Convective H2 Vent

Passive Hydrogen Ventilation Systems-(Available exclusively with Cool Cell™)*

Without proper ventilation, an outdoor battery enclosure can accumulate  explosive concentrations of hydrogen. The explosive power of hydrogen  rich air can blow out the doors, walls, and roof of an enclosure. No  company that deploys outdoor battery enclosures in public places can  afford to ignore the risk of inadequate hydrogen ventilation. 

Thermal Runaway

Batteries in enclosures can go into thermal runaway, which very  rapidly produces hydrogen, whenever several conditions are  simultaneously present.

  1. The batteries are exposed to high temperatures inside the enclosure  (above 100 deg. F) for a sustained period, either because the enclosure  is unprotected, or because the cooling system is inadequate or has  failed.
  2. The batteries continue to be charged at high voltage and current  because there is no temperature compensation in the battery charging  circuit, or because said circuit has failed.
  3. Batteries have aged and become dehydrated

Solar heat loading will cause the internal temperature of a thermally  unprotected enclosure to go above 100 deg. F in most of the country  during much of the year. According to Bellcore, internal enclosure  temperatures will increase to between 21 deg. F and 27 deg. F above the  external daily high temperature, depending on the U. S. location. Thus,  if the external daily high temperature reaches only 80 deg. F, then the  internal temperature of an unprotected enclosure will surely rise above  100 deg. F, setting the stage for thermal runaway. 

Temperature compensation in battery charging circuits is a relatively  new technology. Where it has been utilized, it has proven to be  generally effective, but, as with any system subjected to environmental  extremes, not completely reliable. And, in most cases, a potential  failure is not easily detectable until it has already occurred. Although  thermal runaway remains relatively rare, it occurs with sufficient  regularity to be of grave concern.

Once thermal runaway has begun, hydrogen can accumulate in an  unventilated enclosure to a concentration above the lower explosive  limit (4%) in as little as 35 minutes. While the explosive effect of  such a concentration is small, if hydrogen continues to be released, it  can accumulate to far more dangerous levels over just a few hours. The  concentration can keep rising to the point that ignition will completely  destroy the enclosure and its contents (above 10%). Given the large  number of enclosures in populated areas, the potential for collateral  damage to people and property is unacceptable.

High and low vents are unreliable and hazardous. One expects them to  expel lighter hydrogen rich air through the high vent while fresh air  flows in through the low vent. This will only take place when the  hydrogen rich air is as warm or warmer than the outside air. When the  hydrogen rich air is colder than the outside air, the flow is stifled  and the hydrogen can easily reach explosive concentrations. High and low  vents also admit hot air during hot weather and cold air during cold  weather, eliminating the advantage of an insulated battery enclosure.

The Cool Cell™ Solution


All Cool Cell™ passive temperature regulating battery enclosures are  fitted with one of two patented methods of hydrogen ventilation. These  are the Convection H2 Vent™ (U.S. Patent No. 5660587) and the Diffusion  H2 Vent™ (U.S. Patent No. 5603656).

Generally, the Convection H2 Vent™ is used in applications where  multiple strings of batteries are housed in the Cool Cell™, providing  the potential for a rapid accumulation of a large amount of hydrogen.  The Diffusion H2 Vent™ is installed in Cool Cells™ designed for fewer,  smaller batteries.

Like the Cool Cell™ itself, both H2 Vents™ are completely passive  devices. There are no sensors, fans, or other electrical or moving  parts. Both H2 Vents™ are virtually failure proof, a critical  specification in this application.