Airflow measurement

1 Instrumental in measurement and test

This is a brief presentation on the types of instrumentation that can be used for the measurement and verification of various airflow parameters with specific references to the Healthcare Industry:

• Air velocity • Air volume • Air pressure


The equipment shown will be suitable for the measurement of airflow parameters in a wide variety of applications: • Operating theatres • Cleanrooms • Pharmacies • Fume cupboards • Safety cabinets • Isolation rooms • And many more


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• Velocity Micromanometer & Pitot Tube Rotating Vane Anemometer (100mm) Mini Rotating Vane Anemometer Thermal Anemometer • Volume Balometer / Air Capture Hood Vane Anemometer & Hood Kit Vane Anemometer (Calculated) Thermal Anemometer ( Calculated) Fan (Measured / Room Pressure) • Pressure Micromanometer


Used to measure velocity & then to calculate volume manually. A digital micromanometer is used with a Pitot Tube to measure air velocity in ducts. This is the most commonly used method of accurately measuring the airflow in a supply or extract. The measurement is performed by taken a series of measurements across the duct (horizontally & vertically). This technique is called traversing. The air volume m³/s (Q) of the supply/extract can be calculated using the velocity m/s (V) and the face area of the duct m² (A) Basic Air Volume Equation Q = A x V Typical Range: 4 to 76 m/s (1 to 4 with great care)


Must use a micromanometer which is equipped with units of measurements for velocity. A micromanometer is usually used to measure pressure, however suitable instruments, when used in conjunction with a Pitot Tube, can measure velocity. A Pitot Tube consists of two tubes. The centre tube, with a single hole, faces the air stream and receives the total pressure. The outer tube has a ring of holes around it and measures the the static pressure. Through the two connections on the Micromanometer, the two pressures are presented to either side of the instruments internal pressure transducer. The difference between these two pressures (Total Pressure - Static Pressure) equates to the air velocity m/s. For accurate measurements to be taken a traverse must be performed which takes multiple readings that are then averaged.


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Used to measure velocity to verify the airflow into or out of a room / area / supply / extract grilles, also fume cupboards, safety cabinets or through a filter. A commonly used method of measuring the airflow of a supply / extract, is by traversing the face of the supply / extract., taking average readings of the air velocity with a rotating vane anemometer. The air volume m³/s (Q) of the supply / extract can be calculated using the velocity m/s (V) and the face area of the supply/extract m² (A). Basic Air Volume Equation Q = A x V Typical Range: 0.25 to 76 m/s (not recommended below 1 m/s) Many vane anemometers have the function to input grille / duct dimensions, which enable the instrument to give a direct readout in volume flow. These instruments can also be used with hood kits.


Used to measure velocity to verify the airflow in a supply/extract ducts, also fume cupboards or slot and linear diffusers. Has the same capabilities of the larger rotating vane anemometers, but can also be used for measuring velocities in ducts or slots, due to its smaller dimensions.


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Used to measure velocity to verify the airflow in supply/extracts etc. The principle of the thermal anemometer is that it has a sensing element, which is heated electronically and is kept at a constant temperature. When the element is exposed to airflow, the effect is that there is a temperature change in the element. The temperature is kept constant via the electronics and the electrical current needed to maintain the constant temperature of the element is ascertained. The controlling current is directly proportional to the velocity and this is then electronically indicated as an air velocity reading. Thermal anemometers are particularly useful for the measurement of low velocities as it has no mechanical parts, the other main benefit is related to the smaller dimensions of the equipment, so it can be used in ducts, slots etc. Many thermal anemometers have the function to input grille/duct dimensions, which enable the instrument to give a direct readout in volume flow. Typical Range: 0.15 to 20 m/s


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These are lightweight collapsible assemblies used for the measurements of air volumes on room diffusers and grilles. They are an alternative micromanometer & pitot tube or anemometers and give a direct reading of air volume. The airflow passes over a grid assembly with an integral sensing element. A number of interchangeable hoods or various sizes are available to fit over different types/sizes of grilles and diffusers. Typical Range: 50 to 3500 m³/hr


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These are lightweight fan assemblies that can be used for the measurements of air leakage on rooms such as isolation suites or ductwork. They have variable speed fans so that enclosures can be maintained at a constant pressure, and flow rates are calculated by measuring the pressure drop across an orifice plate.


• Draeger Flow Check / Concept Air Trace

Invisible air movements become visible. The instruments makes it possible to see the direction and effects of air currents. They produce harmless clouds of smoke which float freely with the airflow, showing the direction of flow and the effect in a room / area.


Used to measure pressure such as the differential between rooms such as operating theatres. A digital micromanometer can be used to measure the differential pressure between rooms, by having one of its ports open to the pressure in the room you are standing in and the other port connected to another room using a piece of tubing. The instrument will then indicate the differential pressure between the two points. Typical Range: 0 to 3500Pa (Positive and negative) Typical Resolution: 0.1Pa


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All instruments should be calibrated periodically, usually at intervals of not longer than 12 months. Each instrument should carry a calibration record. If an instrument is damaged, it should be recalibrated as a means of checking its functional accuracy. It is often a requirement of Quality registration to keep a record of your calibrated instrument.


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Open jet wind tunnel


Technology

Airflow measurement