Fridges

[Guest]

We have a Weaco CF-40 (same mechanicals as 50 but a tad less volume) which is the compressor version Weaco do, the other being thermo-electric. Just been using it and some other bits to load the hell out of my micro eco dwelling electrical system to see if it blows up, it doesn't.

 

During that I plugged the fridge in. Batteries were at 12.55V, the space was hot, the fridge empty, had good ventilation and reading 16 degrees.

 

The fridge sucked 5Amps (a smidgen under) and stopped at 2 degrees after 20 minutes. While away with it on the boat I noticed it used close as 1 Amp hour average when cold, loaded and set at 4 degrees. When on the boat it has OK to good ventilation and is shielded from direct sun but can suffer from 2 kids constantly scavenging food. We usually load it and bring it down while plugged into mains and then swap to the boat 12V.

 

I'd say these are a very viable option for getting cold beers on a power challenged vessel.

[wheels 543]

Yes the compressor type is your most economical. In a nutshell, they are a Heatpump. The very same thing as on many walls. They simply pump the heat from the food to the outside. Where as every other type of cooling device works by producing heat to then produce cold, so as it can suck away the heat which it then in turns has to get rid of the heat from the food along with the heat it produced to make the cold in the first place.

There are several different condesors available also. Ones that are an ice box and anything inside the box will freeze, and the rest of the fridge is just cooled. You can have the box opened out so it is a large area flat plate and the third option is a radiator type thing that has a fan that blows the chilled air around the entire fridge area. That keeps everything even in temp and stops ive from biulding and stops things from freezing as they do when food comes in contact with the plate type. The only negative with those type is that you have a little fan constantly running. Not good for a small boat, but a large boat doesn't really notice the power draw.

Once again, the ability to maintain efficiency is in insulation of the freezer/fridge box. The abilioty of getting the temp down as fast as possible is in how well you can get the heat away from the evaporator. That is the radiator part that is usually with the compressor unit. Some fridge units can also have water cooled evaporators.

[w44vi 17]

if you just want to keep beers cold you could do what we use to do, get a large sack tie a rope around the top and lower it over the side

works brilliantly in the sounds

[Guest]

refrigeration and the refrigeration cycle is all about the removal of heat........pure, plain and simple, how you dissipate that heat is a matter of just how much wattage/ complication you can afford, air cooled condensors are the cheapest option as long as they have a good airflow, the aircooled do run a higher head presssure which translated means pressure=temperature= power consumption, generally on the smaller DC units there is quite a gain using water cooling even with the addition of a water pump however.... there aint a really good small DC constant cycling water pump to match, most all danfoss type systems are what is known as direct expansion whichis to say they grab the removable heat quickly, most all engine drive systems are indirect expansion which is to say the refrigerant removes heat from the eutectic/ holdover fluid which in turn removes heat from the product, note there is a lag here though effectively what you are doing is storing energy inthe eutectic/ holdover, heres the funny bit, with these systems you are dealing with what most call brine.....trying to imitate salt water thermal properties without the corrosion aspect, this remains in a latent state at around the -7deg c mark so effectively . if you have a digital thermometer you'll note it looses temp from where you ran it down to rather quickly until it gets to the -10>-8 deg c mark and then it'll stay pretty stable for a long time............holdover........the DC units can and do come with holdover plates ( some called power plates) however the running time can be a bit long and better suited to bigger battery banks, one trick that works amazingly well is to freeze plastic bottles of salt water and use them......effing amazing just how long a 4 litre oil pack bottle frozen lasts

[wheels 543]

one trick that works amazingly well is to freeze plastic bottles of salt water and use them......effing amazing just how long a 4 litre oil pack bottle frozen lasts

Now one of the easier ways of thinking about this, is that heat is radiation and is in fact infra Red light radiation. So think of hot as being brighter light and cold as being darker light and the Hot wants to light up the cold, or the Bright wants to light up the dark. The darker it is, the more light gets "sucked in to the void" like a black hole.

So Heat=energy moves towards Cold=less energy till the two become equal. The "speed" that heat moves to the Cold is dependant on how cold the cold is. In other words, the less energy present, the faster the absorption of energy outside of it. Salt lowers the freezing point of water. Fresh water is 0degC for instance. Saltwater of about the salinity of the sea, is -2DegC. But the main difference is not actually the freezing point. It is how cold you can make the ice. Freshwater turned to ice remains 0degC, no matter how cold it gets. It actually becomes a very good insulator. So you can freeze the ice down to -18degC if want and it still is only 0degC. This is because the water molecules are stationary. Heat, or energy is all about movement of molecules. Once they stop moving, they no longer have energy.

Increasing the level of salt in water, lowers the frezzing piont. A strong solution of Salt can lower the freezing point to -6degC. That means the "brine" can now absorb far more energy than the frozen fresh water can. Of course, the energy taken to freeze the brine was also high and so feezing brine really requires the work to be down at home or on shore power where it doesn't really cost.

[Farrari 4]

KM, as I said earlier we used a Waeco CF-50 portable fridge/freezer in our previous vessel (tracker). For the most part I would say it work really well as a fridge but not so well as a freezer. The fridge was fine for 3-4 days but we always preferred a freezer if we were going away for an extended period of time. Being portable, the amount of insulation is always a compromise.

 

Your eco building test was quite interesting but you may want to think about expanding it to emulate the situation on a boat. The three factors I noticed from a practical point of view that influenced the Waeco's efficiency were;

 

1/ Ambient temperature. Mid summer the inside cabin in our case was high 20's (Celsius). The rate at which the heat absorbed in the gas (ammonia) can be released is dependant on the surrounding ambient temperature. Your test was 16 degrees to which might be accurate during winter but not summer.

 

2/ battery voltage. As the battery discharged and the voltage dropped, the unit became less efficient. This may be less of a problem for you as you have a bigger battery than I had. The Waeco unit had a high/medium/low switch on it for battery protection setting. Even on the medium setting the unit would retard the compressor activation in order to protect the battery.

 

3/ air flow. We had really limited space so air flow became a problem. Our kids aren't the tidiest and they had a tendency to just throw stuff onto the floor in the cabin during the day and that disrupted it even further. Also the heat produced by the fridge had no where external to vent meaning it acted like a heater in the cabin.

 

The other test you may want to consider is measuring how long the compressor runs for for a given hour. This is the real measure of how much battery it will use over a 24 hour period.

 

A better way to test the unit might be to place it in a semi confined space using a fully charged battery for 24 hours. You could then measure the specific gravity of the battery afterwards to roughly figure out how much power it had consumed. Try and get the ambient temperature of your location close to what you expect during summer operation.

 

Hope this helps.

[Guest]

G'day F.

 

1 - The fridge said it was at 16 degrees when I turned it on, the room the fridge was in was bloody hot and it was in direct sun. The room would have easily been mid or higher 20's.

2 - Mines all set on factory defaults at the moment so 4 degrees coldness and the battery cut out thing is at medium.

3 - It had lots of airflow room even if there was no breeze as such.

 

I'll plug it onto a 35Ahr battery and see how long it lasts. Stand by

[Guest]

Interesting comparison between 2 of the leading small/portable fridge dudes.

 

http://www.rvworldstore.co.nz/blog/waecoengel/

 

and one on what type do you need. Aimed at RV's but as RV's are only for people who can afford tyres but knot keels, the same principals apply.

 

http://www.rvworldstore.co.nz/blog/fridgetype/