Recently, I convinced myself that the Tesla HVAC system does not have a reversible heat pump, capable of heating the cabin and batteries as well as cooling them. It took a while because I was convinced that Tesla’s design was too clever to omit such an obvious feature, requiring so little additional complexity. Someone posted the Tesla patent on the thermal management system, which clearly refers to a “refrigeration unit” rather than a heat pump, and the system diagram very clearly omits the reversing valve necessary to switch the working fluid flow.
Subsequently, I also convinced myself that the Nissan LEAF does in fact have a reversible heat pump system that both heats and cools the car. I was amazed by this, since Nissan seems to have been a bit cavalier about thermal management for the batteries. Perhaps this has evolved since the LEAF was first released.
My point here is that Tesla has seriously missed the boat by failing to offer a heat pump capable of heating. Using electrical energy to heat a resistor is just as inefficient (compared with a heat pump) as using an internal combustion engine to turn a shaft (compared with an electric motor). The only thing worse would be to use an internal combustion engine to turn a generator shaft and then use the generated electricity to heat a resistor, but that is no consolation for Tesla owners.
I submit that cold weather heating is the single biggest cause of range anxiety for electric cars, as compared with ICE cars. It has played a prominent part in criticisms of EVs, reaching an apogee with the infamous Broder review of the Tesla for the NY Times. It is certainly the principal cause of range reduction in cold weather, and therefore the principal cause of range uncertainty, which is the true source of range anxiety. If Tesla wishes to decisively and effectively eliminate range anxiety, it is essential to implement a reversible heat pump. Ideally, the modifications of the current system could be readily (i.e.: economically) retrofitted to older (i.e.: my) vehicles. It should require only the addition of a reversing valve with servo and suitable software controls.
Now it might be argued that a reversible heat pump would still not suffice during extremely cold conditions, and this is true. But I submit that it would relegate the current resistance strips to much reduced use as “auxiliary heat” and would make a big difference in all but the most severe weather, when impacts on range are predictable and hence less uncertain.
For truly frigid conditions, as part of the “cold weather package”, Tesla should also implement a biogas or propane fired auxiliary heater that would only be used at such low temperatures that a heat pump cannot produce heat efficiently. The resistance strip heaters could be retained for the case where the heating fuel has been exhausted. Many Tesla or other EV owners find this concept inconsistent with their desire to rid themselves of all burning fuels, but if you have this reaction, please consider the argument above concerning the use of electricity for resistance heat. A combustible fuel is an extremely efficient heater, though a very inefficient motivator or shaft turner. Conversely, a battery is a very efficient motivator / shaft-turner, but a very inefficient heater. When trying to survive in the Arctic, one should seek to use combustible fuels as efficiently as possible, that is, in heaters and stoves, and not for motion. Correspondingly, electricity should be reserved for motion and not used for heat, on energy efficiency grounds alone. To address the emissions aspect of energy use, the right approach is to develop clean and carbon neutral fuels like biogas, which is being used to heat electric city buses in Scandinavia. If you still find these arguments about the cold weather package off-putting, please do not let it cloud your assessment concerning the reversible heat pump point above.
In summary, the implementation of a reversible heat pump with biogas fired auxiliary heating may not increase the range of an electric vehicle, but it will stabilize the range near the values experienced in temperate weather, even when the temperature plummets. This will effectively extend the cold weather range of electric vehicles and, above all, reduce uncertainty about the range that will be achieved when driving in winter conditions. That, alone, will drastically reduce if not totally eliminate range anxiety for EV drivers in most north american locales.
Discussion? Can we persuade Tesla of the necessity of addressing cold weather range as part of "ending range anxiety forever?"
Subsequently, I also convinced myself that the Nissan LEAF does in fact have a reversible heat pump system that both heats and cools the car. I was amazed by this, since Nissan seems to have been a bit cavalier about thermal management for the batteries. Perhaps this has evolved since the LEAF was first released.
My point here is that Tesla has seriously missed the boat by failing to offer a heat pump capable of heating. Using electrical energy to heat a resistor is just as inefficient (compared with a heat pump) as using an internal combustion engine to turn a shaft (compared with an electric motor). The only thing worse would be to use an internal combustion engine to turn a generator shaft and then use the generated electricity to heat a resistor, but that is no consolation for Tesla owners.
I submit that cold weather heating is the single biggest cause of range anxiety for electric cars, as compared with ICE cars. It has played a prominent part in criticisms of EVs, reaching an apogee with the infamous Broder review of the Tesla for the NY Times. It is certainly the principal cause of range reduction in cold weather, and therefore the principal cause of range uncertainty, which is the true source of range anxiety. If Tesla wishes to decisively and effectively eliminate range anxiety, it is essential to implement a reversible heat pump. Ideally, the modifications of the current system could be readily (i.e.: economically) retrofitted to older (i.e.: my) vehicles. It should require only the addition of a reversing valve with servo and suitable software controls.
Now it might be argued that a reversible heat pump would still not suffice during extremely cold conditions, and this is true. But I submit that it would relegate the current resistance strips to much reduced use as “auxiliary heat” and would make a big difference in all but the most severe weather, when impacts on range are predictable and hence less uncertain.
For truly frigid conditions, as part of the “cold weather package”, Tesla should also implement a biogas or propane fired auxiliary heater that would only be used at such low temperatures that a heat pump cannot produce heat efficiently. The resistance strip heaters could be retained for the case where the heating fuel has been exhausted. Many Tesla or other EV owners find this concept inconsistent with their desire to rid themselves of all burning fuels, but if you have this reaction, please consider the argument above concerning the use of electricity for resistance heat. A combustible fuel is an extremely efficient heater, though a very inefficient motivator or shaft turner. Conversely, a battery is a very efficient motivator / shaft-turner, but a very inefficient heater. When trying to survive in the Arctic, one should seek to use combustible fuels as efficiently as possible, that is, in heaters and stoves, and not for motion. Correspondingly, electricity should be reserved for motion and not used for heat, on energy efficiency grounds alone. To address the emissions aspect of energy use, the right approach is to develop clean and carbon neutral fuels like biogas, which is being used to heat electric city buses in Scandinavia. If you still find these arguments about the cold weather package off-putting, please do not let it cloud your assessment concerning the reversible heat pump point above.
In summary, the implementation of a reversible heat pump with biogas fired auxiliary heating may not increase the range of an electric vehicle, but it will stabilize the range near the values experienced in temperate weather, even when the temperature plummets. This will effectively extend the cold weather range of electric vehicles and, above all, reduce uncertainty about the range that will be achieved when driving in winter conditions. That, alone, will drastically reduce if not totally eliminate range anxiety for EV drivers in most north american locales.
Discussion? Can we persuade Tesla of the necessity of addressing cold weather range as part of "ending range anxiety forever?"
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