Page 337 - Ship Construction.DJ Eyres 6Ed

Ch28-H8070.fm Page 326 Wednesday, October 18, 2006 7:02 AM

28
Ventilation, Refrigeration, and Insulation

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Adequate ventilating and air conditioning systems are installed in ships to
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provide reasonable comfort for the crew and passengers, and to maintain
cargo at the correct temperature and humidity. Insulation is provided to
maintain refrigerated cargo and domestic store rooms, and to a lesser
extent to maintain air conditioning requirements, and to overcome acoustic
problems in accommodation and control rooms.

Ventilation

Mechanical ventilation is provided in the machinery spaces of most ships
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but some may have natural exhaust provisions. Stores and working spaces
may have both natural supply and exhaust ventilation but where fumes are
present mechanical exhaust provisions will be provided. The mechanical
supply is by means of light steel sheet trunking, with louvres at each outlet.
Natural and fan exhaust outlets are appropriately placed at the exterior
sides or deckhead of the space being ventilated. Fans may be of the quiet
running centrifugal type with a separately mounted motor.
Air conditioning is a common feature in crew accommodation, within
machinery control rooms and in the accommodation and public spaces of
passenger ships. Room temperatures are controlled by a thermostat, heated
or chilled air may then be supplied as required and humidity control is also
provided. Trunking and louvres are similar to those for mechanical ventila-
tion, smaller bore trunking being possible if a high velocity system is intro-
duced Local air conditioning units are available and may serve an individual
passenger suite if desired, with their own control.
The holds of most dry cargo ships are ventilated by a mechanical supply
and natural exhaust system. Here the object is to reduce the hold temperat-
ures if necessary and prevent large amounts of condensation accumulating
on the hull and cargo. Often the cargo hold fans which are of the axial type
are located in houses on the weather deck that enclose openings to the
holds. In older ships they may have been positioned in derrick posts where
these posts are used to ventilate the tweens and holds (see Figure 28.1). Dry
cargo ships may also be fitted with de-humidification facilities, controls
being provided so that each hold can be supplied with dry air or outside air.