Author Topic: 12/24 Volt Boat Refrigerators Poor Performance Possible Causes  (Read 59 times)


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12/24 Volt Boat Refrigerators Poor Performance Possible Causes
« on: November 01, 2018, 11:10:28 am »

Comparing a boats ice box conversion units performance to a home refrigerator or even to an older boat refrigeration system is a mistake. A home refrigerator is designed around a cabinet size with each component selected to collect and dispose of a given amount of heat energy. Home refrigerators are also assembled, serviced and tested in a controlled environment your boats ice box conversion unit is not treated with the same quality control; this is why performance varies from one boat to another.

Small 12/24 volt ice box conversion units in the past were advertised so the consumer would believed one unit could be efficient in various size boxes. In the last 10 years when buying a 12/24 volt conversion refrigeration unit there are over one hundred options to choose from, compressor size and speed selection, evaporator size and type, and various heat removal mediums. A small conversion refrigeration unit will be efficient and perform properly only when the right unit is selected, installed correctly and the insulation is sufficient to deliver the desired box temperature in a planned geographic climate cruising area. The causes of poor refrigeration performance can usually be corrected by first identifying the deficiency and then correcting it. If a refrigeration system satisfies the desired temperature in the box its performance is good. If the daily power consumption is higher than expected, then conditions that effect short compressor run times or long run time high temperature/pressures, need to be investigated.

The most common causes of poor performance on small 12/24 volt refrigerator are:
Poor airflow through condenser.
Condenser fan is not shrouded.
Heated air that passes through condenser is allowed to pass through it again. Air cooled condensing units are designed to be efficient when boats interior ambient air temperature is between 70 to 90 degrees F.
On condensing units cooled by water, poor or excessive water to refrigerant heat transfer will lower overall performance.
Compressor cycles off and on too often.
Too much refrigerant, this is even possible on a new pre charged units.
Small amount of refrigerant was lost on installation of line connectors or the system has a small leak.
Thermostat incorrectly installed.
Compressor speed too fast or too slow.
Air or incorrect gas mixture in refrigerant.
Very old box insulation or when insulation is wet or VIP insulation has failed. Box insulation is easily evaluated by comparing insulation exterior surface temperatures against boat interior air temperature. If insulations exterior surface temperature is less then five degrees cooler than boat interior air temperatures insulation is generally considered expectable.     

Common misunderstandings about small 12/24 volt boat ice box conversion refrigeration units:
Most refrigeration mechanics do not know how to correctly service and make repairs do to complicated marketing design variations.
The shorter the compressor run time the more efficient the system is, not true, on variable speed models they will run longer and are more energy efficient when running at a slower speed.
Poor refrigeration performance is generally related to lack of insulation, not true, but high energy consumption might be linked to lack of insulation.
A eutectic holding plate with less surface area than the recommended size of a thin plate evaporator are more efficient than thin plate evaporator is not true. Eutectic solution separation do to age is another problem with eutectic plates.
Water cooling a small 12/24 volt unit will provide better performance than air cooling, only true in rare cases and never more reliable than air cooling.

Right or wrong information you decide for yourself. The first law of thermodynamic energy in a refrigeration unit can be transformed from one form to another, but can be neither created or destroyed.

The energy for these small 12/24 volt refrigeration units on a boat originates from ether an engine alternator or generator or alternative electric power from wind and solar. This onboard energy produced is passed through or stored in batteries. The 12/24 volt refrigerator compressor converts electrical energy from battery into gas high mechanical pressure. The refrigeration compressor based on its design can increase input energy to a slightly higher output energy known as improving Coefficient Of Performance (COP). Entire System COP will never be greater than compressors COP. Evaporators whether thin roll bond or eutectic plates can not create more energy than the compressor produces. The best evaporator or eutectic plates COP that an engineer could hope for is a neutral COP energy exchange inside evaporator. Aluminum thin plate evaporators are as close to neutral COP as possible. The eutectic plates especially those with Glycol and water mixture will result in a negative System COP reduction.
Only true eutectic solution plates with brine or other corrosive solutions can match the performance of the correct size thin plate evaporator. It is true that efficiency of eutectic plates are not all the same. Plates that are designed to conduct heat directly through plate skin into refrigerant evaporator coil will react much the same as thin plate evaporators and still store energy the same as batteries. The main disadvantage of eutectic plates is there is a lack of excessive surplus energy that is not available from these small compressors without alternative electrical power from wind or solar.