Chaffoteaux & Maury CORVEC Series User manual

SYSTEMS
MANUAL
for
CORVEC
DOMESTIC
BOILERS
chaffoteaux~
et llhury AA

INTRODUCTION 1
W
1. INTRODUCTION
Chaffoteaux et Maury is one of the largest producers
of gas water heaters and boilers in Europe and one
of the oldest established manufacturers of these
appliances. Chaffoteaux et Maury have been design-
ing and making water heaters since 1919 and low
water content boilers since 1952.
The principle of the weil known instantaneous
water heater is not so different from that of the
central heating boiler - THEY BOTH HEAT
WATER - the former for direct use, the latter as
the medium for transmitting heat.
Comparing the functions of the two appliances it
is apparent that the water heater operates in less
favnlrrable conditions than the central heating
bc
The boiiers made by Chaffoteaux et Maury use a
row water content finned copper heat exchanger.
Why copper? - Why low w.ater content?
+
Copper is universally known and used as the best
material for conveying water, in addition it is both
easily worked and durable. Most important, it is
one of the best conductors of heat.
In the conventional boiler of cast iron or steel, the
boiler probably weighs 80 -. 100 Ibs. with a water
content of probably 20 1 40 Ibs. and it is evident
that there will be a delay whilst all this mass is
heated before the system responds. At the end of
a cycle the boiler dissipates the heat of this mass
some of it to atmosphere, through the flue, before
the thermostat responds and starts the cycle once
ag:
Low water COP+~
,&&nt coupled with light weight means
that we have a low mass resulting in a flexible and
responsive appliance, having efficiencies of 78% -
80%.
Since a boiler providing central heating is designed
to maintain room temperatures at an adequate
level when the outside temperature is - l°C -
(30°F) it follows that the boiler will only be
working under its design conditions for a few days
in the year, for the rest of the time it will cycle due
to its output being greater than the demand. With a
high mass boiler it is necessary on each cycle to heat
not only the water content, but the whole surround-
ing mass of metal. High mass boilers show a marked
drop in efficiency when working under part load
conditions. Low mass boilers, like the Chaffoteaux
boiler, show only a very small drop in efficiency
between full load and half load, between 3% and
4%. In a high mass boiler the drop in efficiency is
more usually about 20%. It has been suggested that
a domestic boiler works 80% of the time at about
30% of load, part load efficiency is therefore
vitally important.
Today with the continual raising of fuel prices and
the depletion of natural resources, it makes sense
to use low water content boilers.
Our boilers are suitable for either open or sealed
systems but because of their construction must be
used on fully pumped systems. All commonly used
external system controls can be used.
This Guide is not a substitute for Installation and
Servicing Instructions which accompany each
boiler. Before going ahead with your first installa-
tions please study that booklet.
This publication is not intended to be a text book
on central heating but, it is hoped that the informa-
tion it contains will help the reader understand our
appliances and that the tables and data will be of
daily use.

2 PRINCIPLESOFOPERATIONOF
CHAFFOTEAUXETMAURYAPPLIANCES
2. PRINCIPLES OF OPERATION OF
CHAFFOTEAUX ET MAURY APPLIANCES
The operation of all Chaffoteaux domestic range
boilers is the same, the units depend on water flow
through the appliance for their operation. It is a
safety feature of the boiler that it will not fire
unless there is a sufficient flow of water.
The minimum flow rates for all models are such
that the boilers can only be used on fully pumped
systems and not with gravity systems.
Water enters the boiler via the return pipe and flows
through the heat exchanger. It then enters the
vent’4 (1 ), across the thermostat (2) and out of
the w pipe (3). When the boiler is firing the
the stat capsule (2) closes a by pass (5) and the
venturi creates a pressure difference in the water
section which lifts the diaphragm (6) against the
gas valve spring (7) pressure. When the temperature
of the water reaches the pre-set value of the
thermostat capsule the capsule lifts off its seat (2a)
and allows the by pass (5) to open. The pressure
difference across the diaphragm is equalised and
the gas valve spring closes the gas valve. The shapes
of the gas valve and thermostat capsule ensure a
modulation of the burner flame.
The thermostat capsule operates at a pre-set
temperature of 82°C and no adjustment is necessary.
The range of boilers utilise a non-electric multi-
functional control that provides all the necessary
interlock features required by current Standards.
With the consumer’s control in the ‘off’ position
(A) no gas can reach the pilot or main burner
i;res, :ive of the operation of the water section.
Wht ;ie consumer’s gas control is turned to pilot
position (B) gas is allowed to flow to the pilot head
and simultaneously a spark is produced to ignite
the pilot flame. The pilot flame heats the thermo-
couple (8) which energises the electromagnet (9)
holding open the thermoelectric valve. When the
pilot is established the consumer’s gas control can
be turned from the pilot to the main gas position
(C) allowing gas to flow to the underside of the
main gas valve (10). The operaticn of the water
section will now determine when gas is allowed
to flow to the burner.
The boilers incorporate standard safety features
throughout the range:-
i) The water section only allows the gas valve
to operate when the correct flow of water is
passing through the appliance.
NO WATER FLOW MEANS NO GAS.
ii) The thermocouple and thermoelectric valve
ensure that no gas can pass to either the
pilot or main burner in the event of pilot
failure.
iii) A high limit temperature overheat is provided
in the form of a fusible link (11) which, if
ruptured, interrupts the circuit to the thermo-
electric valve and isolates gas from the pilot
and main burner.
iv) An interlock is provided so that, if the pilot is
extinguished for any reason, the boiler can
only be refired by repeating the lighting
sequence. The relighting sequence can only be
attempted after a delay of about one minute.

VENTURI
FROM HEAT
EXCHANGER
THERMOELECTRIC VALVE
GAS & WATER SECTION
TO BURNER
t.
FLOW TO SYSTEM
DIAGRAMATIC ONLY
NOT TO SCALE

HEATLOSSES
3. HEAT LOSSES
Before a central heating system can be designed it
is necessary to define the parameters on which the
design is to be based.
The consumer should be made aware that once
installed it will not be possible to increase the
internal ‘temperatures without the installation of
additional heating media.
Generally, in the UK, domestic heating provides
agreed internal temperatures at an external tempera-
ture of - 1°C (30” F).
It may be necessary to consider a lower design
temperature in Northern England and Scotland, or
if the property is on the coast or exposed to high
L k.
I. * current recommended internal temperatures
and air change rates are given in Table 2. Where
bedrooms are likely to be used as a study or play-
room it is as well to provide a higher temperature
of, say, 18°C (65°F).
TABLE 1.
(BS 5449 Pt. 1: 1977)
Temperatures and rates of air changes on which
heat loss calculations should be based.
* These temperatures will only apply for whole
house central heating and for heated rooms
with part house central heating.
t Local building regulations may require a specific
rate of air change for particular rooms.
tt When used part time as bedsitting rooms or for
study purposes additional means should be
provided for maintaining a higher room tempera-
ture.
9 Where continuous mechanical ventilation is
provided due allowance for the greater change
should be made.
Perhaps at this stage it is as well to remember that
mar’, of the mechanical aids available and the ‘rule
Of
lb’ methods are less than accurate and could
result in user dissatisfaction and in the final analysis
*
there is no substitute for proper heat loss calcula-
tion. This has the added advantage of highlighting
the areas of greatest heat loss and gives the designer
the opportunity to consider additional insulation.
It also brings to the designer’s attention, by high-
lighting areas of greatest loss, the positions for
radiators.
The heat loss of a room is based on three criteria:-
1) Area of components of the structure - walls,
windows, floor, ceiling.
2) The conductivity of the component (expressed
as a ‘U’ value).
3) The temperature difference between the two
faces of the structure.
Common ‘U’ values are set out in Table 5. and
worked example is shown.
An alternative to using a lower external temperature
for properties in exposed positions is to use a per-
centage addition as set out in Table 2.
TABLE 2.
I
Orientation I Normal 1 Exposed 1
NORTH 10% 20%
EAST 10% 15%
WEST 5% 10%
SOUTH - 5%
Before commencing the calculation carefully note:-
1) Orientation N. S. E. W. facing.
2) The construction of the building component.
3) The measurements of the component.
4) The temperature of adjacent areas.
In semi-detached and terraced houses the prudent
designer cannot assume that the adjoining building
will be heated to a certain standard and it is
customary, in these circumstances, to assume a
temperature in adjoining areas of 4O (40°F).
As well as the losses through the structure, heat
is lost through the air changes in the room. Air
change rates are given in Table 1.
To obtain the heat loss by ventilalation multiply:-
Volume of room in m3 or it3
by
number of air changes/hour (from Table 1)
by
factor given in Table against the temperature
difference fI T external to internal air.

TABLE 3. TABLE 4.
I
Temp difference A t 1 Factor 1
I 12 I 0.0036 1
t
I
19 1 0.0057 I
I
22 I 0.0066 I
Temp. difference A t
Factor
in “F
20 0.386
25 0.460
30 0.552
1
I
40 I 0.736 I
EXAMPLE
(based on Table 3.)
Room 3 m x 4 m x 2.4 m = 28.8m3
2 Air changes - 22°C t
28.8 x 2 x 0.0066 = 0.380 kW
EXAMPLE
(based on Table 4.)
Room 9.84 ft x 13.12 ft x 7.87 ft = 1016 ft
2 Air changes - 40” F t
1016 x 2 x 0.736 = 1495 btu/h
TABLE 5. Building Heat Losses
HVCAhHVE Guide to Good Practice
Usi = The number of watts that will flow through Uimp = The number of btu/h that will flow through
each square metre for each degree C. each square foot for each degree F.
difference between the internal and ex-
ternai temperatures in the case of external
walls, or in the case of partition walls
between the temperatures on either side
of the wail.
I‘ 351 ” (13% ” )
Cavity (two leaves brick, air space
and 16 mm. plaster)
Both leaves brick (11” nominal)
As 5, outer leaf 220 mm.
(9” nominal) brick
Cavity as 5, inner leaf 100 mm.
(4”) insulating concrete
As 7, outer leaf 220 mm.
These U values are
average figures and
apply to most suburban
and country dwellings.
For North and North-
East exposures on hill
sites, at the coast or
at riversides, however,
Single glazed, wood frames
105 mm. brick, plastered 16 +
16 mm. (4%” nominal)
220 mm. brick (9” nominal)

! Item
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
L-
37
38
CONSTRUCTION Usi Uimp Remarks
Plaster ceiiing, asphalte on
100 mm. (4”) concrete
ROOFS (pitched)
Tiles on boards and felt
Plaster ceiling, roof space above,
tiles on battens
tiles on boards and felt
Plasterboard ceiling, roof space
above
3.41 0.60
2.75 0.48
2.98 0.52
1.92 0.34
tiles on battens and felt
No insulation between joists
25 mm. (1”) glass fibre between
joists
50 mm. (2”) glass fibre between
joists
A
The full difference
between internal and
external temperature
should be taken.
Allowance has been
made for the fact
that the underside
temperature will be
higher than the
external temperature.
75 mm. (3”) glass fibre between
joists
50 mm. (2”) vermiculite between
joists
2.50 0.44
0.90 0.16
0.55 0.10
0.39 0.07
0.88 0.15
GROUND FLOORS
Ventilated wood floor on ioists,
air brick on one side
bare boards
parquet, lino or rubber
Air brick on more than one side
bare boards
parquet, lino or rubber
Solid floors in contact with earth
0.61 0.11
0.59 0.10
0.82. 0.14
0.68 0.12
0.36 0.06
These heat losses are
for a medium 15 x 7.5
metre (1000 ft.2 1 plan
detached house.
Decrease by 50%
for a terraced house.
Increase by up to 25%
for a small house of
5 x 10 m. (500 ft.2) plan.
INTERMEDIATE FLOORS
Wood floor on joists, plaster
ceiling
downward transmission
upward transmission
Concrete 150 mm. (6”) with
100 mm. (2”) screed
downward transmission
upward transmission
Concrete 150 mm. (6”) with
wood flooring
downward transmission
upward transmission
1.50 0.26
1.70 0.30
2.20 0.39
2.70 0.48
1.70
2.00 0.30
0.35
Effect of Fabric insulation
The following tableshows examples of the approxl-
mate reduction in heat flow resulting from insula-
tion:-
IFabric/ Type of 1 Reduction of 1
Ceilings
Cavity wails
Insulation
3” glass
fibre
foam
heat flow
80%
Susoended insulation
2,I

-EXAMPLE OF HEAT LOSS CALCULATIONS
-A
N
W E I 3*..m I I
Temperature in
adjoining area
16°C (60” F)
Temperature in
5 II 0
I
00
I’
000 2.59 m
- I I I--I------II- IS.5 ft)
‘U’ value S.I. ‘U’ value Imp.
SEE TABLE 5 w/m2 /“C btu/ft2 /” F
I External walls 11” cavity
(un-ventilated)
1.50 0.26 ,
I
Internal walls 3” breeze plastered both sides 2.25
Window - single glazed, wood frame 4.30 0.79
Ceiling - wood floor above ceiling, plastered 1.70 0.30
I I I
Floor - solid I 0.36 I 0.06 I
Exposure - Normal. internal temperatures 21 “C (70°F) @ - 1“C (30°F) external.
EXAMPLE
Heat loss - SI units
Component Area
A t Construction ‘U’ Loss
from Table
Wall N 4.26 m x 2.59 m 11.03m2 22 4 (1.5+ 10%) 400
1.65
Wall W (3.66 m x 2.59 m) -(window) 7.29m2 22 4 (1.5+ 5%) 252
(2.19 m2) 1575

Heat Loss - IMP. units
Component Area A t Construction ‘U’ Loss
from Table
Wall N 14’ x 8.5’ 119 ft2 40 4 (0.26 + 10%) 1333
A 90
Wall W (12’ x 8.5’) - (window) 78 ft2 40 4
ICI . A’\
1 U.LO I
1 (0.26 + 5%) 1 842 I
.
IO x41
0.27
Wall E 12’ x 8.5’ 102 ft2 Nil - -
Wall S 14’ x 8.5’ 119 ft2 5 15 0.40 238
,O 9 0.79 758
168 it2 1 40 32 0.06 403
16Rft2 I lfl .34 0 30 wM
Glass 6’ x 4’ 24 ft2 1 4
Floor 14’x 12’
Ceiling 14’x 12’ .-- -- - - . t -.-- I V”T
Air change 14’ x 12’ x 8.5’ 1428 ft3 1 40 1 - 1 Factor from 1 1052
I
lx I I I (Table4 0.736 5129
btu/h
‘JB The very small discrepancy is due to ‘U’ values & dimensions being worked to 2 places only

SYSTEMDESIGN 4
4.1 RADIATOR SELECTION
Having determined, by calculation, the heat losses
it is the time to select a radiator/heat emitter to
satisfy the heat loss.
Radiator manufacturers, in their catalogues,
generally show an emission based on mean water
temperature 170” F.
On full load the temperature difference across a
Chaffoteaux boiler is 20°C (36°F) i.e. a flow
temperature of 82°C (180” F) and a return tempera-
ture of 62°C (144” F). The mean water temperature
is therefore
‘F = 72°C (162°F)
It is, therefore, necessary to adjust the radiator size
in order to achieve the required output and the
multiplying factors are shown in Table 6 and a
worked example is also given.
TABLE 6.
1
21°C I 1.08 J
EXAMPLE
Room Heat loss
for 21 ‘C/70” F
7018 x 1.08 =
7018 btu/h
7579
Select radiator with output of 7579 btu/h. @ 55°C
(100°F) AT.
are taken to the source of the greatest heat loss. See
Fig. 1. By so doing one can avoid col’d draughts at
low level. The word ‘radiator’ is a misnomer, for a
radiator is, in the main, a convector, approximately
70% of the output is in convected heat and only
30% in radiant heat.
Radiators should be placed on wallswith a minimum
distance beneath them of 4 in. No shelf, sill or
other obstruction should be closer than 2 in. above
and should not protrude more than half the width
of the radiator. If it does an additional 10% should
be added to the output to allow for this. Ensure
there is no obstruction to the passage of air over the
rear surface of the radiator, i.e. protruding skirting
board, mouldings etc.
Where full length curtains are likely to be closed in
front of a radiator it must be remembered that a
space of 4 in. should be left in front of the radiator
to allow passage of air across the front surface.
Likewise there should be a 4 in. space between the
bottom of the curtain and the .floor and a similar
space at the top. See Fig. 2.
To obtain the best entrainment it usually, but not
invariably, means that radiators are placed under,
or adjacent to, windows.
When a shelf is used because a radiator is on an
inside wail and it is necessary to make a provision
to prevent ‘pattern staining’ (dust entrained in the
rising air stream which is deposited on and discolours
walls above radiators) recommendations are shown
in Fig. 3.
We have also shown various types of radiator
enclosure and the suggested additional output for
which allowance should be made. See Fig. 4.
In large or irregular shaped rooms two or more
radiators should be considered to provide the best
comfort conditions.
Radiator Positioning
The best air ‘entrainment’ is achieved if the radiators
HEATED AIR
/
DISCOMFORT

f
FULL LENGTH RADIATOR SHELF + 5% to 10%
WINDOW
RADIATOR
FOAM SEAL
BETWEEN
SHELF &WALL
FIG. 2. FIG. 3.
ENCLOSED RADIATOR + 20% to 30%
tici. 4. ACCESS FOR AIR
GRILLE
NB. Make provision for access to valves.
Provide access for venting radiator.
4. 2 PIPE SIZING
Chaffoteaux boilers are suitable for either one pipe
or two pipe systems but, in each case, the pipework
must be correctly sized.
1) So that there is sufficient volume of water
passing through the radiators compatible
with their output.
2)
So that there is a sufficient flow of water
through the boiler so that the boiler achieves
full flame.
3) So that the total system resistance falls
within the range of the domestic circulators
(pumps) available.
The deficiency with a one pipe system is that there
is a temperature drop as the circuit progresses. The
last radiators on the loop will receive cooler water
than the first and, therefore, the mean water tem-
perature will be lower so it will be necessary to in-
crease the radiator size to achieve output. Generally
a one pipe loop in 15 mm should not be designed
to carry more than approximately 20,000 btu/h.
A one pipe circuit is illustrated in Fig. 5.
There are available single entry radiators which are
suitable for one pipe systems when used in conjunc-
tion with a special radiator valve which incorporates
4) So that the water velocity in any part of the
system does not exceed 1m/set, (3ft/sec) for
small boreand 1.2m/sec, (4ft/sec), for micro-
bore.
a by-pass.
FIG. 5. P
ONE PIPE SYSTEM
I
J
RADIATOR
BOILER
ISOLATING
. ..-
VALVt m
7
BOILER %AX 150 mm
(6 ins)
- ‘rn
TAILS SHOULD BE AS
SHORT AS POSSIBLE I
RADIATOR RADIATOR A
\
I
PREFERRED ARRANGEMENT SWEEP 7’
IN DIRECTION OF WATER FLOW BETWEEN Ts SHOULD BE AT LEAST
EQUAL TO THE LENGTH OF THE RADIATOR

FIG. 6.FIG. 6. TWO PIPE SYSTEM
TWO PIPE SYSTEM
FIG. 7.
RADIATORRADIATOR
BOILER
I I
SECTION 1 SECTION 2
I I SECTION 3
I
i
TWO PIPE - REVERSED RETURN
RADIATOR
RADIATORRADIATOR RADIATORRADIATOR
I I I I I lllll
1 A
\ -
I I
- \ I
-
NE. In a revened return wstem the pipe resistance to each
radiator is the same. No balancing is usually required.
The preferred layout is a two pipe system. It will
be seen that the volume of water which flows in
Section 1 is greater than that in Section 2 which
itself is greater than in Section 3. The size of the
pipes should take this, into account. Two pipe
systems are illustrated in Figs. 6 & 7.
This would seem an appropriate time to remind
ourselves that pipework should be graded towards
the radiators and the open vent. Any inverted loops,
which should be avoided are provided with an air
vent and provision is made at any low point to
drain the system.
Where practicable pipes should be fitted clear of
timber joists. If a joist is notched it should not
exceed 15% of the depth of the joist. (10” joist
maximum depth of notch 1Y’z”).
Notches in the same joist shall be at least 4” apart
horizontally. Notches should be lined with pads of
felt to minimise noise. Consideration should be
given to the inclusion of protective saddles to
prevent damage by nails.
Pipe fixings and supports should be fitted at
intervals not exceeding 1.8 m (6 ft.), in exposed
or vulnerable positions the interval between pipe
fixings should not exceed 1.2 m. (4 ft.).
Pipework passing through structure should not be
built in but should be provided with a sleeve.
All pipes not emitting useful heat should be
insulated.
Before the pressure drop (resistance) of the system
can be calculated it is necessary to establish the
volume of water required in the various circuits.
The flow in Ibs/h is derived from the following
formula:-
Circuit heat output (btu/h) = Water flow in Ibs/h.
Temperaturedifference (36°F)
When working in S.I. units the flow rate is expressed
in kg/set and is derived from the tollowing:-
Circuit heat output in kW x 0.238 = kg/set
Temperature difference (20°C)
The velocity in small bore copper pipes should not
exceed 1 m. set (3 ft. set).
The resistances for straight pipes are given in Tables
9 & 10. It is also necessary to know the resistance
for fittings. The best way of calculating this is in
terms of equivalent length of straight pipe.
Some of the more usual fittings are shown in Tables
ll& 12.
The equivalent length for reduced ‘T’s motorised
valves, radiators etc. can be obtained from the
manufacturer’s literature.
There are two worked examples, one for a one pipe
system and one for a two pipe system.

Velocity
in
excess
of3m
secretary
Velocity
in
excess
of1m
secretary
Size

RESISTANCE OF PIPE FITTINGS
TABLE 11
Expressed in equivalent length of straight pipe in metres
I
Equivalent length in feet I
Type of fitting
TABLE 12
Expressed in equivalent length of straight pipe in metres
Valves
Equivalent length in metres
Type of fitting 15 22 28
Straight 0.30 0.30 0.60
Angle 1.6 4.3 6.00
Copper elbow Capillary 0.60 1.oo 1.30
Compression 0.30 0.30 0.60
Tee branch Square
Sweep
I I
1.oo 1.60 2.00
0.60 ‘1.oo 1.oo
EXAMPLE
ONE PIPE SYSTEM
5000 btulh
A one pipe system has load of 17,000 btu/h.
Temperature difference is 36°F.
System has 80’ of 15 mm pipe.
Heat emission from 15 mm pipe assuming 90°F
above room temperature is 36 btu/h per ft. -
Table 7.
Therefore heat load = 17,000 btu/h + (80 x 36
(pipes)) = 19,880
From table by interpolation resistance at
552 lb/h = 0.29 in p.ft.
Fittings 6 sweep Ts Eq. L 12 ft of pipe
12 elbows #I 24 ft of pipe
6 angled valves ” 30 ft of pipe
3 straight valves ” 3 ft of pipe
Equivalent length of fittings 69 ft of pipe
Actual lencth of oioe 80 ft.
Water flow =y = 552 Ibs,h Total pipe & Fittings 149 ft
Resistance = 149 x 0.29
= 43.5 in or 35 ft 7.5 in head.

’ TWO PIPE SYSTEM
8 ft.
q
I I
4 .8000 btulh
I I
SECTION 6
Consider layout and determine the index circuit.
The index circuit is the circuit with the highest
resistance which often means the circuit with the
highest load.
Index circuit is ground floor circuit to rad. 3.
Section A - (Rad. 3 to junction Rads. 4/5)
Load for rad . . . _. . . . . . . . . . . . . . . 16,000 btu/h
! d for pipes 30 ft of unpainted 15 mm pipe
Room 70” F - mean water 162“ F
Therefore temp. difference A t =
92: F
Emission from pipes from Table 7.
(90°F At = 36 btu/h/ft)
(99OF A t
= 41 btu/h/ft)
By interpolation
92°F At = 37 btu/h/ft
30 ft x 37 btu/h/ft . . . . . . . . . . . . . 1,110 btu/h
Total Load for section . . . . . . . . . . . 17,110 btu/h
Convert to Ibs/h 17,110 btu/h = 475 Ibs,h
36”FAt
From Table 9. resistance of 15 mm pipe=0.22
in.w.g. per ft. Length of pipe = 30 ft
(Equivalent length of fittings)
4 elbows = 8ft
2 L valves = 2ft
c /alent length of pipe
I section = 40 ft
Resistance in section = 40 x 0.22 in = 8.8 in.w.g.
Section B
Load - Previous Section . . . . . . . . . 17,110 btu/h
Rads4 & 5 . . . . . . . . . . . _. . . . . . . . 11,000 btu/h
Pipes46 ft. x 37 btu/h . . . . . . . . . . . . 1,702 btu/h
29,812 btu/h
Convert to Ibs:- 29812 btu/h = 828 Ibs
36At
15 mm pipe resistance 0.58” per ft.
Length of pipe = 24 ft. (No fittings).
Resistance = 24 x 0.58 = 13.92 in.w.g.
Section C
Load - Previous sections . . . . . . . . . 29,812 btu/h
Load for 1st floor:-
Rads . . . . . . . . . . . . . . . . . . . . . _. . . . 7,000 btu/h
Pipes - 76 ft. x 43°F per ft. . . . . . . . . 3,268 btu/h
Since room temperature is lower
At is higher.
Therefore pipe emissiokhigher.
Room 60°F - Mean water 162°F
At= 102°F
Load for section . . . . . . . . . . . . . . . . 40,080 btu/h
Convert to Ibs:- 40080 btu/h
36At
= 1l 13 Ibs
(Max. load in 15 mm 1100 Ibs use 22 mm pipe)
22 mm pipe resistance at 1113 Ibs/h = 0.17 in.w.g./ft.
Length of pipe 10 ft x 0.17 = 1.7 in.w.g.
..

Section D
Load - previous sections . . . _. . . e. 40.080 btu/h
Hot Water. . . . . . . . . ; . . . . . . . . . . . . 8,000 btu/h
Pipes 15 mm 20 ft x 37 btu/ft. . . . . . . . -740 btu/h
Pipes 22 mm 14 ft. x 34 btu/h/ft. . . . ; -630 btu/h
49,450 btu/h
Convert to Ibs 49,450 btu/h = , 373 ,bs
36.At ’
Length of pipe ‘14 ft. x 0.21 in.w.g./ft. = 2.9 in.
SUMMARY
Total flow 1373 Ibs/h.
1 gal. weighs 10 Ibs.
Flow in system = 137.3 gph
= 2.28 gpm
Resistance = 8.8 in.
13.92 in.
1.7 in.
2.9 in.
17.32 in. = 2.27 ft.
Minimum required flow through Maxiflame boiler
is 2.6 gpm at which the head loss = 5.5.ft.
. Required pump duty = 2.6 gpm against head loss.
of 7.77 ft.
FIG. 8. .
MICROBORE SYSTEM
BOILER
L
e
.:,.:
-.
ZAX
15Omm
(6 ins)
SMALL EORE PIPES
MICROBORE PIPES
Chaffoteaux boilers are suitable for use with micro- housing. The pipework can be laid in the screed,
bore systems. The essential feature of a microbore with proper provision for insulation, lateral and
system is that each radiator is connected in parallel linear expansion and of course draining. The advan-
back to a central manifold using 6 mm, 8 mm, or tages are that lengths can be laid without there
10 mm soft copper pipes. being joints in the screed.
A typical system is illustrated in Fig. 8. Pipe losses
and resistances are given in tables 13, 14 & 15. A
worked example is also provided.
The velocity in the pipesshould not exceed 4 ft/sec.
- 1.2 m/set.
The advantage of microbore systems is more evident
in new housing with solid floors than in older type

TABLE 13
TABLE 14
Microbore Flow of
water at 150°F through copper pipes.
Microbore
’ Flow Rate
1 kc/s
Bminalpipe size OD
8mm 10mm 12mm
182 46 21
210 55 28
245 68 34
285 81 40
325 94. 47
360 107 53
405 120 60
1~4485 1325 536
1670 665
2030 795
2410 925
2830 1080
3280 1235
3780 1408
- 1710 ’
1860
T..2030
: 2220
2365
2540
r2785
Velocity
1.5 m/s .
Loss of head
:__ per 1 foot run in inches :
Flow Rate WG (62°F)
lb/h Pipe size -
6mm o.d. 8mm o.d. IlOmm o.d.
50 0.86 0.20 I n 05
-.’
60 1.10 0.24 0.06
70 1.38 0.29 0.08 m,
an 171 0.10.
90’ 2.08 0.41 012
100 2.51 0.47 : 0:“14.
110 2.98 0.55 1 Of16
120 3.48 0.65 1 0.110
130 4.02 0.76 I IT91
In the absence of data
I
this table can be used
for light gauge steel
pipes
If an approximation,
based on velocity, is
TABLE 15
Microbore
I
Type of fitting Equivalent length
6mm 8mm 10mm
Two angle valves or one twin angle vaive 5.00 6.00 9.00
Minimum radius smooth bend 0.25 0.25 0.50
Manifold connection 2.00 2.00 3.00

r \
EXAMPLE
MICROBORE
7,000 btu/h
“PPElA FL!OOFl IIIlI[
;.
--
- EQihV. OF 20 ft. EQUIV. OF 40 ft.
OF 22 mm TUBE. OF 22 mm TUBE.
Section 1
Load - Rad & pipe losses 7,000 btu/h
Flow in Section 4 7 000
L = 194 Jbs/hr
36OFAT
Resist, 0.4 in.w.g. per ft.
60 x 0.4 = 24 in.
Section 2
Load - Rads & pipework 22,000 btu/h
Flow in section 22,000 = 611 Ibs,h
36”FAT
Resist.0.034 in.w.g. per ft.
40 x 0.034 = 1.36 in.
Section 3
Load - Rads & pipework 30,000 btu/h
Flow in section 30,000
- = 833 Ibs/h
36OFAT
Resist. 0.09 in.w.g. per ft.
20 x 0.09 = 1.8 in.
System requirement 1.38 g.p.m. against 27.16 in.
4.3 PUMP SELECTION
Having designed your circuits and selected the pump
by reference to the pump manufacturer’s graphs,
the pump position relative to the cold feed and
open vent must be decided.
it is essential that the designer ensures that:-
1) Water is not expelled over the open vent.
2) No part of the system is under sub-atmospheric
pressure.
The point at which the cold feed enters is called
the neutral point.
At this point the pressure is constant and is not
affected by the flow of water round the system. At
all other parts of the system the pressure is a
combination of the pump head plus the static head.
By reference to the pump manufacturer’s graph
against the flow rate for the system, the available
head will be indicated. This is the head available on
the outlet to the pump. This head is gradually
reduced by the resistance of the system until one
arrives at the inlet side of the pump. Most pump
manufacturers require a minimum of 6 ft. static
head at the pump inlet.
PUMP PERFORMANCE AT 240V 82’C 1
(180°F) >
Q)-
-7-F E
t
t;’
~~ LITRES SEC 0.5 1.0 _ 1.6;~
I
GPM )” 8 I I I
12. 16r; ‘i&g
_‘.
1.2 gpm ;:
FIG 9.
Fig. 9 shows the graph for a typical domestic pump.
Let us assume that the heating load is 26,000 btu/h.
The volume of water we will require the pump to
pass will be:-
Flow rate: 26,000 btu/h = 722 ,bs,h
36°F temp. diff.
72 Ibs/h -1 .i;iats per
‘.
10 (Ibs in gal) x 60 (minutes)
.fnin. (GPM).
~“- I -.
At ,I .2 .GPM available head on setting-4 :is approx.
14ft. .: ..
At .1.2 GPM the head loss through the boiter is 4 ft.
of head.
Let us also assume that the system resistance is
5 ft. of head.
Figs. 10 to 13 show the pump in various position ,..
relative to the cold feed and open vent.
Since the temperature at which water boils is’
directly dependent upon pressure - the-higher the
pressure the higher the boiling point..See*Tabte 16.
If -the water in the heat exchanger approaches’
boiling point or actually boils the results are boiler
noise (kettling) or possible damage to-the heat.
exchanger. It is, therefore, important. to obtain
the highest possible pressure in the boiler.
System 1 The pressure at the open vent is always
higher than the static head so the system
will always pump over.
System 2 Pressure in boiler is always less than the
static head. The open vent will suck in
air when the static head is 4 ft. or less.
System 3 Open vent pressure is always the same
as the static head so no pumping over or
air sucked in.
System 4 Preferred position - Highest pressure in
boiler. Open vent pressure always the
same as the static head - no:pumping
over or air sucked in. .

--H-==-l
Ii-7
mwr------ ----
I-
FIG. 10.
‘1 PRESSURE AT
&- BOILER OUTL,ET 1
j *- I I
! ,I I _ _...I.
1 _..
I
I
(~+p==y
801 LER OUTLET
FIG. 11.
, FIG. 12. FIG. 13.

TABLE 16
Atmospheric pressure 14.7 psi.
4.4 COLD FEEDS AND OPEN VENTS
The movement of water in the open vent is relative
to the circuit resistance between the cold feed and
open vent - the lower the resistance the lower the
risk of introducing aerated water into the system
when the pump starts and stops. For this reason
Chaffoteaux recommend that the cold feed and
open vent are placed within 6 in. of each other on
the inlet side of the pump. The .order in which
connections are made is not critical but the pre-
ferred order is cold feed, open vent, pump.
Preferred layouts are shown in Figs. 14 to 16.
Since one of the functions of the open vent pipe is
to vent to atmosphere air circulating with the water,
it is recommended that a low velocity point is
formed. It should be appreciated that, if the open
vent connection is made horizontally into the side
of a pipe, then it is unlikely that the air will be
vented. See Fig 18. The open vent pipe MUST rise
throughout its entire length from its junction with
the system to atmosphere over the expansion tank.
1
Boiling “C ’
113.4
116.2
118.7
It is strongly recommended that an arr separatoc
is used. Their efficiency is due to the reduction in
the water velocity and to the special, movement.
given to the water. They are most:.efficient in
reducing commissioning time and pump failures
and adding to the life of the boiler. .‘-J
1..a-., ‘.
,.v
As a minimum an expanded ‘T’ should be used.as
Fig. 17. “. g:.,<..,
Chaffoteaux recommend that the pump is-placed
in the return. In this position, with” the-. cold
feed and open vent entering on the low pressure
side of the pump as illustrated, one achieves the
following:-
1) Avoids pumping over and air entrainment.
2) Pump in coolest water-for better performance.
3) All the system will be under positive pressure.
4) Highest pressure in the boiler.
The effect of high pressure in the boiler is to ir
crease the boiling point of the water and avoib
kettling. .