Essentials
SELELE MASHILO
Selele Mashilo has a mechanical engineering diploma from Tshwane University of Technology and a refrigeration and
air-conditioning diploma from Unisa. His experience includes over a decade in government as deputy-director building
services before rejoining the private sector in 1998 as HVAC&R project engineer. He is the former chairperson of the
Refrigeration and Air Conditioning Empowerment Forum of SA (RAEFSA), the Air Conditioning and Refrigeration
Industrial Council of SA (ACRICSA), and Black Energy Services Companies (BESCO).
SHIPS COMFORT AIR CONDITIONING
By Selele Mashilo
Although comfort air conditioning is the basic requirement in ships, there are several
other requirements for providing air conditioning.
M
ostly, the requirements will be to protect material conditions
due to high air humidity and salt contamination from ocean
water. Other requirements are to increase crew efficiency, to increase
the reliability of electronic equipment and to safeguard against rapid
deterioration of special weapons aboard naval ships.
ventilation systems. Air quantities of 5.9ℓ/s to 7.1ℓ/s per person
are required. Even higher quantities can be supplied, so air
changes per hour must also be considered and the selection will
be based on the comparison and whichever is higher must be
considered. Sometimes the specification may require maximum air
requirements irrespective of the size of the space, such as 37.8ℓ/s.
DESIGN CRITERIA
Corrosion is one of the critical elements to be considered for selecting
material of equipment construction due to effects of sea, air and
water. The equipment should be able to operate under conditions
of roll and pitch to which the ship is subjected to. Ships on a voyage
are not easily serviced, therefore the equipment should be able
to operate for long periods without interruptions. Noise from the
equipment must be very low especially when in port to maintain good
ship voyage assessment conditions. Equipment weight should be kept
to a minimum. The ship is subjected to various weather conditions
during a voyage within hours or days, therefore the air conditioning
system must be easily adaptable to the changing conditions.
OUTDOOR AND INDOOR CONDITIONS
It can be easy to maintain indoor conditions by using air conditioning
systems. For comfort purposes the human metabolic conditions are
easily maintained to human satisfaction. Indoor temperatures of 24⁰C
dry bulb and 45% to 50% relative humidity can be easily maintained.
The difficult situation can be the outdoor design conditions. As
indicated above the ships are subjected to various weather conditions
on their voyage. Outdoor summer design conditions for the North
Atlantic are 35⁰C dry bulb and 25.6⁰C wet bulb temperatures. For winter
outdoor heating conditions can go as low as -17⁰C. Now the indoor
conditions must be maintained by the same equipment as used for
various outdoor conditions which can make equipment selection work
quite sensitive.
VENTILATION REQUIREMENTS
Due to their environment of operation, ships need particular
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LOAD DETERMINATION
The cooling load estimates should consists of the following:
• Solar radiation
• Heat transmission through decks and bulkheads
• Occupants
• Lights
• Ventilation Air
• Motors for fans and machinery which dissipates heat.
The heat load should consist of the following:
• Heat losses through decks and bulkheads
• Ventilation air
• Infiltration
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Equipment selection
Factors to be considered in the selection of equipment are the
following:
Initial installation costs
Space available for plant rooms and reticulation
Operating costs including maintenance
Noise levels and weight of the equipment
Typical systems may be single zone central systems, multizone
central systems, terminal reheat systems and high velocity dual duct
systems. RACA
References:
1. ASHRAE
RACA Journal I April 2020
63