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CO2 Refrigeration Fundamentals: Energy Efficiency Strategies

Andre Patenaude | Director – Solutions Strategy

Emerson’s Commercial and Residential Solution’s Business

Welcome to the final installment of our CO2 Refrigeration Fundamentals blog series. So far, we’ve examined R-744’s unique properties, servicing tips, system operation and design strategies — all of which correspond with topics in our CO2 Chats educational videos. For our final blog, we’ll explore strategies for achieving CO2 transcritical booster system energy efficiencies in warm climates.

How do you achieve energy efficiency in a CO2 system?

The energy consumption of a refrigeration system is a key factor when evaluating its total cost of ownership (TCO). For a CO2 transcritical booster system, energy efficiency is dependent on many factors, including:

  • The ambient temperature range
  • The humidity of the region
  • The availability of and cost of water
  • The cost of peak demand charges

Among these factors, the goal of improving system energy efficiencies in warmer climates has become a major focus area for equipment manufacturers. Leading high ambient strategies include:

  • Adiabatic gas cooler
  • Parallel compression
  • Mechanical sub-cooling
  • Zero superheat control of medium-temperature (MT) evaporators
  • Ejector controls

Retailers must consider all of these variables and strategies when they work with their equipment suppliers and design engineers to specify a CO2 transcritical booster system — which also includes ensuring that qualified service technicians are available in their region to support CO2 refrigeration.

What is an adiabatic gas cooler used in CO2 systems?

An adiabatic gas cooler is very similar to a dry gas cooler, except that it uses adiabatic pre-cooling pads outside the condenser coils. When the ambient temperature reaches about 72 °F on a CO2 transcritical booster system, a water solenoid valve is energized, causing water to be sprayed along the top of the adiabatic pads. As the water trickles down the pads, a condenser pulls air through these wetted pads, causing moist, cooler air to hit the coils. In turn, the condenser reacts to this cooler air and drops the temperature and pressure, making the system significantly more energy-efficient by operating at lower pressures.

What is parallel compression in a CO2 system?

In a CO2 transcritical booster system, parallel compression refers to the practice of adding a separate suction group to the system. This could be confusing to service technicians, who may think we’re simply referring to a parallel rack used on a traditional hydrofluorocarbon (HFC)-based system.

The concept is relatively simple. A “parallel” compressor is added to the MT suction group, which essentially provides a separate suction group to the system. Thus, instead of the bypass gas circulating from the flash tank to the MT suction as in a standard transcritical booster system, the parallel compressor suction group compresses excess flash gas and circulates it to the gas cooler.

This allows the parallel compressor to operate at a suction pressure of about 550 psi (the same as the flash tank), instead of the MT suction of 425 psi. The net effect of leveraging the higher suction pressure is achieving higher compressor capacity for less effort, which translates into a lower heat of compression and reduces energy consumption. As a result, parallel compression is considered a leading high ambient strategy. When annualized in a typical environment, it can potentially save up to 10% in energy costs. Further, parallel compression can be used in combination with an adiabatic gas cooler to achieve additional energy efficiencies.

Thank you for following our CO2 Refrigeration Fundamentals blog series. To learn more about any topic discussed herein, please view the companion installments in our CO2 Chats video series. For more information about Emerson’s comprehensive CO2 products and capabilities, please visit Climate.Emerson.com/CO2Solutions.

 

 

 

 

 

Explore the Advantages of Lowering Refrigerant Charges

Andre Patenaude | Director – Solutions Integration,

Emerson’s Commercial and Residential Solution’s Business

The need to reduce refrigerant charges in commercial refrigeration systems is often the focus of environmental regulations and sustainability initiatives shared by many supermarket retailers and operators. The reason is simple: lowering refrigerant charges reduces the potential for leaks and their associated environmental impacts. But there are also more pragmatic operational motivations for lowering refrigerant charges — from improving refrigeration system energy efficiency, performance and reliability to avoiding equipment replacement costs. In part two of a recent RSES Journal article series, I examine some of the leading strategies for reducing the refrigerant charges in existing refrigeration systems.

Implement variable fan speed control

Most centralized direct expansion (DX) systems are designed for peak summer heat and use mechanical head pressure control valves to maintain fixed pressure in the condenser equivalent to 105 °F condensing. In cooler seasonal conditions, this approach creates a considerably oversized condenser, where a substantial portion of the condenser volume is being used to store liquid in order to build pressure up to 105 °F minimum condensing.

A potential fix to remedying this situation is to remove the mechanical head pressure control valve and install a variable-frequency drive (VFD) to control the condenser fan’s speed. Instead of operating with a minimum fixed head pressure, this strategy provides variable head pressure throughout the year. This allows the system to operate with less refrigerant by removing the need to have a “winter charge” to flood the condenser in low ambient conditions.

Note: For operators in northern climates with sustained periods of sub-zero temperatures (-20° F to -30° F), utilizing a flooded head pressure approach may be necessary to keep systems running during those periods.

If you discover that a condenser needs to be replaced, an additional charge reduction can be achieved from implementing a split-condenser design. The approach effectively helps to maintain system pressure by cutting the condenser surface area in half as ambient temperatures drop, creating a net reduction in condenser surface area, which further lowers the system charge. In summer months, when the condenser utilizes every inch of its surface area, excess liquid refrigerant can be stored in a large receiver tank designed to hold both the summer and winter charges. Consider also using a low-condensing approach in combination with an efficient liquid subcooling strategy to achieve additional charge reductions while maximizing system performance, energy efficiency and reliability.

Adopt a looped piping strategy

In conventional centralized DX systems, individual liquid refrigerant and return suction lines are fed from the refrigeration rack to each case in a supermarket — which requires a large refrigerant charge to support the full load of all cases. An alternative to this approach would be to adopt a looped piping strategy by running fewer large lines to designated sections of the store, from which smaller lines branch off to individual cases. For example, instead of running 30 long lines to individual cases, four to five line loops would support key store sections — with much smaller lines branched off these loops to feed the individual cases. In doing so, store operators can reduce piping, lower leak rates, and achieve a significant reduction in refrigerant charge.

Disconnect and re-distribute remote refrigeration loads

Another common centralized DX refrigeration challenge is to provide adequate refrigeration for cases that are located farthest from the machine room. Unless the system is operating perfectly, the liquid refrigerant traveling through those long liquid lines can develop flash gas bubbles by the time it reaches these distant cases. This results in a variety of issues, which can ultimately increase the amount of refrigerant needed and impact case temperatures.

One potential solution is to disconnect these remote cases from their suction group and install segments of distributed equipment to handle them individually. This reduces the refrigerant charge in the centralized DX system and allows it to operate more efficiently. The Copeland™ digital outdoor refrigeration unit, X-Line Series is ideal for servicing these remote cases or supporting new refrigeration requirements, such as walk-in coolers for click-and-collect fulfillment. In addition, the Copeland indoor modular solution provides flexible options for spot merchandizing cases, which could also be disconnected from a DX system.

Transition to distributed architectures

The prospect of large-scale leak events is always a possibility in large DX centralized systems, which can often be charged with up to 4,000 pounds of refrigerant. If even half of that charge were to be emitted in a catastrophic leak, operators would face potential environmental penalties and excessive refrigerant replacement costs. But this centralized approach is no longer the only option for large-supermarket refrigeration. In their place is an emerging variety of distributed architectures designed to lower refrigerant charges, deliver improved energy efficiencies, and operate using lower-GWP refrigerants.

Distributed architectures that utilize Copeland scroll compression technology can deliver significant system efficiencies, particularly when using a low-pressure refrigerant like R-513A. For example, Emerson’s distributed scroll booster architecture is designed to overcome common low-temperature system challenges and leverage R-513A’s low pressure and high efficiency to provide:

  • Lower discharge temperatures and compression ratios: 1.9:1 at -10 °F saturated suction temperature (SST) and 20 °F saturated discharge temperature (SDT)
  • Reduced compressor strain and related maintenance issues
  • Increased overall system efficiency and lifespan
  • Reduced stress on pipes and fittings, which lowers the potential for leaks

All the strategies discussed herein will not only help to lower your refrigerant charge but also deliver a variety of system efficiency and reliability benefits.

Strategies for Maximizing Refrigeration System Efficiencies

Andre Patenaude | Director – Solutions Integration,

Emerson’s Commercial and Residential Solution’s Business

For many supermarket operators, reducing energy spend in their refrigeration systems is a key sustainability objective. But as most refrigeration systems drift from their original commissioned states, they inevitably lose efficiencies over time. In a recent RSES Journal article, I explored some of the root causes of this all-too-common problem and presented proven strategies for maximizing refrigeration system efficiencies.

There is often a domino effect that contributes to declining refrigeration efficiencies: setpoints are changed, mechanical subcooling strategies become ineffective, condensing pressures increase, and overall system energy consumption rises. At the same time, maintaining consistent case temperatures can become a constant struggle — often causing the reliability of these systems to suffer.

But this inefficient, unreliable state neither has to be your status quo, nor does it necessarily mean that it is time to replace your existing refrigeration system. In fact, there are a variety of tools and techniques for taking back control of your supermarket refrigeration system.

Shore up your liquid subcooling strategy

Refrigerant (liquid) subcooling results in denser liquid — which packs more BTUs per pound and maximizes system capacity and performance — and is a strategy utilized within many supermarket refrigeration systems. But because this approach is based on design parameters that account for the hottest anticipated day of the year, it can present challenges in other weather conditions. In some regions, this can represent more than 95 percent of the time

As ambient temperatures drop, the condenser operates more efficiently, thus decreasing the subcooling load requirements. The net effect is that the plate heat exchanger — which acts as an evaporator to cool the refrigerant — is oversized for most of the year. And as the system tries to adapt to changing weather conditions, the liquid quality output can become more erratic and cause flash gas in liquid lines, which can starve the evaporator.

To manage this load variability, system designers often use electronic evaporator pressure regulators (EPRs), which must be properly set to maintain ideal liquid-out temperatures. If not, these conditions can combine to create a perpetual state of fluctuation as the system “hunts” for the liquid quality for which it was designed, resulting in a myriad of system issues with the potential to negatively impact energy efficiency and reliability.

Install electronic expansion valves

Replacing a system’s mechanical expansion valves with electronic expansion valves (EEVs) is the key to helping operators overcome these subcooling challenges and restoring system efficiencies. EEVs are typically located at the inlet of the subcooler to control and modulate the refrigerant flow of the heat exchanger much more effectively, regardless of whether it is the hottest or coldest day of the year. As temperatures and liquid quality fluctuate, EEVs allow a system to run at maximum capacity and deliver the performance advantages for which it was originally designed:

  • Higher BTUs per pound of circulating refrigerant
  • Reduced liquid line size and charge reduction
  • Improved efficiency for energy savings

Note: for optimum control of a subcooling heat exchanger equipped with an EEV, consider using a variable-capacity compressor like the Copeland™ scroll digital compressor or adding a variable-frequency drive (VFD) to a Copeland Discus™ compressor to provide a balanced load approach.

Raise system suction pressures

The higher the system suction pressures are, the lower the associated compressor power consumption will be — particularly in lower-temperature refrigeration systems. For every 1 PSI increase in suction pressure, a compressor’s energy efficiency ratio (EER) is improved by approximately 2%.

Electronic evaporator pressure regulators (EPRs) are commonly used in centralized racks to maintain evaporator temperatures within various suction groups and optimize the suction pressure to its highest possible point based on case demand. To save additional energy, technicians may “float the suction pressure” by allowing it to rise slightly when the lowest temperature case is satisfied. This can only be achieved if the EPRs are properly set.

Low-condensing operation

Another way to offset the inefficiencies of a system designed for the hottest day of the year is to implement low-condensing operation (aka “floating the head pressure”). Instead of artificially keeping head pressures near 105 °F with the use of head pressure control valves, EEVs installed at cases allow systems to float head pressures down as the temperatures drop — typically maintaining temperatures at 10–20 °F above the ambient temperature.

On average, systems can achieve 15–20% EER improvements on compressor performance for every 10 °F decrease in head pressure. EEVs are designed to modulate with fluctuations in capacity and liquid quality to digest flash gas and control superheat. Using this technique, supermarket operators can reliably float system pressures to 70 °F or lower and achieve:

  • 15–20% EER improvements on compressor performance
  • Increased compressor capacity for faster pull-down rates
  • Lower pressure, which reduces system stress
  • Higher system reliability, which lowers total cost of ownership (TCO)

Give your system an efficiency boost

Emerson provides the tools, technologies and expertise to help operators implement efficient liquid subcooling and low-condensing pressure strategies. Our EX series EEVs feature a patented ceramic gate port design that can manage a wide range of liquid quality and condensing pressures — and deliver precise refrigerant control via variable-capacity modulation from 10–100%.

The companion EXD-SH1 or SH2 superheat controller regulates evaporator superheat to optimize system performance, regardless of ambient conditions. Its integrated display allows operators to check a variety of system conditions, such as superheat, percentage of valve opening, pressure and temperature values.

New Capabilities Take Supervisory Controls to the Next Level

SamSmith Sam Smith | Product Manager

Emerson Commercial & Residential Solutions

The Emerson Supervisory Controls platform can help to improve operational efficiency, drive greater cost savings and enhance environmental conditions for customers and staff alike. Our latest E360 Product Spotlight highlights how Emerson has re-engineered the industry-leading, total-facility controls platform to streamline performance and simplify management tasks.

New Capabilities Take Supervisory Controls to the Next Level

New Capabilities Take Supervisory Controls to the Next Level

There is no shortage of pressing concerns for operators of small- and large-format grocers, restaurants and convenience stores. Yet in recent years, multiple factors have pushed operational and energy performance to the top of the list.

Tight margins and sustainability goals increasingly call for smarter energy use. A growing shortage of qualified technicians and ever-evolving consumer expectations for convenience further complicate the issue. As a result, the abilities to streamline site performance and simplify facility management are no longer luxuries; they are fundamental to long-term profitability.

In response, Emerson has re-engineered its Supervisory Controls platform to help facility operators achieve a higher level of performance.

Total-facility control made smarter

Supervisory Controls provides building and system management, control, power and simplified operation for refrigeration, HVAC, lighting and other critical equipment and systems. Operations of all sizes rely on the platform for real-time insights into issues that influence operating costs, food safety and customer experiences.

To keep pace with today’s demanding marketplace, we’ve updated our suite of robust, easy-to-use features with capabilities that provide improved visibility and insights into systems and equipment:

Smart Alarms: Alarms are a critical component to maintaining equipment and minimizing system downtime. But a constant stream of unprioritized alerts can degrade productivity. Smart Alarms prioritizes issues using simple language to help operators recognize when immediate action is required. In addition, it generates a list of possible causes and potential resolutions to help operators diagnose the root causes of issues and potentially prevent costly truck rolls.

Site Aggregator: Site Aggregator provides a consolidated view of equipment and systems in facilities that use multiple Supervisory Controllers and/or the E2 Facility Management Controller. Operators can navigate easily and conveniently between controllers from a single location.

Performance Meter: Enterprise-level visibility is essential to fine-tune operations, reduce energy waste and maintenance costs and avoid food safety issues. Performance Meter enables operators to keep a finger on the pulse of their systems by providing access to real-time performance data.

Floor Plans: Floor Plans makes it easy to identify and monitor active alarms in each key facility system by providing 2D and 3D visualizations of the facility’s layout and equipment. The Floor Plans also integrates with Emerson’s Connect+ Enterprise Management software.

These new capabilities build on Supervisory Controls’ existing feature-rich toolset to provide operators with:

  • Powerful control to manage alerts, alarms, energy use, scheduling, maintenance information, advanced reporting and more
  • Rapid response to immediate and potential issues
  • Intuitive navigation that requires no special training for day-to-day operation
  • Simplified setup to accelerate performance management
  • A user-friendly interface that makes scheduling, report viewing and screen organization easier
  • A mobile-optimized solution to provide anywhere/anytime access to data from a mobile device

The food retail and service industry is undergoing a dynamic transformation, and its operators are under tremendous pressure to adjust quickly to changing conditions. Versatility will be key to carving out a competitive space in both the near- and long-term future. That’s why Emerson designed flexibility into the Supervisory Controls platform. It is as equally effective in greenfield applications as selective retrofits and complete remodels. In addition, it can be integrated seamlessly with existing systems to provide operators with the insights they need, where they need them.

Emerson understands the multifaceted challenges that you are up against. Our solutions incorporate emerging technologies with proven expertise to deliver capabilities that support data-driven decision making. Learn more about our latest innovations by reading the full E360 article.

 

[New E360 Webinar] Why Retrofit Your Aging Supermarket Refrigeration Architecture?

AndrePatenaude_Blog_Image Andre Patenaude | Director, Food Retail Marketing & Growth Strategy, Cold Chain

Emerson Commercial & Residential Solutions

Many supermarket operators face a common dilemma regarding their refrigeration systems: they know they need to make changes or upgrade their legacy systems, but they’re not sure what their retrofit options are — or even where to begin. In our next E360 Webinar, I’ll offer guidance on how supermarket owners/operators can embark on this critical journey.

Join me on Tuesday, Aug. 13 at 2 p.m. EDT/11 a.m. PDT for this informative webinar.

[New E360 Webinar] Why Retrofit Your Aging Supermarket Refrigeration Architecture?

There’s no question that reliable refrigeration is the backbone of any supermarket operation; it accounts for more than 50 percent of the electrical consumption for an average supermarket. That’s why keeping your refrigeration system running at optimal efficiency is essential to maximizing profits and ensuring operational success.

But if you’re like many owners/operators, you’ve been relying on the same centralized refrigeration architecture for decades. During that time, these systems have typically experienced declining performance levels and energy efficiencies — all due to progressive deviations from their original commissioned states. And while these systems are perfect candidates for an upgrade or a retrofit, even newer systems can offer opportunities for improvements, especially within the context of today’s rapidly evolving industry and market dynamics.

Compared to just 10 years ago, the drivers behind refrigeration decisions have changed dramatically, and the days of a one-system-fits-all mentality are quickly becoming a thing of the past. Environmental concerns, energy costs, shifting regulations, shrinking store formats, consumer demands and omnichannel delivery have all irrevocably reshaped the supermarket landscape.

As a result, more supermarket owners/operators are reevaluating their existing (and often aging) systems while looking for any retrofit opportunities that are available to them. Our next E360 Webinar is designed with them in mind. To help you better understand the many factors to consider when evaluating a supermarket refrigeration retrofit, I’ll be discussing the following topics:

  • Industry and market trends driving the need for refrigeration system retrofits
  • How to identify deficiencies and baseline performances in centralized architectures
  • A look at the potential architectures of the future
  • Recommended technologies for retrofits and recommissioning
  • Energy-efficiency strategies for refrigeration, HVAC and the complete building envelope

As always, we will take time after the presentation to answer any of your questions. So, be sure to register now and add this event to your August calendar.

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