Date: Wed, 28 Oct 1998 15:08:02 -0600
Reply-To: Blue Eyes <lvlearn@MCI2000.COM>
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: Blue Eyes <lvlearn@MCI2000.COM>
Organization: Vexation Computer
Subject: Re: Fridge ?
Content-type: text/plain; charset=us-ascii
I recall reading a description of what seemed a wonderful improvement
to the Westy Dometic refrigerator's performance. It suggested
installing a tiny electric powered fan to blow air through the cold
internal heat exchanger. While it's been a long time since reading
that, it seems they were suggesting use of a 1.5 volt continuously
powered fan. They said this was justified because the energy draw was
trivial. At least a trivial energy draw won't add much heat load to
the fridge.
I'd like to use the excellent suggestion of forcing air over the
internal heat exchanger. But even if the energy draw is trivial, life
expectancy of such low cost motors probably isn't suitable for any
continuous duty or long term use installation. Besides, I'd rather
use my 12 volt house current.
Does anyone know of any suitable small super low current draw 12 volt
DC fans? If so, please post contact information, current draw,
price, etc. Also, what would be a nice way to power this ONLY when
the main burner heat is driving the refrigeration cycle? That feels
like the right approach to me. Doesn't this appeal to the inventive
spirit of you creative guys like Dave B.? No used three pound boiler
controllers please. Keep saying this: Simple, compact, reliable,
cheap, elegant. Say it, and designs will come.
On a completely different refrigerator design consideration, I don't
like the fact that in even tepid weather, my refrigerator's external
heat exchanger fan keeps cycling on and off. It's distracting,
irritating and calls attention to itself when I prefer to sleep. I
always wonder if it might drain the battery enough to cause a starting
problem if it were left on for a few days without starting the motor
to recharge. Remember, old battery marginal performance failures
always occur at their margins, by definition.
Wouldn't it be good to find (or make from two sizes) some double
walled insulated ducting to better retain flue gas heat? This would
induce more flow through the chimney so the fan wouldn't come on so
often. I even considered trying to move the exhaust location up near
the top of the van. I think it might be possible to snake a duct
between the kitchen windows inside the wall.
Static chimney effect pressure is affected by average
internal/external gas density difference per foot times the number of
feet. So the hotter you can keep it before it exits at the top, the
better it flows. Also the taller it is, the more static pressure it
can develop. But flow is a dynamic state effect that's also affected
by resistance. The smaller the chimney's cross sectional area and the
longer it is, the higher the resistance is. So we have a balancing of
effects. The designers' thinking shown in other RV absorption cycle
installations I've seen usually caused them to create chimney runs as
tall as possible, unlike the Westy design. I think the Westy's short
vertical chimney length was a design error. A fully adequate full
height chimney might require a small vertical interior intrusion
rising between the kitchen windows. But to me, having a well
functioning refrigerator that rarely needs additional air flow induced
by an external fan would make that trade-off preferable.
My overheated mind begins to create a Rube Goldburg cartoon-like
modification wherein this former liability is turned into an asset.
Picture a Westy parked in warm arid environment. An 8 foot chimney
extension is attached to the roof. Inside, the refrigerator is dialed
to it's coldest setting. This is causing air to flow through a small
hidden swamp cooler cast into normally wasted space. A little
electric fan silently blows air from the swamp cooler to the lower
sleeping area or the back seat, depending on how the duct's outlet
louver is directed.
I prefer this kind of distraction to spelling humor, sandwich spreads,
etc.
John
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