It is my understanding that model Y comes with the octo valve heat pump while the model X uses resistance heaters. The question is does the heat pump improve range in cold weather significantly versus the resistance heater of Model X. Model X long-range of 350miles may not make it to North side of Dallas from south side of houston (295 miles). Asking another way, how much does the use of resistance heat strips reduce the range in say 30 to 40 degree weather? I guess I have to ask the same question about the use of air-conditioning for more likely 95 degree weather?
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Does the octo-valve improve range in cold weather?
- Thread starter RidgeRunner
- Start date
Bridor
Member
A heat pump uses the same power as an Air Conditioner as it is just the opposite. Yes, you are going to see significant increase in range in the Model Y due to the heat pump. It is about 3 times as efficient. I feel that it is about time that Tesla started using a heat pump.
Brent
Brent
Not exactly.... while you're correct that about the energy usage, the heat pump may not be able to supply enough heat in the winter. In that case usually you have electric resistance heaters to make up for it. Apparently, if you read the patent on the thermal system in the Y, it has some low voltage heaters that can cycle on to apply extra heat and Tesla can run the compressor and motor in a less efficient method to generate heat. Those will all generate more heat, but at the expense of more energy. The heat pump SHOULD increase range, but I'll be very curious to see if it does at 20F ambient air or something...
(Most heat pumps in houses suck below 35F and only provide about 1/3 the heating capacity that they're rated or sold as. I believe the rated capacity is tested at like 48F. There are some low temp designed heat pumps which are optimized for and tested in sub 30F temperatures but those are harder to find and usually aren't from the big name brands out there that American's known. I hope Tesla oversized the unit for the Model Y and it does well down to freezing temps and it's only when it gets down into the teens and single digits that it needs electric heating help... but it's yet to be seen.)
Good thing our San Diego cold days rarely drop into the 30s in the morning
While I'm not in a super cold area (Washington state), we do get plenty of days around 25 to 35F and a couple weeks of tens to twenties. I'll be VERY curious how my car handles that. My Model 3 had hot air blowing in maybe 20 seconds, but sucked down the energy. Model Y should pump the cabin heat into the battery pack when the car is stopped and then if it's started again and there is heat in the battery it will pump that heat back into the cabin. Hopefully this will help to quick heat the cabin, but I still have no idea how fast it will heat a dead cold car (sitting outside for a couple hours) and how much energy it will take. Maybe I'll have to jump on the YouTube wagon and make a few videos to share around (and collect those sweet sweet referrals
)I don't think we really have much empirical data yet.
The expectation is that it will make a significant difference in HVAC energy usage in the 40-60F range, tapering down as it gets colder and the heat pump becomes less efficient and possibly has to be supplemented with resistance.
The expectation is that it will make a significant difference in HVAC energy usage in the 40-60F range, tapering down as it gets colder and the heat pump becomes less efficient and possibly has to be supplemented with resistance.
saltsman
Member
I agree, we just don't have any empirical data yet.
I think the better way to phrase the question is "Does the octo-valve minimize range loss in cold weather?" The question is really about what method uses less energy since all methods lead to range loss.
IMO, the system has to be more efficient that resistive heat as resistive heat is the absolute least efficient method possible. Even if the heat pump only works above x temp, there will be plenty of drives that will occur above that temp and range loss from heating would be less. Or perhaps when the cabin is already heated and the heat pump can be used to be kept the cabin warm.
Several factors to consider.
1) The funk can get pretty toasty on long drives. The Model Y heat pump was intentionally placed next to known sources of waste heat, thus that area could/should be warmer than ambient outdoor temperatures and thus more efficient - at least in theory.
2) Automotive compressors are unlike home compressors and the octo-valve is unlike anything else... so who knows (other then Tesla engineers). Comparisons against anything else are just academic at this point.
We shall see soon!
I think the better way to phrase the question is "Does the octo-valve minimize range loss in cold weather?" The question is really about what method uses less energy since all methods lead to range loss.
IMO, the system has to be more efficient that resistive heat as resistive heat is the absolute least efficient method possible. Even if the heat pump only works above x temp, there will be plenty of drives that will occur above that temp and range loss from heating would be less. Or perhaps when the cabin is already heated and the heat pump can be used to be kept the cabin warm.
Several factors to consider.
1) The funk can get pretty toasty on long drives. The Model Y heat pump was intentionally placed next to known sources of waste heat, thus that area could/should be warmer than ambient outdoor temperatures and thus more efficient - at least in theory.
2) Automotive compressors are unlike home compressors and the octo-valve is unlike anything else... so who knows (other then Tesla engineers). Comparisons against anything else are just academic at this point.
We shall see soon!
The compressor isn’t particularly special - inverter driven high voltage electric compressor. What’s unique in the Y is the octovalve.
Air conditioning systems run from one evaporator to one condenser.
Most heat pumps add a second expansion valve and can reverse the coolant flow, allowing either end to be the evaporator or condenser.
I’m still not entirely clear on the details, but as I understand it, Tesla has both sides running to liquid coolant, and the octovalve allows that coolant to go to the cabin, the outside, or the pack on each sides - including a dehydrator/resistance mode that puts both ends inside the cabin.
So here is a video that shows how octovalve interacts with the cooling and heating loops. I encourage you to watch all three videos if you haven't seen them as it shows how all modes work. One thing to note is when the COP=1 as stated in the video that means it is operating at 100% efficiency or the same as resistance Heating. Another thing to note is while the system is complex and can be very efficient it is still heat pump and is not efficient in very cold weather. COP can be operating at less than one due to defrost mode or element heaters running in parallel with the heat pump. Another thing to take note of is the interesting way that Tesla will circulate interior air that has been warmed by driving or the Sun or potentially where the car is parked while the car is not in use to heat the battery and other electronics then the system will pull that heat back out of the battery to heat the cabin again later, now that is genius. This explains the Phantom HVAC fan running in my garage when it's chilly and i just got home.
Yep, I watched those videos the other day. It’s no doubt an amazing engineering feature and at the same time very elegant. However, that still doesn’t completely explain the available heating capacity. That heat pump has a set capacity and that decreases as the temperature goes down. Yes the battery generates some heat and the motor generates some heat, but are those enough to make up for the lower capacity from the heat pump? I assume Tesla did their homework and all that balances or exceeds the heating demand, but still very curious how much above 100% Tesla can get... (100% is essentially electric heating)
So what is being done is something a little different than I've ever seen. Anytime the temperature is less than -10C refrigerant is being circulated through the compressor and it's absorbing heat only the compressor is adding to it due to essentially the friction heat loss of the compressor and then that heat is absorbed through the cycle and starts all over again. COP is always 1 in this type of heating. The other way heat is created is through the low voltage element heating for cabin but it doesn't appear that that is used to heat the battery. So when the temperature is less than -10C its not much, if anymore efficient than element unless the motor and electronics produce tons of waste heat which i have a hard time thinking they do. The big gain is cool weather, not cold weather. The other thing is ability to store heat from cabin In the battery then use it again. I live in frigid area in the winter. Will be interesting to see how it does. Another thing to take note of is the heat pump everyone seems to think will save the world is only used down to -10C in this vehicle. Anytime below that is not getting heat from the atmosphere but is using waste heat from the drive components or simply using waste heat from the compressor to generate warm refrigerant for the cycle.
Yep. I think storing heat in the battery will be a nice gain for any around town stuff. That’s a huge amount of mass and probably will be slow to cool.
Hopefully the COP will be above 1 most the time, but if not hopefully it won’t have any downsides compared to electric heating.
Except on longer drives, when the temp<-10C, it appears cop will always be 1 or element heating will be engaged, especially those cold mornings your car sat outside.
I’ve worked in the HVAC industry for almost 30 years. You are using very outdated info. Yes, in the 80’s and 90’s heat pumps were not very capable during extremely cold weather. They were at their best between 40 and 60 degrees. But those days are long over. Modern heat pumps are capable down to about 0 degrees.
Now then, I’m talking about typical home heat pumps. I have no idea about a Tesla automotive heat pump.
Thank you for finding that. 15 different modes!
The thing that surprised me is only one of them is listed as having the resistive element in use. I'm surprised they aren't used in some of the COP = 1 cabin heating modes - there doesn't seem to be a good reason not to..
0F = ~-18C. According to the video above, Tesla's patents say they're using the heat pump on the atmosphere down to -10C.
I wish Lennox had got with the times than... their most expensive unit is trash below 30F with a greatly reduced btu capacity
