DIY FRIDGES - Fridging the Gap

There are two unwritten rules about ‘happy hour’ on a boat — first it always lasts much longer than an hour, and second you can’t serve warm beer and hot champers. That’s why choosing the right boat refrigeration unit for your boat is a serious matter.

If you are planning a DIY boat refrigerator installation into an existing chest icebox there are a number of considerations before selecting your unit. These range from insulation, your battery bank’s capabilities and the climate where you live. Even the most sophisticated refrigeration unit can’t work miracles.

Recently, I replaced my old boat refrigeration unit, a 190lt chest box, on my Gulfstar ketch Aardvark, with a new 12V Waeco CU95 danfoss compressor and a Waeco plate evaporator VD21.

The plate evaporator has a cooling capacity of 250lt refrigeration at 50mm of insulation, while the CU95 has the capacity to refrigerate 400lt with an evaporator, 250lt with an accumulator or 200lt deep freezing.

By going for the overkill I can keep the cool box at an even temperature in the fridge zone — no matter how hot it gets outside.

When buying a fridge for a boat, my first consideration was could the refrigeration unit handle sailing conditions combined with a hot North Queensland summer?

Waeco says its boat fridge cooling units can withstand a constant heeling of 30°C — so that was a big tick for the unit — then the dealer sealed it with the assurances that this particular unit had been built to handle tropical conditions.

CLIMATE CLASS

Here’s a handy tip. The European Union introduced four climate class ratings — SN, N, ST, and T. Not all fridges sold in Australia display this rating but a number do. If yours does it will be on the compliance plate. The SN stands for sub-normal (cold climates) and the letter N for normal and these letters are on units rated to up to 32°C. The ST stands for sub-tropical and is rated to 38°C and finally T is for tropical and rated to up to 43°C. These ratings give you a reassurance that the unit is designed for the environment where you live. My Waeco plate evaporator VD21 had the letter T on it.

BOT FRIDGE SIZE (MATTERS)

If you try to cut corners by using an undersized cooling unit or mount the condenser where there is restricted airflow, your boat fridge will perform poorly and consume excess power.
A first consideration is working out the dimensions of the cool box and matching that against the manufacturer’s technical data sheets.

To work out the capacity of the cool box measure the inside height, width and the depth and multiply the three measurements, this will give you a cubic volume. Don’t forget your decimal point. Most manufacturers in their technical data rate a specified amount of cubic litres of volume to their units to cool, fridge or freeze.

BOAT REFRIGERATOR INSULATION

The next step is working out what insulation material has been used on your cool box and its thickness. As a general rule of thumb a minimum thickness of 35mm for foam polyurethane is acceptable for a fridge. My preference is for at least 50mm. The quality and thickness of the insulation is a major consideration, otherwise the compressor may work overtime.

SEALS

Do your boat frtidge seals need to be replaced? Ice buildup is often due to damaged or poor-fitting lid seals. Good seals keep the humid air out and your fridge virtually frost free. It pays to clean the lid seal regularly.

BATTERY DRAIN

Is your battery bank sufficient to support the new boat refrigerator system? Do you have adequate recharging capabilities to sustain a healthy state of charge in your battery bank?

Your refrigeration unit may use anywhere between 2amp and 6amp on average per hour for a compressor fridge, depending when the contents have cooled down and how often the thermostat cuts in. If you need to convert Watts to amp the simple equation is
Watts divided by Volts = ampere. For example 18W divided 12V = 1.5amp. This can be a useful equation when converting your input wattage from solar panels.

To find out if your battery bank is sufficient you first need to know the total amp hours of all your house batteries combined. Be careful to check the manufacturer’s recommendations on how far the house batteries can be discharged without damage. This will vary depending on the type of battery, be it flooded cell, gel cell or absorbed glass matt.

Thankfully these days many quality mobile fridges have a low voltage cut-off safety feature. This means the refrigeration unit cuts outs when the battery charge level falls below an acceptable safe level thus protecting your batteries from total discharge.

READ THE MANUAL

Don’t be put off by the 200-odd-page manuals — most of it is all in a different language anyway. The part you want will probably only be a dozen or so pages thick and is usually easy to follow.

GETTING BENT 

If you have to bend the feed pipes and or the cold plate to fit into your chest fridge then do so with EXTREME care and only after getting confirmation from the dealer on the recommended bending points and tips on the best way to do it. The last thing you want to do is crimp any pipes. In my case I had to bend the evaporator plate in two places to form a U shape. But I did so only after the dealer had marked the best bend points for me and advised on the radius of the arc.

BOAT FRIDGE INSTALLATION

In my instance there was a hole in the wall of the icebox where the old compressor unit had been removed. After I had run the new pipes through, the hole was patched and reinsulated with high-density foam.

I also made sure the Waeco plate evaporator VD21 had a 10mm clearance between it and the cool box wall. This was achieved with plastic spacers placed behind the evaporator plate and secured with the mounting screws.

Once I was satisfied that both the plate evaporator and the compressor were correctly mounted then it was time to join the two units together.

JOING THE BOAT FRIDGE COMPONENTS

Joining the units is a case of carefully following the manufacturer’s instructions in the installation manual on the final joining of the valve couplings, which integrate the two systems. It is an easy procedure connecting the pipes and virtually impossible to connect them the wrong way as each unit has a male and a female coupling that cannot be reversed.

To make sure the new coupling was leak free I poured a small amount of detergent and water in a jar and shook it vigorously to form bubbles then scooped the bubbles (not the liquid) out and packed this around the newly joined connections. This is a technique used by some gas fitters.

WIRING

The installation instructions may tell you the minimum size 12V wire to use over various distances. As I had upsized the compressor and increased the distance from the battery bank it made sense to replace the original wiring with a heavier gauge to avoid any power loss.

Wiring up a Waeco is a case of following the bouncing ball — everything on my unit was colour-coded and the instruction sheet was well set out and easy to follow. Finally, make sure you use the right size fuse.

DEFROSTING

My general rule of thumb is whenever the frost layer exceeds 3mm to 5mm then it is time for me to defrost. A word of warning — don’t use anything sharp to chip away at the ice as you could damage or puncture the evaporator plate or pipes. To defrost my evaporator plate I simply turn the fridge off overnight and it stays pretty much in the fridge zone anyway.

WAECO TIPS

Waeco advises that heated air must be able to dissipate unhindered and that you should make sure the airflow to the condenser is not restricted. Waeco also warns against placing the cooling unit next to heat sources such as gas ovens and hot-water pipes or in direct sunlight.

Clean the condenser of dust and dirt at regular intervals. The manufacturer also suggests that when the cooling unit is shut off for prolonged periods then you should leave the lid slightly open to prevent odour build-up.

COOL TIPS

Weekend sailors who turn the fridge off when the boat is not in use should consider popping down to the marina and turning on the unit the day before. This will give the refrigerator time to pull down to the required temperature. Another tip is to pack the fridge with food that is already cold or frozen.

FINALLY, HAPPY HOUR

Once your DIY installation is complete it’s time to sit back and enjoy a well-earned beer. Hopefully, you’ve had the Esky packed with ice and the celebratory brew is well chilled.
Then sit and wait intently for the first signs the evaporator plate is getting cold. With my new Waeco unit it didn’t take long. And that deserved another celebratory beer. Cheers