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

The same as any heatpump used to climate control.

 

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

 

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

 

Those are pretty technical terms.

 

Like a house HVAC system apparently

Posted via the PriusChat mobile app.

 

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.

 

Engineering is very cool...or hot...whatever.

Posted via the PriusChat mobile app.

 

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."

 

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.)


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.

 

know your audience.

 

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.

 

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.

 

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.

 

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.

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.

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. 
8. 
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.

 

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.

 

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.

 

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