Model 3 Heat Pump Explained


When it comes to electric vehicles, Tesla is continually raising the bar in designing the most efficient, sustainable technology today. The latest version of the Tesla Model 3 sedan, also known as the Model Y is no different. The 2021 Tesla Model Y has a few new and upgraded features compared to its earlier version. Among them is the addition of the highly efficient Model 3 heat pump system.

The Tesla Model 3 heat pump essentially functions the same as an A/C unit but in reverse. Simply put, the heat pump pulls the air from outside the car, which heats the refrigerant and also warms the air, then the warm air is pumped into the cabin.

Obviously, there is a lot more to how exactly the heat pump heats the inside of your car. Whether or not you understand thermodynamics, the rest of this article will be a basic breakdown of how exactly this new innovative heat pump is, as Elon Musk tweeted “some of the best engineering I’ve seen in a while.”

How Does a Heat Pump Work?

The heat pump itself is comprised of a compressor, a condenser, an expansion valve, an evaporator, and a coil that runs through them all. Inside the coil is a refrigerant.

  • First the low pressure, low-temperature gas refrigerant passes through the compressor, which then converts it into a higher pressure and temperature gas.
  • The heated and pressurized gas then passes through a device called a condenser, where the gas is condensed into a liquid while retaining its high temperature and pressure. At this point the heat pump pushes air across the condenser, from outside the car, absorbing the heat energy, and into the cabin.
  • From there the pressurized liquid refrigerant passes through an expansion valve, which uses mechanical principles to control the amount of refrigerant liquid passing through, effectively slowing it down and reducing it back to a lower temperature and pressure liquid.
  • The liquid refrigerant then passes through the evaporator. Here the outside air is blown over the evaporator coils, which causes the liquid refrigerant to boil (even at cold outside temperatures) and turns it back into a low temperature, low-pressure gas.

Then the whole process starts over again with the compressor heating the refrigerant gas.

What Makes Tesla’s Heat Pump So Special?

As it turns out, the use of a heat pump in an all-electric car isn’t new. Nissan claims to be the first to incorporate a heat pump into their Nissan Leaf, compared to other all-electric cars that use Resistive Heating.

So why is Tesla’s so unique?

The heat pump is really just the tip of the iceberg when talking about the complex thermal management system that is inside Tesla’s Model Y sedan. They’ve combined the heat pump with a liquid-cooled condenser, a chiller, a radiator, as well as pulls energy from the drive unit and battery.

The incorporation of Tesla’s patented Octovalve is instrumental in diverting the refrigerant through some, all, or none of these, allowing it to either heat or cool the cabin of the car.

What is Resistive Heating?

Today, most electric vehicles use what is called Resistive Heating or PTC (Positive Temperature Coefficient). To heat the cabin, a resistive heating element pulls energy from the battery, heating it, then air is blown over the element, which heats the air and is blown into the cabin.

The efficiency rate of PTC in electric cars is 100%. This means that all the energy used to heat the car is pulled directly from the battery, which makes them highly efficient.

The main issue with this way of heating your car is it reduces your total range per charge since the energy is coming directly from the battery to heat the resistive element.

In extremely cold temperatures, relying on the battery to heat the car can pose some problems. Since all electronics inside electric cars are designed to perform better at low temperatures, they don’t provide a lot of heat.

Why is Tesla’s Heat Pump Better Than Resistive Heating?

Simply using the heat pump to pull the outside air in and heating the refrigerant in the evaporator, in addition to using the energy from the battery to run the compressor, boosts the efficiency rating to 300%. 

For example, if it takes 3 kWh (kilowatt-hours) to heat the cabin it would take a Resistive Heater to pull 3 kWh of energy from the battery to heat the cabin.

But with the Model 3 heat pump, it only takes 1 kWh of energy from the battery to produce 3 kWh of heat in the cabin. That’s incredibly efficient!

Do Cold Temperatures Reduce the Efficiency of the Heat Pump?

The refrigerant that Tesla uses has a boiling point of about -15°F (-26°C). So, it’s safe to say that for most climates, even places that drop below freezing temperatures, the heat pump will work just fine. All though, as the ambient temperatures get colder, the less effective the heat pump will be.

This is because, if the outside air that is being drawn in by the heat pump is close to the same temperature of the refrigerant in the evaporator, the less energy that is being drawn in to boil the liquid refrigerant and will not provide heat.

This results in having to rely on energy from the battery to heat the cabin. Which reverts to the resistive heating method and dropping the efficiency rating, or the coefficient of performance, as engineers call it, back down to 100%. This tends to happen at about 0°F (-20°C).

A lot of this has to do with that the amount of frost that builds upon the outside of the evaporator due to the low temperatures and condensation. The frost impedes the evaporator from transferring the outside temperature to the refrigerant.

Does a Heat Pump Still Work in Hot Temperatures?

Typically, in hot temperatures, you wouldn’t need to use the heat pump to heat the cabin of the car. Instead, the Octovalve diverts the refrigerant through the chiller and liquid-cooled condenser (LCC) to cool the cabin.

The 2021 Tesla Model Y has about 12 heating modes and 3 cooling modes pre-installed, which are comprised to be the thermal management system.

Do You Really Save Money with A Heat Pump?

By installing the heat pump, Tesla greatly increased the amount of energy that is coming into the car to heat it, versus relying on just the energy from the battery to heat the car. This allows for a better total range of your battery and effectively reducing how often you’ll have to charge your car during the colder months.

By not charging it as often, you then are reducing the amount of energy being pulled from your power grid, giving you savings on your electrical bill.

What Are the Disadvantages of a Heat Pump?

There are not too many disadvantages to using a heat pump to heat your electric car. Only In temperatures below 0° Fahrenheit (-20° Celcius) will you experience trouble heating the cabin with the heat pump. This is when the car will rely on the battery to heat the car.

Do Any Other Tesla Models Have Heat Pumps?

The Model Y is the first in all the Tesla vehicles to have a heat pump. The rest rely solely on Resistive heat to heat the cabin of the car.

Final Thoughts

The addition of the Model 3 heat pump and advanced thermal management system is a wonderful step forward on the path of electric vehicles becoming our main source of transportation. Hopefully, this will spur more innovation towards making a more affordable electric car in the future.

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Greg

Hi, I'm Greg. My daily driver is a Tesla Model 3 Performance. I've learned a ton about Teslas from hands-on experience and this is the site where I share everything I've learned.

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