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Refrigeration Basics: Understanding the Refrigeration Cycle

         Don Gillis | Lead Technical Trainer

          Emerson’s Educational Services

Welcome to the fourth installment in our series of blogs intended to help not just beginning service technicians, but anyone who wants to learn more about the basics of refrigeration. In this blog, I explain the nuances of vapor injection along with the full refrigeration cycle. For this blog series, we have also created companion videos about each topic that you can cross-reference while accessing related information at Education.Emerson.com.

Comparing Refrigeration to a Baseball Diamond

The refrigeration cycle requires four main components. No matter how small or how large a cooling system might be, its design will include a compressor, a condenser, a metering device and an evaporator.

When I teach new technicians, I often compare the refrigeration cycle to the layout of the field for the game of baseball. I’ve found this analogy makes refrigeration equipment and processes easier for them to understand.

 

 

 

 

 

 

 

 

 

 

 

In my example, a compressor is located at home plate at the bottom of the baseball diamond (shown above). In a refrigeration or cooling system, compression is the first step:

  • Refrigerant enters as a low-pressure (LP), low-temperature (LT) superheated vapor and exits the compressor as a high-pressure (HP), high-temperature (HT) vapor.
  • The compressor mechanically compresses the refrigerant gas.
  • Under pressure, the refrigerant volume is reduced and the temperature is raised.

The second step involves a condenser, located at first base on the right side of the baseball diamond:

  • Hot, pressurized refrigerant gas arrives from the compressor into the condenser, which is designed to reject heat by lowering or returning the temperature of the refrigerant to its condensing temperature.
  • As it rejects heat, the condenser converts the vapor to a sub-cooled liquid.
  • In most condensers, the refrigerant gas enters at the top of the equipment and leaves at the bottom because the refrigerant in a liquid state is much heavier than the weight of refrigerant in a gas state.

In the third step, a metering device located at second base at the top of the baseball diamond regulates the amount of refrigerant released into the evaporator in response to the cooling load and causes a pressure drop.

The metering device also:

  • Measures the superheat at the evaporator outlet
  • Maintains a constant temperature by raising or lowering the amount of refrigerant flowing into the evaporator

At the fourth step, cold liquid refrigerant mixes with vapor causing the saturation temperature as it boils off or vaporizes in the evaporator, located at third base, on the left side of the baseball diamond:

  • The process allows the refrigerant to absorb heat through a series of metal coils.
  • The low-pressure superheated vapor refrigerant gas then returns to the compressor to continue the refrigeration process.

Here is the value of comparing the refrigeration process to a baseball diamond: If I draw a vertical line from home plate up to second base, everything in the system on the right side of that line is under high pressure; everything on the left side of that line is low pressure.

Likewise, if I draw a horizontal line from first base to third base, the refrigerant above the line is in a liquid state; below the line, the refrigerant is a vapor, regardless of whether it is under high or low pressure.

Liquid Injection Cools Compressor and Increases Capacity

A compressor is designed to operate at very high temperatures, so a liquid injection method has been developed to cool the compressor internally. How this works can be confusing; refrigerant is injected in a vapor state, not in a liquid state.

When necessary, liquid injection cools a compressor to enable it to run reliably under difficult high compression ratio conditions normally seen on low-temperature freezer applications.

  • Refrigerant is piped from the system liquid line, through an injector valve to the compressor; in scroll compressors, the refrigerant is injected directly into the scroll elements.
  • Without this cooling, the compression elements can get too hot and the oil breaks down, leading to compressor failures.

Another approach called enhanced vapor injection (EVI) increases refrigeration capacity and, in turn, the efficiency of the system:

  • A heat exchanger is utilized to provide subcooling to the refrigerant before it enters the evaporator.
  • A small amount of refrigerant is evaporated and superheated above its boiling point.
  • This superheated refrigerant is then injected mid-cycle into the scroll compressor and compressed to discharge pressure.

The diagram below shows how enhanced vapor injection (EVI) increases the efficiency of the system.

 

 

 

 

 

 

 

 

 

EVI increases the compression ratio and, in the process, boosts capacity for the refrigeration system. The greatest gains can be achieved during the summer months and other periods when warm ambient temperatures require more cooling.

View our new video series to learn more about the refrigeration cycle. For a deeper dive into all of our training content and access to our other educational resources, visit Education.Emerson.com.

Refrigeration Basics: A Look at Each Step of the Refrigeration Cycle

         Don Gillis | Lead Technical Trainer

          Emerson’s Educational Services

Welcome to the third installment in our blog series intended to help not just beginning service technicians, but anyone who wants to learn more about the basics of refrigeration. In this blog, I introduce some of a refrigerant system’s many basic components, explain what each is designed to do and discuss how they work together. For this blog series, we have also created companion videos that you can cross-reference while accessing other related information at Education.Emerson.com.

Step one: compression

In a compressor-based refrigeration or cooling system, refrigerant enters the compressor as a low-pressure, low-temperature superheated vapor and exits the compressor as a high-pressure, high-temperature superheated vapor. The compressor — which could be centrifugal, reciprocating, rotary, scroll or screw design — mechanically compresses the refrigerant gas. Under pressure, the refrigerant volume reduces, and the temperature rises.

The relationship between pressure and temperature is critical to how efficiently and effectively the system can achieve and maintain its intended setpoint.

Step two: condensing

This second step in the refrigeration process is necessary to convert the vapor to a liquid. As the compressor releases hot, pressurized refrigerant gas into a condenser, it rejects the heat by lowering or returning the temperature of the refrigerant back to its condensing temperature. Condensers utilize three primary cooling methods:

  • Air-cooled — often found in small systems and residential applications; air flows naturally or is forced by a fan over metal (typically copper or aluminum) coils, which carry the heated refrigerant
  • Water-cooled — utilized in commercial systems, large plants and when operating in higher ambient temperatures; cool water replaces natural or forced airflow around the coils carrying the heated refrigerant
  • Evaporative — combines air and water cooling in large-scale facilities such as those for making ice

In most condensers, the refrigerant gas enters at the top of the equipment and leaves at the bottom because the refrigerant in a liquid state is much heavier than the weight of refrigerant in a gas state.

Step three: thermal expansion valve (TXV)

In the third step, the liquid refrigerant is cooled further when pressure is suddenly decreased by the TXV. The valve regulates the amount of refrigerant released into the evaporator in response to the cooling load.

It also measures the superheat leaving the evaporator outlet and maintains a constant temperature by raising or lowering the amount of refrigerant flowing into the evaporator. A precisely controlled flow maximizes the efficiency of the evaporator and ensures that we only have vapor returning to the compressor.

The TXV has multiple ports with bulbs that read:

  • P1 — the temperature as refrigerant leaves the evaporator
  • P2 — the pressure inside the evaporator
  • P3 — the closing force to control superheat flow into the evaporator (if adjustable)
  • P4 — the opening force, liquid line pressure

Step four: cooling in the evaporator

The evaporator is the part of a refrigeration system where the actual cooling takes place. In this fourth step, sub-cooled liquid refrigerant begins boiling off or vaporizes in a process that allows the refrigerant to absorb heat through a series of metal coils. The refrigerant is saturated through this process and this low-pressure, superheated vapor and then returns to the compressor to continue the refrigeration process all over.

What does a suction line accumulator do?

The last system component you should be aware of is the suction line accumulator. This device protects the compressor from a sudden surge of liquid refrigerant and oil that could enter the compressor. Compressors are designed to compress refrigerant in its vapor state. If liquid refrigerant gets into the compressor, we refer to that as “liquid floodback,” resulting in a condition called slugging that can reduce efficiency and cause premature equipment failure.

View our new video series to learn more about the refrigeration cycle. For a deeper dive into all our training content and to access our other educational resources, please visit Education.Emerson.com.

Refrigeration Basics: Troubleshooting Fundamentals

         Don Gillis | Lead Technical Trainer

          Emerson’s Educational Services

Welcome to the second installment in our new series of blogs intended to help not just beginning service technicians, but anyone who wants to learn more about the basics of refrigeration. I will continue to share insights, best practices and other information from our Emerson training program as well as from our commercial and residential solutions experts. In addition, we’ve created companion videos about each topic that you can cross-reference while accessing other related information at Education.Emerson.com.

In this series, I’ll touch on topics ranging from how condensers, compressors and evaporators work, to superheating and subcooling, to the refrigeration cycle, vapor injection and basic refrigeration system troubleshooting.

In this blog, I explain several key topics related to troubleshooting common compressor issues:

  • The role of the condenser
  • Understanding superheat
  • Where to check superheat
  • Understanding subcooling
  • What discharge line temperature really tells us
  • Why compressor overheating is a problem
  • How low you can pump a compressor
  • The difference between floodback and a flooded start

How condensing removes heat from an environment

When we think of the role of a condenser, we’re essentially referring to the place where heat is rejected in a cooling system. What type of heat is rejected? Well, the motor generates heat, and so does the act of compression. The refrigeration system must also reject superheat as well as the load heat from the evaporator.

As part of the refrigeration cycle, the system also condenses the refrigerant. This process involves taking a vapor, removing the heat outside, and condensing it into a liquid by removing the heat and returning it to its condensing temperature.

You’ll notice on most condensers that the vapor enters at the top and leaves at the bottom, where the liquid is much heavier than the weight of the vapor.

What is superheat?    

Superheat is any heat added to a vapor above its boiling point. For example, water boils at 212 oF at atmospheric pressure. The second that last droplet of water evaporates, the temperature rises to 213 oF. That increase in temperature is 1 degree of superheat.

Superheat also is the temperature of the vapor leaving that evaporator on the suction side. A compressor needs superheat in order to function.

Where to check superheat

First, determine what superheat temperature is needed. A system designer more than likely will want to know the superheat leaving the evaporator. If you’re talking to a specialist at Emerson, they’re likely looking for the total superheat or the heat that’s entering the compressor.

Remember that superheat is a vapor, so you can check it on the low side — the evaporator side — of the system. Take a reading of the temperature from the suction line and subtract it from the saturated suction temperature inside the evaporator.

What is subcooling?

Subcooling refers to the heat that is removed from a liquid below its boiling point. For example, if we again use water with a boiling point of 212 oF at atmospheric pressure, its subcooled liquid temperature would be 211 oF.

Subcooling is determined by subtracting the condenser saturating temperature from the liquid line temperature — either leaving the condenser or entering the metering device.

What discharge line temperature really tells us

Discharge line temperature (DLT) is the temperature of superheated vapor leaving the compressor; it can tell us a lot about the conditions inside the compressor.

These temperatures are dependent on model, refrigerant type and application. Refer to Copeland for exact specifications

If the superheat temperature is also high, continue moving down the line to check the temperature leaving the evaporator. The high readings could be caused by a malfunctioning metering device, but more often than not, the DLT temperature is too high because of a high compression ratio.

Why compressor overheating is a problem

When compressor temperatures are higher than normal, it’s typically due to a high compression ratio. A high compression ratio indicates either a high head pressure and a very low suction pressure, or a combination of both.

So what are the typical causes of a high compression ratio? Often, it’s due to thinning of the oil inside the system, leading to more friction on moving parts inside the compressor. Friction adds heat, which can increase wear and tear on the parts and lead to premature compressor failure.

Compressors are designed with a thermal operating disc to provide internal protection. However, it’s crucial to monitor the compressor’s internal temperature; always check the discharge line temperature for an indication.

How low should you pump a compressor?

The answer depends on the model number of the compressor, the application and the refrigerant you’re using. Enter these details into the Copeland™ Online Product Information (OPI) website, where you can find the design specifications for the pump down number.

One more important note to remember with respect to pumping: Never pump a compressor down to zero or into a vacuum.

Know the difference between floodback and a flooded start

Floodback occurs when refrigerant leaves the evaporator and enters the running compressor as a liquid instead of a vapor — which can ultimately lead to system failure. Conditions contributing to floodback include air flow, ice buildup, overcharging refrigerant or misadjusted expansion valves.

Symptoms of floodback include overheating from a loss of lubrication and decreased system efficiency. Prevent floodback by modifying defrost cycles, checking refrigerant charging levels, adjusting or replacing expansion valves, and making sure that evaporator coils are cleaned and not damaged.

A flooded start is different than floodback because it can occur when the compressor is not running — and has not been operated for some time. The difference in the temperature (DT) from the crankcase oil, and the vapor refrigerant in the evaporator causes it to migrate towards the compressor oil. There, it condenses into a liquid and is absorbed by the oil. Then, when the compressor is started, the refrigerant boils into a vapor, diluting the oil in the crankcase and reducing the lubrication of bearings, rods and other critical surfaces.

Symptoms include erratic wear or seizure damage to the rods or bearings and the crankshaft. Prevent a flooded start by installing a continuous pump down cycle on the compressor to remove from the low-pressure side. Pump downs would typically not be used in residential applications.  A crankcase heater can be installed or the compressor can be located where ambient temperatures are controlled.

 

Refrigeration Basics: Understanding Refrigerants With Glide

         Don Gillis | Lead Technical Trainer

          Emerson’s Educational Services

Welcome to our new series of blogs intended to help not just beginning service technicians, but anyone who wants to learn more about the basics of refrigeration. I plan to share insights, best practices and other information from our Emerson training program as well as from our commercial and residential solutions experts. In addition, we’ve created companion videos about each topic that you can cross-reference while accessing other related information at Education.Emerson.com.

In this series, I’ll touch on topics ranging from how condensers, compressors and evaporators work, to superheating and subcooling, to the refrigeration cycle, vapor injection and basic refrigeration system troubleshooting. In this blog, I explain the key environmental considerations of refrigerants, how to account for refrigerant glide, and how the dew point impacts climate control equipment performance.

What’s the difference between ODP and GWP?

A refrigerant’s environmental characteristics are determined largely by two factors: 1) its impact on the Earth’s ozone layer, or ozone depletion potential (ODP); and 2) its potential to produce greenhouse gas emissions, or global warming potential (GWP). Chlorine-containing ODP refrigerants have been banned for use, while high-GWP hydrofluorocarbon (HFC) refrigerants are currently the target of global regulations (i.e., the HFC phasedown). Today, refrigerant manufacturers are introducing a variety of lower-GWP refrigerant alternatives to help commercial and residential customers achieve a full spectrum of sustainability goals.

In the United States, federal and state regulations are accelerating the phasedown of the use of high-GWP refrigerants. Meanwhile, corporate sustainability objectives also are driving more companies to re-evaluate their choices of refrigerants and refrigeration systems.

What is refrigerant glide?

Refrigerants are often comprised of a blend of two or more constituents. These individual components’ different saturation temperatures can impact the refrigerant’s performance characteristics. Working with refrigerants with glide requires understanding the boiling point of each of its constituents:

  • Bubble point, or lowest condensing temperature of a constituent
  • Mean condensing temperature
  • Dew point, or the highest condensing temperature of a constituent

The difference between the boiling points of the first and last constituents is referred to as glide. Essentially, the least volatile component condenses first, and each additional component of a refrigerant blend will start and end at different boiling points. The total temperature glide of a refrigerant blend is defined as the temperature difference between the saturated vapor temperature and the saturated liquid temperature at a constant pressure. An alternate definition is the temperature difference between the starting and ending temperatures of a refrigerant phase change within a system at a constant pressure.

Digital X-Line Series and Lumity™ E3 Supervisory Control Earn Awards

Carmem Valle Pereira | Product Manager – Condensing Units,

             HVACR Technologies

Emerson’s Commercial and Residential Solutions Business

Two of Emerson’s refrigeration technologies were honored with recognition by the 2021 Dealer Design Awards program sponsored by The Air Conditioning, Heating & Refrigeration (ACHR) News magazine. The Copeland™ digital outdoor refrigeration unit, X-Line Series was awarded a gold rating in the Refrigeration and Ice Machines category. The Lumity™ E3 supervisory control took home a bronze award in the Commercial Controls category.

Now in its 18th year, the Dealer Design Awards program recognizes exceptional manufacturing of HVACR technology as well as product designs that benefit HVACR contractors. This year, the awards program received 117 entries, which were judged by an independent panel of contractors.

For the gold: The Copeland digital outdoor refrigeration unit, X-Line Series

Designed specifically for small-format operations, the digital X-Line Series is a compact condensing unit solution that provides refrigeration for multiple fixtures while delivering precise temperature control and significant energy savings. With 20 to 100% capacity modulation, proven Copeland digital scroll technology, large-capacity condenser coils, variable-speed fan motor control and smart controls, the digital X-Line Series is a superior solution for convenience stores (C-stores), small-format food retailers and restaurants.

Standard features include multiplexing capabilities, onboard diagnostics, connectivity, installation flexibility, ultra-quiet operation and corrosion resistance. In addition, expanded refrigerant approvals provide operators with multiple options for selecting a lower-global warming potential (GWP) refrigerant that helps them to meet their sustainability and operational objectives. Many of the X-Line unit’s innovations — including faster, simpler setup, more diagnostics and better communication capabilities that improve reliability and reduce equipment downtime — are the result of direct customer feedback.

Bringing home the bronze: The Lumity E3 supervisory control

Launched in February, the Lumity E3 controller is the next generation in facility management and refrigeration controls. The E3 controller is powered by Emerson’s Lumity supervisory control software to provide food retail and foodservice operators with comprehensive control of critical facility systems. In addition to an intuitive, user-friendly and web-accessible interface, it offers customizable graphs and summary pages; smart alarms to detect, prioritize, troubleshoot and resolve issues; and a performance meter to fine-tune the performance of refrigeration fixtures and equipment.

The Lumity E3 controller’s simplicity provides operators with powerful control to manage and optimize energy use throughout a facility via built-in algorithms which support demand response, curtailment and load shedding programs. The E3 controller was designed to empower contractors and operators across a wide range of skill levels, helping them to work more efficiently, decisively and tackle the challenge of skilled staff shortages. And finally, the E3 controller is engineered for adaptability, providing operators with greater flexibility to revamp their store designs or expand their operations.

Our commitment to innovation

Both the digital X-Line Series and the Lumity E3 controller embody Emerson’s commitment to helping our customers attain greater temperature stability and certainty, improve food quality and safety, minimize equipment failures, curb energy use, and achieve regulatory compliance. The awards underscore our causes to lead our customers through complex technical, regulatory and economic challenges and deliver sustainable solutions that improve efficiency, reduce emissions, and conserve resources.

We are honored to be recognized by the 2021 Dealer Design Awards program and will continue to engage with contractors and end-users to identify ways to further improve our products and solutions.

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