Most generators and engines have a calorifier feed, and I thought I’d measure how much heat is transferred from the generator into the hot water.
When I got to the boat, with cold water in the calorifier, I heated the water using the immersion heater, measuring the water temperature repeatedly over time. This is easy on my boat because the Ortomarine monitoring system tells me the temperature, it just takes patience and the timer app on my phone to keep remembering to record values every five minutes for an hour.
Later in the day when we had used some hot water and the temperature had come down a bit, I ran the generator, again recording the temperatures. The calorifier temperatures over time looked like this:
The slope of the immersion heater line is 0.2484 C/min, while the calorifier heating line has a slope of 0.2716 C/min. The Victron Quattro tells me the AC load power, and switching the immersion heater on results in a change of 1,015 W, which agrees with the nominal 1kW rating of this heater.
As the generator heats the same volume of water slightly faster, a simple sum shows that the generator was putting about 1.1kW of heat into the calorifier. This rate of heating will reduce as the water temperature approaches that of the generator, but that will not be evident for the first couple of hours. The best thing to do then is to have a really hot shower and start heating the fresh batch of cold water!
Our generator will be rejecting about 20kW of heat when it’s running at full power, so the calorifier cooling is only a fraction of the cooling carried out by the skin tank. This is why the engine is not affected by the calorifier temperature rising and losing this small piece of extra cooling.
At last - proof that I can do short blog posts.
One other point -- a BetaGen 10 at full whack (31A/230V/7kW mains output) will put about 10kW into the cooling circuit, the other 10kW goes out of the exhaust -- but as you say, the calorifier is only a small fraction of this.
It's just a photo of a calorifier. Mine is 55L.
Is that a single coil calorifier, and if so, what size? (photo is a Surecal). I was thinking of maybe using a dual-coil one with both coils in parallel to get more flow through it and faster heating.