AIR CONDITIONING
Keeping chillers tip- top in the new normal
Seasonal air conditioning chiller maintenance programs were impacted by the recent working restrictions, resulting in problems for some end users. Marc White of Carrier Rental Systems highlights good basic housekeeping to ensure systems keep running in the new normal.
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uilding closures and working restrictions in the early part of this year resulted in a reduction in service and maintenance activity. It was a particular issue
in relation to air conditioning chillers, which, like motor vehicles, require regular servicing to maintain their efficiency and performance. We are now seeing the effects of this in chiller problems
and breakdowns. From our own perspective, this has resulted in emergency call-outs for temporary hire equipment to provide essential cooling for buildings and industrial processes as they come on stream again, while fixed plant is repaired or, in extreme cases, replaced. The timing of the restrictions, during Spring and early summer, was a significant contributory factor. Service and maintenance programs normally take place in the cooler seasons, to ensure equipment is in good working order when called on to perform at high capacity in the peak summer months. With work on site restricted, in many cases essential pre-
season checks and maintenance could not be carried out. By the time restrictions were eased some three months later, the summer season was upon us. As buildings such as shops, offices, car showrooms and leisure centres reopened, chillers were being called on immediately to perform at peak capacity. The impact on un-serviced equipment is often to exacerbate any incipient issues or faults that would otherwise have been identified and dealt with as part of routine maintenance, with inevitable consequences. We are all learning how to operate in the new normal,
and this is one of those areas with important lessons for the future. It is therefore useful to take stock and remind ourselves of essential housekeeping measures to keep chiller plant in good condition in the event of it needing to be stood-down at short notice, to ensure a smooth and effective return to operation when called on. Despite the availability of remote monitoring, the
fundamentals of chiller maintenance on site have not changed much in recent years. Whichever chiller technology is employed, there are some key elements to any practical
32 September 2020
maintenance programme. Keeping equipment clean is one of those basic tasks that is relatively easy to do, but which can have potentially serious consequences if not done properly or regularly. Chiller performance and efficiency depend on effective heat transfer. Condenser coils clogged with mould, dirt or debris do not operate effectively, and can put stress on the rest of the system, including compressors. Compromised heat exchangers impact chiller performance in two main ways – by reducing air flow through the condenser and by limiting heat exchange between the metal of the coil and ambient air. Simple mechanical clogging can have a big impact on efficiency. The rule of thumb is that a 20% reduction in airflow results in a 10per cent loss in efficiency.
Removing debris that has built up during the winter can dramatically improve chiller operation, in the process taking the pressure of compressors and ensuring a longer life and fewer breakdowns. Cleaning should include mechanical removal of material fouling heat exchange surfaces, and, if appropriate, chemical cleaning of scale build-up within pipework and the system itself. Chiller manufacturers often recommend annual cleaning of condenser pipework, and cleaning of evaporator tubes once every three years. A related hygiene issue is the cleaning of strainers. These can easily become obstructed due to a build-up of suspended contaminants, resulting in blocked pipes and possible pump failure, with all the consequent problems this can lead to. To avoid this, strainers should be inspected and cleaned regularly.
A key indicator of a problem in this area is a pressure
drop. However, some maintenance programs require strainers to be cleaned at least once every three months, irrespective of pressure drop. This protects the chiller against erosion caused by small particles travelling at high speed in chiller pipework, which in extreme cases can lead to total failure. As with motor vehicles, it is essential to protect chillers against ambient frost in the event of a cold snap. Below freezing, chilled water systems can freeze up, in the process
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