23
Hoval STU Wood Pellet Boiler
Boilerhouse Ventilation
Natural Ventilation - General Guidelines
The permanent ventilation of the boilerhouse (not including doors
and windows which may be closed) is essential.
Boilerhouse ventilation serves two essential purposes. Firstly it
permits combustion air to flow freely to the stoker(s) from outside
the building and secondly it maintains a reasonable temperature
level within the plant room.
Heat released from the boiler, the piping and the flues should not
increase the boilerhouse temperature above 30
o
C.
Air Inlet Requirements
It is preferred that fixed air openings are provided at high and low
levels adjacent to the boiler front.
Free inlet area of louvres required for ventilation and combustion air
should be based as the following:-
6.5cm
2
per kW output at low level and a further 3cm
2
per kW boiler
output at high level.
Air inlets and ventilation outlets are best disposed at low level and
at high level so that air convection across the boiler(s) will ensue.
Preferably the high level opening should not be too close to the low
level opening such that any short circuiting of air without providing
adequate ventilation can be avoided.
Boilerhouse ventilation should conform with the
relevant British Standards, Codes of Practice etc.
Where suitably sized louvres are utilised over the boilerhouse door,
louvres over the full door height are satisfactory.
For boilerhouses below ground level, arrangements should be made
to induce fresh air into the boilerhouse where a natural flow of air
is restricted by the buoyancy of air leaving higher level openings.
Air Supply by Mechanical Ventilation - General Guidelines
The supply of air to a space housing the boiler by mechanical means
should be mechanical inlet with natural or mechanical extraction.
Mechanical extract ventilation with natural inlet must not be used.
Any mechanical means of entering air into a basement boilerhouse
should have a balancing outlet so that the air pressure in the
boilerhouse does not exceed 12.5 Pa.
Where mechanical inlet and mechanical extract system is applied,
the design extraction rate should not exceed one third of the design
inlet rate.
Ventilation must continue in kindle mode.
Note:
All air inlet and extract fans should be fitted with automatic
controls interlocked with the boiler controls to give a safe shutdown
or lockout in the event of the inlet or extract air flow failing.
Open Vented / Pressurised Systems
Open Vented Systems
A primary make up water and expansion tank is required for open
vented systems. With low head on calorifier primary system, Hoval
Technical Department should be consulted.
The cold feed pipe should be connected into the return water piping
on the boiler side of any valve.
An open vent pipe should be taken off the boiler flow pipework before
the boiler isolating valve. The vent pipe should be installed with a
continuous rise to a position over the primary feed tank.
Pressurised Systems
For independently pressurised systems the flow connection must
be fitted with an automatic air vent, a safety valve (sized to the
relevant British Standard) and a pressure switch or where applicable
individual boiler pressure limiter(s) as outlined below. No intervening
valve is permissible between the safety valve and boiler connection.
The pressurisation unit control should also be interlocked with the
boiler(s) controls to safely close the stoker(s) down in the event of
a malfunction.
Pressure limiter
(in accordance with BS EN12828:2003 clause
4.6.2.2.2 - Heating Systems in Buildings).
For
STU models 350 to 1000
, each boiler should have an associated
pressure limiter device fitted in the system pipework, as close as
possible to the boiler itself (provided by the installer - not supplied,
fitted, or wired by Hoval).
If the operating pressure of the heating system exceeds the given
pressure limit, or in the case of auxilliary power interruption, the
pressure limiter shall shut off the heating equipment and interlock it
against restarting. The pressure limiter shall be adjusted so that it
responds before the safety valve(s) operate.
