Fridge Automatic Extractor Fan
It's hot in Africa. Well, actually it's not always.... but when it is it can be very hot. We saw 45C in the shade (that's around120F).
When it's this hot the fridge works overtime to keep the contents cool and therefore pumps even more heat out into the box. It was quite noticeable that in spite of having a healthy air gap above the fridge, the worktop directly above the rear of the fridge was getting positively hot - all of this adding to the problem of keeping the whole box cool.
So..... We're going to try to produce a system that will pump this heat out of the box. Sounds simple - it is except that we don't want any air coming back in and bringing piles of dust with it when we're not pumping air out. There isn't a massive amount of room above/behind the fridge, but there's enough to fit a couple of 40mm fans blowing into a box which will be connected to the outside world by a hole in the sidewall. Inside the box there will be a "one-way valve" which will probably be made from a sheet of acetate (or similar) attached on one edge. The orientation of the acetate will be such that with no air movement, gravity will pull it against a sealing edge, but with fan-generated air pressure it will lift and allow air flow. Therefore little air should be able to enter the box throught the fans but warm air can be pumped out. The fans will be connected directly to the fridge main fan, so will be thermostatically controlled by the fridge itself. Simple......????
Oh - I have a sneaky suspicion that by adding fans we might actually SAVE electrical power - by evacuating the heat from the box, the fridge should run cooler, therefore take less power. We'll see.
August 2013 - a simple mod has been fitted and is working quite successfully - it consists of a 24v 40mm fan attached to the truck sidewall behind the fridge wired via a 12v relay (the fridge. fan works off 12v) to come on when the fridge fan is on (there's an inline switch so we can turn it off at night due to the increased noise). There's an airfilter outboard of the fan to prevent dust coming into the truck and a stainless grille over everything. It's cut down the heat coming off the fridge to almost nothing - in fact you can feel the temperature drop when you switch the system on. I've got ideas how to improve it in the future, but for now it's good.
October 2013 - the fridge is playing up, it seems to have lost some gas, the fact that it's 43 degC in the shade during the day doesn't help, but basically it's running 24 hours/day. When we're on charge (ie plugged in), the extractor fan was seeing 28+ volts and was screaming away, so I've put a small voltage regulator to prevent it getting more than 26v which has cured the noise issue. A re-gas in Lilongwe (Malawi) helped, but didn't entirely cure the issue.
July 2014: new domestic batteries seem to have helped the fridge no end.
Dec 2014: I've had some time to develop a tiny fridge fan controller incorporating fridge internal temperature displays. It's based on an Arduino Nano (a micro controller about 1/4 the size of a credit card) and a tiny oled display screen that's less than 1 inch across the diagonal. This measures the air temperature at the back of the fridge where the extractor fan is located and compares this with the ambient air temperature in the rest if the box. If the fridge air temp gets excessive the the fan turns on - but only if the ambient temperature is lower (ie there is cooler air to draw through). The fan speed is continually variable dependant upon the fridge air temperature (this should keep any noise levels low at night when temperatures fall). The small screen alternates between a display showing what is going on with the fan and air temperatures and a display showing the temperatures inside the fridge and freezer along with a yellow alarm display if either fridge or freezer get excessively warm.... This works well on the bench, I'll get it fitted on the truck as soon as possible to see how it works in practice. If it looks good I'll post the circuit/code here.
Jan 2015: during our trip from Nairobi to Arusha the fridge was working overtime (the compressor was running almost all of the time just to keep the fridge at about 5 deg C). Although it was quite hot (up to the high 30s), I decided that this was still not quite right - and was draining the domestic batteries overnight. I dragged the fridge out (again) and watched it closely as it operated. Referring to http://www.fixmyfridge.co.uk/system/files/Confirming%20the%20Correct%20Refrigerant%20Charge.pdf it became obvious that there was a buildup of ice on the return pipe going back into the compressor - it was slightly overcharged and therefore running inefficiently. Basically, the guy who recharged the fridge in Lilongwe had put too much gas into it! Over a couple of hours I adjusted this until a very slight frost was just appearing on the return pipe and refitted the fridge. Hey presto, it works a LOT better now, in fact on a good day the solar panels keep it running without any additional charge at all. This was lucky as just the next day I needed the domestic batteries to get the truck going again - in lion country! Ooops!
I'm still using the fridge fan on hot days as when I turn it on the amount of heat being pumped out is quite incredible, so when we're in the 40s this really does help not only the fridge but also us. I'll be fitting the fan controller later this year and will describe how well it functions (hopefully it'll reduce fan noise and improve cooling efficiency).
It's hot in Africa. Well, actually it's not always.... but when it is it can be very hot. We saw 45C in the shade (that's around120F).
When it's this hot the fridge works overtime to keep the contents cool and therefore pumps even more heat out into the box. It was quite noticeable that in spite of having a healthy air gap above the fridge, the worktop directly above the rear of the fridge was getting positively hot - all of this adding to the problem of keeping the whole box cool.
So..... We're going to try to produce a system that will pump this heat out of the box. Sounds simple - it is except that we don't want any air coming back in and bringing piles of dust with it when we're not pumping air out. There isn't a massive amount of room above/behind the fridge, but there's enough to fit a couple of 40mm fans blowing into a box which will be connected to the outside world by a hole in the sidewall. Inside the box there will be a "one-way valve" which will probably be made from a sheet of acetate (or similar) attached on one edge. The orientation of the acetate will be such that with no air movement, gravity will pull it against a sealing edge, but with fan-generated air pressure it will lift and allow air flow. Therefore little air should be able to enter the box throught the fans but warm air can be pumped out. The fans will be connected directly to the fridge main fan, so will be thermostatically controlled by the fridge itself. Simple......????
Oh - I have a sneaky suspicion that by adding fans we might actually SAVE electrical power - by evacuating the heat from the box, the fridge should run cooler, therefore take less power. We'll see.
August 2013 - a simple mod has been fitted and is working quite successfully - it consists of a 24v 40mm fan attached to the truck sidewall behind the fridge wired via a 12v relay (the fridge. fan works off 12v) to come on when the fridge fan is on (there's an inline switch so we can turn it off at night due to the increased noise). There's an airfilter outboard of the fan to prevent dust coming into the truck and a stainless grille over everything. It's cut down the heat coming off the fridge to almost nothing - in fact you can feel the temperature drop when you switch the system on. I've got ideas how to improve it in the future, but for now it's good.
October 2013 - the fridge is playing up, it seems to have lost some gas, the fact that it's 43 degC in the shade during the day doesn't help, but basically it's running 24 hours/day. When we're on charge (ie plugged in), the extractor fan was seeing 28+ volts and was screaming away, so I've put a small voltage regulator to prevent it getting more than 26v which has cured the noise issue. A re-gas in Lilongwe (Malawi) helped, but didn't entirely cure the issue.
July 2014: new domestic batteries seem to have helped the fridge no end.
Dec 2014: I've had some time to develop a tiny fridge fan controller incorporating fridge internal temperature displays. It's based on an Arduino Nano (a micro controller about 1/4 the size of a credit card) and a tiny oled display screen that's less than 1 inch across the diagonal. This measures the air temperature at the back of the fridge where the extractor fan is located and compares this with the ambient air temperature in the rest if the box. If the fridge air temp gets excessive the the fan turns on - but only if the ambient temperature is lower (ie there is cooler air to draw through). The fan speed is continually variable dependant upon the fridge air temperature (this should keep any noise levels low at night when temperatures fall). The small screen alternates between a display showing what is going on with the fan and air temperatures and a display showing the temperatures inside the fridge and freezer along with a yellow alarm display if either fridge or freezer get excessively warm.... This works well on the bench, I'll get it fitted on the truck as soon as possible to see how it works in practice. If it looks good I'll post the circuit/code here.
Jan 2015: during our trip from Nairobi to Arusha the fridge was working overtime (the compressor was running almost all of the time just to keep the fridge at about 5 deg C). Although it was quite hot (up to the high 30s), I decided that this was still not quite right - and was draining the domestic batteries overnight. I dragged the fridge out (again) and watched it closely as it operated. Referring to http://www.fixmyfridge.co.uk/system/files/Confirming%20the%20Correct%20Refrigerant%20Charge.pdf it became obvious that there was a buildup of ice on the return pipe going back into the compressor - it was slightly overcharged and therefore running inefficiently. Basically, the guy who recharged the fridge in Lilongwe had put too much gas into it! Over a couple of hours I adjusted this until a very slight frost was just appearing on the return pipe and refitted the fridge. Hey presto, it works a LOT better now, in fact on a good day the solar panels keep it running without any additional charge at all. This was lucky as just the next day I needed the domestic batteries to get the truck going again - in lion country! Ooops!
I'm still using the fridge fan on hot days as when I turn it on the amount of heat being pumped out is quite incredible, so when we're in the 40s this really does help not only the fridge but also us. I'll be fitting the fan controller later this year and will describe how well it functions (hopefully it'll reduce fan noise and improve cooling efficiency).