7
Concord CXS -
Installation & Servicing
Particular reference should be made to BS. 6644: Section 2;
Subsection 10 and Guidance note PM5 "Automatically controlled
steam and hot water boilers" published by the Health and Safety
Executive.
The information and guidance given below is not intended to override
any requirements of either of the above publications or the
requirements of the local authority, gas or water undertakings.
Other British Standards applicable are BS.5422 & BS.6700.
The information provided is based on the following assumptions:
1.
An independent open vent/safety pipe connection is made to
the redundant boiler flow tapping or is positioned immediately
after the system flow pipe connection to the header, as shown.
2.
An independent cold feed/expansion pipe connection is made
to the redundant boiler return tapping. Cold feed/expansion pipe
connections made to the pumped system return will result in an
increase in the static head requirement, caused by the additional
resistance of the distributor tube. Surging may also increase.
3.
The maximum flow rate through the boiler is based on a
temperature difference of 11°C at full boiler output and the
circulating pump is positioned in the flow to the system.
4.
The boiler is at the highest point of circulation in the system.
Systems designed to rise above the boiler flow tappings will
automatically require a minimum static head higher than that
shown.
5.
The position of the open vent/safety pipe above the expansion
cistern water level is given as a guide only. The final position will
depend upon the particular characteristics of the system.
Pumping over of water into the expansion cistern must be
avoided.
GENERAL
Note A.
This minimum height must be increased, if
necessary, to comply with the minimum head
required by the pump manufacturer in order to
avoid cavitation.
Note B.
This diagram does not show safety valves, water
flow switches, etc., necessary for the safe
operation of the system.
PUMP POSITIONS
Whenever practically possible the circulating pump(s) should be
positioned so that it pressurises the system being served. The
vertical distance between the pump(s) and any cold feed and
expansion cistern MUST comply with the pump manufacturers
requirements in order to avoid cavitation. These requirements
override the information given in Frame 3 if the static head
required for the pump(s) exceeds that required for the boiler.
MINIMUM FLOW OF WATER - Refer to Table 5
The system design must provide for an adequate flow rate
through the boiler at all times when the boiler is firing. The
minimum flow rate should correspond to a temperature
difference across the boiler flow and return of 35
o
C (63
o
F),
assessed at catalogue rating.
WATER TREATMENT FOR HOT WATER AND
HEATING BOILERS
There is a basic need to treat the water contained in all heating
and indirect water systems, particularly open vented systems. It is
assumed, incorrectly, that because boilers are operating in
conjunction with what is apparently a closed circuit an open vented
system will not, under normal circumstances, allow damage or
loss of efficiency due to hardness salts and corrosion once the
initial charge of water has been heated up a few times.
1mm of lime reduces the heat transfer from metal to water by
10%.
In practice the deposition of these salts is liable to cause noises
from the boiler body or even premature boiler failure. Corrosion
and the formation of black iron oxide sludge will ultimately result
in premature radiator failure.
Open vented systems are not completely sealed from the
atmosphere if proper venting and expansion of system water is to
be achieved. The same tank is used to fill the system with water
and it is through the cold feed pipe that system water expands
into the tank when the boiler passes heat into the system.
Conversely, when the system cools, water previously expelled is
drawn back from the tank into the system together with a quantity
of dissolved oxygen.
Table 5 - Flow rates for fully pumped systems
Boiler
Minimum flow rates for a
temperature difference of 35
o
C (63
o
F)
l/s
g.p.m.
CXS 40
0.28
3.7
CXS 50
0.34
4.5
CXS 60
0.41
5.4
CXS 70
0.48
6.3
CXS 80
0.55
7.3
CXS 90
0.62
8.2
CXS 100
0.68
9
CXS 110
0.75
9.9
CXS 120
0.82
10.9
3 OPEN VENTED SYSTEMS - Minimum static head requirements
