Options to improve cooling and reduce consumption for portable coolers Answered
I recently had to start learning how to service airconditioners on the fast and that learning got me thinking about my portable coolers....
Some of us like to go camping or on longer fishing trips, so there might be one of those 3-way fridges in use or a better cmpressor model.
The one thing they all have in common is that they can only cool down to a difference in ambient temperatures.
No matter which way we turn it the cooling produces heat and that needs to get away somehow.
The other big thing is the cooling cycling - or the lack of it on a warm day.
After some reading and thinking I came up with some ideas that might be applicable to your existing cooler if you are willing to mess around a bit.
Let's start with the produced heat, shall we?
Down here in Australia most people either have the fridge in their4WD or camper.
In a car or small camper trailer there is often the problem of airflow, so the cooler might be doing overtime for no other reason than a lack of airflow.
If you check online sites like Amozon and Ebay you quickly find fan systems meant to be installed inside the cooler to get lower temperatures and a quicker cooling of fresh goods.
The thing is that the box is quite well insulated and the benefit of the airflow goes only as far as it can reach.
And even if the box is quite empty and you would have a benefit of the cold air moving around it won't change the fact that "improved" cooling always comes with more heat in this case.
But if we use one of these fan systems to actually improve the airflow on the hot side we not only get better cooling but also a reduce power consumption - something worth considering if you have no backup power generator....
This of course brings us to placement.
As I have done the mistake myself you might be tempted to put a 3way cooler onto your seat.
Opening it with the back free means the lid always gets stuck on the seat, do it the other way around and you block the airflow.
If you do put it on the seat then make sure two things match:
1. The thing is secured properly.
2. The airflow from your aircon is able to reach the hot side of the cooler.
Even permanent installations in a camper benefit from a good airflow.
Often the fridge or freezer is built into some sort of bench and the airflow behind might be very limited.
A simple solution here is to add a vent on top of the bench to allow the hot air to escape.
A better one is to use a fan that is powered together with the heating element or compressor and drives the hot air to the outside.
How to improve the cold side of the box or fridge?
Well, to be honest there is not much that can be done unless you are prepared for some serious work.
Depending on compartment size, contents and how full it is a little fan can help to keep the temperatures even but it won't help to get it cooler or reduce the cycling periods for the cooling.
The only really working way that I found is to use a "battery" for the storage of the cold.
The cooling works by checking the inside temp of the box and if above the set temp the cooling won't stop.
This is all well and good while we have a constant supply of power but once we are on batteries it would be great to keep the active time to a minimum.
A working solution is to build a container that fits around the cooling element.
Smaller types often use an aluminium heatsink, bigger types might come with a compressor and an evaporator.
In either case proper sealing is important!
Most good models are fully waterproof, meaning even if you would fill them with water they would not leak in other areas than the door.
But double check and if in doubt use a bit of silicone to make sure.
Ok, but how do we "store" the cold coming from the device?
Cold packs ;)
These things contain a ready to use mix that holds cold temperatures quite well.
Another really good alternative is alcohol or radiator coolant, although the last has limited capabilites in terms of holding capaity for the cold as it is desinged to exchange heat fast rather than to keep it.
With a suitable sized and sealed box around the active cooling element we will need longer to actually see any cooling happen (with a warm "battery") but that can be compensated for by good planning or a frozen water bottle.
If the cooling element is covered with a box of cooling gel then it has to cool this first before anything happens inside the box.
But once it does the pack is already far below the normal temp it would have during normal operation.
Remember the inside of the cold pack cools down first before the outside will get cold ;)
So once the set temperature is reached the device will shut off.
But since the cold pack is far below the set temp it will continue to cool our box until the core is warmer than the set temp.
Quick thinkers will now say the benefit is lost as the time required to cool the "battery" down again is much longer than the normal cycle time - and they would be correct.
But as we get much colder temps inside the gel box the overall running will still be less compared to normal operation.
And since from the second cycle on the gel is only warming up to operating temp of the box it will be much faster than with a warm box.
Another benefit might be the ease of cleaning and ice removal.
Some peltier driven coolers have big cooling fins or a quite bad design for the heatsink allowing mould to grow where you can't remove it easy.
If the box is made from stainless steel and flush with the back wall of the box we won't have that problem anymore.
Ok, but how much is good or too much for the size and gel content?
You got me there as it is bit tricky.
You don't want to loose much usable space for starters and you don't want to wait hours for the gel to cool down if the box was not used.
IMHO the size should fit the cooling element with about 20% to spare all around.
If stainless steel is not an option than aluminium is the next best choice.
Thin sheets can either be be cold formed with a hammer or "brazed" with a good torch and the right rods.
Ok, before that route is there anything I should consider or do first?
3-way systems usually use a flame or heating elements to heat an ammoia solution.
After years of neglect corrosion can form and reduce the amount of heat transfered into the system and reducing the efficiency this way.
It might help to take the heating elements out once a year or so to clean them and the contact areas from any corrosion or dirt build up.
With a fixed shedule for this you won't have the problem of never noticing a badly corroded heating element either - and this is the main failure on these systems....
Modifying your camper or making a few mods to your 4WD drawer system is not for the faint of heart and should be done with consideration.
The last thing you want to do is rush things to find out it was not necessary.
Before cutting holes check if you can't find the room for the fan in a different spot and use ducts to control the airflow - sometimes it is easier to blow air in than to get air out ;)
When it comes to creating vents or connections for air to the outside always make sure it is waterproof and insect safe!
If you can let the outlet go downwards so water won't run in, for 4WD trailers consider a flap to prevent water from going during a river crossing.
Flyscreens will not only prevent insects from coming in but on the inside also prevent dust to go eerywhere - allow to the removal and cleaning!
The salts used in these cold packs can be corrosive, so you have to make sure there are no leaks and that there is no steel to come into contact with gel - this includes screw ends hidden in through-holes.
If in doubt use a coat of paint but keep it as thin as possible.
Even on peltier systems it might be impossible to remove the heatsink without massive surgery on the internals.
So before you take it all apart to gain access check if it is far easier to seal around the box opening and possible screw connections using silicone.
The cooling battery can be screwed on and sealed with silicone as well as an easy escape route.
Although for this to work you need to check if the material of the box allows for a proper bond with the silicone!
Some materials just won't allow anything to stick at all, even after sanding them.
So do a test first in an area where you would be able to cut the silicone away without causing damage.
If you can rip or peel it off the surface you should not try to use a cooling battery screwed to the wall, only use a box that is fully sealed with the cooling element and has a seperate back - one complete unit around the cooling element.
I have a 3-way system with a freezer compartment that does the cooling for the fridge too - what can I do?
These units either provide good freezing with the fridge temps too low or good fridge cooling with no freezing capabilites - depending on the thermostat used.
Our problem is that is next to impossible to add a cooling battery of the normal kind to these systems.
The L-shaped freezer box can really only be added with a L-shaped cooling battery from underneath.
Only if you don't need any freezing at all you could add a cooling battery to fit into the freezer box shape.
In either case the benefit is somehow limited by the way the thermostat is used.
If there is no temp control for freezing it should be fine.
Only peltier driven coolers are free from refrigerants.
Every 3-way or compressor system uses refrigerant as evident by more or less piping and heating elements.
Never attempt to screw anything into a cooling element containing refrigerant!
Even if you think between the channels all will be fine it won't be!
The material is just pressed to form the channels and any damage caould mean refrigerant leaking out!
Use silicone instead and make sure all surfaces are properly cleaned before applying it, also wait until the silicone is really fully cured before putting any stress on it.
As said, these cooling gels can be corrosive, especially if DC voltage is involved.
Make sure that everything that is not aluminum or plastic is properly sealed before allowing ongoing contact with cooling gels.
Do not attempt any of this if you have to ask yourself what tools you might need or how make a suitable container for the gel.
If in doubt check Google on how to work with aluminium or stainless steel if there are not enough Instructables for it.
The gel will expand a little bit if it freezes, this no problem in a metal container if you allow for a bit of flex or on the side added strength - whatever suits you better.
Another option is to get a few different cold packs (by the active ingredient) and to do a check in a little container.
Freeze it and note whe level cold and warm.
Little to no difference means nothing to worry in terms of expansion during freezing.