Why does Tesla use a Resistance Heater instead of Heat Pump

[rooter]

I will be very surprised if a heat pump can warm the cabin and pack adequately in Wisconsin or Norway.

Signed,

Fanboi

 

[mongo]

I will be very surprised if a heat pump can warm the cabin and pack adequately in Wisconsin or Norway.

Signed,

Fanboi

And the patent writer's understand that:

An attractive alternative to passenger compartment heating and cooling would be the use of a vehicle heat pump system that is capable of both heating and cooling. However, conventional vehicle heat pump systems suffer from low heating capacity in extremely cold ambient conditions, e.g., minus 10 degrees Celsius and are not suitable for colder environments.

That's the interesting thing about this design. It acts like a heat pump when the ambient environment allows for it, but when it is really cold, the heat all comes from compressor work and inefficient motor drive waveforms for the compressor (HV) and blower (LV, 400W).
So when it is -30C out, it's not a heat pump, it's an electrical heater.See post #557 for the operating modes.

 

[quickstrike12]

Fascinating concept. I’m sure we will get some real world test results from new owners soon.

 

[dlinkeg]

Strange that our fairly bare bones first EV, the Coda, even used a heat pump for passenger all-season comfort AND to heat/cool the battery pack. Why has Tesla remained with inefficient resistance heating?

-Model S is still using an external coolant heater instead of it's inverters even though it has the new PM front motor. At this point, Model 3 is basically doubling the coolant/battery heating power of Model S, even though it has a smaller pack. Also it seems their inverter based heating can do constant power regardless of SoC. Low SoC on S/X results in low power from the resistive heater.

So - we're a bit behind. I wouldn't count on heat pump being in S any time soon. Unless it lets Elon get to 420 miles range ASAP.]

 

[quickstrike12]

Strange that our fairly bare bones first EV, the Coda, even used a heat pump for passenger all-season comfort AND to heat/cool the battery pack. Why has Tesla remained with inefficient resistance heating?

You may not think it’s inefficient and so bad if you lived in a climate that sees regular temps below -20. I think this was a design choice and compromise to make sure these cars could handle the extremes of a harsh environment.
would be awesome if a “extreme cold climate kit” was just an option for cars and the typical car had an efficient heat pump otherwise.

 

[rooter]

That's the interesting thing about this design. It acts like a heat pump when the ambient environment allows for it, but when it is really cold, the heat all comes from compressor work and inefficient motor drive waveforms for the compressor (HV) and blower (LV, 400W).
So when it is -30C out, it's not a heat pump, it's an electrical heater.See post #557 for the operating modes.

Yes I'd already seen that illustration. "Compressor as Heater"? The motor is not that inefficient; motors these days are 92% to 96% efficient. The remainder is waste heat.

Energy can not just be created.

This "mode" needs to be explained in alot more detail before I buy it. Heat pumps are moderate temperature devices.

 

[Reeler]

Yes I'd already seen that illustration. "Compressor as Heater"? The motor is not that inefficient; motors these days are 92% to 96% efficient. The remainder is waste heat.

This "mode" needs to be explained in alot more detail before I buy it. Heat pumps are moderate temperature devices.

The efficiency of the motor can be reduced by software to generate more heat. Think of your body shivering to make waste heat. That inefficient muscle movement heats you up. In Corona Del Mar, you are a long way from any sort of weather a heat pump cannot handle.

 

[rooter]

Is this speculation Reeler, or have to found this at a credible source as applying to the Y?

 

[Bob M]

Cars are subject to more vibrations that a home refrigerator and frequently the refrigerant will eventually leak out. If a fitting doesn't work loose, a small crack in one of the lines can develop.

My last car was one of the last with Freon (a 1992). I put off retrofitting it for a very long time, but eventually the A/C quit working because the Freon leaked out. I think one of the fittings had worked loose after 20 years.



There was all that hair on fire about Freon being the cause of the ozone hole, but nobody ever explained the mechanism how ozone was making from the surface to the upper atmosphere. Freon is a large, heavy molecule that is also fairly inert. It doesn't react with much and doesn't break down in the environment very quickly. Chlorine, which is the element blamed for breaking down ozone is highly reactive and any Freon breaking down near the surface is going to have the chlorine released react with other things near the surface and get bound up.

PBS used to have a program once a year on underreported stories of the year. At the height of the ozone scare they covered a story that one atmospheric scientist had made a pretty strong case the ozone layer breakdown was caused by the frequent shuttle missions at the time. Most rockets are liquid fueled and the exhaust is mostly water, but the shuttle used solid fuel boosters which produced a lot of chlorine as a by product of combustion and the shuttle flights flew right through the ozone layer with these boosters running.

Chlorine doesn't bond with oxygen when breaking down ozone. Chlorine gas does not bond with oxygen. Instead the gas acts like a catalyst accelerating the breakdown of ozone into oxygen molecules. Ozone is three oxygen atoms bonded together and the oxygen molecule is a pair of oxygen atoms. Left on its own ozone tends to break down into two atom oxygen, but chlorine speeds up this process. Sunlight causes some oxygen in the upper atmosphere to combine into ozone.

Ozone is being created and breaking down all the time, but under normal conditions enough sticks around to add a protective layer to the atmosphere. Chlorine speeds up the breakdown process which reduces the overall amount of ozone.

I haven't seen any follow ups to this story in years, but the ozone layer began to come back when NASA cut back on shuttle flights and they are now talking about it healing completely in our lifetime. The last shuttle flight was in 2011. There may have been some solid fuel rockets leave the atmosphere since 2011, but it's been very few.

I'm pretty sure the profit margins on the gases used now for coolants are much larger (the Freon that was banned was old enough to be public domain), so the chemical companies that make the stuff are probably pretty happy with the switch. The switch from 134a to 1234yf might have been driven by the patent status of 134a. I just did a quick search and it looks like the patent for 134a is due to expire in October 2020. It looks to me like they are doing the same thing pharmaceutical companies do when patents run out on their drugs, they come up with something which is virtually identical they can patent and charge an arm and a leg for.

I used a hydrocarbon refrigerant in my old Freon based Acura called Duracool. It was comprised of a mixture of butane and propane with all the methane removed. It required only 1/3 the volume of Freon or 134 and was a larger more leak resistant and 25% more efficient coolant. It also required much lower head pressures, requiring less gasoline to run the compressor and caused fewer leaks. It was legal for me to use it in California as an individual long as I did proper collection evacuation and disposal of prior refrigerant and labeled it properly, but was not legal for professionals to instal?? How damaging are butane and propane to the environment in this application? As a car refrigerant it seemed superior in so many ways. I was told that it was legal in Some other states and was used in household appliances in parts of Europe.

 

[mongo]

Yes I'd already seen that illustration. "Compressor as Heater"? The motor is not that inefficient; motors these days are 92% to 96% efficient. The remainder is waste heat.

Energy can not just be created.

This "mode" needs to be explained in alot more detail before I buy it. Heat pumps are moderate temperature devices.

What? No free energy? I'm shocked! Shocked I tell you.
That illustration shows the system drops to a COP of 1 in cold conditions, which is an electric heater, not a classical heat pump.

As to the mode, they do the same thing with the compressor drive that they do with the propulsion motors, use them as heaters of 3.5 kW each or so to heat the pack.

From the patent abstract:
"The control electronics may control the compressor to operate in an efficient mode or a lossy mode in which the compressor generates heat."

Further down is the extreme more where they boil the refrigerant with the compressor drive electronics before it passes through the scroll compressor portion:
"
[0098]
Using the compressor 214 as a high-voltage heater further enhances heating power/reduces noise using the compressor 214 motor and inverter/cabin blower 222 motor in waste heat mode and various thermodynamic recirculation schemes (air, coolant or refrigerant). These operations support the removal of the conventional high voltage cabin air electrical heater, and instead to repurpose the compressor 214 as an electrical (COP=1), e.g. an inefficient heater when required. An extreme version of compressor 214 waste heat mode, which uses the motor/inverter as a boiler, eliminates the need for recirculating loops.
"

Laws of thermodynamics are well satisfied. The discussion of the bootstrap startup mode is interesting also.

 

[mongo]

I used a hydrocarbon refrigerant in my old Freon based Acura called Duracool. It was comprised of a mixture of butane and propane with all the methane removed. It required only 1/3 the volume of Freon or 134 and was a larger more leak resistant and 25% more efficient coolant. It also required much lower head pressures, requiring less gasoline to run the compressor and caused fewer leaks. It was legal for me to use it in California as an individual long as I did proper collection evacuation and disposal of prior refrigerant and labeled it properly, but was not legal for professionals to instal?? How damaging are butane and propane to the environment in this application? As a car refrigerant it seemed superior in so many ways. I was told that it was legal in Some other states and was used in household appliances in parts of Europe.

Regarding the environmental impact of that mix: Per the IPCC 2007 numbers, butane has a Greenhouse Warming Potential (GWP) of 4x compared to CO2, propane has a GWP of 3.3x CO2.

Methane is somewhere around 30 (100 year number).

HCF-134a is 1,430. So it was better for Ozone, but worse for warming compared to R12 with a GWP of 1,068 .

It seems the issue is the flammability of the mixture.

 

[MP3Mike]

Is this speculation Reeler, or have to found this at a credible source as applying to the Y?

The Model 3 uses the motors to create heat to warm the battery pack when stationary. People have logged it putting ~4kW through each motor for ~8kW of heat.

Now in the Model Y they apparently apply that to the heat pump and HVAC fan as well.

 

[jeremymc7]

Based on what I heard since the Y does use Heat Pump it could be in the S/3/X down the road.

 

[rooter]

I am finding all kinds of articles on setting up a heater in motor windings to prevent condensation, but this business of overloading a motor's windings while simultaneously using it as a heat pump seems like magical thinking.

Are there any credible technical articles?

 

[mongo]

I am finding all kinds of articles on setting up a heater in motor windings to prevent condensation, but this business of overloading a motor's windings while simultaneously using it as a heat pump seems like magical thinking.

Are there any credible technical articles?

That's because it doesn't work like that. It can be either a classic heat pump or a heater, with a transition zone. It can't be a classic COP>1 heat pump if the only energy source is the compressor work + loss.
As the motor enters lossy mode, it moves from being a COP>1 heat pump to being a COP = 1 resistive heater with refrigerant instead of coolant as the heat transfer mechanism. With the additional aspect of transferring the mechanical energy from the compressor into the refrigerant. However, heat out = electrical energy in as ambient drops.
At warmer temps it scavenges existing waste heat from the pack and drive unit to get a COP>1 (relative to energy supplied to the compressor).

At even warmer temps, the pack and drive unit couple the ambient temperature along with their waste heat and COP can get up to 5 or so (relative to energy supplied to the compressor).

As an analogy, if you put a window AC unit in the middle of a room, it heats the room, but COP=1. If you put the unit in a window backwards, then you get heating at COP>1.

 

[rooter]

When you put non-optimal waveforms into the windings to heat them up, this is how it 'works that way' according to your descriptions.

Are there any credible technical articles?

 

[mongo]

When you put non-optimal waveforms into the windings to heat them up, this is how it 'works that way' according to your descriptions.

What is not credible?

There are two main operating modes in the simple version:

Non-heat pump:
When is is using lossy waveforms, it is not behaving like an efficent heat pump. There is little to no ambient energy involved and a COP of 1 or so.

Heat pump:
When it is using optimized drive waveforms, it is harvesting ambient, drive train, and pack energy as energy sources for the heat pump, and achieves a COP > 1.

Note, it can also pull heat from the cabin, but that is a net loss, so does not impact the COP number for cabin heating.

 

[rooter]

Not saying you're not credible on this subject mongo, which you apparently are.

It just seems implausible that heating the coils enough to make a difference wouldn't cause damage over the long- or even short-term, in climates like Wisconsin or Norway. Sure the media would quickly carry away the heat but nevertheless...

I was asking for reference articles which are credible, as opposed to those which aren't. G**gle (which I hate anyway) trips over itself with light queries on this.

 

[mongo]

Not saying you're not credible on this subject mongo, which you apparently are.

It just seems implausible that heating the coils enough to make a difference wouldn't cause damage over the long- or even short-term, in climates like Wisconsin or Norway. Sure the media would quickly carry away the heat but nevertheless...

I was asking for reference articles which are credible, as opposed to those which aren't. G**gle (which I hate anyway) trips over itself with light queries on this.

Oh, I'm just a doofus on the internet, but the patent has lots of good info in it.

Are you concerned with the compressor motor coils? Apparently, they are bathed in refrigerant pre-scroll and the peak compressor outlet temp is 130C or so. The drive switching devices are also cooled, and depending on type, can handle 175C or so.

 

[Reeler]

Based on what I heard since the Y does use Heat Pump it could be in the S/3/X down the road.

Don't hold your breath. There are things like door pockets that are still missing from the Model S even though other models have had them for years and years. It took years for the Model S to get lighted vanity mirrors. At over 8 years since introduction, the Model S is long overdue for a total refresh. Maybe at that point, but maybe Tesla will never refresh it. The roadster hasn't been refreshed in well over a decade.

Buy a Model Y if you need range in cold weather.