Middle East instrument shelter uses passive cooling 21 January 2014

One of the largest passively-cooled instrumentation shelters ever built is being supplied by Intertec to house control and instrumentation equipment for a new natural gas collection project in the Middle East.

Without an external power source, the system reduces interior temperatures by some 20 C in the shelter, which has a volume of 142m3, housoing a PLC, computer network, power inverters, rechargeable batteries and a controller for an external photovoltaic generator.

Intertec is supplying three shelters in all – two with active cooling were delivered at the close of last year, while the third is currently nearing completion.

The shelters were designed to protect SCADA (supervisory control and data acquisition) systems, comprising RTUs (remote terminal units), telemetry equipment and electronics for the new gas pipeline, currently being constructed on the coast of the Persian Gulf.

Environmental conditions at the site are severe, with corrosive salt and chlorine, due to the coastal location, as well as sulphur from the natural gas. Further, during the summer, UV levels are very high and daytime temperatures reach 55 C in the shade.

Intertec constructed all three shelters using 85 mm thick walls are employed – with 4 mm inner and outer skins of GRP sheeting sandwiching a 77 mm layer of insulating foam.

The passively-cooled shelter harnesses thermo-siphoning technology using water – cooled and heated by day and night temperatures in an 8,000 litre thermally stratified water tank. This is connected to two closed-loop thermo-siphon systems, formed by internal wall-mounted and external roof-mounted heat exchangers.

Water circulates by natural convection entirely automatically, without pumping assistance, providing adequate cooling to accommodate the maximum power dissipation of all equipment in the shelter – amounting to 1,080 watts under worst-case conditions.

An Intertec spokesperson explains that passive cooling was required, because connection to an electricity grid was not possible at this remote location. All instrumentation power is derived from inverters, fed by batteries recharged by a photovoltaic generator, but there was insufficient capacity to provide for active cooling.

The other two instrumentation shelters are sited near to the grid so use active cooling i the form of custom-built 3kW air conditioning systems.

A corrosion-resistant external heat exchanger was also developed for this application, while a further design challenge involved creating a cooling system based on a CFC-free refrigerant that could work efficiently in the very high temperatures.

At present, much of the gas from oilfields in this part of the world is burnt off as waste at the point of extraction.

This project is designed to improve resource management by collecting and using the gas to power seawater desalination plants that are currently fuelled by oil.

Brian Tinham

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