Summer block heater testing

Hi folks,

I have been recording the first warm-up: (1) using "N" while parked, (2) "D" while parked, and (3) "P" after using the block heater. The battery current scale is on the right and the air mass flow data in grams per second on the left. I've offset the zero scales so the battery currents are separate from the air flow data:



I have not calculated the relative fuel burn (use 14.7 for a stoimetric air to gas ratio) and this chart only shows the time to the ICE auto-stop. Also, this is a North American NHW11 that has the HC emission system and extended warm-up. The chart shows the block heater is especially useful for my NHW11 03 Prius.

Although "N" had slightly less fuel burned compared to "D", "N" defeats the auto-stop. For "N" to be useful, it needs a timer, say 60 seconds, before flipping over to "P" or "D". But the quantity of fuel saved does not justify the savings when stationary. Worse, "N" does not come even close to the block heater savings.

I was surprised there wasn't an extensive 'charge' put on the battery in the first six minutes. Not shown but the ICE appears to cycle on/off later in the data to sustain the traction battery charge.

Bob Wilson

 

<div class='quotetop'>QUOTE(Godiva @ Aug 4 2007, 09:49 PM) [snapback]490733[/snapback]</div>

The data suggests:

1) ~80 grams / 2.81 oz - "D" stationary
2) ~78 grams / 2.76 oz - "N" stationary
3) ~26 grams / 0.92 oz - "P" with block heater, stationary

Remember, this is a 2001-03, North American Prius, with the HC system. European and Japanese versions will not have the same "D" warm-up cycle. I don't have data for an NHW20.

Bob Wilson

 

Without the block heater in the summer, my morning commute runs:

__10 miles
_492 grams of gas (0.1852 gal)
__54 MPG

With the block heater, I save 54 grams of gas:

__10 miles
_438 grams of gas (0.1649 gal)
__61 MPG

In fact, I'm seeing +60 MPG on my morning commute compared to ~54 MPG before the heater. It takes about 10 weeks of commuting 5 days a week to save a gallon.

If you are doing a cost trade off, the block heater takes about 400W. Although I have not repeated Ken@Japan's report of using the heater for two hours, in North Alabama it would be half as expensive, $0.04, for two hours of block heater than the cost of burning the extra gas, $0.08. At least 1/3d of the USA gasoline is imported.

For those doing a 'green' study, Tennessee Valley power comes from 64% fossil fuel (a lot of USA coal,) 29% nuclear, and 6% hydro:
http://www.tva.gov/power/powerfacts.htm

Bob Wilson

 

This morning it was 85F with high humidity. After unplugging the block heater, I had no problem running the AC at a modest setting to get rid of the heat and humidity. The block heater in summer is a good solution for those who need AC in hot climates.

Bob Wilson
North Alabama