Toyota Prius Prime Breakthrough Heat Pump, Bumps EV Range In Cold

JAN 28 2018 BY MARK KANE 82

Heating is generally one of the weakest points for all-electric or plug-in hybrid vehicles because you can’t typically use waste heat from the engine, while operating in all-electric mode.

Toyota Prius Prime

Electric heating uses a lot of valuable energy from the  battery (up to several kWh per hour of driving), which affects range – mostly in cars with small batteries. Heating seats and the steering wheel is a good supplement to lower general cabin heating.

Some manufacturers use heat pumps (reverse air-conditioning), which is able to lower the energy usage by a magnitude of two to three.

However, the efficiency of the heat pump decreases in low temperatures, so the heat pump doesn’t improve efficiency (or is unavailable) under 0C or -10C. That’s when you need the heat the most.

Toyota has upgraded the heat pump system in the new Prius Prime to increase overall efficiency and extend the operating range of temperatures, through reusing warm vapor (separated from the liquid and injected into the compressor again, bypassing the condenser).

Here is how it works:

“The innovation in the Prius Prime system is the incorporation of a cyclone separator (CS) integrated valve into the system. To understand how this works, an understanding of conventional heat pump operation will help. In a normal heat-pump system, the compressor pumps high-pressure refrigerant vapour to the evaporator core inside the passenger compartment. The compressed vapour is hot and transfers the heat to air blowing through the heater system. This cools the vapour and it starts to turn into a liquid, which flows under high pressure out to the control valve where flow is restricted and the high-pressure liquid turns into a low-pressure liquid that starts to boil. It continues to boil as it passes through the condenser in front of the radiator, absorbing heat from the outside air until the refrigerant is a vapour again and it goes back into the compressor to go through the cycle again. A heat pump is the opposite of the flow when air conditioning is requested.

Now, Toyota has added the Cyclone Separator integrated valve into the system, which uses centrifugal force inside the valve to separate the vapour from any liquid and injects the vapour directly back to the compressor, bypassing the condenser. The vapour is already warm, so it can provide more heat to the vehicle interior, while the liquid is directed back to the condenser, where it can absorb more heat from outside the vehicle. There are now two paths for the vapour/liquid to flow and the efficiency of the system is greatly increased.

Toyota says that efficiency is 63% higher than conventional heating, so the range in cold weather could be up to 21% higher.

Besides reusing warm vapor, the heat pump works in six different modes, depending on the temperature.

Source: Winnipeg Free Press

Categories: Toyota

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82 Comments on "Toyota Prius Prime Breakthrough Heat Pump, Bumps EV Range In Cold"

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Seems like you’d achieve the same efficiency having the refrigerant fully condense. There are probably reasons making that impractical, AC cycles are tricky in the real world.

I doubt the extra energy needed to fully compress 100% of the vapor to liquid would be very efficient.

If the compressor is reciprocating, then the refrigerant must remain a vapor during compression, since a liquid is incompressible. But the compression typically happening in a refrigeration system results in a HOT Gas that is far above its saturation point anyway since the Heat of Compression is added by the compressor doing work on the gas. Such superheated gas is by definition always a gas, since at the (real) condenser, first the superheated gas must be cooled down to the liquification point (or saturated boiling point – same difference), such that the Heat of Compression is removed first. Then additional heat is removed as the refrigerant liquifies. Again, reverse the evaporator/condenser terms in the press release, since those functions are opposite to what is being performed in the summertime.

The idea is to compress the gas to create a higher temperature to be able to air cool it through a heat exchanger.

Constant Entropy compression kinda works that way. There is no way around that – its rather like arguing you don’t like the way GRAVITY works. It is what it is.

At a constant Entropy – the GAS just HAS to get much hotter.. Any reference to any refrigeration table of characteristics will show that.

SJC: “…The idea is to compress the gas to create a higher temperature to be able to air cool it through a heat exchanger.”

Not so. The idea is to restore the refrigerant back to a liquid so that it can perform its function again by boiling.

If you only have a finite amount of liquid refrigerant, please tell me how you plan on recreating the liquid unless you use compression or adsorbtion.

HAHA there is a third way of doing that other than the two I’ve mentioned, but it is rather impractical and costly.

Hence, for earlier cooling needs people in the 18th and the early 19th centuries used to charter Cork-lined ships to go up to icebergs and fill the ship with them.

The price per ton of such cooling was tremendous, since the ship could only carry so many tons, and the labor cost was excessive.

I can see why people do not like you.

Doggydogworld: “…Seems like you’d achieve the same efficiency having the refrigerant fully condense.”

Reading the press release is confusing because what they are calling the Condenser at the radiator outside is actually the evaporator in Wintertime, and the Evaporator in the cabin is now the Condenser in Wintertime.

Going from like -10 deg F to 70 deg F in the cabin, especially if the fan is on low, may at times result in refrigerant that hasn’t fully condensed – so this spinning valve just keeps the vapor and liquid separate. They also use some hot gas injection to warm things up a bit. But it would also be efficient for the hot gas to perform a defrost cycle, as I’m sure they have to do often in cold, moist locales.

So what is the total electric range now? Also how long does it take to warm up the cabin when it is 10 degrees F?

Resistance heat is typically used in EVs with heat pumps in extreme cold. My Leaf heats up faster than any ICE car I have ever owned.

Also you can preheat with wall power in a closed garage, something no ICE car can do.

I’ve been warming ICEs by plugging in for decades. It’s the norm in many cold climates.

And the reason why loads of parking spots have engine heater electrical outlets.

I believe you are referring to a Block Heater, or not? Or do you have an Electric Cabin Heater as part of your Standard items in your car?

Yeah, he’s talking about block heaters, and they are useful, though I hardly ever use one, unless it’s really cold.

Most have both. Warm engine and warm interior.

I grew up on the Hi Line in Montana and we all had Head Bolt Heaters that you plugged in at night and they warmed the engine a bit. If you didn’t, the car probably wouldn’t start. But they didn’t change the cabin temps at all. Would have been nice to have the cabin heater option back in the day. (1970’s) But any parking spot likely to have overnight parking had plugs you could take advantage of for free.

Cabin heaters are usually not standard but are cheap, easy to install and very common.

Come on it’s a Prime. Even if ti retained it’s full summer range it’s still crap. Put that new tricked out heat pump in a Bolt and let’s enjoy a real difference from existing resistance heating system.


Or a LEAF or… This is great news for all BEVs. I hope Toyota’s patents don’t prevent this from spreading to other makes, or at least they will license at reasonable rates.

I disagree. Prime is the perfect vehicle for many people.

True, the new heat pump won’t make it look better, go faster or be fun to drive.

+ 1
Great car, if you can’t afford a Bolt, or Tesla.

Aside from its wierd looks and shorter range the prius is a much nicer car than the volt.

Higher roof makes it far roomier inside, (much) bigger windows and better visability, much better gasoline milage, cheaper to buy and good resale, Typical toyota reliability amd durability……

Most major car magazines say Volt is the superior car. I agree.

Depends what you’re priority is. My priority is the much superior driving dynamics of the Volt in pure EV mode which I spend almost all of my miles in. I’m 6’2″ and it’s not like I can’t fit into the Volt. Sure I could use more headroom but I would never give up the day to day driving fun of the Volt for more headroom.

Dan, I use considerably less than a gallon of gas a month in my Volt because the range is long enough that the gas genset never turns on. The Prime doesn’t have that ability, therefore it uses the gas engine a lot more, albeit at a slightly more efficient rate. But the Prime uses a lot more gasoline that the Volt if you drive 30 or more miles a day. And most do.

This looks to be a bit cheaper way of doing it compared to the liquid sub cooling method described here???

So this was announced before. This article provides a new bit of technical information on how it is done. The old article explains the theory is well known, but the implementation was crude or expensive. Toyota has figured out a low cost way to improve this by-pass architecture, so yes, much cheaper than the dual compressor version.

@Roy H,
Yes it appears to be simpler and lower cost. Looks like they eliminated a heat exchanger and they are using centrifugal force to separate the vapor from the liquid.

PS Keith and I wrote the article (HVACman)

We have another set of 4 articles coming up on the truck. Should be out early next week.

Yeah, they do a little bit of hot-gas injection. Its a bit of a confusing explanation since they are using the summertime functions of the equipment, In winter time, the Condensor is in the Cabin and the Evaporator is by the engine radiator, which is the opposite of what they just said in the ‘official’ explanation.

Mitsubishi pioneered this ‘Cold Heat Pump’ with their line for residential/small commercial heat pumps (up to around 47,000 BTU/Hour). They don’t get an Energy Star rating since their summertime efficiency is mediocre, but their Wintertime performance in 0 degree F weather is fantastic.

Lack of a heat pump is my Bolts biggest negative. Will be a major consideration for my next lease.

Unconventional looks, poor front seats and relatively slow “fast charging” are bigger problems for the Bolt than the lack of a heat pump.

And the Prime is better how?

“Toyota Prius Prime Has Breakthrough Heat Pump System, Bumps Electric Range Up 21% In Cold
Toyota says that efficiency is 63% higher than conventional heating, so the range in cold weather could be up to 21% higher.”

I hope that is ment like in the sentences before, so here they just forgot “heat pump” (conventional electrical heating is for me a heating wire -> 1kW in, (nearly) 1kW out).

Renault says that their heat pump needs 1kW but offers 2kW heating -> (German version)

Now where are that “in/out” values for the one used by Toyota?


Heat pumps are rated by COP, Coefficient Of Performance. as compared to electric heat. Simply put, a typical residential heat pump produced BTU’s for 1/3 the energy of resistive heat. So the Renault would have a COP of 2.0. Half the energy of electric heat.

Heat pumps are great, but illogical in the Prime. The car has barely enough electric range to get me out to the state road. Once the battery runs down, the gas engine will be running 90% of the time. If they ran the gas engine first, and saved the electric for when you get into town, there would be enough waste heat from the engine to never need electric heat.

I guess if you can afford to live in the city it works. But in a logical world, cars wouldn’t be allowed in the city.

You are thinking very small when you are only considering your needs.

It’s great to have it in the prime so people in cold climates can commute without using the ICE.

And stop poluting your sibbling..
This kind of system could also use the heat waste of the engine and inverter all along in true blooded EV for even higher efficiency benefit.

“The car has barely enough electric range to get me out to the state road.”

Well, that’s an ignorant, self-centered comment. Vast majority of people don’t commute 50+ miles to work. This is excellent for people with a 10-mile commute to work who don’t want range anxiety on road trips. For those people, this is the cheapest way to drive 80+% on electricity.


That would be great if most people drove less than 25 miles a day, but they don’t. The Prime just doesn’t have enough range for most people, especially in the winter regardless of heat pump or not. Toyota needs to go back to work and add at least 6 miles of range, preferably 10 or more miles, though.

Warren: Don’t throw out the baby with the bath water…

Yes the Toyota has less than optimal battery range, but that is mainly the only thing it is lacking. 3.3 kw charger is considered puny nowadays but it is more than the plug-in-prius’ 2.4 kw model.

As I keep saying to John, Toyota could make a REALLY good ev should they ever want to.

SO, the Prius Prime is what it is: A Very Impressive vehicle, that may not go all that far, and during the winter time you may not get all that benefit of a cold-weather heat pump for as long as you’d like.

SO for what its worth – the Car shows that in the future, Toyota COULD come out with a really stupendous model – they have all the parts in place to be ready for it should they ever want to do it.

Heat pumps are an improvement, but if its really cold get a diesel car heater. Any manufacturer who makes this a factory option should get extra review stars.

Diesel heaters should be banned and anyone offering it get zero stars on reviews.

Ah, the internet.

How about an alcohol heater then?

It doesn’t make sense to add a fossil-fuel-burning heater when there is already a device built into the car that not only generates heat by burning fossil fuel, but can generate electricity or perform mechanical work at the same time: the internal combustion engine.


Chevy did just that for the 1960 CORVAIR what with its gasoline heater – working great even though the engine wasn’t on.

The nearest production car to it today is the I3 REX which uses a GASOLINE ENGINE to produce electricity for its resistance heater, albeit doing it less efficiently even than the Corvair did, since all waste HEAT from the engine is discarded, and the electric resistance heat, coming from a relatively inefficient ICE is lower efficiency than using a gasoline heater directly. Now using a resistance heater here is doubly silly, since BMW could have run the waste heat by the Heat PUMP evaporator and really toasted the cabin with it with much less gasoline consumption to boot!

But then Plymouth (Chrysler Corporation) ran ads showing how lousy the gas mileage was compared to their compact offering the Valiant, which used otherwise waste jacket heat. The result was so damning that in 1961 Chevy got rid of the gasoline heater and put in air ducts to an air heat exchanger to recoup engine heat similiar to the VW Beetle’s air cooled engine.

I wish it were an air exchanger. My cabin filled with smoke as the pushrod seals dripped oil and the smoke blew in through the heater!

Oh, I stand corrected – I got my information from a retired engineer from Harrison Radiator (GM) regarding the difference between the 1960 and 61 Corvairs. I had no idea they skipped the heat exchanger, as the VW had – of course there, the majority of the heat was coming from the exhaust pipe so isolation was mandatory – only a minority of the heat came from the ‘air-over’ the engine.

It doesn’t have to be too cold for it not to work well, or at all. At freezing 0* C down to -10* C (14* F). So then it is not working at all at or below that low range temperature.

Where I live the longest stretch of cold was 21 days without the temperature rising above
-18* C (0* F).

Well the truth is that very hot and very cold places are very tough for EVs, at least for now and the near to medium future.

Just get a Prius, Ioniq, or Niro hybrid (or Plug in if you drive much in urban areas and want an ev option for in town).

If the car doesn’t do it automatically, the operator can always switch to hybrid mode to quickly generate massive amounts of heat that any BEV would be envious of. In addition to seat and steering wheel heaters, PHEV’s just like BEV’s can also precondition for heat eliminating the need for ICE heat on shorter trips.

BEV proponents always want to point out their inherent efficiencies over ICE but when the shoe’s on the other foot……. 😉

I’m pretty sure the Prime has had this since day 1.

There is a lot of misinformation about how the heat-pump in Prime actually works. Here’s a video I filmed last week with mine to provide real-world detail…

At 8°F, you easily see how it gets used during the warm-up process and how effective the heating continues with the engine off and back into EV driving.

I completely fail to see any reference to the heat pump working and its effectiveness. What your video does show is at the 30 sec point the engine comes on and by about the 45 sec point it is hot enough to provide heat for the car. I can only assume that for all the remaining time the heat pump did not have to be used.

What misinformation?

Drawing attention to misleading info has not been effective, hence moving to video now to convey real-world data instead…

That example shows the heat-pump in action with the temperature just a little above the threshold, running for the entire commute. It’s a nice sample of EV winter driving.

Here’s another…

That one is with the temperature above freezing, but still a definite need for heat. You can see how both coolant & battery contribute to warming near the end of that drive.

John: What is the mechanism for heating the battery in the Prius Prime?

(In GM products a resistance heater (1750 watts for the Gen 1 VOLT) is the only method available, even IF there is spare cooling jacket heat).

I just wondered if, besides resistance heat to heat the battery loop, if either engine jacket heat or Refrigerant HOT GAS could also be used in the PRIME to heat the battery.

The Prime doesn’t have a true battery TMS. It does have a rudimentary heating pad to warm the battery in winter.

Toyota wanted a bunch of effort putting a heat pump in a car that often runs its ICE (providing tons of heat), but didn’t bother designing a real battery TMS.

Is the heating pad you talk about only resistance heat? I suppose they wouldn’t need much seeing as how small the battery is.

This is great, I just want to bring your attention to a technical mistake in your article. When it is heating mode inside the car what you called an evaporator becomes the condenser and the other heat exchanger becomes the evaporator. In cooling mode its vice versa.

For heat, it may be better to have a small fuel tank (Gas/Diesel/Ethanol) and the fuel can be burned to produce direct heat rather than using electricity. Power plants convert only 1/3 of the heat to electricity and using that to heat means more than 2/3 of the heat energy is wasted.

Its already January 2018 and still the Prius Prime MY-2018 has not gone on sale. 4,400 + models (all 2017) are available for sale.

I don’t know whether this is high or low. May be Toyota is waiting for all previous year models to be sold before starting the current year.

So, the range would be even more pitiful without the heat pump? Would it accelerate faster than an electric wheel chair if they removed the heat pump, because that might be worth looking into?

While heat pumps are somewhat effective down to 0F, efficiency really starts to fall off below 32F. There just isn’t enough heat energy for the heat pump to move. And the defrost cycles are problematic.

CCIE what you say may have been true in the past, but these Mitsubishi Style cold weather heat pumps really ROCK! They are mediocre efficiency in the summertime – but its resistance heating in the winter time that really is a problem. My Bolt EV in very cold weather ends up using TEN TIMES the electricity per mile that it would have during the spring or fall. Summer is only a bit less.

At 10 deg F they still have a 2 to 1 coefficient of performance (COP) and don’t get down to 1:1 until -17 deg F. THAT is fantastic performance most of the time. If it is somewhat warmer than 10 deg F outside, then the COP is 3 or better. That is simply fantastic.

“My Bolt EV in very cold weather ends up using TEN TIMES the electricity per mile that it would have during the spring or fall.“

This seems a bit implausible. The Bolt is EPA rated to get about 280 Wh per mile overall. In spring or fall let’s say you are pretty efficient and get 250 Wh per mile.

You say that you are using 10 times the electricity in very cold conditions. So, in other words, you are using 2500 kW per mile?

That would imply a range of about 24 miles for a fully charged Bolt EV. It’s hard to imagine how to get less than 80 miles of range in even the worst winter conditions.

Please explain.

Not 2500 kw per mile, of course, that is a unit of power, so its meaningless. Its more like 2 kwh per mile. Or, I can get 6 miles / kwh in the summertime, but a bit better than 1/2 mile per kwh in the wintertime.

Short trips are the worst since quite obviously 90% of the juice goes to heating something – and with short trips when the car is running the car and battery is always heating, and then when you stop the car is always cooling – needing to be reheated AGAIN for the next segment of the errands.

Having said that, I’m REALLY IMPRESSED by the bolt ev’s ‘honest’ 60 kwh battery. Prior to purchasing the car I had all sorts of worries that there would be the vampire drains of the Tesla S in cold weather.

Turns out there is none of that drain. You can leave the car out in the cold, and it will draw 2-3 kw for an hour or so to warm it back up. For such a MAMMOTH battery, that is quite amazing how little heat it actually needs.

There’s a reason people don’t use heatpumps in the northeastern US. Despite the numbers, they don’t work well anywhere that the temps regularly fall below 32F.

I agree that they look good on paper, even at 0F. But, the heat rise they can generate doesn’t result in air temperatures above human skin temperature. So, the air feels cool when blowing on you. To make up for that resistive heat elements have to be used. And, at low temperatures with high relative humidity, the outside coil develops frost which must be eliminated by putting the system in cooling mode.

Actually that is around 47 degrees. That is when the “evaporator” is around freezing and that is what causes efficiency to drop and capacity. However, capacity can be enhanced by overspeeding the compressor and protecting it using demand cooling, which may not be needed with a belt driven compressor or electric motor not refrigerant cooled.

Many people experience this effect in cooling if they are low on refrigerant. Increase the RPM of the engine and suddenly the air gets cooler. Works to a certain extent.

You see, a certain amount of cooling requires a certain amount of refrigerant moving per minute. If charge is low, not enough refrigerant. If the compressor is sped up, now it moves more refrigerant but at the cost of increased compressor head temperature and early failure, which demand cooling tries to correct.

If you follow me up to this point, congratulations.

Steve B what you and CCIE are describing are the typical ‘old school’ heat pumps.

This system seems much more like the Mitsubishi HYPER HEAT PUMPS used – where the COP at 17 deg F is still over 2 to 1, and the system is good to work at 70% of capacity still at 5 deg F.

As I say, summer performance of this system is somewhat mediocre since it isn’t good enough to get an ‘Energy Star’ rating – but in a car, not much electricity is required in My Northeastern US area most of the time for cooling. Arizona obviously would be exactly the opposite.

But for cold weather climates, the operation of these Heat pumps (and the money they save) is absolutely fantastic. No relation to the performance of old school heat pumps.

Now Toyota should put that brain power to ev technology. Enough with the ice cars.

It’s really only a matter of waiting for the next-gen battery. Heck, just imagine what that higher-density, faster-charging pack would deliver in the current Prius Prime.

All the building blocks are already in place, so refinements to the system… like the heat-pump… and the carbon-fiber… and the aero-glass… are showing up in the affordable category.

It’s easy for the early-adopters here to make the snide remarks, but it is an entirely different matter getting ordinary consumers to buy into their priorities.

Think about how Prius became widely accepted.

John you keep saying carbon-fiber this and aero-glass that, but these comments are just lipstick on a pig. The Prius is so dated and yet Toyota is trying to put little fixes in but the car has an AER shorter than my… Front driveway. Toyota builds cars for soccer mom’s and beta males.

Calling weight-reduction and aerodynamic-improvement efforts “lipstick” shows just how misplaced some priorities are.

sorry that your front driveway is 20+ miles long. now I can understand why some american need to drive more than 100 miles a day.

>> Toyota builds cars for soccer mom’s and beta males.

Ironically, weight-reduction and aerodynamic-improvement is exactly what GM just announced as major upgrades for their large pickups.

I hate to break it to you, John, but the average buyer for a pickup doesn’t resemble a Prius buyer in the slightest manner. The Prius is an efficient gasser w short electric range. It is a poor copy of the Volt since the Volt has so much more AER. The Prime has slightly better mpg rating but since the Volt needs its gas genset so seldom, the Prime just looks lame. Even with its high tech carbon fiber Windows!;-)

I hate to break it to you, John, but the average buyer for a pickup doesn’t resemble a Prius buyer in the slightest manner. The Prius is an efficient gasser w short all electric range. It is a poor copy of the Volt since the Volt has so much more AER. The Prime has slightly better mpg rating but since the Volt needs its gas genset so seldom, the Prime just looks lame. Even with its high tech carbon fiber Windows!;-)

I refuse to accept your double-standard.

But you’re the king of double-standards. Remember when you thought plug-ins were stupid until Toyota finally came out with one?