Designing effective climate control systems
01 August 2015
The internal environment of an enclosure needs to be managed; moisture and condensation levels must be closely controlled while maintaining the interior temperature within a few degrees, as Christian Westwood explains.
To consider an enclosure as merely a metal box is like calling a house simply four walls and a roof. Both are correct but neither come close to describing the complexity of their fully integrated systems and processes without which neither would function effectively. The manufacturing automation systems that enclosures are designed to protect are obviously delicate and very expensive pieces of kit which perform vital functions for the businesses they serve.
And just like buildings, enclosures need close management of their internal environments. Without this management capability, a business may be running serious risks of systems failure and losses associated with replacement equipment, not to mention the effects of downtime on productivity. The cost of a climate control system needs to be weighed against the costs of such eventualities. Adopting a whole-life costing approach to installing cooling units should be considered best practice by facilities managers and panel builders alike.
Like all electrical equipment, a drive creates heat. If we assume an efficiency of 97 percent, a drive with a rated output of 150kW can produce as much as 4.5kW of heat, much - possibly even all - of which will be trapped within the enclosure.
There is also the issue of the ambient temperature within a production facility, which will also have an impact on the temperature inside a panel. The external air temperature may vary seasonally and, as global warming takes a firmer grip, we will almost certainly see these seasonal temperatures rise year on year – a factor that now needs to be taken into consideration for long-term planning.
A typical operating ambient temperature for electrical equipment is 35°C; any higher, then heat is not being effectively dissipated, the system will be running hotter than it should and its service life will be shortened.
The design of an enclosure plays an important role in climate control, not least the extent to which an enclosure has been sealed to keep contaminants such as dust and water away from its contents. An enclosure with an ingress protection category rating of IP67, for example, is important on two levels.
First, where dust can’t get in, heat cannot get out – at least not without help. So you must employ some form of climate control. Second, an IP67 rating indicates that equipment contained within the enclosure is likely to be in a dusty environment, which then gives a steer as to what type of equipment might be needed to cool it. Fan-and-filter units would not be suitable in this instance as they will inevitably draw dust into the enclosure.
On the flip-side, a sealed enclosure will stop cooled air escaping, which minimises energy wastage, while the level of condensate produced by any cooling system will also be kept to a minimum.
Better by design
The process of designing an enclosure and its best-fit climate control system has been made far simpler with the help of software based tools such as computational fluid dynamics (CFD). CFD can assess the cooling requirements of proposed enclosures while providing visualisation of the thermal performance of functioning electrical enclosures. Other software tools (Rittal’s Therm, for example)can help you choose the most appropriate and correctly sized climate control equipment, and remove the need for laborious calculations.
A well-designed cooling system will reduce a customer’s operating costs while increasing the life expectancy of equipment contained within an enclosure; it may even boost its performance. But beware over-sizing the cooling unit, this is not only energy inefficient, but can also result in an increased number of switching cycles for the compressor, reducing its service life.
Regular cleaning and maintenance of the cooling system is vital in order to maintain airflows and (if a condensate drain is not installed), to remove any collected condensate before it overflows. These jobs can be both time-consuming and expensive but there are some novel solutions available that can help, including coating the condenser coil (reducing the tendency for dust to accumulate on its surfaces) and electronically controlled evaporation of condensate (converting it into water vapour which can be removed by an external fan).
In fan-and-filter units, using diagonal fan technology increases energy efficiency and ensures a more constant airflow, thereby reducing the occurrence of ‘hot spots’ within an enclosure. You might also consider installing some of latest compressors and electronically commutated (EC) fans, while not forgetting the optimum arrangement of heat exchangers and ensuring you have an optimised refrigerant volume. Energy efficient cooling units (Rittal’s TopTherm Blue e, for example) employ these technologies and are able to achieve energy savings of up to 45 percent.
If there is a need for cooling elsewhere in the system – in a process coolant, for example - it may be more economical to consider combining air/water heat exchangers with a remote chiller unit, which can chill the coolant as well. The heat can be effectively removed and dissipated externally, using ‘free’ cooling (the outside ambient air temperature) to cool the heated water by means of a separate condenser along with the existing fans and pumps that are integrated into the chilled water circuit.
Christian Westwood is product manager, Climate, at Rittal
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