BY DAVE DEMMA PAYING THE PIPER This is the third and final installment explaining the conversion of a refrigeration system from an HCFC (R22) to an alternative, probably an HFC (R404A or R507). There are other refrigerants to choose from as well: specifically the family of R422 refrigerants. The intention is not to recommend one refrigerant over the other but rather to discuss the final considerations necessary to ensure the conversion is done properly. SEALS AND GASKETS Going back to the early years of converting systems using CFC refrigerants to HFC refrigerants, which also required removing the mineral oil and replacing it with POE (polyol ester) oil, it was commonplace to find multiple leaks in gasket/seal joints where there were none before. Since there were no leaks before the conversion, it was thought that the existing gaskets/seals were not compatible with the new refrigerants/oils. The fact is that there was another explanation for why these leaks were occurring. Let s take a look at the life of an elastomer seal such as an o-ring or quad-ring (tetra-seal), and how it prevents refrigerant from leaking out of the system. First, for a given application such as a common ME10S240 liquid line solenoid valve, the seal material is subjected to extensive testing for compatibility and performance prior to the first manufacturing production run. This testing is typically done by the valve manufacturer and verified by an independent lab before a decision to accept the material is made. In addition to selecting the proper seal material, a precisely sized groove is machined into one of the seal mating surfaces; this is where the seal will reside. During the production phase, the valve body, along with every other required part, is machined to its respective specifications. Final assembly includes fitting the specified seal into its groove, and tightening the joint to the specified torque setting. Prior to sending this valve out into the field, it TABLE 1 NEOPRENE TYPE W SWELL RATES is tested for operation and leakage. Once the valve is put into service, there are several factors that allow the seal to take a set, ensuring that it remains a good seal. These include the torque setting of the joint, the type of seal material, the size of the machined grove which the seal fits into, the pressure that the seal is subjected to (as a liquid line component in an R22 system it will regularly see pressures between 150 psi and 250 psi, perhaps more if the condenser is dirty), and the amount of swelling that the seal will EDITOR S NOTE: Parts I and II of this series ran in HPAC May/June and HPAC September/October. They can be found at www.hpacmag.com. Click DIGImag on the menu on the left to access HPAC s online magazine. experience when in contact with the refrigerant and oil. The elastomer swell rate, along with the pressure the seal is subjected to, are the variables which ultimately determine how effective an existing seal will remain after the conversion. In other words, will the conditions that the seal is subjected to before the conversion remain the same after the conversion? The answer is no. When the R22 is removed, the liquid pressure that would normally act against the seal is gone. When a vacuum pump is used to properly evacuate the system prior to adding the new refrigerant, a further reduction of the Neoprene Type W Seals Refrigerant & Oil Swell Rate Change in Swell Rate R22 with Mineral Oil 4.1% R404A with POE Oil 3.0% R22 with Mineral Oil initially; 4.1% to 2.6% -1.5% Converted to R404A with POE pressure acting against the seal occurs. Since the new refrigerant s pressuretemperature characteristics will be different than R22, the pressure acting against the seal is now different. With a conversion to R404A, it will go from the 150 to 250 psi range to the 175 to 300 psi range (for normal winter/summer condensing temperatures). The final variable is the swell rate (refer to Table 1). The swell rate for Neoprene Type W is greater when in the presence of R22 and mineral oil versus R404A and POE. If the original seal is reused, it actually experiences a net shrinkage of 1.5 per cent. This shrinkage, combined with temporarily relieving the pressure on the seal during CONTINUED ON PAGE 44 42 HPAC 80 years NOVEMBER/DECEMBER 2006
St. Lawrence Chemical Inc. Exclusive distributor of Genetron refrigerants in Canada Ontario and Western Canada, Tel: 416-243-9615 Fax: 416-243-9731 Quebec and the Maritime Provinces, Tel: 514-457-3628 Fax: 514-457-9773 Circle #25
CONTINUED FROM PAGE 42 refrigerant removal/evacuation, then subjecting it to higher pressures with the new refrigerant, causes the seal set to be disturbed, resulting in a high leakage probability. Because of this situation, all elastomer seals must be replaced. In an effort to eliminate the swell factor, some manufacturers have changed to different (non-elastomer) seal types. Prior to January 1998, the FIGURE 1 ENCLOSING TUBE TORQUE SPEC. not essential that they be replaced during a conversion, but it is recommended. It is possible that some older vintages of ball valves will develop leaks after the conversion, particularly in the liquid applications. It may be prudent to replace liquid ball valves before the conversion. In addition, all access valve and seal caps, seals for the liquid level sensor in the receiver, EPR seals, and so on, should be replaced. If in doubt, any elastomer seal in the system should be replaced. TIGHTENING SEAL/GASKET JOINTS Typically, there is a specified torque setting for all seal joints. While it is recognized that most service trucks do not have a torque wrench on them, a technician should be able to feel the difference between a torque setting in the 10 to 15 ft/lb range and a 100 ft/lb setting. In today s climate of no leaks, some might think that a 16 crescent wrench with a three-foot cheater would be the best method for tightening all joints. But remember, it is not necessary to over tighten these joints. In fact over tightening may damage the elastomer seal and cause a leak. Additionally, over tightening some joints may cause valve damage. For example, the evaporator pressure regulator shown in Figure 2 has a very specific torque setting for the suction stop pilot solenoid enclosing the tube locknut; it is nine to 10 ft/lb. If over tightened, this may prevent the valve from opening. The enclosing tube plunger travels up and down in the enclosing tube as the coil is energized/de-energized. There is a small amount of clearance between the plunger and the opening in the lock nut. This allows the plunger to drop down and open the small suction stop pilot when de-energized. In this position, the suction stop pilot FIGURE 2 CUTAWAY VIEW OF PILOT ENCLOSING TUBE TORQUE SPEC: 9/10ft/lb Clearance Between The Enclosing Tube I.D. & Plunger Enclosing Tube Plunger Graphic Parker Hannifin Corporation above-mentioned ME10S240 solenoid valve used a tetra-seal (labelled enclosing tube gasket in Figure 1), set in a groove in the enclosing tube mating surface, to provide the seal between it and the valve body. The current seal is a rubberized metal flat gasket. It does not experience the same swell phenomenon as an elastomer, nor does it require a groove in the enclosing tube mating surface. Gaskets of this type are not subject to the disturbing the set issue that elastomer seals are. It is port is open, allowing high pressure vapour to pressurize the main piston chamber, forcing the valve closed. During the conversion, the enclosing tube seal would be replaced, and the lock nut re-tightened with the system shut down (coil de-energized). In the de-energized mode, the valve is in the suction stop mode. Over tightening the lock nut can cause deformation, changing the round hole into something more elliptical. This will constrict the plunger, preventing it from traveling up when the coil is energized. The result is a valve that is always in the suction stop mode (closed), even when the coil is energized. In most cases loosening the lock nut and re-tightening it to the specified torque setting will cause the hole to regain its original shape. 44 HPAC 80 years NOVEMBER/DECEMBER 2006
TEV PERFORMANCE It is the system conditions (evaporator temperature, liquid temperature, and P across the thermostatic expansion valve (TEV) port) that determine what the actual TEV capacity is. If a supermarket refrigeration rack is outfitted with a liquid subcooler, and the design calls for a 60F liquid refrigerant temperature, you can be assured that the original TEVs were selected based upon this fact. The new TEVs will also have been selected based upon the 60F liquid temperature. Therefore, for proper TEV operation, it is important to ensure that the subcooler circuit is supplying liquid refrigerant at the design condition. It goes without saying that every TEV should be checked to see if it is maintaining the proper superheat at the evaporator outlet. If the superheat is not correct, the TEV should be adjusted. will counterbalance the higher operating pressure of the refrigerant in the system. If the R404A element is used on an R22 system, the opening force would be much greater than required, due to the higher pressure fluid in the CONTINUED ON PAGE 46 R404A bulb. This would cause the TEV to open more than it should for a given condition. CONTROL SETTINGS Evaporator pressure regulating valves TIMEFRAME FOR REPLACEMENT There may be a desire to replace as many components as possible before the R22 is removed. The one component that cannot be replaced prior to the conversion is the TEV. There are two reasons for this: 1) A nominal one-ton R22 TEV will typically be replaced with a nominal one-ton R404A TEV. A given TEV port size will yield a greater capacity with R22 as opposed to R404A. So, the nominal one-ton R404A TEV, if installed before the refrigerant is replaced, becomes a nominal 1-1/2 ton TEV when used with R22 and it is oversized. 2) The thermostatic element on the R404A valve is designed to provide the correct pressure on the top of the element diaphragm to counteract the evaporator pressure of the refrigerant in use. For a 25F saturation temperature the corresponding pressure will be 49 psi for R22 and 62 psi for R404A. Therefore, the fluid charge in the sensing bulb of the R404A element would have to supply an additional 15 psi as compared to the R22 fluid, so that it Moving away from R-22 just got easier. Introducing DuPont ISCEON MO59 and ISCEON MO79. These non-ozone depleting refrigerants provide you with easy-to-use, cost-effective retrofit options to help your customers avoid costly equipment replacement or interruptions while reducing the use of ozone depleting substances. With over 75 years as a leader in the refrigerants industry, we re committed to providing you with reliable, proven and safe alternatives for CFC and HCFC systems. To find the right products, call your local DuPont Refrigerants distributor. DuPont Refrigerants. The Science of Cool. www.refrigerants.dupont.com Copyright 2006 E.I. du Pont de Nemours and Company. All rights reserved. The DuPont Oval Logo, DuPont, The miracles of science, The Science of Cool and ISCEON are registered trademarks or trademarks of E.I. du Pont de Nemours and Company or its affiliates. Circle #26 NOVEMBER/DECEMBER 2006 80 years HPAC 45
CONTINUED FROM PAGE 45 (EPR valves) maintain fairly consistent fixture discharge air temperature by maintaining a constant refrigerant saturation temperature in the evaporator. For example, if the design condition for a particular system calls for a 17F refrigerant saturation temperature, and assuming a pressure loss in the piping is equivalent to a 2F change in saturation temperature, this will be maintained by an EPR setting of 38 psi for R22. After a conversion to R404A, the EPR setting will need to be raised to 49 psi. The rack controller, which attempts to maintain a fairly constant common suction pressure by cycling compressors on/off, will also require resetting. For example, the ice cream case lineup will typically be the lowest operating system on the low temperature rack. If the design calls for a -20F saturation temperature for this system, the corresponding pressure (allowing for a pressure drop equal to a 2F change in saturation temperature) would be nine psi for R22. After a conversion to R404A, this pressure will increase to 15 psi. The condenser fan cycling pressure controls and the head pressure control valves (holdback valve and receiver pressurization valve) are used to prevent the condensing temperature (pressure) from falling below a certain level. If, for example, the design minimum condensing temperature is 80F, the holdback valve would be set for 147 psi with R22. After the conversion to R404A, the holdback valve must be reset to 175 psi. If a split condenser valve is used, and is controlled by pressure, it will also need to be reset. Likewise, the highpressure cut-out controls will require resetting. It is likely that the high-pressure relief valves will also require replacing. FOOD FOR THOUGHT A deepening concern over how we treat our environment, our world, our home (specifically regarding the issues of global warming and ozone depletion) has elevated the topic of refrigerant conversions to the level of importance it now commands. Those of us earning a living in the HVAC/R industry who were less aware certainly now know the impact refrigerant leaks are having on our environment. At the very least government actions have forced us to face the monumentally negative impact refrigerant leaks and improper refrigerant management can have on cash flow. Does the average consumer care about this yet? Many companies seem to believe they do, as evidenced by the large budgetary expenditures devoted to green campaigns. It is my feeling that when Joe Couch-Potato wants a new big screen plasma television, it is the price that determines where he decides to make his purchase. I would be surprised if any variation of the following dialogue ever takes place: Say, I like the price on the plasma TV. I just have one final question; what refrigerant are you currently using in your store s cooling equipment? As if the sales attendant would even know, but the answer might be: Well, we are still using R22. Joe s reply is stunning: Well then, I m afraid I will not be able to support your business until you become a little more environmentally engaged. This scenario is not happening soon but we can hope that, at some point in time, consumer pressure will become a larger factor in the environmental equation. Dave Demma FILTER ISSUES All liquid filter driers, suction filters and oil filters should be replaced. Due to the affinity POE has for moisture, a high water capacity filter drier should be used. POE has the ability to scrub contaminants from the interior walls of the tubing, the compressor, components, and so on, and bring them back into circulation. Because of this, it should be anticipated that there might be contamination problems after the conversion. This should be monitored closely, with additional filter drier replacement as the required remedy. THE FINAL ACT A complete system evacuation must be done before adding the new refrigerant. After the conversion, a thorough leak check should be done. The last thing you want to tell your customer, after they have spent a small fortune on the conversion, is that there were a few leaks. A proper refrigerant conversion is no small task. Allow ample time for ordering parts and creating a plan of attack. Make sure that adequate manpower is available, as the refrigerated product has a limited life while the equipment is inoperative. If required, dry ice can be obtained to keep the product reasonably cold. While conversions seem to be a daunting challenge, like any difficult task they will get easier with repetition. Dave Demma holds a degree in refrigeration engineering and worked as a journeyman refrigeration technician before moving into the manufacturing sector where he regularly trains contractor and engineering groups. He can be reached at 636-239-1111, ext. 242. RATE THE ARTICLE! Will this information be useful? Please circle the appropriate number on the Reader Postcard. Thank you. VERY USEFUL........115 USEFUL........... 116 NOT USEFUL........ 117 46 HPAC 80 years NOVEMBER/DECEMBER 2006