When NOT using A/C, does adjusting the temperature up or down effect efficiency at all? Take for example, if the outside air temp is 75 degrees, is it be optimal to set the temp setting to 75 degrees and ventilate with outside air? (in this case, I assume the system doesn't really have to do anything except run the fan) If you set the temperature to far below the outside air temp, would you see an efficiency hit? I did try to RTFM, but it didn't really address this.
If you're trying to cool the cabin, any efficiency hit would be pretty insignificant. The fan does take maybe a couple hundred watts at the highest speed, so if adjusting the temperature reduces the fan speed to, say, 3 pips or less, that might save you a tiny bit of fuel; but it would be unnoticeable in any conditions other than a thoroughly-controlled laboratory experiment. A/C, on the other hand, can use thousands of watts; I'm not sure what the peak possible power consumption is, but probably on the order of 20x more than the fan alone. And heating is probably about the same as the fan alone, with the caveat that if the engine isn't producing enough heat from normal use, it will need to run more often to supply you with heat, thus hurting efficiency.
macman hit it on the head. Without the AC, your efficiency drop will be if you request heat because the engine will run more often than normal to give you heat.
I had to spend some time idling in parking lots today, so I played around with the AC. The air temp was in the low 90'sF. The max amperage I got (with max fan and LO setting) was 5 amps. That is about 1 KW. I do not think the fan was drawing more than 1/2 amp (100 watts). That is about what I would guess- 3000 btu's or so would be reasonable for a small car. I know it costs a bit of money, but I am too old to not have my creature comforts. I use LO all the time.
Thanks for the info. A/C is important for me (I HATE heat...or even being slightly warm!), but I have no qualms about running it a lot in the Prius since the fuel economy gives me that luxury!
Do you have any reference for this? When I run the AC in park for long periods it makes very little difference in the SOC or EV miles in my PiP.
when not looking for a/c or heat, set your temp to low. otherwise, you risk the ice coming on if outside temp fluctuates. there is no need to try to set it higher than low, it doesn't do anything unless you want heat or are using auto.
Yes, I have a ScanGauge, which can show both total power draw of the car, and even power draw of just the A/C compressor. So I ran out to my car just now to take a look. At "LO", a quick test showed 1500 watts for the compressor (plus ~250 W for the blower, though it's harder to tell about the blower since the gauge can only measure in increments of ~110 Watts, shared with the rest of the systems in the car; the A/C compressor measurement is in increments of 50W). In ECO mode, it dropped to 1350 W. It may be higher in other conditions, I'm not sure - after peaking at 1500W, it dropped back down a little bit (I only ran it for 15 seconds or so anyway), possibly because the interior and exterior air was quite cool, and there's no sun to heat anything up. If you're in park for long periods, and the car is already at a comfortable temperature (and especially if you found a shady spot), then the power consumption can be pretty low; maybe 300 watts or so. That's about equal to the consumption of all the other electronics in the car when idle. And with around 3 kWh of total battery capacity, a power draw of 600W (half A/C, half the rest of the car) would be able to run for 5 hours on one charge.
As a suggestion: set the blower as high as practical, blowing at face and arms increase temperature setting, now possible with higher blower setting internal recirculation This reduces the compressor load and dries the cabin air. Bob Wilson
Thanks for all the information. I have a Scan Gauge but hadn't noticed those measurements are available. Does the AC compressor just run slower when more cooling isn't needed or does it run intermittently as in conventional air conditioners?
A/C Wattage an Xgauge, Adrian Black's Google Docs spreadsheet has the codes you need to program it. The blower power I'm just getting by looking at the total battery amps while adjusting the blower speed (with A/C off, obviously). The compressor is a variable-speed compressor, yes. Since I was in the garage in EV mode last night while getting the data for my post above, I could actually hear the compressor's tone change at each different speed step shown on the Scangauge as it was ramping the power up and down.
The spreadsheet says the total battery amps won't work in the PiP I find the A/C power goes up and down in significant steps with the blower setting.
