Sundown was built in 1982, but never equipped with more than an ice box to keep perishable food cold. It wasn’t a bad ice box at 8.5 cubic feet with good insulation, a molded interior and nice teak shelf. Given Sundown will become our year-round residence soon, however, it’s time for refrigeration.
When it is time to upgrade, replace or install a new refrigeration system there are basic questions to be answered.
Does my boat have an existing box or will I need to make one?
Sundown had a ice box so we decided to use retrofit it with refrigeration rather than rip it out and start over. If we had decided to make one from scratch, I would have considered a pre-made, built-in unit by Engle. They are making very nice, efficient refrigerators. On the ambulances on which I work, we carry cold normal saline on our for therapeutic hypothermia in little Engle coolers and we never have problems with them.
Is my existing box well insulated?
Whether you are designing a new box or considering your current one, the amount of insulation it has is most important. To have a box that will not need a near-continuous power drain to keep the heat out, you need a minimum of three inches of insulation. There should be no drain hole from which the cold air can escape, and if you have a door, it needs to be very well sealed. I think a top-opening lid works well as only the warmest air will leak out when it’s accessed.
We made a custom bi-fold lid and molded the seal to the it. If you open one side, you have refrigerator; the other side allows access to the freezer area.
How many cubic feet do we have?
You need to know the amount of cubic feet inside of your box to determine the size of compressor and condenser or cold plate it requires to function properly. Cubic feet is determined by height x width x length in inches divided by 1,728. A box that will be used for just refrigeration or a freezer can work with this number. If you are splitting the box like we are, you need to take the overall cubic feet and add the cubic feet designed for the refrigerator only. For example, if you have a six cubic foot box and you plan to use two cubic feet for a freezer, then you need to plan for a condenser and compressor for eight cubic feet.
Our freezer/refrigerator box has a freezer thermostat to control the compressor. The refrigerator is cooled by a fan in the partition wall that is controlled by a separate thermostat.
Is our electrical system set up for the power demand of a refrigeration system?
Refrigeration may be the biggest power hog on your boat. As a matter of design, you should provide a 10 gauge wire for both your positive and negative terminals, and assure it’s properly fused. The efficiency of the box really depends on how you use your boat and what you keep in the box. The more efficient the box, the less the compressor runs. As a rule of thumb, plan on your compressor running 50 percent of the time. If your average compressor draws five amps and the box runs 24 hours, then you need to plan for a 60 amp hour budget per day for the refrigerator. Base your battery storage and charging system based on that.
How are we planning on using the boat. Weekend sailing, slip living or cruising?
Efficiency drops off quickly when you plug into the 30 or 50 amp shore power. Suddenly, refrigeration, air conditioning and television become hassle free. If you plan to spend anytime sailing away from the slip you will need to be more intentional about conserving energy. We plan on cruising so will keep our freezer section filled with water bottles and frozen foods. This cold mass will allow us to maintain the refrigerator with less than 50 percent run time and our compressor has a motor control to slow the motor to the most efficient speed. Our battery storage is 480 amp hours, so the refrigerator at a 60 amp hours per day budget will be handled well.
How much is this going to cost and what can I afford?
The bottom line is fuzzy here. What effort and money you put into proper design will save you hundreds of dollars later. The least expensive refrigeration models are air cooled and DIY. They can be passively water cooled which is more expensive, but requires less power, smaller batteries and less charging ability. Plus, cold plates work well for boats with big charging systems and short engine running times.
Here’s a short video explaining the refrigeration side of the installation. Next week, I’ll post about the compressor side.