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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 Hori-
zontal (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 tem-
peratures 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 avail-
able 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 mod-
els 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 refrig-
erator 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 1-1/2” 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 refrigera-
tor 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 run-time 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 me-
dium than air & typically stays at a lower temperature than the air inside the boat or locker. It is gener-
ally 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 wa-
ter 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 sacrifi-
cial 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.
