Date: Wed, 17 May 2000 12:27:23 -0400
Reply-To: David Beierl <dbeierl@IBM.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@IBM.NET>
Subject: Re: Heat in an air-cooled Syncro (long, boring, self-involved)
In-Reply-To: <3921FACD.4BC3DD6B@anent.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed
At 21:50 5/16/2000, ed wrote:
>Some folks have apparently used an oil-water heat exchanger to drive the
>stock system. Good idea, but the oil temp in my own 911 takes a
>donkey's year to get up, especially when the weather is cold - 11 quarts
>of oil is a lot to heat up. One could electrically heat the water til
>the oil comes up to temp, but seems klugey and in any case retaining
>water heat requires pumps, controls and other cruft. MSDS recommends
Some numbers of possible interest:
Specific heat of water: 1 (1 BTU per Lb per Degree F)
Density of water: 1 (8 lb per US Gallon)
Specific heat of oil: a bit under 1/2
Density of oil: somewhere around 0.8
Capacity of Vanagon cooling system: about 36 lb.
*Disregarding losses* which means that this number is pretty low...
Heat input needed to raise cooling system from 60F to 160F in ten minutes:
~22,000 BTU/hr*
*Of course the heater circuit gets warm much earlier because at first the
system is warming only the water in the engine and heater loop. Also of
course the radiator loop might never get to 160 -- but it has a bloody
great radiator in it throwing away heat by the bushel. Also none of this
addresses how much heat the heater actually passes into the cabin, only
what it takes to get the operating fluid up to temp, hence an idea of what
is available from the motor. To figure the capacity of the cabin heating
system you'd need to ask VW engineers or analyze/measure the heat exchanger
capacity.
Weight of 11 qt oil: ~18 lb.
Heat input as above: ~5,400 BTU/hr*
*This is a bit more than the output from an electric room heater, which we
all know is utterly insufficient to heat a Vanagon standing still, let
alone whizzing down the road. Which suggests that if the oil takes a long
time to warm up, the net heat transfer into it, and hence the amount
available eventually for cabin heating, is better than waving matches in
the air, but not all that much better.
Hypothetical capacity of the water in an oil/water loop: 6 lb.
Heat input as above: ~3,600 BTU/hr
Amps @12v to do this electrically, not counting heat going back into the
oil: ~75
Formula: t [minutes] / 60 * Hin [BTU/hr] = Wt [lb] * delta-T [deg F] *
Specific heat [where water = 1]
Rearrange terms as desired or use an equation solver like the one on my
calculator...
david
David Beierl - Providence, RI
http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"