Surprising results with a spill-over fridge.

[GILow]

Hi Cruisers,

Some unexpected results to share for those of you constructing your own refrigeration systems.

About 2 years ago I constructed my own chest fridge/freezer with a lot of great guidance from Pete of Ozefridge, plus some careful reading on this forum.

The fridge has been a terrific success, although at over 220 litres it is probably double the size I really needed.

ANYWAY, about a year ago I finally got around to putting a fan and a control circuit together to stabilise the fridge temperature. For the first year I’d just relied on slightly tilting the divider panel to control the temperature. This technique led to the premature demise of a few cartons of milk and the creation of some seriously inedible yoghurt.

The fan control was a great success. I used the approach of one 50 mm hole drilled through the 75mm full-height xps foam divider close to the top and another at the middle height with a small computer fan on the fridge side of the middle hole blowing air into the freezer compartment. (I can’t remember exactly where I got this particular set of dimensions and hole/fan layout but it seemed to be one of the more popular approaches.). Temperature is sensed with a ds18b20 which talks to a picaxe chip.

But recently I started to find things were freezing up in the refrigerator compartment. The odd lettuce went south, then the other day I found ice in the sodastream bottles. I assumed something had gone wrong with the control circuit so I dug out the laptop today and plugged it in to see what was going on.

It turns out, not a lot. The fan is only operating once or twice a day, usually around when I am preparing dinner. It turns out, there’s enough natural flow between the compartments in this cold weather (10. - 15 degrees C in the cabin) to cause the fridge side to drop below 0 degrees.

So, for those of you building spillover fridges, you might want to carefully consider the hole size in the divider. I cannot remember where I got the 50 mm recommendation from but I am thinking maybe 40 mm would have been better.

Matt

[Uncle Bob]

Originally Posted by GILow

Hi Cruisers,

Some unexpected results to share for those of you constructing your own refrigeration systems.

About 2 years ago I constructed my own chest fridge/freezer with a lot of great guidance from Pete of Ozefridge, plus some careful reading on this forum.

The fridge has been a terrific success, although at over 220 litres it is probably double the size I really needed.

ANYWAY, about a year ago I finally got around to putting a fan and a control circuit together to stabilise the fridge temperature. For the first year I’d just relied on slightly tilting the divider panel to control the temperature. This technique led to the premature demise of a few cartons of milk and the creation of some seriously inedible yoghurt.

The fan control was a great success. I used the approach of one 50 mm hole drilled through the 75mm full-height xps foam divider close to the top and another at the middle height with a small computer fan on the fridge side of the middle hole blowing air into the freezer compartment. (I can’t remember exactly where I got this particular set of dimensions and hole/fan layout but it seemed to be one of the more popular approaches.)

But recently I started to find things were freezing up in the refrigerator compartment. The odd lettuce went south, then the other day I found ice in the sodastream bottles. I assumed something had gone wrong with the control circuit so I dug out the laptop today and plugged it in to see what was going on.

It turns out, not a lot. The fan is only operating once or twice a day, usually around when I am preparing dinner. It turns out, there’s enough natural flow between the compartments in this cold weather (10. - 15 degrees C in the cabin) to cause the fridge side to drop below 0 degrees.

So, for those of you building spillover fridges, you might want to carefully consider the hole size in the divider. I cannot remember where I got the 50 mm recommendation from but I am thinking maybe 40 mm would have been better.

Matt

Matt, I was particularly impressed with the stainless panel that Pete demonstrated that ducted the air from the fridge portion through it without actually entering the freezer portion, I thought mmm smart!! Perhaps an email to louie may yield further information.

[GILow]

Originally Posted by Uncle Bob

Matt, I was particularly impressed with the stainless panel that Pete demonstrated that ducted the air from the fridge portion through it without actually entering the freezer portion, I thought mmm smart!! Perhaps an email to louie may yield further information.

Ooooh... sounds fancy!

I’ll bring the fridge up to your part of the world and we can test it’s capacity to handle rapid beer cycling.

[Uncle Bob]

Originally Posted by GILow

Ooooh... sounds fancy!

I’ll bring the fridge up to your part of the world and we can test it’s capacity to handle rapid beer cycling.

You smooth talking B. Done, I will even supply some of the test material.

[GILow]

Originally Posted by Uncle Bob

You smooth talking B. Done, I will even supply some of the test material.

Happy to report West End stopped making beer in South Australia last week so the average beer quality in the South East of Australia has improved dramatically.

[LittleWing77]

Originally Posted by GILow

Happy to report West End stopped making beer in South Australia last week so the average beer quality in the South East of Australia has improved dramatically.

Come to Canada and you and the Admiral can sample some REAL beer!

LittleWing77

Hope you didn't lose the top of your finger. I hadn't considered the implications of your wearing the "Admiral's regalia" until it was too late to post a brilliantly scathing response because the thread had been closed....

[skipgundlach]

My apologies for the inevitable dictation errors which will creep in as I use my phone rather than my computer to reply.

We have a similar setup in concept but not in actual execution. We have a 5 inch computer fan in the center of our spillover divider and the exact same square inches at the top worked out to be 1 inch of a gap at the top of the divider section.

When everything is working well and it's not too hot outside, I stuffed a small T-shirt remainder in that Gap to control the amount of airflow which occurs by convection.

That also slows down the input of freezing air from the freezer when the thermostat calls for cold. As a result we are able to control our refrigerator temperature between 32 and 34° f supplemented with a circulation fan. That fan is again a computer fan but only 2 inches in this instance.

Therefore, from your description, I would recommend perhaps putting some form of dodger over the space of the return to minimize your Frost issues. You could also have it so that you had a circulating fan in the bottom of the refrigerator which would circulate the coldest air throughout the box and affect what the thermostat was asking.

I also have a small tip that may be useful to you: I used a magnetic reed switch to control the computer fans and the LED Puck lighting inside the box. When the door is open, the fans shut off so as to not cause humid air to be drawn into the freezer. That's simultaneously turns on the lights. Closing the door makes the light go out and the fans come on again. The circulating fan is running all the time that the door is closed and the spillover divider fan runs only when the refrigerator is calling for cold.

Because I'm on my phone I don't have the links to hand for where I bought these, but you should be able to find that at any alarm shop or automotive accessories shop. What you're looking for is a NO / NC magnetic switch. I used a small velcro strip to attach my magnet, as there are frequent times when I want to be able to open the door but have everything shut down. I also remove it when I'm recommissioning it after a Time away from the boat. That allows me to get the freezer down to temperature before I ask for cold for the refrigerator.

Hope that is useful....

[GILow]

Originally Posted by skipgundlach

My apologies for the inevitable dictation errors which will creep in as I use my phone rather than my computer to reply.



We have a similar setup in concept but not in actual execution. We have a 5 inch computer fan in the center of our spillover divider and the exact same square inches at the top worked out to be 1 inch of a gap at the top of the divider section.



When everything is working well and it's not too hot outside, I stuffed a small T-shirt remainder in that Gap to control the amount of airflow which occurs by convection.



That also slows down the input of freezing air from the freezer when the thermostat calls for cold. As a result we are able to control our refrigerator temperature between 32 and 34° f supplemented with a circulation fan. That fan is again a computer fan but only 2 inches in this instance.



Therefore, from your description, I would recommend perhaps putting some form of dodger over the space of the return to minimize your Frost issues. You could also have it so that you had a circulating fan in the bottom of the refrigerator which would circulate the coldest air throughout the box and affect what the thermostat was asking.



I also have a small tip that may be useful to you: I used a magnetic reed switch to control the computer fans and the LED Puck lighting inside the box. When the door is open, the fans shut off so as to not cause humid air to be drawn into the freezer. That's simultaneously turns on the lights. Closing the door makes the light go out and the fans come on again. The circulating fan is running all the time that the door is closed and the spillover divider fan runs only when the refrigerator is calling for cold.



Because I'm on my phone I don't have the links to hand for where I bought these, but you should be able to find that at any alarm shop or automotive accessories shop. What you're looking for is a NO / NC magnetic switch. I used a small velcro strip to attach my magnet, as there are frequent times when I want to be able to open the door but have everything shut down. I also remove it when I'm recommissioning it after a Time away from the boat. That allows me to get the freezer down to temperature before I ask for cold for the refrigerator.



Hope that is useful....

I like your thinking in preventing the fan from running with the lid open.

I’ve got no gap at the top of my divider, just the 50 mm (diameter) hole. I’ve partially blocked that with some pool-noodle off-cut for now, a bit like your T-shirt approach. I’ll see how it goes over time.

I’m just amazed at how small the air-transfer path needs to be.

[hzcruiser]

Originally Posted by Uncle Bob

Matt, I was particularly impressed with the stainless panel that Pete demonstrated that ducted the air from the fridge portion through it without actually entering the freezer portion, I thought mmm smart!! Perhaps an email to louie may yield further information.

I'm in the process of designing and building a fridge as well. Ducting air on demand from the fridge through the freezer sounds very intriguing! It would greatly reduce ice in the freezer, I'd assume? But wouldn't that duct become clogged with ice over time, since the more humid air in the fridge gets pushed through a colder tube?

Are there any pointers where someone has documented this approach on the net?

[skipgundlach]

Originally Posted by hzcruiser

I'm in the process of designing and building a fridge as well. Ducting air on demand from the fridge through the freezer sounds very intriguing! It would greatly reduce ice in the freezer, I'd assume? But wouldn't that duct become clogged with ice over time, since the more humid air in the fridge gets pushed through a colder tube?

Are there any pointers where someone has documented this approach on the net?

Using a spillover approach means that every bit of moisture (atmospheric, usually!) which enters the box/es will wind up condensing in the freezer.

Household ones have isolated evaporators which shut down and go into reverse or are heated to constantly defrost; when that cycle is over, the cold comes back and (presumed; I have not torn one apart) when the air is cold enough it's again circulated.

More complex, but functionally the same, there's one heat-removal source...

[hzcruiser]

Originally Posted by skipgundlach

Using a spillover approach means that every bit of moisture (atmospheric, usually!) which enters the box/es will wind up condensing in the freezer.

Household ones have isolated evaporators which shut down and go into reverse or are heated to constantly defrost; when that cycle is over, the cold comes back and (presumed; I have not torn one apart) when the air is cold enough it's again circulated.

More complex, but functionally the same, there's one heat-removal source...

Yes, and that's exactly what I would like to avoid, having all the ice on the evap plate in the freezer. And I'm aware of the defrost cycle of the household units every 8 hours or so.

Hence my question how well such a duct from the fridge through the freezer and back into the fridge would work?

[skipgundlach]

Originally Posted by hzcruiser

Yes, and that's exactly what I would like to avoid, having all the ice on the evap plate in the freezer. And I'm aware of the defrost cycle of the household units every 8 hours or so.

Hence my question how well such a duct from the fridge through the freezer and back into the fridge would work?

Any moisture present would condense on anything colder. If the duct were available to remove heat, it would condense any moisture as it did...

No way around doing some form of defrosting, unfortunately!

[hzcruiser]

Originally Posted by skipgundlach

Any moisture present would condense on anything colder. If the duct were available to remove heat, it would condense any moisture as it did...

No way around doing some form of defrosting, unfortunately!

Yes, of course, condensation and forming of ice can't be avoided.

My thinking was whether it can be made easier and simpler to defrost, e.g. having a thin film of plastic or silicone over the cold part, whether it's the evaporator or a heat-conducting separation plate between freezer and fridge?

Maybe I'm missing something here? A flexible coating would also act as an insulator, of course, but does that matter between fridge and freezer, as long as the temperatures are within the desired limits?

[Uncle Bob]

Originally Posted by hzcruiser

I'm in the process of designing and building a fridge as well. Ducting air on demand from the fridge through the freezer sounds very intriguing! It would greatly reduce ice in the freezer, I'd assume? But wouldn't that duct become clogged with ice over time, since the more humid air in the fridge gets pushed through a colder tube?

Are there any pointers where someone has documented this approach on the net?

Try contacting Ozefridge, thats where I saw the concept.

[OzeLouie]

Suggest the two air transfer holes be high up in the dividing wall and far apart as in this sketch below. An optional stainless steel 'tray' can be used as a heat exchanger but best to be removable as they can sometimes block with ice. This is mostly an advantage if operating in a high humidity area. Also the fridge side air being contained to within the exchanger greatly reduces the build up of frost / ice on the freezers cold plates.

Important to have 100% lid or *door sealing when using a fan inside a fridge cabinet as the extra air movement will increase the introduction of unwanted warm and moisture laden air that will decrease efficiency and decrease periods between defrosts.
*Use a light inside cabinet on a dark night to locate any seal leaks.

TOP VIEW Click on to expand...