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HAMWORTHY HEATING LTD

WESSEX 100 M

500001080/F

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.

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.

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

BS 6759

Part 1 and sized as shown in

BS 6644

provides comprehensive information for

the selection and location of safety valves and
attention is drawn to the higher capacity
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. The
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.

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.

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.

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

342

. The following notes are of particular

importance:-

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.

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

Drain valves must be located in accessible

positions which permit the draining of the whole
system, including the boiler and hot water storage
vessel.

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

Figure 7.2 Mechanical Ventilation Flow Rates

Flow rate per 1000kW

total rated heat input (Gross)

Inlet air

(Combustion

ventilation)

Extract air

(ventilation)

m³/s.

Volume

1.10

0.45