What is Shipboard Ventilation, and Low and High Velocity System?

In this article you will get to know about the shipboard
ventilation system used on ship. Furthermore, the two system namely: high and
low velocity has also been discussed in detail. Shipboard ventilation is a
necessary action that needs to be carried in order to protect the cargo that is
being taken on ship from spoiling. So, let’s discuss about this process in
detail.  

It is defined as the circulation of air around a space to
clean and refresh it, but not changing the temperature. It also forms an
integral part in the air conditioning system. Shipboard ventilation not only
serves to ventilate the cargo spaces, but also for the human living spaces
also. Thus, it removes carbon dioxide and enriches the space with oxygen. By
doing so, we are also decreasing the heat that present all around and moisture
that may be present.

Shipboard ventilation may be divided in several groups such
as accommodation spaces, sanitary spaces, stores and provisions, engine room
and cargo holds. 

You May also like to read: What is Single and Twin Duct System in Air Conditioning

There are two methods which are used in the ventilation
process:

Natural Ventilation

This type of ventilation as name suggests, involves natural
methods for circulation of air. The difference of temperature and wind pressure
causes the natural ventilation to take place. Actually what happen is that, the
hot air has a less specific density and it tends to move upward. Opposite to
it, cold air is heavy and moves on the down side. And hence it leads to flow of
air. In natural ventilation, cowls and scoops are used to trap the atmospheric
air. Natural ventilation is mainly adopted on small ships and also the inland
vessels. In this system, the ducts are designed to operate on the velocity of
3.5 m/sec and flow co-efficient of 0.5. It has several advantages such as
simple design, low cost, little or no maintenance. But in the case of low wind
speed, the natural ventilation is not good. So, this was all from this system. 

As name suggests, it uses the power driven devices for
carrying out the ventilation. Fans, blowers etc are some of the devices that
are used to carry out the ventilation in the mechanical ventilation. This helps
the manufacturer to use the small ducts system, supply of air is not affected
by the weather conditions that are present outside. In this type of system, the
quantity of air handled is less and hence this makes it more economical as
compared to the natural ventilation. It is generally preferred to have the
vacuum system in living and common spaces. Vacuum system is used to remove the
contaminated air from toilets and galleys. The capacity of blowers and fans are
decided on the basis of the quantity of air need to be handled. 

A low velocity System is one in which the velocity of air at
the beginning of main duct is 5 to 10 m/s and successively lower there after
which results in low frictional resistance. Thus in this system we require a
fan which is having low power rating, but the only problem with this type of arrangement
is that it will require large sized and expensive ducts and installation will
be difficult.

In high velocity system, velocity of air at the beginning of
the main duct is 15 to 30 m/s. Since it includes a high power fan that will
produce a high air pressure, it requires small sized ducts and would result in
economy of material, low manufacturing and installation cost easy installation
on board ship. This system will have high recurring cost and will also result
in high noise levels. Also since the machinery will be running at high speed,
the frictional loses in this system will be more.