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When it’s time to provide your customer's preventive maintenance don’t forget to pay particular attention to system components that are out of sight within the system cabinet or air handler enclosure. The unit’s evaporator coils are among the more important of these hidden components. Problems can develop with dirty evaporator coils as it can effect the system's performance and efficiency. This can also lead to damage and/or breakdowns. Here is some basic information on effectively cleaning evaporator coils.
Evaporator coils are probably the most difficult to clean. They are usually packed tightly inside a blower compartment that are usually difficult to service. They may be located over bathtubs, in tight dark closets, on rooftops in commercial applications, in a hot attic or a myriad of other places that are usually cramped, dark and uncomfortable. Due to these inconveniences, evaporator coils are often left alone and not cleaned until a system problem emerges. An evaporator coil should be inspected every six months and may need to be cleaned every six months to four years, depending on environment and filtration.
Make sure to disconnect the power to the unit while cleaning the coil. This will prevent a potential electrical hazard. Disassemble the unit to the extent that both sides of the coil can be accessed. For applications that have matted hair and dirt on the intake side of the coil, it is important that they be carefully brushed clean. Failure to do so will severely limit the penetration of the coil cleaner and dramatically reduce its effectiveness. There are several disposable types of coil brushes available from different manufacturers that do a very good job of cleaning the surface dirt off while keeping your hands away from the filth and fins. One note of warning - the fins on a/c coils are very sharp and can cause severe cuts to skin. Be sure to avoid contact with the coil with your hands, arms, etc. It’s advisable to wear gloves, face mask and apron during this procedure since potential organisms growing on the coil and contact with lungs, skin, eyes or clothing may transmit disease. Once the surface dirt has been removed, a good evaporator coil cleaner, such as Acti-Klean should be mixed in a low pressure sprayer with water in a dilution ration of between 3:1 to 1:1, depending on the condition of the coil and the type of dirt encountered. Acti-Klean is a concentrated set of soaps and surfactants (wetting agents that help the cleaner penetrate the coil fully). The coil should then be sprayed liberally from both sides of the coil with the coil cleaner solution. This coil cleaner will not create the foam that condenser coil cleaners do, so don’t be shy applying the coil cleaner. Make sure that the liquid does not fall onto electrical components in the system. The cleaner will cut through grease and oils, as well as dislodge any dirt, dust and hair that may be trapped in the coil and rinses them down the condensate drain. An alternative option would be Virginia Coil Klean aerosol coil cleaner. This product will foam out dirt and dust and is certainly more convenient in the aerosol container, although it is more costly than cleaners like Acti-Klean. When the coil is clean, it is recommended that where possible the coil be rinsed off. This will aid in removing any remaining dirt from the coil. If this is not possible, then the condensate created by running the a/c system will rinse off any remaining cleaner. Depending on temperature and humidity conditions, the unit should run for between 15 minutes to 1 hour to ensure all cleaner is rinsed off the coil.
In recent years, indoor air quality receives a lot of attention. Often a case of “black mold” in some air conditioning system is reported in the news and the entire building must be evacuated and sanitized. It is a good idea after cleaning the coil that an EPA registered bacteriostat be used on the coil and surrounding ductwork and insulation to ensure that any minor growths and odors are eliminated. Doing so provides your customer a valuable service by ensuring that mold and other growths do not develop throughout the system. It is important the technician pays close attention to the volume of dirt and other growths coming off the coil. It is not uncommon for release dirt to block the opening of the condensate drain line and restrict the draining of water. If this is observed, the blockage should be removed before the drain pan overflows.
While cleaning the coil, it is a good time to clean the drain pan as well. Simply clean out any rust and deposits that may be sitting in the bottom of the pan with a towel, rag or other means. Once again, be careful not to rub your hand across the coil as the edges are quite sharp. Protective gloves are recommended.
For more information see Catalog G-1.
Article contributed by Chris Reeves, product manager, Contaminant Control Products, Sporlan Division of Parker Hannifin
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Cleaning air conditioner condenser and evaporator coils is a basic need for proper system maintenance. In fact, it is probably the number one performed maintenance task by air conditioning service technicians. It seems however, that with the entrance of so many manufacturers and packagers of coil cleaners, that some of the facts about coil cleaning has been lost. As a premier supplier of coil cleaners for the trade we will discuss in general terms why coils need to be cleaned. The discussion is with aluminum-finned air conditioning applications, but the principles apply to refrigeration applications.
Both condenser and evaporator coils are made for one purpose - to transfer heat. The evaporator coil (indoor coil) is generally designed to pick up heat from the inside air, and the condenser coil (outdoor coil) is designed to give off this heat to the outside air. The exception is a heat pump application in the heating mode where the functions are reversed. As dirt, hair, lint, grass, grease and other contaminants coat the fins and tubes of the coils, the transfer of heat is reduced and system problems increase. A dirty evaporator coil causes less air movement over the coil which results in less heat pickup for the refrigerant.
If the heat pickup is not sufficient to vaporize the refrigerant, then one of two things typically occurs: 1) Liquid refrigerant travels back to the compressor and will either wash the lubricant off the bearings and lock the compressor or cause the rotor to drag on the stator and cause a compressor burnout, or 2) liquid refrigerant travels back to the compressor cylinders and the hydraulic pressure breaks valves, typically the suction valves. In the case of a dirty condenser coil, the reduced heat transfer results in higher than normal head pressure and discharge temperatures. This condition causes the compressor to work harder to pump against the higher pressures. The end result is the compressor motor overheats and wears out prematurely.
In either case, a dirty condenser or evaporator coil, the compressor is the component that is usually affected the most, not to mention that in both cases the cooling capacity of the system is reduced, resulting in higher electric bills. For these reasons, it is important that both condenser and evaporator coils be cleaned at regular intervals.
Accumulated dirt, dust and grease insulate against heat transfer. Dirt prevents the condenser coil from rejecting heat as it was designed and elevate head pressure. When head pressure rises, so does electricity because of power requirements.
Higher head pressure also reduces system BTU capacity, by as much as 30%. A 10 ton unit may now only be capable of providing 7 tons of cooling. This causes an increase in run time and inadequate comfort cooling or refrigeration.
Increased amperage draw combined with longer run time adds up to much higher energy bills. A 10 ton A/C system operating for 1500 hours could use as much as 37% more power when the coils are dirty. With a kWH cost of 8.3 cents this would cost the owner $618 more to operate (or $62 per ton more with dirty coils).
For more information see Catalog G-1 Chemical, Lubricants and Accessories.
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Here is some information concerning refrigeration oils that every HVACR technician will find useful.
Mineral – a by-product in the distillation of crude oil to produce gasoline. Mineral oil can be classified into the following groups: naphthenic, paraffinic, and aromatic. Naphthene based mineral oils are suitable for refrigeration systems using CFC or HCFC refrigerants.
Alkylbenzene (AB) – a synthetic oil suitable for refrigeration systems using CFC or HCFC refrigerants. It is compatible with mineral oil, and compared to mineral oil, it has improved refrigerant miscibility with R-22 at low temperature conditions.
Polyolester (POE) – the primarily synthetic oil for refrigeration systems using HFC refrigerants. It is also suitable for refrigeration systems using CFC, HCFC refrigerants and being evaluated in CO2 systems.
Polyalkelene Glycol (PAG) – a synthetic oil primarily used in R-134a automotive air conditioning systems. It is more hygroscopic that either POE or PVE oils, but it does not undergo hydrolysis in the presence of water.
Polyvinyl Ether (PVE) – a synthetic oil that is being used as an alternative to POE oil. It is more hygroscopic than POE oil, but less than PAG oil. Like PAG oil, PVE oil does not undergo hydrolysis in the presence of water.
Dielectric Strength – a measure of the oil’s resistance to an electric current. A low dielectric strength is indicative of moisture and/or contamination in the oil.
Fire Point – the lowest temperature at which the oil maintains combustion. Flash Point – the lowest temperature at which oil vapor momentarily ignites.
Floc Point – the temperature at which wax will separate from the oil. Above this temperature, wax will remain in solution.
Pour Point – the temperature at which the oil begins to pour.
Specific Gravity – density with respect to water.
Viscosity – a measure of the oil’s resistance to flow. Two units of measure are typically used with refrigeration oil. The older measure is Saybolt Universal Seconds (SUS); the newer is ISO viscosity grade number (ISO VG), a measure using centistokes. For comparison, an oil having a 150 SUS has an ISO viscosity grade of 32.
Esterification – the reverse of hydrolysis. It is the process in which an organic acid and alcohol are combined to form POE oil and water.
Hydrolysis – decomposition of a compound by reaction with water. In the case of POE oil, it decomposes into partial esters, organic acid and alcohol in the presence of water. The degree of hydrolysis is driven by the amount of water present. The speed at which hydrolysis occurs is dependent on temperature and the acid content (acids can act as a catalyst).
Hygroscopicity – ability of the oil to absorb moisture. The most hygroscopic refrigerant oils in descending order are: PAGs, PVEs, POEs, ABs, and mineral oils
Miscibility – ability of the oil to mix with the refrigerant. Some degree of miscibility is necessary between the oil and refrigerant so that the oil can return to the compressor during system operation.
Polar – a molecular structure with an uneven distribution of electron density. PAG, PVE, and POE oils have polar structures which allow them attract water molecules.
Solubility – the ability of one compound to dissolve into another. Water is soluble in various degrees with the refrigerants and refrigeration oils.
One may consult oil approval listings such as the one published in Parker Sporlan Catalog G-1. But one should confirm with the compressor manufacturer which oils are qualified for the particular compressor model, refrigerant, and application.
The Oil Acid Test Kit - Sporlan Test-All® is designed to assist the technician in evaluating the condition of the operating compressor. Using the kit, a sample of any refrigerant lubricant is sent to our laboratory. A complete spectrographic analysis indicating the presence (in ppm) of up to 21 contaminants (including metals which indicate wear), plus a chemical analysis for acid, moisture content and oil viscosity is mailed to the submitter.
1. Avoid exposing POE oil to air for any unnecessary length of time. Keep containers of POE oils tightly closed when it is not being dispensed.
2. Keep the refrigeration system closed except when work is actually being performed on the equipment.
3. Keep POE oil in their original containers.
4. Use a properly sized Catch-All® filter-drier when installing or servicing refrigeration equipment.
HVACR Tech Tip: Prevent Destructive Superheat with TREV Liquid Injection
19 Jun 2018
Most supermarket refrigeration equipment breakdowns are repeat problems. When responding to refrigeration service calls at supermarkets, refrigeration technicians immediately play “problem percentages” upon entering the store—this allows them to get to the root source of the problem as quickly as possible, to prevent perishable product loss.
A common problem with refrigeration systems is when the thermostatic expansion valve (TEV) doesn’t feed enough refrigerant and the refrigeration technician sees high superheat.
The following checks will help the HVAC technician identify the TEV problem quickly and restore refrigerant flow.
Checking these seven points first will save the technician considerable time in troubleshooting and repairing TEV issues with refrigerant flow. Regular maintenance is, of course, essential for maintaining proper TEV flow and function and keeping downtime to a minimum. For more information, contact Sporlan Division technical support at 636-239-1111.
You can also download a copy of 12 Solutions for Fixing Common TEV Problems - Form 10-143 for more troubleshooting tips.
Article contributed by Glen Steinkoenig, product manager, Thermostatic Expansion Valves, Sporlan Division of Parker Hannifin.
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A large percentage of compressor failures in low-temperature vapor-compression refrigeration system applications originate from overheating. Typical compressor capacity rating data is based on an industry standard of a 65°F return vapor temperature. While a 65° return vapor temperature may be satisfactory for high-temperature applications and, perhaps, some medium-temperature applications, unsatisfactorily high-discharge temperatures are virtually unavoidable on low-temperature applications. This is due, in large part, to the thermodynamic properties of the refrigerant.
Refrigeration oils have been highly refined in an effort to elevate the temperature at which chemical decomposition occurs, and experience has shown mineral oil decomposition begins when compressor internal temperatures reach 350°. Compressor manufacturers typically indicate that discharge gas temperatures are 50° to 75° higher at the discharge valve inside the compressor than out on the discharge line, 6-8 inches from the service valve. Therefore, dangerously high temperatures already exist inside the compressor when discharge line temperatures are well below 350°. This lubricant decomposition is accelerated by residual contaminants that are present in a typical system. Studies have shown the rate of chemical reaction doubles with every 18° temperature increase. For example, a chemical reaction that takes 10 years to complete at 100° will only take five years to complete at 118°. At 136°, it would be completed in two-and-a-half years.
However, mineral oils are vulnerable to losing the lubrication film necessary to prevent metal-to-metal contact between bearings and journals, or piston rings and cylinders, prior to the temperature at which decomposition begins. With mineral oil, this occurs approximately between 310° and 330°. When these compressors’ internal temperatures are reached, the probability of extreme piston and ring wear is imminent.
Hydrocarbons (HCs) and other natural refrigerants were employed in early vapor-compression refrigeration application designs. Many of these were highly flammable, toxic, or both. Developments in the late 1920s and into the early 1930s delivered a small group of organic compounds — the chlorofluoocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) for use as refrigerants — and CFCs and HCFCs proliferated into all types of refrigeration and comfort cooling applications. This continued unimpeded for nearly 50 years. These refrigerants typically were selected for various applications in large part based on their favorable thermodynamic properties relative to the system type in which they were to be applied. That is, CFC-12 was predominantly used for medium-temperature refrigeration, CFC-502 was predominantly used for low-temperature refrigeration, and HCFC-22 was principally used for comfort cooling.
However, in the late 1970s, environmental concerns with CFCs and HCFCs arose owing to scientific theories linking these organic compounds to concerns of global ozone depletion. Chorine-containing CFCs were quickly targeted for elimination from use as refrigerants. HCFCs, which contained a smaller amount of chlorine, also were earmarked for eventual elimination.
To speed the move away from CFCs, HCFC-22 initially was more widely specified for new and retrofit use in both medium- and low-temperature refrigeration systems. Additionally, a number of zeotropic blend refrigerants containing predominantly HCFC-22 appeared on the scene and were deployed as interim replacements for CFC compounds.
Prior to this, HCFC-22 had already been in wide use in systems with higher saturated suction temperatures for comfort cooling. However, the extended use of HCFC-22 into medium- and low-temperature refrigeration applications was not without its challenges.
Because of the thermodynamic properties of HCFC-22 — which result in decreased vapor density and increased compression ratios — lower saturated suction temperatures clearly would result in unsatisfactorily high discharge temperatures and the associated oil decomposition and lubrication problems without further intervention.
Consequently, as HCFC-22 was considered to replace CFC refrigerants in medium- and low-temperature refrigeration applications, a need was quickly recognized to address these inherent high-discharge temperatures to ensure a reasonable life expectancy of compressors.
Compound compression techniques were implemented to combat high compression ratios, and liquid injection methods, including the use of desuperheating thermostatic expansion valves (TEVs) to address high discharge temperatures, were adopted for new equipment installations.
One cost-effective method of preventing destructive superheat at the compressor for these HCFC-22 medium- and low-temperature systems was the introduction of the temperature responsive expansion valve (TREV). Using liquid from the high side of the system, the TREV injects saturated refrigerant into the suction line ahead of the compressor in direct response to the temperature of the discharge line.
This valve does not have an equalizer line and is not influenced by system pressure as a desuperheating TEV is. A sensing bulb is placed on the compressor discharge line 6 inches from the compressor discharge outlet connection. The valve responds directly to a rise in discharge gas temperature. Temperature settings are available from 115° through 275°. A bellows assembly similar to that employed in a direct-acting pressure regulating valve is used. The valve power element is charged with a hydraulic fluid that expands as its temperature increases. Multiple capacity sizes are offered for HCFC-22 to a nominal capacity maximum of 5 ton (see Table 1 below).
A liquid supply line to the TREV is connected to a high side location that will provide vapor-free liquid to the valve inlet. The TREV is designed to feed saturated refrigerant directly into the compressor suction line 12-18 inches before the compressor. Other locations are possible, and the suitability of these locations should be determined by proper testing and evaluation. Good thermal contact between the sensing bulb and the discharge line is essential, and insulating the bulb with a high-temperature insulation, such as fiberglass or its equivalent, is recommended.
From the onset of the more extensive use of HCFC-22 to replace CFCs in medium- and low-temperature systems, it was recognized that eventually it, too, would be eliminated from use. Chemical companies conducted ongoing research and development to offer suitable long-term substitute refrigerant compounds, and hydrofluorocarbon (HFC) refrigerants with zero ozone-depletion potential were developed. HFC-404A and -507 quickly became the commonly specified refrigerants for medium- and low-temperature refrigeration systems.
HFC-404A and -507 were considered “cooler” refrigerants by comparison to HCFC-22 regarding discharge temperature. However, even with these HFC refrigerants, destructive superheat caused by higher condensing temperatures has been experienced periodically in some geographical areas of the U.S. during operation in peak summer conditions, specifically in low-temperature applications. Liquid injection has continued to be employed but with less frequency.
As compressor designs evolved, an inherent reduction in compressor temperatures was achieved on specific applications. These design improvements fall into several areas, such as reduced contact between the motor and compressor housing, improved motor designs, reduced volumetric clearances due to improved machining tolerances, and minimization of heat transfer between the high- and low-pressure areas of the compressor.
Meanwhile, the international scientific community initiated concern over global warming. Concerns about greenhouse gases enter the worldwide consciousness, and chemical compounds were evaluated for their global warming potential (GWP). This led to the introduction of HFC refrigerants with comparable thermodynamic properties but lower GWPs than HFC-404A and -507 for medium- and low-temperature applications. HFC blend refrigerants designated as HFC-407A and -407F were developed. Compared to HFC-404A, (GWP = 3,922), HFC-407A (GWP = 2,107) offers a reduction of just less than 50 percent and HFC-407F (GWP = 1,824) provides a reduction of just more than 50 percent in GWP. Of these two refrigerants, HFC-407F exceeds in capacity and efficiency. However, discharge temperatures for HFC-407F are greater by comparison than that of HFC-404A and -507.
Once again, a means of reducing discharge temperatures to maintain quality of lubricant and extended compressor life was desired. Liquid injection using the TREV, while having been developed originally to address high discharge temperatures associated with HCFC-22 use on low-temperature applications, has proven to be a suitable device for application with HFC-407F as well. Because it is a temperature-responsive valve, which is not impacted by system pressures, this liquid injection valve may be satisfactorily applied in HFC-407F applications to eliminate potential lubricant decomposition due to high-discharge temperature operation. And, it can be field-applied as needed to existing systems as they are converted from a previously specified refrigerant to HFC-407F.
The chemical companies continue to pursue safe, low-GWP refrigerants while maintaining suitable performance characteristics to replace those that have gone before. The most recently introduced low-GWP refrigerant alternatives are hydrofluoroolefin (HFO) compounds. Pure HFO refrigerants have GWP numbers below 1, meaning they are of less concern regarding global warming than even carbon dioxide. They are safety-classified as A2L by ASHRAE (nontoxic but mildly flammable); however, it was discovered that by blending HFOs with HFCs, the mild flammability is mitigated, resulting in an ASHRAE classification of A1 (nontoxic and nonflammable) although with an increase in the GWP number.
These HFO/HFC blend refrigerants are entering the marketplace. They are considered as chemically safe, similarly performing refrigerant alternatives with a markedly lower GWP than HFC-404A and -507. HFO/HFC-448A and HFO/HFC-449A are proving to be very suitable alternatives to continue the transition away from HCFC-22. Additionally, they are also considered useful substitutes for the higher-GWP HFC-404A and -507.
In the evaluation of HFO/HFC-448A and HFO/HFC-449A, it has been recognized that, once again, dangerously high discharge temperatures and the associated probability of lubricant decomposition may be unavoidable, particularly on low-temperature systems. Thankfully, the TREV continues to be available as an effective component that may be deployed to allow systems to operate at acceptable compressor discharge temperatures with these new blended refrigerant compounds.
The TREV, as a true temperature responsive valve that is not influenced by system pressures, continues to be an effective problem-solving tool for new alternative refrigerants that may experience potentially destructive high compressor discharge temperatures. It will also more than likely continue in this role as the refrigerant landscape continues to unfold.
HVACR Tech Tip Article contributed by Gene Ziegler, technical training manager, Sporlan Division of Parker Hannifin
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