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Optimize Supermarket Energy Efficiency and Performance With VFD Retrofits

Joe Summers | Senior Product Manager – Scrolls & Drives
Emerson’s Commercial & Residential Solutions Business

The use of fixed-speed (or fixed-capacity) refrigeration systems and HVAC rooftop units (RTUs) is a common strategy in the U.S. food retail sector. If you went into the machine rooms of most grocery stores, you likely would find centralized, direct expansion (DX) refrigeration systems with parallel racks of fixed-speed compressors. On the rooftops, you would find RTUs with air-handler blowers running continuously at full speeds. Varying the capacity of these critical units relies on mechanical throttling techniques that consume energy, cause excess equipment wear, but never quite achieve the desired load matching. In a new white paper, Emerson explore how operators can retrofit these systems with variable frequency drives (VFDs) to deliver significant energy efficiency and performance improvements.

For the most part, the potential uses for VFDs in the food retail sector have been largely unexplored. Simply put, VFD retrofits allow operators to convert existing fixed-speed equipment — such as compressors, fans or pumps — to enable variable-capacity modulation. Benefits include:

  • Reduced energy consumption and electricity costs
  • Improved load matching, temperature precision and performance
  • Extended equipment reliability lifespan

VFDs in refrigeration systems

The inability to match the refrigeration capacity to fluctuating evaporator load demands is a known limitation of parallel rack systems with fixed-speed compressors. Systems are designed and specified to accommodate peak-load conditions and provide reliable cooling during the hottest days of a year — i.e., they’re essentially over-sized for lower load conditions and cooler periods.

Widely varying load requirements, ever-changing ambient conditions and variations in defrost cycles can create undesirable fluctuations in case temperatures. Compressors are constantly switching off and on to try and adapt to these changing demands, which can accelerate wear on system components, increase the potential for food quality issues, and consume excess electricity.

VFDs give operators and service technicians an effective method for alleviating fixed-speed compressor motor challenges and achieving the benefits of variable-capacity modulation. By retrofitting a VFD to the lead compressor in every parallel compressor rack, each lead compressor can then modulate the capacity of the entire rack. This enables fixed-speed compressors to handle the base load, while leveraging the VFD-equipped lead compressor to manage fluctuations in demand. Compared to a traditional fixed-speed approach, this results in:

  • Reduced cycling on/off strain and an extended life of the lead compressor
  • Smoother and almost constant system suction pressure
  • More consistent evaporator (case) temperatures and humidity conditions

Validating VFD ROI in HVAC case study

In HVAC RTUs, air-handler blower capacity is also designed to handle the peak cooling conditions of the installation’s summer season. But as building loads fluctuate widely throughout the year, HVAC systems often operate at only a fraction of their design capacity. Thus, air-handler blower fans run continuously at full, fixed speeds, regardless of load requirements. Technicians often use a mechanical throttling technique to help reduce airflow, but this results in increased energy consumption and a reduction in the equipment’s lifespan.

Retrofitting a VFD onto an existing fan motor allows it to modulate capacity based on varying load requirements — full speed during peak-load periods and slower speeds when less load is required. In this HVAC RTU application, variable-capacity modulation delivers a fast return on investment (ROI) via a non-linear, speed-to-power ratio. By slowing down a blower motor fan speed by 25 percent of its normal operating rate, it’s estimated that facility operators can reduce energy consumption by 50–60 percent.

Emerson validated this principle recently by installing Copeland™ VFDs on a food retailer’s existing rooftop HVAC air-handler blower motors in 78 of their stores. Results included:

  • Reduced energy consumption by 52 percent
  • Saved more than $800,000 in electricity costs
  • Equivalent to adding $10M in sales at an 8 percent margin

Retrofit with Copeland VFDs

Emerson is committed to helping food retailers and technicians to simplify the retrofit process in HVACR applications and improve equipment reliability, performance and efficiency. Copeland VFDs, EVM/EVH Series are designed to reduce the costs and complexities of VFD implementation:

  • The Copeland EVM Series is ideal for chillers, medical refrigeration, display cases, walk-ins and reach-ins.
  • The Copeland EVH Series is designed for large, centralized racks (including CO2), HVAC applications, advanced chillers and industrial refrigeration applications.

Learn more about applying our VFD solutions to your HVACR operations by visiting our webpage.

CO2 Refrigeration Fundamentals: Servicing Tips

Andre Patenaude | Director – Solutions Strategy

Emerson’s Commercial and Residential Solution’s Business

In the first blog in this series, we discussed the many distinguishing properties of CO2 (or refrigerant R-744) — including its high system pressures, low critical point and triple point. These characteristics introduce a multitude of unique servicing considerations that differ significantly from traditional hydrofluorocarbon (HFC)-based systems. In this installment, we’ll review some key tips that technicians need to be aware of when servicing CO2 transcritical booster systems. You can also learn more about a variety of related CO2 topics in our new CO2 Chats video series.

How do you store CO2 refrigerant?

From a refrigerant storage best practices perspective, R-744 tank storage is similar to standard HFC storage, including stacking procedures, safety precautions and keeping them chained off in a designated storage area. But that’s where the similarities end. Because CO2 tanks are designed to handle its high pressures, they weigh significantly more than standard HFC bottles. Empty CO2 tanks can weigh close to 150 lbs.; when loaded with 50 lbs. of refrigerant, each cylinder can potentially weigh nearly 200 lbs.

Many supermarkets prefer to have an entire system charge on hand, which could potentially be up to 2,000 lbs. Storing that would require 40 cylinders totaling a weight of 8,000 lbs. — or 4 tons. It’s important for contractors to understand where to store the reserve refrigerant and if it will affect building codes by having that much CO2 in one space. And if stored on a mezzanine, it must be capable of handling the total storage weight.

How do you charge a CO2 refrigeration system?

When charging a CO2 refrigeration system, the most important consideration a technician should keep in mind is the triple point pressure of CO2. 60.4 psi is the pressure at which CO2 will turn to dry ice. As a result, contractors must be careful not to charge with liquid CO2 when the system is below this pressure, and instead charge with vapor until the system reaches triple point. Failure to do so will result in the formation of dry ice. There are various anecdotes about technicians — who are more familiar with charging HFC systems — charging a CO2 system with liquid and causing the formation of dry ice.

Begin charging by introducing CO2 vapor into the system, and then build system pressure to 60.4 psi and beyond based on equipment manufacturer recommendations — up to 145 lbs. Then, it will be safe to switch to liquid CO2 to finish charging the system quickly and effectively without the risk of dry ice formation.

What is trapped liquid in a CO2 refrigeration system?

CO2’s coefficient of expansion (COE) is higher than a typical HFC refrigerant. One potential scenario that can occur in a CO2 system is when liquid refrigerant gets trapped in between two valves. In this instance, the pressure can increase 145 psi for every 1.8 °F increase in temperature. As a result, some systems may need to be fitted with appropriate pressure relief valves at the location of the trapped liquid to assist with system operation and service.

How do you detect leaks in CO2 systems?

Since there is an abundance of CO2 already present in the atmosphere, R-744 refrigerant can be difficult to detect and requires the use of a capable leak detection system. CO2 is colorless, odorless and heavier than air, requiring leak detectors to be mounted 18 inches off the ground and below the breathing level. Like HFC systems, it’s important to immediately detect and mitigate CO2 leaks as they occur.

Manufacturers such as Emerson have designed CO2-specific leak detection technology that quickly can sense the presence of higher levels of carbon dioxide in a machine room or a walk-in box. Emerson offers both a stand-alone CO2 leak detection solution as well as devices that can be seamlessly integrated into a building management system (BMS), such as the Lumity™ supervisory control platform.

Are there safety issues to be aware of when handling CO2 refrigerant?

Because CO2 refrigeration systems operate at extremely high pressures, technicians should take precautions when handling CO2. Even when the system is shut off, standstill pressures are extremely high and need to be handled carefully. In addition, CO2 can displace oxygen and release it in excessive amounts because it’s heavier than air. As a result, technicians should avoid handling it in confined spaces. But with proper training and equipment design, CO2 can be used safely.

For more information on CO2 servicing tips and best practices, please view the companion topic in our CO2 Chats video series. The next installment of the CO2 Refrigeration Fundamentals blog series will focus on system operation. To learn more about Emerson’s comprehensive CO2 products and capabilities, please visit Climate.Emerson.com/CO2Solutions.

 

 

 

Ten Tips for Preventing Refrigerant Leaks in Supermarket Systems

Katrina Krites | Director of Strategic Marketing, Cold Chain

Emerson’s Commercial and Residential Solutions Business

Refrigerant leaks are a universal challenge for U.S. supermarket operators. These leaks are not only costly from an operational perspective, but emissions of hydrofluorocarbon (HFC) refrigerants also contribute to global warming. Today, commercial refrigeration contractors play a significant role in helping operators to implement best practices to reduce and even prevent refrigerant leaks. I recently contributed to an ACHR The NEWS article where I discussed strategies for leak detection and mitigation best practices for supermarket refrigeration systems.

The Environmental Investigation Agency (EIA) recently reported that numerous U.S. supermarket chains were leaking significant amounts of HFC refrigerants. These findings were consistent with a report by the Environmental Protection Agency’s (EPA) GreenChill program, which stated that the typical supermarket has an annual leak rate of about 25%, which equates to about 1,000 pounds of leaked refrigerant every year.

Understand root causes

Although refrigerant leaks are much more common in large, centralized systems, it’s not as if contractors or operators simply accept leaks as a design limitation. On the contrary, when a refrigeration system is first installed and commissioned, it operates at peak performance. But over time, systems inevitably drift from their commissioned performance baseline, contractors perform repairs to keep systems running, and the potential for leaks can start to rise if a system is not properly maintained and managed.

For a contractor’s perspective on refrigerant leaks, the NEWS also interviewed Todd Ernest, CEO and founder of Climate Pros, a comprehensive commercial refrigeration and HVAC firm with offices in more than 40 states. Ernest agreed that while leaks are a common problem, nearly half of the stores serviced by Climate Pros do not have refrigerant leaks. One common problem that they discovered is that many stores still use the same copper lines and systems that were installed decades ago. Though durable, copper isn’t intended to last forever — and original insulation and mounting hardware will often eventually wear down.

Similarly, mechanical room cleanliness is also essential for helping contractors to identify leaks. Compressor racks, air-cooled condensers, remote headers, walk-in evaporator coils and other components should be kept free of oil and dirt. Corroded steel components should be removed and/or painted with a rust-inhibiting paint to help prevent future corrosion.

Check for leaks

As I explained in the article, service technicians should conduct refrigerant leak checks at regular intervals, depending on the system size or type. For large, centralized systems, this should usually be approximately every 30–60 days. An effective leak detection program should include three key elements:

  1. Accurate detection methods
  2. Reliable notifications
  3. Continuous monitoring for system leaks

Contractors should recommend the installation of a refrigerant leak monitoring, notification and alarm system to ensure the detection of any leaks between regular leak inspections. Detection devices should also be installed in leak-prone locations, such as refrigeration racks and display cases, to monitor the concentration of refrigerants in the air.

By integrating these devices into Emerson’s Lumity™ supervisory control platform, designated store staff and/or service technicians can be alerted when a leak occurs. This powerful facility management system enables continuous monitoring of refrigeration data to help retailers correlate the leaks with respect to different sections of the system or specific maintenance events.

Ernest added that it’s standard protocol for his technicians to perform a leak check every time they go into a store — regardless of the purpose of the actual service call.

Promptly repair leaks

Today’s leak detection devices make it easier to pinpoint leak sources, but it’s important to remember that in many cases, the first refrigerant leak found in a system may not be the only one — or even the largest.

A quick response is most important after detecting a leak to mitigate its impact upon system performance and minimize the associated economic costs. Supermarkets should establish proper leak detection response protocols and institute proactive measures.

If persistent leaks continue, even at lower leak rates of 20%, supermarkets could lose approximately 700 pounds of R-404A annually. At $7 per pound, that equates to a yearly expense of nearly $5,000 — in addition to any potential costs associated with compliance, environmental consequences and overall deterioration of system performance.

A methodical approach can help to achieve all-important early detection and an overall reduction in refrigerant leaks. The NEWS article concluded with these 10 tips:

  1. Perform a leak check on every service call. Conduct refrigerant leak checks at regular intervals, ideally every 30–60 days for large centralized systems.
  2. Periodically replace copper lines as well as insulation and mounting hardware.
  3. Keep refrigeration racks and mechanical rooms as clean as possible in order to spot leaks more easily.
  4. If one leak is found, it may not be the only one, so check the entire system thoroughly.
  5. Once all leaks have been repaired, confirm that refrigerant levels have stabilized, indicating there are no additional leaks elsewhere in the system.
  6. Install a refrigerant leak monitoring, notification and alarm system to detect leaks between regular leak inspections.
  7. During refrigeration system installation, use proper securing mechanisms for piping and the correct piping techniques.
  8. Perform a nitrogen purge and pressure test with every new installation to ensure no leaks are present.
  9. Establish leak detection response protocols and proactive measures to minimize or eliminate leaks altogether.
  10. Implement a refrigerant tracking system to identify significant leaks.

 

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