Designing your system
“Overview”, plus “Holding plates versus aluminum evaporators”
When designing a system from the many components that are available from the Frigoboat line of products,
several criteria need to be resolved. The following is intended to be a guide to help you make those choices.
Evaporators; Vertical, Bin (B), Horizontal (H), or Flat Plate (F).
If you have a single box that you are converting into a refrigerated space, the Vertical Bin or Horizontal (with
door) versions make the most sense, as the area inside the bins becomes a freezer where you can store some frozen
goods & even make ice. The rest of the ice-box is kept at refrigerator temperatures under the control of the
thermostat. Of the two, the Vertical Bin is the most popular in top opening boxes as it is easier to install & use,
whereas the Horizontal version is standard in boxes with front opening doors only. The Vertical Bin is available in
two sizes, and, if the larger size is preferred in a smallish box because of its larger freezer capacity, some of the
surface area may have to be covered with an insulating material to ensure that goods stay frozen inside. The larger
size (340B) is not available in a horizontal configuration with a door, so one will have to be fashioned to stop goods
from falling out when mounted horizontally. Conversely, the smallest Horizontal evaporator (130H) is not available
as a vertical model, but may be used as such without problems.
If you have a large box & require more of a freezer area than the largest Vertical or Horizontal models can offer,
a “spill-over” system may be the answer. In this application, one area is partitioned off with a barrier, & a Flat
evaporator installed that is controlled by a freezer thermostat. A hole is then cut into the barrier and a “Spill-over
Fan & Thermostat” installed that will keep the rest of the box at refrigerator temperatures. A hole or gap over the
barrier will provide a return path for the circulating air.
If you have a box or boxes that will be a dedicated refrigerator or freezer, a Flat evaporator may be bent to shape
with a 11/2” min radius, & installed around the perimeter of a box. See the green spec sheet or the web site for
allowable bending areas. You will need to choose between a refrigerator or freezer thermostat, & there is also a
“Dual thermostat” that is a housing that contains both a refrigerator and a freezer thermostat & also a change-over
switch to enable the user to choose the application.
Aluminum Evaporators versus Holding Plates when used on small 12v/24v systems.
Holding plates are basically re-freezeable blocks of ice that are designed to be frozen down with a large,
powerful condensing unit that is run just once or twice a day. Although 2 sizes of holding plates are available for the
Frigomatic series (12/24v, Danfoss compressor), their use is not recommended, as they are less efficient than
aluminum evaporators on these systems. This is because the capacity of the compressor for heat removal does not
change, but the holding plate must be taken down to a lower temperature, increasing the run time. Although the runtime patterns will be different, the holding plate will require more running time overall. Apart from being less
efficient than aluminum evaporators, holding plates are heavier, bulkier, & more expensive. Their use is now
restricted to very large boats & charter applications, although even here, the super-efficient 12v/24v Frigomatic
systems are replacing expensive, troublesome & noisy holding plate systems.
Condensing units; Air cooled (AV, AH, Capri, Paris), Water cooled (W) or Keel cooled (K).
Air cooling is the least efficient cooling medium compared to water, but is cheaper to buy & easier to install. To
achieved maximum efficiency, they need to have the coolest possible air forced by the fan across the condenser, &
the heated air expelled away into a different area. Water is a far denser medium than air & 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 or pump failure. Using a Keel Cooler is the logical step
up from a pump-fed water cooled system, as now the condenser is outside the boat, & the only moving part of the
system is the compressor. This makes for the quietest, most reliable, & most efficient system of all, although it
requires that the boat be hauled to install the keel cooler. The keel cooler is also available with sacrificial zincs,
which is not necessary in normal applications, but may be required if the boat has a “floating ground” system. It is a
requirement of any installation that the keel cooler be connected to the battery negative as a safety measure, & this
normally will connect the keel cooler to the bonding system & also the shaft or hull zinc which will protect the keel
cooler.