by Tim Dick, Portfolio #669
The Adler-Barbour refrigeration unit (aka heat pump) on Catalina 34s is located under a dinette seat where it receives no ventilation and consequently gets hot in operation. This hurts the efficiency of the heat pump by not allowing it to efficiently dissipate the heat it pumps out of the ice box. My unit stayed on 75% of the time (a 75% duty cycle) which uses much electricity, reduces the life of the pump, and makes that annoying humming noise more than I want.
A simple way of improving efficiency is by making ventilation holes at the top AND the bottom of the heat pump compartment. (NOT THE ICEBOX!!) I drilled three 1 diameter holes at the top and the bottom on the face underneath the dinette directly in front of the heat pump and gelcoated the edges. The heat creates a convection cooling draft which is sucked in at the bottom and expelled at the top holes. You can feel the warm air at the top. This dropped the duty cycle to less than 50% on my boat in San Francisco which is a cool climate ideal for convection cooling. I estimate it is cutting my electricity consumption in half which is close to a free lunch.
For even higher refrigeration efficiency while on 12 volt operation, drill only one hole in the bottom of the compartment, but 3 holes in the top. Install a 1 diameter 12 volt muffin fan (available at Radio Shack or any electronic hobbyist shop for $15) in the bottom hole and wire it to the 12V refrigeration power. This will actively pump cool air into the compartment further increasing the efficiency of the refrigeration unit. This plan is best for warm climates where convection airflow may not be adequate. The current draw of the fan is negligible in comparison with the refrigeration unit.
The fan plan will not be as efficient in 110V operation since the fan only runs on 12V and there is inadequate hole area for convection cooling airflow. However, assuming you have a 110V battery charger, you can still run the unit on 12V while hooked to shore power and gain the benefits of fan cooling.
Separately, a simple ice-box upgrade consists of screwing a pair of hinges on the outboard end of the hatch, and adding a small coil-spring type hatch supporter just inside the edge. The smallest size West Marine sells fits perfectly. Now my icebox lid stays open when I grab a cold one and I dont have to find a place to put the lid when Im bottom fishing in the bowels of the box.