SIST CR 14378:2002
(Main)Ventilation for buildings - Experimental determination of mechanical energy loss coefficients of air handling components
Ventilation for buildings - Experimental determination of mechanical energy loss coefficients of air handling components
This Technical Report specifies unified test procedures and conditions for the experimental determination of mechanical energy loss coefficients for ductwork components such as ducts, bends, diffusors, converging junctions and diverging junctions.
Prezračevanje stavb – Kanali – Eksperimentalno določevanje tlačnih padcev kanalskih komponent
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST CR 14378:2002
01-maj-2002
3UH]UDþHYDQMHVWDYE±.DQDOL±(NVSHULPHQWDOQRGRORþHYDQMHWODþQLKSDGFHY
NDQDOVNLKNRPSRQHQW
Ventilation for buildings - Experimental determination of mechanical energy loss
coefficients of air handling components
Ta slovenski standard je istoveten z: CR 14378:2002
ICS:
91.140.30 3UH]UDþHYDOQLLQNOLPDWVNL Ventilation and air-
VLVWHPL conditioning
SIST CR 14378:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST CR 14378:2002
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SIST CR 14378:2002
CEN REPORT
CR 14378
RAPPORT CEN
CEN BERICHT
January 2002
ICS
English version
Ventilation for buildings - Experimental determination of
mechanical energy loss coefficients of air handling components
This CEN Report was approved by CEN on 10 November 2001. It has been drawn up by the Technical Committee CEN/TC 156.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2002 CEN All rights of exploitation in any form and by any means reserved Ref. No. CR 14378:2002 E
worldwide for CEN national Members.
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CONTENTS
Foreword.3
1 Scope .4
2 Normative references .4
3 Terms and definitions .4
4 Test method.4
4.1 Principle.4
4.2 Test installation.6
4.3 Rectangular and other non-circular ducts and components .7
4.4 Measurements.7
4.5 Calculation method .8
4.6 Calculation of uncertainties.9
4.7 Number of test points.11
4.8 Presentation of data .11
Annex A.12
A.1 Components with inlet different from outlet (diverging or converging).12
A.2 Components with free inlets.12
A.3 Components with free outlets .13
A.4 Components with two inlets (converging junctions).14
A.5 Components with two outlets (diverging junctions).17
A.6 Components without swirl.18
Annex B .20
B.1 Flow rate measurement.20
B.2 Pressure measurement .21
B.3 Temperature measurement.23
B.4 Humidity measurement .23
Bibliography.24
2
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Foreword
This Technical Report has been prepared by Technical Committee CEN/TC 156, ‘Ventilation for buildings’, the
secretariat of which is held by BSI.
This report should be considered with a series of standards for ductwork used for ventilation and air
conditioning of buildings for human occupancy.
The position of this report in the field of mechanical building services is shown in Figure 1.
Mechanical Building
Services
Control systems Ventilation and air Heating systems
conditioning systems
Air handling units Ductwork Installation
Circular sheet Circular sheet metal Rectangular sheet Hangers and
metal ducts ducts Strength and metal ducts supports
Dimensions leakage Strength and
leakage
Rectangular sheet Measurement of Requirements for Flanges
metal ducts duct surface area ductwork
components to
Dimensions facilitate
maintenance
Identification Flexible ducts Determination of Ductwork made
mechanical of insulation
energy loss ductboards
Figure 1 - Position of CR 14378 in the field of mechanical building services
3
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1 Scope
This Technical Report specifies unified test procedures and conditions for the experimental determination of
mechanical energy loss coefficients for ductwork components such as ducts, bends, diffusors, converging
junctions and diverging junctions.
2 Normative references
This Technical Report incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed hereafter.
For dated references the subsequent amendments to or revisions of any of these publications apply to this
Technical Report only when incorporated in it by amendment or revision. For undated references the latest
edition of the publication referred to applies (including amendments).
-
CR 12792 Ventilation for buildings Symbols, units and terminology
ISO 5221 Air flow measurement in an air handling duct.
3 Terms and definitions
For the purposes of this report, the terms and definitions and symbols are principally in accordance with CEN
Technical Report CR 12792.
4 Test method
4.1 Principle
In principle it is possible to give a definition of energy loss produced by a component of air distribution
systems.
1 2
1 2
Figure 2 - Diagrammatic representation of energy flow
The mechanical energy loss in the flow within a typical component, as represented in Figure 2, is equal to the
difference between the energy entering the component through section I and the energy leaving the
component through section 2.
By applying the generalized Bernoulli formula which takes into account the fact that the air is compressible,
therefore its density varies through the component, and that it is a real fluid, the velocity distribution in a
section being non-uniform, the energy loss per unit mass (J/kg) is expressed by:
4
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CR 14378:2002 (E)
2 2
p p v v
2
1 2 m1 m2
y gZ Z (1)
1 A1 A12 1 2
p 2 2
12
where
y is the energy loss per unit mass
pis the absolute pressure
V is the mean flow velocity
m
Z is the altitude
is the fluid density
12
g is the free fall acceleration
is the kinetic energy factor
A
The kinetic energy factor can be determined by Pitot-tube exploration in the cross section under
A
consideration. The density depends on the flow variation through the component.
12
In practice the presence of an air handling component in a duct system modifies the flow structure upstream
and downstream of the component. For this reason the practical determination of the mechanical energy
losses is generally made on the test installation as shown in Figure 3.
0 1 2 3
L
23
L
01
0 1 2 3
Figure 3 - Diagrammatic representation of the test installation
L
A straight duct of the length is installed upstream of the component and a straight duct of the length
01
L
downstream. The measurement sections (0 upstream and 3 downstream) are consequently distant
23
from the component. From the test values obtained in these sections the characteristics of flow are
calculated for the sections I and 2 and then used in the generalized Bernoulli formula to obtain the
mechanical energy loss.
The choice of lengths L and L and the assumptions concerning the flow through these duct sections can
01 23
cause differences in the final results. Therefore an agreement on the choice of lengths shall be established
before the start of the experimental work.
There is no intrinsic value of energy loss coefficient for an air handling component. For each upstream flow
condition a different value will be found. Consequently the use of a long straight duct upstream of the
component is just one of many possible conditions. However the different lengths of this duct and different
entry conditions can produce variations in the flow pattern.
Therefore, it is important to specify in detail all characteristics of the installation upstream of the component.
The upstream straight duct shall have a length equal to 200 and a specified perforated plate at the entrance.
The measuring section shall be located at a distance 5D from the component.
5
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The downstream flow pattern is dependent on the component under test. Usually a very long straight duct is
used and the measuring section is a distance away in order to allow for the correct measurement. The energy
loss of the ducting shall be taken into account in the calculation of the energy loss coefficient of the
component under test. For the same length of straight duct this energy loss may be very different depending
on the flow pattern (essentially in the presence or in the absence of swirl).
As the actual loss is not known the conventional energy loss corresponding to the fully established flow
without swirl is normally used.
A specified flow straightener (as used for fan performance testing specified in ISO 5221) instead of a very long
duct, (it can be as long as 40D) shall be installed immediately downstream of the component under test. The
correct measurement of the pressure is then possible where the loss in the straightener and associated
ducting is taken into account conventionally.
An important advantage of this method is the elimination of the necessity to measure the kinetic energy factor
in the upstream section as well as in the downstream section. It is assumed that is equal to one. If a
A A
particular component produces a very strong swirling flow with an irregular velocity distribution, the energy
loss in the straightener will be far greater than the conventional value used for the calculation. The energy loss
coefficient of the component under test will appear higher.
These characteristics are presented in this way because in practice the rotational energy in fluid flow will be
lost anyway and this loss is produced by the component (though not jn the component itself). It will be noted
that in the usual method (a long straight duct downstream) this assumption is also applied but the
measurement is more difficult and the scatter of results obtained in different laboratories can be important.
4.2 Test installation
The standard test installation is shown in Figure 4.
0 1 2 3 4
G
A B C D E F
A Perforated plate
.
B Upstream measuring section
C Component under test
D Flow straightener “ETOILE’
E Downstream measuring section
F Complementary measuring
G Flow rate control and measurement
Figure 4 - Standard test installation
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The following specification shall be used:
a) Duct diameter: Equal to the diameter of the component under test
b) Perforated plate at the inlet:
diameter of holes: 5 mm
distance between axes : 7,5 mm
free area/total area: 0,40
c) Duct roughness: Smooth metal duct
d) Flow straightener “ETOILE” in accordance with the drawing
Length: 20 (tolerance 1%)
Thickness: < 0,0070
Angle: = 45 5
4.3 Rectangular and other non-circular ducts and components
For ducts and components with non-circular cross sections (essentially rectangular and oval) the notion of a
hydraulic diameter shall be introduced. The hydraulic diameter is calculated as four times the cross section
divided by the perimeter.
For a rectangular cross section with sides a and b, therefore, the hydraulic diameter D is given by:
h
4ab 2ab
D
(2)
h
a b a b
2
The standard test installation shall be made with upstream and downstream ducts of the same cross section
as the component under test; using D instead of D for the circular duct, all calculations will use the same
h
formulae.
As an alternative solution a test installation with circular ducts may be used. The component under test shall
be connected to the upstream and downstream ducts using a transition with the following specification:
the cross section area of the circular duct shall be equal to the cross section area of the component
with a tolerance of 10 %,
The length of the transition shall be equal to one diameter of the circular duct,
For the calculation of the energy loss coefficient under test, the energy loss in the transition shall be
considered equal to the loss in a straight duct having the same length.
4.4 Measurements
The following quantities shall be measured:
a) Atmospheric pressure p , Pa
a
b) Air temperature °C, [T = 273,15 + K]
c) Air humidity from both dry and wet bulb or dew point temperature
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d) Static pressure in the section 0 (mean value of four individual readings), p Pa
s0
e) Static pressure in the section 3 (mean value of four individual readings), p Pa
s3
f) Differential pressure between the section 0 and 3, p Pa
s03
g) Static pressure in the section 4 (mean value of four individual readings), p Pa
s4
h) Mass flow rate (by an appropriate standardized method as given in Annex B), q kg/s
m
4.5 Calculation method
4.5.1 The calculation method is given in 4.5.2 to 4.5.9
4.5.2 The absolute pressures are calculated for the sections 0 and 3 as follows:
p p p (3)
0 a s0
p p p (4)
3 a s3
4.5.3 The mean air density (which is assumed to be constant throughout the test installation) is calculated
from:
p
m
f (5)
T
287
where
p p
0 3
p (6)
m
2
and the humidity factor f is given by:
p
v
f 1( 0,378
7)
p
m
where p is the partial vapour pressure
v
4.5.4 The Reynolds number is calculated from:
4q
m
Re (8)
D
where the dynamic viscosity is given by:
6
17,1 0,048
10 (9)
4.5.5 The mean air velocity is calculated from the following:
4q
m
v (10)
2
D
4.5.6 The pressures in sections I and 2 are calculated from the following:
2
v
p p
(11)
1 0 01
2
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2
v
p p
(12)
2 3 23
2
where
0,30
5 0,0050,42 Re (13)
01
and
0,12 0,30
, , ,
0 95 Re 3 0 005 0 42 Re (14)
23
Values of and for some Reynolds numbers are given in Table 1.
01 23
Table1 — Values of and for some Reynolds numbers
01 23
Re
01 23
50000 0,11 0,32
100 000 0,09 0,29
200 000 0,08 0,27
400000 0,07 0,24
4.5.7 The differential pressure between sections I and 2 shall then be calculated as follows:
2
v
p p p
(15)
1 2 03 01 23
2
4.5.8 The mechanical energy loss per unit mass is given by:
p p
1 2
2
y (16)
1
2
4.5.9 The energy loss coefficient for the component tested is then given by:
p p
1 2
(17)
2
v
2
4.6 Calculation of uncertainties
The uncertainties of the test results are determined by consideration of the formula used for calculating the
energy loss coefficient of a component:
p p
1 2
(18)
2
v
2
p p
In practice the value of - is not measured directly and is calculated from the measured differential
1 2
pressure p by:
03
2
v
p p p
(19)
1 2 03 01 23
2
The energy loss coefficient is therefore given by:
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p
03
(20)
01 23
2
v
2
The term ( + ) represents a calculated conventional value of the correction to be applied. It varies only
01 23
5
slightly with Reynolds number; for example, for a Reynolds number variation of 100 % (for instance from 10
5
to 210 ) this coefficient varies only 8 %. As the Reynolds number can be readily known with an uncertainty of
less than 2 %, it is clear that the uncertainty on ( + ) is very small.
01 23
Therefore, the uncertainty on will be closely related to the uncertainty of the term:
p
03
(21)
2
v
2
In fact the absolute uncertainty of will be very close to the absolute uncertainty of this term.
p
03
The term can be developed as follows:
2
v
2
4 2
p p p
D
03 03 03
(22)
2 2 2
v
8
q
q m
4
m
2 2
2
D
In order to determine the overall uncertainty, the following expression shall be used:
4 2
p
D
03
(23)
01 23
2
8
q
m
We can substitute XY
4 2
p
D
03
where X (24)
2
8
q
m
and Y (25)
01 23
The absolute, and not the relative, values of the uncertainties for each of these terms shall be used to find the
uncertainty associated with , because is calculated as a difference between, and not a product of, the two
terms.
Where the absolute uncertainties of X and Y are X and Y respectively, the absolute uncertainty of will be
given by:
2 2
X Y (26)
Because these are absolute uncertainties it is not possible to produce a general statement for all possible
situations, and the relative magnitude of X and Y is very important
EXAMPLE
Consider the results obtained for a given component as follows:
X Y X – Y
Re =100 000 with = 0,73 and =0,38 the loss coefficient is =
...
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