6
Concord ESi
- Installation and Servicing
GENERAL
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 and 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.
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.
3 OPEN VENTED SYSTEMS - Minimum static head requirements
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 normal design 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.
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.
