How does the heat pump work in a Toyota Prius Prime plug-in hybrid?

Discussion in 'Prime Technical Discussion' started by priuscatprimeguy, May 24, 2017.

  1. priuscatprimeguy

    priuscatprimeguy Senior Member

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    How does the heat pump work in a Toyota Prius Prime plug-in hybrid?

    The challenge of reducing the energy used by traditional heating systems in battery-electric and plug-in hybrid cars is one automakers still grapple with today.

    Reduced battery range in cold temperatures, combined with batteries working overtime to heat the cabin, can produce drastic declines in EPA-estimated range figures.

    The Toyota Prius Prime plug-in hybrid, however, uses an advanced heat-pump design to minimize the loss of range.

    Toyota and Denso engineered the heat pump to include components from stationary commercial units, according to an in-depth look from SAE.

    A liquid refrigerant that turns into a gas and then back into liquid, and a gas-injection circuit, help provide heat in temperatures as low as 14 degrees Fahrenheit.

    How does it work? The basic principle is that gases cool down when they expand, and warm up when they're compressed.

    [​IMG]
    Toyota Prius Prime heat pump


    In heating mode, the refrigerant gas is pushed from the compressor into the condenser, mounted under the dashboard.

    The higher-temperature gas provides cabin heat that would otherwise require resistance heating in traditional systems, using considerably more energy than high-efficiency compressor and condenser.

    The partially condensed gas then passes through an expansion valve for further decompression and then heads to a liquid-gas separator.

    This process provides the heat-pump circuit extra help in cold temperatures.


    [​IMG]
    Toyota Prius Prime heat pump


    Following its trip through the separator, the gas then flows through a throttle passage, outer condenser, and finally absorbs heat from ambient air for interior heat.

    The challenge of controlling humidity is met with two circuits for specific ambient-temperature ranges—one for 32 to 40 degrees F, another for 40 to 60 degrees F.

    The humidity and temperature sensor tell the evaporator to vaporize any liquid refrigerant and to absorb heat from air flowing through the heat exchanger itself.

    When air conditioning is active, the compressor gives up heat and condenses the refrigerant.


    [​IMG]
    2017 Toyota Prius Prime Premium


    Both circuits operate during cabin heating, too.

    The system helps the Prius Prime work efficiently in six different HVAC modes: cabin cooling, cabin heating, serial dehumidification, parallel dehumidification, defrosting, and heat-pump generated cabin heat.

    CHECK OUT: 2017 Toyota Prius Prime: gas mileage, electric range review

    When the car is operating in all-electric mode, the process is trickier since there is no waste heat from the engine to help the process.

    Overall, Toyota and Denso say the system uses 63 percent less energy than a traditional heating system, and helps extend the car's battery range up to 21 percent in cold temperatures.


    [​IMG]
    2017 Toyota Prius Prime Premium


    The complex system lets the Prius Prime keep its gasoline engine off for longer distances, which helps with fuel economy and range.

    Given its success in hybrid applications, Toyota has said it will use the Denso heat pump in future all-electric vehicles as well.
     
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  2. ForestBeekeeper

    ForestBeekeeper Active Member

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    The same as any heatpump used to climate control.
     
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  3. Lee Jay

    Lee Jay Senior Member

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    You should read the link. This one is substantially different in a couple of ways.
     
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  4. bisco

    bisco cookie crumbler

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    how long is the warranty, and what will the repair cost?
     
  5. priuscatprimeguy

    priuscatprimeguy Senior Member

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    short, and bigly:eek:
     
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  6. Prius from Dad

    Prius from Dad Senior Member

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    Those are pretty technical terms. :D
     
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  7. priuscatprimeguy

    priuscatprimeguy Senior Member

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    straight from the current administration :p
     
  8. SaraBBrown94

    SaraBBrown94 Active Member

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  9. Trollbait

    Trollbait It's a D&D thing

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    But not any different than what is available for building units. Using some of the refrigerant to directly cool the compressor, and thus improve its efficiency, is only new to car heat pumps.
     
  10. Breatheintheair

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  11. Lee Jay

    Lee Jay Senior Member

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    Did you read the link? For example:

    "The system helps the Prius Prime work efficiently in six different HVAC modes: cabin cooling, cabin heating, serial dehumidification, parallel dehumidification, defrosting, and heat-pump generated cabin heat."
     
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  12. Trollbait

    Trollbait It's a D&D thing

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    The Leaf and Zoe can handle those basic HVAC functions with a standard heat pump.(Note: I do not see how any heat pump would make cabin heating from waste ICE heat more efficient.)
    [​IMG]

    The gas/vapor injected heat pump is more efficient and provides better heating at lower temperatures, but the Prime's heat pump isn't radically different from vapor injected heat pumps available for building HCAV systems. They are both more complex than a standard heat pump.

    I found the the article light on details. There is a nice schematic included, but the article doesn't make use of it. Leaving the reader to puzzle out what exactly is going on in the device for the vague descriptions.
     
  13. bisco

    bisco cookie crumbler

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    know your audience.
     
  14. drysider

    drysider Active Member

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    A heat pump is not more efficient than using the engine coolant, but it allows you to heat the car while in EV mode and without running the engine. This used to be done with resistance heaters, but a heat pump can be 3-4 times more efficient. Injecting cold gas on the high side of the system allows it to run at a lower head pressure, which is more energy efficient. As noted above, liquid injection has been used commercially for decades- primarily as a de-superheating agent in high compression systems. I am still trying to understand the system drawing. I am pretty sure what they label as a receiver is actually an accumulator. Additionally, a heat pump uses a 4-way valve to shift from heating to cooling because you have to shift both the high side and the low side. The is not one shown, but there are several valves I am not familiar with that may do the same thing.
     
    #14 drysider, May 26, 2017
    Last edited: May 26, 2017
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  15. JamesBurke

    JamesBurke Senior Member

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    Maybe this will help. Link from a previous thread you might have missed. SAE and Toyota Japan docs describing the operation. SAE had an additional diagram of the new liquid/gas separator not in Greencar article. A question about efficient use of A/C in the Prime

    OK now there are SAE links visible in the Greencar link. Droid is so screwy displaying mobile or desktop versions of sites. At least I have working internet ...for now.
     
    #15 JamesBurke, May 26, 2017
    Last edited: May 26, 2017
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  16. drysider

    drysider Active Member

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    It doesn't need a 4 way valve since there are separate evaporator and condenser coils. The way they do the dehumidification is pretty clever. You have to cool the air to remove the moisture and then reheat it. Normally, the cars coolant would do that, but the engine isn't running in the Prime. They bypass some hot gas from the compressor discharge to do the job. I would call this an elegant solution.
     
  17. Trollbait

    Trollbait It's a D&D thing

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    Clicking through to this helps, Inner secrets of the Toyota-Denso heat pump revealed - SAE International

    A simple air conditioner has a compressor, two heat exchangers, one inside and one outside, and an expansion valve. The refrigerant going into the compressor is a gas. As the compressor pumps that gas through the system, the pressure on the gas increases. This generates heat. As the compressed gas moves through the outside heat exchanger, the heat is shed to the environment. The refrigerant is still under pressure, but the loss of heat allows it to phase change to a liquid; thus naming this exchanger the condenser.

    After the condenser, the liquid refrigerant moves from outside to inside. There is passes through the expansion valve that releases the pressure that it was under. Without the pressure, the refrigerant converts back to gas. As liquids change to gas, they absorb heat from the environment. It is how sweat evaporating cools you. The refrigerant evaporates in the inside heat exchanger, or evaporator, and cools the air flowing over it. Then it's back to the compressor to repeat the cycle.

    A basic heat pump simply adds a 4 way, or reversing, valve to an air conditioner. This allows the refrigerant flow through the heat exchangers to be reversed, switching which one is working as the condenser and as the evaporator depending on whether you want heat or cooling. Turn the valve in the diagram, and the refrigerant flows the other way through the heat exchangers and expansion valve.
    [​IMG]
    It gets complicated with a heat pump for a car though. We want to keep the dehumidifying properties of the evaporator available while heating the cabin for windshield defrosting.
    [​IMG]
    This is a pretty clear diagram of a car heat pump. Just needs a translation.
    1. heat exchanger
    2. compressor
    3. accumulater
    4. condenser
    5. evaporator
    6. expansion valves
    7. o_O
    8. :confused:
    9. blower
    10. a valve
    11. another valve
    The accumulator can be ignored for this simple explanation; plus I'm not exactly sure what it does. Same with 7 and 8; they appear to be sensors and electronic controls. I didn't mention a blower or fan before, but heat exchangers need air flow to effectively dump or gain heat.

    The car heat pump gets a third heat exchanger that acts as a condenser or evaporator depending on whether the system is heating or cooling. The two heat exchangers in the dash are dedicated to being a condenser or evaporator. There is no 4 way valve like in the basic heat pump, so the refrigerant always flows in the same direction. Instead, the system uses plumbing loops and valves to control whether we get heating or cooling.

    Yes, the condenser in the dash is always hot while the compressor is running. So is the heater core used for heating an ICE car in most cases. A flap is used to divert air flow through it for when cabin heating is wanted. While heating, valve 10 is closed so the refrigerant flows through an expansion valve. This means the outside heat exchanger acts as an evaporator, and picks up heat from outside the car. Valve 11 diverts the refrigerant back to the compressor, and away from the inside evaporator. Need to defrost the windshield, we just let refrigerant go to that evaporator for dehumidifying.

    For cooling, the first expansion valve is bypassed by opening valve 10. The outside heat exchanger now becomes a condenser. The inside condenser can't condense with the air flap blocking air from it. Valve 11 lets the liquid refrigerant flow to the inside evaporator and its expansion valve.

    To give that Zoe a gas/vapor injected heat pump, we install a dohickey right behind the heating mode's expansion valve. This diverts a bit of the expanding gas back to the compressor an onto the compressor blades. This direct cooling improves the compressors performance. The technical term is because a simple diverting valve isn't good enough. The refrigerant is a mix of gas and liquid at that point, and liquid hitting the fast spinning blades is not a good thing long term operation. The Prime has that liquid-gas separator for that purpose, but there are other options in use.
     
  18. padroo

    padroo Senior Member

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    How does the heat pump in the Prime work in heating and cooling the car? Is it better or worse? I always thought that heating and cooling were both week spots in my Gen 2. My new 2016 four is much improved from my Gen 2.
     
  19. Lee Jay

    Lee Jay Senior Member

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    I always thought the cooling in my 2004 was exceptional. It's just as good in my Prime. Heat is too but you have to know how to use it since it has two additional settings (Eco and s-flow) that affect the way it works.

    Just got home after the car cold soaked in 17F for 5 hours. Car was warm and comfortable after less than 3 minutes of driving.
     
  20. bwilson4web

    bwilson4web i3 and Prime

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    Another write-up that nails it: Toyota Prius Prime Has Breakthrough Heat Pump System, Bumps Electric Range Up 21% In Cold

    “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.

    Bob Wilson
     
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