Any thermodynamic experts out there?

Greenpeace

Greenpeace

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Although this is relevant to my Suzuki Carry I guess any thoughts shared could be applied to our older French classics as well.
With warmer days approaching (I think, they are taking their time this year🤷‍♂️) I've been pondering constructing a cabin cooling system for the Carry van.
Now I'm not looking for something that will provide comfort for interstate trips, rather just some temperature relief for local short hops.

Firstly I would seal the cargo area off with a heavy clear vinyl curtain and insulate the "firewall" behind the occupants legs. This will leave approximately 1 cubic meter of cabin space.
I want to take a small 12V fridge (15 to 20L), place a small submersible pump in the bottom, fit a heater matrix and small thermo fan in the lid. The 3" inlet pipe will be under the fan and obviously the 3" outlet above.
Plan would be to keep a few litres of water in the bottom and add some ice bricks when going for a drive.
I would also like to try and run the unit stand alone from the vehicle by having a motorcycle battery and solar panels supplying the power for it.
The fridge, thermo fan and pump will have a combined draw of just on 200W.
I already have most of the necessary bits and pieces laying around anyway.
What do you gentlemen think, does this idea have some merit, or would it be an abject failure?
 
Running a heat exchanger fed by ice and water on 200W is still adding thermal energy to your closed system. You're better off adding an aftermarket air conditioner.
 
The Gonz said:
Running a heat exchanger fed by ice and water on 200W is still adding thermal energy to your closed system. You're better off adding an aftermarket air conditioner.
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Yes, biggest issue is the lack of engine power to run a conventional AC system. Also the reason for proposing a stand alone power supply, so as to not load up the alternator.
That, and to my knowledge a factory AC system was never offered in this country to even source some donor components, crank pulley, brackets etc. Cabin space is lacking so I don't think there's room for a conventional underdash evaporator either. The idea would be to position the fridge in the cargo area behind the dividing curtain and plumb in short 3" inlet and outlet pipes through the curtain. That way at least the heat from the fridge motor would be isolated from the cabin.
As I said I already have most of the bits, it's just a matter of trying to work out if it would be a waste of my time or not.🤔
 
First law of thermo dynamics, no free lunch, Energy is neither created or destroyed. In as much as cooling is concerned, open the window, this is by far the lowest energy loss in your equations.

Missed your standalone comment, its a tough ask., Its all about energy / temp transfer, the universe will fight you on this.
 
How about an evaporative cooling system. 20 litre drum of water (which ought to last quite a while), small 12v pump, garden watering system tubing, a microspray or two squirting water in front of the vent outlets, and an open window to exhaust the hot air. You're still making use of the latent heat of vaporisation but you are wetting the air rather than drying it.

Roger
 
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Matthew said:
First law of thermo dynamics, no free lunch, Energy is neither created or destroyed. In as much as cooling is concerned, open the window, this is by far the lowest energy loss in your equations.

Missed your standalone comment, its a tough ask., Its all about energy / temp transfer, the universe will fight you on this.
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Yes, by stand alone I meant not connected to the vehicle's electrical system.
I was thinking around a 14 - 16 amp hour motorcycle battery and a 100W solar panel.
The vehicle is 99% short trips (40km = 20km x 2) in daylight hours. The fridge draws 50W, the fan and pump would only be using electricity while the vehicle is being driven. I was mainly thinking of using the fridge to keep the water chilled to some degree while I'm at work for the trip home, otherwise I would just use an Esky.
There are a lot of homemade Esky coolers, swamp coolers on the net with varying reports of success. These are all introducing the water vapour to the atmosphere and apparently do not perform well in high humidity. I want to pump the ice water through a matrix and blow the air over that. I forgot to mention I would fit a drop in panel to isolate the incoming air from the water/ice bricks in the bottom.
The system would be soley relying on heat transfer not evaporation to supply any potential benefits.
That's why I'm unsure if it's worth a go?🤷‍♂️
 
No need to go all out with a suit. Just get an easy-fit vest and throw it on to keep the core cooled before you head out. The rest is just an esky, a tube and a small pump..
 
Roger Wilkinson said:
How about an evaporative cooling system. 20 litre drum of water (which ought to last quite a while), small 12v pump, garden watering system tubing, a microspray or two squirting water in front of the vent outlets, and an open window to exhaust the hot air. You're still making use of the latent heat of vaporisation but you are wetting the air rather than drying it.

Roger
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Yes, I'm just not sure about such a system in high humidity.🤔
I read an article about the swamp coolers that were popular in the US before AC. It said in a dry desert environment they could reduce cabin temperature by up to 30F but in a humid environment would do virtually nothing as the incoming air was already water laden.
As an example, they said you would never have seen one in Florida at the time, but they were everywhere in Arizona.
 
56 Fregate said:
...or you could just drive an old Renault and you'll naturally be cool like the rest of us.:cool:
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Mmm, a Renault diamond on the front, spray on some fake rust, add a Goelette badge to the back.
Be like.🥶🥶🥶

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images (96).jpeg
 
This project sounds like something I'd waste time on only to find out the net gain was zero.

I love the idea though !

Cheers

Justin
 
Greenpeace said:
Yes, I'm just not sure about such a system in high humidity.
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Yes, if humidity is your problem it won't work. Nice simple option apart from that minor detail!

How about a small house-window air conditioner mounted in your new wall behind the cabin, powered by a petrol-driven generator in the back.

Roger
 
Humidity is an issue, just look at the self contained air con in the room, fine in low humidity, useless in high. Here is me chasing a few % with high compression too!
 
Evporative AC is useless in high humidity. The fundamental problem with the fridge is that it is designed to cool an insulated internal space filled with static air/goods using a heat pump to reject heat into the space the fridge is locate in i.e. the cabin. If insulation was perfect, you;d only have to do that once, but the fridge must keep pumping the heat leaking into it from the cabin back to the cabin to keep the inside cool. Your plan requires the fridge to keep moving heat from the cabin to the cabin and it does 'work' in that process. You have to reject the heat externally to make this work, hence the external part of all split systems. All you will accomplish is adding all the energy used for pumping etc to the system and making the overall cabin hotter. A fan blowing across the tray of melting ice might be more effective. Each passenger also generates heat.
 
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Roger Wilkinson said:
Yes, if humidity is your problem it won't work. Nice simple option apart from that minor detail!

How about a small house-window air conditioner mounted in your new wall behind the cabin, powered by a petrol-driven generator in the back.

Roger
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Mmm, I guess I could cut a hole in the front of the Carry van and do this, that way the condenser is getting full airflow.🤔
Chuck a genset in the back, almost looks factory.😉

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David S said:
Evporative AC is useless in high humidity. The fundamental problem with the fridge is that it is designed to cool an insulated internal space filled with static air/goods using a heat pump to reject heat into the space the fridge is locate in i.e. the cabin. If insulation was perfect, you;d only have to do that once, but the fridge must keep pumping the heat leaking into it from the cabin back to the cabin to keep the inside cool. Your plan requires the fridge to keep moving heat from the cabin to the cabin and it does work in that process. You have to reject the heat externally to make this work, hence the external part of all split systems.
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I know the proposed fridge is only small but wouldn't it be attempting to disperse the cabin heat absorbed into the circulating cold water into the separated cargo area via it's condenser?
 
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