f)
The following paragraphs outline the specifications of the items
fitted to the appliances.
PUMP -
The available pump head shown in Figure 6 is that in excess of
the appliance hydraulic resistance, i.e. that available for the system.
0
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
0.5
1
1.5
2
2.5
3
3.5
4
Flow Rate ltr/min
Pr
es
sur
e Dr
op (m H
2
O)
6
APPLIANCE HYDRAULIC RESISTANCE
VBX 30
VBX 18
DRAINING TAP
3.8
A draining tap must be provided at the lowest point of the system, which
will allow the entire system and hot water system to be drained.
Draining taps shall be to the current issue of BS 2879.
SAFETY VALVE OPEN VENTED SYSTEM
3.9
A safety valve need not be fitted to an open vented system. (See 3.16 for
sealed systems)
PUMP
3.10
The pump should be fitted on the flow pipe from the boiler and have
isolating valves each side.
A variable duty pump should be set to give a temperature difference of
no greater than 20°C between the flow and return, with the thermostat
set at “MAX”, which is approximately 80° to give a flow rate as shown in
table 1.
See figure 6 for pressure loss of the boiler.
High resistance microbore systems may require a higher duty pump.
FLOW RATE
3.11
If it is necessary to alter the flow rate, the system can be fitted with a
lockable balancing valve in the main flow or return pipes shown as valve
“A” in figure 7. The flow rate through the boiler must not be allowed to
fall below that given in table 1.
WATER TREATMENT
3.12
WATER TREATMENT, CLEANSING AND FLUSHING THE HEATING
SYSTEM
NOTE:
British Standard BS7593: 1992 stresses the importance of
cleansing and flushing of the system to ensure it continues to run
efficiently with the minimum of maintenance necessary. Halstead
Boilers fully support this professional approach and recommend that
the system is cleansed with an effective chemical cleanser and
protected long term with a suitable inhibitor. Such products are available
from Fernox and Sentinal.
Table 1. Flow Rate
MINIMUM FLOW RATE
200 l/h
This is equal to 20°C differential at minimum heat input.
OPEN VENTED HOT WATER SYSTEM
3.13
The boiler must be supplied from an unrestricted water supply taken
from a feed and expansion cistern situated at a maximum height of 27
metres (90ft) above the boiler.
The cold feed must be 15mm minimum size.
The vent must rise continuously and be unrestricted.
It is important that the relative positions of the pump, cold feed and open
vent are as shown in figure 8.
DOMESTIC HOT WATER CYLINDER
3.14
SINGLE FEED INDIRECT CYLINDERS ARE NOT SUITABLE
The domestic hot water cylinder must be of the double feed fully indirect
coil type.
SEALED HOT WATER SYSTEMS
3.15
The installation must comply with the appropriate requirements of the
current issue of BS4814, BS5449, BS6759, BS6798 and BS7074 Part 1
and 2.
See figure 7 for a suggested layout.
SAFETY VALVE SEALED SYSTEM
3.16
A safety valve must be fitted to a sealed system.
It shall be preset, non-adjustable with a lift pressure of 3 bar,
incorporating seating of a resilient material, a test device and a
connection for drain.
The drain from the safety valve must be routed outside the building,
must not discharge above an entrance or window or any type of public
access area, be clear of any electrical fittings and positioned so that any
discharge can be seen.
13
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