328 air conditioner condensor question...

Not come across this before but to get the best from your ac, the high pressure hot gas need to turn to high pressure cool liquid at the outlet of the condenser- as it is air cooled, if you get the liquid within 5C of the air temp you are doing ok. You might want to compare the surface area of the oem and this parallel condenser- heat transfer is related to the area where the exchange takes place.

 

I think it depends on how you define "hi zoot parallel flow". If by that you mean there is a common tank on one side and a common tank on the other connected by just a multitude of straight finned tubes = no. But both the 328 SPC figure and the aftermarket 328 condensor sold by Maranello Concesionaires show that the inlet and outlet pipes are branched -- i.e. two conventional series condensors connected in parallel:

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The 328 condensor does utilize "multiple tubes rather than just a traditional single tube" (meeting Original Air's definition) -- but just two. The question would be how many tubes does the Original Air condensor use (when in the 328 form factor).

 

Generally industrial condensers have the tubes in the next row offset, so that the air or liquid is made to change direction between rows- the cooling medium then tends to scrub the tube and get better heat exchange. In addition they fit fins to increase the surface area.

 

I changed out my condenser for a parallel flow. I think that last article does a good job at explaining the differences and how the surface area of a modern heat exchanger is so much greater, giving better cooling of the liquid. One thing that the modern condensers have that they don't seem to point out is that all of the passes are not equal. I'm going to make up numbers because I certainly didn't count, but this is the general idea: The first pass across uses 15 rows, it then reaches the other side, drops down the header tank to to go back across, but using only 10 rows. The freon is denser now because it has cooled some. It makes the pass across to the other header tank, drops down and goes across only 5 rows. The last pass is only two rows.
I'm assuming some science went into this design. The tube and fin - even when divided into two parallel tubes - doesn't seem to have any of this magic built in.

 

Its a neat idea but i have never come across one

 

As it goes through its state changes from gas to liquid and a decrease in volumn, hence 15 to 5 tubes.

 

Not to hijack your thread, but I've done a bunch of work on the A/C on my 1988.5 328, and may have some insight to offer that may help you out:
The original condenser in my 328 was copper tube & fin design used with Freon12, which is known to be much less efficient (claims are ~30 to 40%) than the later parallel flow condensers. One reason for the difference in efficiency is that the parallel flow condensers are usually aluminum, which has better heat transfer properties, and another is that there are simply more tubes/surface area to radiate heat. Add to that the "parallel flow" concept, and you get better performance.
Problem is, the condenser in a 328 is configured physically to mount in front of the right front wheel, so it's not a big flat heat exchanger like you see in front of the radiator on other cars, and on the earlier Ferrari 308. That's a problem because I'm not aware of any so-called "parallel flow" condensers available that will fit in the 328.
There is an upgrade path for the 328 condenser, however. Turns out, the Ferrari 348 condenser mounts in the same place (although not exactly the same mounting tabs), and is an aluminum flat tube style condenser. I modified my 328 to use this 348 condenser, and saw a significant improvement over the original copper tube/fin condenser. To be fair, I was using both with R134a, and my tube/fin condenser was damaged, so it wasn't performing up to original specs in the first place. However, my system now achieves 37degreesF at the center dash air register, with R134a.
In 2014 when I restomodded my system the 348 condenser was still available as Modine part number 62590600, as shown in the picture below.
I made some other changes too, like upgrades in the evaporator and blower assembly, and barrier hoses, as well as the Sanden compressor. But FWIW, I think the biggest improvement came from the condenser. It's a big job to retrofit this condenser into the 328 housing, but I think it's well worth it.

 

BTW, you could probably find a parallel flow condenser for a Ferrari 308, because it's a conventional configuration - a large thin slab that mounts in front of the radiator. But then, you'd have to contend with the cooling system issues of the 308, since one reason they moved the condenser to the wheel well on the 328 is to improve cooling system performance.

 

It's counterintuitive that the smaller unit is the one that better as a heat exchanger!
Probably it's not really any help, but the Countach has it's condenser mounted in front of the left wheel in a small cube similar to the 328. I don't know if it's parallel flow or has better exchange, and I'm guessing is not going to be cheaper. But just maybe someone in Lambo land has the ultimate condenser for that space.

It was fairly easy to find a slab that mounts in front of the 308 radiator, but the original has special terminations that route around the radiator. Dealing with hose routing was the hardest part of fitting the generic piece.

 

The previous images look to me to be evaporators not condensers. I used a local auto AC company to upgrade the AC system on my GT4 and purchased a modern high pass condenser. FWIW the advice they gave was that the stock evaporator was perfectly adequate and not as crucial to performance as the condenser and fans.


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The images I posted were indeed condensers.

My Ferrari 328 Evaporator is another area where I made modifications, but not to the evaporator core itself, which, as your A/C advisor said, was perfectly adequate, as a heat exchanger, even though it's an old-fashioned copper tube and fin design. I made two changes to the evaporator assembly - upgraded the blower to increase air flow which is woefully inadequate in the 328, and fabricated a new dehumidifying screen to replace the original open cell foam filter that blows out in bits to your face while driving.

For the blower upgrade, I used a pair of SPAL fans with larger squirrel cages and a more powerful motor. This meant reinforcing the fiberglas evaporator housing to support the new heavier and more powerful blower assembly. These I purchased as a kit from Retroair of Dallas. (www.retroair.com)

To maximize the benefits of increased air flow through the evaporator, I was tempted to eliminate the open cell foam filter screen altogether. However, the resulting air speed would have carried droplets of condensing moisture through the ducts and into the passenger compartment. So, I decided to improve the dehumidifying filter to eliminate the problems of the original design.

For the dehumidifying screen, I designed a new assembly that uses a spun polyester filter fabric like you find in HVAC air filters, sandwiched between two layers of stainless steel hardware cloth. I mounted this assembly by attaching it with stainless steel wire through the evaporator core, much like the original open cell foam was stapled with long-gone rusty steel wire. Thus, the cold, moist air passing through the evaporator cools the filter assembly, so that the moisture in the air condenses on the hardware cloth and the polyester "filter" medium. The droplets that form then drip down the filter assembly and fall into the evaporator housing, draining out of the drain tube. With these upgrades to my evaporator assembly, I no longer have bits of old open cell foam hitting me in the face, and no water droplets, either. I do have 37degree air blowing stronger, which results in more air turns per hour in the passenger compartment, making my 328 cool enough that I actually have to turn down the A/C because my passenger gets too cold. (imagine that: too cold in a Ferrari 328, in Texas, in superheated summers!)

I should mention that my car's evaporator drain tube was clogged with rust, so that water was getting on my passenger's feet before the upgrades. Because this tube is molded into the fiberglas evaporator housing, I chose to drill out the rust, then coat the tube inside with rust-encapsulating paint. This isn't a 100-year fix, but it will probably outlive me, and I didn't have to replace the tube by molding a new stainless steel tube into the fiberglas housing. I could have sourced stainless tube from McMaster-Carr, and made the fix permanent, but I was too lazy to take on the fiberglas work at the time.

I hope this helps in the quest to improve your Ferrari A/C systems. Here are a couple pics of the blower and dehumidifying screen described above:

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From my experience, I agree with mike996, that the original evaporator is a weak link - due to poor airflow, but not the evaporator core itself.

However, my experience proves that R134a is perfectly capable of performance that can make the Ferrari 328 A/C more than adequate, even in the superheated summers here in the Texas Hill Country. With R12, you may not need all the other system upgrades I had to make with R134a, but with those upgrades, even R12 should perform better.

I should add that there is one more upgrade that helped my system greatly - I had my windows tinted with Low-E film that's nearly invisible. This made a HUGE difference in the greenhouse that is the passenger compartment, by making my black leather dashboard cool to the touch, even in bright sun. By reducing the heat load, my A/C system doesn't have to work so hard. I used LLumar tint film, which comes in shades so light that I even coated my windshield legally!

 

See post#12.



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"One reason for the difference in efficiency is that the parallel flow condensers are usually aluminum, which has better heat transfer properties, and another is that there are simply more tubes/surface area to radiate heat. Add to that the "parallel flow" concept, and you get better performance."

This is misleading. Copper is a better conductor of heat than aluminum. The thermal conductivity of Al is about 118 BTU/(ft-hr-deg F). Thermal conductivity of copper is about 223 BTU/(ft-hr-deg F). The fact that copper is considerably more dense than aluminum has no effect on steady state heat transfer. Densities only matter for transient conduction and are not present in the steady state heat transfer conduction differential equation. Furthermore, radiation is based on the 4th power of the absolute temperature multiplied by the Stefan-Boltzmann constant and emissivity. Copper also has a higher emissivity than aluminum. Heat transfer due to air flow through the heat exchanger dwarfs the radiation heat transfer for the relatively low temperatures involved. But radiation helps providing what is radiating is not 'looking' at something that is at the same temperature. Air does not absorb thermal radiation. The part of air that does absorb thermal radiation is CO2 and H2O but the two comprise only a small part of air. Radiation heat transfer at the temperatures in an automobile condenser is negligible compared to heat transfer via forced convection.

Copper is quite expensive so the switch was made to aluminum.

 

+1 -- and Racers like the less weight of Aluminum alloy so it often gets the "it's better" moniker for that reason, but Copper (or really Copper alloy, as very few practical items are made of pure Copper) is better thermally.

 

As I mentioned in my post, I did have the windshield tinted, as well as the other windows. The film that's legal in Texas (and across the country, I was told by my tinting resource) is so light as to be barely noticeable, but still blocks a high percentage of the solar thermal radiation, leaving my black leather dash cool to the touch, where before it was blazingly hot.
I had my tint film applied by SunBusters in Austin. They use the LLumar films, which are available elsewhere. There are alternatives to LLumar that do the same things, thermally.
FWIW, I had them cut a small 'window' in the film for my annual inspection sticker, so I won't damage the film replacing this every year.

 

I greatly appreciate the scientific discussion here, and I strongly support fact-based arguments, rather than unfounded opinions.... The material properties in the science you're quoting here are absolute fact, but are just that - absolute. They support the notion that, all things being equal, copper is better than aluminum at conducting heat. Problem is, in comparing the two in this application, all things are NOT equal. All things being equal, to overcome the lesser thermal conductivity of aluminum, designers should have made the surface area greater in the aluminum heat exchanger. But in fact, the refrigerant-carrying tube surface area in this aluminum condenser is actually less than 90% of that in the copper tube condenser it replaces. Designers could have chosen to make the aluminum condenser thicker, so that its surface area could have been greater than the copper assembly it replaced. But they didn't. So, what were they thinking, when they made this change?

I believe they had already allowed for the differences in thermal properties between copper and aluminum by adding aluminum fins to the copper tubing in the original heat exchanger. This effectively changed the argument to the only other variable, which is airflow through the heat exchanger.

I think they relied on the greater air flow through the aluminum condenser to compensate for its lesser thermal properties. It's clear that airflow through the aluminum condenser is less restricted than that through the copper tube condenser, which I think is why it can outperform the copper tube condenser it replaced.

I'm an engineer, not a physicist, but I'm enough of a scientist to believe the measured performance data from my personal experience. My scientific method was not pure - I changed too many variables to conclude which of them was responsible for the improved performance, but at the end of the day, I'm getting 37F airflow at the center register, in sufficient quantity to cool the passenger compartment to the point where I can run the A/C system at less than wide open, and still be comfortable in Austin's superheated summers. I'm satisfied with that.