Refrigerated Cybertruck Frunk?

ajdelange

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tap the compressor exhaust and run it though a separate condenser and, as long as you can extract enough heat to obtain the phase change, obtain a separate source of liquid refrigerant.
You could do it that way but it's clear that whenever the compressor is running the hot gas has to go either to the in cabin condenser or the liquid cooled one so there will always be a supply of liquid refrigerant available at the input to either in in cabin evaporator or the chiller. This could be tapped.

It occurred to me that multiple taps on a compressor are pretty common these days as in heat pumps with "desuperheaters" which will produce hot water at the same time they are cooling one's house and modern split pack heat pumps which divide a single outdoor compressor's gas or liquid between from 1 to five indoor fan coils.

 

JBee

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You could do it that way but it's clear that whenever the compressor is running the hot gas has to go either to the in cabin condenser or the liquid cooled one so there will always be a supply of liquid refrigerant available at the input to either in in cabin evaporator or the chiller. This could be tapped.

It occurred to me that multiple taps on a compressor are pretty common these days as in heat pumps with "desuperheaters" which will produce hot water at the same time they are cooling one's house and modern split pack heat pumps which divide a single outdoor compressor's gas or liquid between from 1 to five indoor fan coils.
Yeah that is what I was trying to allude too. This would probably be the most efficient and effective way of doing it, and could potentially allow for sub-zero Celsius freezer temperatures and of course fridge temperatures too. Installation wouldn't be that easy though and would likely have a fairly high installation cost, which if this is a retrofit, would need to be included.

I'm also thinking that for normal +5C fridge use, any octovalve cooling mode could be used, and it might be possible to tap the cold side of the chiller output before it goes to cool anything else. Being a glycol circuit, running that through a HX in the frunk with a thermostat might be the simplest, and least intrusive way to add cooling from the HVAC system to the frunk. That way any mechanic could use the existing quick connect couplers and add the fridge plumbing to divert some of the coolant to the fridge compartment instead. After the install you would have to top up and prime the coolant fluids but wouldn't have to regas the A/C etc.

I also thought of, but later dismissed, a way to use a custom HX with two glycol circuits instead of one and replace the the chiller HX with it. That way the refrigerant flow is not effected and the system would work as per usual without the fridge on. Then if the fridge is on it would only reduce the cooling capacity being provided to the rest of the system. Downside is you have to do both a regas and a coolant refill, so installation is even more expensive.

The only other thing I was thinking of, to avoid regas or coolant replacement and reduce the install cost, is to use some sort of pipe bolt on HX, given that we are only looking for about 40-100W of cooling for the frunk. There are some exposed lines, but everything is super short around the octovalve/HP so it's probably not likely to have something sufficient to make that work.

I've also searched for dedicated small fridge compressors, they aren't actually that expensive, you can get an assembly for around the $200-300 mark and about the size of 3 -4 Coke cans. ex China of course.

For version 1 you would then have to package into a frunk lid that can sit on top of the frunk. The frunk would get a aerogel liner for insulation. (that's not as expensive as it sounds, I have a local supplier) Beauty of that arrangement is that it only really needs a 12V power connection (battery is just under the hood panel) and could probably be made so anyone can install it. You just add a Bluetooth connection to it for control from your phone, or push button and display in the lid.

For version 2, given the fairly large side of the frunk you could also do a drop in divider style tub with a insulated lid. Where the divider itself houses the refrigeration unit, and you can choose the temperature of either compartment. With an offset divider, you could then choose between any combination of normal/fridge/freezer storage and how much space you want to use as a fridge. If you don't want it you lift the tub out with some handles and then can use it in your home or camp ground.

Essentially just a custom sized, frunk fitting auto fridge. Bonus is that if it fits in the frunk, it will also fit reasonably well in the under boot compartment in the back of the M3/MY.
 

Bill906

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Is there any other passenger vehicle that has a built in refrigerator that taps into the vehicle's cooling system? I doubt it, but I honestly don't know. I believe any refrigerator, whether built in by the OEM, or third party, simply has its own cooling device powered off 12V. Often a solid state thermoelectric cooler (Peltier).
I think you guys are making something way more complicated than it needs to be. Maybe if you were a door to door ice-cream 🍦 salesperson your ideas would make sense. But for the occasional need for a beer cooler, I'm not seeing the benefits being greater than the cost.
 

ajdelange

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I've also searched for dedicated small fridge compressors, they aren't actually that expensive, you can get an assembly for around the $200-300 mark and about the size of 3 -4 Coke cans
They don't pull much power either. I really think this is much preferable to any scheme which involves opening the existing system. Though it is theoretically possible to do that it just seems too risky, What is wanted is a custom ARB (or other OEM) fridge of the type those OEM make that is configured to drop into or replace the stock frunk tub. If none of those OEM is interested in customizing one of their designs then you will have to do it yourself.
 

ajdelange

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I think you guys are making something way more complicated than it needs to be. Maybe if you were a door to door ice-cream
As I said in my previous post I much favor a drop in solution and I think jBee is leaning that way too. Tapping into the refrigerant circuit is, however, much more interesting to think about.
 


JBee

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Is there any other passenger vehicle that has a built in refrigerator that taps into the vehicle's cooling system? I doubt it, but I honestly don't know. I believe any refrigerator, whether built in by the OEM, or third party, simply has its own cooling device powered off 12V. Often a solid state thermoelectric cooler (Peltier).
I think you guys are making something way more complicated than it needs to be. Maybe if you were a door to door ice-cream 🍦 salesperson your ideas would make sense. But for the occasional need for a beer cooler, I'm not seeing the benefits being greater than the cost.
There are heaps of cars with built in fridge/chiller boxes that do this, most of them are luxury type vehicles. My Landcruiser has a chiller box exactly like this under the middle arm rest, and it is powered by the A/C, as is also the rear seats ducted air-conditioning evaporator etc. If Tesla decided to do this it would be fairly trivial for them to implement. If they don't do it then it's possible a separate compressor will be the solution.

But in saying that, if the CT has the same setup with the octovalve and heat pump as the MY, or at least similar, then for camping purposes an integrated version might make for a more compelling solution. The investigation in itself is still of value to gain better understanding of the systems being used, in my case however, I am actively seeking opportunities to develop custom accessories for EV and Teslas, in particular for my modular CT truck bed camper product. It's also known that the bed will have HVAC, this might also be a "tap" in option to connect something.

If there is an opportunity to include such functionality, in particular with good performance, without significantly adding much equipment and weight, then the thought experiment might validate a design variation that is mutually beneficial. It at least needs to be considered, in fact if you look at the octovalve itself this is what it has done in a rather ingenious way.

In my case for the truck bed camper, I also have the requirement to make hot water for shower and kitchen use. That glycol circuit looks super tempting atm for a built in HX to supply that from, as is commonly done on overlanding ICE vehicles. The combination of these various "requirements" into a single embedded add on system might be the most effective way to meet them, especially so if doing so actually creates heat or cold for another use by reusing existing thermal supplies. For example, in warm climates the battery is actively cooled which produces waste heat in the radiator that I can use for hot water.

Anyways, always fun to think up new ways to do things, or at a minimum figure out how not too. :)
 

Crissa

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I don't know of any working commercial applications for a Peltier cooler. They have to shed heat and while one side gets cooler, the entire physical object heats up so you can't 'coast' like you can with a compressor-heat pump.

-Crissa
 

ajdelange

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I don't know of any working commercial applications for a Peltier cooler. They have to shed heat and while one side gets cooler, the entire physical object heats up so you can't 'coast' like you can with a compressor-heat pump.
Peltier device? I don't think anyone is suggesting those. They are inefficient (COP = 0.64 max @˙∆T = 0 for one commercial device I looked up) that they are only used in systems, commercial and consumer where a small mass is to held to a very precise temperature (e.g I have a density meter that holds its sample cell to ± 0.01°C). Or where the rise is small. But there are thousands of devices that use them in industry, research, medicine etc.

I also had a bunch of Peletier coolers that I used to hold cooling plates bearing rf amplifiers whose gain needed to be very stable at constant temperature. These chillers worked fine when they worked but were basically poorly made and failed frequently.

There are Peltier "refrigerators" for food intended to go in the console of a car or truck, for example, but they are only intended for small loads and modest ∆T (COP goes down as ∆T goes up).

Many computers use Peltier devices to pump away CPU heat.

Etc.
 
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Bill906

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I've owned a couple of electric coolers that used Peltier cooling technology.

1655230461171.png
 
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ajdelange

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Wow! That cooler represents a considerable improvement in efficiency over what Peltier coolers could do 30 years ago. I guess that's to be expected. Yes, it only goes to 40 °F and yes, it uses a little more power than a comparable compressor type refrigerator/freezer but it is much less expensive and 40 °F should be adequate for most applications.
 


Crissa

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I've owned a couple of electric coolers that used Peltier cooling technology.

1655230461171.png
...And it's a big sucking hole for electricity? It moves heat from one side of the panel to the other and makes more and the moment it stops being powered, all that heat goes back to the other side x-x

-Crissa
 

SparkChaser

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Better to just get a yeti or super insulated cooler and use dry ice.
 

Bill906

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...And it's a big sucking hole for electricity? It moves heat from one side of the panel to the other and makes more and the moment it stops being powered, all that heat goes back to the other side x-x

-Crissa
Eh, according to the reviews it draws < 60Watts. It’s not perfect, but not horrible. If the 400Wh/mile assumptions are correct for the CT, it can run for over 6 hours on 1 mile of battery.
If your selling ice cream door to door, it’s a bad idea, if you want to keep your sodas cool for a couple days 8 or 9 weekends a year… I think it’s a good fit.

It does have one cool trait. If it’s not powered, and there’s significant temperature difference between the sides, it creates voltage. I remember one time when I was cleaning out the first one I had after a day of use. It was still kinda cold inside the cooler, warm outside. The power cord was unplugged, but the fan was spinning. Really surprised/confused me at the time. (Was over 20 years ago).
 

ajdelange

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...And it's a big sucking hole for electricity?
No. Only draws 45 Watts (now that's for a 30° F ∆T). A conventional fridge of about that size draws a little less for a bigger ∆T but this thing is pretty amazing.

It moves heat from one side of the panel to the other
Yes, that's what a hear pump does.

...and makes more and the moment it stops being powered, all that heat goes back to the other side
This is a joke, right? The heat that gets pumped through gets blown away by the fan(s).
 

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Thank you all for the great technical analysis and ideas! I have played with Peltier devices, and at the time they were very inefficient. As sexy as the OCTO valve is, it would be even sexier if it gave us a refrigerated frunk or, as JBee describes, a hot shower.

Years ago I read in a book, Better Off: Flipping the Switch on Tecnology by Eric Bende, what he and his wife missed most when they gave up modern technology: a refrigerator. Living without one required at least daily cooking from scratch and allowed no leftovers. Lots of work. How cool if one of the most advanced technologies, Cybertruck, brought with it one of the most necessary.

 

 
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