I’m not sure I got all of this right. But it helped me get my head around the basic design. In most cases, the system should “just work”. The only wrinkle is when the engine has heated the water in the domestic hot water tank and the hot water heater power is off. When that happens (and the hydronic is on), we need to open the water heater solenoid manually using a switch on the panel. Otherwise, it’s closed automatically because the hot water tank is off. For the hydronic solenoid, it’s open by default and can only be closed using a breaker switch. That way, if the hydronic system is off but the domestic system is on, we can bypass the hydronic.
Use cases
Manual interventions in italic
- Summer on shore power: No cabin heat. Water heater is on, hydronic system is off. Water heater solenoid open automatically. Hydronic solenoid closed from the panel.
- Summer under way: No cabin heat. Water heater is off. Engine heats the domestic hot water. Water heater solenoid opened manually from the panel. Hydronic solenoid closed manually from the panel.
- Summer at anchor: No cabin heat. Either run the generator and configure similarly to summer on shore power. Or, put the hydronic system into “summer mode”. Water heater solenoid closed automatically. Hydronic solenoid opened automatically. Diesel boiler provides on-demand hot water.
- Winter on shore power: Cabin heat. Water heater is on. Hydronic system is on. Water heater solenoid opened automatically. Hydronic solenoid opened automatically. Water is heated by both water heater and hydronic.
- Winter under way: Cabin heat. Water heater is off. Engine heats both water heater and hydronic. Water heater solenoid is opened manually from the panel. Hydronic solenoid is open automatically.
- Winter at anchor: Cabin heat. Hydronic is in normal heat mode and diesel boiler is running. Water heater is off and solenoid is closed automatically. Cabin heat and hot water both provided by hydronic. When generator is started and hot water heater is powered, solenoid opens automatically and boat is configured like winter on shore power.