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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.

[Webinar Recap] Global Panel Explores the Essential Role of HVACR Careers

RajanRajendran2 Rajan Rajendran | V.P., System Innovation Center and Sustainability

Emerson’s Commercial & Residential Solutions Business

Throughout the world, HVACR technicians play essential roles in society — providing comfort cooling and maintaining the integrity of the cold chain responsible for preserving food and life-saving medicines. While this career path offers lifelong learning opportunities and salaries often exceeding those of many college graduates, our industry is experiencing a global shortage of qualified technicians. In a recent E360 Webinar, we assembled an international panel of expert technicians, practitioners and apprentices to reflect on their personal career journeys, explore the importance of technician professions, and discuss strategies for attracting the next generation of candidates.

In the U.S., we refer to this career path as HVACR technicians. In other parts of the world, they are known as different titles, such as: engineers in the UK; workers in Asia-Pacific; and experts in the Middle East. As I moderated this engaging discussion, each of the panelists provided interesting anecdotes that spoke to different aspects of the global importance of this role and the expanding opportunities that exist. Here is a brief sample of those perspectives.

Don Gillis, technical training specialist at Emerson
As a 30-year journeyman technician and current educator, Don spoke about a typical technician career trajectory for those starting out in the industry that mirrored his own life experiences. A technician often begins their career as an installer, carrying tools, cutting, cleaning and fitting copper together for new applications. A next logical step would be to shadow a more experienced professional, helping them with preventative maintenance and seeing firsthand how rewarding this career can be. Learning more about servicing, troubleshooting and diagnosis exposed him to a variety of issues that can impact system performance, capacity and efficiency. Don shared that his son has followed in his footsteps and started his own HVACR contracting business.

Joe Healy, director of application engineering, MEA, at Emerson
Currently based in Hong Kong, Joe’s experience serving the Middle East and Asia-Pacific regions provided a unique perspective regarding the variety of HVACR approaches within different countries and continents — from the cutting-edge sustainability initiatives of Australia and New Zealand to advanced HVACR technologies in Japan to the manufacturing-focused China to the challenges of underdeveloped infrastructures in India. Joe explained that this broad diversity makes HVACR-related professions both interesting and exciting endeavors in these regions. He also shared how technicians make it possible to not only live, work and thrive in extreme climates and densely populated environments, but also serve as the wheels on which these diverse cultures run.

Alonso Amor, director of engineering services, Mexico, at Emerson
Alonso explained that the ambient temperatures in the Latin American region place high demands on refrigeration and AC loads. Perhaps these conditions have led to what he observed as an eagerness and commitment to learn the technician trade in this region. He explained that HVACR-related seminars are always very well attended, indicating a high level of interest in these skilled trades throughout the region. From his experience, candidates take the initiative to receive training, achieve certifications, and make their contributions felt, despite the hot climate and difficult working conditions.

Carlos Obella, vice president of engineering services and product management, Latin America, at Emerson

Carlos shared how his distinguished career started 35 years ago as an HVAC field technician. As an engineer with a college degree, he quickly gained expertise in installing and servicing parallel rack compressor systems for large supermarkets, which has served as a foundation for understanding the proliferation of today’s refrigeration architectures. He offered an anecdote about how the most competent refrigeration technician he ever met was not a degreed engineer. This individual went on to start his own refrigeration contracting business and became the primary refrigeration consultant for one of the biggest supermarket chains in Argentina.

Trevor Matthews, HVACR training and development specialist at Emerson
As a first-generation refrigeration technician, Trevor explained how this rewarding career checked other boxes on his job criteria checklist. First, he knew he wanted a career that would be universally in demand and allow him to travel the world. Second, like many job seekers, he was interested in earning potential. Not only did his job as a refrigeration technician allow him to travel, but he was making a six-figure salary after five years. He said his passion for refrigeration is fueled by the opportunity for continuous learning. Even though it can be a demanding career, Trevor loves the fact that it proportionately rewards the level of commitment you put into it.

Becky Hoelscher, director, aftermarket sales at Emerson

Becky discussed the growing urgency for our industry to replace a retiring generation of baby boomer technicians with the next generation of technicians. She explained that there will be an estimated 15% deficit of qualified technicians by 2026, and the industry needs to start recruitment efforts in high school and entice students to consider this career. Becky reiterated the importance of apprenticeships and discussed federal, state and local efforts to support these initiatives. She believes that a combination of classwork learning and on-the-job training can ultimately lead to certification — where students can even start getting paid while working toward a certification.

Nicholas Didier, mechanical technician (HVACR student)

As a high school senior enrolled in an HVACR program, Nicholas shared his experience participating in a pre-apprenticeship opportunity at Emerson’s The Helix Innovation Center. His goals were to understand the basics of refrigeration and get hands-on HVACR field experience. But in the process, he gained insights into the technician profession and uncovered a desire to further explore system design. Nicholas’ passion and accomplishments earned him a $1,000 scholarship from the Today’s Opportunities Offering Lifetime Skills (TOOLS) program and a new Ford Ranger truck. He plans on using the money to purchase tools for the HVACR technician trade and further his education.

All these anecdotes and individual perspectives speak to the opportunities that await those who enter this rewarding career path. To learn more about the importance of HVACR technician careers and how to attract the next generation of candidates, view this webinar.

 

 

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