Far from the minds of the media, journalists and press is the problem of temperature for electricity storage.  Batteries in particular have a major problem of releasing capacity particularly when cold.  A major share of the market for transport batteries is where winter would put a battery energized electric vehicle out of work simply because the chemistry reactions would be too slow.

An answer is on display at the Frankfurt Motor Show.  Ixetic GmbH presented a concept thermal management system for lithium-ion battery packs in electric cars based on refrigerant R-744. R-744 refrigerant is chemically altered C02.

The concept system uses a special compressor that works as a heat pump; it can both cool and heat to an equal extent. The system constantly maintains the battery pack temperature at between 15 to 35 °C (59 to 95 °F), even when the vehicle is parked. If the vehicle is not running, the compressor’s electric motor takes the electricity it uses for cooling or heating directly from the battery.  No power is used for resistance heating.

Ixetic says another advantage to its concept is the use of Ixetic’s compressor as a vehicle heating, air conditioning and ventilation (HVAC) system across the seasons.  Vehicles with combustion engines use waste heat for heating the cabin, but electric cars require an additional electric heating system.

The power savings are substantial.  Ixetic points out a conventional additional heating system uses electricity from the vehicle battery, limiting the possible driving radius by around 40%. The high efficiency of ixetic’s compressor cuts the amount by which driving distance is limited to a significantly lower 10 to 15%.  If Ixetic’s numbers are even semi accurate, that’s a major improvement.

Ixetic's CO2 Compressor

Ixetic's CO2 Compressor

Ixetic began development on an R-744 compressor targeted at mobile air conditioning systems in 1996.  In 2011, European vehicle manufacturers will no longer be allowed to use the R134a refrigerant in air conditioning systems. The leading alternative to R134a is the new R-1234yf refrigerant.

Ixetic was part of the company LuK Fahrzeug-Hydraulik and LuK Automobiltechnik, which in turn belonged to INA Holding Schaeffler KG until March of 2006 when it became an independent company.  Today, Ixetic is owned by the holding company Cognetas. The Ixetic product range covers hydraulic pumps for steering, chassis and transmission applications, vacuum pumps for brake systems and lubricating oil pumps.

The combined heating and air conditioning for the cabin with a battery pack temperature moderator is a good idea for making use of one system to convert three problems.  Even if the battery pack is quite small, or capacitors are used, most vehicle sales are going to need a HVAC system.  HVAC in vehicles are serious power drains.  Going the heat pump route seems eminently sensible.

On the other hand vehicle air conditioning is in this writers personal experience, the most unreliable subsystem in a vehicle.  The air conditioner in most vehicles with much age is complex, expensive to repair and far from the robust engineering seen in the engine, transmission and other power train subsystems.

Yet reliability could be greatly enhanced.  Today’s vehicle air conditioners are problems primarily due to the seal at the compressor input shaft that’s turned by engine power and the connections where lines are connected during assembly.  Substituting a sealed electric motor and compressor as in a refrigerator would solve the seal issue and fore thought can go a long way to reducing the connection points.  Refrigeration can be a very long-lived system; electric drive such as Ixetic suggests can only help.

With two services, the cabin and the battery pack environments, the plumbing will get more complex.  Some means of handling the demand differentials could save energy and enhance driving range.  A running battery pack would give off heat that could be moved by the heat pump to the cabin.  Demands could also get quite high when a battery pack is running and the cabin demands air conditioning.  These systems are going to be larger and more robust than first impressions may suggest.

Even if the ultra capacitor market grows into electric vehicles at exponential rates the need for cabin environmental service will still be there.  A hybrid with a combustion engine for generation would allow some heat to be available and an opportunity for crankshaft power for compressing refrigerants.  But the question will remain, what choices are best for the consumer?

The most encouraging thing about the Ixetic design is the illumination that closed refrigeration systems set up as heat pumps offer automotive engineers a major opportunity to enhance hybrid and EV performance. It should also save some money at the purchase price and one certainly hopes a much lower operation, maintenance and repair expenses.

One wonders, can a 30% saving of battery pack capacity pay for the heat pump system?  Very likely, I’d say.  The unrecognized problem might be an unrecognized opportunity.


1 Comment so far

  1. Matt on September 24, 2009 7:27 AM

    Wouldn’t it be ironic if an electric car carried a gasoline powered charger to power the accessories?

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