Compressors and Condensing Units


The German-made BD35 and BD50 compressors used in the Frigoboat systems are the new 12/24 volt design by Danfoss which feature a 4-speed, brushless, 3-phase motor powered by an electronic controller. Compared to previous models, these compressors are more efficient, draw less current, are smaller and lighter. The Danfoss compressors that Frigoboat uses have variable speed capability.

Why Vary The Compressor Speed?

Frigoboat designates their condensing units as either “35” or “50”, and this corresponds to the model of Danfoss compressor used; i.e. either the Danfoss BD 35 or BD 50 compressor. These high‐efficiency, variable speed compressors look identical, and share the same electronic controller, but the BD 50 has more capacity. However, the extra capacity of the BD 50 is achieved at the expense of some degree of efficiency.

Refer to the Selection Guide and Pricing Matrix (PDF) or call us for assistance in determining which size compressor you should consider using, based on box size and application.

Air Cooled

Paris 35, Capri 35 and Capri 50

Air cooling is the least efficient cooling medium compared to water, but the systems are least expensive to buy and the easiest to install.

To achieve maximum efficiency, air cooled condensing units need to draw in cool air, which is then forced by a fan across the condenser, picking up heat as it passes through. Consequently, the heated air should be expelled into a different area. enabling the compressor to be installed in an engine room or other hot, poorly vented area.

A Keel Cooler can always be added later to an air cooled Frigoboat system using basic tools and with no refrigeration experience necessary. This is a useful feature if cruising plans change, or if some form of refrigeration is required immediately, but it is impractical or inconvenient to haul the boat until a later date.

Water Cooled

W35 and W50

If the vessel is to be based in, or travel to warmer or tropical climates, water cooling should be a serious consideration. If the system is to be a freezer, then water cooling is highly recommended regardless of where the vessel is located.

Water is a far denser medium than air and typically stays at a lower temperature than the air inside the boat or locker. It is generally accepted that water cooling is 20% – 30% more efficient than air cooling, but it involves installing a pump, which adds approx. 1amp (at 12v) to the total current draw as well as adding the uncertainty of a clogged strainer and/or pump failure.

Keel Cooled

K35 and K50

The Keel Cooler is the logical step up from a pump‐fed water cooled system, as now the condenser is outside the vessel, and instead of pumping water into the boat and back out over the side, we take the refrigerant outside the boat to be cooled, and then back in again. The only moving part of this system is the compressor, and this results in the Keel Cooler system being the quietest, most reliable, and most efficient system of all. There are some boat owners that are concerned with “putting another hole in the boat”, but it should be remembered that in a Keel Cooler installation the Keel Cooler itself is simply a tough and sturdy plug, and there is absolutely no water coming on board. The water stays where it belongs; i.e. outside the boat!

Keel Cooled Plus Air Cooled

Occasionally, long-range cruisers may want to operate a Keel Cooled system when hauled out for repairs. If the haul-out is for one or two days, a hose can be rigged to drip water onto the Keel Cooler. For longer stays on the hard, a simple solution is to install a Keel Cooler system with an air cooled condensing unit instead of a K35 or K50. The fan on the air cooled unit is wired with a switch, and the fan is used when the vessel is hauled out. This simple solution is gaining popularity in cruising circles, where a little extra initial outlay buys considerable peace of mind.

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