To begin working in the HVAC industry you will need to pass the Environmental Protection Agency (EPA) HVAC certifications. These certifications are often referred to as the EPA 608 certifications and this is the start of the Discover-HVAC.com course.
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Text Stephen Peters August 2016, updated November 2019
The Environmental Protection Agency (EPA) section 608 type 3 certification covers low pressure Heating, Ventilation, and Air Conditioning (HVAC) appliances. This is the Discover-HVAC.com type 3 course which typically follows the core course.
Students must correctly answer 70% of the 25 questions in the type 3 exam (i.e. 18 correct questions) to pass the test. They must also have passed the proctored core exam for a type 3 certification. To gain universal certification the proctored type 1, type 3, as well as the proctored core tests must also be taken and passed. The type 3 exam is a proctored test which for most students means taking the test in a classroom but some companies are starting to offer online proctored tests.
Type 3 systems typically take the form of large chillers for comfort cooling (air conditioning), Industrial Process Refrigeration (IPR), and commercial refrigeration. Low pressure type 3 systems are different from all other HVAC systems because some parts of the system operate at an internal pressure below atmospheric pressure. In some systems all of the system is below atmospheric pressure which means that in the event of a leak air leaks into the system instead of refrigerant leaking out.
One of the differences found in low pressure systems compared to high pressure systems is the purge unit. These are independent small refrigeration systems attached to the main chiller which are designed to separate noncondensibles and contaminants from the refrigerant charge in the main chiller. An ideal chiller would not suffer from noncondensibles entering the system via air leaks however purge units compensate for this when leaks do occur. The design intent is to separate all noncondensibles in the system refrigerant charge while the system is operating. The unit then returns pure refrigerant liquid back into the system and discharges noncondensibles back into the environment they came from.
As the purge unit is an HVAC system in its own right it requires regular maintenance part of which is replacing the adsorption filters on the purge exhaust. These filters are designed to minimize the amount of refrigerant released into the atmosphere when the purge unit dumps noncondensibles from the system.
Low pressure system purge units are generally triggered when high condenser pressures are detected or system efficiency decreases.
As low pressure system leaks concern air being introduced into the system problems frequently revolve around those caused by noncondensibles in the system. Technicians should be familiar with moisture degrading oil in the system and producing acid byproducts, internal corrosion, and increased head pressure.
High head pressure is a strong indication that air has entered the system. Low pressure chillers typically operate under vacuum in the evaporator stage of the system. Both the Condenser and compressor stages of the system operate at either a mildly negative pressure or a low pressure to a maximum of 15 psig of positive pressure.
When noncondensibles are present in the system the purge unit will operate. Once the purge unit has collected sufficient noncondensibles in the storage tank the evacuation pump will operate. An ideal system would not have leaks and would not need to operate the purge system at all. In practice the purge system should not operate more than a few minutes a day or no more than one hour per week. Purge systems running more than 20 minutes per day indicate a very large leak with the worst case scenario leading to the purge unit running constantly. Purge system logs are a good place to look for indications of a leak.
Conventional leak detection techniques used in high pressure systems may not be as effective with low pressure systems. Electronic refrigerant detectors, soap bubbles, or oil residue inspection rely on refrigerant leaking out of the equipment. Low pressure leaks usually take the form of air leaking into the device which is in turn evacuated from the system via the purge unit. Leaks can be located using these methods if the technician artificially raises the system pressure using either heater blankets or hot water. Nitrogen may also be carefully used to raise the system pressure during leak detection.
Leaks can be detected in the compressor and condenser using conventional means as they both operate above atmospheric pressure.
Once conventional techniques have been exhausted low pressure leak detection frequently involves monitoring the activity of the purge unit on the low pressure portion of the system. If the system is off or has only been running a short time and the purge unit is indicating a leak the problem may be in the high pressure stage of the system. If the purge unit does not continue to register a leak after the system has run for any significant time it is highly likely the leak is in the high pressure part of the system.
If heating to pressurize the system to find a leak refer to the pressure temperature chart for the system refrigerant to find the ideal temperature for leak testing. Remember to keep the system pressure well below the rupture disc burst pressure.
When a leak is suspected in the heat exchanger tubing drain the refrigerant from the system before performing hydrostatic testing on the tubing. This is also a good time to clean the chiller barrel of any sediment and scale build up.
Once a major repair is complete evacuate system and hold the vacuum for 12 hours at 500 microns to confirm the repair has resolved all leaks before recharging the system with refrigerant. Pressure changes during this test will indicate there are still unresolved leaks in the system which must be repaired before recharging the system. ASHRAE standard 147-2013 states that a rise in pressure from 1mm Hg to 2.5mm Hg during a vacuum test indicate a system leak.
Recovery machines usually have their high pressure cut out set for 10 psig, while the system rupture disc will burst at 15 psig. When testing the maximum leak test pressure that can be obtained should be no higher than 10 psig to allow a clear safety margin in order to avoid rupturing the disc and venting the refrigerant charge to atmosphere.
Most of the EPA leak repair requirements for type 3 low pressure appliances are the same as for type 2 systems. EPA record keeping rules are the same as well, making the universal test reasonably straightforward to pass.
Appliances containing a refrigerant charge of over 5 lbs where refrigerant is being removed must have records kept for a minimum of three years, which in practical terms means all type 3 appliances must have records kept. These must include the following information:
Appliances containing a refrigerant charge of 50lbs or over must have records kept for a minimum of three years containing the following information:
Since the 1st January 2019 EPA regulations for large systems changed. Appliances containing 50lbs or more of a regulated refrigerant must have an annual leak test. If a leak is detected the leak must be repaired within 30 days if the annual leak rate is over 10% of the refrigerant charge. Once the leak has been repaired and tested another follow on leak test must be completed within ten days.
The thirty day repair deadline can only be extended for the following reasons:
Should an appliance charged with a regulated refrigerant have a chronic leak of 125% or more of the full refrigerant charge in one year the owner must report this to the EPA. The report must include details of the leak detection and repair actions made by the qualified technicians working on the appliance. The owners report must be submitted by March 1st of the subsequent year.
Comfort cooling (otherwise known as air conditioning) has a new leak threshold rate since 1st January 2019 as part of the recent EPA "final rule" update. The new rate is 10% lowered from the previous threshold rate of 15%.
Both IPR and commercial refrigeration also have a new leak threshold rate since 1st January 2019 as part of the recent EPA "final rule" update. For commercial refrigeration the new rate is 20% lowered from the previous threshold rate of 35%. IPR refrigeration has a new threshold of 30% lowered from the previous threshold rate of 35%. If an appliance serves both IPR use as well as other uses it should be considered to be an IPR appliance only if 50% of system capacity serves IPR use. If an appliance used for IPR or commercial use contains a charge of 500 pounds or more of refrigerant it must be leak tested every three months unless a refrigerant leak monitoring system is installed, or it has kept under the leak rate for successive four quarters.
To calculate leak rate you will need to work out the total system charge. This is typically completed when the system is commissioned, however if the documentation of this is not available or you are commissioning the appliance you will need to know how to calculate the total quantity of refrigerant the system can contain. Typically the appliance manufacturer will provide data sheets showing charge values for condensers, evaporators, and receivers. Charge values for both the liquid and suctions lines will need to be calculated from a piping charge calculation table based on the refrigerant, line size, and length of pipe.
Since January 1st 2019 leak rates must be calculated for appliances containing 50 lbs or more of refrigerant. The EPA has set out two allowable methods of calculating the appliance leak rate, the annualizing method, and the rolling average method. These calculations must be retained for three years and since these calculations are used when calculating the leak rate must be available for technicians who are performing new leak rate calculations.
The annualizing leak rate calculation is defined by the EPA as follows:
| Leak rate (% per year) | = | Pounds of refrigerant added | × | 365 days/year | × | 100% |
| 365 days/year | Shorter of #days since refrigerant last added or 365 days |
When using the annualizing method the first refrigerant addition in 2019 the second term would be 365/365 i.e. 1. Subsequent additions would be 365 divided by either the number of days since the last refrigerant addition or 365, whichever is the shortest.
The rolling average leak rate calculation is defined by the EPA as follows:
| Leak rate (% per year) | = | Pounds of refrigerant added over past 365 days | × | 100% |
| Pounds of refrigerant in full charge |
Using the rolling average method in 2019 the dividend would be the lowest amount of either pounds of refrigerant added since January 1st 2019 or the last successful followup test. In 2020 and beyond the dividend would be the amount of refrigerant added since the shorter of 365 days or the last successful followup verification test.
Before attempting to recover refrigerant from a low pressure system look at the appliance data plate and check for any refrigerant retrofit labels. Low pressure systems are frequently large high cost systems and have a reasonably high likelihood of previously being retrofitted with a new low Global Warming Potential (GWP) refrigerant. As there have been many refrigerant blends introduced following the phaseout of CFC and HCFC refrigerants it is important to identify the type of refrigerant charge in the appliance. Read the appliance owners records to find any refrigerant change details. If unsure what the refrigerant type is in a system check with a pressure temperature (P/T) chart as explained in the core section.
Despite being at low pressure refrigerants in type 3 system can still pose a significant safety risk to both the technician as well as the end user. Technicians should ensure they are familiar with the safety sections of the core exam and ensure recovery equipment is not damaged and is being operated correctly. Retain the materiel safety data sheets (MSDS) for any refrigerants you are working with.
Low pressure systems usually contain large amounts of refrigerant. When recovering these systems start recovering liquid refrigerant first as this will significantly speed up recovery times. Once all of the liquid has been recovered move on to vapour recovery.
Of course being low pressure systems type 3 appliances may not have enough residual pressure to allow full recovery of liquid refrigerant. The obvious answer is to simply increase the system pressure to allow refrigerant recovery to proceed. Technicians may not use add Nitrogen to pressurize the system in order to assist recovery in a system containing all or part of a charge. Heating the system is permitted and will increase system pressure and speed up recovery.
Heating does present some issues which must be considered. First a close eye must be kept on system pressure to avoid bursting the rupture disc and inadvertently releasing refrigerant to the atmosphere. Make sure to identify the refrigerant type and then use the relevant pressure temperature chart when heating the system.
Once all of the liquid phase refrigerant has been removed vapour recovery can begin using the recovery machine compressor. Large chillers contain large amounts of refrigerant vapour which must be removed. The example of roughly 100 pounds of refrigerant remaining in a 350 ton chiller are often used in EPA test examples (and you should remember the example for the test). It is however useful to consider how the example was arrived at.
If a 350 ton chiller has a combined evaporator and condenser volume of 300 cubic feet the amount of remaining vapour can be calculated from refrigerant technical data sheets. Take the vapour density per cubic foot and multiply it by the system volume. Remember that a chiller originally charged with R-11 may now have a charge of R-123 and a chiller originally charged with R-12 may now be retrofitted with either R-134a, R401A, R401B, R409A, R414B, or R417C. Check the system documentation first.
| Refrigerant | Vapour density | Quantity per 300 ft3 |
|---|---|---|
| R-11 | 0.365 lb/ft3 | 109.5 lb |
| R-12 | 0.393 lb/ft3 | 117.9 lb |
| R-123 | 0.404 lb/ft3 | 121.2 lb |
| R-134a | 0.328 lb/ft3 | 98.4 lb |
| R-401A | 0.306 lb/ft3 | 91.8 lb |
| R-401B | 0.303 lb/ft3 | 90.9 lb |
| R-409A | 0.313 lb/ft3 | 93.9 lb |
| R-414B | 0.325 lb/ft3 | 97.5 lb |
| R-417C | 0.289 lb/ft3 | 86.7 lb |
In the table above we compare the quantity of vapour left in a 300 ft3 chiller for a variety of common low pressure refrigerants. There is a 34.5 lb difference between the lowest density refrigerant to the highest. Which is why technicians will use refrigerant scales to measure the amount of refrigerant recovered into the recovery cylinder. It is important to know the density of the refrigerant being recovered to properly calculate how much has been recovered and how much should have been recovered..
Using a water cooled recovery machine connected to the site municipal water supply will make the recovery process faster. Chilling the recovery cylinders will help too. The appliance water circulating pumps should also be running to reduce the risk of water freezing in the heat exchanger tubes (unless the water has been drained during leak detection). Increasing the temperature in the chiller plant room can also speed up the recovery process.
When changing the oil in the system before removing the oil the temperature of the appliance should be increased to 130°F to drive any residual refrigerant from the oil and vaporize it.
Before using recovery equipment to reclaim a refrigerant charge the technician should ensure the machine has been purged of any residual refrigerant from the last job the machine was used on. Service valves should be checked to ensure they are correctly set before connecting hoses and starting to recover refrigerant. Recovery equipment should be fitted with quick connect couplers for use with self sealing hoses to minimize refrigerant releases
Reclamation equipment needs periodic maintenance, which includes oil and filter changes. Recovery equipment filters should ideally be changed each time the machine is used, and at a bare minimum each time the type of refrigerant is changed to avoid contaminating the system being worked on with a mix of refrigerant. As recovered refrigerant can often contain significant amounts of contaminants such as water, oil, acids, and brazing spatter filter changes can significantly lengthen the life of recovery equipment. Technicians should also check the oil level on the recovery equipment before using it.
When using an empty recovery cylinder ensure the cylinder has been fully evacuated before transferring refrigerant to it.
Recovery equipment which contains a hermetic compressor relies on the flow of refrigerant through the compressor for cooling. As with appliances using hermetic compressors pulling a vacuum for a long time with this type of device can cause the compressor to overheat.
Recovering refrigerant in the vapour phase will minimize loss of oil from the system. Vapour recovery accounts for 75-80% of the recovery process time so recovery machines with high vapor recovery rates will take less time to recover refrigerant.
Liquid refrigerant recovery is much faster than vapour recovery, but can remove more oil from the appliance. Liquid recovery is ideal for large systems which are often designed with this in mind. Liquid recovery is however the first step in recovery as any remaining refrigerant vapour must be condensed and recovered once all of the liquid has been reclaimed. Ensure that no liquid remains trapped between the service valves after transferring liquid refrigerant.
Once the recovery cylinder contains more than five pounds of refrigerant it can be chilled in a bucket of ice water to lower the cylinder pressure. This will speed up the recovery process.
Technicians recovering HFC refrigerants must now use equipment solely dedicated to these refrigerants. This means that a dedicated set of gauges, hoses, vacuum pump, recovery machine, oil containers, and recovery cylinders must only be used with these refrigerants.
In the test inches of mercury (HG) are used as a measurement of pressure. Inches of mercury is really a measure of distance as it is used in HVAC applications. It relates to the displacement of a mercury column by atmospheric pressure. Today it is considered a crude measurement and while you will need to know a variety of measurements in Hg measurements in microns of mercury are more commonly used in industry. The main reason for the test using Hg is that the original legislation was written in the past when measurements in Hg were more common.
Large systems are normally fitted with a liquid line service valve allowing charging via the liquid line for faster charging. Large systems often are fitted with service valves for pumping down the appliance to allow for even faster liquid line charging.
If the appliance has a liquid to liquid heat exchanger there is a risk of freezing the heat exchanger when charging through the liquid line. To prevent this begin charging with refrigerant vapour until the system pressure reaches a temperature higher than 32 degrees as indicated by a pressure temperature chart. Once this has been achieved charging can begin through the liquid line.