PLANNING AN AIR CONDITIONING SYSTEM FOR YOUR BOAT?
In order to find the ideal air conditioning solution for your boat or yacht, you should consider the following six factors*:
1. Calculating the required system capacity
To calculate the required A/C capacity, divide your boat into three areas:
Below deck: Cabins where the hull slopes inward toward the keel with minimal port lights and hatches.
Mid-deck: Areas on the main deck with small or shaded windows.
Above deck: Areas with large glass surfaces and direct sunlight. Calculate the area of each space to be air-conditioned.
It is assumed that your boat has an average headroom of about 6.5 feet (2 metres). Next, multiply the area by its load factor to determine the required capacity in BTU/h. Use the table below to find the appropriate load factor for each space and for different locations.
2. The number of units needed and their location(s)
Both are determined by the size and layout of the boat and space limitations for the installation of ducting and plumbing. Consider which areas require their own cabin control and which cabins will be supplied by ducting or a secondary air handler. Temperature control is then only possible by reducing the airflow with an adjustable grille or by controlling the fan speed.
Please ensure that there is enough space around the unit for servicing and the installation of an air outlet duct to a high point in the cabin.
When designing air distribution ductwork, it is important to keep note of air return and supply. Air must have a way to return to the air handler. Taking air from one room and ducting to another may cause negative and positive pressure issues. Negative spaces may become dangerous as make-up air may come from bilges or engine rooms.
3. The seawater cooling system
This system consists of a through-hull fitting, a seacock (water valve), a seawater filter, a pump, a seawater discharge fitting, and a hose or pipe.
Dometic recommends centrifugal seawater pumps because of their maximum efficiency and long service life. The ideal solution calls for all onboard air conditioning systems to use a single pump, which must of course have sufficient capacity. The basic rule for calculating the required capacity assumes a flow rate of 3 gal/min (11.3 L/min) per ton of air conditioning (1 ton = 12,000 BTU/h). See the table below for examples.
4. Duct and grille sizes
Cross-section and size are based on the air conditioning system's capacity in BTU/h. (1 ton = 12,000 BTU/h). See the table below for examples.
5. Cabin Controls
Dometic offers a complete line of cabin controls that can be found in the catalogue.
6. Electrical requirements
All Dometic air conditioning systems are available in 50 Hz or 60 Hz versions and in all standard voltages. All electrical information is listed in the product data sheets. When at port, the power connection must also be dimensioned accordingly. For easy start-up with less current, see the SmartStart product later in the catalogue.
* These methods are for estimation only. Detailed heat load analysis is required for exact BTU/h requirements.
THE THREE TYPES OF MARINE AIR CONDITIONING
Self-Contained Systems
All major components (compressor, condenser, evaporator, and blower) are mounted on a single chassis, which is installed under a bunk, settee, or in a locker.
An air-conditioning unit of this type can either cool a single cabin or can be connected to two or more cabins by ductwork.
The ideal solution for boats up to 40 ft (12 m) due to lower cost of units and installation.
Split-Gas Systems (also called Centralized A/C)
In these systems, the condenser and evaporator units are installed separately at different locations. The two components are then connected via insulated copper refrigerant tubing connects.
Note: the maximum length of refrigerant tubing is 50 ft (15 m).
• The condensing unit (compressor, seawater condenser, and electrical components) mounts in engine room or other mechanical space.
• The evaporator unit installs in the living area.
Two air handlers can be connected to one condensing unit to cool multiple cabins or a single large area, providing a space-saving, quiet A/C solution.
Ideal for boats up to 80 ft (24 m).
Note: the system must be charged with refrigerant by a certified technician.
Chilled (circulated) Water Systems
Installed in the engine room, the chiller circulates cold or hot fresh water in a closed circuit to all of the rooms to be air-conditioned. Air handlers then cool or heat the living spaces. These systems require two pumps; one for the sea water and another for the chilled water.
Chillers offer flexible load management and a reduced peak electrical load.
Chiller systems are well suited for boats over 80 ft (24 m). This is because there is no limitation on the number of air handlers in a system, or on the distance from the chiller to the air handlers.
