Electric AC?

[GM]

I know that this issue might be of interest to a tiny percentage of members, but has anyone looked into putting electric air conditioning (instead of engine-driven) into a Pagoda? According to this supplier, who created a system for a Porsche, it involves putting in a beefier alternator to drive it. Seems to be a smart alternative to putting additional load on the engine and subtracting horsepower?
https://www.classicretrofit.com/collections/electric-air-conditioning

[MikeSimon]

If an accessory requires horsepower, it will require horsepower. That's just physics. The power still has to come from the engine.
The only advantage an electrically driven unit has, is that you can easily switch it off and have no parasitic losses due to a belt drive unit running all the time.
That's why conventional A/C compressors usually have a switched clutch.

[Shvegel]

I agree with Mike.  The larger alternator becomes a larger load on the engine.  Interestingly, it is common practice on modern cars to switch off the alternator and AC compressor under hard acceleration to allow the engine to deliver full power to the wheels.  If someone was interested in maximum "performance" it wouldn't be difficult to wire a relay into the transmission kick down switch on an automatic car or add a switch and a relay to a manual car to break the circuit of the AC compressor under full throttle. 

[GM]

Thanks, gents!

[Merc_Girl]

Hi Gary

I’ve made contact with the chap and hope to meet up in September to discuss potential options.

I have a Frigiking unit for the passenger compartment which I want to link up to the electronic air conditioning system

I’ll let you know how I get on if you are interested, but he certainly seemed interested in the idea

Katie

[GM]

Thanks, Katie.
Always interested in learning new things!

[Mike Hughes]

Here is another idea that requires far less plumbing:

An MGB roadster has a carpeted parcel shelf behind the seats beneath the carpet are two 6 volt battery boxes, one on either side of the drive shaft.  An MGB-GT has the same parcel shelf with a full width seat cushion instead of the carpet.  Of course the rear seat could only accommodate a small child (in the days before seat belts and child seats!) or a teddy bear.  For all intents and purposes it is really just an upholstered parcel shelf.
 
A woman in the local M.G. Car Club designed and built an electric air conditioning system for her '67 GT that consists of a four or five inch tall boxed shelf unit that sits on top of the existing parcel shelf, containing the switches, circulation fan, heat exchanger, duct work and vents facing forward between the seats.  She replaced the two six volt batteries with one twelve volt battery in one of the battery boxes and the electric compressor drops down into the other battery box.  She also converted the 12 volt electrical system from positive to negative ground and replaced the generator with an alternator.  The original rear seat cushion sits atop the boxed shelf unit.

Come winter she just disconnects the power cables, lifts out the whole boxed shelf unit, compressor and all, and replaces the seat cushion, leaving no trace that there was ever an A/C unit in the car, apart from the connection terminals the the second battery box.

Something similar could be done in a pagoda with the two piece carpeted parcel shelf behind the seats.

One could fabricate a replacement "short side" parcel shelf unit with an opening on top for the compressor unit to drop down into the void that serves as the footwell for a Pagoda with a kinder seat, and get some matching carpet for the top of the boxed shelf unit to drop into the area behind the seats.  It would be necessary to run a power cable back to the kinder seat footwell area.  The parcel shelf units are simply constructed from plywood so a duplicate with the access hole should be easy to fabricate and cover with matching carpet.  With the A/C boxed shelf unit installed one would loose some depth in the storage area behind the seats but I don't think that this solution would even interfere with the soft top compartment release handle!

[lpeterssen]

Dear Friends

I read the initial post made by Gary on the electric a/c compressor system and all the comments published afterwords.  Also visited the supplier web site and read the installation manuals and frequent Q&A section.  Here are my thoughts to share:



Bigger Alternator not proportional to engine load
==============================

A Bigger Alternator of course will require more effort from the engine to spin but it is not proportional to the increased power producing capacity.

The explanation comes from actual internal combustion cars tendency to use more and more electrically driven accessories in order to reach higher MPG figures.  See this.

On the early 2000, Honda started using electric steering on his fuel saving oriented car called FIT, or JAZZ in other markets. This particular car was an 1.5 liter 4 cylinder car with two spark plugs per cylinder and had an impressive fuel economy.  They eliminated the classic power steering pump system for an electric servo. Of course alternator capacity was increased.  Nowadays is common to see this approach on many cars.

Another key element that makes us conclude that higher capacity alternators do not demand so much power from the car engine compared to the savings in fuel economy caused by the elimination of another pulley driven accessory is he case of the electric water pumps.  Nowadays most of the cars, Bmw, Ford, etc use electric water pumps instead of pulley driven ones. That also translates into fuel economy, otherwise car manufactures will not take that approach.


Original MB wire harness
================

The wire harness of the Pagoda or any mercedes from the 60’ is not designed to handle such heavy loads as this new electric compressor driven a/c system demands.   The main harness will have to be refurbished and modified by a guy with enough knowledge like…… me….. to be on the safe side.

Charging capacity should be modified to accommodate a beefer alternator in the range of 100A.

This is imperative, and it does not matter if new system loads are taken directly from battery.   It is still necessary to upgrade the original wiring loom to redirect more power to battery.


Electric a/c compressor efficiency
=====================

As we all know electric cars are the future, and of course that depends a lot on the development of new technologies around batteries and the availability of the raw materials used to produce them.  In my opinion internal combustion engines will be there for still a long time. Electric cars technology will force the adoption of many improvements on the Classic Otto cycle engines and derivatives.

Coming back to the point, as on electric cars battery life is the key matter, technologies have evolved in order to safe energy.  That is the case of the proposed electric compressor.  This type of compressor should be for sure very energy efficient, it should have the inverter technology we observe on household air conditioners or refrigerators.  That kind of inverter compressor, do not run at a constant speed, they are able of varying the speed according to the thermal load therefore saving energy.    That is much more efficient than a clutch driven compressor which can only be set to be on the run or off position. And a classic pulley driven compressor in the off position takes out also some energy from the system.

Those are all my thoughts in the matter for the moment.

We have to see how this technology develops over time, but for sure we will see more and more electrical driven accessories in the future instead of their classic pulley driven ones counterparts.

Best Regards
Leonardo Peterssen

Ps I placed all these thought here because Gary asked me to.

[MikeSimon]

Beware of "studies" and "test" supporting the superiority of electrically powered accessories.
I worked in hydraulic power steering (RIP). When electric p/s came out, everybody showed an improvement in fuel consumption.
Now get this:
Everybody agrees, that there is a parasitic loss caused by the hydraulic pump when p/s is not used, i.e.: driving straight ahead without steering.
Everybody familiar with physics also knows that applying a certain force requires a certain energy.
That being said, steering a vehicle electrically or hydraulically will require the same power taken from the engine, resulting in more or less the same fuel consumption.
Consequently, an electric system is superior to an hydraulic system only when p/s is not used, i.e.: driving straight ahead without steering
Most supporting data was taken from the so-called "Cafe Test".
This test is a cycle simulating highway and city driving conditions ON A DYNAMOMETER, with the steering wheel not being turned.
As a result, all the tests with electric power steering showed a reduction in fuel consumption.
Real world driving will not provide any measurable evidence of fuel consumption improvement.

But... it is an engineering innovation and all the design and development engineers who were all 'wet in the armpits" about it were able to sell it to everybody.
Pretty much the same as the general move to EVs right now, which totally ignores the energy need to create electricity for charging and refining the materials to make batteries.

Stepping of my podium...

[lpeterssen]

Totally agree Mike

I am also not convinced thar EV are viable in mass scale as raw materials availability  for actual battery technology is limited.

But…..

If electric compressors are like the digital inverter style used on home refrigerators they are certainly much more energy efficient

[Shvegel]

More efficient than previous electric compressors but not necessarily more efficient than a direct engine driven one.  Remember, there is loss when electricity is created as well as when it is used.

[MikeSimon]

Thanks, Pat! One of my pet peeves. Everybody seems to think that "electric" is more efficient, no matter what. Forgetting exactly what you said.

[mdsalemi]

a/c capacity is measured in "tonnage" with one ton = 12,000 BTU/Hr.
I've heard numbers all over the map, from 2-6 tons of a/c for a car. I tend to believe the lower number rather than the higher, but since a typical window a/c unit for a house is 5K BTU (.4 tons), and the largest single residential a/c unit made is 5 tons (60,000 BTU) we're talking a lot of electricity for a/c.

When a home needs more than 5 tons of a/c they add more units. I have two units at my home here, a 3.5 and a 2.5 ton, one upstairs and one first floor. My last home had a single 5 ton unit. One of my friends has a mansion and he has commercial units with 3-phase a/c units.

Remember, in a car, you are basically trying to cool an oven.

A 2-ton a/c unit requires about 7,000 watts. To get that much wattage in a residential a/c unit, they all go to 220V so as to keep the current a bit lower. That's why in your service panel you see double breakers, sometimes 30 or 40 or even 60 amps.

That watts/ton comes from a common HVAC calculation formula. Even if its off--like WAY OFF by a factor of say, 10--you still have 700 watts.

Now, how big are our alternators? 

[66andBlue]

Determining a car's necessary a/c capacity in "tonnage" is like using your shoe size to determine how long "1 foot" is. 
https://en.wikipedia.org/wiki/Ton_of_refrigeration
"The ton of refrigeration is equivalent to the consumption of one ton of ice per day and originated during the transition from stored natural ice to mechanical refrigeration. Just as horsepower and candlepower were intuitive units of measure for people living through the transition from horse to motorized transport and from flame-based to electric lighting, so was the ton of refrigeration an intuitive unit of measure during a technological change, as the ice trade gradually included growing percentages of artificial ice (ice from ice-making plant) in addition to its natural ice supplies. The TR unit was developed during the 1880s. Its definition was set at the level of an industry standard in 1903, when Thomas Shipley of the York Manufacturing Company led the formation of an industry association (the Ice Machine Builders Association of the United States) along with standardization of several equipment specifications ..."
Fortunately automotive engineers who deal with the thermal management of vehicle cabins probably decided that (a) it would be impractical to put a ton of ice into a stationary cabin and measure how much energy was needed to melt it in 24 hours and (b) the result would be not be very applicable.
Matching a car owner's comfort level expectations with existing technology and also conforming to extant governmental regulations is a lot more challenging than melting ice.
Here is an overview of the problem written by experts in this field. Have fun reading it - probably best while you are melting your favorite ice cream, popsicle, or chocolate in your mouth! 🤣

[mdsalemi]

a/c capacity in "tonnage"

Well thanks for that, Alfred!  I didn't invent the term nor determine its origin. And though you may not like its origin with melting ice, how peculiar is its counterpart, "British Thermal Units"? I mean, seriously? How do the French feel about that? (Most Americans know BTU as BTU not as British Thermal Units).

Nobody uses a ton of ice in determining anything any longer, he says while laughing, but the units of measurement remain. All the load calculations done are based on how much heat you need to remove. And all the parts are the same whether in a car or a house: compressor, condenser, evaporator, liquid line, vapor line, and a few other parts tying them together and making them work and play nice together.

The bottom line is tonnage, BTU/Hr, are all standard units of measurement for heating and cooling. For automotive compressors, the compressors are generally specified in "displacement", and then kW on a curve chart. One ton of refrigeration capacity = 12,000 BTU/Hr = 3.5 kW. Unlike residential or commercial a/c units which generally operate at a fixed rate (unless you're talking about two stage but let's not go there) automotive operate at quite a variance. A small Sanden automotive piston compressor, at higher RPM, is capable of over 6 kW. Like it or not, that's over 20,000 BTU/Hr, or 1.6 tons. That's enough for a small home. It's capacity is seriously reduced at idle speed.

But, because you were dwelling on quaint terminology, you missed the point on this. a/c consumes a lot of electricity. Cars like a Tesla have electric a/c compressors, but they also have massive batteries and electrical capacity to run them. Our cars do not. It takes a lot of electricity to cool even a small car...and I would question whether or not our standard battery and standard alternator could keep up with the electric demands of a properly sized electric a/c unit.

I had two Ford Fusion plug in hybrids from 2015-2017. Though plug in, they were true hybrids, with 4-cylinder Atkinson cycle gas engines. When freshly charged they had a stated 18 mile range before the gas engine would kick in. Turn on the a/c, and you couldn't go a mile without that range dropping precipitously. For the most part, you were using gas most of the time, since it is rare in Michigan not to need either heat or a/c in a car.

[MikeSimon]

As far as using "old standards": How about "horsepower"?? It is the force required to lift a defined mass to a defined height in a defined time. That's what a horse was capable of.

[mdsalemi]

I like it Mike!

I’m sure it used to lead to arguments such as my horse is bigger and stronger than yours! 

[russelljones48]

Since I have removed the engine compartment components of my "period correct" AC system and intend to remove the passenger compartment components as well, here's what I read this thread for: is there are reasonably priced modern compact AC system that I can install to improve (2) passenger comfort (but mostly my wife's) during the summer in this region?

I don't want to be politically incorrect but I don't much care if the proposed system reduces gas mileage by a few MPG, I do care about weight - the components already removed weigh in excess of 20lbs. and are located high and forward in the car and I do care somewhat about performance or HP draw - regardless if it's alternator or mechanical. 

Now the overall impact of of EV's has to be measured against the charging energy source - is your charger tied to a coal fired power plant......  and what will be done with all of those batteries once they need to be swapped out?