Ventilation Flashcards
Air conditioning
Control of temperature, humidity, purity within a space or group of spaces
Ensures effectiveness and efficiency of ships staff and machinery for longer periods of time
Vent
Produce fresh air
Cool electrical equipment
Tolerable living & working conditions
Exhaust
Removes heat, noxious fumes, odours
Heaters
Prevent discomfort or chilling
Serve all occupied spaces
Staff will try to reduce or stop the airflow, leading to potential danger to health
Occupied compartment - capable of maintaining temp of 22’c
Unmanned compartment - capable of maintaining at 13’c
Typical system arrangement
Ensure correct conditions are maintained in each compartment
Air conditioned or mechanically ventilated or natural supply and exhaust
Fan supply - for regularly used for living and working spaces
Fan exhaust - fitted to remove air directly from the vicinity of heat
Prevent build up of noxious gases
Remove odours and vapours
FS/FE - fitted to remove large quantities of heat, moisture or noxious gases
NS/FE - primary objective to remove gases and vapours
TACS
Ship is divided vertically into sections
Completely self contained
Smoke clearance is achieved by installing axial flow fans
With automatic interlocked butterfly valve
Operated at SCC
Fresh air makeup (10%) is supplied at all times via by-pass valve fitted to AFU
Excess air is exhausted into heads and bathrooms by air bleed valves
Centrifugal fans
Used as supply or exhaust fans in a trunked system
Air is drawn into the centre of the fan
Expelled outwards to the tips of the blades by centrifugal force
Axial fan
Fitted in machinery spaces and large centralised ventilation supply and exhaust systems
Air is drawn past the rotor
the fan is inline with the trunking
Takes up less space
Moves large quantities of air against low resistance
Trunking
Circular trunking offers the least resistance
Rectangular is better for space efficiency
Ratio to be near 1:1 as possible
Not more than 1:4
Insulation
Prevent condensation inside and outside trunking
Condensation causes corrosion
Restrict heat pick up passing through warm compartment
Restrict heat loss passing through cold compartment
Material
Aluminium alloy - used for NWT and GT trunking - not subject to heavy treatment
Mild galvanised steel - used for WT trunking and NWT trunking subject to heavy treatment
Filters
Air supplied, exhausted or recirculated can contain impurities: dust, salt, sand, bacteria.
Impurities clog up heaters and coolers, reducing overall efficiency
Odour filters
In recirculation trunks for bathrooms, toilets and galley
Can be carbon granules, carbon cloth, or a combination of chemicals
Life span should be at least 6 months, under normal ships condition
If humidity exceeds 90%, filters efficiency will be impaired
Sewage treatment spaces
Require 15 air changes per hour
With separate exhaust system
Slight excess of exhaust capacity
Limited air supply under closed down conditions for the air compressors
Trunking is at lower level to prevent build up of hydrogen sulphide
LEV
Statutory requirement - HASAWA / COSHH
Mandatory requirement to be inspected and tested by a competent person
Carried out every 12months
Not exceeding 14 months
Performance of the system is within the nominated parameters (60% of design output)
Aspects of CBRNDC design
Smoke migration is restricted to defined zones (crash stop vent)
Post-fire contamination - cleared with minimal loss of operation effectiveness
