DR. ROBERT LAMB, GROUP SALES AND MARKETING DIRECTOR OF STAR REFRIGERATION LTD.

Editor’s Note

As the industrial refrigeration industry in the U.S. looks to the question of long-term viability of HFCs, many are turning to the lessons learned by the industry in Europe, where the R22 phase-out process is nearing completion.

Europe has set out its timetable for the phase-down of HFC refrigerants, with production being cut to 21percent of current levels by 2030. Bans on the sale of new equipment into the market are due to take affect shortly and will result in a complete ban by 2022.

In the technical paper presented in this issue of the Condenser, Dr. Robert Lamb, Group Sales and Marketing Director of Star Refrigeration Ltd., offers a primer for the technical decisions and other challenges facing any facility planning for a phase-out.

While utilizing systems that leverage “drop-in” refrigerants is an option, several challenges that boost the possibility of leakage include higher system operating pressure, shrinkage of existing seal and gasket materials and the general condition of plant into which the new refrigerant has been retrofitted.

The author concludes that a switch to natural refrigerants can help a company avoid the double step of moving to HFC blends and then having to switch again at a later date, while adding the benefit of improved reliability and efficiency

The phasing down of R22 production is well underway and operators are now looking for guidance on what options are available for replacing R22 in their existing systems. A wide range of ‘drop in’ refrigerant options are available to retrofit existing systems, typically consisting of blends of hydrofluorocarbons, or HFCs.

These have been developed to operate at similar pressures to R22 at specific operating conditions and requirements with minimal modifications to the system. Alongside these are the existing HFC refrigerants such as R404A and R507 which can also be retrofitted in R22 systems, albeit that this might require significant changes to the system design to provide the same cooling performance. Finally, there is the option to move to natural refrigerants including ammonia, hydrocarbons and CO2 . This may be possible with modifications to an existing system but in most cases, it is more cost effective to install a new plant.

At first glance, with so many options available it would suggest that the transition from R22 to an alternative fluid is going to be easy. It is only when getting into the detail that the challenges appear. Plant condition, refrigerant glide, material compatibility, oil, cooling capacity, power, leakage, downtime and system pressure are just a few of the issues operators need to look into when changing refrigerant.

There is also the question of long-term viability of HFCs. Fortunately, the US can look to Europe during this time of transition and take advantage of the lessons learned from their R22 phase-out process which comes to a conclusion at the end of 2014. The US should also note that Europe has set out its timetable for the phase down of HFC refrigerants, with production being cut to 21 percent of current levels by 2030. Bans on the sale of new equipment into the market are due to take affect shortly and will result in a complete ban by 2022.

When The Time Comes To Change . . .

R22 refrigeration system designs differ in many ways. These include system type (e.g. pumped circulation, direct expansion), material of construction (e.g. steel, copper), equipment type (compressors, condensers, evaporators), capacity and power consumption (from a few HP to thousands of tonnes), temperature (-40°F to +50°F) and pressure.

When assessing options for an alternative refrigerant all these criteria need to be considered and there are also non-technical criteria including future legislation (e.g. HFC phase down), corporate environmental commitments (natural refrigerant policy) and the affect on the business’ operation (e.g. maintaining cooling and temperatures during the change over period).

SYSTEM DESIGN

The two most common refrigeration system designs are direct expansion (DX) and pumped circulation. Direct expansion is widely used in small to medium sized applications and has the advantages of low capital cost, low refrigerant charge and relative simplicity. Pumped circulation is typically used for medium to large scale applications with distributed pipe work and evaporators.

‘Drop-In’ refrigerants

The use of a ‘drop in’ refrigerant may be an option but the following should be considered:

Leakage – Evidence from conversions carried out in Europe suggests that HFC refrigerants are far less forgiving in terms of leakage than R22. Where systems have a history of leakage and this can’t be resolved, the use of drop in refrigerants should not be considered on both commercial and legislative ground. At prices in excess of $20/lb it could be extremely expensive and it is likely that knowingly adding a replacement gas to a leaking system is contravening environmental legislation. This is certainly the case in Europe under the f-gas regulation.

Even if an existing R22 system doesn’t have a history of gas loss, changing to HFCs could result in leakage. Factors contributing to this increase risk of leakage include higher system operating pressure, shrinkage of existing seal and gasket materials and the general condition of plant into which the new refrigerant has been retrofitted.

Particular areas of concern are seals on compressors and valves which may swell when in contact with R22 and mineral oil but then shrink back to their original size or less when in contact with HFCs and the replacement oils. An overhaul and replacement of seals and gaskets should form part of any replacement gas assessment process and included into the cost of the works.

Where copper has been used for heat exchangers and piping, it is possible that this has work hardened over time and whilst the original material may have been suitably rated for R22 its strength may have weakened over time. This is of particular concern for evaporators with hot gas or electric defrost.

Oil Change – In addition to changing refrigerant, where mineral oil is currently used, experience in Europe has indicated that this should be replaced with POE oil. POE is miscible with mineral oil so it is not crucial to ensure every last drop of mineral oil is removed and the system is flushed through. But, every attempt to flush the mineral is important to remove as much as possible.

Operating Pressure – Changing refrigerant could result in higher operating pressures at design conditions due to the different properties of the new fluid. When assessing the suitability of an alternative refrigerant, consideration should be given to these new operating pressures and whether the existing system components are suitably designed. This includes an assessment of the pipe work and vessel design pressures along with thickness tests and visual inspection for signs of corrosion. Pressure relief valves should also be assessed for the new operating pressures and changed where necessary.

In addition to the theoretical assessment, strength and tightness tests should be carried out to ensure that the rating of components and pipe work is still valid. Corrosion and work hardening may well have reduced the strength of the system and its components.

Change In Capacity – Many of the ‘drop in’ HFC refrigerants have a temperature glide, which affects heat exchanger performance and leads to a loss of cooling capacity. Where an application is already marginal in capacity (particularly during warming summer months), moving to a drop in replacement may worsen the situation.

Application Temperature – It is crucial that the refrigerant type is matched to the application. Differing blends have been developed for low, medium and high temperature application and using a refrigerant for the wrong applications could result in significant loss in performance and damage to components.

Refrigerant Glide – R22 is a single component refrigerant which boils and condenses at a fixed temperature. Many of the replacement refrigerants are blends of fluids which boil and condense over a temperature range often referred to as ‘glide’. Glide has two significant affects on system performance.

Firstly, it results in a reduction in heat exchanger performance when the original evaporator or condenser has been designed for R22. For systems where there are one or more receiver vessels (e.g. surge vessels for pumped circulation plant or high pressure receivers), it can also lead to separation of the blend components and a change in the circulating refrigerant composition. This results in a reduction in cooling capacity and performance.

Long Term Future Of HFCs – The US has followed Europe in the phasing out of CFCs and HCFC refrigerants. With Europe now adopting a timetable for HFC phase down, it is highly likely that the US will follow this lead. Replacing R22 with a replacement HFC gas may buy you time but eventually, the system will need replacing.

It has to be remembered that converting from R22 to a ‘drop-in’ HFC doesn’t provide a new system. The same problems you’ve always had won’t go away and in most cases, they are likely to get worse and new challenges will appear.

‘Drop in’ refrigerants have been viewed as temporary solutions by many in Europe, enabling the customer to continue operating the system but in the knowledge that it is only a matter of time before it needs to be replaced. They have been widely used in small to medium sized DX applications but less so in large flooded systems and rarely for pumped circulation applications.

NONE ‘DROP IN’ HFC REFRIGERANTS

The challenges with replacing R22 with widely used HFC refrigerants including R404A, R507 or R134a are the same as those highlighted above but there are further complications including:

Oil – It is necessary when changing from R22 to other HFC refrigerants such as R404A, R507 or R134a that all mineral oil is removed and the system flushed. This is time consuming and will add to the conversion time.

Capacity – The thermodynamic properties of these refrigerants are different to R22 and will lead to a change in cooling capacity, operating temperature/pressures, pipe work pressure drop and overall performance. It is likely that considerable changes have to be made to the system design including replacing major components (compressors, heat exchangers) and pipe work in order for the system to provide a similar cooling capacity. This typically makes conversion unattractive from a capital cost prospective.

HFC refrigerants have been retrofitted to some applications, mainly DX but in most cases either a drop in fluid is used or the entire system replaced with a new HFC plant.

NATURAL REFRIGERANTS

The uncertainty over the future of HFC refrigerants has resulted in an increased interest in the use of natural refrigerants. For small to medium scale applications (up to 50TR), hydrocarbons and more recently CO2 have grown in popularity. In some cases, CO2 has been used in cascade with HFC or hydrocarbon plant.

Larger scale applications have typically switched to direct ammoia or ammonia with secondary glycol or CO2 . Customers have installed new equipment alongside the existing R22 equipment and carried out a phase changeover as the challenges associated with converting the existing equipment are too complicated and costly. There are some examples of reusing existing pipe work, for example where R22 has been pumped through the floor of ice rinks and has been replaced with volatile secondary CO2 but the main refrigeration plant has been replaced.

NON-TECHNICAL CONSIDERATIONS

As refrigeration engineers, we often focus on the ‘technical’ part of R22 phase out but there are other challenges that need to be considered. These include:

Company Environmental Policy – A growing number of businesses of all sizes have environmental policies which will aid in determining the technical solution for R22 phase out. For example, growing number of businesses, particularly those with links to Europe, have made pledges to move towards natural refrigerants.

Long Term Future Of HFCs – The US has followed Europe in the phasing out of CFCs and HCFC refrigerants. With Europe now adopting a timetable for HFC phase down, it is highly likely that the US will follow this lead. Replacing R22 with a replacement HFC gas may buy you time but eventually, the system will need replacing.

Conversion Period – Changing refrigerant isn’t simply a case of removing the R22 and having the new solution up and running the same day. The system may be out of operation for a period of time which could range from days to weeks depending on the size and complexity. For small, simple DX system undergoing a refrigerant change, this may take a matter of days. For larger, central pumped circulation systems it could take more than a week just to remove the refrigerant.

Maintaining Production/ Storage – Where the end user has a large, distributed system it is typically the case that loss of cooling for a prolonged period (weeks or months) is not an option. For these applications a new refrigeration system is typically installed alongside the existing plant. Major equipment items, pipework and valves stations are installed and prepared for operation before existing R22 equipment is replaced as part of a phased programme.

Two System Operating Together – The necessity to keep existing R22 plant running whilst new plant is commissioned means that two systems are often operating at the same time. This brings challenges including:

Machinery Room – There may be insufficient space in the existing machinery room for new equipment and this may mean a new room is required. It may be possible through careful planning to develop a changeover program to remove R22 plant on a phased basis to make room for new equipment. Where ammonia is being used as the replacement fluid, additional consideration has to be given in terms of the existing machinery room electrical installation, ventilation and gas detection.

Electrical Supplies – It may be necessary to provide power to the new equipment prior to decommissioning the R22 plant. The additional power to run the new and existing equipment in parallel has to also be considered and this may require the site incoming supply to be increased.

Building Structure – Where new equipment is installed in place of existing, an assessment of the existing building structure has to be carried out to determine whether steelwork is of a suitable size. In cases where new equipment is operating alongside existing R22 plant, an assessment must be also be made as to whether the building is capable of taking the combined weight of both systems.

Customer Disruption – Installing new equipment on an operational facility can be challenging. Particular attention has to be taken to times for access to production/ storage chambers. Typically, this can mean out of hours working and protracted programmes with permission for access being withdrawn at the last minute to challenges elsewhere in the business.

NEXT STEPS

For customers with R22 refrigeration systems, phase out is a reality and needs to be on your agenda today. Experience is Europe has shown that those businesses who have addressed the issue of phase out early have benefited in the long term. A plan should be developed to look at alternatives to R22 and assess the business impacts in terms of capital and program.

Those customers who have switched to natural refrigerants have avoided the double step of moving to HFCs and then having to switch again at a later date. They have also reaped the added benefit of improved reliability and efficiency.

The key is to plan early and ensure the R22 phase out is built into your business plans as early as possible.