Date:         Thu, 24 May 2012 12:41:32 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Front Heater shutoff  options
Comments: To: Rocket J Squirrel <camping.elliott@GMAIL.COM>
In-Reply-To:  <4FBD78E4.1020806@gmail.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 07:55 PM 5/23/2012, Rocket J Squirrel wrote:
>* Anyone got a handle on how many Watts** that thing has to get rid of
>on a hot day at, say, 60 miles per hour?

In *extremely* round numbers...you've got an engine that delivers say
70 kW max so it's wasting call it 150 kW at full output, or half a
million BTU/hr.  Some** goes out the exhaust, some radiates/convects
direct from the case including the little radiator fins on the oil
sump, the rest is shed by the radiator (and cabin heaters).  For us
AT types some of the heat rejected by the transmission will also come
out through the radiator.  And of course the A/C condenser
contributes an amount disproportionate to the amount of energy it
uses, since it's pumping heat out of the cabin into the
condenser.  If it's rated at 12,000 BTU/hr and running flat out it's
going to shed 3 1/2 kW over and above its mechanical load.

Running at 60 on the flat of course you're nowhere near full output
(unless there's a monster headwind and the gearing allows 60 mph at
redline).  Automotive engines are designed and rated on the
assumption that they won't be run flat out for extended
periods.  Industrial or marine versions will have significantly lower
rated output and probably expect to run at no more than 80% max in
continuous operation.

**Quite a bit, I think.

Yours,
David