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    Better Systems Through Better Measurements

    June 1, 2007

    What is a service technician's job? I can sum it up in a few words: serving the customer, and taking measurements. We take measurements to select the proper equipment, and make it perform as well and safely in the field as it does in the factory or laboratory. Measurements are made to prove facts, and the fact is good measurements can be used for you, or against you.

    So, why don't many technicians take good measurements? The answers are plentiful and almost painful. Not enough time. Hard to get the same results twice. The equipment "works" without proper setup (even if it doesn't work right). No idea what to measure. Primarily, I find technicians have never been instructed how and why to take measurements.

    Let's face it: we have service technicians with 20 years of experience, and those with one year of experience 20 times. Many keep repeating the same incorrect procedures and processes with substandard measurement instrumentation and techniques, over and over again.

    The results of poor or nonexistent measurements are high rates of system failure, unnecessary warranty claims, poor system performance, callbacks, and dissatisfied customers. A chain of events leading to a mess!

    Tens of thousands of new and existing pieces of heating and cooling equipment are installed and serviced each year without the technician ever knowing if they are operating at or delivering their designed and/or rated capacity. Operational measurements are made to verify temperature rise and drops, airflow, superheat and/or subcooling, but often the total system performance is never quantified. Equipment is sized for a minimum delivery, yet usually never tested after installation for actual performance verification. Measurements are made without an expected result, improper techniques are used to make measurements, and antiquated tools are used for critical measurements. It's like attempting to measure a distance in feet with your car's odometer.

    No Quick Fix
    While our industry is in need of repair, I'm afraid there is no quick fix to provide the needed answers. Test instruments, by themselves, can't fix the problem. Quite simply having the tools, or knowing that you need them to perform the required work, is only part of the solution. It's more important that the technician knows how to use them, and how to evaluate the measured results. The key lies in education.

    The first step in education is making sure technicians don't get in the habit of making estimations whenever a true measurement can be made. Another word for estimation is "guess," and guessing is rarely a good strategy to follow when installing or servicing HVAC equipment.

    The next step is making sure technicians have the proper information to interpret their test results. Making measurements without knowledge of the expected results is a valueless proposition.

    For example, if a technician doesn't know what the airflow measurement should be, what difference does it make what it is? Technicians aren't often privy to information regarding the equipment selection, such as room air requirements, intended application, or design. Many times a proper heat loss and gain are not performed when modifications are made to the duct system, or when replacement equipment is selected in the field. And even if a tech does measure cfm delivered at the register, that's only a small part of the equation; if the heat never gets off of the ceiling or the cooling never gets off of the floor, comfort will be lacking due to stratification of the air in the room.

    Now for Some Good News
    The good news is that with the costeffective solutions in instrumentation that are available, technicians can make an investment in technology. With your help, they can learn its application and proper use.

    Measuring is the most critical part of all service and sales calls. Before any system commissioning is complete, any evaluation of existing equipment is made, or during routine service, accurate measurements of operating conditions and system performance must be made. When replacing existing equipment, a complete evaluation of the duct system including verification of proper airflow is warranted. New technology in HVAC test instruments makes the whole process easier than ever before.

    HVAC performance testing setup and service is principally based upon accurate measurement of temperature, pressure, airflow, humidity, oxygen, carbon dioxide, and carbon monoxide. All of these measurements bear direct correlation to equipment operation, performance, and safety.

    Each segment and process of this testing requires test instruments and measurement probes specifically designed for the task at hand. Airflow, for example, can be measured with a hotwire, Pitot tube, or mini vane anemometer. Each probe has a specific application it's best suited for. No one is better than the other, just better for a specific measuring application.

    Where a vane is an ideal tool for residential airflow measurement, it would not work as well as a Pitot tube in a small diameter duct with an exceptionally high velocity of air. Refrigerant charge is more critical than ever for proper equipment capacity and efficiency. Digital gauges with accuracy of 0.5% full scale are now desirable. Manufacturers are not requiring a range for subcooling on TXV equipped systems; they are requiring a very specific result.

    Quantifying system performance requires not only high accuracy measurements but also high resolution as 1F difference in wet bulb equates to quarter-ton error in a cooling capacity calculation. Depressurization or pressurization of the combustion air zone or outlying rooms is also considered part of the total system performance evaluation, as more powerful blowers can negatively impact these parameters.

    Better Than Ever
    Today's digital instruments and new sensor technology is simply better than ever before. Sensors convert the measured parameter directly, temperature can be measured by contact or non-contact sensing, and there's no mechanical gearing drag. Parallax and fluttering of a needle are a thing of the past. Digital has greatly increased instrumentation's precision, readability, and speed of response.

    A variety of probes for every application are available, as are displays and data management capabilities never conceivable with analog counterparts. Compared with previous generations of test instruments, today's instrumentation is smaller, smarter, easier to use, more reliable, and supported with applications. It's well worth the investment.

    And once your technicians are quipped with the proper instruments, it's well worth your investment to ensure they know how to use them, what to measure, and what their measurements mean.

    Crime Scene Investigation
    Equipment malfunction is like a crime scene. Expert knowledge is required to determine how the equipment was operated, how it was installed, to decipher the original design specifications, or changes that took place in the environment after the installation was performed. The quandary, however, is why the criminal is many times investigating the crime with the same tools with which the crime was originally committed.

    It may be time you do some investigation on your own as to what the future will hold. Quality measurement devices are out there. It's time to look at what you do and how you do it — after all, it's your reputation. How is the equipment you install performing? Don't know? Just wait long enough, and I'm sure someone else will tell you.

    Bill Spohn, P.E. is product manager, HVACR, for Testo, Inc. He has designed, manufactured, and marketed a variety of products in his 25 year career. Spohn is Chairman of the Gas Detection and Analysis Division of the Gas Appliance Manufacturers Association, Chairman of the Oil Heat Manufacturers Association, and a member of the American Society of Heating, Refrigerating & Air-conditioning Engineers and the Refrigeration Service Engineers Society. Spohn holds three U.S. patents relating to test and measurement instrumentation. He can be reached at [email protected].