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DENSO develops cold storage evaporator that limits the rise in cabin temperature during an idle stop

Cross-section of the CS Evaporator. Click to enlarge.

DENSO Corporation has developed a Cold Storage (CS) Evaporator, which limits the increase in vehicle cabin temperature during an idle stop when stop/start technology is employed.

The newly developed CS Evaporator is equipped with a cold insulator, located in the heat exchanging area, which stores cold energy to be used to cool in-vehicle cabin air while the engine and air-conditioning cycle is off in the idle-stop state.

An evaporator is a component driven by engine power that is used in the air-conditioning cycle. Cold refrigerant exchanges heat with warm air to send cooled or dehumidified air to the cabin. For conventional air-conditioning systems, when the engine stops during an idle-stop mode, the air-conditioning cycle also stops, which may impact cabin temperature. In order to cool the cabin on higher temperature days, the engine needs to remain on to continue the air-conditioning cycle, which is not fuel-efficient.

The CS Evaporator has the same basic structure and is the size of a conventional evaporator but it can store cold energy more quickly and discharge cooled air more slowly. To accomplish this, DENSO installed a closed case with inner fins and a cold insulation inside.

The cold insulation case is placed between refrigerant tubes, from which the cold insulator directly and efficiently extracts cold energy during the air-conditioning cycle. When the air-conditioning cycle is stopped, cooled air is slowly released from the cold insulation container via the outer fins connected to the refrigerant tubes. With these functions, storing cold energy can be completed even in a relatively short time of vehicle travel and cooled air can be supplied to the cabin for a long period of time.

This product will be used in the Wagon R, which was launched in Japan on 6 September by Suzuki Motor Corporation. DENSO will progressively make the CS evaporator available for a greater number of vehicle models worldwide.


Nick Lyons

Cold energy? I read the source, and the English translation is pretty goofy. I think the gist of the product is to cool an insulated mass of something within the evaporator body when the engine is running, then let that mass cool the air blown through it when the engine is stopped and the evaporator is not doing its usual thing of cooling the air by boiling the refrigerant.

The cool thing about this is that you don't have to electrify your compressor, etc. Just swap out your evaporator, perhaps adjust some controls and you're good to go.


Whereas with electric A/C, the compressor never stops and the issues of the drive belt, clutch, compressor shaft seal and flexible hoses all disappear.

I keep waiting for a company to make an absorption-cycle A/C running on exhaust heat.  It's very easy to store a bit of heat, or have a reserve supply of refrigerant and absorbent to operate during pauses in the heat flow to the boiler.

Nick Lyons

@E-P: I agree electrification is the future for everything from AC to power steering to water pumps. However, I could see this solution working as a short-term solution for a manufacturer that wanted to add idle-stop to an existing platform at the lowest cost and quickest to market.


If you electrify the accessories (power steering, water pump) to cut parasitic losses there, a bit of battery power for the A/C can also give you launch assist with the idle-stop.  That short-term could be very short indeed.

Account Deleted

This solution will have a great future

william g irwin

Sounds like some phase change materials that change below room temp to me. Great idea! Why not until now? Hmmm! Should help spread out the compressor load in general. Cool!!! (pun intended)


The manufacturers had no incentives to do this, now they are interested in stop & start systems and they need it.

Roger Pham

Even in HEV, this type of cold-storage will reduce wear on the battery and will prolong battery life. In the summer, the battery is already stressed out from the summer heat alone. Heavy usage of the battery by the A/C will heat up the battery even more.

Henry Gibson

LG has its most efficient free piston compressor for refrigerators that was invented by a Stirling engine company. Such compressors can reduce engine fuel use and eliminate hoses and refrigerant loss because the whole system can be mounted on the frame and welded and could last over seventy years. The generator-starter can be built right on the flywheel to eliminate all belts. One company built a self starting engine by injecting fuel and sparks to selected cylinders. Henry Ford did not do this, but could have. ..HG..


HG: Both ICE and Electric motors have been around since about 1850. Electric motors have more or less always been self starting. ICEs were manually started until compressed air and/or electric motor/starters were added about 100 years ago.

Starters were never really been fully integrated to ICEs. They have always been an add-on (belt or gear driven) ancillary. It is difficult to understand, that after 160 years, combined, more efficient (5+ Kw/Kg) starters/generators are not fully integrated on the flywheel or the drive shaft.

Most ICE have very low power density (.03 to 1.0 KW/Kg). Wankels do better with 1.0 to 1.8 KW/Kg. A few formula ICE do up to 7.5 KW/Kg.

Up to date electric motors can do 4.5 KW/Kg to 6.0 KW/Kg.

PEMFCs are improving. The best can do 1.0 KW/Kg to 1.5 KW/Kg.

Many Lithium batteries have surprisingly high Peak power density, 6 KW/Kg @ 32C and up to 21 KW/Kg @ 333C. That's why many BEVs with lithium batteries/electric motors have better acceleration than their ICE counterparts.

Regular ICE cars have very low power density, 53 to 114 W/Kg
Sport cars do a bit better with 129 to 174 W/Kg
Race cars do better with 179 to 403 W/Kg but are not very efficient.

Future BEVs, (with improved batteries..1000+ W/Kg?) and lighter bodies may have better overall power density and higher efficiency (100 Wh/Km).


Will passive thermal energy storage (cold-heat) be more efficient than future batteries and heat pumps?


Future BEVs equipped with lightweight 100 to 140 Kwh battery packs may not require quick recharges. After 800 to 1000 Km, it is very normal to stop overnight for rest while the BEV is getting a slow 8+ hour charge.

All those super 100+ KW high DC voltage chargers may have to be phased out by 2025 or so.


Storing cold or heat is OLD OLD technology but new materials can give it life.

"cold insulation"?

The effectiveness depends on the BTUs per cuin and per pound and per dollar and the toxicity and and and

What are the facts and details here? Without these it's all BS.

And absorption chillers have poor factors of performance.

Roger Pham

Thermal storage is cheaper than battery storage by a factor of 10, based on face value of kWh basis. However, if given the COP of the car's A/C is around 3-4, then the price of thermal is about 1/3 that of battery storage. Thermal storage is more durable than battery storage and does not need a sophisticated monitoring system or cooling system. That ought to bring the cost of thermal storage down a little bit further in comparison to battery energy storage.

absorption chillers have poor factors of performance.
You're forgetting that the heat is free.  I suspect that one significant issue is the greater heat rejection required, and the additional drag from the cooling system.  On the other hand, if combined with a bottoming-cycle engine (a la BMW's Turbo Steamer), it could pay off.

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