Date:         Sun, 16 Oct 1994 11:03:51 -0700 (PDT)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         David Garth <dgarth@cymbal.aix.calpoly.edu>
Subject:      hot water...another way to do it.


As some of you may remember, recently I added hot water to my Westfalia. 
That scheme, which involved using a heat exchanger and a pump worked 
fine, but it did have a few disadvantages. As Derek pointed out, it would 
be vulnerable to freezing. And I didn't like the fact that the water pump 
had to run for 20 minutes to heat the water. So I've installed a new 
system that I think is better, simpler, and more efficient. (As was the 
case with my first try, this system heats all the water in the tank to 
shower temperature, so another source of drinking water is necessary.)

I've now run a coolant loop, teed from the rear heater, through 1/4" 
copper tubing to the water tank. Inside the tank is a 15 foot coil of 
tubing, coiled small enough to fit through the top opening. The hot 
coolant heats all 13 gallons in about 20 minutes of freeway driving.

The problem with set ups like this is usually not heating the water, but 
keeping it from heating the water too much. Here's how I solved that problem:

>From a water bed heater control ($10 new) I removed the thermosat. I 
adjusted it so it could be set at 105 degrees. From the W.W. Grainger, Inc. 
industrial catalog(800-225-5994) I ordered a high temperature selenoid 
valve (1a582) and 24 volt AC selenoid. ($90. From past experience I knew 
that 24 volt AC selenoids work great on 12-14V DC).

It works like this. When the engine is running, 12 volts from the 
refrigerator relay goes through the "water heater" switch, then through 
the thermostat. If the water is less than 103 degrees, the 12 volts goes 
to the selenoid valve, which opens, letting hot coolant flow though the 
tank loop and heating it. As soon as the water temp reaches 105, the 
valve closes, until the water temp drops below 103.

I tested various materials in the oven at 250 degrees to see if the hot 
coolant line would cause problems. Neither rubber nor polyethylene seems 
to be phased by it. So I used rubber grommets through the tank top for 
the coolant loop tubing. The fail safe nature of the system is a plus. If 
the selenoid valve fails, it will be closed.

Hot water and a pump powered hand shower really make the van more usuable 
for us.

As before, I'd be glad to help anyone who wants to do this...either 
e-mail or phone (805-543-2046 pacific daylight time) is fine.

Dave Garth
San Luis Obispo, CA
'86 Westfalia