HVAC aboard large yachts cannot be overestimated in its importance. Having been on the equator with the system down, rebuilding the only seawater pump with parts from
a local agricultural supply, the temperature on board rising quickly, with the crew
operating in stifling conditions and the owner wondering why its so bloody hot inside, I
have a love/hate relationship with HVAC. I love it when its working and hate it when its
not; its the one system that will determine whether you can have shore power or not,
demanding huge start-up power relative to other systems when alongside.
As a whole you have to be constantly aware of its operation around the vessel, from
annoying weeping chilled water pipes, noisy fan coils, weak systems in the galley (as
you watch the chef melting in front of the stove) to the crew systems that form the
emergency back-up supply for the rest of the vessel (often the crew end up with fan
coils that are on or off with no variation, or in one case it was so hot in an aft cabin the
stewardesses were sleeping outside).
Improving energy efficiency of an HVAC system is a continuous operation and as professional
marine engineers you will have long experience of the systems on board; it can be useful to review techniques.
1. Fan Coil Units
These consist of an air supply fan, usually a squirrel cage type, a cooling coil, heating
coil, a motorised valve and possibly ventilation intake. Underneath the whole unit is a
drip tray that captures the moisture buildup; this is then piped off to a holding tank.
I always place a chlorine tablet in the tray to prevent any build-up of sludge in the tray or
the waste pipe. I had one situation where the pipe had become blocked and the water
build-up was s taining the ins ide of a wardrobe and dripping extensively when we
rolled at sea. It is also worthwhile removing the whole unit periodically and replacing the
three bearings for the fan shaft and motor, as well as acid cleaning the fan and housing
body. This will improve fan function, vibration issues and heat transfer efficiency. One
study demonstrated the effect of cleaning coils on HVAC performance, showing that
coils that were left uncleaned had a 27 per cent loss in heat transfer after being in
operation for 18 months. Even cleaned coils showed a nine per cent loss in heat
transfer compared with new coils.
2. Chilled water piping
This circuit transfers the chilled water from the main unit to the various fan coils around
the vessel. It is essential to maintain the volume and pressure, to carry out periodic
flushing and to check the anti-freeze levels. Also, well-maintained insulation improves
efficiency and stops condensation build-up around the pipe or joints.
As with any pump system, spare pumps, motor combinations, and spare bearing
units for both, it is worth checking the pump rotation, especially after maintenance, regular
cleaning of any filter or strainer units.
4. Marine air conditioning raw-water condenser pumps
These frequently fail from plugging with debris. Install a good strainer in the pump
inlet line and consider one of the new selfcleaning units if you use the boat in weedor