According to Jim Bergmann, The News’ 2004 HVACR Instructor of the Year, a small investment in tools will provide users or their employees with dividends, lower the amount of time it requires to perform service, remove the guesswork and back up with the documentation required to ensure that the airflow and refrigerant charge are within the manufacturer’s specifications.
Jim Bergmann recommends using the following:
- Digital refrigeration manifold/system analyser (preferably with data logging capability and the ability to take superheat and subcooling measurements)
- A digital manometer that reads 0 to 80 inches water column (wc) with resolution down to 0.001 inch
- Combination wet bulb/dry bulb/relative humidity (RH) thermometer-hygrometer
- Volt-ohm-amp meter
Additional instruments can provide still more benefits to the technician and the consumer:
- A Pitot tube
- Digital combustion analyser
- Two-channel temperature probe (K-type thermocouples)
Additionally, users can download the following software for free:
- Equipment check sheet in PDF form from the official website of Testo along with step-by-step instructions to properly check the equipment.
- Digital psychrometric programme from HandsDownSofware’s website
Digital instruments are faster, more accurate, reduce the requirement to carry around pressure-temperature (P-T) charts, eliminate guesswork, increase productivity, provide repeatable test results, increase professionalism.
Digital gauges, specifically the Testo 523, 556 and 560 can be ordered in a kit with software and temperature probes that allow the user to print reports from information gathered in real time as the testing and system operation is verified.
A digital manometer can be used for reading duct static pressure, pressure drop across a coil, total external static pressure, and manifold pressure in a furnace. Manometer models with fine resolution and proper dampening are even sensitive enough to read velocity pressure.
A combination wet bulb/dry bulb/rh thermometer-hygrometer is used to check the initial and final conditions of the air that will be conditioned. Some manufacturers have instruments that read in 0.1ÞF and are traceable to NIST standards.
Digital products also eliminate human error that can occur when reading the sling psychrometer; errors from using tap water instead of distilled; and reduce time, as readings are obtained quickly and easily. As system refrigeration charges are becoming more critical, and the window of proper operation is tightening, bourdon tube gauges are not always accurate enough.
Due to the error inherent with bourdon tube technology from effects of ambient temperatures, atmospheric pressure, and the fact that mechanical gauges are most accurate in the center of their range, they cannot provide the accuracy and repeatability that are desired now and into the future. Digital gauges are accurate over the entire working range, and do not hold refrigerant gases inside their porting (bourdon tube) that can affect the pressure readings.
It is not necessary or responsible to check the charge in the equipment that users service on a yearly basis. It should only be checked when a problem is suspected. A few measurements and knowledge of the design operation will usually be all that is needed to verify the charge without gauges. Airflows will not change significantly if the equipment is maintained properly.
Pressure drop across the coil can be recorded and verified, and the refrigerant charge can be checked without gauges once the design conditions are established. The initial commissioning of the equipment will take a few minutes more than a preventive service check, but with digital instrumentation, it will get done faster and more accurately than you would imagine.