Optimal settings for the night stealth camping in cold weather (below 32F) and how often engine...

my advice is to try out sitting in a parking lot in -25C and seeing how the car idles/stops. Right now with my temperature set to 65F (I've got an American car) and fan at lowest speed, at -10C it will start for 30 seconds and stop for 2 minutes, then start for another 30 seconds. Its really annoying and hard on the car as well.

If you have to do it I suggest this, heat the inside of your winter bag with electric heat via a 12V or inverter heated blanket. Physics means you will need much much less energy to heat the inside of an extremely well insulated sleeping bag augmented by your body heat compared to the entire interior of the Prius with zero insulation. That way you can leave the windows cracked open to allow proper ventilation so you don't get condensation. And the bag will naturally evaporate moisture out of it with the heat source inside. If you do it this way you can turn off the HVAC heater completely and the car will rather stay "off" for 30 mins+ and charge for only 5 mins at a time.

If you are concerned about fire or burning yourself, check out heated motorcycle vests and pants. They are designed to be run off 12V and have infinitely variable heat settings and can be worn directly against your body all night with a thin layer underneath. You will have to wire directly to your 12V battery but since its in the trunk it should be easy.

 

Here's my stealth camper solution to this problem (still under development):

Fabricate plastic window inserts from 300 mil clear PETG sheet, cut to fit and wrap with perforated vinyl wrap on one side and 20% ceramic tint film on the other side. Tack-seal the vinyl and tint film edge with super glue, then apply black door edge protector strips around the edge of the wrapped PETG insert. The completed insert is flexible enough to pop into the perimeter recess up against the window, which is air sealed by the door edge protector strips. The inserts are also reversible. If you want to blackout the window entirely instead of using the perforated vinyl with the white side facing out - just install the insert in the opposite window (tinted side and black side of perforated vinyl facing out).

The white vinyl and tint provides sufficient one way view for privacy during the day-time. At night, an additional 1/8 inch black foam-board insert can be used for complete privacy until lights are out (see last photo). The foam board inserts use gorilla tape at the insert edges to provide a light seal. Once all interior lights are out, you can selectively remove any foam board insert to see out. A Pedestrian should not be able to see in, without being right up against the window, since visibility through perforated vinyl into the camper at night requires interior lighting.

In addition to privacy, the inserts also create a dead-air space at the window surface to provide thermal insulation.

Fabrication of these inserts is time consuming, with most of the time spent on perfecting the paper insert transfers needed to outline and cut the PETG sheet. Lots of trial and error is involved, so it is advisable to fabricate the foam-board inserts first (mistakes are less costly with foam-board). However, once you get the shape right, the fabrication process is fairly straight forward. It helps if you have some experience with applying window tinting film.

Note: The foam-board inserts (minus the gorilla tape seal) must be fabricated to a size smaller than the window itself, and a horizontal seam must be cut so that the foam-board can be folded to install. This is because, unlike PETG, foam-board is not flexible.

 

no to AC reverse, its heated via coolant only. No to accumulator pump so cold startups very hard on the engine and builds tons of condensation in the exhaust and oil pan. You can use a DC inverter to power around 800W probably but pointless to try to convert it back into heat. Just leave the Prius in inspection mode and force the engine to run all night if you want cabin heat. Best way to heat food is to stop at a truck stop/gas station microwave before stealth camping. Or a 12V heated lunchbox that draws about 100W generally can heat up non-frozen TV dinners in about 30 mins or slow cook entire meals while you drive.

 

oh and the real issue with insulating your windows is that it doesn't work very well since large areas of the trunk are also non-insulated and lose a ton of heat. Condensation is a big big issue if you are camping for more than 1 night and don't have long drive to unfold your bag and hang up your clothes to blast the AC/heat and dry everything out. After 2 nights my -30 synthetic sleeping bag was damp and lost most insulating property.

 

It would be an interesting modification to turn the AC into reverse cycle so the whole heating/cooling is powered by the traction battery. Some of the electric vehicle conversion people sell the valve required to convert the AC to reverse cycle, just not sure how you would go about upgrading the thermo switching part so it would run the air con once switched on to the desired temperature.
Not sure if that would also remove the moisture from the air though, not really up on how the heating part of the reverse cycle air con works to see if it has the ability to dry the air as well

T1 Terry

 

Most people adapt over a few days and will no longer be roused by the engine starting. The reticular activating system in the brain gets trained to filter out ‘unneeded’ information after awhile. Once your brain is satisfied that the restarts are ‘normal’ and not a danger, you’ll get a full night’s sleep.

I have to get up multiple times in the night for exactly this reason. Far more sleep depriving than the engine starting multiple times.

That said, unless the temps get intolerable, I can just add more blankets and ‘could’ leave the engine off, but I need my little USB fan blowing across my face.

 

Of course, running any moving part more will just bring you that much closer to the need for a repair. Things wear out.

However, you made a claim that

People are just asking where you got this information about them being of ‘cheap design’ and ‘fail often’ and that they are the ‘weakest link in Hybrid Synergy System’. These are serious claims and it’s up to the person making the claims to substantiate them. Otherwise you waste the combined time and effort of multiple people doing searches and potentially not coming up with the information you claim is true. Every time you mockingly dismiss someone who asks you to provide information you claim to have (or have seen) that they have not, you are the one sowing the seeds of doubt against your own claim. At this point, I doubt anyone gives your claims any serious credibility.

 

There's was recall for this pump when the Gen2 were the newest models you could buy... The recall extended into the Gen3 years but was never a problem on Gen3 cars. It's all well documented...

 

So now you're saying that there was problem but it was rectified and now there isn't a problem?

 

When the engine starts, it gets spun up to full idle speed with no fuel injection or spark to get the oil circulating, and then the fuel and spark start ... almost like having a pump.

There's one of those on eBay right this minute.

 

Tesla and others have used heat pumps, which is a reverse AC, instead of resistive heating for a while for cold weather heating. Would be nice to have a 12v mini heat pump. I haven’t seen any.
Model Y is the first Tesla with a heat pump. Here’s why that’s a big deal. | Current Automotive

 

Well, the Prime also has a heat pump, but it's a 200 volt one, not a 12 volt one. The practical reason is the amount of power it needs. If there were one that ran off 12 volts, it would not be the kind of thing to plug into a lighter socket; it would take direct attachment with wires that would look like garden hoses.

 

A part I hadn't thought about but was pointed out to me by someone in the air con system design trade, the evaporator in the heater box would have to be changed as well. In a standard cooling only system, the evaporator is under a vacuum or very little pressure, but reversing the flow would mean the high pressure gas from the compressor would be shedding its heat through this same core so the gas reverts to a liquid and turns the condenser in front of the radiator into the heat absorbing unit by releasing the liquid from the high pressure to a vacuum or lower pressure causing it to change state into a gas again. It is the change of state between a liquid and a gas or the other way around that pumps the heat from one section of the system to the other.

Hot water system heat pumps are becoming the norm around these parts because of their extremely low energy use and can operate down to -10*C but I guess it probably gets colder than that in the USA, fortunately we don't see those sort of temps over this side of the globe ....

T1 Terry

 

Not all of the U.S. gets that cold. And even in places that do, heat pump water heaters will still save a huge amount of energy over the full cycle of seasons. They just need to retain the old style electric resistance elements as backup for when it gets too cold for the heat pump operation.

I haven't looked at the latest products, but should be doing so to have a backup plan for when my current heat pump water heater needs replacement. If modern space heating heat pumps can operate down to -25*C, there is no reason water heating versions can't be built to do the same.

 

The issue around these parts when the outside temp drops below about 2*C is the outside unit freezing because the wind chill factor drops the temp low enough for the water in the air to freeze. It then uses some of the heat it pumped to circulate it through the outside unit to melt the ice, then away it goes again. The refrigerant will go down to -32*C before it won't boil off at atmospheric pressure, but modern pumps create a vacuum on the pump input side so that -32*C increases to around 40*C until it no longer functions ........ I've thought about adding a water radiator in front of the outside unit to circulate warm water through it so the outside stays above freezing, but maybe a water to refrigerant heat transfer unit like they use on cruising boat refrigeration would work better .... well for the cold but not so much the hot, although it could be used as a preheat for the hot water storage.

T1 Terry

 

Defrost cycles ...

... and it has nothing to do with wind chill.

 

If the ambient temp is above freezing then if it's not wind chill dropping the temp to the point of freezing, then why does the evaporator (in this case with reverse cycle operation) ice up? It might form water droplets but for it to form ice the temperature in the core would need to drop below freezing point ...... wouldn't it?

T1 Terry

Brain just kicked in, the gas is compressed to a liquid and the change of state pulls the energy from the air passing through and that is what drops the temperature below zero ......