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The recently released Model Y is the first Tesla to feature a heat pump and the Cybertruck will also benefit from a heat pump, confirmed Musk tonight in this tweet.



What's the big deal about a heat pump instead of the resistive heating system used in all Tesla models until now? The Model Y’s heat pump is estimated to be 300% more efficient than the resistive heating system and this efficiency advantage will increase the Cybertruck's range in cold weather.

The Model Y's heat pump is located in the front trunk and it both warms the vehicle's batteries as well as providing cabin heat.

Here are two good videos detailing the heat pump in the Model Y.





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I've discussed this in another post so I won't rehash it all here. People, including Sandy Munroe, apparently don't understand what a heat pump is nor what it does. He keeps referring to the compressor (which is, of course, a critical part of the heat pump) as being the heat pump.

A heat pump is a device that moves heat from a source to a destination that is at higher temperature. For example if we are in the cabin of our Tesla and it is 80 °F inside with the sun beating down on us we'd like to pump that incoming heat to the outside of the car even though it is 100 °F outside. To do that we turn on the car's heat pump (which we call an air conditioner) and the interior stays cool. Thus every Tesla has a heat pump.

The thing that is different with the Y is that the valves (octovalve) can switch the flow of refrigerant through various paths according where we would like to send heat and from where we want to get it. In particular we can take heat from outside air (at temperatures down to freezing and even below) and pump it into the cabin. Therefore, as long as it is not too cold outside, we can get cabin heat from the air and not the battery as would be the case with an electric heater. Now it takes some energy from the battery to run the pump but roughly speaking we might expect to be able to draw 2 or 3 kW of heat from the air for every kW battery juice invested. A 1 kW electric heater produces 1*3412 = 3412 BTU/hr. The electical energy sent to a heat pump gets converted to heat too but that same 1 kW sent to a heat pump with a COP of 3 would extract 2*3412 = 6824 BTU/h from the air and the total heat delivered by the unit would thus be 3*3412 = 10236 BTU/h (5/6of a ton). Thus the 300%. Some calculations in the other thread indicate that in moderately cold weather we might expect a 10% improvement in range over the use of an electric heater. That's the big deal. The redesign of the system with the octovalve, better heat exchangers, better refrigerant metering etc. have probably resulted in more efficiency (better COP over all modes) than was available from earlier designs. This would translate into better range in all modes but not as spectacularly as it does in heating. And we hope it reduces some of the reported short comings of the older designs in which cabin cooling has to be reduced for the sake of the battery in very hot weather.
 
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I've discussed this in another post so I won't rehash it all here. People, including Sandy Munroe, apparently don't understand what a heat pump is nor what it does. He keeps referring to the compressor (which is, of course, a critical part of the heat pump) as being the heat pump.

A heat pump is a device that moves heat from a source to a destination that is at higher temperature. For example if we are in the cabin of our Tesla and it is 80 °F inside with the sun beating down on us we'd like to pump that incoming heat to the outside of the car even though it is 100 °F outside. To do that we turn on the car's heat pump (which we call an air conditioner) and the interior stays cool. Thus every Tesla has a heat pump.

The thing that is different with the Y is that the valves (octovalve) can switch the flow of refrigerant through various paths according where we would like to send heat and from where we want to get it. In particular we can take heat from outside air (at temperatures down to freezing and even below) and pump it into the cabin. Therefore, as long as it is not too cold outside, we can get cabin heat from the air and not the battery as would be the case with an electric heater. Now it takes some energy from the battery to run the pump but roughly speaking we might expect to be able to draw 2 or 3 kW of heat from the air for every kW battery juice invested. A 1 kW electric heater produces 1*3412 = 3412 BTU/hr. The electical energy sent to a heat pump gets converted to heat too but that same 1 kW sent to a heat pump with a COP of 3 would extract 2*3412 = 6824 BTU/h from the air and the total heat delivered by the unit would thus be 3*3412 = 10236 BTU/h (5/6of a ton). Thus the 300%. Some calculations in the other thread indicate that in moderately cold weather we might expect a 10% improvement in range over the use of an electric heater. That's the big deal. The redesign of the system with the octovalve, better heat exchangers, better refrigerant metering etc. have probably resulted in more efficiency (better COP over all modes) than was available from earlier designs. This would translate into better range in all modes but not as spectacularly as it does in heating. And we hope it reduces some of the reported short comings of the older designs in which cabin cooling has to be reduced for the sake of the battery in very hot weather.
You can also direct heat away from the motors, batteries, etc and direct that heat into the cab. Basically, the heat pump lets you move the heat where you want. Ambient air matters but we can get the heat from internal sources as well.
 

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The recently released Model Y is the first Tesla to feature a heat pump and the Cybertruck will also benefit from a heat pump, confirmed Musk tonight in this tweet.



What's the big deal about a heat pump instead of the resistive heating system used in all Tesla models until now? The Model Y’s heat pump is estimated to be 300% more efficient than the resistive heating system and this efficiency advantage will increase the Cybertruck's range in cold weather.

The Model Y's heat pump is located in the front trunk and it both warms the vehicle's batteries as well as providing cabin heat.

Here are two good videos detailing the heat pump in the Model Y.





Poor Elon has discovered the cyber void too.
 

ajdelange

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Technically the heat pump is the part of the heat management system that transfers heat uphill via phase change. When inverter heat is transferred to a cold battery or into the cabin that does not involve the heat pump but rather the parts of the system (valves, coolant to air heat exchangers, pumps) that direct the flow of glycol (but if you want to pump inverter heat to a hotter outside it does involve the heat pump). Tesla filed a patent a couple of years back that shows an intricate arrangement of pumps, valves, compressors, metering devices, sensors, fans, heat exchangers (gycol to air, refrigerant to air)... that looks as if it covers all the bases. Lins to it have been posted but I don't recall where. Perhaps you might find it at one of the other Tesla fora.

Another interesting aspect of all this is that there are rumors to the effect that when it is so cold outside that the heat pump cannot supply enough heat to keep the cabin and/or battery warm enough they change the gating to the transistors such that they switch much less efficiently thus producing waste heat which is then picked up by the glycol and routed where it is needed. This would not involve the heat pump but it would, of course, the valves, glycol pumps and heat exchangers.

All this leads to the question "Where is the heat pump?" You can't point to the cylindrical shaped thing that Sandy Munroe calls the heat pump and adequately answer that question as the compressor is only part of the heat pump. Where are the other components then? I guess the answer is all the components that are on, or can be switched into, the refrigerant circuit (reversing valve, metering devices, filter/dryer, receiver,...). I see more confusion coming. Perhaps it would be best to refer the "thermal management system" rather than the heat pump. "Basically, the heat pump lets you move the heat where you want." may be incorrect when the transfer is from inverter, battery, or motor to the cabin but "Basically, the thermal management system lets you move the heat where you want." is correct whether the thermal management is actually pumping heat or not.

I guess I should be careful here because I just thought of a system that transfers heat downhill (overall but one step is uphill) by phase change (the geothermal heat pump in my house). I don't know if the Tesla system does that but then I don't know that they don't either so I still think it is better to refer to the thermal management system.
 
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He doesn't appear to but perhaps he does. In any case given those two videos it looks as if an explanation of how a heat pump works might be in order.

Let's start with some liquid tetrafluoroethane (R134a commonly used in automobiles) at 200 psia and 100 °F. We spray this through a nozzle into a heat exchanger at the front of the vehicle over which the outside air blows. In going through the nozzle pressure drops to 20 psia, 30% of the liquid flashes into gas and the temperature drops but the remaining 70% remains a liquid which gets distributed over the interior surface of the radiator where it boils absorbing heat from the air as it does so. At 20 psia the boiling temperature is a little below 0 °F so if the air is any warmer than that it will boil. Each pound that boils picks up about 62 BTU of heat from the air even though the air is as cold as 0 °F. Obviously the gas is very cold at this point but it still contains heat and we want to get that out. So we run this cold, low pressure gas into a compressor with a 10:1 compression ratio. What comes out is gas at about 150 °F. In compressing it we did extra work on it thus adding about 25 BTU per pound. That energy comes from the battery, Next this hot gas goes to a radiator in the cabin (if we are trying to heat the cabin) or a refrigerant to glycol heat exchanger (if we are trying to heat the battery) or both (that's where all the fancy valving comes in) where it cools and condenses back to a liquid (at 128 °F) thus giving up heat to the cabin air or battery loop glycol. Note that the 128 °F liquid is still hot relative to cabin air and so the liquid in the radiator or heat exchanger will continue to transfer heat as it cools but the majority of the heat transferred from the liquid (about 61 BTU/lb) comes from the condensation with only about 18 BTU/lb coming from the liquid and superheat (heat above condensation temperature i.e. 150 - 128), Thus the energy extracted from the cold air plus the energy put into the gas by compressing it wind up being delivered to the radiator or heat exchanger.

By changing the flow of refrigerant so that the hot gas from the compressor goes first to the radiator at the front to condense (as long as the outside air temperature is less thatn 128 °F) and the liquid from that to boil in the heat exchanger in the cabin we can cool the cabin with this same gear. It should be evident that by clever switching of refrigerant paths and glycol paths that great flexibility is possible. This makes it clear that the evolutionary (not revolutionary - the basic system has been around since Kelvin) breakthrough in the Y is the octovalve - the heat pump is the same old.
 
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I really hope they will lose the 12V battery. It just seems dumb and redundant to have it when you are sitting on a 100KW battery pack.
Doubtful that they will. If they go to a DC/DC converter to power the 12V bus and that converter or the main battery or BMS fail you are completely dead in the water. There is nothing you can do. If, with a 12V battery, any of those components fail you still have the 12V battery available to unlock the car, communicate diagnostic info to the mother ship, put it into tow mode so it can be gotten onto a truck etc. I find that backup capability neither dumb nor redundant. Nor do I see what this has to do with heat pumps.
 

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I've discussed this in another post so I won't rehash it all here. People, including Sandy Munroe, apparently don't understand what a heat pump is nor what it does. He keeps referring to the compressor (which is, of course, a critical part of the heat pump) as being the heat pump.

A heat pump is a device that moves heat from a source to a destination that is at higher temperature. For example if we are in the cabin of our Tesla and it is 80 °F inside with the sun beating down on us we'd like to pump that incoming heat to the outside of the car even though it is 100 °F outside. To do that we turn on the car's heat pump (which we call an air conditioner) and the interior stays cool. Thus every Tesla has a heat pump.

The thing that is different with the Y is that the valves (octovalve) can switch the flow of refrigerant through various paths according where we would like to send heat and from where we want to get it. In particular we can take heat from outside air (at temperatures down to freezing and even below) and pump it into the cabin. Therefore, as long as it is not too cold outside, we can get cabin heat from the air and not the battery as would be the case with an electric heater. Now it takes some energy from the battery to run the pump but roughly speaking we might expect to be able to draw 2 or 3 kW of heat from the air for every kW battery juice invested. A 1 kW electric heater produces 1*3412 = 3412 BTU/hr. The electical energy sent to a heat pump gets converted to heat too but that same 1 kW sent to a heat pump with a COP of 3 would extract 2*3412 = 6824 BTU/h from the air and the total heat delivered by the unit would thus be 3*3412 = 10236 BTU/h (5/6of a ton). Thus the 300%. Some calculations in the other thread indicate that in moderately cold weather we might expect a 10% improvement in range over the use of an electric heater. That's the big deal. The redesign of the system with the octovalve, better heat exchangers, better refrigerant metering etc. have probably resulted in more efficiency (better COP over all modes) than was available from earlier designs. This would translate into better range in all modes but not as spectacularly as it does in heating. And we hope it reduces some of the reported short comings of the older designs in which cabin cooling has to be reduced for the sake of the battery in very hot weather.
Thanks. I’ve worked in HVAC for 25+ years and there is so much confusion out there whenever someone says heat pump.

It’s important to note (as you said) that even air below freezing contains heat. Just not as much. But modern heat pumps are very effective at pulling heat out of air all the way down to about zero degrees F.

Regarding the tweet, my favorite part is Elon’s excitement to get the CT out there. Hope he maintains that excitement and beats the schedule.
 

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He did give a big shout out to the octavalve design team.

Keep in mind that heat content depends on absolute temperature so that gas at 20 °C (293 K) contains only 7% more heat than gas at 0 °C (273 K).
 

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Keep in mind that heat content depends on absolute temperature so that gas at 20 °C (293 K) contains only 7% more heat than gas at 0 °C (273 K).
This is the most helpful clarification I've seen in years. So simple, so true, albeit counter-intuitive when used to C or F. Thank you!
 

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I really hope they will lose the 12V battery. It just seems dumb and redundant to have it when you are sitting on a 100KW battery pack.
The Propulsion Battery and Electronic Information Systems Battery have different tasks and different power needs. It's really not a "dumb" set up.
 

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Thank you everyone in this thread for knowing what a heat pump is and explaining how it works. I’m tired of reading posts from people who don’t really understand heat pumps but tell us how they work (incorrectly) anyway.
Does anyone have any ideas on whether the Model Y has, or CT will have, a resistive heater for cases when when the heat pump cannot adequately warm up the cabin or batteries. I’m specifically thinking of when it’s -20°F outside and my new CT has been parked all night and plugged in and I turn on the climate system from the app. I‘ve heard people say they may adjust the firing of the transistors in the inverters to make the inverter run inefficient creating heat, but I’m not sure the inverters are running when parked. I would also think (I could be wrong) that creating heat would be more efficient with a dedicated resistive heater than turning the inverter into one.
 

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When it gets cold enough heat pumps stop working so there has to be another source of heat. Rumor has it that this is the inverter. I can't tell you how it works because I don't know but I can point out a couple of things from which we can deduce how it probably works. Refer to the following sketch:
trans 1.jpeg


The items A, a, B, b, C and c are solid state switches which can be "gated" on and off electronically. When driving A, b and c would be turned on allowing current from the battery to flow into the coil at 10 o'clock and out of the coils at 2 and 6 o'clock. This results in a magnetic field directed at 10 o'clock. Those switches are then gated off and B, a and c are turned on. This results in current flowing into the coil at 2 o'clock and out of the coils at 6 and 10 resulting in a field oriented towards 2 o'clock. Finally those are turned off and C a, and b are turned on giving a field oriented towards 6 o'clock. The sequence then repeats with the result that one has a magnetic field rotating in a clockwise direction in steps of 120 °. In fact there are more than just 3 coils and the field rotates in smaller steps.

The resistive power dissipated by a switch (or any other device) is the product of the voltage across the switch with the current through it. When any of the switches are turned off the voltage across it is high and only a small leakage current flows through it so that the power dissipated is small. When one is turned on there is a large current through it but the voltage across it is small and, again, the power dissipated in it is small. But the switch has to get from the off state to the on state and in doing so it passes through states where both current and voltage are intermediate and power is dissipated. Engineers strive hard to get the switch from off to on and back to off as fast as possible to minimize the energy (integral of voltage times current with respect to time) lost to heat. So one strategy for getting heat from the inverter, the one that would be used when moving and more battery heat is required than supplied by the battery's internal resistance or the heat pump, would be to slow the switching speed (apply a gating waveform with a more gradual rise time).

When trying to pre-warm the battery (car not moving) a possible strategy is to turn all the transistors on part way. No current flows through the motor coils under these conditions - just through the transistors which will get warm. Yet another strategy might be to turn on one capital letter transistor and the other two small letter transistors. Current then flows through the transistors (which get warm) and through the coils which also get warm (the motor is also on a glycol loop). All the energy going to the motor gets converted to heat in this arrangement as the motor is not turning and none gets converted to mechanical energy.

Thus my guess is that one or the other or some combinations of these techniques is used for supplemental heat in the Y and will be in the CT when it's too cold for the heat pump.

I^2R is I^2R whether the current is flowing through a resistor or transistor so this method is just as efficient as a resistive heater. What other form could the battery energy be converted to?
 
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