Airflow Capture Hoods/Balometers
An airflow capture hood or balometer is a device used for measuring the volume of air coming out of grilles and diffusers in HVAC systems. “Balometer” is actually a term coined by Alnor in 1983 that has become synonymous with “airflow capture hood” today. Before the invention of this technology these measurements were typically made with a deflecting vane anemometer and the appropriate diffuser probe. These types of anemometers required that the technician apply the correct A
k, or area factors specific to each grille manufacturer. An airflow capture hood allows the user to take measurements much more quickly and easily because it uses a one-step, direct volume measurement that doesn’t require area factors.
Airflow capture hoods are mostly digital today. These instruments are typically auto ranging and can automatically detect supply or return airflow. The sensors used in these instruments are either thermo-anemometer (hot wire) or pressure sensors. Pressure-based digital airflow hoods are more versatile because the meter is actually a detachable manometer. These instruments also commonly incorporate auto-zeroing functions. Some digital airflow hoods use analog displays or incorporate both digital and analog. Do not get confused by this. To easily tell which type you are looking at check if the unit requires batteries; a true analog airflow hood will not require batteries.
The fabric skirt and frame of an airflow capture hood can be found in a variety of sizes to fit different grilles and diffusers. Most units, such as those from Kanomax and TSI/Alnor, allow for interchangeability of the fabric skirt and frame. Spare skirts and frames are available in various sizes. There are also units specifically designed for very low airflow volumes, such as the LoFlo series from TSI/Alnor. Both analog and digital instruments are available.
This video from TSI/Alnor gives a break down of the company's EBT series of Balometers.
Manometers
Manometers are instruments used by HVAC professionals to measure low pressures, such as duct static pressures and differential pressures. Originally manometers used glass U-tubes filled with water or another fluid of known specific gravity (such as mercury) to measure pressure. Hoses connected to each end of the U-tube. As differential pressure was applied, the fluid displaced, creating a height difference between columns which represented measurable pressure. Today digital manometers are the most common type. TEquipment sells only digital manometers. These instruments completely eliminate liquids and replace them with either absolute, vacuum, gauge, or differential pressure sensors. As a result digital manometers can be used in any position and do not require leveling (although periodic zeroing is recommended).
Special Features of Manometers to Consider:
- Data logging and internal memory
- Ability to measure flow in cfm (cubic feet per minute) or m3/h (cubic meters per hour)
- Ability to download stored data to PC
- Adjustable dampening or time response
- Density correction to compensate for elevated temperatures and altitude
- Humidity or temperature measurement capabilities
Types of pressure sensors:
- Absolute: measures pressures relative to perfect vacuum
- Gauge: measures pressures relative to atmospheric pressure. When it reads zero, it is really measuring the ambient pressure
- Vacuum: measures pressures below atmospheric pressure, showing the difference between measured low pressure and atmospheric pressure
- Differential: measures the difference between two pressures, with one connected to each side of the sensor.
This video from Testo gives a break down of the popular
510 Pocket Pro manometer.
Micromanometers
A micromanometer is a special type of manometer specifically designed to detect and measure extremely small pressure differences. Similar to regular manometers, most micromanometers today are digital. These instruments often incorporate data logging capabilities and some can also measure humidity and temperature.
Typical HVAC uses include:
- Properly balancing ventilation and occupant loads
- Optimizing performance of equipment
- Duct leakage testing
- Checking filter condition
Hydronic Manometers
Hydronic systems for HVAC use hot and cold water as their means for heat transfer. These systems should be able to efficiently distribute water throughout to various terminal devices under design load and part load conditions. If this balance is achieved, the system is operating properly. However if the system is not balanced, operating costs will be higher than normal.
To correctly balance a hydronic system one needs a hydronic manometer. These devices can be connected to pressure taps on specific balancing valves throughout the system to measure flow. The instrument does this by taking the differential pressure reading across the balancing valve and applying it to a “pressure versus valve setting”chart which is developed by the valve manufacturer.