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Post by sailbleu on Nov 8, 2017 7:11:59 GMT
I've found that I need different temperature setpoints depending on how full the fridge is. At the beginning of a trip if it's too cold then the stuff nearest the cooling plate is going to freeze if I set it too cold. The bottom of the fridge is warmer than the top because it takes a long time to get the energy out of there. As the fridge empties there's more airflow inside the fridge and the setpoint needs to come down a degree or two because the temperature is more uniform. Bottom line is that it doesn't really matter where you put the thermostat as long as you adjust the setpoint accordingly. You're going to have to play with it to learn what keeps the milk from going bad while not freezing the lettuce . Installing a small (computer) vent that runs when the compressor is working will distribute the internal heat/cold (how you like it) . Mine is positioned in the top corner and aimed to the evaporator. Go for a quality vent because the cheapies will complain ( rattling) in the cold environment. Regards
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Post by so32foot on Nov 8, 2017 7:46:44 GMT
So36idavid: many thanx for your explanation, it sounds logic. I already made the fridge less deep because my wife couldn't reach the bottom of fridge. I made it less deep by adding insulation material at the bottom. But it's still deep, so may be I add some more insulation material, so that the fridge becomes smaller and I have to cool less air.
Sailbleu: I have several computer vents left at home: which diameter did you install?
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Post by sailbleu on Nov 8, 2017 13:48:40 GMT
So36idavid: many thanx for your explanation, it sounds logic. I already made the fridge less deep because my wife couldn't reach the bottom of fridge. I made it less deep by adding insulation material at the bottom. But it's still deep, so may be I add some more insulation material, so that the fridge becomes smaller and I have to cool less air. Sailbleu: I have several computer vents left at home: which diameter did you install? Not on the boat right now , but will be in 3 weeks time so I can measure , but I believe it was a 50 or 60 mm one. The smaller , the less power draw but unfortunately also less flow rate . Although you don't need a tornado to equalize the inside temperature . Regards
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Post by so32foot on Nov 8, 2017 18:17:17 GMT
So36idavid: many thanx for your explanation, it sounds logic. I already made the fridge less deep because my wife couldn't reach the bottom of fridge. I made it less deep by adding insulation material at the bottom. But it's still deep, so may be I add some more insulation material, so that the fridge becomes smaller and I have to cool less air. Sailbleu: I have several computer vents left at home: which diameter did you install? Not on the boat right now , but will be in 3 weeks time so I can measure , but I believe it was a 50 or 60 mm one. The smaller , the less power draw but unfortunately also less flow rate . Although you don't need a tornado to equalize the inside temperature . Regards Many thanks, Sailbleu, no need to take a further look. The indication of 50 tot mm is sufficient. I have both and I will check the power consumption and decide which one I will use.
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Post by zofiasailing on Nov 10, 2017 2:08:26 GMT
Friends on a Hanse have the same fridge. They asked a refrigeration expert to quote on a eutectic plate as they were unhappy with cold distribution across the contents of their fridge. The advice given was to remove the freezer compartment door to allow colder air to spill out into the main body of the fridge. If no improvement, only then consider the expense of alternatives. We decided to give it a go. Outcome: We can still make ice. Fridge contents do appear cooler throughout. No appreciable change in power consumption. No appreciable acceleration in rate of icing up around the freezer box. Someone with some technical knowhow and a scientific approach may like to test it out. It merely requires the flap to be removed. We have no plans to reinstate ours.
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Post by sailbleu on Nov 12, 2017 14:49:42 GMT
Friends on a Hanse have the same fridge. They asked a refrigeration expert to quote on a eutectic plate as they were unhappy with cold distribution across the contents of their fridge. The advice given was to remove the freezer compartment door to allow colder air to spill out into the main body of the fridge. If no improvement, only then consider the expense of alternatives. We decided to give it a go. Outcome: We can still make ice. Fridge contents do appear cooler throughout. No appreciable change in power consumption. No appreciable acceleration in rate of icing up around the freezer box. Someone with some technical knowhow and a scientific approach may like to test it out. It merely requires the flap to be removed. We have no plans to reinstate ours. Missed your post here but would like to add a comment. I've done this also , open the evaporator lit so more cold can ' fall down ' from the evaporator. That doesn't mean the cold is dispersed more around the whole inside area of the fridge & here's where a inside circulation fan /vent comes in handy. These inside fans are often used these days in modern fridges by the way . But !!!! In a normal case ( boat fridges) the temp sensor that drives the compressor (via the thermostat unit) is built in/on the evaporator itself .That means when the temp. of the evaporator gets too high/warm - due to new stuff/food put in the fridge or higher outside temps or opening the fridge door too often - the compressor switches on and the refrigerant-gas starts running , in other words the cooling process starts. Evaporator gets colder , >>>>>>>>>>> fridge content gets colder . However , when you convert the fridge like many of us have done ( mine goes back 5 or 6 years) with a fancy digital temp controller , than usually the sensor is placed somewhere else because most of us also want a real inside temp of the fridge ( in my case near the bottom ) . These digital controllers can offer that advantage. And here's where it goes bad. These boat fridges are originally really well designed you know , relation between compressor size - evaporator size - inside fridge size - insulation capacity . So the surface of the evaporator must meet a certain content of fridge - or vice versa - the evaporator temperature will be a reference for the overall temp. inside the fridge. In short , the temp. of the evaporator will guarantee or agree with a specific fridge temp. Higher inside temp. will result in a higher evaporator temp. and the attached sensor will start the compressor. I admit , and in the past I've posted this on the board in other (similar) topics , wanting to replace my digital sensor to the evaporator again , these terrific digital controllers can handle the range down to minus 50°C and therefor it would be better to do it , but then I would not have an actual inside temperature anymore ! So torn between two worlds I have not yet passed the alteration . Adding an extra/other display would solve the dilemma , but where to put it Regards
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Post by rene460 on Nov 13, 2017 4:46:57 GMT
Hi Sailbleu, I think you have pointed to the missing piece of the puzzle. The way I see it is this.
Our refrigerators have only one pressure reduction capillary and evaporator combination, and one temperature measurement point, so can actually only control one independent condition. But our food storage needs require two temperature zones, a freezer and a general food storage compartment, with different temperatures. The manufacturer puts the thermostat on the evaporator, where it best measures the evaporator temperature, which is directly related to the evaporator pressure. The lower the pressure, the lower the temperature, but the harder the compressor must work, so it draws more current. The location of the thermostat is fine for the freezer compartment. The manufacturer then attempts to balance the heat flow into the freezer compartment, including the door arrangement, so that the heat gain through the insulation of the much larger food compartment results in a satisfactory temperature in that zone. The freezer stays cooler due to the restricted heat flow between zones. It actually relies on that lack of insulation we have all complained about to keep the food zone warmer. Perhaps overthinking there, to infer it might be deliberate elegant design when "it's cheaper" is a perfectly adequate explanation. However, it can only work totally as planned for a very specific outside temperature for each thermostat setting. When we add more insulation, we upset that balance, and in particular, we bring the freezer and food compartment temperatures closer together. To control two zones, expensive domestic refrigerators have two compressor units independently controlled. But we don't want the extra weight, and don't have the space anyway, at least on a smaller boat.
That is where your extra thermostat and the internal fan come in. Rather than remove the original freezer door or thermostat, arrange your fan and second thermostat as that second controller. A little baffle, to prevent unintended transfer from the food compartment to the freezer might be required but the fan can then have some control over the air flow, hence heat transfer and hence the temperature difference between the zones. Place your thermostat where you feel best represents the desired food zone temperature, and use the fan to increase the air flow from the food compartment around the evaporator/freezer compartment to provide food zone cooling. Use your thermostat to switch on and off the fan. The original thermostat will look after the compressor and freezer compartment and the total heat load.
It might take a little fiddling with the temperature settings to avoid any excessive on/off switching of the compressor, better to switch the fan, and play with the on - off settings. However while it is not a total solution, it gives a degree of independence to the two zone temperatures. I am sure there will be a better way than just a simple baffle as I have suggested.
Yes, I know, another highly theoretical solution, but understanding the theory can help guide experiment in a productive direction.
rene460
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Post by so32foot on Nov 13, 2017 15:53:14 GMT
Regarding the fridge of my SO32:
It took a lot of power as the compressor was switched on during about 45 minutes of each hour. The outer temperature had not so much influence. I contacted the Dutch representative of Frigoboat and his conclusion was that for the type of equipment the fridge was too large. He concluded that from the fact that the evaporator was mostly iced, although I removed the small metal lid of the evaporator as I do not store frozen food on my boat. Apparently the fridge became on the wished temperature in few days time after filling and the ice melted so I had lots of water in the fridge. But the temperature was constant after these few days. I also found that is was badly insulated, especially towards the motor compartment!
So I made the fridge smaller by adding insulation on the inside (bottom and motorside) I also tried to get in some foam, which partly succeeded. After this the power consumption seems to be better. But the icing problem on the evaporator is still there.
So I want to try the digital temperature controller with the sensor at the place where I like to have a 5 - 6 degrees Celsius temperature, with the original controller out of operation. And see what happens.
I noticed also that the upper side of the fridge is alway cold. That's why I hesitate to install a fan in the fridge, because the coldness is spread throughout the fridge. So theoratically I will loose more coldness through the upper side. Cold air falls down, so it's on the place where I want to have it.
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Post by so36idavid on Nov 14, 2017 4:48:54 GMT
But the icing problem on the evaporator is still there. This is caused by moist air getting into the fridge. I recommend replacing the seal with some weather stripping which should be inexpensive and available at any hardware store. It comes in many sizes and cross sections, get something that looks roughly like what you already have and be careful to minimize gaps in the stripping when you install it. It will reduce the amount of moist air in the fridge and reduce the power draw too. David
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