Standard SFS 5512 AIR CONDITIONING. MEASUREMENTS OF AIR FLOWS AND PRESSURE CONDITIONS IN AIR CONDITIONINGS SYSTEMS Contents
1. Area of application
This standard specifies the methods, which are used when the air flow is inspected
-during building time
-in purchasing a building
-when building is in use
2. References
SFS 5147 Ventilation. Fans. Aeraulic measurements. 1986
SFS 5331 Air conditioning. Adjustment and blocking devices. Testing. 1987
SFS 5511 Building indoor air. Field measurements of heating conditions. 1989
3. Definitions
3.1. Air flows
The names of air flows are as follows in picture 1:
1.
outdoor air
2.
supply air
3.
transferred air
4.
exhaust air
5.
return air
6.
extract air
7.
circulated air
8.
indoor air.
Picture 1
Picture 2 shows, how air flows are measured in buildings, what kind of methods can be used
(which are specified in unit 5).
Air flows
1. outdoor air flow
2. supply air flow
3. transferred air flow
4. exhaust air flow
5. return air flow
6. extract air flow
Lower indexes:
1. a - System, main duct
Picture 2
b- Common or collector duct
c - Room or cross-over main.
Picture 2. The air flow’s of buildings and conditionings systems and the methods suitable for
measuring those air flows. The markings can be seen in the picture 1.
4. Measurements of air flows
4.1. Precision requirements of measurements and measuring devices
The allowed deviations of measurement results are as follows:
- Room air flows ±20%
- System air flows ±10%
The air conditioning systems’ minor deviations can be defined separately.
The acceptable deviations contain both the deviation of measurement results and also the
inaccuracy of methods. That method is used, if the inaccuracy is usually not more than a half of the
acceptable deviation.
4.2. Performance of measurements
Measurements must be done according to the description of measuring methods and using
instructions of measuring devices. Besides air temperature, air pressure must be measured.
Humidity must be measured if it differs from normal level.
Supply and exhaust air flows in the same space or in the same ventilation station must be measured
by methods with equal accuracy level.
Air flows’, pressure and pressure differences’ measurements, which require especially high
accuracy, must be measured according to the methods of standard SFS 5331.
5. Methods of air flows’ measurements
5.1. General information
The measuring method must be chosen according to table 1, also compare picture 2. Further more,
units 5.1.1.-5.1.3. must be taken into account.
Table 1. Measuring methods.
Duct
Measuring place or item
EXHAUST AIR PART
A
A0 Fitted measuring elements
B
B0 Fitted measuring elements
A1 Fixed measuring elements
B1 Pressure difference
measurement
C1 Pressure difference
measurement
B11 Measuring by sensors
C11 Measuring by sensors
B12 By solid or integrated
measuring element
C12 By solid or integrated
measuring element
A2 Multipoint measuring
SUPPLY AND OUTDOOR AIR
PART
C
C0 Fitted measuring elements
B2 Average velocity method
rectangular elements
A21 round duct
A22 rectangular duct
(A3 tracer measuring)
B3 Measuring by anemometer
horn
(C3 Measuring by anemometer
horn
C4 Bag-method
5.1.1. Measurements of air flows in air conditioning systems
Air flows (see picture 2.) are measured in air conditioner or in the duct.
Measuring methods
- Fitted measuring element, methods A0, B0 and C0.
- Calibrated measuring element, methods A1 or B1, in duct or in air conditioner, or type calibrated
component as measuring element.
- Multipoint measuring in the duct, method A2.
5.1.2. Measurements of air flows in rooms
Rooms’ or air terminal devices’ air flows are measured first of all by method of fitted measuring
elements or by Calibrated sensors (methods B0 and C0, as well as B1 and C1). Also methods B2
and B3 as well as C3 and C4 can be used.
5.1.3. Protection distances
Measuring point must be chosen in order to provide enough distance from centre of flow
disturbance so that methods’ inaccuracy would not be higher than in unit 5.2.
Protection distances are calculated as follows:
L  N1  D
Round duct:
Rectangular duct:
L  N1 
ab
2
(1)
(2)
where L is distance between measuring point and centre of flow disturbance
D - diameter of the duct
a and b are dimensions of the rectangle
N1- coefficient of protection distances in direction of flow before measuring point
N2- coefficient of protection distances in direction of flow after measuring point
5.2. Measurement methods
Measuring devices must be type approved or calibrated according to the requirement of Standard
SFS 5511.
Every measuring device must have detailed instructions for use, where the criteria for evaluation
(unit 6.2.) and restrictions of use must be stated in detail.
5.2.1. Air flow measurement by solid or integrated measuring element (methods A1,
B12 and C12)
Method applicability
Method of solid or integrated measuring element can be used in follow measurement:
-
air flow measurement in the duct (outdoor, supply, exhaust and extract air flows), picture 3
-
air flow, which is coming for supply air terminal device, picture 4
-
air flow, which is going from exhaust air terminal device, picture 5
Picture 3
Picture 4
Picture 5
Measurement devices
Type approved or calibrated measuring element or integrated measuring element, which is installed
in duct by type approval or calibration specified way. Pressure difference measuring device, scale
interval is not more than 2 Pa, if measuring range is between 20 and 100 Pa, or 5 Pa, if measuring
range is between 50 and 250 Pa.
Minimum coefficients of protection distances which are usually approved, are in pictures 3-5. In
this case the inaccuracy of method is not more than ±10%. Minimum protection distances can be
used, if measurement device functioning is mentioned. Protection distances of different accuracies
can be defined according to the needs of each measuring device.
Measurement performance
First the pressure difference is measured. Air flow can be read from calibration curves of measuring
element or integrate, example of this is in picture 6.
Picture 6
5.2.2. Multipoint measurement
Method applicability, measurement devices
Pitot-pipe (pictures 7-9) is applied for air velocity and air flow measurements in the duct, if air
minimal velocity is 3 m/s when flow is constant. If flow velocity is less than 3 m/s, it can be
measured by multipoint method using hot wire sensor. Pitot-pipe does not need the re-calibration.
Picture 7. Principle of pitot-pipe.
Picture 8.Pitot-pipe in overpressure duct.
Picture 9. Pitot-pipe in low pressure duct.
Pictures 7-9:
pt - total pressure
ps - static pressure
pd - dynamic pressure
Measurement performance
The most common measuring methods are (picture 10):
- 5 points-method
- log-linear-method (measuring in 2, 3 or 4 diameters)
- rectangle-method
- log-Tschebyschew-method
Measurement accuracy, protection distance (curve on picture 10) and duct size have influence on
choosing the method. In every point where the dynamic pressure is measured, it is necessary to
calculate prevalent air flow velocity in valid points. It is necessary to measure air flow velocity in
every measuring point during dynamic pressure measuring. The average result of velocity from
those measuring results must be, if necessary, corrected with coefficient k (picture 10).
5 points-method
k=1 (round)
k=0,96 (rectangle)
Picture 10 (continue on the next page)
Log-linear-method
Rectangle-method
Log-Tschebyschew-method
m- measuring line number
n- measuring point number on measuring line
Picture 10 (continue on the next page)
Inaccuracy estimation curves
Method accuracy
Coefficient of protection distance
1- midpoint method
2- 5 points-method
rectangle- method, when n=4
3- log-linear-method, 12 points
rectangle- method, when n=6…10
4- log-linear-method, 24 points
rectangle- method, when n>= 12
In any case N1 ≥ 2
Picture 10
5.2.3. Air flow measuring in supply- and exhaust air terminal devices by measuring
sensor, which is calibrated product-specifically. (methods B11 and C11)
Method applicability
Method is applied for air flow measuring in outdoor-, supply- and exhaust air terminal devices,
picture 11.
Picture 11. Measuring by calibrated measuring sensors.
Measuring devices
Pressure differences’measuring devices as in unit 5.2.1. Extra equipment are measuring sensor and
measuring instrument for measuring positions of air terminal devices (if device does not have
position indicator). Device’s calibration curves must be done for different installations or other
choice is that required protection distances must be presented.
Measurement performance
Pressure differences and position of device measured according to picture 11. If device has position
indicator, it must be checked.
Method inaccuracy is about 5%, if measuring conditions and detecting element are defined exactly,
in other situations- usually 10-15%.
5.2.4. Measurement by anemometer horn (methods B3 and C3)
Method applicability
Method is applicable to air flow measurements in exhaust air terminal devices, picture 12.
Anemometer horn must cover measuring device fully, in same time it shouldn’t choke the air flow.
According to above mentioned, this method is unsuitable for measuring of the cooker hood air flow, for
example. Method is not recommended, if pressure loss of anemometer horn is more than 20% from
pressure loss of measuring terminal device.
Measuring error, which was induced by pressure loss of anemometer horn, must be corrected using
the following equation:
qv  qn 
Δp
Δp n
(3)
where
qv - air flow without anemometer horn
qn - air flow, which was measured by anemometer horn
∆ pn - total pressure difference of
measuring time
measuring terminal device and anemometer horn during
∆p- pressure difference of measuring terminal device without anemometer horn
Measuring devices
Anemometer horn, picture 12, and fitted or replaceable air flow velocity measuring device, which have
common calibration.
Picture 12. Measurement of exhaust air flow by anemometer horn
1. seal
2. anemometer horn
3. velocity measuring device
Measurement performance
Air flow is measured according picture 12.
Method inaccuracy is minimum 5% for measurement in exhaust air terminal devices, and minimum
10% for measurement in supply air terminal devices, usually it is substantially higher.
5.2.5. Average velocity method (method B2)
Method applicability
Method is applied for air flow measurement in rectangular exhaust air terminal devices. With this
method one usually can not measure the air flow with required accuracy. For room air flow
measurement this method can be used only, if free flow port of frontal surface is minimum 70% of frontal
surface and if local flow velocity doesn’t deviate more than 50% of average velocity in any point.
Measurement devices
Calibrated flow velocity measuring devices are for example hot-wire anemometer or blade wheel
anemometer with small diameter.
Measurement performance
Frontal surface of device, which must be measured, is divided at least by 6 equal parts, of which the
smallest side is at least equal to sensor diameter. Air flow velocity must be measured in midpoint of
every frontal surface part.
Average air flow velocity is v.
Air flow qv can be calculated from equation:
q v  0,85  v  A o
( 4)
where Ao is area of frontal surface
Method inaccuracy is as minimum +10%, if measuring points are at least on 3 lines and if points’
number is at least 9, and about +15% if 6-8 points are used.
5.2.6. Bag-method (method C4)
Method applicability
Method is applied for air volume flow measurement in supply air terminal device. Bag must be put
closely around the device. There must be enough overpressure in the duct to fill the bag up and in
front of measuring device there must be enough space so that bag can swell.
Measurement devices
According to picture 13.
Measurement performance
Bag filling time is measured according to picture 13. Measurement must be repeated at least
once.
Air flow is qv calculated from the equation:
qv 
where V is bag volume
t is average time of bag filling
1. seal
2. framework
3. pressure measuring hosepipe
V
t
(5)
4. pressure difference measuring device
5. plastic bag, which coating thickness is, for example, 0,03 mm, for example, polyethylene
Picture 13. Air volume flow measurement by bag-method
On the left side- measurement starting moment: bag is empty, timekeeping is started
On the right side- measurement finishing moment: bag is full, ∆p=3 Pa, timekeeping is
stopped.
Method inaccuracy is ±5-10%, depending on the bag volume inaccuracy, the timekeeping
inaccuracy and the bag installation inaccuracy.
5.2.7. Other methods
Also other air flow measuring methods can be used, but there is no description of those
methods in this standard, because those methods are inaccurate or difficult to apply in
present form.
Those methods are:
- tracer measurements (also air change rate measurement, field surveying applications are
being developed)
- supply air flow measurement by anemometer
- compensation method, for example for supply- and exhaust air flow measurement in air
conditioning system
6. Processing the results of air flow measurements
6.1. Presentation of results
In measuring protocol the following information must be presented:
- date of measurement
- measured object (for example room space, engine etc.)
- measurer and measuring supervisor
- measuring devices, which were in use; description of their calibration
- weather conditions
- air flow temperature and humidity when needed
- description of disturbances, which have influence on measuring results
- actual measuring results
If density of air deviates from the standard air density 1,2 kg/m3 for more than 2%, measuring
results must be corrected in the following way:
q V  q Vo 
ρm
ρo
( 6)
where
qv is real air flow
qv0 is measured air flow
ρm is air density at day of measurement
6.2. Estimation of inaccuracy
Reliable miscalculation estimation requires that relatively big systematic errors, which have
influence on measuring results, are eliminated by the correct use of methods as well as calibration
of measuring instruments. To estimate the inaccuracy of measurement caused by remaining random
errors and by small systematic errors, which influence is unknown, the following equation can be
used.
m  a 1  m12  a 2  m 22  ...  a n  m 2n
(7)
m = is a relative inaccuracy of the measurement
m1, m2 … mn are relative inaccuracies of those factors, which have influence on the final measuring
results. These are equipment errors of measured component quantity, inaccuracies of the methods,
detection errors and so on.
a1, a2 … an are coefficients, which observe the influence of every individual inaccuracy on the final
result.
Commonly each coefficient ai=1 in case of remarkable deflections of equipments. These values
must be shown in calibration information of the equipment.
7. Pressure conditions and measurement of pressure differences
7.1. Determination of pressure conditions
7.2. Measurement of pressure differences in buildings
7.3. Measurement of pressure differences in air conditionings systems
Tutor information
- Reference
-Prerequisites of measurement