Making Measurements

Customer service aside, what is a service technician’s job? I can sum it up in a few words; simply it is to make measurements. We make 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. 

Why don’t technicians make 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. 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 each time expecting a different or better result. One might just as easily chalk all this up to insanity.

The result; high rates of system failure, unnecessary warranty claims, poor system performance, loss of confidence by the consumer and technician, callbacks, and dissatisfied customers. A chain of events leading to a mess! According to a recent EPA Energy Star presentation a quoted study shows that up to 70% of residential A/C systems installed today have improper airflow, and additionally 74% of A/C systems have improper charge. While our industry is in need of repair, I am afraid there is no quick fix to provide the needed answers. Furthermore, neither will capture hoods, vane anemometers, hotwires or pitot tubes, digital gauges or combustion analyzers fix the problem, by themselves. Quite simply having the tools or knowing that you need them to perform the required work is only part of the solution. More importantly the technician must know how to use them, and how to evaluate the measured results. The key lies in technician and consumer education.

Tens of thousands of new and existing pieces of heating and cooling equipment are installed and serviced each year without 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 is like attempting to measure a distance in feet with your car’s odometer.

Consider, if you do not know what the airflow measurement should be what difference does it make what it is? For example, to select a register, we need to consider not only air volume, but also the face velocity and throw.  Technicians are not often privy to information regarding the register selection such as room air requirements, intended application or design. As can be seen from past experience, many times a proper heat loss and gain are not performed during the design phase, or when modifications are made to the ducting system, or when replacement equipment is selected in the field. I would care to bet register selection is more often based on cost, color and size. Measuring CFM delivered at the register is only a small part of the equation; face velocity and throw are just as integral parts of information. If the heat never gets off of the ceiling or the cooling never gets off of the floor, a correct quantity will not provide comfort do to stratification of the air in the room.

Technicians should not get in the habit of making estimations whenever a true measurement can be made. With the cost effective solutions in instrumentation that are available, technicians not only need to make an investment in technology, but also in its application and proper use. Again, making measurements without knowledge of the expected results is a valueless proposition. 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 ducting system including verification of proper airflow at the registers is warranted.

HVAC performance testing setup and service is principally based upon accurate measurement of temperature, pressure, airflow, humidity, and O2 and CO when combustion safety is concerned. All of these measurements bear direct correlation to equipment operation performance and safety. Each segment and process 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 is 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 1 difference in wet bulb equates to ¼ 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. Pressure imbalances are measured in Pascal’s or 1/25 of an inch of water column.  

Digital instruments and new sensor technology is just better, Sensors convert the measured parameter directly, temperature can be measured by contact or non-contact sensing, no mechanical gearing drag, or large masses. Parallax and fluttering of a needle are a thing of the past.  Digital has resulted in greater precision, readability, and speed of response. A variety of probes for every application is available and displays and data management capabilities never conceivable with analog counterparts are available today. Today’s instrumentation is smaller, smarter, easier to use, more reliable, and supported with applications. Well worth the investment. 

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. If we don’t take the initiative now I am afraid it will be the equivalent of Nancy Drew competing with CSI. As the ANSI standard for QI/QC (Quality Installation/ Quality Contractor) moves forward and building scientists continue to cross the line into the realm of HVAC performance evaluation, it may be time you do some investigation on your own as to what the future will hold.  It’s time to look at what you do and how you do it, after all it’s your reputation. How is your equipment performing?  Don’t know? Just wait long enough and I am sure someone else will tell you.