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HVAC tech weighing in

After looking into an electric conversion for myself, I found this discussion. I've been reading this thread and notice one crucial point is missing. BTU capacity of the system has not been mentioned. Typical car AC systems are in the neighborhood of 24,000 to 36,000BTUs. Your house AC is going to be that size depending on square footage and climate. These compressors run at 240V AC and draw around 20 amps.
At 12VDC, the amp draw would be tremendous for a 3 ton (36KBTU) system.

The Jegs compressor someone linked to is a 4,000btu compressor. The idea of electric AC compressors in a car isn't a bad idea... A belt driven compressor changes RPM (translating into cooling capacity) continuously. The advantages of an electric compressor are obvious, in terms of linear performance. Then you have the issue of airflow over the condenser. Notice your home AC condenser fan runs at one speed. Airflow changes over the condenser are going to affect cooling capacity as well.

But until we go to high voltage systems in a car, this isn't feasible. Hybrids can do it because they have those huge battery packs and higher voltage.

Last edited by BenzKompressor; 07-28-2016 at 04:43 AM..
Old 07-28-2016, 04:38 AM
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I don't think it's that wild. 4,000 BTU is about the output one would want for a window AC unit in a small bedroom. While the bedroom doesn't have an engine and transmission beneath it, and it's not moving through hot air, it is probably 10x the air volume over a 911.

These cars are insulated poorly from the factory, and I think there is room to improve cooling potential in that department...Historically, however, the hard part has been getting any reasonably cool air into the cabin to insulate in the first place.

Given a few thousand dollars, I suspect we'll have a choice between having an excellent Griffith system plumbed through the car and having a barely-adequate system in a compact machine up front. I can see the value in both, and I'd love to have the choice.

The stock solution, in perfect condition, is barely adequate and plumbed throughout the car...
Old 07-28-2016, 05:55 AM
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Old 07-28-2016, 06:15 AM
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Quote:
Originally Posted by Tremelune View Post
I don't think it's that wild. 4,000 BTU is about the output one would want for a window AC unit in a small bedroom. While the bedroom doesn't have an engine and transmission beneath it, and it's not moving through hot air, it is probably 10x the air volume over a 911.
A 5000 BTU window a/c, installed in a small room (16X11X8), and running in addition to the home's central a/c (thermostat set on 78), is only good for a 2-3 degree drop in temperature of that room if outside ambient is in the 90's. In other words, a 4000 BTU a/c system would not do anything in a car operating in a hot environment - probably almost no change in vent temps above ambient and definitely not enough to cool the cabin.

Last edited by Rawknees'Turbo; 07-28-2016 at 08:34 AM..
Old 07-28-2016, 08:30 AM
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I really want this to be a reality so I'm not being a naysayer. Here's an article that illustrates testing of electric AC in cars. The executive summary is that it's not enough cooling. That said, I'm pulling for some kind of breakthrough from the OP.

http://www.vintageair.com/Tech%20Articles/Electric%20Compressors/Electric%20Compressors.pdf
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Old 07-28-2016, 08:48 AM
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That said, I'm pulling for some kind of breakthrough from the OP.

Same here - it is a neat idea and will be fascinating to see the performance results after he's addressed key areas mentioned before (like enabling cabin air recycling - the only way to effectively cool in hot climates). Obviously, for his system to work in an area like Texass, it will have to be capable of way more than 4000 BTU - probably four times that at a minimum.
Old 07-28-2016, 08:54 AM
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Old 07-28-2016, 09:29 AM
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Quote:
Originally Posted by Rawknees'Turbo View Post
Same here - it is a neat idea and will be fascinating to see the performance results after he's addressed key areas mentioned before (like enabling cabin air recycling - the only way to effectively cool in hot climates). Obviously, for his system to work in an area like Texass, it will have to be capable of way more than 4000 BTU - probably four times that at a minimum.
Try 9 times. 36,000 is what a typical AC in a car is rated.
Old 07-28-2016, 10:00 AM
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Originally Posted by BenzKompressor View Post
Try 9 times. 36,000 is what a typical AC in a car is rated.
Agreed - my 4X was way too conservative (especially for hot climate operation).

I would love to know what my home-built, custom a/c system in my 1987 930 is generating in terms of BTU - don't know how to go about calculating that but in upper 90s and high humidity weather, I have steady vent temps in the high 20s (headliner temp in the mid 50s, passenger seat temp in the mid 40s, etc), rapid recovery from parking lot heat soak, and so forth - could hang meat in there, in other words.
Old 07-28-2016, 10:14 AM
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Quote:
Originally Posted by Rawknees'Turbo View Post
Agreed - my 4X was way too conservative (especially for hot climate operation).

I would love to know what my home-built, custom a/c system in my 1987 930 is generating in terms of BTU - don't know how to go about calculating that but in upper 90s and high humidity weather, I have steady vent temps in the high 20s (headliner temp in the mid 50s, passenger seat temp in the mid 40s, etc), rapid recovery from parking lot heat soak, and so forth - could hang meat in there, in other words.
Do you drive around with meat hanging down? Okay though, it does not count if it don't touch.
Old 07-28-2016, 10:17 AM
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^^^ Wow, and no freeze up with that much humidity? Damn, nice work Brother!

I wish there was a safe way to keep heat off of the dash and windshield, in desperation I put my see thru screen sun shade while on the dreaded 91 at noon. Believe it or not it cooled her down drastically. I AM NOT RECOMMENDING THIS as it is seriously dangerous and not to mention ILLEGAL in probably all 50 states and Puerto Rico.
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Old 07-28-2016, 10:19 AM
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IB, remember to factor in "no eye contact", too!!!

Draco, correct, no evaporator freeze-up (thermostat working very well), and thanks! It is amazing to see the water pouring out of the evaporator box when the system is on full tilt boogie - looks like my car is a water-pumper conversion with a leaking radiator hose just behind the steering rack!

I've taken great pains to block all outside air entry into the cabin (including making a blocking plate for the fresh air intake beneath the windshield - totally non-visible, too), but one of my next projects will be to try out that clear, windscreen film that supposedly does a great job of blocking sun/heat without reducing visibility.
Old 07-28-2016, 10:34 AM
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Oooh yeah the film

Please post your findings I want to do that at minimum when I replace my cracked wind shield
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Old 07-28-2016, 10:58 AM
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Old 07-28-2016, 10:59 AM
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How much does it run? DIY compatible?
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Old 07-28-2016, 11:26 AM
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Quote:
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Ah poop :-(
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Old 07-28-2016, 12:26 PM
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I'd followed Jonny's original development thread and a few weeks ago called him up to find out more.

At that time it hadn't been fully installed in his car or the production spec. finalised but but after talking to him I believed enough in his company to take the risk of offering it up as a solution on a high profile work project I'm busy with.

He worked night and day to hit a very tight deadline, as I took a leap into the unknown I could have been made to look a fool (never ever needed any help with that) in front of a bunch of hard nosed, skeptical engineers that never give anything a 2nd chance if it doesn't work straight out the box.

Glad to say it all went well, the demo left everyone very impressed. This system works and works very well. Considering how much reserve has been left on the table through compromises that can easily be overcome on the next development instal there is still a lot more to come, maybe even Texan levels of chilled interior.

Not only will it easily out perform the asthmatic, waft of warm air found with all mechanical air cooled Porsche systems it brings performance benefits too. Weight saved on the car and the weight moved forward. Also don't forget that old school, minimalist look instead of the lump of 60's AC technology that haunt the engine bay of a good comfort hot rod build.

I have no business interests in this just think it is a very cool (pun intended) comfort upgrade that many owners are crying out for and as fellow Porsche enthusiast that's seen it with his own eyes I'm more than happy to recommend it to other Porsche enthusiasts.
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Old 07-28-2016, 01:43 PM
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Quote:
Originally Posted by Captain Ahab Jr View Post
still a lot more to come, maybe even Texan levels of chilled interior.
An air con for England perhaps?

Quote:
A Mintel report in 2008 found that just 0.5% of houses and flats in the UK had any kind of air con.
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Old 07-28-2016, 02:29 PM
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Quote:
Originally Posted by Captain Ahab Jr View Post
I'd followed Jonny's original development thread and a few weeks ago called him up to find out more.

At that time it hadn't been fully installed in his car or the production spec. finalised but but after talking to him I believed enough in his company to take the risk of offering it up as a solution on a high profile work project I'm busy with.

He worked night and day to hit a very tight deadline, as I took a leap into the unknown I could have been made to look a fool (never ever needed any help with that) in front of a bunch of hard nosed, skeptical engineers that never give anything a 2nd chance if it doesn't work straight out the box.

Glad to say it all went well, the demo left everyone very impressed. This system works and works very well. Considering how much reserve has been left on the table through compromises that can easily be overcome on the next development instal there is still a lot more to come, maybe even Texan levels of chilled interior.

Not only will it easily out perform the asthmatic, waft of warm air found with all mechanical air cooled Porsche systems it brings performance benefits too. Weight saved on the car and the weight moved forward. Also don't forget that old school, minimalist look instead of the lump of 60's AC technology that haunt the engine bay of a good comfort hot rod build.

I have no business interests in this just think it is a very cool (pun intended) comfort upgrade that many owners are crying out for and as fellow Porsche enthusiast that's seen it with his own eyes I'm more than happy to recommend it to other Porsche enthusiasts.
Dammit Ahab, you are getting some of us all excited about finding the white whale of 911 cooling. I just hope I don't have to sell the Pequod to afford it.
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Old 07-28-2016, 02:30 PM
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Old 07-28-2016, 02:34 PM
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