The MarineAir Coolmate

The MarineAir Coolmate



Chilled water air conditioning systems are nothing new ... they kept sailors cool aboard fighting ships in the South Pacific during World War II and they've been used in large office buildings for years. What is new, however, is that the size of boat on which a chilled water air conditioning system can be installed is steadily shrinking.

Once the province of the megayacht, chilled water systems are now viable on yachts as small as 48 feet (and a new 30-footer may try it as well), providing a host of advantages not available with conventional air conditioning systems.

Most yachts under 60 feet are equipped with direct expansion air conditioning, which utilizes the cooling properties of freon gas to chill the air blown through ducts into staterooms and other living areas. Smaller boats may have self-contained air conditioning units installed in bulkheads or under cabinets, while larger yachts often rely on a central system where the compressor and other equipment is installed in the engineroom and ducting carries the cool air around the yacht.

The chilled water system takes a different approach to cooling the air and, instead of pumping cold air around the boat, it pumps cold water through tubing from a central compressor in the engine room. Throughout the yacht, each outlet has what is called an air handler, which is really a radiator of tubing with a fan to propel the air through the coils and into the area to be cooled.

Because the chilled water method requires two separate heat transfer steps (ocean water to the condenser and fresh water within the chiller), it is more expensive than the direct expansion method. This is one reason for their use primarily on large yachts. In addition, there are more components and a labor-intensive installation (particularly as a retro-fit) on small yachts, which can be satisfactorily cooled with one or two self-contained air conditioning units that simply drop into place.

But manufacturers are starting to recognize the advantages of the chilled water system in production yachts and, when the closed-loop freshwater system is installed as original equipment, it's simply a matter of running the plumbing and insulating the pipes.

Why choose chilled water systems if they're more expensive? For two simple reasons: they're quieter and they provide more usable air conditioning.

According to Mason Heydt of Marine Air Systems, a typical self-contained direct-expansion air conditioning system runs at about 68 dB while chilled water air handlers range from 48 dB to 55 dB, depending upon the type and the installation.

But for most owners, it is the infinite flexibility of the chilled water system that is particularly attractive. With a separate direct expansion unit installed to cool, for example, the saloon of a yacht, you can never exceed the output of that particular unit, even if units throughout the rest of the boat are inoperative or running on low capacity.

With the chilled water system, however, you can have more air handlers scattered throughout the boat than you have rated BTU capacity, allowing you to focus all of your cooling power in one area. If you have an 80,000 BTU system, you can install 100,000 BTUs of air handlers at minimal cost. Then, if you have a dozen people (at 500 BTU per person) in your saloon on a warm day, you can turn on the extra air handlers in that area to keep pace with the rise in heat and still have enough to handle the constant opening of the cabin door. After the party, you simply turn down the thermostat to normal. With a conventional single air conditioning unit in that saloon, you would have been overly warm since you could never exceed the power of that one unit even if the units in the other staterooms were shut down.

The flexibility also extends to other uses, such as putting an air handler into the engine room. Then, when you want to work on the engine, you simply cool the area down without having the expense of a complete air conditioning unit that is rarely needed. When the owner is absent, the crew can shut down the air handlers in areas of the boat that are unused, and new air handlers can easily be tapped into upgrading the entire system. After all, with only water flowing through the tubing, it can be refilled from the dock hose whereas a conventional system requires a freon refill.

Another advantage to chilled water systems is that on larger yachts, several compressors are used rather than a single large one. This allows the system to operate in stages to reduce the starting load on the generator or dock power, and to use only the number of compressors needed to maintain the desired temperature. It also allows the system to operate in spite of a compressor breakdown. Most manufacturers have an automatic staggering system that rotates the compressors so that the first unit is not always the initial unit to go on line.

There are some down sides to chilled water systems, and one is in using a reverse cycle for heating. In cold water areas, where you would probably need cabin heating, the heat pump efficiency is severely impaired if the seawater temperature drops below 45 degrees Fahrenheit. This is why several of the companies offering water chillers provide electric hot water heat that use a reservoir and heating elements, similar to a home hot water heater.

The systems are designed to sense the need for more (or less) power and actuate themselves automatically. For example, a single compressor may be sufficient to keep a yacht cooled in the early morning but, as the sun rises, additional compressors will switch on automatically to maintain the setting and, late in the day, will shut down as the need for cooling is reduced.

On small yachts, which are now starting to use chilled water systems, a single compressor unit is usually sufficient, although it may take some juggling of air handler controls. A single 16,000 BTU compressor on a small yacht can easily be run off a 4 kW generator, but it may not cool the entire yacht at one time. During the day, the crew may want the main cabin cooled and, in the evenings, they can focus the cooling air on the sleeping cabins instead.

As an example of these systems on smaller yachts, Sea Ray has chosen chilled water as original equipment for its new 50-footer, and Carver is considering the system for their new 55. As the systems become more commonplace, their usage on small boats is certain to increase and that's good news for overheated boat owners.