Date: Thu, 6 Jan 2000 10:11:22 -0500
Reply-To: Bulley <gmbulley@BULLEY-HEWLETT.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Bulley <gmbulley@BULLEY-HEWLETT.COM>
Subject: (long) EVERYTHING you want to know about heat,
was Porsche 6 cyl heating van
(c)Copyright 2000, Bulley-Hewlett & Associates. ALL RIGHTS RESERVED
As many of you know, I've spent a number of years studying and
experimenting with air-cooled vehicle heating systems. I thought I'd share
a few thoughts about the "911 motor heating the Vanagon" question, since it
appears to be generating some confusion/misinformation. You can apply this
information to any heating situation...
Every heating SYSTEM (home, car, other) consists of a three essential
parts:
1. the ELEMENT
2. the CARRIER and
3. the CONTAINMENT
The ELEMENT is the hot thing, the source of the heat. In your home heating
system, the element may be a gas-fired or coal-fired exchanger, a
wood-pellet furnace, or something else that combusts a fuel (or 'captures'
heat from air, a heat pump).
We typically don't use the primary "element" (wood, coal, motor heat) for
heating our bodies, because most elements are dirty, unsafe, or
inaccessible. Cave men used open wood fires, so do Montana Militia members.
Most of the rest of us use a SYSTEM; we 'translate' the heat through a
carrier and direct it where we want it through containment (that makes it a
system).
In a water-cooled car, the element is the engine, specifically, the
cylinders and heads. In an air cooled car the element is the EXHAUST TUBES.
Read that again, it is important.
This is our first critical difference in air cooled and water-cooled
heating systems. The lubricants and internals of your motor can't bear
temperatures much above 300 degrees F. Conversely, your exhaust tubes can
get up to 500-600 degrees F, or more. So, the element in an air-cooled
system gets far hotter. The size of the motor dictates how "much" heat is
available from either source. A 2.7 liter Porsche motor theoretically will
have far more heat available (through the exhaust tubes) than the 2.0 air
or 2.1 water VW motors. Great. Onward.
The CARRIER can be electricity, oil, air, water, or something else. Each
TRANSFER of state from the ELEMENT to the final destination causes loss of
heat, inefficiency. So if the element in your home heater is an electrical
coil, the primary element is back at the power-station where perhaps they
burned coal to make steam to drive a turbine to drive a generator to make
electricity, which traveled through wires and transformers, loosing
efficiency the whole way, finally arriving to warm the element in your
home. Through all of these 'transfers', you have lost a 95% of the heat
from the original coal fire. Inefficient, (that is why it is so expensive
to heat with electricity).
Water-cooled vehicles pick up the heat from the combustion process in the
motor with water, (transfer 1) next, they move that water to an exchanger
to warm the exchanger (transfer 2), which in turn warms air (transfer 3),
which warms you (transfer 4).
Air-cooled motors have much more efficient and direct heat transfer. The
air that will warm you passes through exhaust tube heat exchangers (tran
sfer 1). Fiery-hot air moves directly to the vehicle to heat you (transfer
2). So why do air-cooled VW heaters have crappy performance? Read on.
The limiting factors however, are the CARRIER, and the CONTAINMENT. Water
(a carrier) has greater "thermal capacity" than air; once you get it hot,
it is less apt to cool down. Therefore, water encounters less loss on the
way to the heater core in the car. This is great, more heat for you. On the
downside however, water does not transfer ALL of its heat to the exchanger,
it departs the exchanger warm, still carrying heat you could use. Not so
great.
Air (as the carrier) directly warms your body without additional transfers.
It isn't leaving lukewarm for another go around in the motor, it is here to
stay, to warm you, so it is a more efficient choice. Air, however, is more
likely to cool down on the way from the exhaust heat exchangers to you.
This is a point VW ignored, causing poor performance, but you can resolve
this easily. More on that in a minute.
Air as a carrier has another deficiency. It is far more apt to loose
VELOCITY than water. Velocity is important for the carrier. If the carrier
isn't moving quickly enough, it doesn't pick up as much heat from the
element as it could. Further, if it moves slowly, it looses more heat as it
travels in the CONTAINMENT. If that was a little confusing, read it again
slowly if you need to, it is important.
Water, when introduced into a tube at a velocity of 30 cubic feet per
minute, will (generally) come out the other end of the tube at the same
velocity (don't flame me about my fluid dynamics theories, I know I am
making some generalities here, but we are talking about car heating, not a
nuclear power plant, okay? Good.). So, using hydraulic principles, the
water pump can shove your water through the motor, through the containment
(rubber hoses) toward the heat exchanger in your van, and the water won't
slow down or "get lost" on the way.
Air, on the other hand, needs LOTS of help to move through the exhaust heat
exchanger fins, the flapper boxes (where it makes a turn of about 90
degrees), the noise dampers, the 7 foot duct, the directional valves, more
ducting, and (finally) out through your vents. VW just about fixed this on
the Vanagon, with the introduction of the big belt-driven squirrel-cage fan
on the alternator shaft. Only in city idling is there too little velocity
from the fan to accomplish all the gathering of heat from the exhaust
system and distribution to the ducts. We can fix that, too. (in a minute).
Finally, we come to the CONTAINMENT. Water is routed through rubber tubes,
and plastic valves; high-temp threshold of about 320 degrees. Your metal
ducting and paper tubes bear 400 degrees with a grin. I've never tested VW
ducting to see at what temperature it scorches, but I guarantee, if we put
VW heater hose, and VW ducting in the oven, and turned up the heat until
one failed, you'd be scraping rubber off the oven floor. Paper can handle
much hotter heat.
As we learned above however, water doesn't slow down much in those rubber
tubes, and (since water has greater thermal capacity than air) it doesn't
loose as much heat as air would in transit through the containment. This is
where water-cooled heaters appear to have the upper hand, (but we can level
the playing field and get far more heat! (see below))
Finally, the body of the vehicle is also a part of the containment. If the
body of your van is not insulated (made of metal, conducts heat easily),
you can expect to loose 100% of the heat introduced by any source of heat.
So here are the keys to fantastic heat:
1. Have a VERY hot element. An exhaust system is 500+ degrees. Engine
coolant is 240. Pick one.
2. Make few transfers between the element and your body.
Cylinder-Water-Exchanger-Air-You, or Exhaust-Air-You. Pick one.
3. Keep the velocity high across the element and through the containment.
(see below)
4. Insulate the containment to prevent heat loss. (see below)
So if you want to use a Porsche 2.7 in your van, or if you just want to
heat it with your 2.0, the answer is the same...you have FAR better heat
than a water-cooled, rubber-hosed van. You just have to do a couple of
things VW didn't do. Nothing terribly expensive or troublesome.
On my heater page, (http://www.bulley-hewlett.com/VWindex ) one of the key
improvements is INSULATING the pitiable VW paper main duct and all the
fittings with R-6 or R-4.3 Mylar/fiberglass ducting. Keep the air hot on
the way to you, and (obviously) you get more heat.
The other, is introduce a "booster" fan in the duct directly below the
gearshift. JC Whitney has one for about $90 that is a metal 200+ cfm
squirrel cage fan. It is durable, extremely quiet, and the intake and
exhaust fits the VW duct EXACTLY. This, coupled with the belt-driven fan on
the alternator will give you all the velocity you need. (On a side note:
DON'T waste your money on those stupid, noisy $25 bilge fans. They only
move about 100 cfm, the noise will drive you out of your skull, and the
heat (once you have insulated your ducts) will melt them into little blobs
of plastic. BTDT.)
Finally, if you are really ambitious, insulate your van. Even if you just
do the back door, and the sliding door (easy), you have cut the heat loss
by maybe 5-8%. That's a lot. It will help out in the summer for AC season
too. The instruction are on our site. I'm not on the type2 list, so p-mail
questions. (c)Copyright 2000, Bulley-Hewlett & Associates. ALL RIGHTS
RESERVED
Now you know about Heat. God Bless, and Stay warm.
G. Matthew Bulley
Bulley-Hewlett
Corporate Communications Counselors
www.bulley-hewlett.com
Cary, NC USA
888.468.4880 tollfree
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