2011/12 Re-Route Heater Core to HV Cooling instead of PTC?

[miscrms]

It seems like the PTC Heater efficiency is pretty high on people's list of gripes about the 2011/12 Leafs. I had been planning on leaving it out of my conversion all together, given how mild the climate typically is here in Phoenix, but our current lows in the 30s are reminding me that it would be handy to have "some" heat on occasion. I'd really rather not add the weight / space / power draw of the PTC heater loop if I can help it though.

That's gotten me to wondering if it would be feasible to route the HV cooling system loop through the heater core. Has anyone ever looked into the possibility? Seems like this might be of interest to any 2011/12 owner in milder climates.

From what I can tell from the service manuals, the HV cooling system control targets keeping the coolant temp around 58-60C. Not sure what typical coolant temperatures look like in cooler weather though. That's a bit cooler than the 70C target for the heating fluid, but still maybe warm enough to provide a bit of heating when needed in mild climates?

I haven't been able to find a clear description of the various air pathways through the HVAC unit, so I'm unclear as to whether the blower airflow is always across the heater core or not. The function of the "Air Mix Door" between hot air and cool air leads me to believe there is a bypass path around the heater core, and air is only blown across the heater core when heating is requested.

There could also be some challenges in regard to the hvac control system. So far I can't find any discussion of failsafe conditions beyond those that shut down the AC compressor. Hopefully the system will still allow for heating controls to be applied to the HVAC unit in the presence of DTCs related to disconnecting the PTC control (as long as the PFC HV interlock is still intact or bypassed).

Any thoughts?

Rob

 

[miscrms]

It also seems like the HV coolant temperature is measured at the outlet side of the radiator, so the temperature could be higher at the return side.

Rob

 

[GerryAZ]

I don't think the HV coolant gets hot enough in "cold" weather to do much good for cabin heating or defrost. I will try to check the temperature after my morning commute tomorrow in the 2015. Since the hot water tank is not very big, I doubt the weight saving would be enough to worry about if you have space for it. Insulate the tank and lines to minimize the losses and keep the system intact to avoid dealing with DTCs.

Update: I drove the 2015 about 5 miles this evening on surface streets and the hoses between the components in the power stack as well as the hoses between the stack and the radiator (both upper and lower radiator hoses) were not above ambient temperature. I will check tomorrow morning after my 25-mile commute.

Gerry

 

[miscrms]

Thanks Gerry, appreciate you checking it out!

 

[miscrms]

Did you ever get a chance to check after your commute Gerry?

Its certainly feasible that there just isn't enough waste heat to do anything useful with. I'd be a little surprised though. I know that running the OBC on the bench at 1.5kW (L1) the temps pretty quickly were up to 100-120F, or about 40-60F above ambient. I would think the inverter would put off quite a bit more heat even as efficient as it is. But I guess its possible that the liquid cooling system is just really good at dissipating that heat.

Rob