Can a 25-year-old chiller still perform well?

Introduction

The service life of a chiller often far exceeds that stated by the manufacturer. In practice, units are operated for 20-25 years and more, especially in industry and facilities with limited capital investment budgets. It is necessary to take into account the preservation of the resource of the main units, decrease in efficiency as they wear out and compliance with modern safety requirements. The analysis of the design features of the machines of 2000-s allows to estimate their potential for long-term operation.

Fig. 1 – The oldest working YORK chiller is 32 years old (photo 2016)

Fig. 2 – Year of manufacture 1984

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Design features of chillers from the 2000s

Compressors at that time were of two main types: piston and screw. Piston units had cast iron housings and removable cylinder-piston groups, which made overhaul easier. Their service life averaged 40-60 thousand hours, and when replacing rings, valves and bearings could be increased up to 80 thousand. The main failures were wear of rubbing surfaces, destruction of valve plates and contamination of the oil system with wear products. Screw compressors of that period had housings of high-strength cast iron, working pairs with wear-resistant coating and bearings with a design life of 50-100 thousand hours. The limiting factor was seals and lubrication systems that were sensitive to oil quality and degradation.

Heat exchangers were mainly shell-and-tube. Copper tubes with diameter of 19-25 mm and wall thickness of 0,9-1,2 mm were used, which provided sufficient safety margin. The most common problem during long-term operation was corrosion on the water side, as well as overgrowth of sediments in case of insufficient water treatment. Plate heat exchangers were used to a limited extent, mainly in small capacity machines. Their weak point was the gaskets, whose lifetime was limited to 8-12 years.

Refrigerants changed as chlorinated compounds moved from chlorine compounds to HFCs. Until 2000, most chillers used R22 with operating pressures of 5-7 bar at suction and 15-17 bar at discharge. Later, R407C and R134a became common. The R134a machines used in heavy-duty installations had lower operating pressures, which reduced the load on heat exchangers and compressors, increasing their durability. R22 operation generally provided high reliability, but is now limited by environmental and regulatory factors.

Automation systems in the 1990s were mainly based on electromechanical pressure switches and thermostats. They were characterised by simplicity, high maintainability and resistance to parameter fluctuations. Since the early 2000s, manufacturers have started to introduce microprocessor controllers, which increased the accuracy of regulation, but today creates difficulties due to obsolescence and shortage of spare parts.

In general, the equipment of that time was characterised by a structural safety margin. Thick-walled tubes, massive compressor casings and enlarged oil systems ensured a high service life, which allows many machines to continue to operate successfully even 25 years after commissioning.

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Degradation of main components during long-term operation

Compressors are the most stressed and resource-dependent element of a chiller. In piston machines, after 20-25 years of operation, wear of the cylinder-piston group is observed: increased clearances, loss of compression, increased oil consumption. Valve plates lose elasticity, cracks are formed, which leads to increased leakage in valve blocks. Crankshaft and connecting rod bearings are subjected to fatigue wear, and scoring may occur if oil filtration is insufficient. In screw compressors, the main limitation is the rotor bearings. Even with correct lubrication their life rarely exceeds 100-120 thousand hours. Table 1 shows the average operating hours of the component groups. In addition, the seals deteriorate over a long period of operation, which manifests itself in increased oil and refrigerant leakage.

Table 1. Scheduled preventive maintenance of compressors

Heat exchangers are subject to both chemical and mechanical degradation. Copper tubes of shell-and-tube units gradually lose wall thickness due to corrosion on the water side. When unsoftened water is used, calcium and magnesium carbonate deposits overgrow, which reduces heat transfer and increases hydraulic resistance. After 20-25 years of operation the total reduction of heat transfer coefficient can be 20-40 %. In plate apparatuses the main failures are gasket leaks. Service life of elastomers is limited by material ageing, and after 10-12 years tightness of joints decreases.

Fig. 3 – Deposits on the heat exchange surface of a plate heat exchanger

Fig. 4 – Deposits on the heat-exchange surface of shell-and-tube heat exchanger

The automation and electrical parts also show degradation. In electromechanical systems the main failures are burned contacts and worn relays. Electronic controllers are characterised by microcircuit failures and damage to non-volatile memory, which leads to incorrect control algorithms. Electric motors of compressors and pumps lose insulating properties of windings over time. The ageing of the varnish increases the risk of inter-turn faults, especially under overheating conditions.

Pipelines and valves experience accumulated damage from thermal cycling and vibration. Pipeline metal is subject to fatigue wear at welded seams and micro-cracks may occur. Valve and flange sealing materials gradually lose elasticity, resulting in leaks. In systems with R22 there is an additional problem: old seals designed for this refrigerant are often incompatible with modern substitutes, which makes retrofit difficult.

Taken together, these processes mean that, with a service life of about 25 years, the equipment remains operational only with regular maintenance, replacement of worn components and competent operation. Without these measures, the probability of failure increases exponentially, especially in the compressor circuit.

Long service life and resilience of chillers with a long service life

The actual life of a chiller is determined by the total compressor life and the condition of the heat exchange equipment. For reciprocating machines, the service life rarely exceeds 60-70 thousand hours without overhaul. After rebuilding the cylinder-piston group, the service life can be extended for another 20-30 thousand hours, but reliability is reduced due to fatigue damage to the crankshaft and connecting rods. Screw compressors have a much higher service life: with correct maintenance they can work up to 100-120 thousand hours. In practice, this corresponds to a service life of 20-25 years in part load mode. The limiting factor is the bearings and sealing systems, as well as the degradation of the automation.

Shell-and-tube heat exchangers in most cases remain functional even after 25 years if regular mechanical cleaning and corrosion control of the tubes have been carried out. In the absence of water treatment or when using process water from open sources, the tubes deteriorate much faster. With regular maintenance, the probability of accidental leaks remains low. Plate heat exchangers have a shorter service life due to the ageing of the gaskets, so after 15-20 years of operation they often require complete replacement of the package.

In terms of automation and electrics, the older generation equipment is of a dual nature. Electromechanical pressure and protection switches remain functional even after decades, but are characterised by reduced accuracy. Microprocessor controllers from the early 2000s fail much more frequently, and replacing them with original components is in most cases impossible. This reduces the fault tolerance of the system as a whole.

Thus, chillers aged 20-25 years continue to operate in industrial installations, provided that overhauls of compressors and heat exchangers are performed, and the automation is maintained in serviceable condition. In general, fault tolerance of such machines is lower in comparison with modern analogues, but due to massive construction and excessive safety margin some units can keep working even after 25 years of operation.

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Energy efficiency of long-life chillers

The energy performance of chillers manufactured in the late 1990s and early 2000s was originally up to the standards of the time, but is noticeably inferior to modern units. For reciprocating compressor-based machines, the energy efficiency ratio (EER) was typically in the range of 2.5-3.0 at a condensing temperature of 40 °C and an evaporating temperature of 5 °C. Screw machines showed slightly higher values, up to 3.2-3.4. Modern chillers based on screw or centrifugal compressors with frequency control and optimised automation show EERs of 4.5-6.0 under similar conditions.

Figure 5 – Achievable chiller COP between 1970 and 2010 (energy.gov.au, Factsheet, Chiller Efficiency)

The decline in efficiency of older chillers is not only due to the original design, but also due to degradation of components over 20-25 years of operation. In compressors, declining compression, internal leakage through seals and increased mechanical losses lead to increased energy consumption. In heat exchangers, heat transfer coefficient may decrease by 20-40 % due to overgrowth and corrosion, which causes increased temperature differences and additional load on the compressor. Together, this leads to a further 15-25 % reduction in actual COP/EER compared to the nameplate data.

A separate factor is the refrigerant. Most of the machines of the 1990s operated on R22, which had good thermodynamic characteristics. After its production ban and transition to retrofit blends (e.g. R407C) there is a decrease in energy efficiency by 8-12 % due to large temperature slips and differences in heat capacity. Chillers originally designed for R134a maintain more stable performance, but also suffer from a drop in efficiency due to equipment wear and tear.

There are limited opportunities to improve the energy efficiency of older chillers. Mechanical cleaning of heat exchangers, adjustment and balancing of the refrigeration circuit, and modernisation of control systems have the greatest effect. Installation of frequency converters on pumps and fans can reduce energy consumption in partial modes. However, even after such measures, old machines rarely come close to modern energy efficiency standards.

Figure 6 – ASHRAE COP classification for chiller-based refrigeration systems

Thus, a 25 year old chiller can remain operational, but its energy efficiency is significantly inferior to newer units. The difference in EER between old and new generation equipment can be as much as 30-40%, which has a direct impact on operating costs.

Economic feasibility of operating long-life chillers

The economic evaluation of a 20-25 year old chiller includes three main components: repair and maintenance costs, the cost of electricity consumption and the risk of emergency downtime.

Repair costs depend on the type of compressor and the condition of the heat exchangers. Overhaul of a reciprocating compressor after 15-20 years of operation can be 25-40% of the cost of a new unit of similar capacity. For screw machines, the cost of rebuilding the working pairs and replacing bearings often exceeds 40-50% of the price of a new compressor. In some cases, the manufacturer discontinues the production of original spare parts, which increases the cost of repair or makes it impossible. Replacement of the shell-and-tube heat exchanger costs 30-50% of the chiller cost, which also casts doubt on the expediency of equipment refurbishment.

The energy costs of operating older chillers increase due to reduced energy efficiency. The difference in EER compared to modern machines is on average 30-40 %. For a 500 kW unit with 4,000 hours of operation per year, this results in additional electricity consumption of 500-700 MWh annually. In monetary terms, at a tariff of 0.12-0.15 €/kWh, this amounts to 60-100 thousand euros per year. Thus, the operating costs of electricity are many times higher than the potential savings from not replacing the equipment.

The risks of emergency downtime are also of significant economic importance. The failure of a compressor or heat exchanger can lead to a complete shutdown of a process or climate system for days to weeks. Given that older machines have a high probability of failure, especially when operating over 100,000 hours, the risk of unplanned downtime becomes a key factor in life cycle assessment.

In sum, operating a 25 year old chiller is only viable when utilisation is limited, electricity tariffs are low and back-up equipment is available. In other cases it is economically justified to replace the unit with a modern chiller with higher energy efficiency. The payback period is usually 3-5 years due to energy savings and reduced repair costs.

Safety and regulatory requirements

The operation of 20-25 year old chillers involves a number of factors that directly affect industrial safety and regulatory compliance.

Of greatest importance is the issue of refrigerants. Most of the machines manufactured before 2000 are designed to operate with R22. Its use in the European Union and most developed countries is prohibited and its production has been stopped. In Ukraine, the use of R22 is not completely banned, but the refrigerant circulation is limited and the cost of charging has increased significantly. Retrofit to substitutes (e.g. R407C or blends based on R422D, R438A) reduces energy efficiency and may cause compatibility problems with seal materials and oils. Machines originally designed for R134a are compliant with current regulations, but their energy efficiency ratings are outdated.

The second critical aspect is the condition of the pressure vessels. Evaporators and condensers of older generation chillers have massive walls and significant safety margins, but the metal is prone to corrosion and welds to fatigue damage. Current industrial safety regulations require that such units undergo periodic hydraulic testing and non-destructive testing. If the service life exceeds 20 years, the probability of defects requiring decommissioning increases significantly.

Fig. 7 – Hidden microcrack in the area of a weld seam

The electrical part is also a risk factor. Motor winding insulation degrades due to thermal cycling, which increases the likelihood of inter-turns and short circuits. Old starters and circuit breakers have high contact resistance and are prone to overheating. Regulations require regular checks of insulation resistance and testing of overload protection devices.

Separately, it is worth noting the obsolescence of automation systems. Many controllers from the early 2000s do not support modern dispatching protocols (Modbus TCP/IP, BACnet), which limits the integration of old equipment into modern building management systems.

Thus, operation of chillers 25 years old requires increased attention to industrial safety issues. The main areas of concern remain the handling of obsolete refrigerants, the condition of pressure vessels and electrical reliability. Without additional inspections and regular maintenance checks, these machines can pose an increased risk of accidents.

Conclusions

Chillers aged 20-25 years can continue to operate, but their operation requires increased attention to the condition of key components and regular maintenance. The longevity of the equipment depends directly on the type of compressor, the condition of the heat exchangers, the quality of the refrigerant and the functionality of the automation.

Piston compressors with timely overhaul can work additional 20-30 thousand hours, but the risk of failures after this period increases significantly. Screw machines demonstrate a higher service life and, if operated correctly, can operate for up to 25 years or more. Heat exchangers of shell-and-tube type remain functional with regular cleaning and corrosion control, while plate heat exchangers require replacement of gaskets after 10-12 years.

Energy efficiency of old chillers is significantly lower than modern chillers – COP/EER drop reaches 30-40 %. Retrofit for new refrigerants additionally reduces efficiency by 8-12 %. Economic feasibility of operation remains only at limited load, availability of reserve equipment and relatively low electricity tariffs.

The decision to continue operation of a chiller 25 years and older should be made on the basis of a comprehensive assessment of technical condition, economic efficiency and industrial safety risks. In some cases it is justified to continue operation, especially when modernising units and maintaining the equipment in good condition. In other situations, it is more rational to replace the unit with a modern machine with higher energy efficiency and resource.

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Author of the article:

Sergey Stafiychuk, Head of Sales Department

11.08.2025