Method and system for ventilation control

All patent and non-patent references cited in the application, or in the present application, are also hereby incorporated by reference in their entirety.

Field of invention

The present invention relates to a method and system for controlling performance of a ventilator, in particular, the invention relates to the integration of a control unit, a computer and a measuring unit in a ventilation system.

Background of invention

Animal barns require ventilation to keep cows, poultry, and other farm animals comfortable and productive year round. Ventilation provides fresh air and removes excess heat and moisture. Ventilation requirements vary, depending on the barn configuration, climate zone and the type of animals being housed, as well as the growth of the animals being housed.

Dairy cows can better tolerate cold than warm weather. In un-insulated dairy cow barns, calm summer weather may create adverse climatic conditions due primarily to heat radiation from the roof. In order to improve the climatic conditions for dairy cows, installation of free blowing ventilators may create high velocities in the animal zone, thus improving the cows' ability to dissipate excess heat. It is desirable to control the performance of the ventilation to meet the requirements for air movement.

The control of ventilators using discrete feedback of motor speed with a speed control unit, having a temperature responsive speed controller is known from US 5,125,571 to Heber. However, if a temperature measurement is used as control parameter for the rotation rate of a ventilator, it is not very precise. The temperature is measured at one point in the room and is not a very good parameter for controlling the ventilator, with respect to the airflow rate.

In US 6,009,763 to Berckmans et al. a system with a flow sensor is described. A free running impeller in the system is used as a flow sensor by measuring the rotation rate

of the impellor and converting the rotation rate value to the correspondent flow rate value.

Another method for controlling the airflow by using a sensor positioned in the air ventilation duct is known from US 6,719,625 to Federspiel.

WO 92/22791 to Starck describes the determination of the airflow according to the determination of the air velocity in the inflow duct of the ventilation installation.

Independent of method it is normal when purchasing a ventilator that a performance chart from the manufacturer is required to determine the airflow capacity caused by the ventilator at various speeds.

Summary of invention

The present inventors have found that it is possible to determine and control the airflow rate provided by a ventilator using the axial force exerted on the propeller as a measure for the airflow rate.

Accordingly, the object of the present invention is to provide a method for controlling performance of a ventilator by measuring an axial force perpendicular to the propeller disc of the ventilator and converting the measured axial force value to the equivalent airflow rate.

By converting a force measurement to an airflow rate as a parameter for controlling the performance of the ventilator, the sensitivity for variations in actual airflow will increase, and it is possible to more precisely determining and controlling the airflow rate. In particular the present invention obviates the need for the use of a performance chart.

Furthermore, the present invention allows for determination of airflow rate even for free blowing ventilators, in particular large free blowing ventilators.

Accordingly, in one aspect the invention relates to a method for controlling performance of a ventilator ventilating an airspace in a construction, said ventilator comprising

an attachment fixture for attaching said ventilator to the construction, said attachment fixture comprising a measuring unit, and

- a propeller comprising at least one ventilator blade and means for attaching the propeller to the attachment fixture,

said method comprising measuring an axial force perpendicular to said propeller disc by said measuring unit, and controlling said ventilator performance based on said measured force.

In another aspect the invention relates to a system for controlling performance of a ventilator ventilating an airspace in a construction, said system comprising

a ventilator comprising

- an attachment fixture for attaching said ventilator to the construction, said attachment fixture comprising a measuring unit, and

- a propeller comprising at least one ventilator blade and means for attaching the propeller to the attachment fixture, said propeller defining a propeller disc during rotation,

and a control unit comprising

- an algorithm for converting an axial force measured perpendicular to said propeller disc to an airflow volume or mass rate.

Furthermore, the invention relates to a construction comprising a system as defined above.

The method according to the invention may also be used for testing new ventilators, and accordingly the invention relates in one aspect to a method for testing a ventilator ventilating an airspace in a construction, said method comprising

establishing a ventilator having an attachment fixture for attaching said ventilator to the construction, said attachment fixture comprising a measuring unit, and a propeller comprising at least one ventilator blade and means for attaching the propeller to the attachment fixture,

- measuring an axial force perpendicular to said propeller by said measuring unit, and testing said ventilator performance based on said measured force.

Description of drawings

Figure 1 . Shape of the free blowing ventilator

Figure 2. Plan lay-out of the laboratory with the horizontal position of the free blowing ventilator and velocity measurement cross-sections.

Figure 3. Air space above the free blowing ventilator.

Figure 4. The attachment fixture connecting the complete free blowing ventilator to the I-beam.

Figure 5. The transducer unit installed between the top and the bottom plate of the attachment fixture.

Figure 6. Theoretical relation between the vertical force and the airflow rate and average air velocity created.

Figure 7. The three dimensional ultrasonic anemometer used for velocity measurements

Figure 8. Measured force at different control signals

Figure 9. Relationship between the control signal and airflow rate

Figure 10. Diagram showing the vertical, horizontal and total air velocities 1 m below the propeller in the gate-office cross-section at maximum propeller speed.

Figure 1 1. Diagram showing the distribution of the total velocity in the gate-office cross- section, 3 m and 0.75 m above the floor and at maximum propeller speed.

Figure 12. The distribution of the total, vertical and horizontal velocity 0.75 m above the floor in the wall-column cross-section at maximum propeller speed. For comparison the total velocity in the gate-office cross-section is also shown.

Figure 13. Effect of propeller speed on total velocity in the in the gate-office cross- section 0.75 m above the floor

Figure 14. Effect of propeller speed on total velocity in the in the column-wall cross- section 0.75 m above the floor

Figure 15. Control diagram of control unit and ventilator with sensor feedback

Definitions

Airflow rate - the airflow rate is generated by the ventilator and can be expressed as a volume airflow rate in for example cubic meters per second or a mass airflow rate in for example kilograms per second, preferably volume airflow rate in cubic meters per second.

Axial force perpendicular to the propeller disc - the force generated by the ventilator and transmitted to the propeller shaft.

Blade - used synonymously with propeller blade or ventilator blade or fan blade, i.e. that part of the ventilator extending to the circumference of the propeller disc.

Circular functional area of the propeller disc - the circular area covered by the propeller during rotation.

Free blowing - a ventilator arranged without a housing, tunnel, channel or casing.

Propeller disc - the area covered by the propeller blades or ventilator blades during rotation of the blades.

Ventilator- a propeller on a propeller shaft.

Description of the invention

Ventilator

The present invention relates to a method and a system for controlling the performance of a ventilator moving air in an airspace in a construction. The ventilator may be any suitable ventilator, such as an axial ventilator, a centrifugal ventilator, or a ventilator in the form of turbines. In a preferred embodiment the ventilator is an axial ventilator, and the example herein is conducted with an axial ventilator.

The ventilator may be a conventional free blowing ventilator or it may be a ventilator in a ductwork, such as where the propeller of the ventilator is arranged in a housing, a channel, a tunnel or a casing. In a preferred embodiment the ventilator is free blowing.

The ventilator may be arranged in any type of construction wherein a need for ventilation exists; both open and closed constructions are possible. In the present context ventilation is understood as supply of air, circulation of air, transport of air, or removal of air, or a combination of two or more. Transport of air also preferably includes the situation wherein air is used as transport medium transporting for example for straw. The construction may be selected from a group consisting of a building, a vessel and a vehicle, and it is preferably a building. In particular the present invention is suitable for moving air in barns or other large rooms wherein the need for a large ventilator is present.

The ventilator comprises an attachment fixture for attaching said ventilator to the construction, and it is preferred that said attachment fixture comprises a measuring unit and optionally a motor. The measuring unit may be arranged in any suitable arrangement in relation to the motor. Thus, in one embodiment the measuring unit is

arranged in the motor, and in another embodiment the measuring unit is arranged between the motor and the ventilator.

The ventilator furthermore consists of a propeller which comprises at least one ventilator blade and means for attaching the propeller to the attachment fixture.

Conversion

The performance of the ventilator is controlled by measuring the axial force perpendicular to the propeller disc created by air acceleration, and then converting the measured axial force to an airflow rate.

The conversion of the axial force to airflow rate is based on the basic equation:

V M

K = Ma = M ^■ v = m ^■ v and substituting m = p - L t t

and

Constant definitions: K = Force (N) M = air mass (kg) a = acceleration (m/s ² ) v = velocity (m/s) t = time (s) m = mass airflow rate (kg/s) p = air density (kg/m ³ ) L = volume airflow rate (m ³ /s)

A = area of the propeller disc (m ² ) R = radius of the propeller (m)

An example of determining the airflow rate created by a ventilator is shown below, for a ventilator wherein the axial force on a propeller with radius 2m is determined to 1 N. What is the airflow rate created?

R = 2 m p = 1 .205 kg/m3 (20 ⁰ C)

K = 1 N

L = R- Jπ-V I p = 2 ^{■ ■} y/π- 1/ 1.205 = 3.23m ³ I s = 11.626m ³ / h

Furthermore, using the same basic equation it is possible to convert a predetermined airflow rate to an axial force and thereby to determine the rotation speed of the

propeller and/or angle of attack of the propeller blades when a predetermined airflow rate is desired.

Attachment fixture

An attachment fixture may be constructed to connect the ventilator to a solid load carrying structure, such as an I-beam.

The force perpendicular to the propeller disc is preferably isolated and measured by a force transducer in order to estimate the airflow rate created. The attachment fixture should thus be constructed to remove torque and vibrations that can adversely influence the force transducer.

The attachment fixture preferably comprises at least one suspension between the motor and the propeller or the motor and the load carrying structure.

Measuring unit

The measuring unit is arranged at any suitable location in or near the ventilator in order to measure the axial force generated by the ventilator.

In one embodiment the measuring unit is attached to the construction, such as wherein the measuring unit has a top plate that is attached to an I-beam and a bottom plate that the motor of the ventilator is attached to. In this embodiment the bottom plate may move freely in the direction perpendicular to the propeller disc.

Both plates and connecting means, such as rods, need to be of sufficient stiffness to remove torque and horizontal vibrations. Space is provided for a force transducer unit to be attached between the top and bottom plate, i.e. the measuring unit comprises the force transducer.

The person skilled in the art may envisage other arrangements of the measuring unit.

Transducer unit

The measuring unit of the attachment fixture is designed to house for example a force transducer unit that measures the axial force. The force transducer may for example be connected to a top and bottom plate of the attachment fixture and may be installed into the measuring unit.

Any suitable force transducer may be used, however the force transducer is preferably selected from the group consisting of a piezo-electric element, a strain gauge transducer, and a vibrating wire force transducer.

Propeller and blades

The propeller may be any conventional propeller suitable for being attached to the ventilator. The propeller may comprise at least two propeller blades, such as at least three propeller blades, such as at least four propeller blades, such as at least six propeller blades, such as at least eight propeller blades, such as at least ten propeller blades.

The propeller blades may be individually attached to the ventilator or may be attached as integrated units, such as a two blade integrated unit, or a three blade integrated unit.

The present invention is suitable for small as well as large ventilators. In one embodiment the diameter of the circular functional area of the propeller disc is at least 0.1 m, such as 0.25 m, such as 0.5 m, such as at least 1 .0 m, such as at least 1.5 m, such as at least 2.5 m, such as at least 3.0 m, such as at least 3.5 m. For practical purposes the diameter of the circular functional area of the propeller disc is at most 10.0 m, such as at most 8.0 m, such as at most 6.0 m, such as at most 5.0 m, such as at most 4.0 m.

In one embodiment the propeller blades are capable of changing angle of attack when receiving a signal therefore. As discussed below change of angle of attack may be part of changing the airflow rate.

Control unit

In a preferred embodiment the ventilator comprises at least one control connected to the measuring unit and said control unit comprises an algorithm for converting the measured axial force to the airflow rate. Furthermore the control unit may comprise a display for displaying the computed airflow rate. The axial force is typically measured constantly however the measured axial force may be computed by the control unit at intervals as preferred by the user. For example a number of force measurements may be averaged and optionally filtered to remove noise before the force measurement data is computed by the control unit. The outcome of the computation is a measure of the airflow rate that may be displayed at the display. Furthermore, the control unit may comprise means for comparing the computed airflow rate to a preset airflow rate. The control unit may further comprise means for alerting the user that the airflow rate has changed and/or means for adjusting the ventilator to the preset airflow rate.

The control unit furthermore is capable of converting the determined airflow rate to a rotation rate of the propeller of the ventilator and/or angle of attack of the propeller blades thereby adjusting or regulating rotation rate and/or angle of attack if necessary. Thus, the control of the performance of the ventilation may be conducted as a closed loop system, see for example Figure 15.

In one embodiment the control unit further comprises or is connected to sensors, such as temperature and/or moisture sensors in order to improve the performance control.

Control of performance

The present invention provides as discussed above a method for controlling performance of a ventilator, i.e. the airflow rate. The term control includes monitoring whether the performance of a ventilator during rotation fulfils the preset requirements for airflow rate. Furthermore the term includes regulating the ventilator to a predetermined airflow rate.

In the following a monitoring method is described:

The ventilator has been set to a predetermined airflow rate A. During ventilation the control unit as described above periodically computes the airflow rate performed by the

ventilator. If the performed airflow rate deviates from the preset airflow rate A then the control unit may alert the user that the performance has increased or decreased.

Furthermore, it is possible that the control unit through conversion of airflow rate to actual rotation speed and/or angle of attack may provide information to the ventilator to adjust to the preset airflow by adjusting the rotation speed and/or angle of attack. In the latter scenario the ventilator is self-adjusting to a preset airflow rate and need not be surveyed by the user.

Another embodiment includes regulation of airflow rate:

It may be desirable to change airflow rate if one or more external factors change, such as temperature and moisture content in the air.

The user may regulate the rotation speed and/or the angle of attack and the changed airflow rate is then computed and may be displayed to the user who may decide whether further regulation is necessary to obtain the desired airflow rate.

It is also possible to include automatic regulation depending on input from one or more sensors of external factors, such as temperature and/or moisture sensors.

Thus, by the method according to the present invention the rotation rate of the propeller and/or the angle of attack of the blades of the ventilator may be regulated through feedback from the control unit and the airflow rate generated by the ventilator may be regulated by regulating the rotation rate of the propeller and/or the angle of attack of the blades of the ventilator.

Therefore, in one embodiment controlling of the ventilation comprises a closed loop system, and said closed loop system comprises a measuring unit comprising a force transducer measuring the axial force and being connected to a control unit comprising the algorithm for converting said axial force to airflow rate, and means for monitoring the actual airflow rate and comparing the actual airflow rate with the desired airflow rate and converting said airflow rate to said rotation speed and/or angle of attack, thereby controlling the performance of said ventilator ventilating a construction.

Example

A free blowing ventilator has a free blowing propeller intended for low-pressure, high- volume air moving applications such as air circulation within an air space without attached ductwork.

In this example the force measurement and conversion to airflow rate is described

Free blowing ventilator

The free blowing ventilator had a 6 bladed propeller with 4.3 m diameter, Figure 1 . It was driven by a frequency controlled 1 .1 kW motor. The total weight of the propeller and motor was estimated to 75 kg.

Testing facility

Room

To get representative data for the velocities created below the ventilator ample distance above the floor was needed. An existing test laboratory with a sturdy I-beam at a height of 4 m above the floor was selected.

The laboratory was 20 m long and 13.6 m wide with a center column supporting the roof and a heavy duty I-beam connecting the column with the side walls as shown on the plan-layout, figure 2. The free blowing ventilator was attached to the I-beam with its center 3.2 m from the center column and 3.7 m from the side wall, i.e. slightly off-set towards the column. In the other direction the distance from the center of the propeller to the sidewalls was 10 m.

Velocities were measured in two cross-sections. The cross-section referred to as the "gate-office" cross-section was used both for validation of force-based airflow rates and for determination of velocities in the animal zone. The other cross-section is referred to as the "wall-column" cross-section and was perpendicular to the first. The wall-column cross-section was used for velocity measurements in the animal zone in order to determine the asymmetric flow effects created by the nearby wall.

The I-beam had dimensions 220 x 220 mm with 16 mm steel thickness and was spanning from the sidewall to the center column. Air space was available above the beam to allow air to the suction side of the propeller as shown in Figure 3.

Attachment fixture

An attachment fixture was constructed to connect the free blowing ventilator to the I- beam. The fixture should carry the weight of the complete free blowing ventilator. The fixture weight was estimated at 25 kg, i.e. a total weight of propeller and motor with fixture of 100 kg.

Only the vertical force was of interest in order to estimate the vertical air movement created. The fixture was particularly required to remove torque and horizontal vibrations that could adversely influence a vertical force transducer. The resulting design is shown in Figure 4.

The attachment fixture had a top plate that was attached to the I-beam and a bottom plate that the free blowing ventilator motor was attached to. Both plates were 400 by 400 mm of 40 mm thick steel. The top plate had a 0 40 mm threaded hole in each corner, into which four 0 60 mm steel rods were screwed. The bottom plate could move freely in the vertical directions on ball roller bearings. There was space provided for a force transducer unit to be attached between the top and bottom plate.

Transducer unit

The attachment fixture was designed to house the force transducer unit required to measure the vertical forces. During operation a maximum lift of the propeller was assumed to be of the order of 25 kg. The S-shaped transducer selected had an upper force limit specified at 2500 N. It was connected to a top and a bottom plate that could easily be installed into the fixture as shown in Figure 5.

Performance test procedure

The control signal to the frequency controller could be adjusted continuously from 0 to 10 (9.88) VDC. Performance testing was carried out in steps of 1 VDC within the control range. For each step the following parameters were measured:

• Vertical force in N was recorded at 10 Hz for approx. 5 min using a NTT force transducer type TCS-91 10-0.25T and HBM software Catman for data capture and on-line monitoring.

• Propeller speed in rpm was recorded by hand held counter averaged over a 1 minute period

• Voltage in VAC, power in W and current in A were recorded by a Norma 4000 Watt meter

The force was converted to airflow rate using the equation shown above. For a propeller with diameter 4.3 m the airflow rate and the average velocity created is given as a function of the recorded force in Figure 6.

Velocity measurements

The air velocity was measured at two vertical levels above floor in the velocity measurement cross-sections shown in Figure 1 :

1. 1 m below the propeller equal to 3 m above floor in order to verify the airflow rates determined on the basis of force measurements

2. 0.75 cm above floor in order to specify the velocities created by the propeller in the animal zone.

The circle described by the propeller tips was divided into 6 concentric sub-circles. In Table 1 is shown the division circles and the radius chosen for sensor position.

Table 1. The chosen radiuses for sensor positions under the free blowing ventilator.

The velocities were measured with a three-dimensional Gill Instrument Ltd. ultrasonic anemometer model Windsonic type 1086M. The velocities were recorded in a 3-D air volume between the ultrasonic senders and receivers 150 mm apart as seen in Figure 7.

Results Performance

Force

The results of the force measurements are shown in Figure 8. As the control signal is stepped downwards from the maximum 9.88 VDC the force also steps downwards. Some fluctuation in the force is noticed at each step.

The detailed results of the force measurements are summarized in Table 2, including control signal, power consumption, propeller speed, force, and resulting airflow rate.

Power supply to frequency converter (Breeze ventilator motor is controlled by signal 0 - 10 VDC)

Table 2. The results of the force based performance test.

At maximum propeller speed the control signal from the potentiometer was 9.88 VDC. This resulted in a power consumption of 1.30 kW and a propeller speed of 87 rpm. The average vertical force created by the propeller was 213 ±5 N. The theoretical airflow rate according to the equation given in the appendix is 182 601 m2/h, which is rounded up to 183 000 m3/h.

There was a linear relationship between the control signal and the airflow rate within the range investigated as shown in Figure 9.

Velocity verification

In order to verify the airflow rates determined on the bases of force measurements the velocity components were measured in the 12 sensor points 1 m below the propeller. The results are given in Table 3. It is seen that the average velocity in the downward V direction was 3.17 m/s, and the average velocities in the horizontal U direction were only 3.5% and in the V direction only 1.9% of this value.

Table 3. Velocity components and resulting velocities in the measurement points 1 m below the propeller.

The horizontal and total velocities were calculated for each measurement point as

Horizontal = λJU ² +W ²

Total = Vt/ ² +V ² +W ^:

The variation in the measured vertical, horizontal and total air velocity 1 m below the propeller in the cross-section perpendicular to the I-beam is shown in Figure 10. Fourth order polynomial trend lines are also indicated. Positive distances are from the center of the propeller towards the gate and negative towards the office. It is seen how the

largest total velocity and hence the largest airflow is generated by the outer half of the propeller but it falls drastically close to the propeller tips. From the outer half the velocities gradually decline to nearly nothing at the center. The total velocity consists primarily of the vertical component as the horizontal component is small.

On the basis the average total velocity of 3.40 m/s, the airflow rate was determined as 177731 m3/h. This was only 2.7 % lower than determined using the force measurement, Table 4.

Table 4. Comparison between velocity based and force based airflow rates.

Air velocities in the animal zone

Height above floor As the jet created by the propeller is approaching the floor, the vertical velocities are gradually transitioning into horizontal velocities along the floor. The proximity of obstacles may influence this process.

In Figure 1 1 is shown the change in total velocity from 3 m to 0.75 m above height above floor. Compared with height 3 m the profile at height 0.75 m is flattening out primarily near the tips of the propeller as the airflow is spreading out towards the sides.

Effect of wall

The effect of the adjacent wall is shown in Figure 12. At a distance of 1.8 m from the center a total velocity of 3.6 m/s was recorded on the column side, but it declined to 0.9 m/s at the wall side.

On the column side the total velocity was similar in the two cross-sections. The total velocity on the wall side, however, was much lower than on the column side. The vertical, downwards velocity was contributing the most to the total velocity on the column side. On the wall side it was the horizontal velocity that dominated.

Effect of propeller speed

The average of the three velocity components and the total velocities measured 0.75 cm above floor is shown in Table 5. It is seen that in average the total velocity was 2.48 m/s in the gate-office cross-section at 10 V falling to 85% at 8V and 71% at 6 V.

Table 5. The average of the three components and the total velocities measured 0.75 cm above floor.

There was considerable variation in the two cross-sections. In the gate-office cross- section the variations were fairly symmetrical as shown in Figure 13. Compared to the gate-office cross-section the total velocities in the column-wall cross-section the velocities were lower at 1.76 m/s (100%), 1.47 (84%) and 1.18 (67%), but the effect of control signal fairly similar.

The variation of the velocities in the column-wall cross-section is shown in Figure 14.

Conclusions At maximum propeller speed the control signal from the potentiometer was 9.88 VDC. This resulted in a power consumption of 1.30 kW and a propeller speed of 87 rpm. The average vertical force created by the propeller was 213 ±5 N. The theoretical airflow rate according to the equation given in the appendix is 182 601 m3/h, which is rounded up to 183 000 m3/h.

The average velocity in the downward direction 1 m below the propeller was 3.17 m/s, and the average velocities in the horizontal direction 1.1 1 m/s. The largest velocities and hence the largest airflows were generated at the outer half of the propeller tips and were gradually declining to nearly nothing in the center. The velocity-based airflow rate was only 2.7 % lower than the force-based airflow rate.

The total velocity in the animal zone in the gate-office cross-section was 2.48 m/s (100 %) at 10 V control signal falling to 2.10 m/s (85%) at 8 V and 71 % at 6 V. In the column-wall cross-section the velocities were lower at 1.76 m/s (100%), 1.47 (84%) and 1.18 (67%), but the effect of control signal fairly similar.