Does Climate Temp "setpoint" affect mileage?

tomforst · 06-10-2005, 06:35 PM

On some cars with interior temp control, the air conditioner runs at maximum and heat is added to bring the temp up to setpoint. If this is the case, then the air conditioner is working equally hard regardless of the temperature setpoint. My 'ideal' temperature is 74, but 78 is just about as comfortable and if I get better mileage at 78 than at 74, I'd set the temp at 74. I don't want ot do this, though, if I'm just fooling myself that I'm helping my mileage. Anyone out there know how our electric AC works?

KTPhil · 06-10-2005, 07:13 PM

The compressor has more than one speed (2? infinite?) so if it shuts down with the higher set temp then you drain your HV battery less, which should decrease the need to run the ICE, which should increase your MPG.

Don't expect huge savings, though, since the compressor is efficient and it can run at a slower speed, so there is less waste to "not waste" by setting the higher temp.

galaxee · 06-10-2005, 07:14 PM

I think if you set it to Auto, then it works the way you describe. I usually just turn on the fan and turn off the AC. As long as I have some air cicrulating I'm OK. When my husband is in the car, however, we do have to use Auto AC set to 70 degrees or so. The MPG hit isn't too noticeable.

jeromep · 06-10-2005, 07:43 PM

A question along these lines was asked in the fuel economy forum. Please read this link. It should answer your question.

http://priuschat.com/forums/-vp97341.html#97341

Remember, the HV battery is dependant on cabin air temp for its cooling. If the HV battery gets too hot it will not run as well as if it were cooler and that will have a negative effect on your fuel economy.

DanMan32 · 06-13-2005, 03:56 PM

To answer your question directly, yes, putting the HVAC at a higher temp will use the compressor less and save energy.

As mentioned, the compressor is a continuously variable speed. It pulls quite a bit of energy and is quite loud when it is running full blast to cool down an overheated cabin. Once things are equalized, it runs much slower, quieter and more efficiently. It can get to a point that it reaches its minimum speed, after which it will cycle on and off to maintain cabin temp and humidity as desired. If you set it at a higher temp, then it won't need to run as often or as fast.

06-10-2005, 06:35 PM	#1
tomforst Join Date: Feb 2005 Posts: 26 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Does Climate Temp "setpoint" affect mileage? On some cars with interior temp control, the air conditioner runs at maximum and heat is added to bring the temp up to setpoint. If this is the case, then the air conditioner is working equally hard regardless of the temperature setpoint. My 'ideal' temperature is 74, but 78 is just about as comfortable and if I get better mileage at 78 than at 74, I'd set the temp at 74. I don't want ot do this, though, if I'm just fooling myself that I'm helping my mileage. Anyone out there know how our electric AC works?

06-10-2005, 07:43 PM	#4
jeromep Join Date: Dec 2004 Location: Eastern Washington State Posts: 821 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Re: Does Climate Temp "setpoint" affect mileage? A question along these lines was asked in the fuel economy forum. Please read this link. It should answer your question. http://priuschat.com/forums/-vp97341.html#97341 Remember, the HV battery is dependant on cabin air temp for its cooling. If the HV battery gets too hot it will not run as well as if it were cooler and that will have a negative effect on your fuel economy.

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06-10-2005, 07:13 PM	#2
KTPhil Senior Member Join Date: Jan 2005 Posts: 1,213 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	The compressor has more than one speed (2? infinite?) so if it shuts down with the higher set temp then you drain your HV battery less, which should decrease the need to run the ICE, which should increase your MPG. Don't expect huge savings, though, since the compressor is efficient and it can run at a slower speed, so there is less waste to "not waste" by setting the higher temp.

06-10-2005, 07:14 PM	#3
galaxee running WOT until out of fuel Join Date: Mar 2005 Location: central NC/ western WI Posts: 9,081 My Car: 2005 Prius Package: #5 Nominated 5 Times in 3 Posts TOTM Awards: 0 Friends: 21	I think if you set it to Auto, then it works the way you describe. I usually just turn on the fan and turn off the AC. As long as I have some air cicrulating I'm OK. When my husband is in the car, however, we do have to use Auto AC set to 70 degrees or so. The MPG hit isn't too noticeable.

06-13-2005, 03:56 PM	#5
DanMan32 Join Date: Aug 2004 Location: Tampa Bay, FL Posts: 3,775 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	To answer your question directly, yes, putting the HVAC at a higher temp will use the compressor less and save energy. As mentioned, the compressor is a continuously variable speed. It pulls quite a bit of energy and is quite loud when it is running full blast to cool down an overheated cabin. Once things are equalized, it runs much slower, quieter and more efficiently. It can get to a point that it reaches its minimum speed, after which it will cycle on and off to maintain cabin temp and humidity as desired. If you set it at a higher temp, then it won't need to run as often or as fast.