catalogo tecnico cobra pex ing
TRANSCRIPT
COBRAPEXhigh density cross-linked
polyethylene tube
Technical and practical manual for COBRAPEX tubes in heating and sanitary systems
1
This technical manual, which is addressedto the professionals who are working inhydrothermosanitary field, results from thedevelopment strategy which has beenadopted in the last few years. TIEMMERaccorderie firm has been investing itscapital in high technology and humanresources since it was incorporated inLumezzane Gnutti Group. Thanks tothese actions, the traditional range ofproducts was renewed, including a widerrange of articles in order to comply withcustomers’ requests and meet theirneeds.
The new TIEMME general catalogue, notonly includes traditional pipe fittings, butalso the following new products which arealready available on the market:
• Patented simple and coplanar brass manifolds
• Ball valves• COBRA-PEX high density reticulated
polyethylene tubes • AL-COBRAPEX aluminium core
multilayer tubes • Multilayer tube pipe fittings which are
available both in the traditional mechanical compression version and in pressing version.
• COBRA-THERM random polypropylene welding tubes and pipe fittings for the construction of water systems and sanitary facilities.
As it can be seen, TIEMME firm made agreat effort, as it not only offers singleproducts, but also a wide range of productswhich are similar and compatible one withthe other, forming a “system”.This manual, just like those which arerelated to other firm products, aims atemphasising this new concept of “system”,also providing all information which arenecessary to easily and correctly usevarious components.
Besides considering above-mentionedpoints, it is necessary to remind all stepswhich were taken to guarantee firm andproduct certification. Contrary to recenttrend and custom, our firm first preferred toguarantee product certification according tospecific rules (if they are present), withoutforgetting firm quality system certification,which will be issued soon.
According to our firm, it is necessary toguarantee product certification in order tomeet customer’s needs, as the customerhimself will have to issue a ConformityDeclaration with system rules, thus assumingprecise responsibility.
According to various and reliable articleswhich were published in the magazineswhich are specialised in this field, single firmcertification does not prove and guaranteethat the products which have been createdand manufactured according to a certainpurpose are correctly used.
Therefore, it is necessary to supplementfirm quality system certification with productcertification and not vice versa. This isexactly what TIEMME firm did, knowing thatit was possible to guarantee firm qualitysystem certification having recentlyinvested its capital in high technologies andhuman resources.
Moreover, after having invested its capital inhigh technologies and human resources, ourfirm also intends to concentrate its attention oncommunication and information field in order togive its commercial partners and installers alladvice and technical information which arenecessary to correctly use our products.
To meet these needs, TIEMME firm showsa series of technical and practical manualswhich are necessary to use our productsaccording to the system concept, alsomentioning dimensioning methods.
Wishing You a good and profitable work andhoping that You will appreciate this usefulmanual, we remain with our best regards.
TIEMME Raccorderie S.p.a.
The Chairman
1. Introduction
2
As it was previously mentioned in theintroduction, these manuals aim at betterexplaining how to use our product systems.In order to reach this target, systems mustbe divided into different groups and afterhaving divided them into the two traditionalclasses of water systems and sanitaryfacilities and air-conditioning units, it isnecessary to subdivide them into othergroups. These groups must be split upstarting from the system which is included inthe group in question. For example, air conditioning units includemanifold, single-tube, radiant panelsystems and so on. Considering TIEMME system-productpurposes, this manual only deals with andanalyses those systems which are compatiblewith them. It will be possible to provide useful informationwhich are necessary to use various systemproducts and guarantee system dimensioning,according to existing specific rules. In case of those systems whose dimensioningis calculated following complex procedures,it will only be possible to give generalinstructions, referring the reader to thespecific regulations on the subject. This manual thoroughly examines traditionalsupply systems (with series-connectedsanitary facilities) – picture 1 – and manifoldsupply systems (with parallelly-connectedsanitary facilities) – picture 2.As regards air conditioning units, consideringabove-mentioned limitations, it will bepossible to provide all information which arenecessary to use of COBRA-PEX tubesand pipe fittings for the construction ofmanifold, single-tube and radiant panelsystems – Picture 3.Considering that wall boiler independentsystems are commonly used and centralplant horizontal secondary supply systemsare similar to those of independentsystems, it will be possible to make somecalculation examples related to these kindsof heating plants, integrating them withthose which are contained in the followingparagraphs. The manual includes an appendix concerningall specifications which are commonly used,hoping that they can be rapidly and easilyconsulted by technicians and installers.
2. Generalities
Picture 1
Picture 2
Picture 3
3
High density reticulated polyethylene plasticCOBRA-PEX pipes are manufactured byusing high density and high molecularweight PE raw material, and this meansthat d value is ≥ 0,95 g/cm3.Polyethylene is a plastic material whichresults from ethylene polymerisation.Ethylene is a petroleum gas-derivativewhich is made up of one carbon atom (C)and two hydrogen atoms (H). Polymerisation process determines theformation of long molecular chains – Picture 4.
Carbon atom is black-coloured and the twohydrogen atoms are red-coloured. By carefully checking polymerisation process,it is possible to achieve molecular chainswith different lengths and a raw materialwith varying density.In the last decades, it has been experiencedthat it is necessary to use high molecularweight polyethylene in order to achieve anhigh mechanical and chemical resistance. PE-LD low density and PE-MD mediumdensity polyethylene pipes are only used toachieve very low pressure and temperaturevalues. In order to guarantee long-lasting workingconditions at temperatures which are higherthan 40 °C, it is necessary to usehigh-density material which is subject toa molecular cross-linking process in orderto improve its chemical and physicalcharacteristics. Cross-linking process consists in creatingtransverse molecular bonds among thevarious independent chains in order toachieve a three-dimensional reticulatedstructure – Picture 5. Cross-linking bonds which are createdamong the various molecular chains aremarked by blue lines and cross-linkingpercentage varies according to the kind ofproduction process.
However, in order to guarantee the goodcharacteristics which are necessary for pipeproduction, cross-linking percentage mustbe equal to 65÷75%. PE-X tube lowest cross-linking percentageis fixed and imposed by the followingregulations: DIN, AENOR, UNI, etc. PE-X tubes are well-known; without providingfurther information, it is possible to identifythe kind of tubes, their common applications,highest temperature and pressure values,etc. X letter comes from “X-linked” or “cross-linked”English expression which indicates thecross-link which is created among thedifferent molecular chains and which is dueto reticulation process. Each country uses different expressions,such as for example, Italy and France usePE-R expression, which stands for reticulatedpolyethylene, while German countries useVPE expression. All COBRA-PEX pipe physical characteristicsare shown in Table I. The parameters indicated below which arethoroughly analysed and the relativeregulations which are followed during testmethod certify that COBRA-PEX tubes can
be used in hydrothermosanitary field.Without checking if plastic tube systems arecheaper than metal pipe systems and afterhaving thoroughly discussed about the widediffusion of plastic tubes instead of metalones, it is necessary to analyse the followingtechnical and practical characteristics ofCOBRA-PEX reticulated polyethylenetubes which gave them successful technicaland economic results:• Lower pressure loss thanks to their
smooth inner coating.• Very good mechanical and functional
characteristics (duration, pressure,temperature, expansions, applications, etc.).
• Lightness during transport, handling andlaying.
• Non-toxicity; they can be used to carryfoodstuffs.
• Very good dielectric properties.• Low thermal conductivity level.• Soundproofing properties; plastic material
damps sound-wave propagation.• Very good behaviour in the presence of
deposits and abrasion phenomena.• They can be easily installed.• Thermal storage.
3. COBRA-PEX tubes
PHYSICAL CHARACTERISTICS TEST METHOD TEMP. UNIT VALUE
Specific weight ISO-DIN 1872 - g/cm3 0,943
Breaking load DIN 53455 20 °C Kg/ cm2 200÷260
Breaking strain DIN 53455 20 °C % 350÷450
Coefficient of elasticity DIN 53455 0 °C Kg/ cm2 14.000
DIN 53455 20 °C Kg/ cm2 6.000
Shock resistance DIN 53453 -150°C - It doesn’t break
DIN 53453 20 °C - It doesn’t break
Yield point DIN 53455 22 °C Kg/ cm2 170÷230
Cross-linking percentage DIN 16892 20 °C % > 65
Inner pressure drag DIN 16892 20 °C MPa > 12
DIN 16892 95 °C Mpa > 4,4
THERMAL CHARACTERISTICS TEST METHOD TEMP. UNIT VALUE
Application field - - °C -100/+100
Linear expansion coefficient - 120 °C mm/mK 0,15
Softening point (VICAT) ISO 306 - °C 120
Specific heat - - Kcal/Kg°C 0,51
Thermal conductivity - - W/mK 0,38
ELECTRIC CHARACTERISTICS TEST METHOD TEMP. UNIT VALUE
Dielectric constant BS 2782-205A 20 °C 2,2
Volume resistivity BS 2782-202B 20 °C Ohm cm >1·1016
Dielectric rigidity BS 2782-201B 20 °C Kv/mm 20
Table 1
Picture 5
Picture 4
COBRA-PEX TUBE PHYSICAL CHARACTERISTICS
4
CO
BR
A-P
EX T
UB
E M
OD
ELA
ND
SIZ
E TA
BLE
– IS
O 9
002
Cer
t. –
EN 2
9002
– E
R n
°- 1
14/2
/95
Oute
r Ø x
Thi
ckIn
ner Ø
Wei
ght
Wat
er c
onte
ntRo
llsBa
rKi
nd o
fTu
beHi
gh fl
ex.
Shea
thEV
OHW
ater
at 1
0°C
Wat
er a
t 80°
C
[mm
][m
m]
[g/m
][l/
m]
[m]
[m]
pres
sure
colo
urs
Mod
elM
odel
Mod
el[c
][n
][c
][n
]
10 x
18,
030
0,04
7710
0(*)
3,5
(**)
Ser
ies
5 F
ranc
eB
/WN
oYe
sN
o0,
021
1,75
0,01
71,
75
12x1
,19,
837
0,07
5410
0(*)
3,5
(**)
Ser
ies
5 F
ranc
eB
/WN
oYe
sYe
s0,
082
1,72
0,00
671,
72
12x1
,88,
358
0,05
5310
0(*)
3,5
(**)
Ser
ies
3.2
Spa
inB
/WN
oYe
sN
o0,
017
1,75
0,01
41,
75
12x2
,08,
064
0,04
7710
0(*)
3,5
(**)
PN
16
B/W
Yes
Yes
No
0,02
11,
750,
017
1,75
14x2
,010
,00,
0785
100(
*)3,
5 (*
*)P
N 1
0B
/WYe
sYe
sYe
s0,
008
1,72
0,00
651,
72
15x2
,510
,096
0,07
8510
0(*)
3,5
(**)
PN
16
B/W
Yes
Yes
No
0,00
81,
720,
0065
1,72
16x1
,513
,066
0,13
2610
0(*)
3,5
(**)
Ser
ies
5 F
ranc
eB
/WN
oYe
sN
o0,
0027
1,72
0,00
221,
72
16x1
,812
,480
0,12
0710
0(*)
3,5
(**)
Ser
ies
5 S
pain
B/W
No
Yes
No
0,00
311,
750,
0025
1,75
16x2
,012
,088
0,11
3410
0(*)
3,5
(**)
PN
10
B/W
Yes
Yes
Yes
0,00
371,
750,
003
1,75
16x2
,211
,693
0,10
5610
0(*)
3,5
(**)
PN
16
B/W
Yes
Yes
Yes
0,00
621,
700,
0051
1,70
16x2
,311
,499
0,10
2010
0(*)
3,5
(**)
B/W
Yes
Yes
No
0,00
631,
700,
0053
1,70
17x2
,013
,00,
1326
100(
*)3,
5 (*
*)P
N 1
0B
/WN
oN
oYe
s0,
0027
1,72
0,00
221,
72
18x2
,014
,098
0,15
3810
0(*)
3,5
(**)
PN
10
B/W
Yes
Yes
Yes
0,00
191,
750,
0016
1,75
18x2
,513
,011
80,
1326
100(
*)3,
5 (*
*)P
N 1
6B
/WYe
sYe
sN
o0,
0027
1,72
0,00
221,
72
20x1
,916
,210
90,
2060
100(
*)3,
5 (*
*)S
erie
s 5
Spa
inB
/WN
oYe
sN
o0,
001
1,70
0,00
081,
70
20x2
,016
,011
50,
2009
100(
*)3,
5 (*
*)P
N 1
0B
/WYe
sYe
sYe
s0,
0012
1,70
0,00
11,
70
20x2
,814
,415
10,
1628
100(
*)3,
5 (*
*)P
N 1
6B
/WYe
sYe
sYe
s0,
0014
1,77
0,00
111,
77
22x3
,016
,017
50,
2060
100
3,5
(**)
PN
16
B/W
Yes
Yes
No
0,00
121,
700,
001
1,70
25x2
,320
,416
30,
3266
503,
5 (*
*)P
N 1
0B
/WYe
sN
oN
o2
• 10
-41,
7616
• 1
0-51,
76
25x3
,518
,023
70,
2543
503,
5 (*
*)P
N 1
6B
/WYe
sYe
sN
o54
• 1
0-51,
7544
• 1
0-51,
75
28x3
,022
,023
10,
3799
503,
5 (*
*)P
N 1
0B
/WYe
sN
oN
o17
• 1
0-51,
7514
• 1
0-51,
75
32x2
,926
,222
40,
5388
503,
5 (*
*)S
erie
s 5
Spa
inB
/WN
oN
oN
o6
• 10
-51,
765
• 10
-51,
76
32x3
,026
,027
40,
5306
503,
5 (*
*)P
N 1
0B
/WYe
sN
oN
o6,
3 •
10-5
1,76
5,2
• 10
-51,
76
32x4
,423
,236
80,
4225
503,
5 (*
*)P
N 1
6B
/WYe
sN
oN
o16
• 1
0-51,
7513
• 1
0-51,
75
40x3
,732
,642
90,
8342
---
3,5
(**)
PN
10
B/W
Yes
No
No
2 •
10-5
1,77
16 •
10-6
1,77
50x4
,640
,865
01,
3067
---
3,5
(**)
PN
10
B/W
Yes
No
No
6,6
• 10
-61,
785,
4 •
10-6
1,78
63x5
,851
,499
82,
0739
---
3,5
(**)
PN
10
B/W
Yes
No
No
1,9
• 10
-61,
791,
6 •
10-6
1,79
1/2”
Iris
h11
,23
700,
0990
100
3,5
(**)
12 b
arB
/W/C
No
No
No
3/4”
Iris
h16
,68
116
0,21
8550
3,5
(**)
12 b
arB
/W/C
No
No
No
1”
Iris
h21
,93
200
0,37
7750
3,5
(**)
12 b
arB
/W/C
No
No
No
(*) –
Fro
m 1
20 to
200
met
re lo
ng ro
lls a
re a
vaila
ble
upon
dem
and.
(**)
– 6
met
re lo
ng b
ars
are
avai
labl
e up
on d
eman
d.
Ava
ilabl
e co
lour
s: B
= B
lack
– W
= W
hite
– C
= C
oppe
r ➜R
ame
E
VO
H =
Ant
i-oxy
gen
barr
ier
Ta
ble
II
5
4.1. – Pressure losses COBRA-PEX high density reticulatedpolyethylene pipes are characterised by a verysmooth inner coating whose roughnessvalue is lower than that of metal pipes. Thanks to this characteristic, extrudedworkable material avoids pore and crackformation.As it will be seen in the following paragraphs,thanks to this long-lasting characteristic,COBRA-PEX tubes avoid the formation ofdeposits which inevitably alter pipe innersliding surface.The diagram of Picture 6 on the right sideof the page shows the curves related to thetubes which are used for the constructionof thermal systems at a water temperatureof 80°C.The diagram is located in this position onlyfor convenience; large-scale calculation chartsand nomograms are shown at the end ofthe catalogue to be easily and immediatelyconsulted. By using this diagram, it is possible todetermine pipe calculation parameters,such as [R] unit pressure loss value and [v]speed value related to [Q] flow. Consequently, considering [L] pipe lengthwhich is indicated in metres or equivalentmetres, it is very easy to calculate totalpressure loss value of the system length inquestion.The paragraph 4.2.2. shows how it ispossible to define a straight “equivalent”pipe length related to every local pressureloss point. Considering the diagram which is shownin Picture 6 which, as it was previouslysaid, refers to a fluid temperature of 80°C,at different working temperatures, [R]value must be updated according to [fc]correction factor which is shown in thediagram of Picture 7. For example, if a system supplies a water flowwhich is equal to 300 l/h at a temperatureof 45°C, as in case of radiant panelsystems, according to the diagram which isshown in picture 6, considering, for example,Ø 20x2,0 tube flow, it results that [R] valueis equal to 17,5 mm of c.a./m and flowspeed is equal to approximately 0,46 m/s. But, as real working temperature is of 45°C,[R] value must be recalculated according tothe data which are shown in diagram 7 andwhich correspond with a correction factorwhich is equal to approximately 0,875.As real working temperature value is lowerthan that which is indicated in the calculationdiagram of Picture 6, [R] value must bedivided by [fc] correction factor, thusachieving the following expression:
R = 17,5/0,875 = 20 mm of c.a./m
4.1.1. Local pressure lossesBesides continuous pressure losses whichare d0ue to the resistance caused by thefriction which is exerted along pipe walls, itis necessary to mention local pressurelosses which are caused by the presenceof nodes, branches, pipe fittings, etc. Any jet disturbance causes a local pressureloss whose extent depends on the kind andconsequence of the disturbance. The following methods are commonly usedto calculate local pressure losses: thedirect method and equivalent metremethod. The direct method is based on the specificcalculation of each pressure gradient whichis due to fluid flow stoppage.According to the equivalent metre method,on the contrary, each obstacle must bereplaced by a fictitious system length whichdetermines the same pressure loss.
4. Specifications
PRESSURE LOSS DIAGRAM – WATER AT A TEMPERATURE OF 80°C
R [mm of c.a./m]
Flow
[l/h
]
Correction factor [f/c]
Fluid temperature [°C]
Picture 7
Cor
rect
ion
fact
or [f
/c]
Picture 6
6
4.1.2. Direct method[H] local pressure loss can be calculatedthanks to the following expression:
H = Σζ • v2 • γ / 2g [1]
and:ζζ indicates local drag coefficient v stands for fluid speedγγ indicates fluid specific weight [Kg/m3]g stands for gravity acceleration [m/s2][ζ] values related to any kind of pipe fittingare indicated in table III, while, thanks to thenomogram which is shown in picture 8, it ispossible to rapidly calculate [H] valueaccording to [v] speed and [ζ] drag coefficientvalue.[ζ] local drag coefficient value depends onthe number of Reynolds [Re], e/D relativeroughness value and pipe geometricparameters, such as divergence or convergenceangle, diameter ratio in case of sectionreduction or expansion, etc.According to some researchers, diagramsrelated to [ζ] local drag coefficient value showwater flow speed values which range from0,6 to 3 m/s and which are nearly unchanged. Considering speed values which are commonlyused in this field, as [ζ] value is slightlydifferent from [Re] value, [ζ] value isindependent of [Re] value.[z] values which are shown in Table III weredetermined according to a water flow speedvalue which is equal to 0,7 m/s.
4.1.3. Equivalent metre methodThanks to equivalent metre method, it ispossible to calculate local pressure lossesconsidering system [Le] fictitious lengthvalues which are shown in table III.These lengths are added to real systemdevelopment indicated in metres, thusachieving a total fictitious length which willbe used to calculate continuous pressurelosses thanks to traditional method.This calculation can be easily and rapidlymade. As it will be seen in the following paragraph,as [λ] and [ζ] values have a similar speed,[Le] values are considered as independentof [v] values, considering the values whichrange from 0,2 to approximately 2,5 m/s.
4.1.4. Comparison of the two methodsConsidering that the two methods areequivalent, [Le] equivalent length could becalculated as follows:
R = ζ • (v2/2g) = λ • (v2/2g) • (Le/D)
thus achieving the following equation:
Le = (ζ/λ) • D
According to this relation, [Le] valuedepends on [λ] friction coefficient, thereforelocal pressure losses are not only due tospeed as it is stated by direct method.
Recent experiments seem to confirm thistheory, but even if [ζ] local drag coefficientcan be affected by Reynolds number, itsvariation not always corresponds with thatof [l] friction coefficient.
4.1.5. [c] and [n] valuesThe Table II on page 4, besides including allCOBRA-PEX tube dimensional and technicaldata, also shows [c] and [n] values in thelast columns on the right side of the table. These data are necessary to calculate PEXtube continuous pressure losses, withoutusing common diagrams. The curves which are shown in the diagramof page 5 and which determine tube pressurelosses are straight lines which are drawnalong a series of points. [c] and [n] values, which were determinedaccording to a linear regression by a seriesof points which resulted from tests whichwere conducted on COBRA-PEX tubes, arethe parameters which are necessary to exactlycalculate tube continuous unit pressure lossvalue, considering the possibility of makinga max. error of ≤ 1%, thanks to the following[2] mathematical expression:
R [mm of c.a./m] = Qn • c [2]
and Q value stands for water flow indicated in l/h
It is possible to calculate system length totalpressure loss value according to equivalentmetre method related to local pressurelosses, thanks to the following equation:
∆p [mm of c.a.]= Qn • c • meq [3]
In some cases, besides calculating pressureloss value, it is also necessary to determineother variables, such as, for example,speed or, considering tube and pressureloss value, it is necessary to calculate itsconsequent flow. Considering ∆p value indicated in mm ofc.a., the tube and [n] and [c] values, it ispossible to calculate [Q] value indicated inl/h according to [3] equation:
n
Q = √ ∆p / (c • meq) [4]
Considering the flow value, COBRA-PEXtube and its [di] inner diameter indicatedin metres, it is possible to calculate speed orcheck its value without exceeding prescribedlimits, thanks to the following equations:
v = Q [m3/h] / (2827 • di2) [5]v = Q [l/h] / (282,7 • 104 • di2) [6]v = Q [l/s] / (785,4 • di2) [7]
Pres
sure
loss
[m o
f c.a
.]
Drag coefficient [ζζ]Picture 8
Speed [m/s]
7
Similarly, after having determined [v]speed value indicated in m/s, it is possibleto easily and rapidly calculate correspondingwater flow as follows:
Q [m3/h] = v • 2827 • di2 [8]Q [l/h] = v • 282,7 • 104 • di2 [9]Q [l/s] = v • 785,4 • di2 [10]
As it can be noticed, thanks to [2] and [9]expression, which is characterised by anhomogeneous measurement unit,considering [c] and [n] values, it is possibleto calculate all other variables. By using these simple mathematicalexpressions, for example, it is possible tocalculate system balancing check
procedures, determine sanitary facilitysupply system water flow speed orcalculation formula and parameterswhich are necessary for the creation ofautomatic programs for hot and coldwater supply system dimensioning.
Local resistance calculation table - [ζζ] and [eq. m] values
CO
BR
A-P
EX tu
be d
iam
eter
s
[ζζ] 2,0 1,8 1,6 3,0 4,0 0,5 2,0 1,8
Table III
0,50 0,45 0,40 0,80 1,20 0,20 0,50 0,45
∅ 12x1,1∅ 14x2,0 0,60 0,55 0,50 1,20 1,50 0,25 0,60 0,55∅ 15x2,5
∅∅ 20x1,9∅∅ 20x2,0 1,30 1,15 1,00 1,90 2,70 0,50 1,30 1,15∅∅ 22x3,0
∅∅ 25x3,5 1,40 1,30 1,15 2,20 3,50 0,60 1,40 1,30
∅∅ 25x2,3 1,80 1,60 1,40 2,50 4,30 0,65 1,80 1,60
∅∅ 28x3,0 2,00 1,80 1,60 3,20 4,80 0,70 2,00 1,80
∅∅ 32x4,4 2,30 2,00 1,80 3,80 5,80 0,75 2,30 2,00
0,70 0,65 0,55 1,30 1,70 0,30 0,70 0,65
0,80 0,70 0,60 1,40 1,80 0,35 0,80 0,70
0,90 0,85 0,70 1,50 1,90 0,40 0,90 0,85
2,70 2,30 2,00 4,20 6,30 0,85 2,70 2,30
∅∅ 40x3,7 3,00 2,60 2,30 5,00 7,50 1,00 3,00 2,60
∅∅ 50x4,6 4,60 4,20 3,80 6,70 10,0 1,30 4,60 4,20
∅∅ 63x5,8 6,40 5,80 4,90 9,30 14,0 1,90 6,40 5,80
∅∅ 18x2,0 1,00 0,90 0,80 1,60 2,10 0,45 1,00 0,90
∅∅ 20x2,8 1,10 1,00 0,90 1,70 2,20 0,45 1,10 1,00
∅∅ 32x2,9∅∅ 32x3,0
∅∅ 10x1,0∅∅ 12x2,0
∅∅ 16x2,2∅∅ 16x2,3
∅∅ 16x2,0∅∅ 16x1,8
∅∅ 16x1,5∅∅ 18x2,5
8
4.2. Mechanical characteristicsIn order to determine COBRA-PEX tubemechanical characteristics, it is necessaryto analyse the following parameters:pressure, temperature, duration, thermalexpansions etc. Thanks to the regression curves which areshown in the diagram on the right side of thepage, it is possible to determine reticulatedpolyethylene pipe characteristics. The curves resulted from accelerated testsconcerning pressure and working temperatureswhich were conducted according to theregulations in order to determine PE-X pipelowest life cycle. Regression curve diagram is commonlyused to determine PE-X pipe system lifecycle, considering pressure and workingtemperature values.It is also possible to calculate system durationand highest working pressure in the periodin question.Highest permissible stress is calculatedthanks to the following equation:
σσ max = σσ eq / f [11]
and: σσeq = value stands for equivalent stress
indicated in [MPa] which is exertedon pipe walls and which is shown inregression curves according totemperature value and supposed lifecycle.
σσmax = value stands for highest permissiblestress indicated in [MPa] which isexerted on pipe walls resulting fromequivalent stress value withoutincluding safety factor.
f = value indicates safety factor which isgenerally equal to 1,5.
In order to easily and rapidly determine [σσmax]value, see Table IV. After having been calculated or taken fromTable III, this parameter is used to calculateCOBRA-PEX tube highest working pressurevalue, according to [12] equation, afterhaving made check calculations. Highest permissible working pressure valuewill be the following:
Pmax = (20 •• s •• σσmax) / (D-s) [12]
and: Pmax = indicates highest permissible working
pressure value indicated in bar relatedto a tube with [D] outer diameter and [s]thickness, according to yearly durationand highest working temperature.
σσmax = value is shown in Table IV, accordingto duration and temperature value inquestion.
D = value stands for tube outer diameterindicated in mm
S = value stands for tube thicknessindicated in mm
Considering, for example, a COBRA-PEXtube with 18 mm outer diameter and 2,5 mmthickness which is used for hot water supplyat a temperature of 80 °C having a 50 yearlife cycle, according to Table IV, it results thathighest permissible stress value is equal to:
σσmax = 3,30 MPa
thus achieving, according to [12] equation, thefollowing highest permissible pressure value:
Pmax = (20 •• 2,5 •• 3,3) / (18-2,5) =10,64 bar
Then, dividing Pmax value which has beencalculated by real working pressure valuewhich is reached by the tube at operatingspeed (and which is equal, for example, to6 bar), it is possible to achieve real safetyfactor, which is the following:
fr = 10,64 / 6 = 1,77 ≥ 1,5
Working temperature
Years 20°C 30°C 40°C 50°C 60°C 70°C 80°C 90°C
1 7,00 6,20 5,67 5,00 4,60 4,00 3,13 2,80
5 6,87 6,00 5,57 4,93 4,55 3,88 3,43 2,78
10 6,79 5,96 5,53 4,86 4,42 3,86 3,39 2,77
25 6,73 5,86 5,40 4,80 4,36 3,33 2,93 2,66
50 6,70 5,80 5,33 4,73 4,33 3,73 3,30 2,60
Table IV
Regression curve diagram
EQU
IVA
LEN
T ST
RES
SES
[N/m
m2 ]
HOURS
YEARS
9
4.3. Thermal expansionsCOBRA-PEX tubes are characterised by athermal expansion coefficient which is higherthan that of metals and commonly usedbuilding materials, but system componentsare easily installed underground.This is due to supply system routedeviations which favour expansionabsorption.Even if all this does not happen, orCOBRA-PEX tubes are laid under-floor,expansions can be absorbed by polyethylene,thanks to its deformation properties whichare due to its low elasticity coefficient. In order to prove that undergroundinstallation does not generally cause anyproblem, thanks to the presence of insulatingsheaths which are necessary for theconstruction of hot and cold water supplysystems with a thickness which rangesfrom 9 to 20 mm, it is possible to compensatethe stresses which are caused by thermalexpansions.On the contrary, in case of exposedsupply systems, thermal expansionscause circuit length twisting and bendingwhich, besides being unaesthetic, canexert undesired stresses on some systemcomponents such as elbow joints, tees,curves, etc. In these cases, it is necessary to usespecial pipe clamps and create a supplysystem which is able to compensatethermal expansions. PE-X high density reticulated polyethylenepipe thermal expansion linear coefficientis equal to the following value:
αα = 0,15 mm/m °C
this means that if every pipe length indicatedin linear metres is subject to a temperaturerise which is equal to ∆t = 1K, linearexpansion value will be equal to 0,15 mmand, consequently, it is very easy to calculatesystem length total expansion value, whichis the following:
∆∆L = L •• αα •• ∆∆t
and:∆∆L = stands for total expansion value [mm]αα = indicates linear expansion coefficient∆∆t = indicates the thermal head the tube is
subject to [K]
For designer and installer’s convenience,the Table V on the right side of the pageshows linear expansion values related tosome system lengths and commonly usedthermal head values.
LINEAR EXPANSION TABLE [mm]
4.3.1. Expansion compensationPipe linear expansion which is caused bytemperature rise and shrinkage which isdue to refrigerated water supply cangenerate tensions which act on somesupply system points and, above all, onpipe fittings.When expansions or shrinkage reachvalues which cannot be compensated bysupply system development and naturalform, it is necessary to use appropriateanchoring points (PF), sliding supports (PS)and expansion arms (BD).The calculation procedures which areindicated below are necessary to solve theproblem of thermal shrinkage and expansionabsorption of COBRA-PEX tubes.
4.3.2. Expansion joint calculationIn order to create an expansion joint formingone or more curves, the minimum [BD] armlength to be achieved – see Picture 9 -must be calculated as follows:
BD = k •• √ de •• ∆∆L
and:k = stands for material constant = 30de = indicates the outer diameter of the tube
which is used∆∆L = indicates thermal expansion to be
compensated
Considering, for example, the following data:• ∅ 20 mm tube which is used• 10 metre long system • Thermal head ∆t = 40 K (10 → 50°C)
calculation is solved as follows:
∆∆L = 10 • 0,15 • 40 = 60 mm
BD = 30 • √ 20 • 60 = 1040 mm
Even in this case, to facilitate technicianand installer’s work, all calculations havebeen converted into a graphic form andthanks to the nomogram which is shown inpicture 11, it is possible to rapidly calculateexpansion arms. While positioning fixed points, it isnecessary to use, if possible, supply systemcourse deviations to compensate thermalexpansions. System and tap rigid pipe fittings will act asfixed points. Sliding supports will be installed betweentwo fixed points according to pipe length,supporting pipes and favouring expansionand shrinkage phenomena.The maximum distance between the supportsshould not be higher than 1 metre in case oftubes having a diameter which is up to25x3,5, 1,25 metres in case of tubes with adiameter which ranges from 28x3,0 to40x3,7 and 1,5 metres for all other tubes. Fixed points must be achieved by usingcollar supports which are connected to teesand intermediate curves or joints – Picture 10.Support clamp jaw section and coatingmust be suitable for plastic tube connection.
Table V
Length
L [m] 10 20 30 40 50 60
∆∆t [°K]
1,0 1,50 3,00 4,50 6,00 7,50 9,002,0 3,00 6,00 9,00 12,0 15,0 18,03,0 4,50 9,00 13,5 18,0 22,5 27,04,0 6,00 12,0 18,0 24,0 30,0 36,05,0 7,50 15,0 22,5 30,0 37,5 45,06,0 9,00 18,0 27,0 36,0 45,0 54,07,0 10,5 21,0 31,5 42,0 52,5 63,08,0 12,0 24,0 36,0 48,0 60,0 72,09,0 13,5 27,0 40,5 54,0 67,5 81,010,0 15,0 30,0 45,0 60,0 75,0 90,0
TO BE NOTICED:[L] pipe length which is necessary to calculate[∆∆L] expansion coefficient always correspondswith system parts which are measured betweentwo fixed supports.
Picture 9
Arm
Arm
Pipe
leng
th [m
]
Pipe
leng
th [m
]
Slidingsupport
Slidingsupport
Fixedpoints
Fixedpoints
10
Sliding supports must be chosen followingthe same procedures, paying attention tocollar diameter which must be dimensionedto let pipe run freely.
4.4. Application fieldsConsidering above-mentioned COBRA-PEXtube specifications, it is possible to determinethis technological system application fields. Considering highest permissible temperatureand pressure values related to a systemduration which is equal to 50 years, thissystem can be used both in civil andindustrial field.Civil systems includes hot and cold watersupply systems for sanitary use, high andlow temperature heating plants, refrigeratedwater air-conditioning units, garden irrigationsystems, air-conditioning unit condenserwater drain pipes, etc.The applications in industrial field include,besides above-mentioned systems, compressedair supply systems, purifying systems whichare used for the supply of processing fluidsor fluids which are used in food industry(after having previously checked their chemicalcompatibility with carrier fluid), farm supplysystems, etc.COBRA-PEX tubes, thanks to their technicalcharacteristics such as salt-water andvibration resistance, soundproofing properties,lightness, non toxicity, etc., are used for theconstruction of boat and ship technologicalsystems. They can also find other applications, butphysical and chemical working parametersmust be compatible with material and producttechnical purposes.
4.5. LightnessCOBRA-PEX system tubes and pipe fittings,besides offering all above-mentionedadvantages, are also very light andconsequently, they can be easily handled. For example, a ∅ 18x2,5 100 metre longCOBRAPEX tube coil which is used for theconstruction of hydraulic systems and sanitary
facilities and heating plants, approximatelyweighs 12 kg., including cardboard packing. Thanks to this characteristic, which canseem to be obvious and relatively important,it is possible to avoid down times and speedup installation procedures.
Picture 10
Nomogram which is used to calculate expansion arm
SYSTEM LENGTH [m]
LENGTH VARIATION ∆∆L [mm]
TEM
PER
ATU
RE
VAR
IATI
ON
∆∆T
[°C
]EX
PAN
SIO
N A
RM
LO
WES
T LE
NG
TH [m
m]
Tube
out
er d
iam
eter
[mm
]
Picture 11
11
4.6. Non-toxicityPE-X high density reticulated polyethylenepipes can be used for the construction ofsupply systems which carry fluids which areused in food industry.COBRA-PEX pipes are manufacturedaccording to the following Regulations:
• M.D. dated March 21 1973• Health Ministry Circular n° 102 dated
December 2 1978 • Official Gazette n° 104 dated April 20
1973 indicating “The list of the substanceswhich are used to create products whichare in contact with foodstuffs”.
COBRA-PEX tubes are suitable for drinkingwater supply thanks to the certification n°99/96, concerning total migration and dyetests pipes were subject to.
The Table VI on the right side of the pageshows COBRA-PEX tube compatibility withsome commonly used chemical substances.The data which are shown only refer to theresults of expansion and tensile strengthtests which were conducted on PE-Xreticulated tube samples, after havingsoaked chemical substance in water or plungedit into the atmosphere for a long time. Consequently, resistance data which areindicated only refer to the behaviour of areal pipe which contains the chemicalsubstance and which is under-pressure. If the data which are shown in Table VI andthe results which have been achieved in thelast twenty years are not enough, samplepipes must be subject to further tests.
4.7. Dielectric propertiesThe raw material which is used for theconstruction of COBRA-PEX system has avery high volume and surface resistivity.Thanks to this characteristic, PE-X highdensity reticulated polyethylene is one ofthe best electrically insulated materials.Consequently, supply systems which areachieved wil l never be subject toelectro-erosion phenomena, unlike metaltubes which are subject to stray currents,battery ignition effect which is due to thecombination of non-homogeneous materialssuch as copper and steel, etc. According to the values which are shown inTable I on page 3, this material is alsocharacterised by a very low dielectric constantvalue and a reduced pressure loss factor,becoming totally insensitive to the magneticfield action of any frequency, consequentlyCOBRA-PEX systems can never generateelectro-magnetic interference, unlike metaltube systems. Nowadays, buildings are characterised bymanagement, check and measurementcomputerised systems, reception and datatransmission networks, therefore watersystems with above-mentioned characteristicsare considered as a great technological stepforward.
4.8. Low thermal conductivityThermal conductivity value of these pipes,which is equal to 0,38 W/mK and heat lossper linear metre are lower than those ofmetal tubes. A lower heat loss which passes throughpipe walls also determines a lower condenserwater formation in special outer thermo-hygrometric conditions. Condenser water formation is obviouslydue to carrier fluid temperature, ambienttemperature, relative humidity value and thediameter of the tube in question.The experimental data which have beencollected thanks to a direct observation withthe help of practical tests are available upondemand. In any case, if COBRA-PEX system is usedfor hot or refrigerated fluid supply, it isnecessary to follow the thermal insulationregulations which are in force.
4.9. Sound-proofing propertiesHigh density reticulated polyethylene,thanks to its very good mechanical anddynamic properties, is able to absorbmechanical stresses, such as vibrations orsmall water hammers which always takeplace in the system, highly reducing theirsound diffusion along the supply system.
Conc. T. [°C]Substance/Fluid [%] 20 70
Acetone 100 •Acetic acid 100 • •Benzoic acid water conc. • •Hydrochloric acid conc. • •Chromic acid 50% • •Phosphoric acid 95% • •Formic acid --- • •Hydrofluoric acid 70% • •Nitric acid 30% • •Nitric acid 50% • •Sulphuric acid 50% • •Sulphuric acid 98% • •Water --- • •Distilled water 100 • •Drinking water --- • •Sea-water --- • •Aqua regia --- • •Ethyl alcohol 100 • •Liquid ammonia water conc. • •Carbon dioxide --- • •Aniline 100 • •Plant pesticides --- • •Petrol --- • •Benzene --- • •Beer --- • •Butane --- • •Ammonia chloride water conc. • •Potassium chloride water conc. • •Synthetic detergents --- • •Washing detergent --- • •Hexane --- • •Petroleum ether --- •Fluoride --- • •Wet chloride gas --- • •Methane gas --- •Gas oil --- • •Glycerine --- • •Ethylene-glycol --- • •Sulphured hydrogen --- • •Sodium hypochloride --- • •Milk --- • •Bleaching lye --- •Engine lubricants --- • •Methanol --- • •Diesel oil --- • •Fuel oil --- • •Linseed oil --- • •Paraffin oil --- • •Transformer oil --- • •Silicone oil --- • •Vegetable oils --- • •Potassium permanganate 20% • •Hydrogen peroxide 30% • •Hydrogen peroxide 100% • •Petroleum --- • •Propane --- • •Liquid soap --- • •Caustic soda --- • •Toluene --- • •Vaseline --- • •Wine --- • •
Table VI
• Resistant
• Quite resistant
• Unresistant
12
4.10. Deposits, abrasion and corrosionCOBRA-PEX tubes are resistant to theelements which are commonly presentin hydrothermosanitary facility waterand they are also characterised by avery smooth surface.For this reason, it is possible to avoidall problems which are due to tubecorrosion and those which are due todeposit formation, thus preventing rustyparticles, calcareous or galvanictreatment deposits from detaching frompipe walls. PE-X polyethylene pipe thermal expansioncoefficient, which is higher than that ofcalcareous deposits, facilitates depositremoval.Thanks to tube expansion and shrinkage,which are higher than those of calcareousdeposits, the latter ones are detachedfrom pipe walls and removed. It is well-known that high densityreticulated polyethylene is highlyabrasion-resistant, even if water containssuspended impurities and at an highflow speed.
4.11. Easy installationCOBRA-PEX tubes, thanks to theirmalleability, can be used for systemconstruction according to the sameassembling procedures which are followedto install traditional steel pipes and forthe creation of innovative horizontalsupply systems. As it is shown in the following diagrams,COBRA-PEX tube supply systems canhave different shapes and purposesand they can be also used for theconstruction of removable systems. Tubes can be correctly installed followingsimple procedures without using specialequipment – see section 6.
4.12. UV ray resistanceIt is well-known that polyethylene tubesare not highly resistant to ultra-violetrays – Picture 11. Consequently, white-coloured PE-Xtubes must not be installed or stored inplaces which are directly exposed tosun rays. Black-coloured COBRA-PEX tubesmust be used outdoors as they are UVray stabilised thanks to Carbon Blackaddition and they can be exposed toindirect sun light during storage andinstallation, without causing anyalteration, thus solving the problem ofhigh density reticulated polyethylenetube limitations.
4.13. Thermal storageCOBRA-PEX high density reticulatedpolyethylene tubes, thanks to theirmolecular structure, are characterisedby the so-called thermal storage whichallows them to reassume their originalshape during cross-linking process. Thanks to this characteristic which isonly typical of reticulated polyethylenetubes, during cross-linking process,molecules take the same room. This molecular state corresponds withmaterial minimum quantity of energy. Because of pipe deformation or bendingwhich takes place after cross-linkingprocess, molecules are differentlypositioned, thus increasing materialquantity of energy. If COBRA-PEX tubes are subject toair-heating at a temperature ofapproximately 130 °C, material minimumquantity of energy will be restored, thuslocating the molecules in their initialposition. For example, if the tube is crushed, itreassumes its original shape afterhaving been heated it by using a specialhot-air tool – see Picture 12.
4.14. Permeability to gasesCOBRA-PEX tubes are commonlyused in hydrothermosanitary field andalso for the construction of gas supplysystems. Even if high density reticulatedpolyethylene tubes are usually consideredwaterproof, they are permeable tosteam and gases. This characteristic is not only typical ofPE-X tubes, as also random polypropyleneand polybutylene pipes are subject tothis phenomenon. In case of water systems and sanitaryfacilities, all this does not cause anyproblem, but in case of heating plants,for example, it is necessary to solve theproblem of oxygenated water which iscontained in the plants. For this reason, COBRA-PEX pipes areprovided with an oxygen and gas-proofouter barrier.This so-called 0200B pipe range isavailable in the diameters which arecommonly used for the construction ofradiator and radiant panel heatingplants – see Table II on page 4.
4.15. Fire-resistanceAs COBRA-PEX tubes are achieved byan hydrocarbon, they are combustible. Because of cross-linking process, materialdoes not drip, unlike non-reticulatedtubes; this phenomenon takes placeonly if the temperature is higher thanapproximately 400°C.In any case, if COBRA-PEX pipes weresubject to combustion because of a fire,combustion products would be madeup of carbon dioxide and pure water,which are non-toxic and non-corrosivesubstances.
Picture 11
Picture 12
13
5.1. Compression mechanical pipe fittingsCompression mechanical pipe fittings arecommonly used for COBRA-PEX tubeconnection – Picture 13. These kinds of pipefittings are perfectly sealed and reliable.
All this proves that PE-X tubes have so farachieved successful results.In fact, most of the pipe fittings which havebeen used up to now were manufacturedaccording to TIEMME range buildingtechnique – Picture 14.Thanks to their building techniques, PE-Xtube compression pipe fittings are versatileand suitable for many applications. High density reticulated polyethylene pipesare used for the construction of watersystems and sanitary facilities and heatingplants in order to avoid underground joints. In case of manifold systems, for example,branches coming from and to sanitaryfacilities are achieved by using a single tubelength without creating intermediate joints,as in the case of radiant panel systems and“removable” tube sanitary facility supplysystems. Therefore, branch terminals are alwayslocated in accessible positions and they canbe easily inspected.This is the case, for example, of manifoldfittings/adapters, valves and lockshieldvalves which are placed on heating bodiesand Art. 1428 curves which are connectedto special wall plastic fairings, thus achievingremovable systems. It must be stressed that these pipe fittingscan be disassembled and reused and it ispossible to change the system or replacesome of its parts without following complexprocedures.
The other PE-X tube pipe fittings, on thecontrary, such as bending or self-lockingcoupling pipe fittings, cannot be disassembledand reused; if supply system is removed orchanged, it is necessary to cut the tube,with all relative consequences.
5.1.1. SpecificationsCompression mechanical pipe fittings areavailable for COBRA-PEX tubes with adiameter which ranges from ∅ 10 to ∅ 63 mm.All pipe fittings are produced by hot pressedbrass billets which are then machined inorder to guarantee an high and steadyproduction quality level. This production process guarantees finalproduct good mechanical characteristicswithout achieving brass bar derivatives.COBRA-PEX tube pipe fittings have thefollowing working nominal values:
• Highest working temperature = 95°C• Highest peak temperature =110°C• Highest working pressure = 10 bar
Trade-mark is stamped on pipe fitting bodyand tube and thread side dimensions arestamped on pipe tightening nut.
5. PE-X tube pipe fittings
Picture 13
COBRA-PEX TUBE PIPE FITTINGS
Picture 14
➊ Part of OT58 pipe fitting➋ OT58 pipe tightening nut ➌ Broken clamping nosepiece➍ COBRA-PEX polyethylene tube
14
Partially summarising what was previouslymentioned about tube specifications,please find some simple procedures whichare necessary for COBRA-PEX tubeinstallation.During tube transport, do not damagepackaging exposing the tube to direct sunlight and avoid scratches or abrasionswhich are caused by foreign bodies. Store the tube in a covered place on asmooth bearing surface.During pipe laying, avoid tube outer surfacecutting which is due to contact with sharpparts, such as, for example, brick piecesand which takes place especially when tubeis laid underground. White-coloured excess COBRA-PEX tubesmust be repacked in order to be reused.
6.1. Pipe cuttingCut COBRA-PEX tube by using the specialArt. 1496 shears in order to avoid burrformation. Make sure that pipe cutting is perpendicularto tube axis – Picture 15. If tube is cut by using different kinds oftools, before connecting it to the pipe fitting,make sure that burrs are not present.
6.2. Cold-bendingCOBRA-PEX tubes can be cold-bent manually,as it is shown in Picture 16 or by using specialpipe clamps, as it is indicated in Picture 17. According to bending procedure which isshown in Picture 16, minimum bendingradius is the following:
Rmin = 8 • Dand: D stands for the outer diameter of the pipeto be bent.
In case of cold-bending with a bendingradius which is lower than 8D, use thespecial Art. 1480 pipe clamps – Picture 17. By using this tool, it is possible to bend thepipe without crushing it.
6.2 Hot-bendingHot-model COBRA-PEX tubes by evenlyheating the outer surface of the pipe lengthto be bent. Heat the pipe length to be moulded by usingan hot-air tool having a temperature regulationwhich is lower than 500 °C – Picture 18. Evenly heat the pipe length to be bent at atemperature of approximately 130 °C.This value can be visually checked, asCOBRA-PEX tube becomes transparent.
Do not overheat pipe length to be bent. If this happened, tube surface would bebrown-coloured and, in this case, pipelength must not be used as its mechanicalcharacteristics have changed. After having reached right temperature,manually bend the tube starting fromheated length central point and graduallydeviating from it without causing tubeovalisation or deformation. Lowest permissible hot-bending radius isthe following:
Rmin = 2,5 • D
After pipe bending, keep COBRA-PEX tubebent cooling it with a sponge or a clothwhich is soaked in water. All hot-modelling operations can be correctedand repeated by heating the pipe length tobe bent until it becomes transparent. (seesection 4.13 about thermal storage).
6.3. Connection between tube and pipefittingAs it is shown in chapter 5, COBRA-PEXtubes are connected one to the other or toother system components by using thespecial pipe fittings and adapters which areshown in Picture 14. In order to achieve a perfect connectionbetween tubes and pipe fittings, follow theinstructions which are indicated below:
• cut the tube as it is shown in section 6.1.• then, insert clamping nut and broken
nosepiece into the tube. • insert the tube in pipe fitting hose
connector.• tighten clamping nut by using an ordinary
spanner.
6. Assembling procedures
Picture 15
Picture 16
Picture 17
Picture 18 Picture 19
15
6.4. Underground installationCOBRA-PEX tubes can be laid undergroundeven without using any sheath or coating –Picture 20.
However, it is always necessary to followpipe insulation regulations which are inforce.Considering the installation of pipeswhich are coated with expanded elastomerinsulating sheaths, it is not necessary totake special measures to solve the problemof thermal expansions.In fact insulating sheath thicknessalready compensates expansion effects,as in the case of COBRA-PEX tubesused for the construction of removablesystems which are coated with corrugatedsheath – Picture 21.
In this case, thanks to the distance betweentube outer diameter and sheath innerdiameter, tube is subject to axial andradial expansions. In case of underground bare pipes withworking pressures which are up to 6 bar, itis necessary to create a seat which is2,5÷3 times as deeper than tube outerdiameter in order to avoid plaster cracking.For any information about COBRA-PEXtubes which are used for the constructionof radiant panel systems, see relativeparagraph.
6.5. System pressure testing Supply systems are subject to apressurisation test in order to check ifleaks are present. In fact, in most cases, PE-X high densityreticulated polyethylene pipe supplysystems are laid underground, “covered”with the structures and hidden. Consequently, before including thesesystems in building structure, they mustbe necessarily subject to pressure testingin order to check if leaks are presentalong the whole system.However, the rules which regulate watersystem testing standards (according toUNI 9182 – DIN 1988 regulation), notonly include this test, but also otherimportant tests such as contemporaryhighest flow test and loudness test whichconcern designing and dimensioningaspect and not installation merely“mechanical” aspect. Therefore, this section only deals withtechnical regulations concerning systempressurisation test, while the followingchapters deal with calculation procedures.According to UNI 9182 regulation – Sect.5 – Par. 27.2 – Clause 27.2.1.”Coldhydraulic tests”:“Tests are conducted on the whole hotand cold water supply system beforefitting taps and closing holes, innercourtyards, double ceilings etc., whilepipes are subject to a more than fourconsecutive hour exposure to a pressurevalue which is 1,5 times as higher thanhighest working pressure with at least600 KPa.Tests are passed if, after this period, themanometer shows that pressure initialvalue has a tolerance which is equal to30 KPa. It is possible to carry out separate testsaccording to different systems”.The regulation in question is referred tohigh density PE-X pipes. In case of PE-Xsystems, pressure test must take place ata steady temperature throughout testperiod. As these pipes are subject to thermalexpansion, a temperature variation of10°C can also determine a pressurevariation which ranges between 0,3 and0,8 bar (30÷80 KPa). As regards DIN 1988 regulation, pressuretesting is divided into three phases: thepre-check, the main check and the finalcheck. Each phase is characterised by specificpressure value and test duration. During pre-check phase, test pressure is1,5 times as higher than highest workingpressure and this value must be reached
within 30 minutes during the twofollowing tests, with a 10 minute intervalbetween the two tests. After a furtherperiod when pressure value is reachedwithin 30 minutes, final pressure valuemust not fall below 0,6 bar (60 KPa).During this first check, water leaks mustnot be present along the system.The main check lasts 2 hours and takesplace at a pressure value which correspondswith that which was achieved duringpreliminary test. After the check, the pressure value whichis achieved must not be lower than 0,2bar (20 KPa) compared to initial value.
6.6. Supply system washingHot and cold water supply system forsanitary use which is suitable for humanconsumption must be subject to a preliminarywashing operation in order to remove allworking and installation residues whichare potentially unhealthy. Thanks to COBRA-PEX system componentcharacteristics, it is only necessary towash the system with water in order toguarantee its inner cleaning. In fact, apart from the presence of dust orbuilding loam, PE-X tubes are installedwithout using glues, solvents or othernoxious substances. Tube and pipe fitting packing and productnon-toxic properties guarantee fluid slidinginner surface good conditions.Make sure that oils and fats do not filterthrough the system whether accidentallywhether through operator’s negligence,thus compromising system cleaning. If supply system lengths are unfinishedat the end of the day, it is highlyrecommended to cover open terminalswith a clean cloth or other suitable water-proofing protections.
Picture 20
Picture 21
16
7.1. IntroductionThis chapter analyses the proceduresand calculation methods which arenecessary to dimension water systemsand sanitary facilities of two bathroomsand a kitchen for domestic use.As this manual is not specifically used tocalculate sanitary facility dimensioning, itis not possible to consider every singlecase.Therefore, the case in question representsalmost all kinds of sanitary facilities,considering that bathrooms which arepresent both in civil or industrial buildingsand those which are present in barracksare dimensioned following similarprocedures.In fact, it’s only the main supply systemwhich is created according to the kindof building and its purpose and notsecondary supply system which isconnected to the bathroom. For example, the water supply tube of acivil or canal washbasin which is locatedin barracks or in a gymnasium change-roommust always guarantee a flow which isequal to 0,10 l/s with an input residualpressure value which is equal to 0,5 bar. Two calculation examples related to a hotand cold water domestic supply systemare indicated below, considering theinstallation of COBRA-PEX multilayertube and the relative compression andpressing mechanical pipe fittings, accordingto the case in question.Calculation examples refer to the twokinds of systems which are commonlyused and summarised as follows:
• with series-connected sanitary facilitiesand compression mechanical pipe fittings– Picture 22
• with manifold parallelly connected sanitaryfacilities – Picture 23
Contemporaneity factor was previouslyused to dimension water systems andsanitary facilities. In other terms, thanks to this method, itwas possible to determine how manysanitary facilities which were connectedto a certain circuit or part of it could beused at the same time, thus calculatingthe highest supply flow during peakperiods.This effective method was replaced byUNI 9182 regulation which is based onthe concept of “load units” and systemdimensioning is calculated according tothis parameter. Calculation examples are made accordingto this regulation.
7.2. General specificationsIn order to make real technical dimensioningcalculations, it is necessary to consider ahouse which is part of a residential complexwhich is made up of 86 apartments and whichis located in the outskirts of Milan.As it often happened in the last few years, it will bepossible to install independent heating systemsand hot water supply systems for sanitary use.Consequently, main cold water supplysystem will be connected to single wallboilers and bathrooms.From wall boilers, horizontal hot water supplysystem will be connected to every singledomestic sanitary facility.Considering the kind of generator andsmall-sized horizontal supply system, it isnot possible to install hot water circulationsystems for sanitary use.The house which was considered as a calculationexample and which is shown in Picture 24, is madeup of two bathrooms (a main bathroom and aservice one with washing machine) and a kitchen.
Considering present standard current meterswhich are installed in civil and not luxury houses,it is not allowed to use washing machines anddishwashers at the same time, therefore thecase in question is not considered.Domestic sanitary facilities have the followinggeneral characteristics:
7. Sanitary facilities
Series-connected sanitary facility supply system – picture 22
Parallelly-connected sanitary facility supply system – picture 23
Table VII
Load unit
Kind ofsanitary facility
Flow[l/s]
coldwater
hotwater
Sink 0,15 1,50 1,50Washbasin 0,10 0,75 0,75Bidet 0,10 0,75 0,75WC 0,10 3,00 ---Bathtub/Shower 0,20 1,50 1,50Washing machine 0,15 2,00Dishwasher 0,15 2,00
17
7.3. Series-connected sanitary facilitysupply systemConsidering the specifications which areindicated in previous paragraph, it is possibleto calculate the flows which are necessary forevery single sanitary facility or supply point.It is now necessary to determine contemporaryhighest flow value which is achieved by agroup of sanitary facilities. Considering the main bathroom which ismade up of a washbasin, bidet, WC andbathtub, it is possible to start dimensioningcold water supply system which will be fedby [A] riser.If all sanitary facilities were used at thesame time, contemporary highest flowvalue would be equal to supply point wholeflow, that is to say it would be equal to 0,5l/s (see Table VII).As it is not possible to consider the case inquestion, it is necessary to determine whichkind of sanitary facilities can be used or notat the same time. According to the traditional method of“contemporaneity factor”, the above-mentionedsanitary facilities should reach a highestflow value which is equal to 0,29 l/s(contemporaneity factor is equal to 57%).On the contrary, UNI 9182 regulation isbased on [lu] load unit method and,according to the data indicated in the tableF.2.1. of the regulation itself, considering thekind and number of main bathroom sanitaryfacilities, calculation would be the following(see l.u. values indicated in Table VII):
• cold water: 3,0 lu• hot water: 6,0 lu
However, in the presence of severalsanitary facilities in the same bathroom, it ispossible to calculate [lu] value of all sanitaryfacilities (see regulation F.2.2 table).As regards bathroom sanitary facilities inquestion, whose supply diagram is indicatedin picture 25, cold water supply system [lu]value is equal to 4,5 and, according to thevalues indicated in Table F.4.1.1. and in UNI9182 regulation F.4.1.3. diagram, this loadunit value corresponds with a contemporaryhighest flow value which is equal to 0,30 l/s.Following the same calculation procedures,hot water supply system will reach a loadunit total value which is equal to 2,25 and,consequently, a contemporary highest flowvalue which is equal to 0,25 l/s.Then, it is possible to start dimensioningbathroom hot and cold water supply system.First, it is necessary to number every singlesystem part as it is shown in picture 25,then it is possible to make analyticcalculations by using calculation tablewhich is shown on page 19.
It is necessary to start calculation procedurefrom the sanitary facility which is in the mostunfavourable condition up to supply risershaft, thus determining separating pressurevalue.As regards cold water supply system, firstconsider system length which is connected tothe washbasin and which is indicated by n° [1].As this system length is connected to asingle sanitary facility, it will be dimensionedaccording to sanitary facility highest flowvalue, which, in this case, is equal to 0,10 l/s.According to COBRA-PEX tube pressureloss diagram and considering the flow valuein question, it is possible to use a pipehaving a diameter of 16 x 2,2 mm and,consequently, a unit pressure loss valuewhich is equal to 0,013 bar per linearmetre.Then, in order to determine [1] systemlength pressure loss from sanitary facility to[x] node, it is necessary to define systemlength and pressure losses which are dueto the presence of pipe fittings, curves etc.The problem can be solved in two differentways: the first method consists in evaluatingreal system length, calculating pressurelosses and adding them by using coefficientmethod [ζ].The second easier procedure is based on“equivalent metre” method; this means thatpressure losses are calculated consideringa system fictitious length which determinesthe same resistance value.
This more practical and rapid method will beused to make calculation examples, as it isshown in Table III.Then, it is necessary to calculate [1] systembranch, considering the following values:
• real length: for example 2 metres• under-sink pipe fitting : 1,3 eq. metres• 2 90° curves: 1,4 eq. metres
Adding all these values, it is possible toobtain a length which is equal to 4,7 eq mConsequently, [1] system length up to [x]node is characterised by a pressure losswhich is equal to:
∆∆p1 = 4,7 [eq m] • 0,013 [bar/m] = 0,061 [bar]
As in the case of length [1], n° [2] branchpressure loss will be calculated achievingthe following results:
• sanitary facility flow : 0,10 [l/s]• branch length: 3,7 [eq m] and:
real length = 1,0 [m]under-bidet pipe fitting = 1,3 [eq m]2 90° curves = 1,4 [eq m]
• COBRA-PEX tube: ∅ 16 x 2,2 mm• unit pressure loss: 0,013 [bar/m]
consequently:
∆∆p2 = 3,7 [eq m] • 0,013 [bar/m] = 0,048 [bar]
Picture 24
18
[1] and [2] branches come from [x] nodeand, as it was previously seen, they havetwo different pressure loss values. In order to calculate system dimensioningand above all to determine the lowest pressurevalue which must be guaranteed whenseparating from [A] riser, ∆p1 higher valuewill be considered. This value will be added to the residuallowest pressure value which must be reachedby water supply tube after having neutralisedcontinuous and local system resistance.This pressure value is generally equal to 0,5[bar] and this means that [x] node lowestadmissible pressure value must be equal to:
P(x) = ∆p1 + 0,5 = 0,561 [bar]
[x] node calculation procedures must befollowed to calculate all other node values.
It is now possible to calculate n° [3] length,considering that system length contemporaryhighest flow value can be equal to bidet andwashbasin whole water flow, which is equalto 0,20 l/s.According to the above-mentionedcontemporaneity factor method, flow valuewould have been equal to 0,15 l/s, whichcorresponds with 75% of total value.As the two sanitary facilities in questioncannot be used at the same time, calculationwill be made considering length [3] lowerflow, thus obtaining the following data:
• max. contemporary flow : 0,15 [l/s]• COBRA-PEX tube: ∅∅ 18 x 2,5 mm• branch length: 3,2 [eq m]
real length = 2,3 [m]T-pipe fitting = 0,9 [eq m]
• unit pressure loss: 0,014 [bar/m]consequently:
∆∆p3 = 3,2 [eq m] • 0,014 [bar/m] = 0,045 [bar]
After having calculated ∆∆p3 value andhaving added it to ∆∆p1 value, it is possible todetermine [y] node system lowest workingpressure, which is the following:
P(y) = ∆p3 + ∆p1 = 0,56 + 0,045 = 0,605 [bar]
As in the case of previous system branches,n° [4] branch pressure loss will be calculatedachieving the following results:
• sanitary facility flow : 0,20 [l/s]• branch length: 3,2 [eq m]
real length = 1,3 [m]male elbow joint = 1,2 [eq m]1 90° curve = 0,7 [eq m]
• COBRA-PEX tube: ∅∅ 20 x 2,6 mm• unit pressure loss: 0,015 [bar/m]
consequently:
∆∆p4 = 3,2 [eq m] • 0,015 [bar/m] = 0,048 [bar]
As in the case of previous [x] node, comparing[y] node resistance values, it results that∆∆p4 value is lower than P(y) value, thereforethe latter value will be used to makefollowing calculations.N° [5] system length will be connected tothree sanitary facilities, whose total load unitvalue is equal to lu = 3, consequently, flowvalue is equal to approximately 0,25 l/c.Considering, for example, 4,0 [eq m] n° [5]length and using 20 x 2,8 mm diameterCOBRA-PEX tube, [z] node lowest pressurevalue will be equal to:
P(x) = ∆∆p5 + P(y)
P(x) = (4,0 • 0,022) + 0,605 = 0,693 [bar]
N° [6] branch will be calculated accordingto the following procedures, as in the caseof previous branches:
• sanitary facility flow : 0,10 [l/s]• branch length: 4,3 [eq m]
real length = 1,5 [m]elbow joint = 1,4 [eq m]2 90° curves = 1,4 [eq m]
• COBRA-PEX tube: ∅∅ 16 x 2,2 mm• unit pressure loss: 0,013 [bar/m]
and, consequently:
∆∆p6 = 4,3 [eq m] • 0,013 [bar/m] = 0,056 [bar]
Adding this value to the residual supplylowest pressure value, it is possible toobtain the value which is indicated in TableVII – column 9. Then, it is necessary to calculate n° [7]length until it is separated from the riser. System branch load units are achieved by allbathroom cold water supply system sanitaryfacilities in question, and, as it is shown byUNI 9182 regulation, they are equal to 4,5[lu] having a flow value which is equal to0,3 [l/s] - see Table VIII – column 3 and 4.Calculation procedure is unchanged, but it isnecessary to consider system cut-off cock.As the latter can be available in variousversions and models, it is not possible toindicate its approximate resistance value interms of equivalent metres. The pressure gradient which is caused bycut-off cock will be calculated according to atraditional pressure loss diagram which isprovided by the manufacturer or, in theabsence of this diagram, by using its [Kv]value according to the following formula:
∆∆pv= (Q/Kv)2
indicating “Q” value in [m3/h] and ∆pv valuein [bar].In the case in question, cut-off cock, havingfor example a Kv value which is equal to 6,8and a 0,3 l/s contemporary highest flow, hasthe following pressure loss:
Picture 25
19
∆∆pv = ((3,6 • 0,3) /6,8)2 = 0,025 [bar]
In conclusion, [7] pipe length total pressureloss is equal to:
∆∆p7 = 4,0 [eq m] • 0,031 [bar/m] = 0,124 [bar]
Adding above-mentioned value to cut-offcock pressure loss, it is possible to obtainthe following equation:
∆∆p7 = 0,124 [bar] + 0,025 [bar] = 0,15 [bar]
Indicating this value in column 8 of Table VIIIand adding it to [z] node lowest pressurevalue, it will be possible to achieve thefollowing pressure value which must bereached while separating from [A] riser inorder to correctly feed [B1] main bathroomsanitary facility cold water supply system.
∆∆pB1 = ∆∆p(x) [bar] + ∆∆p7 [bar] = 0,84 [bar]
As regards hot water supply system forsanitary use, calculation procedure isunchanged and results related to [B1]bathroom are indicated in Table IX.As it can be noticed, in this case lowestpressure final value is referred to [Q] node– see picture 26 – and two bathroom supplysystems start from this point. Considering that [B2] bathroom hot watersupply system values are similar to those of
[B1] bathroom supply system, [Q] nodemust supply 4,5 load units (in fact, even inthis case, 3 sanitary facilities have the sameflow). This [lu] value, which is shown in curve 1 oftable F.4.1.3., has a contemporary maximumflow which is equal to 0,3 l/s.Consequently, pipe length will have 20 x 2,8mm diameter until it is separated from kitchenwashbasin, with a pressure gradient whichis equal to 0,031 [bar/m] which, considering10 [eq m] length, corresponds with thefollowing value:
∆∆p = 10 • 0,031 = 0,31 [bar]
Adding this value to the lowest pressurevalue which is necessary for [Q] nodebathroom supply system, it is possible todetermine the pressure value which mustbe guaranteed until pipe length is separatedfrom kitchen washbasin. Considering [B1] bathroom [Q] nodepressure value, it is possible to achieve thefollowing equation:
P(J) = P(Q) + ∆∆p(Q-J) = 1,08 [bar]
Then, it is necessary to calculate last lengthup to the boiler in order to determine [A1]riser lowest pressure value.
Picture 26
Caldaia
COLD WATER SUPPLY SYSTEM CALCULATION
HOT WATER SUPPLY SYSTEM CALCULATION
Lengthn°
l.u.Max.
contemporaryflow [l/s]
Branchlength[eq m]
Pipediameter
[mm]
Unit pressureloss
[bar/m]
∆∆p length[bar]
∆∆p length +Min. p. (*)
[bar]
∆∆p totalsupply
system [bar]
[n°] of sanitaryfacilities whichare connectedto the system
1 1 1,50 0,20 4,5 20 x 2,8 0,015 0,067 0,567 0,567 (k)2 1 0,75 0,10 3,7 16 x 2,2 0,013 0,048 0,548 —3 2 1,50 0,20 3,2 20 x 2,8 0,015 0,048 — 0,615 (w)4 1 0,75 0,10 3,5 16 x 2,2 0,013 0,045 0,545 —5 3 3,00 0,25 6,3 20 x 2,8 0,022 0,139+0,018 — 0,77 (Q)
(*) – Min. P. = water supply tube residual lowest pressure value (which is generally equal to 0,5 bar) Table IX
Lengthn°
l.u.Max.
contemporaryflow [l/s]
Branchlength[eq m]
Pipediameter
[mm]
Unit pressureloss
[bar/m]
∆∆p length[bar]
∆∆p length +Min. p. (*)
[bar]
∆∆p totalsupply
system [bar]
[n°] of sanitaryfacilities whichare connectedto the system
1 1 0,75 0,10 4,5 16 x 2,2 0,013 0,061 0,561 0,561 (x)2 1 0,75 0,10 3,7 16 x 2,2 0,013 0,048 0,548 —3 2 1,50 0,15 3,2 18 x 2,5 0,014 0,045 — 0,605 (y)4 1 1,50 0,20 3,7 20 x 2,8 0,015 0,048 0,548 —5 3 3,00 0,25 4,0 20 x 2,8 0,022 0,088 — 0,693(z)6 1 0,75 0,10 4,3 16 x 2,2 0,013 0,056 0,556 —7 4 4,50 0,30 4,0 20 x 2,8 0,031 0,124+0,025 — 0,84
(*) – Min. P. = water supply tube residual lowest pressure value (which is generally equal to 0,5 bar) Table VIII
20
Adding [Q] node load units (which areequal to 4,5) to kitchen washbasin loadunits (which are equal to 1,5), it results thatfinal system length up to the boiler must bedimensioned by 6 [lu], thus achieving acontemporary highest flow value which isalways equal to 0,3 l/s (UNI 9182 regulation– Table F.4.1.3). Consequently, as in case of previouslength, tube will have 20 x 2,8 mm diameter,unit pressure loss will be equal to 0,031[bar/m] and, considering 5 [eq m] length,Dp total value will be equal to:
∆∆ptot = ∆∆p(J) + (5 •• 0,031) = 1,24 [bar]
The value which has been determinedwhose pressure loss is generated by theboiler and relative fittings is the lowestpressure value which must be guaranteedduring separation from [A1] riser in order tocorrectly feed domestic sanitary facility hotwater supply system, considering that watersupply tube has a residual pressure valuewhich is equal to 0,5 [bar]. Then, it would be necessary to calculatemain supply system dimensioning, but asthis manual is not specifically used to calculatesanitary facility dimensioning, the readercan go on making his calculations followingUNI 9182 regulation specifications.
7.3.1. Practical considerationsThis section makes a calculation examplewhich is based on a real case. Picture 26 shows hot and cold water supplysystems.As it can be noticed, [B1] and [B2] bathroomsare different one from the other: [B1]bathroom is characterised by traditionalunder-floor water systems, while [B2]bathroom is characterised by wall watersystems (as it is shown in picture 26).The installer chooses the method he prefersaccording to his needs. Wall water systems less interfere withwaste pipes, demanding fewer connections,therefore they are more rapidly installed.From the analysis of Tables VIII and IX, itresults that various system lengths shouldbe achieved by using pipes with differentdiameters according to contemporary highestflow values which must be guaranteed.However, standard tube diameters aregenerally suitable for all sanitary facilities,thus standardising all components, facilitatingbuilder’s yard organisation and speeding uplaying procedures.In this case, the PN 16 high densityreticulated polyethylene standard tubewhich is commonly used for the constructionof the whole domestic supply system has20 x 2,8 mm diameter.
This tube causes sanitary facilityover-dimensioning, but it successfullyreaches its target; on the contrary, tubeswith a lower diameter could have a lower flowand be noisy.Series-connected sanitary facility supplysystems which are achieved by usingcompression mechanical pipe fittings arecommonly used in case of bathrooms whichare provided with high-tech walls.All system tubes and pipe fittings can alwaysbe inspected, unlike other common systems.It is well-known that compression mechanicalpipe fittings are commonly laid undergroundwithout causing any inconvenience, even ifthey should be located in accessible places.However, some inset unit pipe fittings wereused by high-quality chromium-plated tapmanufacturers, confirming that it is sometimespossible to use underground pipe fittings.All this depends on system technical andpractical parameters, such as workingpressure and temperature, right expansioncompensation, laying conditions, etc.
7.4. Parallelly-connected sanitary facilitysupply systemConsidering the example which was made inprevious section and the same specifications,it is now possible to analyse manifoldsupply system.This system distinguishes itself from thesystem which was previously examined forthe different sanitary facility supply system.While traditional method is based on aseries-connected sanitary facility supplysystem, which means that circuit lengthscan be connected to several sanitaryfacilities, according to manifold method, onthe contrary, branches coming from and toa certain supply point are directly connectedto the manifold, consequently creating aparallelly connected sanitary facility supplysystem.
But why is it necessary to emphasise thisdifference?Because each of the two methods calculatessupply system dimensioning in a differentway.According to series-connected sanitaryfacility supply system, it is necessary toconsider the number of sanitary facilitieswhich must be connected to a certainsystem length, while according to sanitaryparallelly-connected facility supply system,each branch is calculated according to itshighest contemporary flow value irrespectiveof all the others.Even in case of this system, it is possible tomake a short calculation example which,with the help of picture 27, will explain thisprocedure better than words.Picture 27 indicates a supply system whichis connected to the two adjoining bathroomsby using a single point or supply manifold.This is possible because every singlebranch is provided with a cut-off cock whichis directly fitted in the manifold, therefore it isno longer necessary to separate bathroomsupply systems and install cut-off cocks inevery single manifold – see picture 28.In the case in question, sanitary facilitysupply system will be achieved by connectingseveral simple sectional manifolds, thuscreating 9 cold water lines and 5 hot waterones. Table X shows single branch calculationswhich are made following the proceduresindicated in previous section which arerelated to [1], [2], [4], and [6] lengths.
Picture 27
21
In other terms, it is necessary to knowbranch highest flow value, length indicatedin equivalent metres and water supply tuberesidual lowest pressure value. Considering these data, after havingdetermined tube unit pressure loss with thehelp of the diagram which is shown on page10, it is possible to determine branch totalpressure loss following calculation procedureswhich are indicated in previous section.After having calculated all manifold branches,it is necessary to determine system lowestpressure value, starting from pressure lossvalue which is higher than all other branchvalues; in this case, n° 9 branch value willbe added to ∆p manifold value.In order to calculate hot water supply system,from the manifold to the boiler, follow theprocedures indicated in previous sectionstarting from [Q] node up to the separationfrom the washbasin and heat generator.Similarly, it will be possible to calculate coldwater supply system length, from the manifoldto [A] riser.
7.4.1. – Rapid calculation tableAs it is necessary to follow repetitiveprocedures to calculate manifold watersystems and sanitary facilities, it is possibleto make preliminary calculations whichare indicated in special tables in orderto guarantee an easy and rapid systemdimensioning.Table XI shows manifold lowest pressurevalues, according to the kind of sanitaryfacility, branch length and tube diameter.From the intersection between the linewhich is related to the tube which must beinstalled according to the kind of sanitaryfacility, and branch length column, it ispossible to achieve manifold input lowestpressure value. For example, a washing machine which isconnected to 18 x 2,5 mm diameter tube at8 [eq m] distance from the manifold musthave a lowest pressure value of 0,68 bar,thus achieving a residual pressure valuewhich is equal to 0,5 bar.
7.4.2 Graphic calculation methodBy using the simple nomogram which isshown on the following page, it is possibleto dimension manifold water systems andsanitary facilities.Trace an horizontal line, starting fromcontemporary highest flow value of thebranch to be calculated, up to the curverelated to the pipe which must be used - [A]point.Then, besides reading pipe water flowspeed value, drawing a vertical line which isperpendicular to the first one, it is possibleto determine unit pressure loss per tubemetre [bar/m], thanks to first diagram baseintersection - [B] point.[C] point is determined drawing the linealong the second diagram up to equivalentmetre length curve.Then, trace an horizontal line leftwards,thus determining branch total pressure losswhich indicated in [bar] and after havingcrossed the scales which are placed on theleft side of the nomogram, it is possible todetermine manifold lowest pressure valueaccording to residual lowest pressure value. The nomogram shows four residual lowestpressure values ranging from 0,5 to 1,5 [bar].
Picture 28
HOT AND COLD WATER SUPPLY SYSTEM CALCULATION
Branchn°
Max.flow value
[l/s]
Pipediameter
[mm]
Unitpressure loss
[bar/m]
Branchlength[eq m]
∆∆pbranch[bar]
∆∆ptotal value
[bar]
Lowestflow value
[bar]
1 0,10 15 x 2,5 0,019 4,0 0,076 0,5 0,5762 0,20 18 x 2,5 0,023 4,8 0,110 0,5 0,61 (*)3 0,10 15 x 2,5 0,019 4,4 0,084 0,5 0,584 (*)4 0,10 15 x 2,5 0,019 4,2 0,080 0,5 0,580 (*)5 0,10 15 x 2,5 0,019 5,0 0,095 0,5 0,5956 0,10 15 x 2,5 0,019 4,0 0,076 0,5 0,576 (*)7 0,15 18 x 2,5 0,014 3,0 0,042 0,5 0,5428 0,10 15 x 2,5 0,019 5,0 0,095 0,5 0,595 (*)9 0,20 18 x 2,5 0,023 8,0 0,184 0,5 0,684 (*)
(*) – Calculations refer to cold water and to hot water supply systems. Table X
TABLE FOR THE RAPID CALCULATION OF MANIFOLD INPUT LOWEST PRESSURE VALUES
Table XI
Kind ofsanitary facility
Flow[l/s]
Tubediameter
P.l.[bar/m]
V[m/s]
Branch length [m]
2 4 6 8 10 12 14 16 18
Residualpressure
value
Sink
Bidet 0,10 15 x 2,5 0,019 1,2 0,54 0,58 0,61 0,65 0,70 0,73 0,77 0,80 0,84 0,5
W.C. cistern
Dishwasher 16 x 2,2 0,026 1,4 0,55 0,60 0,66 0,71 0,76 0,81 0,86 0,92 0,97
Washing machine 0,15 18 x 2,5 0,014 1,2 0,53 0,56 0,58 0,61 0,64 0,67 0,70 0,72 0,75 0,5
Washbasin 20 x 2,8 0,009 0,9 0,52 0,54 0,55 0,57 0,59 0,61 0,63 0,64 0,66
Bathtub 18 x 2,5 0,023 1,5 0,55 0,59 0,64 0,68 0,73 0,78 0,82 0,87 0,91
Shower 20 x 2,8 0,015 1,2 0,53 0,56 0,59 0,61 0,62 0,62 0,62 0,63 0,63
Flowmeter 1,50 32 x 4,4 0,052 3,5 1,60 1,71 1,81 1,92 2,02 2,12 2,23 2,33 2,44 1,5
0,20 0,5
22
COBRA-PEX TUBEMANIFOLD LOWEST PRESSURE VALUE CALCULATION
Manifold lowestpressure value
Tube
s w
hich
are
use
d fo
r the
cons
truc
tion
of re
mov
able
sys
tem
s
Bra
nch
leng
th in
dica
ted
in e
quiv
alen
t met
res
(from
man
ifold
to s
anita
ry fa
cilit
ies)
∆∆ p b
ranc
h [b
ar]
Flow
[l/m
in]
Flow
[l/s
]
R [bar/m]R [mm of c.a./m]
Water supply tube residual lowest pressure value
23
7.5. Removable systemsInspectionable supply systems arecommonly used in order to guaranteerapid and simple routine and specialmaintenance operations. As market needs have changed in thelast few years, passing from newhouse construction to old houserestructuring, besides consideringinstallation costs, it is also necessary toconsider working and maintenancecosts. Moreover, while restructuring abuilding, existing technologicalplants are generally replaced byothers with better characteristics,thus using new high technologymaterials and systems withoutunderground joints and installingcomponents which can be easilymaintained and replaced withoutdemanding additional costs.PE-X tube manifold water systems andsanitary facilities offer all theseadvantages. As it was previously seen, COBRA-PEXtubes offer the following advantages:corrosion and deposit resistance,soundproofing properties etc. Removable systems, besides havingall above-mentioned characteristics, aremanufactured by using high-flexibilitytubes which are coated with specialcorrugated sheaths (Art. 0800 EXTRA)in order to replace branches if necessary.This is certainly the peculiarity of thissystems. Following simple laying procedures,it is possible to remove damagedpipe from the sheath replacing it by anew one, without causing water leaksand breaking expensive ceramiccoatings which are not easily repairedor replaced.These systems, besides having thispeculiarity, offer other advantageswhich are typical of manifoldsystems.Parallelly-connected sanitary facilitysupply systems determine water tapconstant pressure value, thus avoidingundesired flow variations which aretypical of series-connected sanitaryfacility supply systems and which takeplace turning on many taps at the sametime. In this way, it is possible to achieve acold and hot water mixing ratio whichis more constant than that which isachieved by using other systems, asin the case of single-control taps orthermostatic mixing faucets.
COBRA-PEX tubes are coated withcorrugated sheath in order to speed up laying procedures and avoid possibledamages. Tube outer diameter and sheath innerdiameter ratio is calculated in order tofacilitate branch removal and favourthe absorption of pipe stresses whichare due to thermal expansions thanksto bending process.Even if these systems are mainly usedfor the construction of water systemsand sanitary facilities, they are alsosuitable for the construction of heatingplants and air-conditioning units in thepresence of heating bodies.Obviously, in order to easily removeand insert the pipe, it is necessary tofollow the simple laying proceduresindicated below which must also befollowed for sanitary facility installation: • do not se reduced bending radiuses• leave a certain distance at the end of
the branch to remove and later insertthe tube.
• seal the sheath along bending pointswhich are subject to stress after tubeinsertion.
All accessories which are necessary forthe construction of these systems havebeen specially designed to guaranteeeasy and rapid laying procedures. Besides high-flexibility COBRA-PEXtubes which, as it was previously said,
are coated with plastic sheath, it isnecessary to mention the threefollowing components: wall plasticsheath (Art. 1490) which is shown inPicture 29, sectioning double clamp(Art. 1491) which is shown in Picture30 and the 105° flange curve (art.1428), which is shown in Picture 31.
The clamp is used to support wallsheaths, adjust their insertion depthand connect outlet pipe fittings to acentre distance which is suitable fortaps and fittings which are available onthe market.
Picture 29
Picture 31
Picture 30
24
8.1. IntroductionCOBRA-PEX polyethylene tubes are notonly used for the construction of watersystems or sanitary facilities as it waspreviously seen, but they can also beused for the construction of civil buildingair-conditioning units, as it is shown in thischapter.In this case, unlike sanitary facilities, it isnot possible to make any calculationexample.This is due to the fact that air-conditioningunits are very different one from the otherand each of them distinguishes itselffor its dimensioning characteristics,consequently it would be necessary tomake long and thorough calculationexamples. This manual is not specifically used tocalculate system dimensioning, but it onlygives technical and practical informationwhich are necessary to use multilayertubes instead of other traditional tubes. Among the wide range of systems whichare used in European Countries, thefollowing four systems can be manufacturedby using COBRA-PEX tubes: radiantpanel, manifold and single tube systemsand systems which are provided with 2 or4 tube ventilating convector mobiles, withor without primary air systems.These systems can also be divided intoother groups; for example, radiant panelsystems can be divided into floor, ceilingand wall systems, etc.The considerations which have beenmade for general systems are extendedto all subgroups and, in conclusion, itcould be said that the purpose of thesetubes is similar to that of so-called“horizontal supply” systems which can besuccessfully used instead of metal orcomposite tubes.
8.2. Horizontal supply systemsThese systems are characterised byunder-floor pipes.Apart from radiant panel systems, havingspecial technical characteristics, horizontalsupply systems are divided into two largegroups: manifold and single tubesystems. Manifold systems are moredemanded than single tube systems onItalian market. As it is well known, according to manifoldsystems, all branches coming from and toan heating body, are connected in parallelto a single supply node (which is themanifold itself), while single tube systemsare characterised by supply rings whichare series connected to various radiators.
Without considering a system better thananother (according to the market,manifold systems are the best), it must benoticed that manifold systems arecharacterised by a wider under-floorsupply system.These branches are made up of small-sizedtubes which can be easily laid under-floor,but, in some cases, this system caninterfere with other pre-existing systems(such as, for example, electric sheaths orgrey water waste pipes, etc. ).In these cases, single branch tubes mustnecessarily get over obstacles as it isshown in picture 32.
In other cases, above all in case of slightrestructuring works without reconstructingfloors or if works are subject to certainconditions, it could be necessary to installskirting-board branches, thus crossingthresholds, doors or other similar obstacles– see picture 33.
In all these cases, apart from the kind of
system, siphons and counter-slopephenomena can take place, totally stoppingsupply system water circulation in thepresence of air.This is due to [a] counter-slope angleincrease and to pipe water flow speedreduction.The Table XII related to COBRA-PEXtube characteristics, according to pipediameter, fluid temperature and [a]counter-slope angle, shows lowest speedvalues which must be reached withoutfalling below them in order to avoid watercirculation stop. In other terms, besides speed limits whichhave been indicated, an air bubble wouldbe swept away and mixed wi ththermo-carrier fluid and it would bediffused in another point in the presenceof a speed reduction.As it is shown in picture 30, the air bubblewhich is present in the branch would beswept away by fluid following radiator ormanifold direction.In both cases, it would converge in twopoints and it would be easily removedthanks to speed reduction and in thepresence of air vent automatic or manualparts. Naturally, speed values which are shownin Table XII are included among theparameters which must be considered tocalculate horizontal supply systems, butas this section only analyses COBRA-PEXpolyethylene tube characteristics, seespecific calculation manuals for furtherinformation.
8. Air-conditioning units
picture 32
picture 33
25
8.3. - Manifold systemsAs the first manifold systems weremanufactured thirty years ago,system technical and practicalaspects have been thoroughly analysedand optimised.Metal and above all copper pipes aretraditionally used for the construction ofthese systems, instead of successfullyusing COBRA-PEX ret iculatedpolyethylene pipes.Besides guaranteeing a more rapidand cheaper laying procedure andbeing used for the construction ofremovable systems, PE-X tubes, as itwas previously mentioned, have thefollowing characteristics, which arealso necessary for the construction ofair-conditioning units: soundproofingproperties, dielectric resistance,lightness, lower inner surface roughnessand reliability. High density reticulated polyethylenetubes are also used for the constructionof the so-called “removable” systemswhich are described on page 23. The techniques and the componentswhich are used for the construction ofsanitary facility supply systems aresimilar to those which are used for theconstruction of manifold supplysystems.As in the case of water systems andsanitary facilities, it is necessary todefine the flow limits of COBRA-PEXtubes and pipe fittings which are usedfor the construction of manifoldsystems.With the help of pressure loss diagramwhich is indicated in the appendix, itis possible to determine pipe flowlimits and, considering thermal head,define thermal capacity which isguaranteed by every single pipe orbranch.
According to calculation parameterswhich usually refer to this kind of systems(∆tn = 15 °C – Vmax = 0,6÷0,8 m/s or a valuewhich determines a random noise whichis equal to </=30÷35 dBa), by using15 x 2,5 mm diameter tube, it could bepossible to meet civil heating plantthermal requirements.Thanks to wall boiler pump head, it ispossible to feed a 3500 Watt heating bodyat about 15 equivalent metre distancefrom the manifold (backward and forwardmovement is indicated in eq. m).This means that most of the componentswhich are used in the builder’s yard,such as tubes, pipe fittings and valves,can be standardised, thus reducingdowntimes and guaranteeing morerapid laying procedures.
8.3.1. Pipe fittingsIn case of air-conditioning units withmanifold supply system, under-floorbranches which are coming from andto heating bodies are made up of asingle pipe length without using anyintermediate joint.Manifold and adjusting and cut-offparts which are placed on heatingbodies, such as valves and lockshieldvalves, are located at the end of thesebranches.As the connections between the tubeand these components are alwaysvisible and inspected, it is possible touse mechanical compression pipefittings/adapters with lock nut – seepart [A] and [B].[A] Pipe fittings/adapters are used incase of male side connection manifoldsand for valve and lockshield valveconnection.In case of female side connectionmanifolds, it is necessary to use malestraight nipples (Art. 1400) – see Part [B].
[A]
Picture 34
[B]
Table XII [α] counter-slope angle
15° 30° 45° 60° 90°
T [°C] 15 80 15 80 15 80 15 80 15 80
10 0,10 0,15 0,11 0,20 0,12 0,22 0,15 0,25 0,18 0,30
12 0,11 0,18 0,12 0,23 0,14 0,25 0,17 0,30 0,20 0,35
14 0,12 0,25 0,15 0,30 0,18 0,35 0,20 0,40 0,25 0,45
16 0,15 0,30 0,20 0,35 0,22 0,40 0,25 0,45 0,30 0,50
20 0,20 0,35 0,25 0,45 0,30 0,50 0,35 0,60 0,40 0,70
Water flow speed [m/s]
Tube
inne
r dia
met
er [m
m]
26
8.4. -Single-tube systemsBesides manifold systems, other kinds ofsystems spread and they were characterisedby a heating body series supply systemwhich is achieved by using an under-floorsupply ring, rarely acting as a skirtingboard – see picture 35.This so-called single tube system wassuccessfully used in the past and eventoday it is widespread on an internationalscale. In case of manifold systems, eachbranch is dimensioned according toevery single heating body flow value,while in case of single-tube systems,supply ring must be calculated accordingto the flow values which are guaranteedby the radiators which are connected tothe ring itself.Consequently, it is necessary to usepipes whose diameter is up to 20 x 2 mm.Tube diameter must not be higher thanthis value for two reasons:
• the difficult connection betweentubes with a diameter which is higherthan 20 x 2 mm and single-tubevalves, which is due to the kind ofconnecting thread and centre distancebetween two valve connections.
• if single-tube ring flow is guaranteedby a tube with a diameter which ishigher than 20, it means that variousheating bodies or high-capacityradiators are connected to single-tubering.In both cases, as single-tube ring heatingbody supply temperature tends todrop, it is necessary to divide supplysystem into two or more rings whichare connected to areas with similarpurpose such as for example flatliving and sleeping areas.
8.4.1 - Pipe fittingsAs it was previously said in [8.3.1]paragraph, even in case of single-tubesystems, various horizontal supply systemlengths which are connected to heatingbodies, are made up of a single pipelength which is separated from the others.Even in this case, pipe fittings areconnected to single tube valves whichare placed on the radiators and at theseparating line from the boiler or themanifold.In any case, these pipe fittings arevisible and can be inspected, therefore[A] compression mechanical pipe fittings/adapters can be connected to the valvesand [B] male straight nipples can beconnected to supply ring terminals.
8.5. - Radiant panel systemsThanks to plastic pipe diffusion,radiant panel systems successfullydeveloped and spread.These systems, after having beenupdated according to modern planttechniques, are now used for roomheating and cooling. This manual is not used to makesystem dimensioning calculations,but, as it was previously said, it onlygives the information which arenecessary to correctly use COBRA-PEXpipes and relative pipe fittings andaccessories. Nowadays, in most cases, radiantpanel systems are achieved by usingplastic tubes.“Spiral” panel installation – picture 36–, unlike traditional “coil” installation,guarantees an uniform average floortemperature.Obviously, among system basiccomponents, tube plays a technicalrole and distinguishes itself for its“reliability”.User’s attention, in fact, is mainlyconcentrated on the tube which is thecrucial element which determinesplant duration.From this point of view, PE-X highdensity reticulated polyethylenepipes are successfully used for theconstruction of this kind of systems. As it has been experienced in the last
decades, PE-X tube reliability and lifecycle are compared with or considered even better than those of otherpipes which are commonly used inthe field of building trade.But, besides considering this basicaspect, it is necessary to mentionthat the kind of pipe which is usedalso provides other parameterswhich are necessary to guaranteesystem economy, including thermalemission per linear metre and easylaying procedures. COBRA-PEX tube easy installationis due to the following characteristics:tube lightness and malleability. It is clear that these aspects cansuccessfully affect working time; seeinitial sections for further informationabout tube characteristics. COBRA-PEX tube thermal emissionvalue per linear metre is equal to0,35 W/m°K; this value is lower thanthat of similar metal pipes. This does not mean that a radiantpanel system which is achieved byusing metal tubes has a thermalemission value which is higher thanthat of other systems. The parameter which mainly affectspanel thermal emission value is thesurface average temperature of thestructure where panel is located,such as floor, sometimes walls andrarely ceiling.
[A][B]
Picture 35
27
As in case of under-floor panels, thistemperature value cannot exceedprecise physiological limits, the choiceof a certain tube instead of anotherdoes not affect user’s comfort. According to the European regulationrelated to radiant panel systemdimensioning calculation (EN 1264),highest thermal emission value is equalto 100/Wm2 in covered area.
8.5.1 – Pipe fittingsAs in the case of commonly usedplastic tubes, radiant panel systemswhich are manufactured by usingCOBRA-PEX tubes are separated onefrom the other. Consequently, as it is shown in picture36, only the two ends of the panelwhich is connected to the manifold areprovided with a pipe fitting. As, as usual, manifolds and pipefittings are located in a special inspectionbox, it is possible to use pipefittings/adapters like those which areindicated in picture 36 by [A] and [B]letters. Pipe fittings/adapters are chosenaccording to the kind of manifold whichis installed.For example, in case of building damages,it is necessary to use an under-floorintermediate joint.In these cases, as pipe fitting is inevitablylaid under-floor, carefully install it, then
conduct an hot-testing and lay the pipefitting in a visible place [C].8.6. - Ventilating convector systemsThese systems, which are present inbuildings which are not strictly residential(such as offices, hospitals, shops etc.)are heating and cooling plants. If the ventilating convector which isinstalled is provided with a single heatexchange battery, traditional supplysystem will carry hot or refrigeratedwater during seasonal changes. Ventilating convector is provided with adouble battery in case of a doublesupply system: an hot water and a coldwater supply system. This means that in case of somebuildings, above all those which areprovided with large glass surfaces,some rooms can be heated and, at thesame time, other rooms can be cooledduring in-between seasons. These supply systems can be achievedin two ways: by using riser supply systemor an horizontal supply system which isconnected to one or more manifolds.Considering technical differences, seeconsiderations and manifold systemdiagram indicated in section 8.3; in factthese systems are similar, apart fromtheir different heating bodies. As regards technical differences, itmust be noticed that as these systemsalso guarantee room cooling duringsummer periods and as ventilating
convectors are convection dynamicheating bodies, [∆tn] nominal thermalhead value is much lower than that ofcommon radiator systems. Consequently, branch flows will behigher and tubes which are commonlyused have a 16 x 2,2 mm, 18 x 2,5 mmand sometimes 20 x 2 mm diameter. Considering system branch high flowvalues, as in the case of radiant panelsystems, manifolds with 1.1/4”diameter and 1/2” or 3/4” diameterventilating convector connections areused according to device size. In case of 1.1/4” diameter manifoldswith 3/4” diameter Eurocone male sideconnections, [A] pipe fittings/adaptersmust be used.In case of manifolds with 1/2” diameterfemale side connections, [B] pipefittings must be used.
8.7 - Final considerationsThis chapter briefly analysed thegeneral characteristics of most commonair-conditioning units which are presenton the market. COBRA-PEX tube rapid laying proceduresand easy installation, except for the case ofradiant panel and removable systems,are due to high density reticulatedpolyethylene pipes which are providedwith an insulating sheath as it isprescribed by the law.
Picture 36
[C]
[B] [A]
28
COBRA-PEX TUBE PRESSURE LOSS DIAGRAM AT A WATER TEMPERATURE OF 80°C
R [mm of c.a./m]
Flow
[l/h
]
29
COBRA-PEX TUBE PRESSURE LOSS DIAGRAM AT A WATER TEMPERATURE OF 10°C
Flow
[l/s
]
Flow
[l/m
in]
R [bar/m]R [mm of c.a./m]
TABLE FOR THE RAPID CALCULATION OF MANIFOLD INPUT LOWEST PRESSURE VALUES
Sink
Bidet 0,10 15 x 2,5 0,019 1,2 0,54 0,58 0,61 0,65 0,70 0,73 0,77 0,80 0,84 0,5
W.C. cistern
Dishwasher 16 x 2,2 0,026 1,4 0,55 0,60 0,66 0,71 0,76 0,81 0,86 0,92 0,97
Wash./machine 0,15 18 x 2,5 0,014 1,2 0,53 0,56 0,58 0,61 0,64 0,67 0,70 0,72 0,75 0,5
Washbasin 20 x 2,8 0,009 0,9 0,52 0,54 0,55 0,57 0,59 0,61 0,63 0,64 0,66
Bathtub 18 x 2,5 0,023 1,5 0,55 0,59 0,64 0,68 0,73 0,78 0,82 0,87 0,91
Shower 20 x 2,8 0,015 1,2 0,53 0,56 0,59 0,61 0,62 0,62 0,62 0,63 0,63
Flowmeter 1,50 32 x 4,4 0,052 3,5 1,60 1,71 1,81 1,92 2,02 2,12 2,23 2,33 2,44 1,5
Kind ofsanitaryfacility
Flow
[l/s]
Tube
diameter
P.I.
[bar/m]
V
[m/s]
Branch length [m] Residualpressure
value2 4 6 8 10 12 14 16 18
Table XI
0,20 0,5
30
COBRA-PEX TUBEMANIFOLD LOWEST PRESSURE VALUE CALCULATION
Flow
[l/s
]
Flow
[l/m
in]
∆p b
ranc
h [b
ar]
Bra
nch
leng
th in
dica
ted
in e
quiv
alen
t met
res
(from
man
ifold
to s
anita
ry fa
cilit
ies)
Tube
s w
hich
are
use
d fo
r the
cons
truc
tion
of re
mov
able
syst
ems
Water supply tube residuallowest pressure value
Manifold input lowest pressure value PN 16 pressure value
R [bar/m]R [mm of c.a./m]
31
Castegnato, September 23 1998
CONFORMITY DECLARATION
TIEMME RACCORDERIE S.p.a. firm, which is located in Via Cavallera 6/A – 25045 – Castegnato (Bs),and which manufactures hydrothermosanitary system parts, according to the regulations which are inforce and in particular:
• 46/90 Law – Art. 7 – “System safety rules”• P.D. n° 477 of December 6 1991 – Art. 5 – “46/90 Law enforcement regulations”
DECLARES
• that COBRA-PEX high density reticulated polyethylene tube is carefully manufactured by using a quality control method which is certified according to ISO 9002 – EN 29002 – cert. n° ER – 114/2/95 regulations.
• hat COBRA-PEX high density reticulated polyethylene tube is suitable for drinking water supply thanksto its non-toxic properties, according to the Cert. n° 99/96.
• that COBRA-PEX high density reticulated polyethylene tube is carefully manufactured according to UNI 9338 – UNE 53-381 – DIN 16892 Regulations.
• PE- X tube SERIES 1400 compression pipe fittings are carefully manufactured, being also available in DZR brass upon demand, and in the absence of a specific certification regulation concerning this kind of products, internal laboratory test and control procedures are followed.
TIEMME S.p.a.
TIEMME RACCORDERIE S.p.aVia Cavallera 6/A (loc. Barco) - 25045 - Castegnato (Bs) - Tel. 030 2140158 r.a.- Fax 030 2140180 - E mail: [email protected]
Via Cavallera 6/A (Loc.Barco) - 25045 Castegnato (BS) - ItalyTel. ++39 030 2142211 r.a. - Telefax ++39 030 2142206
E mail: [email protected]
It is
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with
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