FEATURE CASES & ENCLOSURES The cabinets’ internal rear walls
are fitted with a high efficiency heat exchanger (Figure 3), comprising one or more aluminium cooling plates and stainless steel coolant pipes. Heat dissipated by the equipment in the cabinets is absorbed by the water and transferred to the vessel’s main water cooling system, from where it is dissipated to the environment. In this application, the power dissipation of the cabinets range from 140 to 900W. Intertec has also used the same technique but with underground water – to cool electronics systems sited in mainland Europe. One further extension of this concept is the use of a water chiller mounted externally to the cabinet or shelter to augment performance. This is explained later.
ADVANTAGES OF HYBRIDISATION There can be a number of advantages to system building with semi-passive cooling. The size of semi-passive shelters – compared to pure passive systems which require a large water tank – can be reduced significantly. In addition, the use of liquid cooling means that conductive heat transfer can be employed, which is much more efficient than convection cooling. Unlike conventional HVAC, no air
ducts are required, providing protection against dust and sand ingress - which can be a major issue in some environments. In addition, HVAC systems will often also need to be explosion proof, raising costs substantially. However, the semi-passive or passive
cooled cabinet or shelter requires little or no electrical power of its own and is virtually maintenance-free, making it ideal for long life-cycle applications.
Figure 2.
A semi-passively cooled shelter for a remote wellhead
Semi passive cooling also opens up Figure 3.
Cool water from the ocean provides cooling for these analyser and instrumentation cabinets on an offshore vessel in an equatorial region
the possibility of providing ultra-reliable cooling strategies for critical equipment. A current example that Intertec is involved with is the cooling of cabinets that house critical PLC-based control functions at a refinery. In this application, there is usually plenty of electrical power available, but the client needs more than one layer of protection redundancy against power loss – as a system failure could shut down the entire process. So, three separate strands of cooling are provided. In normal operation, when power is available, an electrically powered chiller feeds cool water into the cabinet’s internal heat exchanger-based passive cooler (the PLCs are cooled by an efficient conductive plate, which is connected directly to the aluminium PLC enclosure). If the chiller should fail for any reason, there is also an electrically powered air conditioning unit that will switch on. If both should fail, the passive cooling system retains enough capacity to keep the cabinets cool for several days, allowing plenty of time for repairs to take place.
THE TREND TOWARDS RIES The need for such high reliability is increasing substantially. More and more control and instrumentation systems are being sited deep inside processing plants, much closer to the process – eliminating a lot of the cabling and marshalling style cabinets previously used. Such remote instrument enclosure (RIE) installations are often then connected using fibre optics to the control system, and they need to be ultra reliable. The protection challenges here for the enclosure provider can include dealing with corrosive
14 NOVEMBER 2016 | INSTRUMENTATION
atmospheres and media, blast and fire protection, and cooling in hazardous areas, among others. Composite GRP-based cabinets and
shelters are ideal for this purpose. GRP offers exceptional resistance to corrosion – as it does not rust or degrade in any meaningful way. Intertec has developed many additional processes to extend GRP’s natural protective advantages, by combining special grades of high-quality GRP with composite layers to achieve extra degrees of protection. The most commonly specified forms provide embedded insulation to optimise energy consumption and the efficiency of heating or cooling, anti- static properties, and protection against ultraviolet exposure and abrasion. But this technique can also be used to provide fire safety. The intrinsic flexibility of GRP also makes it simple to design cabinets and shelters with the appropriate resistance to blasts, which can handle forces up to 1200 mbar or more. An example of this is RIE shelters
produced to house the automatic emergency shutdown and fire suppression systems on offshore gas production platforms. The shelters’ basic GRP construction protects against corrosion. The key protection capability however is an extremely high degree of fire resistance that will maintain internal temperatures below 60˚C for up to two hours – even in the presence of a high temperature hydrocarbon fire. This protection is provided by novel composite layered construction combining GRP sheets and mineral wool insulation. The lightweight shelters are also blast resistant.
Intertec Instrumentation
www.intertec.info
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