Why can’t anyone reduce an air conditioner or refrigerator down to truly portable size?



There seems to be a lower size limit for conventional, compressor-based refrigeration. The result is that portable cooling devices are always simple fans, or at best, evaporative cooling units. What prevents conventional refrigeration and air conditioning from working at sizes much smaller than a dorm refrigerator?

In: Technology

Because much smaller than a dorm refrigerator wouldn’t be able to hold many things. No one is going to build a fridge to hold a single can of beer, or even just a six pack.

Are you talking about walking around with a personal A/C unit strapped to your back and keeping you cool while you move about your day? The main issue is the fact that you’d basically be conditioning the atmosphere around you and net no benefit. A/C units work because they take heat from one location and exhaust it in another (window unit sucks room air into the fins, transfers the heat the the refrigerant, the now cooled air is blown back into the room, and the hot refrigerant is then cooled by the outside air and the cycle repeats). If you don’t have a closed environment to pump the cooled air into and a separate environment to pump the heated air into you’re just spending energy for no net gain.

In order to have a mobile, air conditioning unit that you can take around with you, you’d basically have to wear a suit that traps the cooled air against your body to benefit you.

For a fridge, it’s mostly because any smaller is not really useful. Part of the thing with a fridge is that it needs to be full of stuff to easily stay cold. Every time you open it, the cold air in it pours out and needs to be rechilled. If you have it mostly full of food/drinks, then that extra stuff in there helps to regulate the temperature. If you only have a single carton of milk in a fridge when you open it, it’s going to warm up a lot before the fridge is sufficiently chilled again.

As for an air conditioner, the main problem is that they don’t create cold from nowhere. They are just moving heat extremely well from inside your home to outside. This is why one side is always outside of your home. If you don’t move the hot air it produces out, then you’ve just got a device with a cold end and a hot end. Those are actually still made and sold — we call them dehumidifiers. You can actually get a small desk sized dehumidifier, although they tend to be larger so that they have enough capacity that they don’t need to be emptied for a day or two.

The HVAC system in a modern vehicle is not only portable, it’s about as small as practically feasible. The compression required by the system demands a fairly strong power source to drive the refrigerant pump. It’s not just a fan.

For fridges, the main issue is lack of demand. There are small devices that use the Peltier effect instead of a compressor but they’re not very efficient.

With air conditioners, the fundamental issue is that you can’t just make heat disappear; you can only make it colder inside by making it hotter outside. A portable unit would need an indoor and outdoor part with pipes linking the two, or maybe fit in an open window space without letting too much air leak in around it. That doesn’t sound very portable. And air conditioners need much more power than a fan, making the compressor motor big, heavy and noisy, and the condenser needs to be big as well, even for quite a small room.

Cooling cycles don’t generate cold. They simply move away heat, and thusly they need a hot side.

Which means for these things to have any effect at all you need to be able to place the hotside outside of the room/system that you want to cool. If the entire device has a small form factor this wouldn’t really be possible

Basically, it’s physics. You can certainly create a smaller AC unit, but you’ll have a smaller amount of cool air created. If you look at your typical AC unit, a split system with an indoor unit and an outdoor condenser….you’ve got a system where, outdoor you have a coil that goes around and around with coolant running through it and you’ll note there are these thin fins that surround the coolant line. The fan blows air through the fins and it supercools ” the state of the coolant being less than than the temp it would normally freeze but it stays liquid due to pressure” so it goes around and around gets colder and colder then heads into the house really cold and enters the coil above the furnace typically and kicks on the fan so the fan blows inside temp air over a, now, really cold coil….the warmer air is raised about 20+ degrees but the liquid now turns to a gas….” phase change” …. The gas now travels through the refrigerant line back to the outdoor coil and does another phase change back to liquid. If you can imagine, it’s basically a system, a circle which grabs heat in the house and takes it outside and releases it, heads back in to grab more and takes it back outside to release it… .over and over and over. “side note this system works in reverse with a heat pump” So, all that to say there is no way to hack this system, no matter how an AC is created it always needs to grab head inside and take it outside to release…window unit, rooftop unit, split system….whatever. And to remove heat you must find a way to cool the coolant…..that takes moving air and surface area “the fins” and the exact same thing needs to happen inside. So you can imagine….smaller means less cool air. I hope I was able to give you some understanding of the restrictions related to making AC units smaller. They have actually gotten somewhat smaller over the years, but they do bump up against the same physics restrictions no matter what they do. They can mess with metals that transfer heat faster, speed of airflow, types of refrigerant etc…but many times making a product available for the public means using easily available metals and easily created refrigerants…so no groundbreaking changes likely any time soon.

There are relatively small portable AC with compressors.

Here is a [12 pounds compressor AC](https://www.amazon.com/Zero-Breeze-Mark-2/dp/B08Z3HNXH1/ref=sr_1_3?dchild=1) that has a built-in battery pack for power.

A major problem with them is that cooling requires an enormous amount of energy so a large part of the weight is the battery. Its cooling capacity and operational time are also quite limited so it is not especially practical.

There is a nice video debunking the claim of that AC. It is a working product that can produce cool air. The problem is that it is not practical for the shown usage cases. [https://www.youtube.com/watch?v=zol–A-CT8M](https://www.youtube.com/watch?v=zol–A-CT8M)

A major problem with them is that cooling requires an enormous amount of energy so a large part of the weight is the battery. Its cooling capacity and operational time are also quite limited so it is not especially practical. There is a nice video debunking the claim of that AC. It is a working product that can produce cool air. The problem is that it is not practical for the shown usage cases.

There are AC build to be used with batteries for campervans and similar applications, [like this 12V 9500 BTU AC](https://www.campervan-hq.com/products/nomadic-cooling-2000-12v-rv-air-conditioner-9500-btu) It draws 40 A in normal operation with a weight of 61 pounds The batteries you need to run if for any reasonable amount of time will weigh a lot. A 270 Ah 12V lithium phosphate battery weighs around 80 pounds and costs over $2000. It could run the AC for 270/40=6.75 hours.

The result is that portable “AC” are evaporative cooling units because the weight vs power usage is a lot higher. Even if you could make very small compressors for an AC the power requirement will be so high that if you like to get a lot of cool is you need very large batteries and they are not longer portable. If you need an outlet there is not a lot of reason for very small size, you need cooling capacity.

For refrigerators, the size limitation will be because you need an internal storage volume. Ther are [11-liter compressor coolers](https://www.dometic.com/en-us/food-and-beverage/coolers/electric-coolers/dometic-cdf-11-139583) , It weighs 18 pounds and needs an external power source. There will always be a base cost for compressors so most will be larger because the more internal volume is required.
The result is that the smallest you find is for car usage. They can operate for quite a long time with quite small battery packs.

There is not a marker for battery power refrigerators intended to be carried around, The cost and weight time that would be used will not compare favorably to just an isolated container and icepacks. So if you carry them the time then need work is a few hours and then ice and isolation is cheaper and lighter.

So the market for a portable refrigerator is for car and similar usage where it needs to keep cool for multiple-day and you need enough volume in them.

There’s no need? Fridges need space to store what’s being cooled so they have compressors big enough to that space. For more portable applications with smaller spaces, such as car coolers, they use thermo-electric, which also has the advantage of being able to warm the contents if you choose.

They exist. Powered by 12 and 24 volt. Professional cooling boxes cost 500$ but they exist.

because its useless. AC doesnt emit cold air, it makes warm air around an area colder. If youre going to have a portable AC that will work, its either you cool the whole earth or you make a portable room where you are inside and cool that area.

Or put it under your clothes it will probably work just like on astronauts


Also there are already portable refrigerators