I know water cooling grow lights is an esoteric concept, as just about every other company in the world only makes lights that are air cooled. I decided to write a bit on this topic to help explain liquid cooling grow lights and why and when you may want to do it instead of air cooling.
First, let me give you a little background about me and my adventures with water cooling grow lights – this is definitely not a new concept for me, I purchased my first water cooled HPS grow light system back in the late 90’s when I first started experimenting with growing plants under artificial lights. So, have lots of years messing around with various systems and methods. Still, even today, there are some water cooled HPS and Metal Halide systems around.
Why water is MUCH better vs air as a heat conductor & coolant
As you can see from this simple and fun experiment – (that you can try yourself!) water does a much better job than does air. This demonstration proves it quite simply.
Why is water that much better than air for cooling HPS & LED grow lights?
This involves a little physics, so please try to follow along:
1 – Specific Density of water and air at 20° C:
Water density is 998.2071 kg/m^3
Air density is 1.204 kg/m^3
This means that water is about 829 times denser than air.
2 – Heat capacity of water and air (J/°C g):
Water heat capacity – 4.18
Air heat capacity – 1.01
This means that per gram, water has about 4 times more heat capacity than air.
3 – Putting it all together now:
Since at normal atmosphere air takes up 829 times more volume and has about 4 times less heat capacity we can figure out how much of each we would need to cool a light:
For simplicity’s sake let’s assume that it takes you 100 CFM (cubic feet per minute) to cool your light by 10° F. How much water would you need to achieve the same thing?
We know that air takes up 829 times more volume and has about 4 times less heat capacity so, the math is 829 x 4 = 3,316 times more air needed than water.
Then let’s divide the 100 CFM Air by 3,316 to get water CFM needed.
The results: you would need 100 CFM of air vs 0.03 CFM of water to get the same 10° F cooling effect. In water speak that would be 0.224 GPM (gallons per minute).
That’s 3,316 times LESS water volume vs air to accomplish the same cooling task! Insane, right?
Now you can see why WATER is SO MUCH BETTER for cooling grow lights or just about anything than is AIR and hopefully realize why we made sure to have a water cooling option in our LED grow lights!
Main methods of water/liquid cooling HPS grow lights in use today:
1 – Using air/water heat exchangers to cool hot air exhaust from grow light hoods (Liquid-to-Air Heat Exchangers)
Method 1 works pretty well but is not a true water cooling system as it still uses air as the main heat mover, so this is more of a hybrid air/water cooling system, with double the complexity of either single system alone.
This company has a very informative video, demonstrating one of these setups and explaining how it works, as well as discussing some of the benefits of using such systems for grow light applications. This video can be viewed below:
2 – Water-cooling the HPS grow light bulb directly (Liquid Cooling Systems)
Method 2 is a true water cooling method, as it’s only using the liquid for heat transfer. Unfortunately, this method is very tricky to make work reliably and safely just about every water cooled hps grow light product that comes to market is soon discontinued due to the factors mentioned.
Esoteric nature of water or liquid cooling grow lights
Water/liquid cooling of HPS or LED grow lights is just not that well known or understood by most commercial growers. The majority just don’t know how to make it all work or are afraid of trying something different so the products never sell very well. Though some hardcore water cooling enthusiasts out there still do manage to find these products or make their own DIY water & liquid cooled grow lights because they understand the advantages of liquid cooling grow lights.
Note: This page is a work in progress, I will add more material as time allows so please be patient and do check back often…
For now, here is some general information on some water/liquid cooling methods:
Liquid-to-Air Heat Exchangers
Commonly known as Chilled Water Systems, help to reduce unwanted heat in various applications. Just as their name implies, these systems use a combination of liquid and air to provide heat management.
In a typical Chilled Water System, hot air will enter the system from the process and pass over a network of cooling channels. These channels usually consist of tubes and/ or cooling fins made up of highly conductive material, such as copper. As cool liquid (either water or some type of specialized coolant) flows through these channels, some of the heat from the incoming air is transferred to this fluid. The result is that the air flowing over the cooling channels can exit the system with less heat than when it entered.
This fundamental process is illustrated in the diagram below.
However, because the cool liquid picked up heat from the incoming air, it must now pass on through a separate part of the system, where it is cooled back down and recirculated through the system to continue cooling the hot incoming air.
This is where the chiller comes into play. A chiller is a part of the overall Chilled Water System that removes heat from the warm liquid after it leaves the exchanger, as previously described. The chiller operates on a heat-exchanging process of its own.
Most chillers are made up of two primary sections, or “cycles”- a fluid cycle, and a refrigeration cycle. The warm liquid coming into the chiller passes first through the fluid cycle and then continues to the refrigeration cycle. Finally, a condenser is used to expel the heat; there are air-cooled and water-cooled variations of this device, depending on the application.
This process involving the chiller is illustrated in the diagram below.
The liquid leaving the chiller is now cooler than when it entered. Thus, this liquid can be recirculated through the rest of the system, to continue absorbing heat from the incoming hot air.
As you can see, this process represents a Closed-Loop Cooling Circuit, since the cooling fluid and the air being cooled never directly contact one another. This form of heat management is very common for various procedures.
For standard High-Pressure Sodium (HPS) grow light applications, these types of systems are typically installed inside the Grow Room, and help to eliminate the need for a larger A/C system. Usually, a fan is attached to a duct network and used to draw in the room’s ambient air; this air will flow by the Light Reflector, absorbing heat generated by lighting. On the exit-side of the reflector duct, compact Liquid-to-Air Heat-Exchangers can be installed and used to efficiently remove the heat from this air as it passes.
An example of one of these common systems, offered by Hydro Innovations, is illustrated in the diagram below.
As it pertains to grow light applications, these Liquid-to-Air style heat management systems offer affordable and effective heat management solutions. However, opinions tend to vary about the value of these systems compared to other available methods. As such, some of the advantages and disadvantages associated with these systems will be discussed below.
These systems typically offer a more energy-efficient option than larger A/C systems, which may prove to be overkill for certain grow light applications. For reasonably sized operations, these systems offer a sufficient means of heat management without the high electricity demands.
Due to their ability to cut down on overall power requirements, and their usage of relatively inexpensive components, these systems tend to be more cost-friendly than more traditional air conditioning options.
Since these types of systems depend on both air and liquid components to operate effectively, they can potentially lead to more complexity, regarding setup and maintenance. This may lead some to pursue a more basic approach, such as simple air-only cooling techniques.
Considering the robustness of these systems, mobility can be a challenge. For those who are frequently changing locations or shifting setups, these systems may require significant time and effort to reconfigure.
Overall, for those who don’t mind the added complexity, Liquid-to-Air cooling systems offer a reasonably effective and affordable means of heat management for grow light applications.
Liquid Cooling Systems
As opposed to the Liquid-to-Air Cooling Systems previously described, many liquid-only options exist for heat management. Commonly referred to as Liquid Cooling Systems, or Water Cooling Systems, these devices eliminate the need for forced-air to remove heat from the process.
In a typical Liquid Cooling System, a pump is used to send water through some form of a piping network (typically made up of highly conductive materials, such as aluminum or copper), where it absorbs heat created from the process. After absorbing this heat, the water will then pass into a dedicated chiller or some other type of heat exchanger, which helps to cool the water back down so that it can be re-circulated through the system.
The fundamentals of this process are illustrated in the diagram below.
For many grow light applications, systems like these can be even further simplified by removing components not necessarily needed, such as the chiller unit. A common alternative would be to use a simple reservoir, which can often be sufficient for collecting and cooling the water down after it absorbs heat from the lighting source.
As with the numerous other heat management options, Liquid Cooling solutions present underlying advantages and disadvantages. Some of these prevalent factors are presented below.
Liquid Cooling setups are generally simple in nature; they consist of only a few different components and are relatively easy to install. This is appealing to those who prefer to avoid the complicated and potentially pricey systems which require many more working parts.
Due to the elimination of fans, Liquid Cooling systems are typically space-savers. By closely integrating the water with the light source itself, these setups are typically rather condensed, compared to larger systems that involve bulky air-cooling equipment. This is especially attractive for operations that are space-constrained.
Largely considered the biggest drawback to Liquid Cooling systems, maintenance is a continuous effort with these setups. The liquid in motion often results in frequent complications with equipment. Pumps tend to fail pre-maturely, and water seals are known to be temperamental. Issues like these can lead to considerable upkeep, which is what often deters many people from relying upon these types of systems.
One of the most obvious caveats associated with using water as a means of cooling electronics is safety concerns. Systems like these often face problems with leaks, which not only runs the risk of permanently damaging lighting equipment but can also potentially cause severe harm to personnel. This is another factor that is worth considering when evaluating Liquid Cooling options.
Considering these factors, if the safety and reliability challenges are effectively addressed, these Liquid Cooling Systems can prove to be an ideal setup for various grow light applications.
In Summary: After discussing some of the fundamental concepts of heat management, and exploring some common solutions that exist for grow light applications, one can see that there are numerous options to be employed for a wide range of setups. Despite each of these methods having its own benefits and drawbacks, every application is unique in its own way, so it’s important to evaluate your own needs in order to determine a solution that works best for your operation.