The Heat Exchanger
Ball Valves and Fittings.
The tees are 1/2 X 1/2 X 1/2" PEX fittings.
The tee'd off hose is standard heater hose into a ball valve with 1/2" PEX fitting one end and 3/8" compression fitting the other. The 'barbs' are home made out of 3/8" copper tube with brass wire wrapped around in 3 places and soldered. This gives a better fit and grip for the blue neoprene air hose that will connect here.
Cut off valves are to stop the flow of engine coolant into the heat exchanger, and to allow cabinetry and heat exchanger to be removed easily without disturbing the vehicle's cooling system again.
Teeing into the rear heater hoses.
The top heater hose is the "hot" side, and is shown here clamped on both sides ready to be cut and the tee and ball valve inserted. The bottom hose is completed.
Turns out that the VW heater hoses are larger than 1/2" but smaller than standard 5/8" ID heater hoses. The hose clamps had to be screwed down very tightly on the heater hoses.
The grey plastic under the heater unit was installed after repairing a leak in the core. If there is a future leak, it will catch any tell-tale drips before they can run under the flooring.
Making the Exchanger.
3/8" copper tubing being wrapped around a pipe mandrel to form the heat exchanger. The 3 1/2" pipe was the perfect size as the resulting coil was just under 4 1/2" diameter - the maximum that would fit through the water tank hole.
Although the coiling was done on the lathe, lathe power was not used. The chuck was turned by hand for slower controlled wrapping.
Finished Heat exchanger.
The finished heat exchanger coil with 14 turns of tubing, giving about 15' of tube. The pipe up the centre had to be soldered in afterwards as I couldn't get it to fit in the pipe mandrel. The maximum length of the unit is 15" since the tank is 15 1/2" deep.
The brass ferrule with hex nut, one brass washer and two rubber washers will go inside the water tank. Since I couldn't find a feed-through fitting for 3/8" pipe I had to make one out of pipe nipple and reducer fittings, machined to fit each other and silver soldered together. The ferrule is then silver soldered onto the copper exchanger tube.
Another rubber washer, a brass washer and the elbow will fit outside the tank. The spring wasn't needed in the end. The trick was to get the elbow to screw down tightly on the pipe thread, while at the same time compressing the rubber washers just enough to hold the unit firmly and watertightly into the tank.
The hot engine coolant should enter the exchanger down the centre of the coil so it has most effect on the water at the bottom of the tank... however...
Fittings into the Tank.
Two 5/8" holes were drilled in the top of the water tank with a Forstner bit. A block of wood was clamped inside to allow the bit to cut cleanly through. The tank thickness was a suprising 1/4" thick. The spacing of the holes was 2" to suit the particular exchanger coil I made. The holes were set far enough back from the tank lid so as not to interfere with removing it, but also far enough away from the back of the cabinet opening to allow wrenches free movement.
The blue hose is 3/8" neoprene air hose with 3/8" pipe fittings swaged on. Because the swaged fittings will not turn on the hose, the hose had to be spun around as the fitting was tightened then fed through the openings in the back of the cabinet.
The hose exits through the same hole in the back corner of the cabinet wall as the tank vent pipe.
... as for the hot engine coolant entering down the centre of the coil - I originally connected the blue hoses the wrong way around! The hottest engine coolant entered the coils above the level of the water in the tank, wasting their heat on the air in the tank rather than heating the water. That has been fixed.
Routing The Hose.
The hose was routed from the water tank cabinet through the back of the shallow storage area into the electrical area of the side cabinet using existing holes in the cabinetry. It means a longer hose run, but avoids defacing the cabinets.
Each hose is 6' long. They are not insulated, but were fed through a black corrugated plastic sheathing which provides some insulation and prevents kinking. There is enough heat through them that high efficiency is not a priority.
Routing The Hose Into The Seat Base.
Under the rear seat base, the Digifant ECU unit was swung out of the way. As well, the heater had to be unbolted from the floor and tilted out of the way to allow room to drill into the corner.
A 1" hole was drilled in the left side of the seat base, 2" up from the floor and as close as possible to the front. The hole was angled slightly forward so it would reach to the electrical area of the side cabinet. A Forstner bit was used with wood clamped to the back of the cabinet wall. The holes were then filed into an oval to better accept the two 3/8" neoprene hoses in their corrugated sheathing.
The hoses have to pass through the gap between the seat base and the side cabinet. I chose this low forward position to avoid the scissor-like action of the seat hinge in that space!
When assembled, the hoses run down and along the floor to the back of the seat base. A notch was cut in the bottom back corner of the wooden heater box to allow the hoses in.
The Hoses Braced.
After discovering that I needed to remove the heater box to shut off one of the ball valves, I decided it needed improving.
An aluminum brace was fabricated, held down by the heater mount bolt at the bottom and just resting on the back of the floorpan/firewall. The ball valve is tied to this brace.
The hoses run behind the white styrofoam insulation under the Digifant ECU..
Access to the Ball Valve.
With a hole saw, a 2 1/8" hole was drilled through the wooden heater box, immediately above the ball valve. A stainless steel plate is held on by one screw and can be swung out of the way to allow access to the ball valve below.
As the water tank will be drained in winter, I wouldn't want hot engine coolant flowing through the exchanger coil inside the dry plastic water tank.
Wrapping the Tank
While the cabinetry was out for an interior refit, the tank was wrapped with insulation. It was fitted around the plumbing fixtures and held together with aluminum foil tape, intended for hot surfaces. Holes were cut for the electrical connections.
The small black wire is from the remote thermometor sensor taped to the tank under the insulation. Eventually a thermostat probe was be fitted under the insulation also.
Refitting in the Cabinet
After the tank was was wrapped in a single layer of foil on the top, bottom, sides and front, another layer was added to the back. There is plenty of room behind the tank, next to the engine compartment. Another layer may be added to the top before final refitting.
The piece of white polystyrene foam is only temporary. There is not room under the tank for a piece this thick.
As well, due to the added thickness of the insulation on the sides, it was a squeeze getting the cabinet back into the van!
Thermostat
Finally on eBay, found a thermostat that seemed suitable. It is out of a BunnTM commercial coffee maker! Originally it switched only between 55oC and 95oC, which was too high for shower water. To lower the bottom switching temperature down to about 250C, I crushed the tip of the sensing bulb a small amount.
The thermostat is is to be mounted in the bracket, which will be covered with the temperature scale.
The sensing bulb is mounted underneath the water tank, between the tank bottom and the insulation.
Solenoid Valve
The solenoid valve is a 12V, normally closed solid brass valve. It draws 600mA of current when opened. The orifice size is rather small, about 1/8", but the fittings are 3/8" FPT. The fittings are 3/8" to 1/4" barb.
The heavy black wire on the left is the protective covering for the thermostat sensor, fitted under the water tank.
Circuit Diagram
The wiring for the thermostat, solenoid valve and junction block will be mounted in the cabinet next to the water tank.
The ON-OFF switch, and indicator lights will be mounted on the wall above the cabinet.
Control & Temp Display
A cheap ($9) indoor/outdoor thermometer is used to indicate the temperature of the water tank.
The control unit is mounted on the pillar between the windows, held by the original screws for the grab-strap. The black cover will be replaced. The control wiring was placed inside the pillar. The thermometer wiring was left outside the pillar because the display unit is portable, and also for easy replacement or repair of the sensor. The thermometer is held to the bracket by Velcro TM.
The blue light indicates that the circuit is powered, the red light shows that the water is heating.
It seems that the heat exchanger could have been much smaller - perhaps only 6 feet of tubing would be enough.
Half a tank of water was more than enough to provide 2 showers, 1 hair washing and 6 meals of dishwashing.
The Shower
The water pump.
The original VW pump had long ago burnt out so it was replaced with a Proven Pump from Princess Auto (Canada). This unit appears to be much sturdier than the original. The inlet side has 1/2" male pipe thread (MPT) fitting which screws directly into the PVC ball valve. This then requires a 1/2" MPT down to 3/8" FPT reducer, and a further conversion of 3/8" MPT to 3/8" barb fitting.
The output side was much easier, requiring only a 3/8" FPT to 3/8" barb fitting.
The ball valve is bulky, but may be needed someday if the pump needs repairing or replacing.
The switch and mounting block.
Since we never used the original sink, I had already made a stainless steel sheet to cover the sink to allow hot pans to be set on it. The spigot and valve/switch was removed because it was in the way.
It was replaced with a block of plastic below the sink counter, countersunk and fitted with an on/off rocker switch for the water pump. This keeps the switch below the level of the counter and out of the way of hot pans.
The Shower Sprayer.
The hose will reach out the driver's window or out the sliding door into our annex tent. A kitchen sink type hand held sprayer with a 'push to spray' button was fitted to the end of the hose. The original sink sprayer hose was discarded as it was only about 30" (75cm) long, and had a smaller ID, which required that a new fitting be made to match the 3/8" ID hose to the spray unit.
Back of the Sink Unit.
A new back (of 3/8" Baltic birch) and bottom (of 1/8" Baltic birch) was made for the drawer. Then only a small cutout was needed in the back to clear the shower hose.
The spring on the hose is to prevent kinking where it will bend downward at the van wall.
The sink open.
When the shower hose and spray are not needed, they are coiled up and stored in the sink.
The sink closed and ready for cooking.
The black circle in the upper right is the countersunk shower pump switch.
We've just done a long camping run and tried it out. My 'happy camper' spouse was ecstatic over having a hot shower after 2 days of +38oC heat inside the van. As well, it made my job of washing dishes so much easier - just pull out the shower hose, flip the switch and fill the washpan with hot water. Saves on propane by not boiling water, as well. A mod well worthwhile.
A further refinement being worked on is to use excess heat from the flue pipe of the Dometic fridge to keep the water hot overnight. Stay tuned!