Air Supply By Mechanical Ventilation; Water Circulation System; General; Pressure Relief Valve (Safety Valve) - Hamworthy Wessex 100 M100 Installation, Commissioning And Servicing Instructions

7.2 Air Supply by Mechanical Ventilation

Air supplied to the boiler room by Mechanical means
should be as follows: -
1) Mechanical inlet and mechanical extract can be
utilised providing design extraction rate does not
exceed one third of the design inlet rate.
2) Mechanical extract ventilation with natural inlet
ventilation MUST NOT be used.
NOTE: For Mechanical ventilation systems an
automatic control should be provided to cut off the
gas supply to the boiler, in the event of failure of air
flow in either inlet or extract fans.
Figure 7.2 Mechanical Ventilation Flow Rates
Flow rate per 1000kW
total rated heat input (Gross)
Inlet air
Atmospheric
(Combustion
Boilers
ventilation)
m³/s.
Volume 1.10

8.0 WATER CIRCULATION SYSTEM

8.1

General

The Wessex Boiler has a low water content and the
requirements of minimum water flow are given in
Section 8.8: Minimum Water Flow Rates (p10)
and Figure 2.2 (p4). Recommendations for the water
circulation system are given in BS 6644 and CP
342. The following
importance:-
1) In a combined central heating and hot water
system, the hot water storage vessel must be of the
indirect cylinder or calorifier type. The hot water
storage vessel should be insulated preferably with
not less than 75mm (3 in) thick mineral fibre, or its
thermal equivalent.
2) Circulating pipework not forming part of the useful
heating surface should be insulated to help prevent
heat loss and possible freezing, particularly where
pipes are run through roof spaces and ventilated
cavities. Cisterns situated in areas, which may be
exposed to freezing conditions, should also be
insulated. Insulation exposed to the weather should
be rendered waterproof
3) Drain valves must be located in accessible
positions which permit the draining of the whole
system, including the boiler and hot water storage
vessel.
4) Each boiler has G1½ male flow (indicated with a
red spot) and return connections (indicated with a
blue spot). Boilers should be connected by flow and
return headers. Headers should be connected to the
HAMWORTHY HEATING LTD
Extract air
(ventilation)
m³/s.
0.45
notes are of particular
system in a "reverse return" arrangement (the water
flow in each header is in the same direction) to
ensure equal flow in each module, or with a "single
pipe header system". Figure 1.1 (p2) shows typical
layouts.
5) Due to the higher pressure loss of the Wessex
heat exchanger compared to the conventional
boilers, it may be necessary to install a shunt pump
or balancing valve to enable correct flow through the
boiler.
6) Ideally, individual valves should be fitted to each
module to enable isolation from the system,
however, the arrangement must comply with the
requirements of BS 6644. See Section 10.3 Water
Connections (p14).

8.2 Pressure Relief Valve (Safety Valve)

The most important single safety device fitted to a
boiler is its safety valve and each boiler, or in the
case of a modular installation, each bank of boilers,
must be fitted with a pressure relief valve to BS 759
or BS 6759 Part 1 and sized as shown in BS 6644.
BS 6644 provides comprehensive information for
the selection and location of safety valves and
attention
requirements of safety valves for pressurised hot
water systems.

8.3 Open Vent and Cold Feed Pipe

(See BS 6644 for further information.)
Every boiler or group of boilers should have an open
vent pipe and cold feed pipe installed between the
boiler and the first water isolating valve.
minimum bore (mm) of these pipes per installation is
as follows:-
The vent pipe must rise continually, must not be
valved except by a design which when closed for
maintenance the boiler is open to atmosphere. The
pipe shall be protected against freezing where this
might occur.
Figure 8.3. Cold Feed and Vent Pipe Sizes
Boiler Output
< 60 kW
60 kW - 150 kW
150 kW - 300 kW
300 kW - 600 kW

8.4 Altitude Gauge (Water Pressure Gauge)

Every boiler or group of boilers should be provided
with a gauge complete with isolating cock. See
Figure 1.1 (p2) for typical position.
9
WESSEX 100 M
is drawn to the
Feed
19
25
32
38
higher capacity
The
Vent
25
32
38
50
500001080/F