The rollout of Controlled Humidity Environment (CHE) and Battery Management System (BMS) is underway in the UK, Germany and at BATUS in Canada, but what does it really mean and how is it helping the British Army?
In April 200I, the British Army made the decision to start a pilot CHE and BMS scheme in the UK and Germany. The Germany location was originally an old NATO site with, 28 storage sheds that had all been fitted with CHE or 'dry air' systems. The basic concept behind CHE is that dehumidified (dry) air is circulated throughout a closed environment, such as storage sheds, and allowed to circulate both inside and outside of all of the equipment stored there.
So how does this help the Equipment and why is a controlled humidity environment so important?
Moisture in the air, or the relative humidity, has an enormously bad effect on all types of military equipment, even over short periods of time. Corrosion can set in extremely quickly and reach very high levels on a wide range of materials and components, including mild and armoured steel, aluminium, tyre rubber, Perspex and leather to mention but a few.
Moisture doesn't just effect corrosion rates of materials exposed to the elements; it also causes electronic failures, because the wiring or gold plated contacts have been corroded. Even hermetically sealed parts can be affected by moisture and it is estimated that over 20 per cent of electronic failures are caused by moisture-induced corrosion. Another by product of high relative humidity is mould growth. This is a major issue for the inside of vehicles and even a slight increase in relative humidity can dramatically increase growth rates of mould.
It is easy to see that a combination of these problems will lead to major problems with the operational readiness of vehicles and equipment. Instead of vehicles being able to be deployed at short notice many will need time consuming servicing and repairs which places a huge burden on units, both in man hours required to achieve the job and financially in terms of the replacement parts.
So with a compelling case for CHE it was decided to convert some existing storage hangars at DSDA Ashchurch (UK) and Ayrshire Barracks (Germany) into CHE facilities and provide a controlled humidity environment for long term storage of surplus unit vehicles. Each hangar has a series of dehumidifying machines that extract moisture from the air and keep the air at a constant 45-50 per cent relative humidity. This is the optimum level to store vehicles and it provides the biggest bandwidth of protection for all the different types of materials.
At Ashchurch the whole system is managed by computers on site. There are six probes situated in the roof of each of the hangars monitoring the humidity 24 hours a day seven days a week. The probes provide data to the computers and the computers automatically adjust the dehumidifiers. So if there is a sudden rise in the relative humidity due to a change in the outside weather it is picked up instantly and adjustments are made automatically.
The dehumidifier is actually based on a Desiccant Wheel Dryer. The air in the hangar is drawn in and passes through a slowly rotating drying wheel. The dry air then leaves the dehumidifier and is released back into the hangar and the wet air leaves via ducting to the outside and is released back in to the atmosphere. The units are very easy to install, can operate in very cold or very hot conditions and can process up to 9000m3 of air an hour.
This article first appeared in the Journal of Royal Electrical and Mechanical Engineers - 'The Craftsman' - March 2005
