Looking back at Electric Air Conditioning Research and Development

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Research and development of our successful electric air conditioning kits for classic Porsche 911s began in 2015, when we started studying how modern small cars used clever electric a/c compressors to control the climate in a cabin sized for five adults while running an engine size of under 1-litre, or no engine at all in the case of the Tesla and (to some extent) the Prius.

We bought an electric compressor and began working on how this could be integrated into something like an early 911. The aims were:

• A system that would be fully contained in the luggage bay/frunk and weigh under 30 lbs. This would save weight off the rear and drag on the crankshaft, increasing power and economy.
• A cooling output double that of the factory 964 A/C at idle
• A bespoke smart controller that would regulate system output to avoid draining the battery
• A system that would be fully climate cell tested to 100% humidity and shown to work perfectly throughout.

We spent two years looking at how modern small cars do A/C effectively. When the Prius and Tesla cars came out with decent A/C, I was intrigued to know how they got decent cooling from an electric compressor with half the BTU of an engine driven one. I have since been asked the same question of our system at least a dozen times!

It came down to two things:

1) The BTU of an engine driven compressor is quoted at MAX RPM. Most of the time it is running at half that quoted BTU or less. They are also 'cycled' with a clutch, so they are not doing work 100% of the time. On, Off, On, Off is a prehistoric control strategy.

2). Electric compressors typically run all the time. They adjust their speed to suit the cooling demand. Once you have cooled the car down, you don't need as much power so you can back off the speed. Better use of energy. If you have an 'inverter' domestic A/C unit, you will be familiar with the variable speed.

Our system was developed to be mid price. I received quotes from other suppliers which were more than our system and some that were less, nbut they remained old technology and the systems were heavier than standard. Our system was also developed to include a new blower fan so buyers would be getting an upgrade for the whole ventilation system too.

We also considered the cost (and ease) of installation. Our system would be designed for installation with just hand tools comfortably in a weekend. Even in a car that has never had A/C, one would not have to cut a single hole in the bodyshell.

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The heart of our system is our own custom power management controller. This can be configured to match the power budget of the car. The controller regulates the compressor speed in order to maintain a healthy charging system and battery.

The early development was all carried out in our own 911 SC test mule/development car. Here's some video of an early system in testing on a trip to Tuthill Porsche:

 

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With the prototype running well, we did some back to back testing with a modern Range Rover and the 911 came out rather well!

We also kept measuring vent temperatures and did some more research there.

"I found reports of zero (0C / 32F) vent temperatures interesting," said Jonny. "Given that there will be a rise of temperature in the ducting, that would mean the evap is below freezing. Most TXVs are designed to stop the evap going below 0 to prevent icing. 42F is a more typical lowest vent temperature according to A/C service manuals."

"Having said that, measuring the vents can be misleading. We have a good quality infrared thermometer here and it tells me that parts of the inside of the vent is -3C. I simply don't believe that. We've since moved to thermocouples for measurement. Btw, the outside air temp was 27 degrees C when we did the RR / 911 showdown. That isn't particularly hot but the point of the test was to compare the two vehicles."

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In February 2017, we released pics of our prototype A/C kit as it would ship in the first batch. Jonny also posted this information:

The compressor module (front centre in the picture) goes in the smuggler's box on a LHD car. The condenser goes under the fender (replacing the washer bottle on an impact bumper car). The blower unit (top right) contains a modern fan and evaporator. All original (non A/C) vents now blow A/C air. You can now push A/C air out of any vent in the car, including warm A/C air for rapid defogging. The blower also adds recirculation capability and assists heated air flow for hot air without the need for footwell blowers.

It is pretty innovative - here's the best part. The kit in the picture weighs just 15kg (33 lbs). Using a smaller washer bottle and accounting for removal of the existing fresh air blower results in a weight increase of ~7kg (15lbs) for a non A/C car. Converting a factory A/C car to our system results in a weight saving of ~18kg (40 lbs).

 

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On the subject of adding electric heat, Jonny said:

We did consider the full two way heat pump but it is too complex and bulky to implement. We still use the hot air from the heat exchangers but we can put that hot air through the a/c evaporator, so you get warmed a/c air. This is how new cars defog their screens so quickly and something that the factory Porsche system can't do.

We mount the condenser and fan assembly in place of the washer bottle which puts it in a better place than over the engine or in the rear fender as per other systems. We figure most people can find a place for a smaller washer bottle (and we have a nice solution for that too now).

With regard to the comments about having a single 'small' condenser, our testing which was done in a climate chamber at 42 C / 110 F, did not suggest that condenser size was a problem. Our system actually held the vent at a lower temperature than the modern car (that we also tested alongside). The bottleneck in cooling appears to be the airflow through the cabin which is why we have redesigned the blower. Having said all that, there is nothing stopping folks running two condensers with our system.

We looked to Italy as a hot country (as hot as Texas?) with a history of producing small cars with good a/c systems. Can't find a Fiat car or any small city car that has more than one condenser and some of them are tiny.

If you're going to bake your 911 in the desert sun all day, then bemoan the a/c for not 'blowing ice cubes', you'd better check your modern car first as I doubt it will fair much better. Seriously, on the full cold setting, the lowest vent temperatiure I've recorded on a 2016 Range Rover is 43F.

One of the key benefits is that no major surgery is required to the body shell. I catergorically will not cut any holes in my car and will do everything in my power to avoid any irreversible modifications. The installation is straighforward with basic tools and should be easily accomplished in a few hours.

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Our first batch of kits shipped to destinations all over the world with a wide variety of climates, including California, Florida, Texas, Virginia, New Mexico , Australia, Singapore, Puerto Rico, Austria and Norway.

Soon after, we began working on our "half kit" for 3.2 Carrera and later cars. We had a really nice late model US LHD Carrera 3.2 come to us. It was an original AC car but the compressor clutch had expired and the condensers looked a bit worse for wear. The original A/C blower, fan and evaporator were in excellent shape so we decided to do a hybrid system, pairing the original evaporator in the smuggler's box with the electric compressor and ECU. Interfaced the ECU to work with the original console AC controls too. The original blower doesn't blow as hard as our blower but it certainly gets nice and cold.

We also began working on our 964 and 993 air conditioning systems, putting two 964s in build. Again, using the electric compressor with the original blower and evaporator (refurbished). The thought behind this was that if we could get the condenser AND the compressor ahead of the front left wheel, it would be invisible A/C.