This is part one of the Discover HVAC EPA section 608 certification core course.
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Text Stephen Peters August 2016, updated December 2019
Safe handling of refrigerants is part of the EPA section 608 core certification. Learn which topics are covered in the core exam as well as refrigerant hazard classification and pressurising a system with nitrogen.
During 1985 British scientists announced the discovery of a hole in the ozone layer above the Antarctic. It had been discovered that damage to the ozone layer was caused by man made chemicals such as chlorofluorocarbon (CFC) commonly known by the DuPont brand name Freon as well as hydrofluorocarbon (HCFC). The Ozone layer is located high above the surface of the earth in the stratosphere between 6 to 30 miles above sea level. The ozone layer naturally absorbs ultraviolet radiation from the sun and acts as a natural shield preventing ultraviolet radiation reaching the ground.
Ozone is an inorganic molecule comprised of three oxygen atoms with the chemical formula O3. It is an allotrope of oxygen and is much less stable than the more common diatomic allotrope O2 forming 21% of the atmosphere. O2 of course being the familiar form of molecular oxygen in the atmosphere that you breathe. When high energy sunlight hits molecular oxygen in the stratosphere the oxygen atoms produced combine with other molecular oxygen to form ozone. If the oxygen atom instead meets an ozone molecule they recombine into two molecular oxygen molecules. These two reactions operate constantly in the atmosphere both creating and destroying ozone in a delicate balance. This process is known as the Chapman cycle.
Chlorine is an extremely reactive element which forms part of the stable chemical composition of CFC and HCFC refrigerants. Being stable they are nontoxic and have a long lifespan, CFC's can last for more than 100 years. However this stability means that when they are released into the atmosphere they can diffuse into the upper stratosphere over long periods of time. Once in the stratosphere strong ultraviolet radiation from the sun breaks the chemical bonds freeing chlorine atoms to react with ozone depleting it. This depletion then happens faster than the natural Chapman cycle can replace it leading to the hole in the ozone over the poles today.
Should ozone depletion increase it is likely to cause widespread crop damage, deforestation, damage to marine life, increases in skin cancer rates, and increases in eye diseases. When this became apparent it caused widespread alarm globally.
During 1987 an international agreement called the Montreal Protocol was agreed and signed by 196 states and the European Union. The treaty came into force on 1st January 1989. It was intended to phase out many chemicals responsible for damage to the ozone layer including some refrigerants used in cooling equipment. This was included in the amended Clean Air Act which passed into law during 1990. The updated CAA contained sections 608 and 609 covering both stationary heating ventilation and air conditioning (HVAC) and motor vehicle air conditioners (MVAC).
The federal government introduced the Clean Air Act (CAA) in 1970 to establish National Ambient Air Quality Standards (NAAQS) in order to protect public health. This built on the earlier 1963 act, and was again modified in 1977 and 1990. The 1970 Act represented a major policy shift in environmental regulation, one goal of the 1970 Act was to achieve NAAQS by 1975. During 1985 British scientists announced the discovery of a hole in the ozone layer above the Antarctic. It had been discovered that damage to the ozone layer was caused by man made chemicals such as chlorofluorocarbon (CFC) commonly known by the DuPont brand name Freon. As the ozone layer acts as a natural shield against ultraviolet radiation from the sun further damage could spread to inhabited areas of the planet, causing widespread health issues.
These CAA sections address the handling and recycling requirements of refrigerants as well as the mandatory certification requirements of technicians. When the act passed into law anyone repairing or servicing equipment containing refrigerants must be certified. The sections also restricted sales of refrigerant to certified technicians with requirements for vendors to record purchases of refrigerants.
The care, installation and maintenance of HVAC systems present a number of safety risks to technicians. As the EPA is the responsible agency for many of the substances and procedures carried out on HVAC equipment they have included safety training alongside environmental training. Refrigerants and HVAC systems contain deadly hazards which you should be fully aware of before working on equipment. Refrigerants are not only potentially damaging to the environment they can cause life changing injuries. Some refrigerants are toxic, some are highly flammable, some are under extreme pressure, and all of them can be present in a very hot or cold state in the same equipment. The same can be said of Nitrogen during testing.
To protect against the hazards of working with refrigerants a number of items of personal protective equipment are available. You should always wear safety glasses and gloves when handling or filling refrigerant cylinders. They should also be worn when operating refrigerant recovery or recycling equipment, as well as when working on HVAC systems. Make sure you know if respiratory protection is required when working with the refrigerant you are currently using, and if it is wear it.
You must also follow safe handling procedures when working with cylinders and use the correct valves, hoses, regulators, and gauges for the gas you are working with. The equipment you use must be in good condition and be free from damage or corrosion. All connectors should be properly and fully engaged to avoid the inadvertent release of refrigerant.
The following sections cover the safety topics that will form part of the core test. There will be test questions on the information in these sections so make sure you have covered them.
For the EPA section 1, 2, and three exams you will need to remember the toxicity and flammability classification. You will need to remember which classification a refrigerant falls under and if you need to wear personal protective equipment such as safety gloves when handling it.
Oxygen free nitrogen (OFN) is used to pressurize a system when leak and pressure testing. OFN is also known as dry nitrogen. Once system tests are complete the system is evacuated and the OFN is dumped. Nitrogen forms seventy eight percent of the atmosphere so releasing it does no environmental damage. Pressurizing with OFN must be performed in a safe manner so the test will contain questions on the correct safe methods to use.
Make sure you remember the following:
When you are using nitrogen to pressurize a system this must always be done with a pressure regulator on the nitrogen tank. The tank pressure is much higher that the system working pressure and is probably greater than the maximum on the nameplate. In this practical demonstration students use nitrogen to charge a system during a leak test.
Early home refrigeration began to take off in the early 1900s when people began to harvest ice from nearby lakes and rivers in the winter. Some large houses and communities had stone ice houses sunk into a pit to store ice and keep it frozen. By the end of the 1800s many Americans stored food in an icebox with a large block of ice inside to keep perishable food cold. Electric refrigerators starting appearing during the early 1900s but were too expensive for most people. During 1927 General Electric introduced the Monitor Top refrigerator which was the first truly affordable refrigerator. These early refrigerators used methyl formate (R611), methyl chloride(R40), and sulphur dioxide (R764) as refrigerants.
These older refrigerants were used up until the 1950s and the refrigeration systems that use them are very low pressure, often using soldered joints in the system. They were replaced by Dichlorodifluoromethane (R12 or Freon-12) as they were considered either highly toxic, highly flammable, or both.
The core principle underlying refrigeration technology the transfer of heat, which is the movement and conversion of heat from one system to another. In HVAC systems refrigerant is used for heat transfer. Refrigerants absorb heat when they evaporate at low pressure and temperature. Conversely refrigerants release heat when they condense at a higher temperature and pressure.
Refrigeration systems are broadly classified into three categories according to the temperature range they transfer heat within. The end use of the refrigeration system and the required operating temperature range defines which classification the system falls into. The categories are:
There are four fundamental components to the refrigeration cycle. Here you can learn what they are as well as how they relate to each other in mechanical refrigeration systems. You will also learn what state and pressure to expect the refrigerant to be in at each part of the cycle.
When heat is applied to a mass its temperature rises. This increase in heat is known as sensible heat. It is also called sensible heat when heat is removed from a mass and its temperature falls. Any heat that causes a mass to change temperature is known as sensible heat. This is also referred to as the dry bulb temperature, meaning the heat can be measured by a thermometer freely exposed to the air. Sensible heat is not the type of heat that is hidden and constant, this is known as latent heat. Only sensible heat can be measured with a thermometer.
When a material is heated it may be at the specific temperature that it undergoes a phase transition (or phase change). An example of this is when water boils and becomes steam, the water has undergone a phase transition. During this change the water temperature does not change despite heat being transferred to it. This type of heat is known as latent heat. Latent heat does not register on a thermometer as it is hidden and driving the phase change in the mass being heated.
Enthalpy is the sum of both the sensible and latent heat in a mass. This is often referred to as total heat. It is equal to the total internal energy of a system plus the product of pressure and volume.
In this lecture you are introduced to some of the underlying theory behind refrigeration technology. You will come across more and more of the topics covered here as you progress towards your exams. All of this is fundamental knowledge you must know. This lecture covers pressure points, boiling points, pressure/temperature charts, temperature glide, and the refrigeration cycle.
Once a liquid has absorbed sufficient sensible heat to reach its phase change temperature it remains at that temperature absorbing latent heat while the liquid boils off as a gas. The gas itself however is now still absorbing sensible heat and can rise in temperature. This increase in temperature of a gas above the liquid boiling point is known as superheat. The number of degrees of superheat is the amount of degrees above the boiling point the gas is at.
For example water boils at 212°F and will absorb heat as latent heat, remaining at 212°F until either all of the water has boiled or the heat is removed. The water that has turned into steam can now rise in temperature. If enough heat is applied over time the steam could reach 248°F while the still boiling water would still be 212°F. In this case the degree of superheat is 36°F as the temperature of the steam is 36°F higher than the boiling point of water.
Saturation is the term used to describe the temperature that a change of state in a substance takes place. Water once it has reached boiling point is at its saturation temperature. Steam once it absorbs enough sensible heat to rise above the saturation or boiling point has become superheated and is no longer at saturation point.
Subcooling is any temperature of a liquid or solid that is lower than the saturation temperature. Water at sea level has a saturation temperature of 212°F, i.e. it boils. If heat is removed from the water its temperature will fall below the saturation point and it becomes subcooled. If for example the water temperature drops to 200°F then the water has become subcooled by 12°F.