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"Free" heat in cabin

Posted: Tue Feb 12, 2019 2:52 pm
by trevmar
Apologies if this has been covered before, but is it true there is a way to bleed off the small amount of heat from the battery/electronics into the cabin without using the resistive heater? Is it enough to keep the screen free of condensation on the inside when it's about 40-50F ambient?

Re: "Free" heat in cabin

Posted: Tue Feb 12, 2019 3:25 pm
by gpsman
I wish it could do that but is doesn’t.

The first week I had mine I was fooled into thinking it could. I thought the car only had an electric heater like a plug in space heater for your home.

I used heat for my first trip then turned it off and parked for half an hour. Drove on my second trip and had subtle, gentle heat in the cabin. I was so happy becuase I thought waste heat from the electronics was heating the cabin. It wasn’t. I was fooled.

The car heats a tank of water, and then the hot water heats the air exchanger going to the cabin. While parked, that hot water will retain heat for quite a while.

TIP: Turn off the “heat/cool” button 5 or 6 minutes before reaching your desrination to save energy. You might as well use up that “stored” hot water, and no use parking with a hot water tank, unless you will be parked for only a few minutes.

Re: "Free" heat in cabin

Posted: Tue Feb 12, 2019 8:33 pm
by GetOffYourGas
gpsman wrote:TIP: Turn off the “heat/cool” button 5 or 6 minutes before reaching your desrination to save energy. You might as well use up that “stored” hot water, and no use parking with a hot water tank, unless you will be parked for only a few minutes.


Yes! I do this too. It's probably a minor savings, but it has no impact to your comfort level.

Re: "Free" heat in cabin

Posted: Fri Apr 12, 2019 4:10 am
by Telek
I suspect that the reason that they don't do this is the added complexity is probably not worth the small amount of heat that you would get.

Don't forget, we're talking about electrical components here that are very efficient. Your cabin heater runs at up to 7500W.

The motor is about 93-97% efficient, and the SPIM (single power inverter module) I think is about 95%, so on the highway pulling 24kW you're wasting about 1.4kW of power which could be recovered.

I guess that's not nothing. Since it appears that the transmission and motor and electronics can operate up to about 80C, I guess there would be no harm in having a single system, or at least allowing a valve which would tie them together, or at the very least have a heat exchanger between the two.

I can only assume that they had a good reason for not doing this.

Re: "Free" heat in cabin

Posted: Fri Apr 12, 2019 4:13 am
by Telek
gpsman wrote:The car heats a tank of water, and then the hot water heats the air exchanger going to the cabin. While parked, that hot water will retain heat for quite a while.

TIP: Turn off the “heat/cool” button 5 or 6 minutes before reaching your desrination to save energy. You might as well use up that “stored” hot water, and no use parking with a hot water tank, unless you will be parked for only a few minutes.


That tank is very small, and cools down very quickly (within about 15 seconds). You're not really recovering much heat there, as much as you are just tolerating the cabin cooling down before you get to your destination.

Even on a really cold day, it should take about 2500W to maintain the cabin temperature. If you turn off the heat 5 minutes before, you're going to save about 200W of power. That's about $0.02 in electricity.

Meh.