How Important Is Refrigerant Leak Detection?

By: Daniel Stouffer

Refrigerant leak detection in HVAC and RAC systems is a challenging task even for the most experienced service technicians as any leak can be very well hidden in a system component, tubing, or in a safety control switch.

With the Environmental Protection Agency (EPA) regulation documented in The U.S. Clean Air Act (Sections 608 & 609), refrigerant leak detection takes on great urgency. The intent of the regulation is to lower emissions of gases harmful to the environment. As such, the new government rules no longer give service technicians the option of adding refrigerant when the system is low due to a leak. Rather, the leak has to be found and fixed within a specified period of time.

There are numerous types of testing equipment that can be used in refrigerant leak detection, some of it automated and others acting as sniffers for on site testing. To find the leak, service technicians have to determine the best method to use. Methods include a soap solution, a halide torch, dye interception, isolation of a component from the system, or pressurizing the system with dry nitrogen gas.

All of these methods take time and money, which can turn into a very expensive service call. A less costly alternative for companies is utilizing refrigerant management software that pinpoints the origin of a leak by either tracking service events over time to establish trends or to implement an automated leak detection technology.

An electronic leak detector is one of the fastest methods used in refrigerant leak detection. Leaks of HCFCs and CFCs can be found using refrigerant leak detectors. Quick identification of a leak is important because the release of these gases is heavily regulated by the EPA, with companies subject to fines if their emissions are not fixed within a certain time frame.

Refrigerant gas management software is a valuable tool in refrigerant leak detection. Such systems will be able to provide companies important details on the performance of its heating, ventilation and air conditioning (HVAC) and refrigeration and air conditioning (RAC) systems, monitor and detect refrigerant gas leaks, provide reports on refrigerant use, and accurately keep records on maintenance and repair.

Regulations on refrigerant leak detection describes and governs the proper repair of a leak and appropriate disposal of any refrigerant system which can't be repaired. These extensive requirements are in force in the United States, as well as several foreign countries. The treaties set forth a worldwide response to improving and protecting the planet.

Quick action of refrigerant leak detection is a great importance to the environment. Refrigerant gases are identified to cause damage to the ozone layer which have high global warming potential. To comply with environmental standards, many companies are investing in a refrigerant management program to monitor and track equipment usage.

Because of environmental and cost concerns related to refrigerant leak detection, many facilities with systems that use refrigerants are relying on refrigerant tracker applications. A refrigerant tracker monitors refrigeration and air-conditioning (RAC) systems and heating, ventilation and air conditioning (HVAC) systems around the clock and instantly detects the location of any leaks. Various studies confirm that industrial and commercial facilities will be able to save money every year by using leak detection monitoring systems.

About the Author

Sustainability Resource Planning (SRP) software from Verisae helps to manage carbon emissions tracking and reporting requirements across global organizations. The SRP platform makes it easier to report carbon emissions and track refrigerant gases. Learn more at http://www.verisae.com/articles

(ArticlesBase SC #2039354)

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Carbon Dioxide Could Replace Global-Warming Refrigerant

ScienceDaily (July 4, 2000) — WEST LAFAYETTE, Ind. – Researchers are making progress in perfecting automotive and portable air-conditioning systems that use environmentally friendly carbon dioxide as a refrigerant instead of conventional, synthetic global-warming and ozone-depleting chemicals.

It was the refrigerant of choice during the early 20th century but was later replaced with manmade chemicals. Now carbon dioxide may be on the verge of a comeback, thanks to technological advances that include the manufacture of extremely thin yet strong aluminum tubing.

Engineers will discuss their most recent findings from July 25 to 28, during the Gustav Lorentzen Conference on Natural Working Fluids, one of three international air-conditioning and refrigeration conferences to be held concurrently at Purdue University. Unlike the two other conferences, the biannual Gustav Lorentzen Conference, which is being held for the first time in the United States, focuses on natural refrigerants that are thought to be less harmful to the environment than synthetic chemical compounds.

"The Gustav Lorentzen Conference focuses on substances like carbon dioxide, ammonia, hydrocarbons, air and water, which are all naturally occurring in the biosphere," says James Braun, an associate professor of mechanical engineering at Purdue who heads the organizing committee for all three conferences. "Most of the existing refrigerants are manmade."

Purdue engineers will present several papers detailing new findings about carbon dioxide as a refrigerant, including:

• Creation of the first computer model that accurately simulates the performance of carbon-dioxide-based air conditioners. The model could be used by engineers to design air conditioners that use carbon dioxide as a refrigerant. A paper about the model will be presented on July 26 during a special session sponsored by the U.S. Army in which researchers from several universities will present new findings.

• The design of a portable carbon-dioxide-based air conditioner that works as well as conventional military "environmental control units." Thousands of the units, which now use environmentally harmful refrigerants, are currently in operation. The carbon dioxide unit was designed using the new computer model. A prototype has been built by Purdue engineers and is being tested.

• The development of a mathematical "correlation," a tool that will enable engineers to design heat exchangers – the radiator-like devices that release heat to the environment after it has been absorbed during cooling – for future carbon dioxide-based systems. The mathematical correlation developed at Purdue, which will be published in a popular engineering handbook, enables engineers to determine how large a heat exchanger needs to be to provide cooling for a given area.

• The development of a new method enabling engineers to predict the effects of lubricating oils on the changing pressure inside carbon dioxide-based air conditioners. Understanding the drop in pressure caused by the oil, which mixes with the refrigerant and lubricates the compressor, is vital to predicting how well an air conditioner will perform.

Although carbon dioxide is a global-warming gas, conventional refrigerants called hydrofluorocarbons cause about 1,400 times more global warming than the same quantity of carbon dioxide. Meanwhile, the tiny quantities of carbon dioxide that would be released from air conditioners would be insignificant, compared to the huge amounts produced from burning fossil fuels for energy and transportation, says Eckhard Groll, an associate professor of mechanical engineering at Purdue.

Carbon dioxide is promising for systems that must be small and light-weight, such as automotive or portable air conditioners. Various factors, including the high operating pressure required for carbon-dioxide systems, enable the refrigerant to flow through small-diameter tubing, which allows engineers to design more compact air conditioners.

More stringent environmental regulations now require that refrigerants removed during the maintenance and repair of air conditioners be captured with special equipment, instead of being released into the atmosphere as they have been in the past. The new "recovery" equipment is expensive and will require more training to operate, important considerations for the U.S. Army and Air Force, which together use about 40,000 portable field air conditioners. The units, which could be likened to large residential window-unit air conditioners, are hauled into the field for a variety of purposes, such as cooling troops and electronic equipment.

Refrigerants in subcritical applications

In subcritical applications, refrigerant is metered by a capillary tube or thermostatic expansion valve, the control strategy being to inject liquid into the evaporator and maintain a given superheat entering the compressor. The metering device is selected or designed to ensure that there is complete evaporation ahead of the compressor.

Superheat is maintained to ensure that evaporator efficiency is optimal, and that liquid refrigerant does not enter the compressor. Excessive superheat may lead to overheating of the compressor.

In systems where a thermostatic expansion valve is used rather than a capillary tube, superheat is maintained by placement of a sensing bulb at the outlet of the evaporator. The modulation of the valve is then controlled by the temperature transmitted to it from the bulb and the pressure at an internal or external equalization port.

A different control strategy is needed in transcritical cycles.

A system based on the transcritical CO2 cycle uses a high pressure expansion valve (HPEV). Rather than controlling refrigerant metering from the low-pressure side of the system, modulation control comes from the high side of the system. A mechanical HPEV will control refrigerant injection into the evaporator by opening and closing based on the increase or decrease in gas cooler pressure.

In the HPEV, spring force is a closing force that acts on the top of a diaphragm. Increasing spring force throttles the valve, causing a backpressure in the gas cooler; the valve will not open until that back pressure, opposing spring force, increases to the point where it can overcome spring force and open the valve. The valve set point for the inlet pressure can be adjusted manually by compressing a spring in the valve.

Unlike a TEV, an HPEV does not control evaporator superheat. The HPEV injects refrigerant into the evaporator, but superheat is not directly controlled — instead it is indirectly regulated by system design.

The system charge, its distribution between the components, evaporator design, and the heat load, along with other external operating conditions, determines system superheat. By controlling the gas cooler pressure, the HPEV will indirectly influence system superheat, but the system must be designed so that liquid refrigerant in the evaporator outlet is not allowed to return to the compressor.

The HPEV was designed to control gas cooler pressure rather than suction line superheat as does a TEV. An HPEV, therefore, must withstand high-side CO2 pressures that can reach 1500 psia, at the same time accurately controlling gas cooler pressure. Slight capacity and energy efficiency (COP).

Simulation model of a low-temperature supermarket refrigeration system.

HVAC & R Research

| October 01, 2006 | Getu, Haile-Michael; Bansal, Pradeep Kumar | COPYRIGHT 2008 American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)Copyright

This paper presents a computer simulation model of a low-temperature supermarket refrigeration system whose main components include a compressor, a display cabinet, a condenser, and a thermostatic expansion valve. The energy consumption of the system was evaluated as a function of the store relative humidity, which was measured every 16 seconds for 15 days. The model results were validated with the measurements taken from a representative in-situ supermarket in Auckland, New Zealand. The simulation results indicated that the rate of heat transfer in the evaporator was reduced by nearly 10.5 W for each 1% increase in daily average store relative humidity due to the insulating effect of the frost. The frost thickness was found to grow at 0.0354 mm for each 1% increase in the daily average store relative humidity over a 12 hour operation period between the defrost cycles. The pressure drop of the air over the evaporators increased by around 12 Pa for every 10% rise in the daily average store relative humidity.

INTRODUCTION

Supermarkets, which contain heating, cooling, and ventilation (HVAC) as well as refrigeration systems, are the most energy-consuming commercial establishments (Mei et al. 2002). According to the real measurements in the current study, the average power consumption of compressors/rack systems for both the low- and medium-temperature refrigeration systems of the supermarket amounts to roughly 20% of the total energy use. The energy consumption due to auxiliary equipment (defrosting, anti-sweat resistance heaters, display cabinet lights, and fans) and the air-conditioning system of the building are, respectively, 14% and 17%, while the remaining 49% is attributed to water, heating, and lighting systems of the establishment. Defrosting of evaporator coils is one of the most energy-consuming processes in supermarket refrigeration systems. A large amount of frost accumulation decreases the performance of the coil due to reduced rate of heat transfer and airflow. This consequently reduces the refrigerating capacity of the evaporator. Hence, frosting needs attention and should be minimized to improve the energy efficiency of the system and temperature control.

The impact of store relative humidity on refrigerated display case performance has been studied by Howell (1993a, 1993b), Orphelin et al. (1997), and Henderson and Khattar (1999), where the possible energy savings were predicted by reducing the store relative humidity and the energy penalty realized by the air-conditioning system. Among other studies by Inlow and Groll (1996), McDowell et al. (1995), Horton (2002), and Walker and Baxter (2003) on supermarket refrigeration systems, Ge and Tassou (2000) have presented a mathematical model for direct expansion supermarket refrigeration systems using TRNSYS (2001). Their display cabinet model, however, was quite restricted and used loads only due to infiltration, conduction, convection, and radiation, and the model was validated only for medium-temperature display cabinets. The simulation and the experimental work carried out so far in the supermarket industry has mainly focused on medium-temperature refrigeration systems. Further, dynamic frosting, as a result of store relative humidity, is ignored except in the medium-temperature cabinet models of Ge and Tassou (2000). Therefore, there is a need to develop a complete simulation model for low-temperature supermarket refrigeration systems, since they are most affected by the store relative humidity. This paper, therefore, presents a numerical model to investigate the performance of in-situ low-temperature display cases as a function of store relative humidity. The model includes major components of the refrigeration system, such as compressors, display cabinets, condensers, and thermostatic expansion valves. Specific correlations were used to compute frost thickness, rate of heat transfer across the evaporators, and COP. The model results were validated against the measurements taken from an in-situ supermarket located in Auckland, New Zealand, from December 1, 2004, to January 10, 2005. The model was written in a software package called Engineering Equation Solver, or EES (2004), which has built-in properties of many refrigerants. The computer model can be used as a convenient tool to accurately calculate the energy savings of the low-temperature refrigeration systems as a function of store relative humidity.

THE LOW-TEMPERATURE SUPERMARKET REFRIGERATION SYSTEM

Supermarkets have three different types of cooling systems. The first one is the air-conditioning system, whose operating temperature is roughly 5[degrees]C, which regulates the relative humidity and temperature in the occupied store. The second one is the medium-temperature refrigeration system. It has an evaporation temperature of around -8[degrees]C and provides refrigeration for fresh food such as meats, vegetables, and dairy products. The third system has an evaporation temperature down to -40[degrees]C and is called the low-temperature refrigeration system. Nowadays, there are various types of refrigeration systems, such as direct expansion/multiplex, secondary-loop, distributed, and cascade refrigeration systems. However, the direct expansion refrigeration system is the most commonly employed configuration in most supermarkets for providing refrigeration to display cabinets located in the store.

The low-temperature direct expansion refrigeration system under consideration (see Figure 1) consists of display cabinets/freezer rooms of varying geometry, multiple compressors, air-cooled condensers, thermostatic expansion valves (type DANFOSS TUA/TUAE), and evaporator pressure regulating valves (EPRVs). The function of EPRVs, as presented by Tahir and Bansal (2005), is to keep the evaporating temperatures of the respective display cabinet/freezer room at the required levels. The pressure and temperature at the suction manifold of the compressors are also determined by these valves. The dotted line enclosure shown in Figure 1 contains the evaporator assemblies, including drain points for condensate collections during defrost periods. These components in the enclosure are located within the bottom parts of the display cabinets and on the walls of the freezer rooms.

The low-temperature refrigeration system (Figure 1) consists of three major circuits that feed refrigerant R-404A to three sections of the supermarket, such as frozen food cabinets, fish/meat cabinets, and freezer rooms. The geometrical parameters and the operating temperatures of each type of cabinet and freezer room are given in Table 1.

DEVELOPMENT OF SIMULATION MODEL

The development of the simulation model for a low-temperature supermarket refrigeration system, which includes major components such as compressors, display cabinets, condensers, and thermostatic expansion valves, is discussed in the following sections.

Compressor Model

Multiple compressors (rack) in a supermarket refrigeration system are mostly of the semi-hermetic reciprocating type. If the compressor performance data are known, the compressor model may be developed based on the philosophy presented by Popovic and Shapiro (1995). Their model requires inputs such as refrigerant inlet state, outlet refrigerant pressure, clearance volume, polytropic exponents for specific refrigerants, and motor speed to calculate refrigerant mass flow rate and refrigerant.

WORLD ENVIRONMENT DAY 2007; SOME DO AND DON’T TO HELP THE PLANET

Energy savings at home

People all over the world are taking measures to reduce the greenhouse gases emitted as a result of the way they live. Turning the heating thermostat down, and the air conditioning up, by 1.5deg saves around 1 tonne of CO2 (carbon dioxide) a year. An energy- efficiency refrigerator could save nearly half a tonne of CO2 a year, compared with an older model. Insulating windows, doors, and electrical outlets and adding more insulation to the attic and basement reduces energy consumption. Compact fluorescent, spiral light bulbs are 75 per cent more efficient than standard light bulbs.

Energy savings on the road Keeping tyres optimally inflated uses less fuel and cuts down emissions. Driving at 8 kmh below the speed limit over an 13km commute to work saves 350kg of CO2 a year.

Reducing Garbage

On average a person throws away 10 times his or her bodyweight in rubbish a year. One kilogram sent to landfill produces 2kg of methane.

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Source: The Atlas of Climate Change

Mapping the World's Greatest Challenge

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The Press, Copyright of Fairfax New Zealand Limited 2007, All rights reserved.

Provided by ProQuest Information and Learning Company. All rights Reserved.

Climate control

Fox's Tales
by Graeme Fox
Graeme Fox is an RAC contractor based in Dundee. He is a director at AREA (Air Conditioning & Refrigeration European Contractors' Association) and a member of the Institute of Refrigeration.

23/03/2010 14:14:00
It's been a strange start to 2010. Heavy snowfalls grinding much of the south of England to a halt, while on the east coast of Scotland we've seen very little snow since the turn of the year. It has been a very cold winter.

From memory and from anecdotal evidence, it is quite normal to have a good, warm summer following a cold, hard winter.

It will be interesting to see, after so much bad news for the dedicated doomsday-warning brigade recently, if they immediately jump on this and proclaim it as evidence of chaotic climate change caused by man's recklessness.

Personally, I'm far from convinced of the extent of man's impact on global climate patterns.

I've been interested in the subject of planets and the universe for a long time and, having read so much on the subject over the last 30 or so years, the main thing that strikes you is the vastness of the universe around us - and consequently the relative size of Earth itself.

But even when you look at the Earth in isolation this same contrast in relative size is apparent. Viewed from space the Earth is an extremely beautiful planet but you don't see the myriad life forms that dwell on it because we are all so small.

I know that even the smallest creature can have a catastrophic effect on large life forms - after all, even viruses are life forms of a kind that can and have wiped out entire species in the past and continue to threaten us from time to time now.

But man does have an overblown opinion of his importance and influence, both existing and potential, on greater things. Many animals living in the wild have very similar family and network groups to western human society - and all without the infrastructure we seem to believe is necessary. In the distant past there is evidence aplenty of man's ability to live in harmonious communities long before there was any form of bureaucracy.

There is also a wealth of evidence proving that much of the planet has had a number of significant warmer and cooler periods than we are currently witnessing. Warm enough for certain crops to grow in the British Isles that wouldn't survive even now - at a time when we are told that we face imminent catastrophe - and long before the chemical emissions that man is guilty of discharging to atmosphere became an issue.

Environmentalists talk of global sea levels rising and cite Bangladesh as an example of the threat. But globally sea levels aren't rising - as surely they must if the cause were glacial melting! Isolated cases of minimal sea level rise are contrasted with the majority "no change", and the flooding in Bangladesh is apparently coming from rivers bursting their banks, not the sea! Other factors and influences are affecting these patterns, not just man's emissions.



The fact is that man has very little ability to control the weather, let alone climate patterns, despite his over inflated opinion of his worth.

So, before those with a vested interest in promoting their green jobs and positions start bleating this summer about how each sunny day we may be lucky enough to enjoy this year is evidence of catastrophic climate change, remember to give them a reality check on the insignificance of man in the great scheme of things.