Sunday, January 16, 2011

Hot Water Plumbing Complete!

     It's done - finally. The heater is secured to the hull, the plumbing is done, and the electrical and pressure relief systems are complete too:
     I had to enlarge the pressure relief line from 1/2" to 3/4", to accommodate the larger water heater. Of course, the through hull fitting had to be enlarged as well. It is very important to make sure that the pressure relief line is not restricted in any way, and does not reduce in diameter from the tank outlet. You can also see a thermostatic mixing valve (tempering valve) in the picture, mounted directly to the hot water heater discharge. It is very important that any hot water heater that will be connected to the engine, and that will utilize the engine coolant to heat water, be outfitted with a tempering valve. Engine coolant temperature can exceed 180 F, so the hot water will also approach this temperature. Imagine a child, or even an unaware adult, turning on the hot water to wash something or take a shower. Severe burns could result. The tempering valve reduces the temperature of the outgoing water to a safe level, by mixing a controlled amount of cold water with the hot water. The outgoing temperature is easily adjustable between 120 F - 160 F. An added benefit is that, once the tank is up to full temperature, the hot water volume is further extended.

     Example: If we assume the hot water is 180 F (82 C), and the cold water is 68 F (20 C), then how much hot water is available at 140 F (60 C)?
     Since Q = mc(Delta T), from this follows: (3785 g/gallon)(12 gallons)(4.18 J/cg)(82-60) = X(4.18 J/cg)(60-20), where X equals the number of gallons of cold water, at 68 F, needed to reduce 12 gallons at 180 F to 140 F. The result is 6.6 gallons. So, in effect, the hot water capacity of this boat has been increased from 6 gallons (since the factory did not use engine coolant through the heat exchanger, there was no tempering valve, and the water was only heated electrically to 140 F maximum) to approximately 18.6 gallons.
     A side benefit is that the area adjacent to the exhaust manifolds, and the spark plugs, is now completely opened up, and the hot water heater has been moved forward, which is a better location, in terms of weight balance. If you look at the following pictures, you can see that a person can now easily stand next to the engine (once it goes in). With the old layout, there was no room for engine service at this location.

     Other features of the install include a back-flow preventer in the cold water feed to the water heater, a shut off valve, for servicing, and a drain valve, for winterizing and flushing. I also added a hot water line up to the wet bar, so I can have both hot and cold water there. I will be detailing the wet bar modifications in a future post. For now, it is on to the bilge pumps and discharge lines....

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