iii) proceed towards plants without interference.
Reflectors & transparent barriers both absorb a portion of the light they receive and may become hot over time. In other words the radiant energy associated with light is able to accumulate in these components. This is an important area to scrutinise and to understand, because here lays the potential to create and store heat and also the potential to minimise its production and accumulation... The devil may lurk where light does its’ work ?
Eg) An 85% reflective surface absorbs 15% of the light that strikes it and a 95% reflective surface absorbs 5%. In practical terms, the less reflective material accumulates 3 times more heat and also emits 10 % less light (that’s significant). The same theory applies for transparent barriers. Cheap, thick, heat barriers (low quality glass plate or tube etc) may absorb >10 % of the light they receive and hence accumulate significant quantities of heat (another potential hot spot).
So it follows that a lot of heat can be eliminated from the grow room if reflectors are made from light weight highly reflective components and if transparent barriers are made from thin “crystal clear” material. For these reasons I recommend that indoor gardeners choose top quality lighting products made from the highest grade of materials.
Having identified that reflectors and transparent barriers can vary considerably in terms of quality and efficiency, one might question why gardeners don’t simplify their setups and do away with all types of light interference ? There is a simple answer to this. Most indoor gardens have size, shape or functional characteristics which require light manipulation and or light interference for effective operation. Below are some examples to help with that explanation.
Eg. 1) HID lamps emit light in cylindrical patterns and specialised reflectors are commonly used to transform these patterns into horizontal or flat sheets of light. Flat lighting patterns are desirable because indoor garden beds are traditionally flat in shape.
Intelligently designed reflector systems compensate for the losses associated with reflection by providing a broad even light pattern that allows lights to be placed close to plants without creating dangerous heat levels. In these “flat bed” grow room designs, light and heat levels can be adjusted by raising or lowering the lights.
Eg. 2) Circular shaped gardens surround their lamps with plants and do away with the need for reflectors or light footprint manipulation, however circular gardens generally require heat barriers with air cooling (cool tubes) to function reliably.
To be more specific, plants grown in circular gardens are limited by size. If they become taller than planned they could grow too close to the lamps and burn. There is very little chance for escape in this situation as the distance between lamps and plants cannot easily be increased (or decreased for that matter) in circular gardens.
I will move on quickly from light because it is heat that we are chasing.... The devil is evasive and loves to side track her pursuers.
Getting to know Infrared (EMR 750 - 6000 + nm)
Just as visible light is EMR that we can see, infrared radiation IR may be described as EMR that we can feel. IR covers a wide range of frequencies which are often split into 3 categories to help explain their characteristics. Up to 25 % of the total radiant energy emitted by HID lamps is in the IR spectrum so this is an important area for attention and understanding. Remember that a large majority of this infrared radiation is created by the arc tube casing and the lamps outer glass envelope.
Near IR (EMR 750 - 2000 nm) is high frequency IR radiation that has a lot in common with visible light. It will pass through glass like light but not quite as well and it will reflect like light but not quite as well, hence it transfers its energy (heat) to objects in the grow room with more vigour than light. The most interesting thing about Near IR is that it is readily absorbed and transported by air.
Mid IR (EMR 2000 - 3500 nm) is mid frequency IR radiation. It reflects well off shiny metal surfaces and is partially absorbed by glass but what I find most interesting is that it’s readily absorbed by water and not absorbed well by air. Note : plants are > 90% water !
Far IR (EMR 3500 - 6000 + nm) is low frequency IR radiation. It reflects very well off metal surfaces, reflects well off glass, it is absorbed by water & not absorbed well by air, but what I find most interesting is that Far IR has the power to penetrate biological and other solid / dense objects and create deep seated heat.
If God (for plants) is light, then Mid and Far IR must surely be in allegiance with the Devil !!!
Dancing with Heat,
From the above information we can conclude that HID lighting is responsible for creating most of the heat in artificially illuminated grow rooms. Further we can conclude that the majority of that heat is emitted from the HID lamps and is transmitted as infrared radiation of 3 categories, Near, Mid, & Far IR. On top of all that we have learned that poorly designed reflectors & low quality transparent heat barriers can convert light to heat, store it, reemit it, and significantly increase the total amount of Mid and Far IR in the grow room.
So how do we keep our cool, now the music is playing and the Devil is in our embrace ?
We dance.... damn it !!!
The first step and the most effective step in removing heat from the grow room is to reduce the amount of lamps per area, or to be more precise, the amount of lighting watts per area. Less watts per area gives a significant and quantifiable heat reduction, period.
Eg. 1.) If a grow room with 4 x 1000 watt lamps is modified (without changing its size) so it requires 3 x 1000 watt lamps to operate efficiently, the power consumption will be reduced by 25% and the heat production will be reduced by 25% (that’s significant).
Eg. 2.) If a grow room with 1 x 1000 watt lamp is modified (without changing its size) so it requires 1 x 600 watt lamp to operate efficiently, the power consumption will be reduced by 40% and the heat production will be reduced by 40% (that’s massive).
By the laws of physics the above examples must achieve the power and heat reductions claimed, but what if I was to suggest that yields could be maintained or even increased in those same situations ? ..... “You’d lose light intensity and therefore you’d have to forfeit some yield.” I hear you say ? .... But that’s not necessarily the case and I will explain how this can be done !
As lamps are brought closer to plants the light intensity at plant level will increaseby the square of the relative distance decrease in feet (using the inverse square law in reverse). This simply means that if you bring lights two times closer you will have 4 times the light intensity, or if you bring lights 3 times closer you will have 9 times the intensity etc.
Now if a grow light that is usually run at 4’ from plants could be run (under special circumstances) at 2’, the grower who is able to utilise the 2’position would have 4 times the light to play with. With this amount of “free light” at his disposal he could afford to use specialised reflectors and other neat devices to spread the light and heat from the lamp all around the grow room. As a result the size of the lights useable foot print could be increased by 25% to 40% or even more.
This is far more than just a theory and I have proven it to work time and time again. This is an integral part of my daily business and modern growers worldwide are constantly adopting this energy efficient & heat reducing step.
The second step is to understand and work with (short wavelength) Near IR. As stated previously, HID lamps produce significant quantities of Near IR and Near IR is readily absorbed by air. So my suggestion here would be to maintain a consistent flow of cool air around the lamp in an effort to capture most of the Near IR. This would create a plume of warmed air that could be expelled from the room via exhaust fans etc or recycled (have its heat removed) via split cycle air conditioning. The main concern here is to avoid Near IR absorption and its’ transformation into stored heat. Absorption and storage of Near IR can be avoided using the same or similar principles as outlined above in the “Dancing with Light” section.
The third step is to understand and work with (intermediate wavelength) Mid IR. You will remember that Mid IR is produced by the Lamp in reasonable quantities and also that Mid IR is created in places where light is absorbed and where energy can accumulate (Poor quality reflectors, transparent heat barriers, ducting etc). Since Mid IR is not well absorbed by air it is more difficult to remove from the grow room than Near IR. So the best way to deal with Mid IR is to avoid its production (see Dancing with Light section).
Because Mid IR is not produced by HID lamps in large quantities, the moderate amount that is emitted can be diluted or spread around the grow room evenly by reflection and other similar strategies.
If lighting systems are poorly designed and Mid IR is created and or concentrated instead of eliminated and or spread, the consequences for associated plant life can be catastrophic. Remember, Mid IR is readily absorbed by water (it’s actually attracted to water) and plants are 90% water, so my suggestion is to eliminate Mid IR creation or concentration in your grow room at any cost !
The fourth step is to understand and work with (long wavelength) Far IR. Far IR is only produced in small quantities by the lamp (from the protective glass) and is most commonly created in areas where the energies from poorly reflected and or poorly transmitted EMR frequencies are accumulated. If objects that have high density and high mass are in close proximity to HID lamps they will inevitably absorb energy from light and from the lower wave length IR emissions. Airflow past the lamp and past these high mass objects will absorb some Near IR but it will do little to stop heat accumulating from light and Mid IR absorption. Thick glass “heat barriers” and heavy low quality reflectors are definitely the major contenders for the low level, high volume, heat accumulation that produces Far IR emissions.
So again, if lighting systems are poorly designed and Far IR is created and or concentrated instead of eliminated the consequences for associated plant life can be devastating. Far IR could be described as IR’s bass frequency. It can travel long distances without losing intensity, it can travel through air without losing energy, and when it strikes something dense or with high mass (a dense layer of flowering or fruiting plants) it will penetrate deeply before its energy is dissipated and transformed to heat... The deep seated heat that is created by Far IR will not be detected by measuring room temperature (air temperature) and is the common culprit when the temperature is “pleasant” but the plants look dull, tired or heat stressed.... Again, eliminate Far IR creation or concentration in your grow room at any costs !
The fifth step is the final step and the “coup de grace”. Harness the basic principles of conduction and convection to combat the negative effects of undesirable radiation frequencies in the grow room.
Vent cool air into the grow room from below the plants and let it rise gently through the plant mass towards the lights. The Near IR that is emitted from the lamps will heat the surrounding air. That heated air will naturally rise above the lights to where it can be removed from the room via the exhaust system. This starts a convection driven air current that continually draws cool air through the plants and past the lights absorbing & removing heat by conduction as it goes..... As cool air passes through the warm plant mass it collects water vapour and cools the transpiring plants via evaporation. The water vapour there created rises past the lighting system, travelling with the air in the convection current, and is available for the absorption of Mid Infrared Radiation and Far Infrared Radiation along the way.
That’s dancing with heat, the devil has done her dash and you’ve found yourself a new friend... !
Hello fellow horticulture / floriculture freaks. This is a story about physics, about discovery, about life and about love. We love our plants & our plants love light !… Right ? This is a story about a phenomenon that you may already be familiar with, because it’s about a recent evolution………..
“In the beginning there was light”, or so we’ve been told, but what can be said for sure is that in the beginning of the indoor horticulture movement there was HID light !! 30+ years ago HID lamps were discovered by indoor gardeners and proven to be efficient precursors for photosynthesis and vigorous plant growth, however (30+ years ago) the associated reflective materials and reflector designs were comparatively backward.
In those early times H.I.D. lamps were used for street lighting or industrial lighting applications and most early model horticultural reflectors were designed by industrial engineers rather than plant enthusiasts. They were constructed from cheap and readily available materials such as white powder coated steel or anodised aluminium and bore exciting titles like “parbolic dome”, “china mans hat”, and “low bay”. I mean these things worked ok, but since when was “ok” actually any good ? You know the rules ! Give me excellence or get outa my god damned grow room….. !!!!
Ok, so all that’s ancient history.
In more modern times (lets say the nineteen nineties) more literature, more education, more discussion, and more competition between growers became commonplace and a new age of experimentation and discovery was borne. Hydroponics as a hobby and an art form was beginning its marriage with science and I was lucky enough to witness and participate in that union.
My area of specialisation was power efficiency and reflector design and I was fortunate enough to achieve some early notoriety. Anyhow it was through my work and my interest in lighting technology that I heard about a new innovation in reflective material, loosely known as “glass coated aluminium”. This stuff was rumoured to be super reflective, corrosion proof and strong. It was also difficult to procure and its cost was around 5 times that of common reflective aluminium.
It took me almost a year to source and receive my first parcel of samples. The material I was chasing was actually called “Miro coated” aluminium and when I finally set my eyes on it, I knew my efforts had been rewarded. This material wasn’t simply shinny, it sparkled like a diamond ! I remember taking a piece outside my house and reflecting the suns rays back towards my face. BANG !!! The reflected light smacked me in the retinas, hardcore, like welding flash…. I’d been taught that anodised aluminium wasn’t as reflective as it looked and that flat, polar white, white paint was the premium surface for reflectivity and diffusion etc, but this Miro coated gear was in a class of its own. I had to find out what made this stuff tick. I was in shock. All my theories had been turned upside down & I could smell a revolution.
I rang Alanod Germany, the manufacturers of “Miro”, and ended up speaking directly with the head metallurgist (Dr Petros as I recall). He informed me that the Miro coated material was quite new and that their company had recently invested the equivalent of USD$ 100 million on building a machine that could continuously miro coat industrial sized coils of aluminium sheet.
This is how the process works :-
Alanod use a multi compartmental machine (100 metres long). The first stage supports the raw aluminium coil and continuously feeds out the sheet. The second stage cleans the materials surface. The third stage is an anodising process and in the fourth stage things start to become interesting. In this stage, a layer of pure aluminium atoms is deposited onto the base metal in an electrified bath. Pure aluminium is one of the most reflective substances known to man, but if it comes into contact with oxygen it will chemically react and “lose its shine”. For this reason it’s extremely important to eliminate all traces of oxygen from this electro plating style process. “Anoxic” conditions are achieved by creating a vacuum around the bath and loading the plating solution with a high concentration of oxygen scavenging molecules.
Step 5. While remaining under vacuum, the freshly electroplated base material is fed into a large kiln containing a bed of pure silica oxide crystals. 3 x half mega watt laser guns (Buck Rogers, stand aside) blast the silica oxide until it vaporises, creating a molten steam that rises and makes contact with the continually progressing sheet above. This molten steam coats the pure Al layer and locks the super reflective atoms in an “impenetrable tomb” of liquid glass !
Step 6 is a repeat of step 5 except the silica oxide crystals are replaced with titanium oxide. The molten titanium mist rises and bonds with the molten silica layer to produce a finish coat with increased strength + improved reflection.… Alanod guarantee that the Miro coated surface of their material will not corrode, tarnish, crack, or loose reflectivity, even after 25 years of indoor grow room use !!!
Step 7. The miro coated material rolls back into a neat coil at the other end….
The above process can only be performed using perfectly flat sheets of aluminium base material because it would be near impossible to create a vacuum seal along the edge of the moving material if the surface was textured. That’s all well and good and makes technical sense but here’s what I find interesting. The miro coating is tuff enough to allow any typical surface pattern to be hammer rolled etc onto the finished sheet without causing any damage to the reflective surface !!! That’s tuff and what this proves is the miro “surface coat” is much more than just a “surface coat”. The molecules of the base material, the pure Al layer, the silica layer, and the titanium layer have mingled and fused into a complex molecular fabric, inseparable from each other… That’s some seriously cool technology and I’m still gob smacked just thinkin about it !
Ok, so I choose some miro material of the correct hardness and thickness, with a nicely diffusive surface pattern, and proceed to make some prototype reflectors.
Those prototype reflectors performed 20% better than anything that I had built before. I used the same designs, the same dimensions and just changed the material. My previous models were made using flat finish, bright white colour bonded steel. The reflectivity of that material was supposed to be 80 to 85%. So an immediate question arose. How in the hell could a 10 - 15% increase in light output create a 20% yield increase ? That’s better than 100% efficiency and that’s not supposed to be possible in this universe !
Anyway who was I to complain ? My company started making reflectors out of the Miro material and selling them at almost twice the price of the white ones. The white reflectors worked great but when the Miro arrived and the growers got them in their hands they never looked back. To this day, sales of our Miro coated Avenger Wings and Super Spreaders are increasing monthly and keeping up with the escalating demand is still a major concern.
Theoretically, increasing reflected light by 15% should increase yield by around 5 – 10% (not 20%) and it’s taken me years to get a handle on what might be going on. The theories that I’ve derived to explain this phenomenon involve a couple of complimentary factors….. The first and most obvious is that aluminium is 60% lighter than steel and is a better conductor of heat. Hence, more light + less heat gives an improved yield, (not by 20 % though) maybe 12% by this point. However if we take my 2nd and more unorthodox postulation into account, we may just come up with a suitable solution.
I mentioned earlier on that the Miro coated aluminium sparkled like a diamond ? ? When you pay close attention to this phenomenon that diamond-like sparkle is created by the prismatic effect of light passing through the titanium - silica (glass) layer and being refracted. i.e.) mixed spectrum “white light” goes in and bands of (refracted) coloured light come out ! Just like a rainbow ? ….. Rainbows are made of water droplets….. water droplets also refract light….. Think water droplets on plants and in the air, all refracting light… Think naturally stimulated plants with their stomata wide open, basking in a sun shower on a warm summers day…. I think that just about explains it….. bio stimulation through increased levels of refracted light….. Can you dig it !!!???
Now days most companies that are serious about producing horticultural lighting reflectors have bitten the $ bullet and include high performance models amongst their reflector range and almost all of those high output machines depend on the unparalleled reflective qualities of Miro coated aluminium !
Brothers & sisters, the age of the Super Reflectors is upon us……………