Sudden Increase in Consumption Rate

[mknox]

It was minus 14C today with a windchill of minus 29 - I hit a new record power usage of 3685 wh/km after being parked outdoors for about 7 hours. (My Tesla outdoor temp reads 2 degrees high).

That is really just a rounding error because you've only driven a fraction of a km and the car is trying to extrapolate. I often see well over 10,000 at this distance and one member reported over 100,000 Wh/mi in the US. What you have to look at is the final number after your drive to see the total trip average consumption. If I drive in the neighborhood of 80 km or more at one time, my trip number is no more than 20 to 25% above my summer consumption numbers and sometimes I can even match summer consumption. If I drive only a few km from a cold start, I might see 300% above summer consumption for the trip.

 

[David99]

AC or operating in both modes as a heat pump is much more efficient than resistance heating because it moves existing heat instead of converting electrical energy to heat. So not only is the car overcoming twice the temperature differential, but it's taking roughly twice as much energy for every degree of difference. So you're looking at 4x as much energy to heat the car from 30 to 70 than to cool it from 90 to 70.

According to EVTripplanner.com the amount of energy to cool or heat the cabin to the same temperature difference takes the same amount of energy.

 

[Krazaak]

According to EVTripplanner.com the amount of energy to cool or heat the cabin to the same temperature difference takes the same amount of energy.

Then either EVTripplanner.com is wrong or Tesla has a very inefficient AC system. My GE GeoSpring water heater wouldn't be a thing if heat pumps and resistance heating shared the same efficiency.

 

[rush6410]

As a point of reference, my 100% charge is 257 rated miles. In order to maintain the rated consumption, you need to average 326 wh/mi. If range is your concern for a particular trip, reduce your speed to maintain the rated consumption as I stated.

 

[rush6410]

This past weekend, I took a 372 mi round trip. I planned it out to "destination" charge at out our destination. What works well for me is to coordinate the percent remaining to destination using the navigation. I tried to keep it at 10% increasing and decreasing speed in order to maintain. Notice the major consumption difference impacted by outdoor temperature.
Outgooing

Return

 

[verygreen]

I had my first drive in 37F (3C) today. To my surprise there was almost no range impact, in fact the trip (~150 miles roadtrip) was almost as efficient compared to the very first time I took it sometime in early April after I first got my car. Back then I averages were 352 Wh/mi on the way there and 306 Wh/mi on the way back (mostly on highway speeds of 705-80 mph, about 15 miles at 40-50 in a place with traffic lights.

Today on the way there it was 366 wh/mi and 309 wh/mi on the way back (temperature got a bit warmer in the meantime - 44.5F (7C).

I did start with preheated battery (charged from 80->90 preparing for the big range impact from the cold weather). A little bit of cabin heater use, but not too much since pretty fast everybody was feeling too hot (no wonders given that they all had winter clothes on).

Now on the other hand rain made that same trip (also in April) much worse - 419Wh (359Wh/mi on the way back, but it was a different and much slower route on the way back so probably is not directly comparable).

rated mile is 332Wh for my X100D

 

[int32_t]

I want to get in on the resistance heater vs heat pump fun! Heat pumps are great when there's a source of heat to exploit — units meant for heating houses don't work so great below about -10˚C. Conversely a resistance heater simply converts the electrical energy thrown at it to thermal energy, at very very high efficiency. You don't have to worry about finding somewhere to get the heat from, like when your car has been sitting in the parking lot cold-soaking for several hours. From a simplicity standpoint as well as an efficiency standpoint, a resistance heater is a great solution. The exception to this may be in certain locales where it never gets particularly cold and thus a heat pump could always function. My $0.02.

Perhaps it would make sense to wait until spring to see if Ski Krazy's excessive energy consumption goes away before getting too concerned? It's only your first winter, after all. I mean, have Service look at it and all but don't worry too much until spring.

 

[BerTX]

I want to get in on the resistance heater vs heat pump fun! Heat pumps are great when there's a source of heat to exploit — units meant for heating houses don't work so great below about -10˚C. Conversely a resistance heater simply converts the electrical energy thrown at it to thermal energy, at very very high efficiency. You don't have to worry about finding somewhere to get the heat from, like when your car has been sitting in the parking lot cold-soaking for several hours. From a simplicity standpoint as well as an efficiency standpoint, a resistance heater is a great solution. The exception to this may be in certain locales where it never gets particularly cold and thus a heat pump could always function. My $0.02.

Perhaps it would make sense to wait until spring to see if Ski Krazy's excessive energy consumption goes away before getting too concerned? It's only your first winter, after all. I mean, have Service look at it and all but don't worry too much until spring.

Wow, there are two with identical wrong information. What are the odds.

Air source Heat pumps today produce about 4 times the amount of heat for a given amount of energy put into them. Resistance heat is 1:1. Heat pumps produce more heat from the same amount of energy down to about -20˚C.

 

[Krazaak]

Wow, there are two with identical wrong information. What are the odds.

Air source Heat pumps today produce about 4 times the amount of heat for a given amount of energy put into them. Resistance heat is 1:1. Heat pumps produce more heat from the same amount of energy down to about -20˚C.

What I think confuses people is that resistance heating is very efficient at converting electrical energy to heat, but heat pumps don't convert energy to heat at all (with the exception of mechanical waste heat). They convert electrical energy to mechanical energy which in turn uses phase change of the refrigerant to transfer heat from one place to another. Air that is cold by human standards still has plenty of heat energy in it and as long as the refrigerant can boil on the evaporator side, then it can pull heat from the surrounding air and pump it to the condenser. Refrigerant in residential heat pumps boils at -48C or so. I'm assuming an automotive heat pump would need to use R134a instead of R410a and that boils at -26C. Since both those temps are at 1 bar, the temps lower even further with a suction pressure.

The only real advantage that resistance heat has over a heat pump is that they're much more compact.

 

[mknox]

I had my first drive in 37F (3C) today. To my surprise there was almost no range impact, in fact the trip (~150 miles roadtrip) was almost as efficient compared to the very first time I took it sometime in early April after I first got my car.

Yep. Long trips are great in the cold. Short trips not so much. There is a relatively large draw when you first set out as the cabin and battery heaters work hard (which you can mitigate with shore powered pre-heating) but as everything warms up and the car starts harvesting and recycling waste heat from the motor, inverter and batteries, consumption drops down to near summertime levels. Over a long trip, that high initial consumption gets averaged out against many miles of lower consumption.

 

[aesculus]

Air source Heat pumps today produce about 4 times the amount of heat for a given amount of energy put into them. Resistance heat is 1:1. Heat pumps produce more heat from the same amount of energy down to about -20˚C.

Speaking for my house units (which I really wish I would have bought propane heaters), the exception is when it's humid outside. Then they ice up and you have to run the resistive heating to not only heat the house but combat the fact that the heat pump is working as an air conditioner to melt the ice that has built up on the coils. Not sure what happens in a car.

So my experiences are that heat pumps are wonderful when the outside air temp is above about 40F and the humidity is low.