GB2516613A - An in-situ method of airflow measurement for fans and ventilation systems - Google Patents

An in-situ method of airflow measurement for fans and ventilation systems Download PDF

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Publication number
GB2516613A
GB2516613A GB1309321.6A GB201309321A GB2516613A GB 2516613 A GB2516613 A GB 2516613A GB 201309321 A GB201309321 A GB 201309321A GB 2516613 A GB2516613 A GB 2516613A
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GB
United Kingdom
Prior art keywords
airflow
measurement device
flow channel
air velocity
measurement
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB1309321.6A
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GB201309321D0 (en
Inventor
Colin Biggs
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nuaire Ltd
Original Assignee
Nuaire Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nuaire Ltd filed Critical Nuaire Ltd
Priority to GB1309321.6A priority Critical patent/GB2516613A/en
Publication of GB201309321D0 publication Critical patent/GB201309321D0/en
Publication of GB2516613A publication Critical patent/GB2516613A/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F25/00—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
    • G01F25/10—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of flowmeters
    • G01F25/15—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of flowmeters specially adapted for gas meters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/70—Control systems characterised by their outputs; Constructional details thereof
    • F24F11/72—Control systems characterised by their outputs; Constructional details thereof for controlling the supply of treated air, e.g. its pressure
    • F24F11/74—Control systems characterised by their outputs; Constructional details thereof for controlling the supply of treated air, e.g. its pressure for controlling air flow rate or air velocity
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/30—Control or safety arrangements for purposes related to the operation of the system, e.g. for safety or monitoring
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2110/00—Control inputs relating to air properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2110/00—Control inputs relating to air properties
    • F24F2110/30—Velocity

Abstract

An airflow measurement apparatus comprises an enclosure 38 having at least one wall defining a flow channel. The channel has a first open end defining an inlet and a second open end defining an outlet. An air velocity measurement device 34 is located at a fixed location along the length of the channel. The enclosure and the measurement device are configured such that the cross sectional area a of the enclosure at the location of the measurement device is greater than the cross sectional area of the measurement device across the same plane, with the ratio of the two cross sectional areas being fixed and pre-defined. A support 40 holds the air velocity measurement device in the fixed position such that a space is defined around and between the measurement device and the wall of the channel. The cross sectional area may be constant along the length of the channel. Te measurement device may be an anemometer. The apparatus may surround a vent 24 that passes through walls 26, 30 of a building. The airflow may be determined from the product of the measured air velocity and the predetermined cross section area. A calibration method is also claimed.

Description

An In-Situ Method of Airflow Measurement for Fans and Ventilation Systems The present invention relates to an insitu method and apparatus of airflow measurement for fans and ventilation systems, and in particular a method for commissioning a ventilation system.
Fans are commonly used to provide extract or supply ventilation to buildings. The selection of a suitable fan is carried out by the designer of the ventilation system having a knowledge of the airflow requirements of the area to be served by the fan, and the parameters of the ventilation system into which the fan will be integrated. Based on the system requirements the designer will select an appropriate fan and other elements of the ventilation system based on the manufacturer's published performance data for the products.
is Fan performance data is typically derived using standard test methods such as those described in [BS 848 Part 1 2007: Industrial fans. Performance testing using standardized airways]. The performance data is subject to recognised tolerances and as such the actual performance may deviate from the calculated value, at least within the recognised tolerance range. Furthermore, when a ventilation system has been constructed and installed in-situ, the airflow characteristics of the installed system may not match those of the original design due to unanticipated variations imposed by the construction process or the layout of the building.
Any such variations from the calculated system parameters may result in the ventilation system failing to deliver the required airflow to the building.
It is therefore necessary to measure the airflow rate in-situ to verify that it matches the expected values. The common practice of measuring the airflow rate delivered to thc building when the installation is complete is known as conunissioning.
There are many available methods of measuring airflow in ducted systems, and their correct application can result in accurate measurements. In order to achieve an accurate measurement in a ducted system is it necessary for the measurement station to be located at a point in the system where the airflow is relatively stable and uniform. This is shown by way of example in Figure 1 where airflow indicated by the arrow A1 flows through a duct 1. The plane B-B located before the bend in the duct I represents a suitable measurement location. The plane C-C is located closely after the bend in a region of turbulence 2 and hence would not provide as accurate a measurement. Locations close to the fan or at contractions in the system should similarly he avoided.
In certain systems the ducting may be physically inaccessible andlor the system may not include suitable positions for conducting dueLed measurement, which would prevent the use of standard ducted measurements, Alternatively it may be that a less complex method is required. In which case, a measurement may alternatively be taken at the point of airflow ingress to or egress from the room or building. As showrn in Figure 2, a ventilation unit 4 is mounted to an internal wall 6 with a duct 8 passing through the internal wall 6 and the external wall 10 to the external vent 12, A measurement device 14 such as an anemometer is connected to a conical or tapered hood 16 that collates the airflow A2 to the ventilation unit 4 causing the entire airflow A2 to pass through the anemometer 14.
Vane anemometers or electronic anemometers are often used for commissioning residential systems, typically having a diameter of around 100mm. Such devices are cost effective and can give accurate results provided the devices are correctly calibrated. In order for such anemometers to calculate the flow rate of the air the entire airflow must be chaimelled through the anemometer in order that the volume of airflow can be accounted for by the device. It is for this reason the devices are in conjunction with a conical or tapered hood arrangement. However, the requirement to channel all of the airflow through the restricted diameter of an anemometer imposes an additional airflow resistance on the system, which can be particularly significant if the system is driven by natural ventilation means or by low pressure fans, and/or when the system is operating at larger flow rates of around 30 1/s or more for example. As such the presence of the anemometer can alter the airflow it is seeking to measure and can significantly effect the accuracy of the measurements.
More accurate measurements may be provided using more sophisticated tools such as a Balometer, which uses a larger air path and differential pressure grid system, or a powered flow hood that incorporates its own fan to compensate for its inherenL resistance. However, since these systems are considerably more expensive than the anemometer and cone solution, there is a reluctance to use them in all sectors of the market, resulting iii systems that are not commissioned properly due to inaccurate use of the anemometer method or not commissioned at all. This is in direct conflict with the aims of the industry to provide properly performing and efficient systems.
It is therefore desirable to provide an improved method of airflow measurement for fans and ventilation systems which addresses the above described problems andlor which offers improvements generally. I0
According to the present invention there is provided an airflow measurement apparatus as described iii the accompanying claims.
In an embodiment of the invention there is provided an airflow measurement apparatus IS comprising an enclosure comprising at least one wall defining a flow channel, the flow channel having a first open end defining an inlet and a second end having an opening defining an outlet, An air velocity measurement device is located at a fixed location along the length of the flow channel, the enclosure and the measurement device being configured such that the cross sectional area of the enclosure at thc location of the measurement device is greater than the cross sectional area of the mewurement device across the same plane, with the ratio of the two cross sectional areas being fixed and pre-defined. Support means is provided for holding the air velocity measurement device in said fixed position such that a space is defined around the measurement device between measurement device and the wall of the flow channel. The measurement device measures the velocity of the air flow through the flow channel. Airflow is able to be calculated from the air velocity and the known cross sectional area of the flow channel, with the ratio of the cross sectional area of the measurement devoiee to that of the flow channel ensuring that the effect of the device on flow through the channel is miniinised.
Preferably the cross sectional area of the flow channel is substantially constant along the length of the flow channel thereby minimising flow disruption that may otherwise effect the measurement.
The measurement device is preferably an anemometer, which can be provided cost effectively to installation contactors compared to the more expensive solutions discussed above, One of the inlet and the outlet may configured to receive and surround an air ye at to ensure that all of the airflow through the vent is chamielled through the flow channel.
In another aspect of the invention there is provided a method of measurement of a ventilation airflow comprising: providing an enclosure comprising at least one wall defining a flow channel, the flow having a first open end defining an inlet and a second end having an opening defining an outlet; locating one end of the flow channel against a surface surrounding a ventilation duct; locating and supporting an air velocity measurement device at a fixed location along the length of the flow channel having a predetermined cross sectional area such that a space is defined around the measurement device between measurement device and the wall of the flow channel; using the measurement device to measure air velocity through the flow channel; and determining the ventilation airflow from the product of the measured air velocity and the predetermined cross sectional area.
The method may further comprises: generating an airflow of known flow rate; directing said airflow through the flow channel; measuring the velocity of the airflow; using the measurement device to measure air velocity of the generated airflow through the flow channel; determining a value for the generated airflow from the product of the measured air velocity and the predetcrmined cross sectional area; comparing the determined airflow with the know generated airflow; and calibrating the air velocity measuring device based on said comparison.
This method of calibration ensures greater accuracy of the system.
Alternatively the ventilation airflow may be determined from the product of the measured air velocity, the predetermined cross sectional area and a correction factor determincd by S empirical means for the size and shape of flow chatmel The present invention will now be described by way of example only with reference to the following illustrative figures in which: ic Figure us a ventilation airflow system according to the prior art; Figure 2 is a ventilation airflow system according to the prior art; Figure 3 is an airflow measurement apparatus according to the is present invention; Figure 4 is a cross section of the measurement duct of Figure 3 taken along the plane D-D; and Figure 5 shows the aspect ratios for various duct configurations.
Referring to Figure 3 a ventilation system comprises a ventilation unit 24 mounted to an internal wall 26 of a building. A duet 28 extends through the intcrnal wall 26 defining a duct opening 29 and through the external wall 30 to an external vent 32. Air is drawn from the internal volume of the building 33 by a fan 36.
To measure the airflow through the ventilation unit a ventilation measurement system is provided comprising an air velocity measurement device 34 such as an anemometer and a measurement duct 38. The measurement duct 38 has a length land a cross sectional area a defined a fixed point along the length I and indicated in Figure 3 by the measurement plane D-D. The cross sectional areas a and cross sectional shape of the measurement duct is preferably consUmi along its length /.
The anemometer 34 is located on the measurement plane D-D which has a predefined cross sectional area a. The cross sectional area a is selected such that it is greater than the cross sectional area of the anemometer 34. A support bracket 40 or other suitable support means hold the anemometer in a fixed location within the measurement duct 38 such that it is spaced on all sides from the walls of the duct 38.
As shown in Figure 4, the area surrounding the anemometer is greater than the cross sectional area of the anemometer itself As such, the volume of air flowing around the anemometer 34 is greater than through the anemometer 34. In this way, the impedance of the airflow by the anemometer 34 is minimised. The measurement system is therefore constructed such that all of the relevant ventilated airstream passes through a common measurement plane IJ-D on which the anemometer, but does not all pass through the anemometer itself. As such, the anemometer is able to operate as an air velocity measuring is device in a substantially free air stream.
The measurement area is defined by the cross sectional area a of measurement duct 38 at the plane D-D. The measurement duet 38 is therefore constructed to known pre-defined dimensions, The dimensions of the measurement duct 38 are selected such that the resistance to airflow presented by the duct 38 and the anemometer 34 combined roportional to the square of velocity) shall he readered negligible for the range of flow rates considered.
This simple pre-determined relationship between the anemometer 34 and the measuring duct 38 enables an approximate determination of airflow rate to be made, with the airflow being the product of the measured velocity and the cross sectional area a of the measurement plane, While this provides an approximate airflow value, the calculated result is of limited accuracy due to the distribution of flow across the cross sectional area a of the duct, local effcets of disturbances in the flow entering the measuring duct 38, and those flow disturbances due to the presence of the anemometer 34 itself.
Where measurements of greater accuracy are desired (typically within +1-5%) a method of calibration is provided in which the airflow measurement apparatus of the present invention is compared againsi a range of known air flow rates. The resulting calibration data may be presented as a table or plotted curve relaling measured velocity to actual air flow rate, This approach enables the specific dimensions of the measuring duet section 38 to be varied to suit a wide range of ventilating equipment and systems The method of calibration comprises: I) Establishing a range of relevant aspect ratios for rectangular measurement ducts and construct ducts with these aspect ratios and of equal area (the number of duct arrangements to he tested will depend on the regression stability over thc range) as shown in Figure 5; 2) Position and centralise the selected anemometer on the measurement plane D-D and centralised in the measuring duct; 3) Conduct velocity measurements at known airflow rates qkl... ii over the range of interest; 4) Based on the comparison of the velocity measurements to the known values calculate correction factor (ka) for each arrangement as: known airflow rate qkn = k * measured velocity x measuring duct area 5) Correlate the aspect ratio against ka to enable suitable factors to be interpolated for other duct dimensions; A similar approach as above may be applied to circular ducts of varying diameter.
The proposed invention is intended to provide a relatively simple solution to this problem that will enable accurate site measurements to be made cost effectively, typically in the range of flow rates below 60 I/s.
S
Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims (6)

  1. Claims 1. An airflow measurement apparatus comprising: an enclosure comprising at least one wall defining a flow channcl, the flow channel having a first open end defining an inlet and a second end having an opening defining an outlet; an air velocity measurement device located at a fixed location along the length of the flow channel; support means for holding the air velocity measurement device in said fixed position such that a space is defined around the measurement device between the measurement device and the wall of the flow channel.
  2. 2. An airflow measurement apparatus according to claim 1 wherein the cross sectional area of the flow channel is substantially constant along the length of tile flow IS channel.
  3. 3. An airflow measurement apparatus according to claim 1 or 2 wherein the measurement device is an anemometer.
  4. 4. An airflow measurement device according to any preceding claims wherein onc of the inlet and the outlet is configured to receive and surround an air vent.
  5. 5. A method of measurement of a ventilation airflow comprising: providing an enclosure comprising at least one wall defining a flow channel, the flow having a first open end defining an inlet and a second end having an opening defining an outlet; locating one end of the flow channel against a surface surrounding a ventilation duct; locating and supporting an air velocity measurement device at a fixed location along the length of the flow channel having a predetermined cross sectional area such that a space is defined around the measurement device between measurement device and the wail of the flow channel; determining the ventilation airflow from the product of the measured air velocity and the predetermined cross sectional area.
  6. 6. A method according to claim 5 comprising: generating an airflow of known flow rate; directing said airflow through the flow ehauinel; measuring the velocity of the airflow; using the measurement device to measure air velocity of the generated airflow through the flow channel; determining a value for the generated airflow from the product of the measured air velocity and the predetermined cross sectional area; comparing the determined airflow with the know generated airflow; and calibrating the air velocity measuring device based on said comparison.8. A method according to claim 7 wherein the ventilation airflow is determined from the product of the measured air velocity, the predetermined cross secLional area and a correction factor determined by empirical means for the size and shape of flow channel.
GB1309321.6A 2013-05-23 2013-05-23 An in-situ method of airflow measurement for fans and ventilation systems Withdrawn GB2516613A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB1309321.6A GB2516613A (en) 2013-05-23 2013-05-23 An in-situ method of airflow measurement for fans and ventilation systems

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Application Number Priority Date Filing Date Title
GB1309321.6A GB2516613A (en) 2013-05-23 2013-05-23 An in-situ method of airflow measurement for fans and ventilation systems

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GB2516613A true GB2516613A (en) 2015-02-04

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB466628A (en) * 1936-04-01 1937-06-01 Boulton Aircraft Ltd Improved rotary fluid flow meter
FR2673293A1 (en) * 1991-02-26 1992-08-28 Moinet Jean Anemometers, in particular for indicating flow rates, and ventilation systems provided with such apparatuses
GB2275115A (en) * 1993-02-12 1994-08-17 Anthony Richard Case Commissioning of fluid flow systems
JPH07158360A (en) * 1993-12-06 1995-06-20 Sekisui Chem Co Ltd Ventilation device
US20030154803A1 (en) * 2002-02-21 2003-08-21 Modera Mark Peter Method and device for measuring airflows through HVAC grilles

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB466628A (en) * 1936-04-01 1937-06-01 Boulton Aircraft Ltd Improved rotary fluid flow meter
FR2673293A1 (en) * 1991-02-26 1992-08-28 Moinet Jean Anemometers, in particular for indicating flow rates, and ventilation systems provided with such apparatuses
GB2275115A (en) * 1993-02-12 1994-08-17 Anthony Richard Case Commissioning of fluid flow systems
JPH07158360A (en) * 1993-12-06 1995-06-20 Sekisui Chem Co Ltd Ventilation device
US20030154803A1 (en) * 2002-02-21 2003-08-21 Modera Mark Peter Method and device for measuring airflows through HVAC grilles

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Publication number Publication date
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