State-of-the-Art HVAC/Rs Call for High-Tech Troubleshooting & Performance Measurement

Proper airflow is crucial to the performance and longevity of today's advanced technology HVAC/R systems, as well as maintaining the thermal comfort of a building's occupants. Measuring airflow speed and pressure should be the first step in an initial system installation as well as any maintenance process.

The basic principles of airflow in HVAC/R tell us that airflow must be sufficient enough to transfer enough energy to heat and cool the conditioned space, and that the airflow must be sufficient enough to allow heat energy to flow through the heat exchanger of the conditioning equipment. Heat pumps and air conditioners are especially sensitive to irregular airflow volume.

If airflow is too low:

• Seriously effects compressor performance in heat pumps and AC units.
• Causes furnaces to cycle on the limit switch.
• Reduces flow of registers.
• Produces noise if ducts are restricted.
• Decreases duct efficiency in AC and heat pumps.

If airflow is too high:

• Causes poor moisture removal
• Produces noise.
• Increases high fan electrical consumption.
• Decreases occupancy comfort from drafts.
• Prohibits the ability to check charge using common methods.

It's not uncommon to find a forced air system operating 30% to 50% low on airflow. Making sure an HVAC/R system is supplying the appropriate amount of air to a home or building requires a thorough knowledge of manometers and anemometers to measure air volume and velocity in air ducts so you can adjust the performance of the HVAC/R system.

Anemometers

Anemometers are one of the most effective instruments for measuring air flow, or the speed of the air, and are available in vane and hot-wire technologies.

Vane anemometers can average air velocities at supply openings, walk-in ducts and filter banks. They work when the airflow makes contact with, and rotates the vane blades. A magnetic or optical sensor converts the signal to a velocity measurement in feet per minute (fpm) ranging from 50 to 6000 fpm.

Hot wire anemometers measure wind speed based on the rate of heat loss to air flowing by a sensor using a very fine wire (micrometers) that has a measurement range spanning from 0 to 10,000 fpm. The wire is electrically heated up to some temperature above the ambient temperature by passing a current through an electrical resistance. The energy is then converted to heat. Air flowing past the wire has a cooling effect on the wire. As the electrical resistance of most metals is dependent upon the temperature of the metal, a relationship can be obtained between the resistance of the wire and the flow speed.

A digital anemometer like the Testo 405 Pocket-sized thermal anemometer is ideal for measuring the flow in ducts or at duct openings or draughty windows. It can also measure air volume flow and temperature.

Manometers

While the main function of a manometer is to measure system air pressure in heating, ventilation, and air conditioning systems, it can also check airflow, measure positive and negative pressure in ducts, monitor differential pressure across filters and coils, and measure differential pressure for clean room monitoring.

Digital manometers like the Testo 510 Differential Manometer can measure total external static pressure, differential pressure, duct velocities, manifold pressures, and air flow with an optional pilot tube. The Testo 512 Differential Pressure Meter has a measuring range from 0 to 0.29 psi and is ideal for measuring pressure differences at filters and for carrying out pitot static tube measurements in air ducts at air flow speeds between 16 and 180 fps. Both Testo manometers are ideal solutions for checking differential pressure measurements to see if filters and ducts of heating systems are still working properly or if they need to be replaced. Air pressure measurement in ventilation ducts is particularly important in heating systems that have sat dormant all summer. If the air flows are smaller than intended, the removal of room loads (heating, cooling and substance loads) may not be adequate. Manometers are useful in troubleshooting other heating concerns by measuring heat exchanger pressure drop, flame sensing, and nuisance ignition lockouts.

Today's digital manometers save time by eliminating time-consuming conversions, which reduces the possibility of mistakes. Digital manometers are ideal for HVAC/R technicians that require a highly accurate standard to check their instrumentation or equipment to ensure proper system performance. Some standard features of digital manometers may include back lighting, battery power, timed leak test, record mode, damping, minimum/maximum value capture and field re-calibration support. Their durable construction makes them functional in not only hazardous atmospheres, but other rough environments.