Pete Gossett (Forum Supporter)
Pete Gossett (Forum Supporter) GRM+ Memberand MegaDork
7/25/21 10:34 p.m.

At the 17:30 mark in this video the owner/builder talks about using a peltier cooler as a small air conditioning unit in their van. Unfortunately he doesn't provide a very detailed description(or any images) of the system, other than stating it uses their fresh water tank for cooling. 
 

From his description I presume he's using something like this.


 

Are these intended to be mounted directly on the CPU like a normal PC heatsink & fan?

I understand that the coolant needs circulated - either through a tank like he describes, and/or through a heat exchanger to pull heat out of the system. What I don't understand is how/where the cool air is blowing from?

Anyone here familiar with these & know the answer?

Honsch
Honsch Reader
7/26/21 12:12 a.m.

The cool air will be blown out by the fans.

Peltier coolers are just solid state heat pumps, and they're not very efficient.  They take a lot of amps to move a real amount of heat.  Each individual Peltier device might be able to make a 20C temperature drop if you can remove enough heat from the hot side.

It looks like there's four devices in parallel on that block which will increase the BTUs but not increase the temperature differential.

The actual Peltier devices are sandwiched between the water cooling block and the aluminum finned heatsinks with the fans bolted to them.  You can see the wires coming out of the devices.

Pete Gossett (Forum Supporter)
Pete Gossett (Forum Supporter) GRM+ Memberand MegaDork
7/26/21 5:41 a.m.

In reply to Honsch :

Ahh...ok. I just assumed that was hot air being moved by the fan. Thanks!

From the math it seemed like they're not as efficient as a compressor-based system, but I don't want to mount anything on the roof that will reduce clearance.

alfadriver
alfadriver GRM+ Memberand MegaDork
7/26/21 6:05 a.m.

In reply to Pete Gossett (Forum Supporter) :

Depending on how much you need, there are a number of 12V compressor systems out there.  From a pretty small unit that should cool a car to a full mini-split set up.  We had the same debate for our trailer, and could not find a compressor system other than a portable unit that met our needs.  I wish it was 12V, but it's 120V.

The 12V systems are pretty expensive right now- between being so new and with some high demand for the units.  But I hear that the systems are moving quickly toward better set ups.  I'd like to put a better A/C into our camper, too- without the roof top units.

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
7/26/21 7:10 a.m.

For cold A/C in the van without losing roof clearance, I'd just put a little portable A/C unit next to the side door and exhaust it out the pop out window.

Maybe things have changed, but when I was looking into it the laws of physics basically said you need shore power or a generator no matter what, unless you install 4+ big deep cycle batteries (and charge them every night). 

alfadriver
alfadriver GRM+ Memberand MegaDork
7/26/21 7:51 a.m.

Since it's still important to me- I've reopened the search...

When I first looked into a 12V system- I found this one- https://www.rigidhvac.com/micro-dc-aircon-12v but after swapping a few e-mails, I determined that it was not large enough.  They though the 48V one would work, however, I could not come up with a good 48V power supply.  

Then this morning, I saw a video about this- https://www.cruisencomfortusa.com/ which sounds closer to what I want- especially since you can install it in a modular manner, if you have the space and plumbing.  And being able to put part if it below the vehicle is very appealing.  I've done no other look into this other that just finding it, though.

There are also a number of marine systems that are also 12v- but they are designed to be cooled in water vs air- I'm sure one can use a car condenser to the system- but when I saw the cost, I dropped the idea.  

I have also seen some hints to a 12V mini-split system- but my google fu does not come up with anything.  But if I were going to do it- finding the split system from above that just showed up this morning would certainly be the way I would go.  Maybe I will in the future- who knows.  

One ironic thing- the smallest water heater I could fit was 5 gal- if I could acutally find a 2.5gal that was shorter, I would certainly put it in thanks to the smaller size.  Which would make installing an A/C system in kind of a remote and unused area a lot easier.

alfadriver
alfadriver GRM+ Memberand MegaDork
7/26/21 8:18 a.m.

You know, the more you see these systems, the more they look all the same.  Especially how they look to be identical to vehicle mounted systems- all of the components can be found in a lot of places- condenser, evaporator, heat exchanger, fans, etc.  The only thing that is really unique is the 12V compressor....

The whole system is about sizing all of the components correctly.  (and feeding them enough power to operate)

edit- one possibility is if one can find an entire A/C unit from a plug in hybrid or EV.  Including all of the controls.  

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) GRM+ Memberand MegaDork
7/26/21 10:46 a.m.
alfadriver said:

You know, the more you see these systems, the more they look all the same.  Especially how they look to be identical to vehicle mounted systems- all of the components can be found in a lot of places- condenser, evaporator, heat exchanger, fans, etc.  The only thing that is really unique is the 12V compressor....

The whole system is about sizing all of the components correctly.  (and feeding them enough power to operate)

edit- one possibility is if one can find an entire A/C unit from a plug in hybrid or EV.  Including all of the controls.  

I was temporarily excited about the cruisencomfort link that was posted above.... until I saw that it draws 50A.  One night of needing A/C to sleep in the van would require about 600 lbs of lead-acid batteries and about 10 cu ft of space.

alfadriver
alfadriver GRM+ Memberand MegaDork
7/26/21 11:36 a.m.

In reply to Curtis73 (Forum Supporter) :

But it's not continuous.  It's just 50A when it's running the whole system.  And with really good insulation, you will reach temperature, and it will be less frequent.

Yea, that's still a lot of energy.  

Honsch
Honsch Reader
7/26/21 12:52 p.m.

Looking a the rigid HVAC stuff, it seems it would be suitable to modify to run as a coolshirt style chiller.

Considering we go through at least $50 of ice a race it would pay for itself in a few years.

Pete Gossett (Forum Supporter)
Pete Gossett (Forum Supporter) GRM+ Memberand MegaDork
7/26/21 3:47 p.m.

Thanks everyone. Care to check my math & make sure it sounds correct?

Lets call our interior space 350 cu-ft. Based on BTU calculators I'm seeing online that should require about 4060 BTUs. 
 

Converting BTU -> Watts give me 1190W, so I'll round up to 1200W. 
 

Converting from watts to 12v Amp-Hours I'm getting 700AH. Does that seem correct? That's easy enough(if not cheap) to get with a couple Battle Born batteries. With 700W of solar on the roof & driving all day I think we'd come pretty close to 700AH.
 

We could also pre-charge the batteries prior to leaving home, and since we'll only be doing 2-day trips for the foreseeable future, it shouldn't be a problem(if my math is correct).

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) GRM+ Memberand MegaDork
7/26/21 5:33 p.m.

When it comes to poorly-insulated spaces like vehicles, I might considerably overestimate on the BTUs.  Not sure how well yours is insulated, but the best A/C sizing happens when, on the hottest day, your A/C is able to maintain temps while running constantly.  If you oversize it, you'll have humidity and electrical waste issues.

So assuming you size it properly and it runs constantly on a hot night, you're looking at 50A, so you need 50A times the number of hours it will be running which suggests 500AH for a 10 hour night.  Factor in a significant buffer on AH, because as batteries discharge and drop voltage, the amperage increases.  It makes the batteries discharge faster, but you also run the risk of blowing fuses or damaging the compressor.  You need enough AH to make sure you get a consistent 12v the whole time and it's not pulling the battery down as it nears the end of its charge.

I wouldn't convert BTUs to watts for the calculation.  I would go straight to the amperage.  A/C is measured by BTUs in the thermal sense of how much heat they can actually transfer, but those numbers don't account for the amperage needed for the thermostat, control panel, fan, etc.  That is to say, I don't believe that the nice, round BTU numbers listed on the appliance accurately convert to wattage, so I wouldn't use BTUs in the calculations.

500AH with a little safety margin means about 6 group 27 batteries or 3 group 4-D monsters.

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