Proper Hydrogen Venting - Avoiding Dangerous Hydrogen Gas Buildup with a Simple H2 (Hydrogen Gas) Vent
Unfortunately for those who disagree, physics is not only a good idea, but it represents the laws that govern the world as we know it. Using these principles and a little rational thought it is easy to discover the common mistakes made by many as they develop and install the venting systems for their battery boxes.
First off lets look at the gas we are trying to ventilate, Hydrogen. Hydrogen is generally lighter than air as it has a molecular weight less than that of oxygen, nitrogen, and carbon. Therefore, as long as there are no currents (winds) in the area, hydrogen will rise to the highest point in an enclosure. Conservation of mass rules in physics also tell us that if one thing leaves, something else must take it's place. This brings us to the first couple rules for venting hydrogen.
Vents must go up. - No matter how you try, you will not successfully vent hydrogen through the bottom of a box.
Intake and Output tubes. - One vent tube should vent the hydrogen upwards, the other shall bring in fresh air to the bottom of the box or enclosure.
The final rule is a bit more difficult.
Remove thermal differences in vent pipes to retard hot and cold air movement. AKA heatsinks, thermal syncing
DO NOT VENT BATTERY GASES IN THIS MANNER
The 3 major types of venting that are used for most HVAC installs are pictured above. Each is VERY WRONG when it comes to Hydrogen venting. These venting systems are borrowed from the heating and ventilation community where thermal (temperature) differences called the "Stack Effect," which drive hot air up and cold air down to provide ventilation. Lets say for instance, that it is 90° outside and we have the AC on. Indoors the temperature is roughly 75°. If our battery box is inside, below the vents, with a lower temperature, than the hot air outside will want to rise, not fall, and therefore, if one was to look at the graphic above, it is easy to see how a colder battery box will at least retard, if not reverse or stop the flow of ventilating air, creating the red hydrogen pockets. The fan driven system is prone to both mechanical failures and power outages. The other demerit for fan driven systems are the sparks that can originate from the drive motor, leading to separate and catastropic events.
To remove the thermal air currents present in a battery box venting system, you must create a natural heat sink between the vent tubes to neutralize the difference in temperature. This in turn will stagnate the air, allowing the hydrogen which is lighter than air, to rise and escape the battery box. Make sure the smaller tube, the one inside, extends to the bottom of the box. This will allow "heavier" fresh air to fall to the floor of the box and retard hydrogen entry. The intake for the hydrogen is at the top of the box, the exterior tube in the system. Hydrogen will travel in the opposite direction through the larger outer pipe as it is lighter than the air surrounding it. Several good methods for constructing this vent system exist, we particularly like to see 1/2 inch copper pipes inside 1 inch pipe. Any highly conductive metal pipe will work it will transfer heat quickly. Galvanized, steel, and other pipes that spark when rubbed aren't as great. DO NOT USE THESE IN EARTHQUAKE ZONES.
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