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→Ventilation
== Ventilation ==
Fresh air ventilation is required to replenish oxygen removed by people and sources of combustion, and to dilute odours and pollutants. Local exhaust ventilation is required in heads and the galley to remove airborne odours before they spread through the boat. From a ventilation viewpoint, the most effective method is an integrated HVAC system with air distribution and local controls in each cabin. Such a system can include an air-to-air heat exchanger to precondition the temperature of the air and recover energy, and a humidifier/dehumidifier to control levels of indoor moisture. Humidity control is especially important in hot humid climates where unconditioned ventilation can deliver 1-pound (lb ) of water per cubic foot (ft^3) of intake air.
Excess humidity causes condensation on windows and water pipes. It can blister paint, rust metal and warp wood, and cause electrical faults. Dust mites, fungus, mildew and mould thrive in humid conditions, aggravating allergies and sometimes damaging lungs. Insects like clothes moths, cockroaches and fleas also like high humidity.
People prefer a relative humidity of 30 to 50% and find anything much higher to be very uncomfortable.
Unfortunately I decided against an air distribution system choosing in favour of a water system for heating and air coolinghas further consequences. This was to minimise A water system minimises the scope of pass-throughs in water-tight bulkheads but like many design decisions this had further consequencesit forces trade-offs. It made an integrated ventilation/humidification system impossible.
The alternative to running fairly large air vents the length of the boat is local ventilation in the main zones of the boat. This is far from ideal. In both summer and winter the air intakes will be working against the air conditioning and heating systems, respectively, and deck-mounted dorades for intake and return air are multiple hull openings. The ventilation system must be designed carefully to minimise these risks of water entering.
For example, assume a boat having 6,000 cubic feet of volume and berths for five people. Using 1.0 ACH this yields 99.6 CFM and 15 CFM/p yields 75 CFM.
Maximum air velocity in ventilation ducts and vents should not exceed 2.6-3.3 ft/s (feet/second) (0.8-1.0 m/s) to minimise noise and differentials in air pressure. Air In comparison, air ducts for combustion systems can run as high as 40-66 ft/s (12-20 m/s).
Let’s work a complete example. Assume a salon of 1280 cubic feet. At 1.0 ACH this requires 21.3 CFM:
Close enough.
In this case, we could put a 5- x 5-in inch intake vent at one end of the salon and a vent of the same size at the other end with an exhaust fan driving 2 ft/s.
== Air Conditioning ==