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: http://priuschat.com/forums/care-ma...g/37794-high-hv-battery-temp-cooling-fan.html 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?
There's a similar exhaust port on the left side. No, see above. Sure, see 1, and the cabin is not completely airtight, except for the Hang Zheng. 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. If you are comfortable, the HV battery will be too.
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.
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?
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.
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.
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
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.
My thanks to the posters who have come up on this non-earthshaking matter. This is purely a "thought experiment" at this point. From your responses, it is clear that I didn't know as much as I thought I did. From other inquiries I've made into the whole fuel tank/fuel vapor area, and into the functioning of the brakes, it is clear to me that this is a vehicle of systems -- and subsystems and meta systems. And so, intuition and logic aren't enough to really understand what's happening. This lead me to a suspicion that the pax air and the HV battery cooling air systems would have some tight linkages. Chap's post has a good example: In addition to the air supplies and exhaust, I've thought about the pax air HEPA filter. At first view, it seems much larger than would be necessary to clean the air for human respiration. OK, it gets dirty so it needs to be larger. It also must work at low speed/low pressure, as well as high speed high pressure. It seems that it must also be sized for HV battery flow through. So there's the probability that dust free air is better for the battery as well. For viewers unfamiliar with NACA ducts visit this site: SPEKTR PRODUCTS DUCTS AND VENTS Well, a NACA duct would have no dust protection, and could in fact suck in bugs, other stuff floating about, and even small birds -- I bet that would put the nix on any warranty claim. Even though I see any such system as easily mounted/unmounted, as Pat says, on balance it probably is not worth the trouble/expense. But all this does raise a non-linear thought. When there is finally a set of good looking, rear wheel skirts/spats available, I wonder what the effect of pressurizing the rear wheel well with a NACA duct in the skirt/spat would be. :brick: Back off boys and girls, its only a thought experiment ! ! :behindsofa:
