03 October 2023
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Dave Palmer, general manager for the UK at ICS Cool Energy, looks at the steps needed to prepare temperature control equipment for winter.
In today’s competitive business, minimising operating cost and mitigating risk while keeping focused on energy efficiency and delivering the temperature control a business needs to keep running and succeed is important.
Experienced plant and facility managers know that deferring regular maintenance to save money in the near term is a poor practice and will likely cost the organisation more in the long term. Delaying the maintenance of complex process cooling applications places crucial assets at risk for more extensive damages and costlier repairs in the future. Decreased system life, decreased reliability, increased failure rates, and increased downtime are typical byproducts of deferring maintenance to later dates.
In this article we want to address the steps needed to prepare your temperature control equipment for the inevitable winter, but a good practice that helps maximise investment is to have a proactive maintenance plan customised to the process needs and all times of the year. A combination of regular and preventive maintenance helps optimise system performance and reliability throughout the year and throughout the lifecycle of the equipment.
Getting ready for winter
It may seem that during winter, the demands on the chiller plant system are lower, but the production in industrial applications hardly ever stops and cold weather can create added pressures on the equipment situated outside.
Autumn is the perfect time for a thorough review of the system and to apply the right proactive maintenance measures to avoid costly interruptions or downtime when temperatures drop significantly and things go wrong. In-depth reviews of your systems will also allow you to consider technologies and ways in which your system could be enhanced to reduce operating costs and increase performance.
Let’s look at some of the elements that need to be addressed when preparing for winter.
Water treatment, glycol dosage, its quantity and quality
Cooling systems depend on the fluid circulating within the equipment. A water treatment plan is essential for the longevity, efficiency and reliability of the process equipment.
In winter, glycol, or anti-freeze is important to lower the freezing point in the application of the chilling system and prevent the fluid inside the system from freezing. However, it’s not merely about adding glycol. Utilising the correct glycol concentration is essential, but it’s quality matters just as much. It goes without saying never to use automotive antifreeze, as it is formulated for engine cooling and can cause problems with flow rates/ pressures and reduced heat transfer.
Uninhibited glycol and water mixtures are very corrosive, hence inhibited type plays a crucial role in ensuring the fluid in your system doesn’t freeze and the pipework doesn’t corrode. Inhibitors protect against corrosion, scale and rust and act as a pH buffer and a biocide. It’s best never to use less than 25% Glycol, which will ensure that an adequate quantity of inhibitors is present and protect you from the winter freeze. Going below this threshold makes it a feeding ground for bacteria.
It’s also important not to mix different types of glycol or different brands. Incompatibilities can lead to formula separation which clogs filters, strainers and pump suctions as well as reducing its transfer properties. Over-mixing can also cause problems so it’s best to use only the glycol concentration necessary to protect the equipment.
Adding just glycol to a system isn’t enough when it comes to treating your water. The chilled water system must be flushed, cleaned and sanitised prior to adding a new water/glycol solution.
Selection of the appropriate water treatment also isn’t a once-size-fits-all matter. While there are universal products available in the marketplace, it would be beneficial to have a fluid analysis carried out on any hydraulic circuit prior to the administration of glycol/antifreeze. It is equally important to ensure the fluid is checked regularly. The water/glycol solution must be regularly sampled and tested to ensure there are no underlying or progressive contamination and/or corrosion issues arising.
Adiabatic systems – protection first
If your system is equipped with dry air coolers or adiabatic coolers, they have unique requirements. They are a cost-effective and environmentally friendly alternative to a cooling tower. Providing significant savings on water usage, they require significantly less maintenance and operational costs and no ongoing chemical treatment or registration with local authorities, while operating at optimal efficiency in high ambient temperatures.
Given their operational nature, adiabatic systems can be vulnerable in winters. In winter, the glycol level must align with the predicted lowest ambient temperatures. In case there is no glycol/antifreeze in the system, switching off and draining down the adiabatic system will prevent the pipe work from freezing. Alternatively trace heating can be applied to protect the adiabatic feed pipework.
Managing dormant equipment
For equipment left dormant in winter, the risk isn’t just freezing, but also the degradation of moving parts. Regular circulation prevents the fluid from settling and keeps the internal components lubricated. With no glycol/antifreeze in the system, it’s important that the system pumps are switched on to circulate the fluid particularly when ambient temperatures drop below 3°C. If this happens for an extended period of time, the pump will heat the fluid and this may require to switch the chiller back on to make sure the fluid temperatures are controlled.
Embracing technological upgrades
Both large and small companies are under pressure to reduce energy consumption and improve the operating efficiency of their equipment. Winter is also a good time to embrace technologies that are not just an efficiency measure but a step towards sustainability that will benefit the operations throughout the year.
- Heat Recovery - With cooling systems comes the potential of heat recovery. Recycling waste heat from cooling systems will help to increase the efficiency of the system. Combined heating and cooling applications provide unique opportunity to reclaim or harvest energy available within the same plant or building. The waste heat energy from cooling, that would have been rejected to the atmosphere, can be harnessed effectively and re-used by heat recovery at medium temperature for space heating, preheating water, etc. or the recovered energy can be boosted up to 120°C with high temperature heat pumps for other processes. Combining heat recovery from chillers with a booster heat-pump opens an untapped opportunity to lower overall energy demand and reduce CO2 emissions. Low temperature processes are large thermal efficiency opportunities when using heat recovery and heat pump boosters.
- Variable Speed Drives (VSD) - Controlling the flow of air and water in process temperature control systems is an effective, permanent way to meet the ever-changing demands put on a system and enhance its efficiency, therefore it’s important to consider technologies that maximize part-load efficiency. Constant volume cooling systems operate at one speed, regardless of the cooling load. This means that they consume the same amount of energy, whether the cooling load is high or low. By contrast, installing a VSD - an electrical/electronic system that provides infinitely variable speed control of AC induction motors - you can meet varying system flow rate requirements or just increase energy efficiency. Variable speed components meet the actual load required during any given time over a wide operational range, meaning their speed and output varies to reflect the conditions and demands. By precisely matching output to the cooling demands, compressors and fans operate at their fastest levels when demand is high, and modulate to slower levels when demand is lower, for a high Seasonal Energy Efficiency Ratio (SEER), a measurement of part–load performance. The result is lower annual energy use and typically smaller annual energy bills. Variable-speed technologies are applied by chiller manufacturers across product portfolios, but VSD technology can also be retrofitted to existing chillers, making it an excellent option for businesses looking to improve the efficiency and reduce the energy consumption of their cooling systems. Variable speed pumps are also key to matching the flow of the system to the required capacity. They avoid wasted power and energy compared to traditional on/off pumps and have the potential to save up to 50% on pump energy. What’s more, the cost and power output savings are magnified on larger systems with pumps greater in capacity than 15kW, with the initial investment quickly offset by energy bills and prolonged equipment life.
- Free Cooling - Any organisation using an externally sited chiller to cool their process can benefit from free cooling. It can be implemented whenever the outside temperature is low enough to cool down the process fluid without the intervention of a chiller (mechanical cooling). This can be in the form of partial free cooling (where the chiller’s compressors are still doing some of the work to cool) to full free cooling (where the full load on the chiller is offset). In contrast, an externally sited chiller’s compressors with no free cooling capabilities will be working flat out to achieve the same. Free cooling can be achieved in one of two ways, either by integrating a free cooling coil into an existing chiller installation, or as a standalone (sometimes referred to as a bolt-on) unit. Standalone and integrated free cooling offer many benefits depending on the application and the site in question. As the ambient air temperature continues to fall, the amount of process heat taken out of the process fluid by the air increases, progressively reducing the load on the chiller. At 5°C Celsius below the process supply fluid temperature, all the process heat is removed by the ambient air in the free cooler – providing full free cooling. This makes free cooling the cheapest and greenest way to provide cooling.
Conclusion
Winterisation of process cooling systems demands a comprehensive, meticulous approach. Beyond the
immediate need to prevent freezing, there’s a broader objective and opportunity to ensure equipment health, optimise performance, and embrace energy efficiency upgrades. With this article we hoped to present a roadmap to achieve all these goals, ensuring that when winter arrives, your cooling systems are more than just prepared. Ensure your equipment is operating at its best by having a proactive service in the autumn. Being proactive ahead of time will save you a lot of downtime.
