Impact on Energy Consumption and Environmental Degradation by Switching of Refrigerants in Small Scale Commercial Refrigeration Units


Master's Thesis, 2019

87 Pages


Excerpt

TABLE OF CONTENTS

Abstract

Table of Contents

List of Figures

List of Tables

List of Abbreviations

1. Introduction
1.1 Motivation
1.2 Objective
1.3 Scope
1.4 Outline

2. Fundamentals and Related Work
2.1 Ozone Layer and Its Depletion
2.2 Refrigeration
2.3 Refrigerant
2.4 Montreal Protocol
2.5 ODP and GWP
2.3 Flammable Refrigerant
2.7 Current Status
2.8 Designation of Refrigerants
2.9 Selection of Refrigerants
2.10 Hydrocarbons as Refrigerant

3. System Design
3.1 Design Parameters
3.2 Experimental Setup Parameters

4. Experiment and Findings
4.1 Course of Experimentation
4.2 Placement of Sensors
4.3 R134a Against HC Blend System in Natural Ambience
4.4 R134a Against R290 System in Natural Ambience
4.5 Variation of Efficiency During Volume Modification
4.6 Performance in Modified Ambience Conditions

5. Challenges Faced
5.1 Human Error Factors
5.2 Machine Error Factors

6. Implementation Scenario in The E.U.
6.1 HFC Regulations in Various Countries
6.2 International Developments With HCs
6.3 Possible Usage Areas in Germany

7. Challenges in Switching

8. Conclusions

VI Aknowledgements

VII Bibliography

Appendix A

Appendix B

Appendix C

Abstract

World population has reached 7 billion people in 2013 and there has been an increase in energy consumption, especially in emerging countries. In 2050 it will be more than 9 billion people living on the planet. Because of this, there has been a rapid increase in CO2 concentration levels, so the average planet temperature is rising, causing a greenhouse effect, as the CO2 is trapping in the heat and not releasing it. Consequently, ocean levels are rising, because of the shrinking polar ice caps. We also have seen an increase in the frequency of extreme atmosphere events around the globe. The refrigeration industry has contributed a lot to the global ozone depletion and global warming. To reduce the environmental impact by the heating, ventilation, air conditioning and refrigeration industry – both commercial and domestic – there is an urgent need to look for solutions that are both ozone friendly and CO2 friendly (greenhouse effect friendly). Eradicating the damage to the environment has encouraged the industrial and commercial refrigeration industry to investigate refrigerant alternatives that reduce the environmental impact although a good transition to them will also depend on the training that technicians acquire, as well as the understanding of the current and future benefits for the companies and the end users. This thesis aims at such a system which is both above mentioned. Once such a system is designed, it is of the utmost importance to test it and compare it with the systems that are being used currently to assess the benefits of using such system. The thesis has a focus on the liquid cooling systems such as water coolers and small commercial systems that help attain cooling of the liquids to a set temperature. In this thesis, the improvement of energy consumption and environmental degradation prevention is attained by switching the refrigerant used from R134a (current) to R290 (Propane) which is a natural refrigerant and Hydro Carbon Blend which is a mixture of refrigerants but is safer and environmentally friendlier. A comparison of both systems is done against the current system in terms of efficiency, energy consumption and chemical properties with respect to global warming potential and ozone depletion potential and ultimately proven that natural refrigerants and HC Blends are the refrigerants of the future.

LIST OF FIGURES

Figure 1 Natural Ozone formation in Environment

Figure 2 Depletion of Ozone Layer from ODS

Figure 3 Refrigeration System

Figure 4 Refrigeration Cycle

Figure 5 Categories and single substances as refrigerants

Figure 6 Alternative Refrigerants

Figure 7 Volumetric Efficiency vs. Compression Ratio

Figure 8 Comparison of Pressure Ratio

Figure 9 Working mechanism of a water cooler

Figure 10 Sample Experimental Unit

Figure 11 Actual Experimental Setup

Figure 12 Cooling Tank

Figure 13 Compressor View

Figure 14 R134a Compressor

Figure 15 Hydrocarbon Blend Compressor

Figure 16 Propane based compressor information tag

Figure 17 Refrigerant Charging unit

Figure 18 Signal processing and data acquisition System

Figure 19 Watt meters used in the Experiment

Figure 20 Modified Ambient Temperature

Figure 21 Circuit Diagram

Figure 22 Circuit diagram for the single system

Figure 23 Course of Experimentation

Figure 24 Compressor Head Temperature Sensor

Figure 25 Compressor Crank Case Temperature Sensor

Figure 26 Suction Line Temperature Sensor

Figure 27 Water Tank Temperature Sensor

Figure 28 Liquid Line Temperature Sensor

Figure 29 R134a system against HC Blend system – Natural Ambience

Figure 30 Graph of temperature vs. time

Figure 31 R290 system against R134a system – Natural Ambience

Figure 32 Graph of Temperature vs. Time

Figure 33 Testing in modified ambient conditions

Figure 34 Graph of Temperature vs. Time - HC Blend

Figure 35 Graph of Temperature vs. Time - R290

Figure 36 Base Assembly

Figure 37 Brazing the Joint - 1

Figure 38 Brazing the Joint - 2

Figure 39 Final Result

Figure 40 Vacuum Pump Assembly

Figure 41 Gas Charging Station – User Interface

Figure 42 Gas Charging Station - Assembly

Figure 43 Overcharged System - Frost on Compressor

Figure 44 Technical information of units used in Waldbühne

LIST OF TABLES

Table 1 Survey of Refrigerants

Table 2 Natural Refrigerants used in Industry Today

Table 3 Specification of R290 according to DIN 8960 - 1998

Table 4 Performance analysis on a set point at 20 °C

Table 5 Performance analysis by external volume modification

Table 6 Performance Comparison

Table 7 Estimated number of units used in locations around Germany

LIST OF ABBREVIATIONS

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1. INTRODUCTION

1.1. Motivation

In the 1970s, scientists discovered certain man-made compounds contributed to the depletion of the Ozone Layer. These are the Ozone Depleting Substances (ODS) that have both Ozone Depletion Potential (ODP) and Global Warming Potential (GWP). The compounds can be found in such every-day household items as refrigerators, Styrofoam cups, spray deodorants, and cushions. In 1984, international attention was drawn to the urgent need of appropriate measures when it was confirmed that the Ozone Layer over Antarctica was disappearing.

In 1985, the global community then adopted the Vienna Convention for the Protection of the Ozone Layer. Then, in 1987, they signed the Montreal Protocol on Substances that Deplete the Ozone Layer. Because of the international agreement, the ozone hole in Antarctica is slowly recovering.

But the Ozone hole is not the only problem that we are dealing with. Global warming due to the greenhouse effect and excessive CO2 release in the atmosphere is also one of the major problems that need to be addressed. The 19th Meeting of Parties (MOP) held in September 2007 in Montreal, decided to advance the phase-out of production and consumption of Hydrochlorofluorocarbons (HCFCs) by 10 years for an early recovery of the ozone layer (Decision XIX/6). HCFCs are not only Ozone depleting substances, but also are potent greenhouse gases (GHGs). It is a challenging task, particularly to developing countries like India, to shift from HCFCs to environment-friendly alternatives.

HCFCs are being replaced by alternatives, like Hydrofluorocarbons (HFCs) and natural fluids. Worldwide, there are well established and energy efficient technologies available with non-ozone-depleting HFCs, particularly R-410A, in the unitary air-conditioning sector. But R-410A has a significant Global Warming Potential (GWP).

Due to environmental issues of high GWP refrigerants, natural fluids with negligible GWP are gaining more popularity for various applications. Among the hydrocarbons, HC-290 has similar properties to HCFC-22. Many studies reveal that the performance of HC-290 in air-conditioners (AC) is better than HCFC-22. Air conditioners with HC-290 have far better energy efficiency than HCFC-22 while having heat transfer characteristics which are similar or superior to HCFC-22. The heat transfer coefficients are better for HC-290 for both condensation and evaporation.

1.2. Objective

The aim of this work is to understand the working of a refrigeration (liquid cooling) system along with understanding the regulations and policies that have been enacted by the world governments which affect the manufacturing industry and the consumer consumption of liquid cooling products. It is important to select a refrigerant which helps us attain the goals of energy efficiency and environmental protection, which would then be compared with the existing systems and at the end a conclusion could be drawn to determine, which system is a better alternative to achieve the target of reduced energy consumption.

In view of the needs to attain the level of better environmental conditions and to reduce the energy consumption and to attain the goals of the Paris Agreement and Kigali Amendment, the objectives of the study can be summarized as follows:

- Experimentally determining the Energy Consumption of an R134a based Water Chiller System with set specifications
- Experimentally determining the Energy Consumption of an R290 based Water Chiller System with similar specifications as of above
- Experimentally determining the Energy Consumption of an HC Blend based Water Chiller System with similar specifications as of above
- Determining the effective savings with respect to energy consumption
- Determining the safety aspects and other issues associated with the conversion and their solutions

This thesis aims at understanding the results attained from the experiments performed on the systems under a static ambient temperature as well as under increasing ambient temperature and testing the systems to the limits. This, in turn, helps to understand the logistics of switching to a system based on R290 (Propane) or HC Blend versus currently used system (R134a).

1.3. Scope

The scope of the thesis includes the understating of a refrigeration system and along with it understating the types of refrigerant and their effects on the environment. This thesis focuses solely on the natural refrigerant – Propane (R290) and Hydrocarbon Blend (a mixture of Iso-Butane and Propane) against the HFC R134a, which is being used currently in most of the systems in developed countries as well as developing countries.

This thesis does not curtail an individual detailed research in all the natural refrigerants available and not on all the HFC available. The refrigerants that form the backbone of this thesis have been carefully chosen by consulting the industry and by understanding the current and future market trends.

A careful study of the refrigerant systems and the global policies dictated the scope of the thesis. The base system that is to be compared for factors like energy consumption, refrigerant charge and cooling efficiency was selected to be industry standard which is 1,1,1,2-tetrafluoroethane i.e. R134a. For the comparison, an HC Blend was used in another system which is a blend of Propane (R290) and Iso-Butane (R600a) in a certain ratio which varies from manufacturer to manufacturer. In this thesis, the HC Blend used was from an Indian company - Godrej & Boyce Manufacturing Company Limited. The third system was based on propane (R290), which is one of the highly flammable refrigerants. First of all, a prefabricated refrigeration (water cooler) system with R134a was selected, which was defined as the standard for the project. The system was then tested for leaks and other faults which may lead to failure or false reporting of data values. Once the leak testing was completed a clone system was designed but instead of R134a, it was designed for Hydrocarbon Blend. Similarly, it was also tested for leaks and other problems which may lead to failure or false reporting of values. A third system was then designed with Propane (R290) as its refrigerant and tested for leaks and other faults. After completing this step all three of the systems were run under the same ambient conditions for a certain period of time in which various values were observed and calculated such as temperatures and pressures at various points, energy consumption etc. Finally, all the relevant data was recorded into the data logger and then transferred to a computer for manipulation purposes.

1.4. Outline

This thesis has been separated into 8 Chapters, which have further been subdivided into segments for easier understanding of the thematic as well as to provide a transition from the fundamentals till the conclusion of the master thesis in a definite and an explained manner.

Chapter 2 deals with the fundamentals of the issues discussed in the thesis such as the Montreal protocol and associated terminology like ozone layer, its depletion, refrigerants and refrigeration systems, impact of refrigerants and other related topics in detail. The work already done or in progress related specifically to this thesis has also been discussed in this chapter.

Chapter 3 deals with designs of the systems those were used in this thesis as well as the designs of the systems currently being used in the market. This chapter also explains the necessary changes that need to be kept in mind when switching refrigerants and the importance of such modifications.

Chapter 4 deals with the experimentation performed in the course of this thesis along with the out comings of the same. This section elaborates the course of experimentation while also covering important aspects of data recording and interpretation.

Chapter 5 deals with the challenges that were faced during the course of experimentation required in the thesis. These include but are not limited to human errors and machine errors.

Chapter 6 covers the implementation scenario the thesis in the European Union and across the globe while also outlining the current HFC regulations in these countries as well as the actions that have been put into place by the respective authorities. Special emphasis is given to the possible usage scenario in Germany.

Chapter 7 deals with the possible challenges that may be faced while switching from traditional refrigerants to natural refrigerants. These outline the various policies, regulations, technological shortcomings and other such issues that prevent a rapid changeover from the traditional refrigeration.

2. FUNDAMENTALS AND RELATED WORK

2.1 Ozone Layer and its Depletion

The ozone layer is a layer in the Earth's atmosphere containing high concentrations of ozone. It is typically said to exist between about 20 and 30 km above the Earth's surface, but it does not have definite edges.

The ozone layer protects us from harmful radiation from the sun. In particular, it protects us from UVB, which is a type of ultraviolet radiation. Small amounts of exposure to UVB can result in sunburn, but high levels of exposure would cause us - and most other life on earth - to die.

The natural existence of ozone is described in Figure 1. High in the atmosphere, some oxygen (O2) molecules absorbed energy from the Sun's ultraviolet (UV) rays and split to form single oxygen atoms. These atoms combined with remaining oxygen (O2) to form ozone (O3) molecules, which are very effective at absorbing UV rays. The thin layer of ozone that surrounds Earth acts as a shield, protecting the planet from irradiation by UV light. (UNEP, 2017)

Since the mid-1970s scientists have been concerned about the harmful effects of certain chlorofluorocarbons (CFCs) on the ozone layer. These CFC compounds are relatively inert and nontoxic, and humans found a use for them as cooling agents in refrigerators and air conditioning systems amongst other things. Because they are so inert, when CFCs become discharged into the atmosphere they diffuse and do not decompose straight away - not until they are hit by shortwave UV radiation. This occurs in the ozone layer.

One chlorine atom can destroy up to 100,000 ozone molecules before it is removed by some other reaction. This can be devastating for the ozone layer. It disrupts the delicate flux and causes ozone to be destroyed faster than it is created.

When a CFC is hit by UV radiation, it loses its chlorine atom. This chlorine atom acts as a catalyst. It is able to steal one oxygen atom away from an ozone molecule, leaving an oxygen molecule and chlorine oxide. Chlorine oxide can then react with a single oxygen atom to form an oxygen molecule and a chlorine atom. This cycle means the chlorine atom is free to break up another ozone molecule. Figure 2 summarizes the depletion of the ozone molecules and hence the ozone layer pictorially. (Wadhwa, A. et.al., 2016)

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Figure 2 Depletion of Ozone Layer from ODS

The PSCs (Polar Stratospheric Clouds) essentially provides a surface for the harmful CFCs and other such chemicals used in the refrigeration industry to react with the ozone molecules present in the stratosphere in the presence of the Sun’s UV (Ultra-violet) rays. They play the role of an adsorbent. It means that the clouds do not play role in any chemical reaction that is happening instead provide a surface for the reaction to happen. Polar stratospheric clouds also catalyze ozone depletion by active chlorine. (GIZ Proklima, 2016)

2.2. Refrigeration

Refrigeration, or cooling process, is the removal of unwanted heat from a selected object, substance, or space and its transfer to another object, substance, or space. Removal of heat lowers the temperature and may be accomplished by use of ice, snow, chilled water or mechanical refrigeration. Mechanical refrigeration is the utilization of mechanical components arranged in a "refrigeration system" for the purpose of transferring heat.

A refrigeration system is divided into two parts. One is of high pressure (shown in red) and the other is of low pressure (shown in blue). As shown in figure 3, the vapor compression refrigeration system consists of components, such as a condenser (1), a Figure 3 Refrigeration System capillary/expansion device (2), an evaporator (3) and a compressor (4). (GIZ Proklima, 2016)

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Condenser: The condenser removes heat given off during the liquefaction of vaporized refrigerant. Heat is given off as the temperature drops to condensation temperature. Then, more heat (specifically the latent heat of condensation) is released as the refrigerant liquefies. There are air-cooled and water-cooled condensers, named for their condensing medium. The more popular is the air-cooled condenser. The condensers consist of tubes with external fins. The refrigerant is forced through the condenser. In order to remove as much heat as possible, the tubes are arranged to maximize surface area. Fans are often used to increase air flow by forcing air over the surfaces, thus increasing the condenser capability to give off heat.

Flow control device (expansion valve): A flow control device, generally known an expansion valve controls the flow of the liquid refrigerant into the evaporator. Control devices usually are thermostatic, meaning that they are responsive to the temperature of the refrigerant.

Evaporator: This is the part of the refrigeration system that is doing the actual cooling. Because its function is to absorb heat into the refrigeration system, the evaporator is placed in the area to be cooled. The refrigerant is let into and measured by a flow control device, and eventually released to the compressor. The evaporator consists of finned tubes, which absorbs heat from the air blown through a coil by a fan. Fins and tubes are made of metals with high thermal conductivity to maximize heat transfer. The refrigerant vaporizes from the heat it absorbs heat in the evaporator.

Compressor: Of the reciprocating, rotary, and centrifugal compressors, the most popular among domestic or smaller power commercial refrigeration is a reciprocating compressor. The reciprocating compressor is similar to an automobile engine. A piston is driven by a motor to "suck in" and compress the refrigerant in a cylinder. As the piston moves down into the cylinder (increasing the volume of the cylinder), it "sucks" the refrigerant from the evaporator. The intake valve closes when the refrigerant pressure inside the cylinder reaches that of the pressure in the evaporator. When the piston hits the point of maximum downward displacement, it compresses the refrigerant on the upstroke. The refrigerant is pushed through the exhaust valve into the condenser. Both the intake and exhaust valves are designed so that the flow of the refrigerant only travels in one direction through the system.

A vapor compression refrigeration cycle, as shown in figure 4, consists of four processes (1) evaporation, (2) compression, (3) condensation, (4) expansion.

The liquid refrigerant which is at low pressure in a heat exchanger absorbs heat from a suitable source, e.g. air source or a body or substance to be cooled, changing its state to vapor. The process of a liquid refrigerant evaporating to a vapor state is called ‘evaporation’. The component in which evaporation takes place is called an ‘evaporator’. The design of an evaporator should be such that the refrigerant should reach a superheated state at its exit. The low-pressure refrigerant vapor compressed. In this process, the pressure and temperature of the refrigerant increase substantially. The refrigerant entering the compressor should be dry and adequately superheated. The vapor which emerges from the outlet of the compressor is highly superheated.

After compression, the high-pressure superheated refrigerant flows through a heat exchanger where heat is rejected to a suitable sink e.g. atmospheric air or cooling liquid. This heat exchanger is known as a condenser. The heat rejection in the first part of the condenser is known as de-superheating. The de-superheated refrigerant further rejects heat and it starts condensing in the heat exchanger to a liquid state. In the last part of the condenser, the condensed refrigerant is subcooled.

When the high pressure condensed liquid refrigerant flows through the capillary, its pressure decreases. The capillary also controls the refrigerant flow or quantity into the evaporator. Hence, appropriate capillary diameter and length should be used.

2.3. Refrigerant

According to the Business Dictionary, a chemical used in a cooling mechanism, such as an air conditioner or refrigerator, as the heat carrier which changes from gas to liquid and then back to gas in the refrigeration cycle is defined as a refrigerant. (Business Dictionary, 2016)

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Figure 4 Refrigeration Cycle enters the compressor and gets

There are a number of different substances used as refrigerants, with the main ones (that are single substances) summarized in Figure 5.

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Figure 5 Categories and single substances as refrigerants

All of these substances except for chlorofluorocarbons (CFCs) and HCFCs are permitted under the Montreal Protocol; thus the remaining ones may be considered as alternative refrigerants. Amongst these, there are the “synthetic” refrigerants and the so-called “natural” refrigerants.

Whilst some of these substances may be used as pure refrigerants, it is common practice to mix two or more substances (sometimes up to seven components) in order to achieve a certain set of desired characteristics (i.e., related to saturation pressure, flammability, oil solubility and so on).

Mixture refrigerants can be further subdivided into “zeotropic” and “azeotropic” types. Zeotropes exhibit a temperature glide and composition change during phase change, whilst azeotropes behave as pure substances during phase change. However, some zeotropes are sometimes classed as “near-azeotropic refrigerant mixtures” (NARMs) as their temperature glide and composition is sufficiently small that from a practical perspective, their behavior mimics a pure refrigerant. (Mota-Babiloni et.al., 2015)

Other means of categorizing refrigerants include:

- Ozone depletion potential (ODP)
- Global warming potential (GWP)
- Safety characteristics (flammability, toxicity)
- Pressure level

Such characteristics affect the selection of the refrigerant and often dictate the manner in which they are applied.

2.4. Montreal Protocol

The Montreal Protocol on Substances that Deplete the Ozone Layer was designed to reduce the production and consumption of ozone-depleting substances in order to reduce their abundance in the atmosphere and thereby protect the earth’s fragile ozone Layer. The original Montreal Protocol was agreed on 16 September 1987 and entered into force on 1 January 1989.

In addition to adjustments and amendments to the Montreal Protocol, the Parties to the Protocol meet annually and take a variety of decisions aimed at enabling effective implementation of this important legal instrument. Through the 22nd Meeting of the Parties to the Montreal Protocol, the Parties have taken over 720 decisions. (UNEP, 2014)

2.5. ODP and GWP

Refrigerants are evaluated for their environmental friendliness on the basis of their Ozone Depleting Potential (ODP) and Global Warming Potential (GWP).

ODP is the measure of the ozone-depleting capability of a refrigerant compared to that of CFC-11 which has been given an ODP value of 1.0 (Baseline).

GWP is an index which compares the warming effect over time of different gases, relative to equal emissions of CO2 by weight.

2.6. Flammable Refrigerant

The term “flammable” means “substance with the capacity to develop an exothermic oxidation reaction”, (In atmospheric pressure, i.e. 1 atm = 101.325 kPa = 760 mm Hg) whilst within the ATEX directive, the definition of explosive atmosphere (which is specifically to what the directives apply) is: a “mixture with air, under atmospheric conditions, of flammable substances in the form of gases, vapors, mists or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture”.

Flammability is the ability of a substance to burn or ignite, causing fire or combustion. Two important chemical characteristics that contribute to the flammability of a substance are a flash point and vapor pressure. The flash point of a substance is the lowest temperature at which it can vaporize to form an ignitable mixture in the air while the vapor pressure indicates the evaporation rate. Higher vapor pressures lead to lower flash points and therefore higher flammability.

Information on the flammability of refrigerants is available from SNAP substitute risk screens, chemical manufacturers, published literature, and safety data sheets (SDS) for all chemicals. Lower flammability limit (LFL) and upper flammability limit (UFL) for all flammable gases and vapors define the range of flammable concentrations in air. These limits are measured using testing methods based on visual observations of flame propagation and are used to determine guidelines for safe handling. (ASHRAE Standard, 2010)

2.7. Current Status

2.7.1. Montreal Protocol

The year 2012 marked the 25th anniversary of the signing of the Montreal Protocol. Accordingly, the Montreal Protocol community organized a range of celebrations at the national, regional and international levels to publicize its considerable success to date and to consider the work ahead for the future. Among its accomplishments are: The Montreal Protocol was the first international treaty to address a global environmental regulatory challenge; the first to embrace the "precautionary principle" in its design for science-based policymaking; the first treaty where independent experts on atmospheric science, environmental impacts, chemical technology, and economics, reported directly to Parties, without edit or censorship, functioning under norms of professionalism, peer review, and respect; the first to provide for national differences in responsibility and financial capacity to respond by establishing a multilateral fund for technology transfer; the first MEA with stringent reporting, trade, and binding chemical phase-out obligations for both developed and developing countries; and, the first treaty with a financial mechanism managed democratically by an Executive Board with equal representation by developed and developing countries.

Within 25 years of signing, parties to the Montreal Protocol celebrate significant milestones. Significantly, the world has phased-out 98% of the Ozone-Depleting Substances (ODS) contained in nearly 100 hazardous chemicals worldwide; every country is in compliance with stringent obligations; and, the Montreal Protocol has achieved the status of the first global regime with universal ratification. UNEP received accolades for achieving global consensus that "demonstrates the world’s commitment to ozone protection, and more broadly, to global environmental protection". (GIZ, 2013)

2.7.2. Kigali Amendment

In Kigali, Rwanda at the 28th Meeting of Parties of the Montreal Protocol from October 10th – 15th, 2016 delegates worked tirelessly day and night to negotiate and reach a deal on a timetable that would mandate countries to phase down the production and usage of hydrofluorocarbons (HFCs). Following seven years of continuous consultations, Parties to the Montreal Protocol struck a landmark legally binding deal to reduce the emissions of powerful greenhouse gases in a move that could prevent up to 0.5 degrees Celsius of global warming by the end of this century, while continuing to protect the ozone layer.

Some of the features of the Kigali Amendment are:

- Countries that ratify the Kigali Amendment commit to cut the production and consumption of powerful greenhouse gases hydrofluorocarbons by more than 80 percent over the next 30 years.
- Reducing hydrofluorocarbons under the Kigali Amendment is expected to avoid up to 0.5° Celsius warming by the end of the century
- All prior amendments and adjustments of the Montreal Protocol, which marks its 30th anniversary this year, have universal support.

Environmental experts note that the Kigali Amendment to the Montreal Protocol on Substances that Deplete the Ozone Layer could be the single largest real contribution the world has made so far towards keeping the global temperature rise "well below" 2 degrees Celsius, a target agreed at the Paris climate conference in 2015; this amendment is a huge step forward to achieving that target.

The final deal divided the world economies into three groups, each with a target phasedown date. The richest countries, including the United States and those in the European Union, will reduce the production and consumption of HFCs from 2019. Much of the rest of the world, including China, Brazil and all of Africa, will freeze the use of HFCs by 2024. A small group of the world’s hottest countries such as Bahrain, India, Iran, Iraq, Kuwait, Oman, Pakistan, Qatar, Saudi Arabia, and the United Arab Emirates have the most lenient schedule and will freeze HFCs use by 2028.

As pressure mounts on governments worldwide for less talk and more action to address climate change, the Kigali Amendment is indeed, a commendable move that adds momentum to a series of new global climate change agreements, including the Paris agreement which will officially enter into force on 4 November 2016.

2.8. Designation of Refrigerants

All the refrigerants are designated as:

Fully-saturated halogenated compounds, designated by the formula R XYZ Where,

- R indicates refrigerant
- X indicates the number of carbon atoms (C) – 1, is omitted if the digit is zero
- Y-1 indicates the number of hydrogen atoms (H)
- Z indicates the number of fluorine atoms (F)

For example:

R12 (CFC12) has a formula (CCl2F2) R22 (HCFC22) has a formula (CHClF2) R134a (HFC134a) has a formula (C2H2F4)

Inorganic refrigerants are designated by ‘7’ followed by their molecular weight. For carbon dioxide, the designation works out to be R744. Other examples are R717 (ammonia) and R718 (water). In the case of mixtures, azeotropic mixtures are designated by 500 series e. g. R502 and zeotropic mixtures are designated by 400 series, for example, R410A, R407C, and R417A etc.

All hydrocarbons are also designated as per formula mentioned above:

For example, propane (C3H8) is designated as R290, n-butane is designated as R600 and iso-butane are designated as R600a.

Refrigerants like HFC134a which have more than one molecular formulation are designated with lower case letters ‘a’, ‘b’, ‘c’ and so on at the end of the designation. As shown, ‘R’ indicates ‘refrigerant’; 1 is because, in the molecular structure of HFC134a, two carbon atoms are present; 3 because of two hydrogen atoms, and 4 because of four fluorine atoms.

Mixtures like R404A are designated by their respective refrigerant numbers and mass proportions. In the case of R404A, R indicates ‘refrigerant’; the first 4 indicates 400 series, 04 indicates chronological numbering designating the components of the mixture, but not the percentage of the constituents; the upper case ‘A’ indicates specific composition i.e. percentage (%) composition. In the case of another composition of the same mixture, it will be denoted by the upper case letter ‘B’ for example, R407A, R407B, and R407C.

It has now become customary to indicate refrigerants by the chemical family along with their refrigerant designation number, for example, HFC-134a to indicate that R-134a belongs to HFC family. Therefore, refrigerants like R-22, R-161, and R-290 are written as HCFC-22, HFC-161 and HC-290 respectively.

2.9. Selection of Refrigerants

The refrigeration progression can be divided into slots of years or generations. In the first generation that ranged from the 1830s to 1930s, the most common refrigerants were familiar solvents and other volatile fluids, effectively including whatever worked and was available. Nearly all of these early refrigerants were flammable, toxic, or both and some were also highly reactive and hence accidents were common. Examples of the refrigerants used are ethers, CO2, NH3, SO2, HCOOCH3, CCl4 etc. The second generation was distinguished by a shift to fluoro-chemicals for safety and durability and it lasted from about 1931 to 1990s. This was the period which saw the invention of CFCs and other refrigerants like HCFCs, HFCs etc. The third generation from 1990 – 2010s was considerately strict under the Montreal Protocol and hence it aimed at Ozone Protection. HCFCs with low ODP, HFCs, and HCs were hence used widely over these years. The fourth generation which is the most current since 2010 aims at reducing the effect of global warming and climate change caused by the refrigerants having high GWP. The refrigerants being used nowadays or being developed have zero ODP, low GWP, short atmospheric life and high efficiency as desirable characteristics. The natural refrigerants like R290, CO2 etc. and Hydrocarbon blends fall into this generation. (James M. Calm, 2008)

The refrigerants were selected on a criterion which includes the industry standard, i.e. R134a, which has 0 ODP but still has a high GWP of around 1300; Propane (R290) which is a natural refrigerant with ODP of 3 (negligible) and a GWP of 0 and an HC Blend similarly with both low ODP and GWP. The table below shows a comparison between various Refrigerants and their characteristics.

Table 1 reflects the chemical traits of some of the most common and popular refrigerants known to us not only in terms to their prevalence in the atmosphere once released from the surface but also the ozone depleting potential and global warming potential for each one possesses. The comparison makes it clear that we need to move towards the refrigerants that have negligible GWP and ODP if we need to protect the environment from threats like ozone layer depletion and greenhouse effect leading to global warming.

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Table 1 Survey of Refrigerants

The new refrigerants raise interesting questions on the balance between the conflicting environmental targets and between environmental goals and the safety or compatibility of the refrigerant itself. Considering all the uncertainties that the future refrigerants may or may not hold, the best way to move forward is to move towards the untapped potential of the natural refrigerants. Natural refrigerants are substances that are viable, environmentally sustainable, natural substitute refrigerants that are used in refrigeration systems. They are alternatives to hydrofluorocarbons (HFC), hydrochlorofluorocarbons (HCFC) and chlorofluorocarbons (CFC) based refrigerants. Unlike other refrigerants, they are not synthetic chemicals that are not found in nature.

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Table 2 Natural Refrigerants used in Industry Today

Table 2 describes the presence of the natural refrigerants in the industry today. It could be noticed that more industries, be it small, medium or big, are trying to switch over to natural refrigerants because of the technical, logistical and financial support provided by various governments under various programs. (GIZ – BFS Maintal, 2016)

2.10. Hydrocarbons as Refrigerant

A classification of the alternative refrigerants helps to understand the possible scenario and areas of usage and the potential of a sensible exploitation. The usage of hydrocarbon blends and natural refrigerants is so far an untapped region of application that may prove to be the definitive solution of the upcoming years in HVACR (Heating, Ventilating, Air Conditioning and Refrigeration) Industry. Amongst the alternatives discussed in figure 6, Propane (R290) is one of the most fitting single compound alternatives to the current technologies. It was a misunderstood and feared belief approximately 5 to 7 years ago that propane could only be used in the regions which have a moderate ambient temperatures conditions (ambient temperatures ranging up to 35 degrees Celsius), as a result of which the research and development to use propane as a refrigerant suffered irrevocably. Years of research, development, and testing by various organizations and manufacturers have now substantiated that the propane-based systems can be easily used anywhere across the globe. However, an increase in the measures of safety while using propane, considering that it is highly flammable, is an issue that should not be overlooked. (Panato, VH et.al., 2017)

Figure 6 describes the alternative refrigerants which either are being used currently by the commercial and domestic sector or could be used in future with some improvements on the manufacturing line of the products.

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Figure 6 Alternative Refrigerants

Since a great emphasis is being paid world-wide to search for suitable and viable alternatives for the future of HVACR industry; researching and developing a single compound refrigerant is not the only way to go forward. Apart from the single compound refrigerant, hydrocarbon blends have also proved to be a viable solution to the questionable gases/chemicals that are being used in the industry as a refrigerant. Hydrocarbon blends like HFC-134a – HC-600a have already proven to be a substitute for the CFC-12. (Sekhar, SJ. et.al. 2004)

The term transitional / service refrigerants are being used for the refrigerants which are not the long-term alternatives to the currently used refrigerants and are only being used to phase out the harmful refrigerants by switching to less harmful refrigerants. These refrigerants would also be eventually stopped from being produced and used at some stage.

The term medium and long-term refrigerants, as the name suggests, are the final alternatives and solutions to the current refrigerants as they are the ones which would provide the safety and security of development with absolutely minimal to no damage to the environment while also improving the efficiency of the devices. Most of the natural refrigerants are termed under medium and long-term refrigerants. (Agarwal, RS. 2001)

2.10.1. General Properties of Hydrocarbons

The properties of the hydrocarbons intended to be used as a medium or long-term alternative are discussed as follows:

- Minimal Ozone Depletion Potential – The ozone depletion potential for these hydrocarbons or hydrocarbon blends is either 0 or almost close to 0.
- Minimal Global Warming Potential – These hydrocarbons or hydrocarbon blends have been proven to have a minute global warming potential when compared to the current chemicals being used in the sector
- These have a short atmospheric lifetime – The lifetime of a greenhouse gas refers to the approximate amount of time it would take for the anthropogenic increment to an atmospheric pollutant concentration to return to its natural level as a result of either being converted to another chemical compound or being taken out of the atmosphere via a sink. This time depends on the pollutant's sources and sinks as well as its reactivity. The lifetime of a pollutant is often considered in conjunction with the mixing of pollutants in the atmosphere; a long lifetime will allow the pollutant to mix throughout the atmosphere. Table 1 gives an overview of the mean atmospheric lifetimes of some of the refrigerants.
- These are natural substances present already in the atmosphere – Most of the hydrocarbon blends are a mixture of two or more compounds. Such individually occurring compounds are found in either pure or adulterated form naturally. These naturally occurring compounds have to be treated to improve the purity before being used a refrigerant or forming a blend.
- They have a very good compatibility with lubricants and minerals – A Lubricant is an important component in the refrigeration cycle that helps to maintain a smooth functioning of the mechanical components of a system, be it a compressor, expansion valve or the piping itself. Specifying the correct lubricant (oil) for a refrigeration system is important to ensure optimum system performance. Various refrigerants use different oils. Older CFC and HCFC refrigerants tended to use Mineral Oil (MO) and Alkyl Benzene (AB) oils. Modern HFC and HFO refrigerants tend to use Polyolester (POE) oils. The hydrocarbons and the hydrocarbon blends in the discussion are compatible with all of them, vis-à-vis Mineral oils, Alkylbenzene oils as well as Polyester oils. Nonetheless, care must be taken to select a lubricant that is most suitable for the refrigerant being used.
- They have a lower density as compared to that of an HFC – Due to the chemical and molecular structure and lack or continuing large chains in these hydrocarbons, these have a lower, when not significantly, densities when compared to the Hydrofluorocarbons or chlorofluorocarbons.
- They have a higher coefficient of performance – The coefficient of performance or COP (also used as CP or CoP) of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work required. Higher COPs equate to lower operating costs. These hydrocarbons, by the virtue of their lower density, have a higher coefficient of performance. The equation for COP is:

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Q is the useful heat supplied or removed by the considered system.

H is the work required by the considered system.

They have lower discharge temperature - The compressor's discharge temperature is very important because it's an indication of the amount of heat absorbed in the evaporator and suction line and any heat of compression generated by the compression process. This discharge temperature should never exceed 225°F. Carbonization and oil breakdown can occur if compressor discharge temperatures exceed 225°. Since the hydrocarbons have a low discharge temperature, the faults in the compressor are a rare occurrence which in turn adds to the efficiency and cost saving.

They have better heat transfer coefficients - The heat transfer coefficient in thermodynamics and in mechanics is the proportionality constant between the heat flux and the thermodynamic driving force for the flow of heat (i.e., the temperature difference, ΔT). The equation for heat transfer is:

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They have a low-pressure ratio - The compression ratio is the ratio of the absolute discharge pressure (psia) to absolute suction pressure (psia), found using the formula:

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The high compression ratio leads to high discharge temperatures, which then have multiple burnouts of the system as a consequence. Similar to a lower discharge temperature, this helps the system to run fault free, smoothly and adds to the efficiency and cost saving. Section 2.10.2 provides an in-depth study of the pressure ratio and its comparison.

They are easily combustible and normally highly flammable -The hydrocarbons generally are combustible and most hydrocarbons will burn over a flame- the hydrocarbon reacts with oxygen to produce carbon dioxide and water. For example:

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Due to the safety concerns of every component involved in the product life cycle ranging from the manufacturer until the end user, extra caution must be practiced while handling such refrigerants.

2.10.2. Comparison of Pressure Ratio

Volumetric efficiency is the ratio of the amount of refrigerant gas entering the compressor (suction) versus the amount of gas leaving the compressor (discharge). For example, if the compression cycle is 100% efficient, it means that all of the gas coming into the compressor’s suction fitting is traveling through the system and leaving the compressor’s discharge fitting. Volumetric efficiency is typically expressed as a percent, using the formula volume pumped divided by displacement.

Because of the limitations on clearances in reciprocating compressors, (the area between the top of the piston and bottom of the valve plate), there is always a small amount of re-expansion gas left behind in the cylinder. Even at the top center of the discharge stroke, a small amount of gas still remains. This gas occupies the space between the top of the piston/valve plate and in most cases, the discharge port(s) must re-expand upon returning to the suction stroke of the compression process. This volume of gas (clearance volume) reduces the overall volumetric efficiency incrementally as it grows.

[...]

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Details

Title
Impact on Energy Consumption and Environmental Degradation by Switching of Refrigerants in Small Scale Commercial Refrigeration Units
Author
Year
2019
Pages
87
Catalog Number
V540811
ISBN (eBook)
9783346187680
ISBN (Book)
9783346187697
Language
English
Tags
commercial, switching, small, scale, refrigeration, refrigerants, impact, environmental, energy, degradation, consumption, units
Quote paper
Anant Wadhwa (Author), 2019, Impact on Energy Consumption and Environmental Degradation by Switching of Refrigerants in Small Scale Commercial Refrigeration Units, Munich, GRIN Verlag, https://www.grin.com/document/540811

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