Refrigeration Transition

Very few of the USCG exam questions pertain to refrigeration transition. Most of USCG engineer exam questions refer to old R-12, and ammonia systems. However as an engineer you are required to work on refrigeration systems and should be familiar with the new laws.

Due to the global consensus that CFC's (chlorofluorocarbons) and HCFC's Hydrochlorofluorocarbons, refrigerants R-22, -124, -123. HCFC's are less detrimental to the atmosphere, have less ozone depletion and global warming potential than CFC's CFC's Chlorofluorocarbons, refrigerants R-11, -12, -113, -114, -115, -502. CFC's have not been produced since 1995 due to the very harmful ozone depletion effect. (hydrochlorofluorocarbons) released into the atmosphere damage the ozone layer, new laws have been implemented.

As of July 1, 1992 it became unlawful to vent chlorofluorocarbon (CFC's ) and hydrofluorocarbon (HCFC's ) refrigerants into the atmosphere. On November 15, 1995 this law was extended to ( HFC's Hydrofluorocarbons, refrigerants R-32, -134a, -143a, -152a, -125. HFC's have a ozone depletion potential of zero. R-134a is the refrigerant of choice to replace the CFC R-12. ), alternative refrigerants, and all refrigerant blends. If you are not recovering refrigerants aboard ship you are in violation of international law.

As of November 14, 1994 all personal working on refrigeration equipment and machinery must be certified equal to the level of maintenance, installation, or service. Proof of certification is required to purchase CFC and HCFC refrigerants.

The law requires all personal working on refrigeration equipment and machinery to be certified. The question, is a USCG licensed Chief Engineer certified, or are all licensed engineers required to pass a certification exam?

The Process of Ozone Depletion

The ozone depletion process begins when CFC's and other ozone-depleting substances (ODS) are emitted into the atmosphere(1). Winds efficiently mix the troposphere and evenly distribute the gases. CFC's are extremely stable, and they do not dissolve in rain. After a period of several years, ODS molecules reach the stratosphere, about 10 kilometers above the Earth's surface (2).

Strong UV light breaks apart the ODS molecule. CFC's release chlorine atoms, and halons release bromine atoms (3). It is these atoms that actually destroy ozone, not the intact ODS molecule. It is estimated that one chlorine atom can destroy over 100,000 ozone molecules before finally being removed from the stratosphere (4)

Picture, courtesy of NASA GSFC

Ozone is a oxygen molecule with an extra oxygen atom attached (O2 + 1 = O3). Ozone is formed when oxygen molecules (O2) are split into 2 separate oxygen atoms by ultraviolet radiation from the sun. 90% of the earths ozone is located in the stratosphere, where it forms a natural layer that shields the earth from the harmful effects of ultraviolet radiation.

CFC and HCFC molecules released into the atmosphere from refrigeration systems, and solvents make there way to the stratosphere where they break down from Ultraviolet radiation, releasing a chlorine atom. The released chlorine atom binds to one of the oxygen atoms in the ozone molecule (O3), breaking it into oxygen (O2) and chlorine monoxide (CLO). A free oxygen atom then binds with the oxygen atom in the chlorine monoxide molecule, resulting in a oxygen molecule, and a free chlorine atom. The chlorine atom is then free to repeat the process.

Links to learn more

• NASA Stratospheric Ozone, An Electronic Textbook

• Table of all Regulations, Dates, and Federal Register Citations

• List of Ozone-Depleting Substances, ODPs, GWPs, and CAS Numbers

• Numbering Scheme for Ozone-Depleting Substances and Substitutes

Class I Ozone-Depleting Substances

On January 1, 1996 the ENVIRONMENTAL PROTECTION AGENCY stopped the production and use of all class 1 ozone depleting substances.

EPA Certification

Type I - Small Appliances

Small Appliance, manufactured, charged, and hermetically sealed 5 Lbs or less. Refrigerators, freezers, room air conditioners, package terminal heat pumps, dehumidifiers, ice makers, vending machines, and water coolers.

Hermetically sealed small appliance compressors are equipped with process stub, a small service tube on the low side. It is usually a small piece of tubing that can be pierced with a piercing valve.

Piercing valves are used to access a small appliance and are installed by driving a sharp needlelike steel instrument through the copper or aluminum tubing. When the needle is backed out of the tubing, the system can be accessed. Piercing valves come in two types, clamp-on or solder-on. Clamp on valves must be removed once the recovery has been completed. Solder-on valves can be permanently installed on the system.

Schrader valves are installed on small appliances to assist in the recovery of refrigerant. These valves must be checked for leaks or damage. All schrader valves must be capped to prevent leakage.

Recovery machinery for use with small appliances

Built prior to November 15,1993:               

80% of refrigerant must be recovered, 4" Hg vacuum evacuation.

Built on or after November 15, 1993:         

(Operative compressor) 90% of refrigerant must be recovered, 4" Hg vacuum evacuation.

(Inoperative compressor) 80% of refrigerant must be recovered, 4" Hg vacuum evacuation.

System Dependent Recovery (Passive), a device which depends on the appliance components or the refrigerant pressure to remove refrigerant.

Refrigerant is recovered to a non-pressurized container. The use of system dependent devices are permitted on appliances containing 15 pounds of refrigerant or less. A chilled recovery cylinder may be used with the systems compressor to recover refrigerant. Recover refrigerant as a vapor from the high side to minimize the amount of oil removed from the system. CAUTION hermetic compressors rely on refrigerant flow from the evaporator to cool motor windings. Avoid overheating the compressor when using it for recovery. If the compressor is inoperative, recover refrigerant by accessing both high and low side. Heat (130°F) and tap the compressor sharply to release trapped refrigerant from the compressor oil.

Self contained recovery (Active), a device used to recover or recycle refrigerant from a an appliance without the aid of the system components.

If the compressor is in working order, refrigerant should be recovered as a vapor by accessing the high side. This will minimize the amount of oil removed with the refrigerant.

When charging the refrigerant should be added as a vapor to the low side of the system.

Type II - High Pressure, and Very High Pressure Appliances

High Pressure Appliance, refrigerant boiling point between -50°C (-58°F) and 10°C (50°F) at atmospheric pressure. Refrigerants- 12, 22, 114, 500 and 502.

Very High Pressure Appliance, refrigerant boiling point bellow -50°C (-58°F) at atmospheric pressure. Refrigerants- 13 and 503.

System Pump-down

Pumping down the system confines the refrigerant to the receiver, allowing access to most of the systems components without evacuating the system. The king valve located on the outlet side of the of the receiver is closed.  The low pressure cutout switch will need to be jumped in order to run the compressor below the preset cutout pressure. Also solenoid valves must be opened and back pressure regulators bypassed or adjusted. Run compressor until system pressure is reduced to the prescribed vacuum. Shut down the compressor, close the compressor suction and discharge valves, and monitor the system pressure. If the pressure holds steady the system can be opened. To minimize the entrance of air, moisture, and other non-condensables to the system, break the vacuum with dry nitrogen.

Refrigerant must be recovered when system repairs are made to the high pressure side of the system, up stream of the king valve, or when the compressor is inoperative.

Recovering Liquid - push-pull method, draw vapor from top of recovery cylinder with recovery unit and discharge to system, which helps to push the liquid into the recovery cylinder. Vapor recovery will be required after liquid recovery to pull down the system to the mandated evacuation levels.

Recovering Vapor - the recovery unit takes suction from the low and high sides and discharges to the recovery cylinder.

Required levels of evacuation for air conditioning, refrigeration, recovery, and recycling equipment.

Leaks - systems with a charge of 50 lbs or more must be repaired when the rate of leakage equals or exceeds 35% per year for commercial and industrial process refrigeration systems, and 15% per year for all other systems.

Records - Owners and operators of systems with a charge of 50 lbs or more are required to maintain records of refrigerant usage.

Very High Pressure Systems - due to the high pressures and very low temperatures associated with this type of system special precautions must be followed:

• use of special rated hose and gauge sets

• use of special rated recovery cylinders

• use of rubber gloves and side-shielded goggles

Type III - Low Pressure Appliances

Low pressure appliance, refrigerant boiling point above 10°C (50°F) at atmospheric pressure. Refrigerants- 11,113, and 123.

Equipment - low pressure appliances are of particular concern to the EPA. These units, numbering about 80,000 primarily use centrifugal compressors with CFC-11 refrigerant. Initially, as CFC-11 is phased out, it will most likely be replaced by HCFC-123

Because chillers that use CFC-11 and CFC-113 often operate at below atmospheric pressure, the migration of air into the system is a constant problem. The best preventative is to keep the system free of leaks. With large systems this is often difficult and contamination remains a problem. To minimize the effect of this contamination, purge cycles are often used.

Purging is accomplished with a purge system made up of a compressor, oil separator, and purge drum. The primary purpose of the purge system is to remove non-condensables, and water vapor from the system. Air collects in the upper part of the condenser, occupying space and displacing volume normally devoted to cooling refrigerant gas. This effect reduces the condenser size and increases condensing pressure and compressor horse power. The inlet of the purge compressor is typically connected to the top of the condenser. During a purge cycle, non-condensables mixed with a small quantity of refrigerant vapor are drawn off and sent to the purge drum. At the purge drum, the non-condensables and refrigerant are separated using distillation. The non-condensables are purged to the atmosphere, and the refrigerant is returned to the system.

The use of a purge system will be even more important as the EPA regulates emissions from chillers. It is estimated that purging contributes to 15% of all refrigerant emissions from chillers. The need for purging can be reduced by checking for and repairing any leaks on a regular schedule.

Required levels of evacuation for air conditioning, refrigeration, recovery, and recycling equipment.

Refrigerant from chillers is recovered using liquid recovery followed by vapor recovery. Liquid recovery will typically recover about 70% of the total refrigerant. The push-pull liquid recovery technique is most commonly used, because of the large volume of liquid to be recovered. Liquid pumps are also used. many liquid pumps designed for recovery are specifically built for low pressure refrigerants and cannot be used with high pressure systems.

A rupture disc is found on the evaporator and is a pressure reliving device set at 15 Psig. Any pressure over 15 Psig will vent refrigerant to the atmosphere. During recovery this pressure must not be exceeded.

Because a high pressure line from a recovery unit is often used to increase the pressure inside the pressure of a low pressure chiller. There must be a limit on the discharge pressure of the recovery unit. This limit is controlled by a high pressure cut out switch, set for 10 Psig. The recovery containers used on low pressure refrigerant units, must be approved for ASME high pressure use, or fitted with a rupture disc set for 15 Psig.

Refrigerant in chillers can also be recovered using the push-pull method of liquid recovery. Using this technique, an equalizing high vapor pressure line should be used between the recovery cylinder and equipment. The pressure in this line can be increased by applying heat to the recovery cylinder, but must not exceed 10 Psig.

Universal Certification - Certified in all the above: Type I, II, III.       Get Certified