Heat exchangers - Method of measurement and evaluation of thermal performances of wet cooling towers

This European Standard specifies requirements, test methods and acceptance tests for thermal performances pumping head verification of wet cooling towers and plume abatement for wet/dry cooling towers.
This European Standard is applicable to natural draught wet cooling towers (see in 3.1.2.2) fan assisted natural draught cooling tower (see 3.1.2.3), wet/dry cooling towers (see 3.1.2.4) and "Mechanical draught cooling towers", except series ones.
It specifies the test methods, the apparatus required, the limitation of errors and the method for results examination.
The acceptance testing covers the verification of the thermal performance data and pumping head of the cooling tower as specified in the contract between the supplier and the purchaser. If these tests are required then this should be recognized at the time of the contract, as additional fittings, and preparations for the test may be required.
Deviations from the rules laid down below as well as additions need special agreement between purchaser and supplier and should be documented.
This standard does not apply to mechanical draught series wet cooling towers which are dealt with in prEN 13741.
NOTE   Terms like "design", "values", "guarantee" and "acceptance" used in this standard should be understood in a technical but not in a legal or commercial sense.

Wärmeaustauscher - Verfahren zur Messung und Bewertung der wärmetechnischen Leistungskenndaten von Nasskühltürmen

Diese Europäische Norm legt Anforderungen, Prüfverfahren und Abnahmeprüfungen zum Nachweis wärmetechnischer
Leistungskenndaten, der Pumpförderhöhe für Nasskühltürme sowie zur Verminderung von
sichtbaren Schwaden für Nass-/Trockenkühltürme fest.
Diese Europäische Norm gilt für Naturzug-Nasskühltürme (siehe 3.1.2.2), für Naturzugkühltürme mit
Ventilatorunterstützung (siehe 3.1.2.3), Nass-/Trockenkühltürme (siehe 3.1.2.4) und mit Ausnahme von
Serienkühltürmen auch für zwangsbelüftete Kühltürme.
Es werden Prüfverfahren, die erforderlichen Prüfgeräte, Fehlergrenzen und das Verfahren zur Auswertung der
Ergebnisse festgelegt.
Die Abnahmeprüfung umfasst den Nachweis wärmetechnischer Kenndaten und der Pumpförderhöhe für
Kühltürme, die im Vertrag zwischen Lieferant und Käufer festgelegt sind. Falls Abnahmeprüfungen gefordert
werden, sollten sie bereits im Vertrag festgelegt werden, da zusätzliche Prüfausrüstungen und -vorbereitungen
erforderlich werden können.
Abweichungen von und Zusätze zu den nachfolgend festgelegten Regeln bedürfen einer besonderen
Vereinbarung zwischen Käufer und Lieferant und sollten dokumentiert werden.
Die vorliegende Norm gilt nicht für zwangsbelüftete Serien-Nasskühltürme, die in EN 13741 erfasst werden.
ANMERKUNG Ausdrücke wie Auslegung, Werte? Garantie und Abnahme werden in dieser Norm im technischen
und nicht im juristischen oder kaufmännischen Sinne gebraucht.

Echangeurs de chaleur - Méthode de mesure et évaluation des performances thermiques des aéroréfrigérants humides

La présente Norme européenne spécifie les exigences, les méthodes d'essai et les essais de des performances thermiques, de la vérification de la hauteur de refoulement des aéroréfrigérants humides et de la réduction du panache des aéroréfrigérants humides/secs.
La présente Norme européenne est appliquée aux aéroréfrigérants humides a tirage naturel (voir 3.1.2.2), aux aéroréfrigérants a tirage naturel assisté par ventilateur (voir 3.1.2.3), aux aéroréfrigérants humides/secs (voir 3.1.2.4) et aux " aéroréfrigérants a tirage mécanique ", a l'exception des aéroréfrigérants a tirage mécanique réalisés de série.
Elle précise les méthodes d'essai, les appareillages nécessaires, la limitation des erreurs et la méthode d'évaluation des résultats.
Les essais de réception couvrent la vérification des données de performances thermiques et de la hauteur de refoulement de l'aéroréfrigérant telle que spécifiée dans le contrat entre le fournisseur et le client. Lorsque ces essais sont exigé, cela doit etre précisé lors du contrat, comme des équipements complémentaires et la préparatoire des essais peut etre nécessaire.
Des divergences par rapport aux regles décrites ci-dessous ainsi que des additions nécessitent un accord spécial entre le fournisseur et le client et il convient qu'elles soient consignées par écrit.
La présente norme ne s'applique pas aux aéroréfrigérants humides a tirage mécanique réalisés en série qui sont traités dans le prEN 13741.
NOTE   Il convient de comprendre les termes tels que "utile", "valeurs", "garantie" et "réception" utilisés dans la présente norme dans un sens technique mais non pas dans un sens juridique ou commercial.

Prenosniki toplote – Merilna metoda in ocenjevanje toplotnih lastnosti mokrih hladilnih stolpov

General Information

Status
Published
Publication Date
30-Sep-2005
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Oct-2005
Due Date
01-Oct-2005
Completion Date
01-Oct-2005

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SLOVENSKI STANDARD
SIST EN 14705:2005
01-oktober-2005
Prenosniki toplote – Merilna metoda in ocenjevanje toplotnih lastnosti mokrih
hladilnih stolpov

Heat exchangers - Method of measurement and evaluation of thermal performances of

wet cooling towers
Wärmeaustauscher - Verfahren zur Messung und Bewertung der wärmetechnischen
Leistungskenndaten von Nasskühltürmen
Echangeurs de chaleur - Méthode de mesure et évaluation des performances
thermiques des aéroréfrigérants humides
Ta slovenski standard je istoveten z: EN 14705:2005
ICS:
27.060.30 Grelniki vode in prenosniki Boilers and heat exchangers
toplote
27.200 Hladilna tehnologija Refrigerating technology
SIST EN 14705:2005 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 14705:2005
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SIST EN 14705:2005
EUROPEAN STANDARD
EN 14705
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2005
ICS 27.060.30; 27.200
English version
Heat exchangers - Method of measurement and evaluation of
thermal performances of wet cooling towers

Echangeurs de chaleur - Méthode de mesure et évaluation Wärmeaustauscher - Verfahren zur Messung und

des performances thermiques des aéroréfrigérants Bewertung der wärmetechnischen Leistungskenndaten von

humides Nasskühltürmen
This European Standard was approved by CEN on 24 March 2005.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European

Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national

standards may be obtained on application to the Central Secretariat or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official

versions.

CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,

Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,

Slovenia, 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

© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 14705:2005: E

worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST EN 14705:2005
EN 14705:2005 (E)
Contents page

Foreword ..........................................................................................................................................................3

1 Scope ...................................................................................................................................................4

2 Normative references .........................................................................................................................4

3 Terms, definitions and symbols ........................................................................................................5

3.1 Terms and definitions.........................................................................................................................5

3.2 Symbols...............................................................................................................................................7

4 Performance tests – General............................................................................................................11

5 Guarantee ..........................................................................................................................................12

5.1 General ..............................................................................................................................................12

5.2 Guarantee documents ......................................................................................................................12

5.3 Validity conditions for measurements ............................................................................................13

6 Test procedure ..................................................................................................................................15

6.1 Test parameters ................................................................................................................................15

6.2 Quantities to be measured ...............................................................................................................15

6.3 Quantities to be determined.............................................................................................................17

6.4 Measurements and calculation of the mean quantities .................................................................17

6.5 Arrangement of measuring devices ................................................................................................24

6.6 Measuring apparatus ........................................................................................................................29

7 Conducting the performance tests..................................................................................................30

7.1 Definition of a test.............................................................................................................................30

7.2 Duration of the test ...........................................................................................................................31

8 Calculation methods.........................................................................................................................34

8.1 General ..............................................................................................................................................34

8.2 Methods .............................................................................................................................................34

9 Evaluation of thermal performances ...............................................................................................38

9.1 General ..............................................................................................................................................38

9.2 Basic thermal performance test evaluation ....................................................................................38

9.3 Extended thermal performance test evaluation..............................................................................39

10 Test tolerance....................................................................................................................................47

10.1 General ..............................................................................................................................................47

10.2 Error created by non-measurable systematic deviations of operating parameters.....................47

Annex A (informative) Performance curves................................................................................................50

Annex B (normative) Requirements concerning the measuring apparatus used for the tests ..............54

Annex C (normative) Calculation of the evaporated water flow rate ........................................................56

Annex D (normative) Reminders on error calculations .............................................................................59

Annex E (normative) Cold water temperature correction for heat added by pump.................................61

Bibliography...................................................................................................................................................62

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SIST EN 14705:2005
EN 14705:2005 (E)
Foreword

This European Standard (EN 14705:2005) has been prepared by Technical Committee CEN/TC 110 “Heat

exchangers”, the secretariat of which is held by BSI.

This European Standard shall be given the status of a national standard, either by publication of an identical

text or by endorsement, at the latest by December 2005, and conflicting national standards shall be withdrawn

at the latest by December 2005.
This document includes a Bibliography.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following

countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic,

Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland

and United Kingdom.
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SIST EN 14705:2005
EN 14705:2005 (E)
1 Scope

This European Standard specifies requirements, test methods and acceptance tests for thermal performances

pumping head verification of wet cooling towers and plume abatement for wet/dry cooling towers.

This European Standard is applicable to natural draught wet cooling towers (see in 3.1.2.2) fan assisted

natural draught cooling tower (see 3.1.2.3), wet/dry cooling towers (see 3.1.2.4) and "Mechanical draught

cooling towers", except series ones.

It specifies the test methods, the apparatus required, the limitation of errors and the method for results

examination.

The acceptance testing covers the verification of the thermal performance data and pumping head of the

cooling tower as specified in the contract between the supplier and the purchaser. If these tests are required

then this should be recognized at the time of the contract, as additional fittings, and preparations for the test

may be required.

Deviations from the rules laid down below as well as additions need special agreement between purchaser

and supplier and should be documented.

This standard does not apply to mechanical draught series wet cooling towers which are dealt with in

EN 13741.

NOTE Terms like "design", "values", "guarantee" and "acceptance" used in this standard should be understood in a

technical but not in a legal or commercial sense.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

EN 306, Heat exchangers - Methods of measuring the parameters necessary for establishing the performance

EN 872, Water quality - Determination of suspended solids - Method by filtration through glass fibre filters

EN 60751, Industrial platinum resistance thermometer sensors (IEC 60751:1983 + A1:1986)

EN ISO 5167-1, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-

section conduits running full - Part 1: General principles and requirements (ISO 5167-1:2003)

ISO 1438-1, Water flow measurement in open channels using weirs and Venturi flumes - Part 1: Thin-plate

weirs

ISO 2975-3, Measurement of water flow in closed conduits - Tracer methods - Part 3: Constant rate injection

method using radioactive tracers

ISO/TR 3313, Measurement of fluid flow in closed conduits - Guidelines on the effects of flow pulsations on

flow-measurement instruments
---------------------- Page: 6 ----------------------
SIST EN 14705:2005
EN 14705:2005 (E)
3 Terms, definitions and symbols
3.1 Terms and definitions

For the purposes of this European Standard, the following terms and definitions apply.

3.1.1
cooling tower
apparatus in which water is cooled down by heat exchange with ambient air
3.1.2
wet cooling tower

cooling tower in which the heat exchange between the water and the air is achieved by a direct contact

3.1.2.1
mechanical draught wet cooling tower
wet cooling tower where the air circulation is produced by a fan
3.1.2.1.1
series type mechanical draught wet cooling tower

mechanical draught wet cooling tower, the design of which is fixed and described in the manufacturer's

catalogue and for which the performance data are available, which allows tests evaluation over the defined

range of operating conditions
3.1.2.1.2
non series type mechanical draught wet cooling tower

mechanical draught wet cooling tower, the design of which is project dependent and for which the

performance data and test evaluation at specific operating conditions may be subject to agreement

3.1.2.2
natural draught cooling tower

wet cooling tower where the air circulation is produced only by a density difference between the cold air

outside the cooling tower and the hot air inside
3.1.2.3
fan assisted natural draught cooling tower
natural draught cooling tower with the addition of fan to boost the draught
3.1.2.4
wet/dry cooling tower (reduced plume cooling tower)

cooling tower comprising two parts. In the first part, the heat exchange between the water and the air is

achieved by direct contact and through a tight wall in the second part
3.1.2.4.1
reduced plume wet/dry cooling tower
wet/dry cooling tower designed for plume abatement
3.1.2.4.2
water conservation wet/dry cooling tower
wet/dry cooling tower designed for water conservation
3.1.3
air flow

total quantity of air, including associated water vapour flowing through the tower

3.1.3.1
counterflow
where air and water flows are in opposite direction in the filling
---------------------- Page: 7 ----------------------
SIST EN 14705:2005
EN 14705:2005 (E)
3.1.3.2
cross flow
where air flows perpendicular to the water in the filling
3.1.4
ambient wet (dry) bulb temperature

wet (dry) bulb temperature of air measured windward of the tower and free from the influence of the tower

3.1.5
approach
difference between recooled water temperature and inlet air wet bulb temperature
3.1.6
inlet water flow
quantity of hot water flowing into the tower
3.1.7
cold water basin

device underlying the tower to receive the recooled water from the tower and direct its flow to the suction line

or sump
3.1.8
cooling range
difference between the hot water temperature and the recooled water temperature

NOTE The term "range" is also applied to this definition, but is regarded as a non-preferred term.

3.1.9
drift loss

water lost from the tower as liquid droplets with the same chemical characteristics as the circulating water,

entrained in the outlet air
3.1.10
heat load
rate of heat to be removed from the water within the tower
3.1.11
hot water temperature
temperature of inlet water
3.1.12
inlet air wet (dry) bulb temperatures

average wet (dry) bulb temperatures of the inlet air; including any recirculation effect

3.1.13
make-up

water added to the circulating water system to compensate for water loss from the system by evaporation, drift,

purge and leakage
3.1.14
purge (blow down)

water discharged from the system to control concentration of salts or other impurities in the circulating water

3.1.15
recooled water temperature

average temperature of the water at the cold water basin discharge excluding the effect of any make-up

entering the basin or at the exhaust of the exchanger for wet/dry cooling tower
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SIST EN 14705:2005
EN 14705:2005 (E)
3.1.16
recirculation
portion of the outlet air that re-enters the tower
3.1.17
interference
intake of outlet air of adjacent cooling towers
3.1.18
tower pumping head

total head of water required at the inlet to the tower, to deliver the inlet water through the distribution system

3.1.19
surfacic flow

inlet water flow expressed in quantity per unit of plan packing area of the tower

3.1.20
wet (dry) bulb temperature

the temperature indicated by an adequately ventilated and wetted (non-wetted) thermometer in the shade and

(where applicable) protected from any radiation effect
3.1.21
atmospheric gradient

air dry bulb temperature variation with altitude expressed in degree Celsius per 100 m

3.2 Symbols
For the purposes of this European Standard, the symbols of Table 1 shall apply.
---------------------- Page: 9 ----------------------
SIST EN 14705:2005
EN 14705:2005 (E)
Table 1
Symbols Designated parameters Units
A Transfer surface per unit of volume m
a Angle of an elbow degree
ap Approach (t - t ) K
c w
C Heat coefficient -
-2 -1
CEV Evaporation coefficient related to the difference in water content
kg⋅m ⋅s
C Load loss coefficient -
-2 -1
CFV Evaporation coefficient related to the difference in water content
kg⋅m ⋅s
C Specific water consumption
kg⋅J
-1 -1
c Mass heat capacity of the air at constant pressure
J⋅kg ⋅K
-1 -1
Mass heat capacity of the water J⋅kg ⋅K
-1 -1
c Mass heat capacity of the vapour at constant pressure
J⋅kg ⋅K
D Direction of the reference wind in relation to the north degree
d Hydraulic diameter m
F Fan motor power kW
F Guaranteed fan motor power kW
g Gravity acceleration m⋅s
H Draught height m
h Mass enthalpy of the air
J⋅kg
1 Mass enthalpy of the air at the air inlet calculated from p , t and ϕ J⋅kg
a s
h Mass enthalpy of the saturated hot air at the air outlet downstream
2 J⋅kg
from the drift eliminators
h Mass enthalpy of the saturated moist air at the water temperature
J⋅kg
h , h Mass enthalpy of the saturated moist air at the water temperature
J⋅kg
s1 s2
with 1 = inlet, 2 = outlet
k Number of tests
Merkel number -
KAV
L Water vaporization latent heat at temperature t
vt J⋅kg
3 -1
m Circulating water volume flow rate at the cooling tower inlet
m ⋅s
3 -1
m Calculated blow-down water volume flow rate
m ⋅s
3 -1
m Measured blow-down water volume flow rate
m ⋅s
(to be continued)
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SIST EN 14705:2005
EN 14705:2005 (E)
Table 1 (continued)
Symbols Designated parameters Units
3 -1
m Evaporated water volume flow rate
m ⋅s
3 -1
Make-up water volume flow rate m ⋅s
m Number of a wind velocity class
3 -1
m Volume flow rate of water entrained by drift losses m ⋅s
N Characteristic index of nominal pattern
n Constant exponent of the exchange law
n 0
Number of tests per m class
n m
Number of recorded values for each test
P Thermal load kW
p Atmospheric pressure Pa
Saturating vapour pressure Pa
p Static pressure Pa
p Partial pressure of vapour in the air Pa
q Dry air mass flow rate
kg⋅s
mas
Circulating water mass flow rate at cooling tower inlet kg⋅s
Recooled water recuperation system leaking water volume flow rate 3
m ⋅s
q Local volume flow rate 3
m ⋅s
3 -1
q Volume flow rate of circulating pumps
VPC m ⋅s
S Flow section corresponding to the measurement point i m
S , S Cross sections perpendicular to the pressure taps on the water m
1 2
circuit
S Exchange body front surface m
T Test starting time h, min
t Temperature °C
t Dry temperature of the ambient air °C
t Blow-down water temperature °C
t Mean temperature of the recooled water immediately above the °C
plane of the cold water basin (rain water cooling tower) or
immediately above the plane of the water in the troughs (water
recuperator cooling tower)
t Mean temperature of the recooled water for the test i °C
c,i
(to be continued)
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SIST EN 14705:2005
EN 14705:2005 (E)
Table 1 (continued)
Symbols Designated parameters Units
T Guaranteed mean temperature of the recooled water for the test i °C
cG,i
t Mean temperature of the cold water at the cooling tower outlet °C
(mixture of cooled water and make-up water)
t Mean temperature of the hot water in the cooling tower inlet °C
t' , t'' Mean temperatures of the hot water in the inflows °C
h h
t Local temperature °C
t Make-up water temperature °C
t Wet bulb temperature at the air inlet °C
t Wet bulb temperature of ambient air °C
t Dry bulb mean temperature at the air inlet °C
T Basin cold water renewal time min
V Total volume of the exchange body m
Mean frontal velocity of the air at the exchange body inlet m⋅s
Local flow velocity m⋅s
v , v
Water velocities perpendicular to the measurement sections m⋅s
1 2
v Reference wind velocity 10 m above ground level m⋅s
W10
Difference in level between the spray hole nozzle outlet and the m
water plane of the cold water basin
γ Coefficient of correction in the Merkel integral -
τ Student coefficient -
xϕ Absolute humidity of the ambient air
kg water
kg dryair
Absolute humidity of the air at air inlet
kg water
kg dryair
xϕ Absolute humidity of the air at cooling tower outlet
kg water
kg dryair
ϕ Relative humidity of the ambient air %
ϕ Relative humidity of the ambient air at air inlet %
ϕ Relative humidity of the ambient air at cooling tower outlet %
Φ Fan power influence factor K/%
ρ Density of the air kg⋅m
(to be continued)
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SIST EN 14705:2005
EN 14705:2005 (E)
Table 1 (concluded)
Symbols Designated parameters Units

ρ (t) Density of the water of the circulating water circuit at temperature t kg⋅m

ρ Density of the air entering the cooling tower kg⋅m
ρ Density of the hot air at the outlet, downstream from the drift kg⋅m
eliminators
σ Standard deviation of the wind velocity at 10 m (V ) during the m⋅s
w10
test
α Weighting coefficient of the class r reference wind velocity
∆p Circulating water pressure loss Pa
∆p Differential static pressure measured on the water circuit between Pa
sections s and s
1 2
∆t Weighted difference on the recooled water temperature K
z Difference in temperature on the water between the cooling tower K
inlet and outlet (Cooling range)
t - t Difference to the guarantee on the recooled water temperature for a K
cK cG
test
∆t Recooled water temperature difference for the class r reference K
wind velocity
θ Instantaneous temperature of the recooled water °C
λ Universal load loss coefficient for water conduits
h − h
2 1
Coefficient µ =
h − h
s1 1
h − h
s1 s2
Coefficient ν =
h − h
2 1
4 Performance tests – General

The performance tests forming the subject of this standard shall be carried out, unless otherwise specified, in

the contract at least after three months of continuous operation and definitely after commissioning. It concerns

the following performances:
 pumping head - flow rates and pressure loss (see 6.4.5);

 thermal performances - determination of the recooled water temperature at measured conditions

(see 6.4.4.4);
 emission performances (drift losses);
 plume characteristics at the outlet (only for wet/dry cooling towers).

The method described in this standard for the verification of thermal performances apply to all cooling towers

defined in the scope.
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SIST EN 14705:2005
EN 14705:2005 (E)
5 Guarantee
5.1 General

Prior to the contract the supplier shall have submitted performance documents available setting out the

guaranteed properties as a function of the admissible influence parameters in order to document the

guaranteed properties of the cooling tower supplied.
5.2 Guarantee documents
The supplier of a cooling tower shall guarantee:
a) the cooling tower pumping head;
b) the mean recooled water temperature (t ) as a function of;
. dry bulb temperature, t
. relative humidity, ϕ or wet bulb temperature t
. cooling range (z), or hot water temperature t
. water flow rate (m or q )
and where applicable as a function of other parameters such as
. fan power consumption, F
. interference factor
. recirculation factor
. ambient (atmospheric) pressure, P
. atmospheric (vertical) temperature gradient, G

However for natural draft cooling towers extended tests checking wind effect at site on tower performance

may be performed subject to the contract. If so, the supplier shall guarantee the average temperature of the

recooled water t as function of
. wind velocity, V
. wind direction, D

The guarantee documents can be in the form of spread sheets, curves, analytical expressions, computer

program etc.

Performance curves should be presented in the format shown in Annex A, however other formats or

appropriate formulas as acceptable provided they give the same information.

Curves shall have reading accuracy of 0,1 K. The area in which acceptance tests are permitted shall be

indicated as per 5.3.2.
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SIST EN 14705:2005
EN 14705:2005 (E)

If correction curves are provided for the effect of other parameters (e.g. wind speed, atmospheric gradient,

plume abatement, atmospheric pressure, interference factor, recirculation factor), they shall be used subject to

contract.

c) For hybrid cooling towers the outlet air status has to be predicted for all specified boundary conditions:

. dry bulb temperature, t
. relative humidity, ϕ or wet bulb temperature t
Other parameters may be guaranteed subject to the contract.
5.3 Validity conditions for measurements
5.3.1 General

The measurement results obtained during the course of the tests shall only be taken into account if the

requirements mentioned below are met.
5.3.2 Acceptable operating conditions
a) During the tests:

The values of the following quantities may differ from the design values of the percentages shown below:

 circulating water volume flow rate m: ± 10 % of the design volume flow rate m ,

 cooling range t - t : ± 20 % of the design temperature rise t - t ,
h c h cN
 thermal load P: ± 20 % of the design thermal load P ,

b) During the hour finishing at the end of the measuring period, the following gradient conditions shall be

fulfilled:
 water flow rate ≤ ± 2 % per hour;
 heat load ≤ ± 5 % per hour;
 ambient wet bulb temperature ≤ 1 K/hour.
5.3.3 Water conditions

The quality of the circulating water flow as well as that of the make-up water shall be within the range of the

specification defined in the contract.

In particular dissolved and suspended solids, oil and organic components concentration shall be checked.

The total dissolved solid shall not exceed the greater of the following:
a) 5000 ppm;
b) 1,1 time the design concentration.

The circulating water shall contain not more than 10 ppm of oil, tar or fatty substances.

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SIST EN 14705:2005
EN 14705:2005 (E)
For measuring methods, see EN 872 for solids.
5.3.4 Other conditions
5.3.4.1 Equipment-related requirements

The whole cooling tower shall be in proper operating condition. In particular, the water distribution system, the

drift eliminators and the exchange body shall not contain a quantity of foreign bodies likely to interfere with the

normal flow of the water and air.

In order to establish that the cooling tower operates well, it shall be visited by both parts of the contract

together before testing.
5.3.4.2 Climatic conditions-related requirements

The climatic conditions shall be within the normal operating ranges, these being defined by agreement

between the customer and the manufacturer.

If the wind conditions are agreed by contract, the average wind velocity and peak wind velocity shall lie within

the design limits specified in the contract. In that case, wind effect shall be provided by the cooling tower

manufacturer, as mentioned in 9.3.2 or as shown in Annex A.

If no limits are defined in the contract, the average wind velocity shall not exceed 3 m.s . The wind stability

condition shall be that the standard deviation σ of the wind speed (m.s ) of the reference wind shall not

exceed a limit value during the half hour (30 min) preceding and during the measurements, whatever the

duration of the test period may be.
σ < 0,5 + 0,2 V for all cases
mean

Furthermore, during the test, the atmospheric conditions shall comply with the following conditions:

 no rain, snow or hail;

 no fog, the difference between the dry temperature t and the wet temperature t shall be greater than

a w
0,1 K;

 in the event of high obstacles (other cooling tower, machine room, ...) being in the vicinity of the cooling

tower, only those tests for which the wind does not come from the direction of these obstacles are taken

into account.

 the wet bulb temperature of the ambient air averaged at the air inlet t shall be greater than or equal to

2 °C:
t ≥ 2 °C

Mainly for natural draught cooling towers it is essential to control the atmospheric gradient during the test

since it affects the inlet air density which is part of the driving force that makes the cooling tower perform. If

the atmospheric gradient is agreed by contract, the average gradient measured up to twice the cooling tower

height shall be in the range of specification. If the atmospheric gradient is not defined in the contract the

average gradient shall be negative and over -1 K per 100 m.

An indicator of the gradient may be the absolute difference between the dry mean temperature in the cooling

tower air inlet t and the dry temperature of the ambient air t . Between -1 K and 0 K corresponds in most

s a
cases to an atmospheric gradient between + 0 K per 10
...

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