The Evolution of HVAC-R Processing: A Guide for Selecting the Ideal Solution for Evacuating, Charging and Run Testing
October 23, 2012
The whole is only as good as the sum of its parts. This adage delivers a message that every HVAC-R manufacturer should take into consideration when selecting and implementing the parts that will eventually make up the whole system. With today’s demanding markets dictating the need for fast-paced assembly lines, proper part selection has become even more crucial to ensure continuous product quality while increasing productivity and efficiency. Therefore, manufacturers should be looking to incorporate solutions that improve production and quality to keep customer satisfaction high and costs low.
By FasTest. *All tests were performed at FasTest Inc. lab facilities. Roseville, Minnesota
Within refrigeration and air conditioning applications, there are several commonly-used methods for introducing or removing air, liquids and refrigerants into the system. For instance, the Schrader style valve has been an industry-standard solution for many years; however, it may not be ideally suited for all applications. Over time, additional solutions have been created, such as high flow valves and process tubes paired with connectors, to overcome some Schrader valve limitations. For enhanced processing results, recent technological advancements have produced the valve, quick-connection system, which is designed to simplify HVAC-R manufacturing and in-the-field servicing to improve productivity and profitability.
This white paper will provide comprehensive insight to the evolution of HVAC-R processing methods, highlighting the operating principle of each solution and describing its advantages and performance limitations. By knowing and understanding this information, manufacturers will be able to make informed decisions on which option best complements their specific requirements.
Purpose of HVAC-R Processing
During HVAC-R manufacturing, units must be evacuated and charged in order to preserve the integrity of the system, ensuring performance and product quality prior to distribution. Evacuation requires all the moisture, air and any other impurities be removed from the system. If air is not removed, it can become trapped in the condenser and reduce the condenser capacity. Moisture must be evacuated because water vapor can freeze and impact system performance. Additionally, any remaining moisture can also combine with refrigerate, and when this is exposed to heat from the system it can form acids, which can mix with oil and metal wear particles to create sludge that can build up and prevent discharge valves from sealing.
Once a system is properly evacuated, it can be charged with refrigerant. In order to maximize unit performance, the HVAC-R system must receive the correct amount of refrigerant, as overcharging and undercharging can result in higher utility costs, shorter compressor life and reduced efficiency.
Given the importance of properly executing these procedures during manufacturing and servicing, selecting the correct processing method can directly impact a unit’s performance. For instance, using a method that is prone to leaks can result in system inefficiencies and reduced cooling capacity.
Conventional HVAC-R Processing
Manufacturers of air conditioning systems, refrigeration systems or heat pumps are all presented with the same questions: What type of process do I use for evacuation, charge and run testing? Should I use a valve or process tube? If I use a valve, should it be Valve in or Valve out? When evaluating traditional process solutions—Schrader valves, higher flow valves and process tubes paired with connectors—users should consider several factors specific to each application prior to implementation: ease-of-use, flow rate, leak rate, cost and field service requirements.
Schrader Style Valves. The Schrader valve, also referred to as the American valve, is one of the most common styles used for refrigeration and air conditioning (HVAC-R) applications. As bicycles began to use pneumatic tires in the 1890s, inventor August Schrader developed his most popular invention—the eponymous valve—to provide a simple, effective way to fill tires. A basic eponymous valve is comprised of a valve and core. This valve, now commonly referred to as the Schrader valve, is still used to fill car and bicycle tires.
Though originally developed to fill tires, manufacturers have found additional uses for this valve solution, including HVAC-R applications. The Schrader valve is also a viable solution to provide production and service access ports on many HVAC-R systems.
One advantage of using a Schrader style valve in HVAC-R equipment is that it is typically inexpensive compared to high flow valves. The valve can be used to mount the different pressure switches on the system and for providing quick, yet restrictive, access to systems compared to the high flow valves. Further, designed to accommodate application flexibility, Schrader valves are available in various design styles to suit individual system requirements. For instance, a stub tube design is brazed directly on a stub tube that is brazed to the system tubing, while saddle mount styles are brazed directly on the tubing itself. For easy accessibility, panel mount designs are also offered to allow manufacturers to attach the valve on a flat surface instead of the pipe itself.
Though one of the most frequently implemented system access solutions, the Schrader valve does lack the larger flow diameter that high flow valves possess for faster evacuation, charge and recovery times, but also seem to have a larger leak potential. Schrader valves feature two potential leak paths, one being the sleeve seal between the valve stem and the valve, and the other is the elastomer seal on the valve stem.
The original Schrader valve was engineered for lower-pressure applications, like car tires, where small leaks and limited flow rates were not a concern. For instance, consider how often one needs to check the pressure of their car tires. However, on an HVAC-R unit, leaks can be costly and negatively impact the cooling capacity of the system. The Schrader valve used in HVAC-R equipment is not unlike the design still used for tires on bikes and cars, making their construction and performance capabilities more compatible with the pressure requirements for refrigerants such as R22. With the new higher-pressure refrigerants, like R410A, and the even higher pressures of the CO2 system currently being evaluated, will the current Schrader designs hold up?
High-Flow Valves. Since decreased processing times results in faster production, a higher number of completed systems and an increased capacity for profitability, HVAC-R manufacturers are challenged with finding a method to produce a high-quality unit while simultaneously shortening the time it takes to evacuate contaminants and fill or charge a system. As seen above, Schrader valves may be too restrictive to provide the necessary flow rates for fast, efficient evacuating or charging processes. Therefore, some manufacturers may choose to implement a high-flow valve like an Eaton Stove Pipe style featuring a larger flow diameter in order to lessen the time it takes to complete these tasks.
Though not widely used today, some manufactures may also choose to partner high-flow valves with Schrader valves. With this solution, the high-flow valve will be used during processing in the manufacturing plant and the Schrader valve will provide technicians with system access in the field. This pairing is necessary because while high-flow valves may provide necessary flow rates to improve tact times in the factory, they lack the associated tooling to connect gauge sets and vacuum pumps in the field.
Connectors Used with Process Tubes. Not all conventional methods require the manufacturers to implement a valve solution, with the exception of the service-only access valve that is still required for field service. In place of a valve, a specialized connector can be used to grip and seal onto a process tube. Since flow rate is dependent on the size of the tube’s inside diameter, this method delivers higher flow for charging and evacuating the system because users are now processing through the unrestricted hole of an open tube.
While this method increases processing flow, it also adds additional steps in the process. For instance, after charging the system, the tube must be pinched and brazed in order to properly seal it. A process similar to soldering, brazing is accomplished by heating metals together to form a bond, and properly brazing the process tube closed can be a time-consuming process that can still result in leaks if brazing is not done correctly. Utilizing the correct brazing technique to form a leak-free brazed joint is challenging, as leaks can result from minute mistakes, such as uneven heating, overheating and excessive oxidation.
Additionally, since the joint is made after the system has been evacuated of impurities and charged with refrigerant, correcting any leaks would require the system to be opened, refrigerant to be reclaimed and the whole process must be completed again.
One example of where this process is widely used is the manufacturing of packaged terminal air conditioning (P-TAC) units. P-TAC units are typically found in hotel rooms and most of the time, these systems are easier and cheaper to replace then service. Since the refrigerant volumes are low and system access in the field is not necessarily needed, there is less likelihood that the unit will need to be re-opened, making the use of process tubes ideal. The same cannot be said with larger expensive equipment.
The Need for Evolution
Though each of the methods mentioned above provide individual strengths, as well as offer a viable solution for charging and evacuating HVAC-R systems, their performance limitations demonstrated the opportunity to create a new solution designed to overcome these deficiencies, improve productivity and decrease costs. Plus, with the recently mandated conversion from ozone depleting CFC refrigerants, such as R-22, to environmentally friendly non-CFC refrigerants, evacuation and charge processes have become even more crucial with the higher-pressure systems and the increased SEER ratings.
Valve, Quick-Connection Systems. A unique and proven solution engineered for evacuating and charging during manufacturing is the use of a high-flow valve paired with its matched process tools. This system features a high-flow valve and a seat that can be brazed into the system, and offer two sealing methods, an elastomer and a metal-to-metal seal, to provide sealing redundancy. The valve core pin positioning is manufactured to exacting tolerances for consistent sealing and valve opening, and to accommodate diverse application requirements, its seat designs are equivalent to Schrader-style seat options to provide high-level compatibility with common systems and tools.
Processing through the high-flow valve is accomplished by using a high-flow, internally valved connector specifically designed for this system. These ergonomic, sleeve-operated connectors grip at the base of a valve—rather than the threads—to prevent costly thread damage. The connectors can be used at any process station and feature an automatic valve shut-off on each side of the connection, instantly halting the flow on refrigerant one the connector is removed. When using this solution, standard processing times can be improved by up to five times over traditional Schrader valves because of the larger flow diameter of the valve. (See Figure 1)
On the service side, these valves are constructed to industry standards of thread, pitch and actuating pin, allowing service technicians to use their existing gauge sets and connection tooling to service the system. Since these systems offer a higher flow rate—up to 80 percent faster that Schrader valves—they allow greater line throughput for evacuation, charge or recovery. (See Figure 2)
Performance Comparison of the Schrader Valve vs. Valve, Quick Connection System
Existing Schrader style access valves and process tubes used in HVAC-R package unit manufacturing plants are outdated and inefficient, causing slow evacuation and charging times with no connection tooling that is ergonomic or leak proof compatible. Plus, additional time needed for a pinch and braze operation for process tubes increases process inefficiency. Processing with the valve, quick-connection system removes the pinch and braze operation associated with process tubes and greatly reduces the evacuation and charge times that are associated with the Schrader valve.
To demonstrate these improvements, tests were conducted to show that the valve, quick connection system can reduce processing times by up to five times over alternative methods. The following charts illustrate the findings after testing the flow rates, evacuation rates and evacuation time of Schrader valves and the valve, quick connection system.
Flow testing was done using compressed air at 60 psi. The flow rate was monitored using 2.5-25 SCFM, and 10-100 SCFM Dwyer VF series flow meters. Each valve was mounted inline between the regulator and the flow meter. Pressure gauges were mounted on both the upstream and downstream sides of the valve. The flow meter was vented to atmosphere.
Figure 1 shows the respective flow rates for a Schrader valve and the valve, quick-connect system at 60 psi air. All numbers are in standard cubic feet per minute (SCFM) and have been rounded to nearest whole number. The test found that the flow rate for the Schrader valve (core in) w/standard twist-on yellow jacket connector was 4 SCFM, the valve, quick connect system w/standard twist-on yellow jacket connector had a flow rate of 20 SCFM and the flow rate of the valve, quick connect system w/matched sleeve connector was 23 SCFM. These tests reveal that the flow rates of the valve, quick connect system can as much as 80 percent higher than that of a Schrader valve.
Evacuation Testing Methodology
The evacuation testing methodology was the same for both Figure 2 and Figure 3. Evacuation testing used a Ritchie model 93200 two stage, 7.5 SCFM capacity, high vacuum pump connected through the valve to a vessel having a volume of 150 cubic inches. The evacuation rates were monitored using an Omega PX603 pressure transducer that fed data to a computer running DazEZ data acquisition software.
The evacuation test was completed to show the amount of time a Schrader valves needs to evacuate a system compared to the valve, quick-connect systems. The maximum rate of evacuation testing was measured after reaching a reading of approximately 29 inHg in a vessel with a volume of 150 cubic inches.
Figure 2 outlines the following results: The Schrader valve (core in) w/standard twist-on yellow jacket connector took a total of 41 seconds to evacuate. Valve, quick-connect system w/standard twist-on yellow jacket connector completed evacuation in 15 seconds, and the valve, quick-connect system with matched sleeve connector evacuated the system in only 8 seconds. These results verify that valve, quick-connect systems can be as much as five times faster than Schrader valve solutions.
The evacuation rate test was completed to demonstrate the difference of flow rate, measured in inHg/s, between a Schrader valve and the valve, quick-connect systems. Upon test completion, it was found that the Schrader valve (core in) w/standard twist-on yellow jacket connector has an evacuation rate of 3 inHg/s. Alternately, the valve, quick connect system w/standard twist-on yellow jacket connector presented evacuation rated of 7 inHg/s, while the valve, quick connect system w/matched sleeve connector showed a rate of 13 inHg/s, revealing a 75 percent higher evacuation rate over Schrader valves with standard twist-on Yellow Jacket connector.
Advantages of the Valve, Quick-Connect System
By implementing the valve, quick-connect system for processing and service, manufacturers and technicians can experience a variety of advantages that could not only enhance production, but also improve their overall product quality, which directly impacts customer satisfaction, and ultimately, profitability.
Improved Quality and Efficiency. Since valve, quick-connection systems eliminate process tubes, production quality and line throughput is improved. Without process tubes, these removable high-flow valves can eliminate one or more brazed joints. This increases the HVAC-R manufacturing process by preventing downtime for brazing. The efficiency of the system itself is also improved by reducing the number of potential leak paths that allow refrigerant to escape.
Reduced Processing Time. The valve, quick-connection system enables users to achieve high levels of flow as demonstrated in the tests discussed above, which in turn, results in a significantly shorter processing time. A shorter processing time will minimize the amount of downtime experienced for system evacuation and charging, thereby reducing lost profits caused by production halts and resulting a faster manufacturing process.
Improved Field Service. Compatible with commonly used service connectors and caps, valve, quick-connect systems use the same thread, taper and sealing surface as standard HVAC-R access valves. This prevents service technicians from having to purchase special tools for in-the-field servicing. Plus, the high-flow access valve allows field evacuation and recovery rates to be faster then using the standard Schrader valve and its smaller diameter through put, dramatically reducing service times. (See Figures 2 and 3 above)
Cost Reduction. By no longer relying on process tubes and Schrader valves, manufacturers can reduce potential leak paths and the total cost of operation. For instance, leaks often require time-consuming repairs and equipment replacements. Also, using process tubes impacts production efficiency, requiring time to pinch and braze the tubing, increasing labor expenses and suffering the cost of lost production. Costs are also incurred due to the limited flow capacity of the Schrader valve, which further slows production and drives up the cost of manufacturing. Therefore, utilizing a system that eliminates the need for both these solutions reduces both labor costs incurred when mitigating leaks, profits lost to slow production and the added expense of additional processing steps.
The Future of HVAC-R Manufacturing
The need to improve production, increase product quality and maximize profitability will continue to drive HVAC-R manufacturing. In order to achieve these goals, it is critical that manufacturers select the proper valve/connector solution for charging and evacuation is critical. Understanding the advantages of the valve, quick-connect system processing method enables users to implement a solution that not only delivers the necessary performance capabilities, but also meets current and future cost-efficiency and maintenance requirements that refrigeration and air conditioning manufacturing demands. In an industry where producing more efficient, trouble-free equipment is a requirement, and not merely a desire, this system not only meets, but exceeds that challenge.