Delivering the thinking behind technology
The weather is getting colder and colder, and electric car owners in the north have begun to cross the sea again, showing off their magical powers. Everyone is thinking about how to spend the long winter in electric cars.
Faced with the crazy situation of halving battery life when the air conditioner is turned on, everyone is constantly creative. Some buy USB heated kneepads; some make their own power bank and inverter to power the heater; some buy a diesel engine for heating, which is all they need to put a coal-burning stove in the car!
Just when everyone was at a loss when facing the cold winter, a roar from Tesla Model Y came from the sky: I have a heat pump, follow me!
For a moment, the car owners were excited. Some shouted that the savior had finally arrived; some lamented that they had bought the Model 3 too early (the new model is already equipped with a heat pump); some activists began comparative testing and concluded that the heat pump is more efficient than traditional PTC heating3 times conclusion; someone calmly pointed out that Tesla is not an innovation, heat pumps are not new, and Tesla was not the first to use them;
It seems magical, stealing heat from the cold outside into the warm inside? This is like a bank, which collects money from the poor through savings and then lends it to the rich.
Today I will take a look with readers to see how amazing this heat pump is and how it works?
Pumps and heat pumps
A heat pump is also a pump. First we need to understand what a pump is.
A pump essentially increases the potential energy of a fluid by doing work, which seems a bit too convoluted.
To put it bluntly, it means pumping water from a low place to a high place. Phew, it feels so good to speak human words. This is the fun of popular science!
So the pump is essentially something that goes against the trend. Since it goes against the trend, it has to consume energy.
Heat pumps also go against the trend. What trend does it go against?
The second law of thermodynamics learned in high school states that heat can be transferred from a high-temperature object to a low-temperature object, but it cannot “spontaneously” transfer from a low-temperature object to a high-temperature object.
Therefore, the heat pump uses external force to transfer heat from the low-temperature area outside the car to the high-temperature area inside the car!
The principle of heat pump
Now that you know what a heat pump does, you also need to know how it works.
To be honest, there are many articles on the headlines about heat pumps, but most of them use Tesla’s schematics, octopus valves, and some diagrams from the air conditioning field to explain them. I can’t say they are not good, but they are not intuitive enough.
Next, I will try to explain the working principle of the heat pump in the simplest terms.
Let’s first look at a phenomenon that everyone can understand, as shown below:
When we boil water (left side), the water in the kettle absorbs heat and reaches 100 degrees, the water boils and starts to produce water vapor. As we all know, the boiling point of water at one atmosphere is 100 degrees, so we assume it is at one atmosphere.
Then we use a pipe to send all the water vapor to the right side, assuming that no heat is lost during this transmission process. Then the 100-degree water vapor reaches the right side. Since there is no heat source, it begins to condense and turns into water droplets again. This process also releases heat, and the temperature gradually becomes lower, let’s say it drops to 90 degrees.
As you can see, under one atmospheric pressure, we transfer heat from the 100-degree area on the left to the 90-degree area on the right through water vapor. The temperature goes from high to low, which seems understandable. This is also the case when everyone boils water.
Next we have to see a magical phenomenon. Suppose we take the kettle on the left to the main peak of the Himalayas. Well, let’s just pretend that we asked Wang Shi to help us bring it up.
The main peak of the Himalayas is more than 8,000 meters high, with a pressure of almost 0.41 standard atmosphere. Therefore, the boiling point of water becomes lower on the mountain. What does it mean? It means that when the water is heated to 77 degrees, the water will boil and the temperature will not be higher. This phenomenon is easy to understand because the air pressure is low, so the pressure of the atmosphere on the water surface is smaller, making it easier for water molecules to turn into steam and float away.
Next, we still used a pipe to transmit the water vapor, but this time it was different. The pipe was very long, really very long, and directly transmitted the water vapor to Beijing, which has a pressure of one atmosphere. Let’s still assume that no heat escapes during this process and the quality of the tube is very good. The water vapor reaches the top of the basin again, repeats the same condensation process as above, and also releases heat, and then turns into water, but the water is still 90 degrees.
Did you find that through this long tube, we transferred heat from the low temperature area of 77 degrees to the high temperature area of 90 degrees.
Doesn’t the second law of thermodynamics say that heat cannot be transferred from a low-temperature object to a high-temperature object without external force?
What is the external force in the above experiment? The secret lies in this long pipe. In the Himalayas, the atmospheric pressure is 0.41, so the water vapor must also be 0.41, but when it reaches Beijing, it becomes 1. This process requires continuously pressurizing the water vapor in the tube, and pressurization consumes energy, that is, external force is required to do work.
If we make a long enough tube, we can send a kettle to space, where water can boil at minus 40 degrees Celsius. In other words, we can obtain heat from a subzero environment through water, provided that the atmospheric pressure of this environment is small enough.
However, the ideal is very full and the reality is very skinny. We cannot make such a long tube. And the boiling point of water is too high.
But the core of the above experiment is that the pressure on the left and right sides is different, which leads to different boiling points of water vapor on both sides.
Then we only need to find a substance that can achieve a large change in boiling point when the pressure change is not so large. Wouldn’t it be easy to obtain energy from low-temperature areas?
Fortunately, there is this substance, which is refrigerant, also called refrigerant. In some places, it is also called ice. Anyway, it is the most basic thing in air conditioners.
We just need to build a closed circulation system with two pipeline areas: a low-pressure pipeline and put it in the low-temperature area, and the other is a high-pressure pipeline and put it in the high-temperature area.
Then let the refrigerant circulate from the low-pressure pipe to the high-pressure pipe in this system. The refrigerant can easily absorb heat in the low-pressure area and boil, turning into steam. Then it is pressurized into the high-pressure area, where it releases heat and condenses, and then passes through the reduction tube again. The pressure valve enters the low pressure area and continues to absorb heat.
Over and over again, the heat moves from the low-temperature area into the high-temperature area.
Whether it’s air conditioning or heat pump heating, this is the same principle.
Both pressurization and circulation require electric energy. The less electric energy consumed and the more heat transported, the more efficient the heat pump will be.
It can be said with certainty that as long as it is not very