How does the heater work in the REx?

[Rizi3]

I know the the BEv has a heat pump and may get it's heat source from the heat pump. But where is the heat source coming from the REx?

 

[Lecram]

https://drive.google.com/file/d/0B3oSgcvM3UaLMDlYTGp6VGEtVTQ/view?usp=sharing

Read this doc

 

[ultraturtle]

Surprisingly, it is actually the same refrigerant loop system (what most folks would call a heat pump system) augmented with an electric resistance heater that the BEV uses, lacking only the additional heat exchanger located between the coolant pump and electric heating element :

The additional heat exchanger of the BEV heat pump system enhances efficiency:

 

[BrianStanier]

That is a surprise. So the BEV will use some electrical heating and the Rex effectively has a heat pump too with the expansion tank acting as a (poor) heat exchanger. One think I have noticed is that the estimated range reduction from using the heater in the Rex is much less than our Gen1 Leaf. But both are only guesses and I don't have any real measurements to compare them.

 

[ultraturtle]

One of the least touted, but most brilliant features of the BMW i3 is that is the first EV to use a refrigerant based system for thermal management of the battery pack. The lack of complaints about decreased range due to heat during the past summer is more deafening to my ears than the complaints now trickling in about range reduction due to cold weather.

Fact is, while the heating cycle of an air source heat pump is highly efficient (potentially 300% or more) to as low as 40 degrees ambient temperature, efficiency falls off rapidly below that point, with BMW recognizing that no benefit is to be gained by 15 degrees F, and shutting down the heat pump completely. It then relies on only electrical resistance heating for both the battery pack and the cabin. Bottom line is that while significantly more efficient than air or water based battery thermal management systems at high temperatures, the i3's refrigerant based thermal management system is essentially on par with a LEAF, Tesla, or Volt's efficiency at very cold temperatures.

A completely untouted benefit of the refrigerant based thermal management system of the i3 battery system is that it is significantly less explodey than a liquid based thermal management system. The R134a refrigerant used is inert, and does not react with the lithium in the battery pack in a collision event. This is a bit technical, but chemists on this forum probably recognize the formula: water + lithium = bad, bad juju.

 

[ultraturtle]

...the Rex effectively has a heat pump too with the expansion tank acting as a (poor) heat exchanger.

A configuration not uncommon in automobiles. My guess is that BMW may have wanted to include room for the heat exchanger in all models, but simply ran out of space.

Personally, I would trade the worthless frunk storage space for a heat exchanger any day.