EV Fundamentals: Heat Pumps
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Heat Pumps
03.33
| 00:00 | There's been a lot of talk around heat pumps in recent years when it comes to replacing traditional home heating and air conditioning systems. |
| 00:05 | In many countries around the world, this type of system has already become the norm and for good reason. |
| 00:10 | Heat pumps move heat rather than create it. |
| 00:12 | They can be used for both heating and cooling and they are effectively no different than the air conditioner at your house, with the exception that they have a reversing valve, which allows them to both heat and cool. |
| 00:21 | Heat pumps are becoming more popular with EVs as the efficiency gains to be had with the heat pump simply can't be ignored. |
| 00:28 | Due to resistive heating, a heat pump can transfer heat with 3-5 times less input energy for the same amount of output heat. |
| 00:34 | This is called COP or coefficient of performance. |
| 00:37 | The higher the COP, the more heat is being pumped per unit of input energy. |
| 00:41 | The other advantage of heat pumps is that they can move heat around at temperatures that would be otherwise impossible with direct air conduction. |
| 00:48 | Remember in the previous module when we mentioned trying to cool a battery to 45 degrees Celsius when the road temperature is also 45 degrees Celsius? The amount of heat transfer is almost zero in this situation, but with a heat pump, it's possible to work really effectively in these conditions. |
| 01:02 | The only downside being that the efficiency of the system is slightly reduced. |
| 01:05 | The clever thing with heat pumps and valving arrangements is that it allows the vehicle designer to move heat in a desirable way, often killing two birds with one stone. |
| 01:13 | For example, if the driver's compartment wants cooling while at the same time the battery needs heating to prepare it for DC fast charging, the heat pump can be used to cool the cabin and the heat that's removed in the process can then be pumped into the battery. |
| 01:26 | For motorsports applications, a mix of air cooling and a heat pump can be used in combination. |
| 01:31 | The hot coolant first passes through the radiator, then the heat pump works to offer additional cooling, possibly even below ambient. |
| 01:37 | The fundamental concepts of a heat pump are the same as any air conditioning system, a compressor, an evaporator, and a condenser. |
| 01:44 | In addition though, there's also a reversing valve, which can switch the direction of operation and turn the condenser into the evaporator. |
| 01:50 | The compressor pumps the hot refrigerant gas into a condenser, which then cools the refrigerant causing it to condense into a liquid. |
| 01:57 | This phase change is what makes heat pumps so good at moving heat, as transferring from a gas to a liquid releases or absorbs so much more heat than simply pumping gas. |
| 02:06 | Once the condensed liquid leaves the condenser, it goes through the expansion valve. |
| 02:11 | This valve suddenly allows the high pressure hot liquid refrigerant to rapidly expand and lose pressure, and it's now being sucked by the compressor rather than being pushed by it. |
| 02:20 | The liquid goes to the evaporator, where it's heated by the air or liquid passing through it, which then causes it to evaporate, absorbing a ton of heat in the process. |
| 02:27 | Modern heat pumps, including the ones found in EVs, use inverter-driven compressors that can operate at variable speeds, as well as a variable expansion valve. |
| 02:35 | Sensors monitor the pressure in the low and high pressure side of the system, allowing the compressor and expansion valve to work at their most efficient operating point, which is much better than simply cycling on and off like most air conditioning units. |
| 02:47 | Right now, we've yet to see any aftermarket heat pump kits for EV conversions, but I'd expect in the relatively near future, this will be an in-demand product for high performance battery cooling, and something may even be available already depending on when you're taking this course. |
| 03:00 | And that covers just about everything you need to know when it comes to heat pumps for EV purposes, so let's just quickly run through what we've learned. |
| 03:07 | Heat pumps don't create heat, but instead move it. |
| 03:10 | They can move heat even when there's a large difference in temperature between the condenser and evaporator, but at a lower efficiency. |
| 03:16 | For the most part, they share the same components as a traditional air conditioning system, but thanks to a reversing valve, they can be used for both heating and cooling. |
| 03:24 | Heat pumps are incredibly efficient when compared to traditional resistive heating, and also have the advantage of being able to move heat around the vehicle to be used in different ways. |
