Warm Vs Cold days. Where does the energy go?

Hi everyone

In this post I showed you how I measure the energy flow within our GenIII Prius. I have been recording the necessary data since December 2011 so I can plot the different energy flows in warm and cold days in my usual trip described here.

Just to refresh my usual trip, that descends 28.1m (92.2ft) of elevation, this is the scheme:




And this is the scheme of the power flow I measure within our Prius:





In the colder days, the mean ambient temperature of the four trips I averaged here was 3.2ºC (37.8ºF). The speed was 42.8Km/h (26.6mph) and the fuel consumption was 3.80l/100Km (61.9mpg). The energy flow in kilojoules was:



You may notice that the ICE efficiency in these cold days was 6860/21028 = 32.62%

The arrow that goes into the ICE represents the (135kj) energy drained by the ICE when is turning with injection cut-off. This energy goes to pumping air and internal friction.

In the warmer days, the mean ambient temperature of the six trips I averaged here was 23.5ºC (74.3ºF). The speed was 43.6Km/h (27.1mph) and the fuel consumption was 3.23l/100Km (72.8mpg). The energy flow in kilojoules was:



The ICE efficiency in these warm days was 5612/17878 = 32.39% just a bit lower than in colder days.


We can also display the differences of the energy flow between the cold days Vs the warm days and see where the energy goes to.



We see that the final destination of the 3150kj of chemical energy used in cold days Vs warm days is heat. Two thirds of this heat is generated in the ICE (as always) and of the remaining third, some 65% is lost in PSD and transmission friction, some 30% is lost in heat due to tires friction and some 9% is lost in heat in the inverters. Those numbers do not total 100% because the lower aerodynamic drag (due to lower speed) and the lower hybrid battery current adds the extra 4%

I hope you like the post.

Big hugs from Frank