PC-MAR23-PG40.1_Layout 1 06/03/2023 14:09 Page 40


WATER & WASTE TREATMENT


CHEMICAL PROTECTION TO KEEP CHILLERS CHILLED


Simon Mattock, from Advanced Water Technologies (AWT), ICS Cool Energy Preferred Water Treatment Specialist Partner, explains how to protect chiller systems from freezing


s much as we need protection from cold weather and the effects it can have on us, our homes, our cars etc, we need to protect our chillers. It can be very costly if pipework splits due to the lack of frost protection. If not appropriately addressed beforehand, once temperatures drop below zero, we can quickly get into a situation which is uncoverable.


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Here, we mainly focus on the use of chemicals to protect chiller systems from freezing, but trace heating is also a means of protecting pipes from freezing.


When considering chemical protection, one may think of over-the-counter anti-freeze that can be used in cars, but automotive anti- freeze is not designed or formulated for the types of complex mixed metal systems that we find in industrial applications.


In addition, such products contain additives such as silicate that are incompatible with chiller systems. Indeed, silicates readily coat metal surfaces and with that reduce the efficiency of heat transfer (typically by around 10%), which adds to overall energy costs. Silicate, in the right environment, can also form polymers, turning fluid into a gel, again adding further economic cost and possible fouling. Silicates also have an abrasive nature, and can attack pump seals.


So what products are available and in what concentrations?


Generally, there are two commercially available products designed for use to protect industrial closed water systems from freezing. Both are formulations that contain glycol: 1. Mono-Ethylene Glycol (commonly referred to as MEG) is the most popular. MEG antifreeze can be used in industrial applications where there is no special requirement or need for a low-toxicity chemical. The main benefit is that it has the best heat transfer profile rate and with that helps reduce ongoing energy costs. 2. Mono-propylene Glycol (commonly referred to as MPG). MPG may not have the level of heat transfer efficiency of the MEG, but


is considered suitable for use in food factories/ pharmaceutical manufacturers, being recognised as a ‘food grade’ chemical product. As MPG is less efficient than MEG, it often requires a ‘correction’ to allow for this differential that affects cooling capacity. This is typically managed by reducing the chiller settings and with that increasing plant workload and thus eventually increasing energy costs.


The types of glycol are recommended as part of any commissioning process and/or by the relevant chiller manufacturer. The concentration of glycol will be determined by the level of freezing-point protection required. Typical protection levels for closed systems in the UK require minimum glycol concentration levels of 25% v/v, which would provide a freeze protection average of -12°C. Fig 2 (below) expresses the concentration vs freezing point protection correlation for both MEG and MPG. The additional consideration for achieving a minimum concentration of 25% relates directly to the suppression of bacteria. Gycols are carbon-based, which means as a food source, they are susceptible to attack from bacteria. However, at levels of 25% and beyond, such concentration creates what is known as a biostatic status and as such inhibits the proliferation of microorganisms associated with the breakdown of glycol (Fig 1 above ). Should such a breakdown occur due to their presence and growth within the water system, not only are the correct levels of anti-freeze protection lost, but this bacteriological activity will drive down system pH levels, leading to increased corrosion.


On the other hand, ‘overdosing’ of glycol brings with it its own challenges. Too much glycol will see efficiency levels drop due to the increase in the power needed to circulate the fluid contained within the system, as well as the reduction in heat transfer performance, again increasing overall running costs. What other considerations should we think about when using a chemical antifreeze?


Fig. 1


If we get back to basic principles, we might need to avoid using direct mains-fed water. This is due to the varying quality we see across the UK, which includes the concentration of deposits and additives that, given the right conditions, can damage chilled pipework. To help combat this we might need to consider filtering and adding a non-oxidising biocide to our water source. In addition to pre- conditioning of the water being used, we will need to add appropriate additional chemicals (inhibitors), that will help protect chillers and their multi-metal components.


Both water and glycol have properties, which without adding chemical inhibitors, can promote corrosion, and depending on the area of the country, the scaling of pipework if the water used is ‘*hard water’ (*rich in calcium). Inhibitors are carefully selected depending on the metals used in a system. They can be included in a mix of what is referred to as inhibited glycol, which is a common approach seen across the UK. These two chemical components can also be added separately as the situation dictates, with tailored levels of both glycol and inhibitor administered. Once we have added our glycol and inhibitor (and if needed non-oxidising biocide) we should not overlook the need for regular maintenance sampling. Once an investment has been made to achieve the optimum blend of glycol and inhibitor to protect our system, we need to closely monitor that they remain intact, retaining the right concentrations. We also learn from maintenance sampling how stable the conditions within the system are, whether we are seeing an increase in bacterial activity, or any active corrosion, pH depression etc. This regime is key to avoiding costly system failures and keeping the entire system as energy efficient as possible. As part of our Planned Preventative Maintenance (PPM) plans we will carry out water sampling and laboratory analysis to determine the current quality of the water used in your cooling system. If any defects are found outside of the recommended parameters, our Service Technicians will put together a plan to help return your water to the required quality.


Fig. 2 40 MARCH 2023 | PROCESS & CONTROL


ICS Cool Energy www.icscoolenergy.com


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