Passenger Air vs. HV Battery Cooling Air

[Rokeby]

I am trying to puzzle out the relationship between how passenger [hereafter,
"pax"] compartment air is handled as compared to HV battery cooling air.

I would greatly appreciate any comments, other sites, etc, on my thoughts
below.

What I think I know: (Windows closed)

The HV battery is cooled via air through the vent on the pax side of the rear
seat backrest.

The HV battery cooling vent is open all the time, that is, it is capable of
passing air whenever the pax compartment is pressurized. HV battery
cooling can be supplemented by a small fan in the ductwork that is
controlled by a thermostat inside the HV battery containment.

HV battery cooling air is exhausted at the left rear of the body, under the
rear fender plastic cover piece. For pix, see:

High HV Battery Temp and Cooling fan

There are two basic conditions for pax compartment air circulation: outside
air and recirculated air.

When outside air is selected, the pax compartment is under a slight positive
pressure.

Outside pax compartment air comes from a plenum at the base of the
windshield.

My unanswered questions (Windows closed)

1. Where is outside pax compartment air exhausted?

2. If outside air is exhausted through the HV battery cooling ductwork, is
this the sole exhaust?

3. If outside air is exhausted through the HV battery cooling ductwork, and
the vent near the rear seat is blocked, can there be any airflow from outside
the car into the pax compartment?

4. If the pax air is set to recirc, then presumably the pax compartment is
not pressurized. If the HV cooling fan were to come on, where does the air
come from outside the car to allow positive air flow through the HV battery?

5. Does having the A/C running have any relevance to pax compartment or
HV battery air supply source or exhaust routing?

[Bill Merchant]

Originally Posted by Rokeby

My unanswered questions (Windows closed)

1. Where is outside pax compartment air exhausted?

2. If outside air is exhausted through the HV battery cooling ductwork, is this the sole exhaust?

3. If outside air is exhausted through the HV battery cooling ductwork, and the vent near the rear seat is blocked, can there be any airflow from outside the car into the pax compartment?

4. If the pax air is set to recirc, then presumably the pax compartment is not pressurized. If the HV cooling fan were to come on, where does the air come from outside the car to allow positive air flow through the HV battery?

5. Does having the A/C running have any relevance to pax compartment or HV battery air supply source or exhaust routing?

1. There's a similar exhaust port on the left side.
2. No, see above.
3. Sure, see 1, and the cabin is not completely airtight, except for the Hang Zheng.
4. Watch out for this situation. Your head will explode unless there is sufficient vacuum inside to balance. Also, some outside air comes in even in recirc.
5. If you are comfortable, the HV battery will be too.

[patsparks]

Of course it goes without saying, never actually block the battery vent.

[Rokeby]

Bill and Pat,

Thanks guys. I won't block that vent. I've got to wondering...

Posts have reported that HV battery temps can be reduced by opening the pax
rear window for a while. I'm just wondering if, on really warmish days, you
couldn't help HV battery cooling along by supplying outside air directly to the
HV battery, without sending it through the pax compartment. That way it
seems like you could run the A/C at a reduced setting to keep cool yourself.

I am contemplating an insert for the rear pax-side window with a NACA style
duct leading directly to the HV battery vent -- overkill? First, I'm trying to
understand the airflow supply/exhaust in the car.

[patsparks]

You can try but personally I wouldn't bother. If the AC in in recirculate it isn't working any harder and if the battery needs cooling the fan will come on. I wonder if the battery cooling fan comes on, does the AC go into vent mode too?
If not, where does the air come from to replace what the fan pumps through the battery and out of the car?

[David Beale]

Again, even on "recirc" there is some outside air being used by the A/C system. This is because even engineers ( ) want to slightly pressurize the cabin. Mainly to ensure dust will not enter, but in the case of the Prius, to also supply battery cooling air.

[Patrick Wong]

Originally Posted by Rokeby

My unanswered questions (Windows closed)

1. Where is outside pax compartment air exhausted?

Regarding this query, note that there are two large rectangular vents on either side of the vehicle (potential entry points for rodents.) The rear bumper cover hides both vents from view. When the hatch trim is removed, the vents are visible.

[ChapmanF]

Originally Posted by Rokeby

4. If the pax air is set to recirc, then presumably the pax compartment is
not pressurized. If the HV cooling fan were to come on, where does the air
come from outside the car to allow positive air flow through the HV battery?

This is from the new-car-features manual for the 2001-2003 generation, but I expect it would be true of the later model as well:

Battery ECU Forced Fresh Air Mode:

When the air conditioning ECU receives the forced fresh air mode signal from the battery ECU via the HV ECU and the ECM, the damper forcefully switches to the FRESH mode. (p. 171)

-Chap

[tochatihu]

Again reporting on NHW11 (a 2001). When I noticed (Graham Davies miniscanner) that the HV battery temperature was higher than desired, I would use the A/C on flow-through, not recirc mode. The battery cooling was much faster this way, than in recirc mode.

[archae86]

Originally Posted by tochatihu

Again reporting on NHW11 (a 2001). When I noticed (Graham Davies miniscanner) that the HV battery temperature was higher than desired, I would use the A/C on flow-through, not recirc mode. The battery cooling was much faster this way, than in recirc mode.

That sounds as though the car can provide the traction battery temperature on the CAN bus. It sure would be nice if someone could figure out an XGAUGE coding for the ScangaugeII which would display this.