For The Love of Water… and Marine Air Conditioners

If you love to be on a boat or yacht, then worry not about air conditioning option. Marine air conditioners are made available for you, should you need one.

Why marine air conditioners are important while you’re fishing, making a weekend getaway from land, or just feeling like being in your favourite aqua-transporter?

Because it will get unusually uncomfortable, be it during cold season, and especially during hot summer.

You’re exposed on an open space, with no radiant heat barrier. The only heat insulation you have, is your boat’s wall and windows.

Needless to mention, heat loss during winter will be high, and heat gain during summer will be very high.

It shares similar fate with automobiles, only slightly worse. Humidity in air can be very high due to proximity with water.These justify the need of air conditioning on a boat.

Marine ACs operate under the principle of mechanical air conditioning cycle, where cooling is achieved by boiling refrigerant in the evaporator.


Overview of marine air conditioners:

I would like to classify marine air conditioning units into two,

  1. Specific marine ACs, and

  2. Common units. These units may be used in marine environment, or on land

Specific marine ACs are,

Common units consist of three types,

Suitable air conditioning units for marine have sizes from,

  • Spot cooling only – with 12 volt portable air conditioners, to

  • 30,000 BTU/hr (or 2.4 ton or 7.8 kWh or 6 hp) – with chilled water systems

Marine air conditioners do not come with EER, or SEER rating, but you can compare efficiency between your choices, using simple formula specified in this page.


Design features:

We’ll begin with,


Specific marine air conditioners - design and parts

  • One fundamental difference with common, land air conditioners – the cooling method of the condenser.

    Condensers for common land air conditioners are cooled using air. However, air conditioning on water gives you an added advantage for condenser cooling. Water.

    These air conditioners use water (instead of air) to cool condenser. Hence, a marine unit can be kept compact as it is more difficult to change temperature of water, compared to air

  • Condenser shape and type is also totally different from air cooled condensers.

    Air cooled condensers are of tube and fin type, whereas marine air conditioner condensers are of tube heat exchanger.

    These tubes will be wound into a coil shape

  • Water is delivered to the marine air conditioning condenser by using sea water pump.

    You will need to find the correct pump size according to the condenser's requirement. The size is normally rated in gpm or gallons-per-minute. It ranges from around 5 gpm, to around 20 gpm.

    The pump (which is of seal-less type - where the motor and the pump are connected using a single shaft, and share the same casing) is electrically driven using the boat's electrical supply.

    Common type of sea water pump for marine ACs is centrifugal (using composite impellers), or positive displacement type (using rubber lobes)

    Water discharge line for water cooled condensers must be placed above the suction line.

    Water suction line, suction filter and pump must be placed below the water level, especially if you are using centrifugal type pumps.

    You may want to install a two-way valve at the discharge of the pump, to easily remove trapped air during start-up. Just do not forget to switch the valve to send water to the condenser once the pump priming is completed.

    You can either select air-cooled or water-cooled (using the sucked water) sea water pump

  • Marine scoop will be fitted outside of the hull and fitted to the sea water hose (which is attached to pump's suction).

    It serves the function of directing sea water into the pump, and preventing formation of air bubbles (air bubbles will cause centrifugal pump cavitation, and erosion of the pump impeller)

  • A basket strainer will be placed just before the sea water pump suction, to prevent any unwanted trash into your pump - that would otherwise damage it

  • Another important marine air conditioning part is the shut-off valve (a.k.a. sea water cock). You'll definitely need this if you want to remove your pump for one reason or another, while not sinking your expensive boat

  • Ethylene Propylene Diene PolyMethylene or EPDM hose will usually be used for directing water into the pump, and out of the condenser.

    Use double stainless steel hose clamps to secure your hose to the fittings, for better leak sealing

  • Through hull discharge fittings for the sea water is not really a necessity, if you would like that extra aesthetics to your boat - that would be good

  • Installing sea water pump will definitely require you to make a hole on your boat hull, and that is no good to keep your marine transporter above the water level, as there will be gap between the hose and the hull.

    The gap can be sealed using modified polymer adhesive marine sealant. You will either need polysulfide or polyurethane selants, but I suggest you go for polyurethane as hose fitting for marine air conditioning pumps will be fixed

  • Corrosion is a huge threat for these units.

    Therefore, manufacturers will provide these units with a special coating. Normally used coating is baked enamel, as an excellent corrosion barrier

  • Other parts will also be covered to prevent from water splash and chloride attacks.

    Plastic covering is a commonly used material, and stainless steel parts will prolong parts’ life from corrosion

  • Chilled (or heated) water air conditioners are used for large conditioning applications.

    Brine will be used as a secondary refrigerant. Chilled (or heated) water systems are essential in large scale air conditioning to minimise primary refrigerant quantity used, and to maintain good compressor lubrication

  • 12 volt air conditioners operate using direct current derived from a generator, engine’s alternator or battery bank.

    However, we have to bear in mind that air conditioners consume a lot of power. Hence we’ll need to size the power input such that, it will be enough for other electrical equipment

  • Properly sized ducts can be used with larger air conditioners, for central air conditioning.

    Central air conditioning in marine application. Now that’s cool

Next,


Common air conditioners – used in marine application

  • The simplest one is the 12 volt portable air conditioner.

    12 volt portable air conditioners available in market do not have any compressor.

    These are equipped with a blower, and you have to fill in ice to cool air. So, 12 volt portable air conditioners can only cool a very small space, or used for spot cooling

  • Rooftop air conditioners are mounted on the… roof of your cabin.

    However, this type of air conditioners are not only used in marine application. It can also be used in your residence or even your RV (recreational vehicle).

    These marine compatible air conditioners come with corrosion resistant parts, and water proof cover when not in use.

    Condenser part will be on the top side (outside) of the roof, and the evaporator on the bottom side (inside) of the roof.

    The condenser is air cooled.

    It’s like a window air conditioner, only not. It’s placed on a roof, and "umm" looks better

  • Portable rooftop marine air conditioners is an evolution to rooftop air conditioners.

    However, this type of air conditioning unit will be useful, if you feel like being creative and use it for your land vehicle – normally on RVs


General design conditions

  • Voltage requirement for all marine air conditioners are similar to land air conditioners, except for 12 volt air conditioners

  • Marine air conditioners will usually come with heating option, either with a heating coil, or with heat pump option.

    12 volt portable air conditioners do not have this option

  • Since generators and marine ACs can’t be separated, then a CO (carbon monoxide) detector is a must


Service and maintenance:

Maintenance for marine air conditioning unit is similar for air cooled air conditioners.

Check out the details of air conditioning maintenance here.

However, there are some differences in the maintenance,

  • Water pump’s suction filter has to be kept clean

  • You will have to watch out for coating peel off, or degradation of the tube coating. It is also essential that the tubes are checked for leaks

  • Check for corrosion on other parts as well

  • Cover your air conditioner if you are not going to use it for a long period

  • Keep the water side tube of the condenser, clean and dry, if not used for a long period


Which one of marine air conditioners to choose?

Difficult choice? Worry not.

As a general guide, 12 volt portable marine air conditioners are for spot and budget cooling.

Other marine air conditioners can be used for space by space, or central cooling.

Just make sure that you have enough voltage supply and power for these.



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