Westfalia

Auxilliary Water Heater

The installation of the engine powered shower water heater was a great success. The water heated within half an hour of driving and would stay hot well into the evening. However, we usually found that it was not warm enough after an overnight stop.
So, the plan is to use the waste heat from the Dometic fridge overnight to keep the water in the tank warm enough to use in the morning. In its job of heating the ammonia solution to cool the inside of the fridge, the Dometic puts at least 50^oC of heat out the flue pipe - wasted heat!
Click on the image to see it full size.

Auxilliary Water Heater

The Plan for the Heater A length of 1/4" copper pipe would be bent to fit against the flue pipe, underneath the fibreglass insulation.
Cooler water from the bottom of the tank would enter the tubing at the bottom of the serpentine, be heated by the flue pipe and return to the top of the tank, heated. If the levels between the flue pipe and the tank are correct, this will take place by thermosiphon effect. In my '88 Westfalia, the sink water comes from an outlet near the bottom of the tank. However, I discovered that in an '89, the in-tank pump pumps water out the top of the tank. If things do not line up, a small circulating pump will be installed.

Bending the Tube

A bending jig was made from scrap maple hardwood flooring. As the first few kinks were bent, the formers were unscrewed and moved further along to the right.

Curving the Serpentine
With an armature press, a 3/4" steel bar, the same diameter as the flue pipe, pressed the serpentine of copper tubing into another jig (also of scrap maple flooring) with a 1 1/4" diameter concave shape in it.

The Curved Serpentine
All bent, curved and ready to install. The result uses nearly 42" of tubing within 14" of length. The nearly semi-circular shape was used because the tubing could not be wrapped completely around the flue pipe. The 12V and 120V heater elements, as well as the ammonia boiling tube are bonded to the flue pipe for the lower 1/4 of its length. As well, installing it would mean removing the brass ferrule and flexible flue.

Fitted to the Dometic The stainless steel shroud has been unclipped and slipped off the flue pipe and the fibreglass insulation peeled back exposing the flue pipe, boiler tube and heater elements.
The copper tube serpentine has been fitted to the flue, tied with wire so it is in direct contact with the flue pipe.
At the moment there is 6' of 3/8" plastic hose on the inlet and another 6' on the return side of the heating tube. This length is greater than the distance between the fridge and the water tank when properly installed in the Westfalia.

The Test Setup
With a fridge, propane bottle, battery and water tank (from an '89), testing takes place.
In the first test a 1 liter water tank was used. By thermosiphon action, the temperature of the water was raised from 13^oC to 53^oC in 5 hours. Meanwhile the fridge was chilling the beer!
However when the experiment was enlarged to using the Westfalia tank, thermosiphon effect would not work! The storage was at the same height as the heater tube, so water would not circulate.
At this time neither the tank nor the plastic tubing is insulated, so probably loses a lot of heat in the transferring process.

Graph of Results Because thermosiphon effect would not work, a small submersible pump was installed in the tank, which was was filled about 1/3 full.
The water temperature rose from 19 to 35^oC in 11 hours, despite neither the tank nor the tubing being insulated.
Part way through the experiment the tank was insulated with a blanket, and the temperature rose to 42.6^oC - which should be perfect for a shower.
For a final test, the tank was filled to the FULL indicator (about 39 litres of water) and left for 12 hours. It maintained around 40^oC.
Since the aim of the project is to simply maintain the temperature of the stored water at around 42^oC over night, after it has been heated by the vehicle's engine, this looks promising.

The next difficulty in designing this mod is to allow the fridge to be removed and replaced without difficulty. Since the copper serpentine tubing will be built into the fridge heating pipe, some form of quick connect or unions for the water tubing will be needed. That has yet to be worked out in detail.
As a footnote the indicator lights on the stove panel represent the following non-linear degree of fullness:
RED light = about 4 litres left, although not all may be useable,
ORANGE light = about 8 litres above the RED light, (12 litres total)
GREEN light = about 27 litres above the ORANGE light, (about 43 litres total).

The owner takes no responsibility for anyone else making these modifications.
Photos provided by owner. Contact the postmaster for permission for use.

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F. Griffiths

Last updated July 30, 2009

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Auxilliary Water Heater
The Plan for the Heater	A length of 1/4" copper pipe would be bent to fit against the flue pipe, underneath the fibreglass insulation. Cooler water from the bottom of the tank would enter the tubing at the bottom of the serpentine, be heated by the flue pipe and return to the top of the tank, heated. If the levels between the flue pipe and the tank are correct, this will take place by thermosiphon effect. In my '88 Westfalia, the sink water comes from an outlet near the bottom of the tank. However, I discovered that in an '89, the in-tank pump pumps water out the top of the tank. If things do not line up, a small circulating pump will be installed.
Bending the Tube	A bending jig was made from scrap maple hardwood flooring. As the first few kinks were bent, the formers were unscrewed and moved further along to the right.
Curving the Serpentine	With an armature press, a 3/4" steel bar, the same diameter as the flue pipe, pressed the serpentine of copper tubing into another jig (also of scrap maple flooring) with a 1 1/4" diameter concave shape in it.
The Curved Serpentine	All bent, curved and ready to install. The result uses nearly 42" of tubing within 14" of length. The nearly semi-circular shape was used because the tubing could not be wrapped completely around the flue pipe. The 12V and 120V heater elements, as well as the ammonia boiling tube are bonded to the flue pipe for the lower 1/4 of its length. As well, installing it would mean removing the brass ferrule and flexible flue.
Fitted to the Dometic	The stainless steel shroud has been unclipped and slipped off the flue pipe and the fibreglass insulation peeled back exposing the flue pipe, boiler tube and heater elements. The copper tube serpentine has been fitted to the flue, tied with wire so it is in direct contact with the flue pipe. At the moment there is 6' of 3/8" plastic hose on the inlet and another 6' on the return side of the heating tube. This length is greater than the distance between the fridge and the water tank when properly installed in the Westfalia.
The Test Setup	With a fridge, propane bottle, battery and water tank (from an '89), testing takes place. In the first test a 1 liter water tank was used. By thermosiphon action, the temperature of the water was raised from 13^oC to 53^oC in 5 hours. Meanwhile the fridge was chilling the beer! However when the experiment was enlarged to using the Westfalia tank, thermosiphon effect would not work! The storage was at the same height as the heater tube, so water would not circulate. At this time neither the tank nor the plastic tubing is insulated, so probably loses a lot of heat in the transferring process.
Graph of Results	Because thermosiphon effect would not work, a small submersible pump was installed in the tank, which was was filled about 1/3 full. The water temperature rose from 19 to 35^oC in 11 hours, despite neither the tank nor the tubing being insulated. Part way through the experiment the tank was insulated with a blanket, and the temperature rose to 42.6^oC - which should be perfect for a shower. For a final test, the tank was filled to the FULL indicator (about 39 litres of water) and left for 12 hours. It maintained around 40^oC. Since the aim of the project is to simply maintain the temperature of the stored water at around 42^oC over night, after it has been heated by the vehicle's engine, this looks promising.
The next difficulty in designing this mod is to allow the fridge to be removed and replaced without difficulty. Since the copper serpentine tubing will be built into the fridge heating pipe, some form of quick connect or unions for the water tubing will be needed. That has yet to be worked out in detail. As a footnote the indicator lights on the stove panel represent the following non-linear degree of fullness: RED light = about 4 litres left, although not all may be useable, ORANGE light = about 8 litres above the RED light, (12 litres total) GREEN light = about 27 litres above the ORANGE light, (about 43 litres total).