If that's true, you should hear the compressor running when the heat is on. I don't believe that is the case.
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Heater on/off Button?
- Thread starter gavine
- Start date
If that's true, you should hear the compressor running when the heat is on. I don't believe that is the case.
Yes those dehumidifiers have two Heat exchanger sections. The cooling section where the expanded refrigerant is used to cool/condense the air, then it is compressed and used in a separate heat exchanger to reheat the same air.
A heat pump/AC unit only has one heat exchanger section, and changes the flow through it from compressed/expanded to change whether it is cooled or not. And a separate heat exchanger in a different air space to remove/add heat.
And I am with Amped Realtor I haven't seen proof that the Tesla is using the AC as a heat pump. I know it is being thrown around as known but it isn't in any specs or been confirmed.
I don't know for sure either, but you might have to listen very carefully because it's variable speed and it might only be running a minimum speed when defogging happens.
Apparently both AC & Heat kick-on with defrost. Yesterday, I smelled the heater again and looked down to see if it was on feet and I noticed that I had accidentally hit the windshield defrost button just prior. I guess Tesla decided that the AC and heat together will defrost better. Just another reason to have an indicator telling when the heat is on. Had I not smelled it, I wouldn't have known the defrost (and heater) was on.
mknox
Well-Known Member
This is how ICE cars work also. On an ICE, the heat is always there in the heater core, so if it's cool out, some heat will be coming into the cabin, then if you turn your defrosters on, the a/c compressor will start.
I can see the value of a heat on/off button myself. Tesla is trying to mimic how an ICE car's HVAC works, but there is a critical difference. ICE engines generate so much heat that a lot of complex plumbing and hardware goes in to simply throwing it overboard. It makes no difference if there is heat in the cars heater core. Just deflect the air flow away from it if you don't want any in the cabin. ICE car air conditioners, on the other hand, have a switch. Why not just let the a/c run all the time too, and regulate it by directing the air flow? Because the a/c is a draw on the engine and has a fuel efficiency penalty.
Well on an EV, your electric heat does have a fuel efficiency penalty just like a/c. So for that reason, a discrete switch is not a bad idea.
You crystalized my thoughts exactly. There's an AC on/off button, why not heat?. Like you said, trying to mimic ICE but since it has a power draw, it should be optional. If/when we ever get this "feature", I will brag to everyone that it was my idea.
ThosEM
Space Weatherman
Tesla seems to be quiet on the subject of how the climate control system works, but Teslatap is pretty forthcoming.
Model S Top Features | TeslaTap
It would be pretty sad if Tesla had failed to implement a reversible heat pump, because resistance heating is much more expensive than heat pump heat. One of the functions of the energy saving "Range" mode is that it blocks out the resistance heat, limiting cabin heating to the capacity of the heat pump, which may be a bit thin in sub-freezing weather.
Model S Top Features | TeslaTap
It would be pretty sad if Tesla had failed to implement a reversible heat pump, because resistance heating is much more expensive than heat pump heat. One of the functions of the energy saving "Range" mode is that it blocks out the resistance heat, limiting cabin heating to the capacity of the heat pump, which may be a bit thin in sub-freezing weather.
The Roadster manual also recommends that for defrost the AC and heat should both be on.
ThosEM
Space Weatherman
Ventilation Too
I'd also like to see a single button "Ventilate" button, that in one push would turn off AC (including heat), turn on external airflow, set all the vents to open, and turn the fan up about halfway. Any of those could clearly be overridden, but this would be a very handy feature when one finds oneself fiddling with the controls to deal with a cool but sunny day on the superhighway where one just needs airflow to keep the car comfortable without opening up windows to highway noise. It might be called the "Green" button for its relative lack of energy use.
I'd also like to see a single button "Ventilate" button, that in one push would turn off AC (including heat), turn on external airflow, set all the vents to open, and turn the fan up about halfway. Any of those could clearly be overridden, but this would be a very handy feature when one finds oneself fiddling with the controls to deal with a cool but sunny day on the superhighway where one just needs airflow to keep the car comfortable without opening up windows to highway noise. It might be called the "Green" button for its relative lack of energy use.
Canuck
Well-Known Member
+1 -- I really want this. I'd prefer if the fan could be controlled, and turned off, so that just the movement of the can bring in the fresh air. Driving through the mountains a lot, this is all that's often needed and breathing that fresh mountain air, with no ICE motor it has to flow over, would sure be nice!
This is not correct. I had the car in Range all winter last year and it most definitely used the resistance heater. What it does limit is the pack resistance heater.
Knobby
Member
I'd like to be able to turn off the heat too. Now that it is cool in the morning, I want the fan on for ventilation, but the heat insists on coming on. To defeat the heater I have to set the temp to Lo, AC off, and then fan speed to what I want. How cumbersome. But it is nice that I can put the fan speed on the right thumbwheel, like that a lot. As for the heater maybe I just need to set it to 20 and forget it. I guess that's the intent.
mknox
Well-Known Member
Not on my car it doesn't. I get resistance heating right from the get go in freezing temps... just not as much of it. I believe it does stop heating to the battery pack (unless it gets extremely cold).
TeslaTap makes the claim briefly on the "Features" page, but doesn't seem to document it on their other pages, nor refer to any source.
I'm not entirely sure this claim is true... and as mentioned below enabling range mode does not preclude resistive heat being enabled...
There is absolutely no evidence to support this. Here's an easy way to check for yourself. Crank up the heat, step outside of your car, and tell me if you can hear the compressor ramping up. If it's a reversible heat pump design, both heat and and AC will require the compressor to fire up. Did you hear the compressor?
No.
ThosEM
Space Weatherman
I can't claim to be certain of this yet. But I can explain your result. If you crank the heat way up, the system may not run both the heat pump and the resistance heat. Try just activating the heat a bit.
I don't hear much difference between heat and AC, so this seems inconclusive to me so far. I'll be very disappointed if Telsa doesn't use the compressor for heat also.
There is no heat pump in the Model S, only A/C. The heating in the cabin is exclusively from a 6-7kW PTC resistance heater. There is also no path for using waste heat from the powertrain or electronics to heat the cabin. (Though it can heat the battery)
Tesla could (should) have added a reversing valve and controllable expansion valves to allow heat pump capability, the cost would have been negligible, and it would be 2-3 times more efficient at heating.
The battery can be cooled by a second circuit in the A/C running though a heat exchanger and it can be heated by it's own resistance heater as well.
I agree that when the A/C is manually shut off it should not run either the heater or the A/C (vent only). Since most people don't understand that the A/C is needed for defroster dehumidification, it should continue to enable the A/C system when in defrost mode regardless of A/C mode setting.
Nissan made these same mistakes in the LEAF in 2011-2012. They listened to us in 2013 and added the heat-pump capability and a way to disable the heat.
Tesla could (should) have added a reversing valve and controllable expansion valves to allow heat pump capability, the cost would have been negligible, and it would be 2-3 times more efficient at heating.
The battery can be cooled by a second circuit in the A/C running though a heat exchanger and it can be heated by it's own resistance heater as well.
I agree that when the A/C is manually shut off it should not run either the heater or the A/C (vent only). Since most people don't understand that the A/C is needed for defroster dehumidification, it should continue to enable the A/C system when in defrost mode regardless of A/C mode setting.
Nissan made these same mistakes in the LEAF in 2011-2012. They listened to us in 2013 and added the heat-pump capability and a way to disable the heat.
Canuck
Well-Known Member
Thanks for educating me. I've been giving people unintentionally false information.
No prob, it's crazy to think that a car this otherwise well-thought-out and this pricey would skimp on the marginal cost a true heat-pump would add. I thought for sure if Nissan added it to their EV's, Tesla would see this and follow, but so far they haven't.
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