Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

Ventilation of Passenger Compartments

Ventilation Measure

Ventilation is a subject that can occupy a HVAC
(heating, ventilation, and air-conditioning)
engineer for a lifetime of study. Controlling
temperature and humidity, reducing system
noise, maximizing efficiency, laying out
extensive duct systems, and more are com-
plex subjects in themselves. A full discussion
of ventilation includes heat and humidity
control. For instance, when it gets cold you
want less airflow through a compartment,
but you can’t seal the compartment airtight
because you need to breathe. Humidity and
air velocity combine to govern comfort, and
in cargo ships, they can make the difference
between a load arriving fresh or completely
spoiled. For this discussion, however, we’ll
assume that our object is simply to keep
things cool and comfortable using relatively
simple systems, and that the crew will actively
go around closing ventilators, hatches, and
windows and turning off fans as the weather
gets colder. We will review straightforward
approaches to meeting basic ventilation
requirements on boats.

The Volume Change Rate

(VCR) or Air Changes

Per Hour (ACH)

The amount of ventilation in a compartment
can be evaluated as the number of air
changes in the compartment in a given time
(usually 1 hour)—say, 5 changes of air per
hour for a bilge area, for example. This is the
volume change rate (VCR) or air changes per
hour (ACH).
As a practical matter, you need to find
the airflow in cubic feet per minute (cfm)
or cubic meters per hour (m^3 /hr) required
to meet the VCR requirement for a given
compartment.

Formula 14-1. Required Airflow

Required Airflow, cfm =VCR×vol ÷ 60

min./hr.

Or

Required Airflow, m^3 /hr. =VCR×vol

Where:

VCR =volume change rate

vol =compartment volume, cu. ft. or m^3

Example:Say you have a master state-

room that is 9.9 feet (3.02 meters) long by

8.8 feet (2.68 meters) wide. It has a head

compartment in one corner that is 3.25 feet

(1 meter) by 4.67 feet (1.43 meters) wide.

Headroom is 6.5 feet (1.98 meters). Then

9.9 ft.×8.8 ft.×6.5 ft. headroom =566 cu. ft.

3.25 ft.×4.67 ft.×6.5 ft. headroom =98 cu. ft.

566 cu. ft. −98 cu. ft. =468 cu.ft.

VCR should be between 6 and 8 times per

hour.

6 ×468 cu. ft. =2,808 cu. ft./hr., or

2,808 cu. ft./hr. ÷ 60 min./hr. =46.8 cfm

to

8 ×468 cu. ft. =3,744 cu. ft./hr., or

3,744 cu. ft./hr. ÷ 60 min./hr. =62.4 cfm

Chapter 14:Ventilation of Passenger and Storage Areas

TABLE 14-1.VOLUME CHANGE RATE

(VCR) OF VARIOUS COMPARTMENTS

Time to

VCR per Change Air

Compartment Hour (Minutes)

Galley 10 to 20 3 to 6

Lavatories

and WCs 8 to 10 6 to 7

Sleeping Cabins 6 to 8 7 to 10

Saloons 5 to 10 6 to 12

Forepeak and

Lazarette 5 12

Bilges 5 12

Storage

Compartments 8 to 12 5 to 7

Engine

Compartments 150 to 250* 0 .24 to 0. 4 *

Battery

Compartments Covered separately, see

below

*See engine-vent section below.

Formula 14-1.