Brigadoon - An Occasional Corner on the Internet
Houseboat Hot Water System
Designed by Mark Little
Hot Water System Power Control
The trigger for the whole system is the flow of water in the hot water line, but there is no direct way of measuring that flow. However, the pump must be operating to maintain flow, so it is possible to measure the current to the pump from the battery to detect when hot water is needed. Once that flow is detected, power can be switched on to the Inverter to produce power to the Hot Water System (HWS). When the flow stops, the pump stops and the power can be removed from the Inverter.
Of course, nothing is that simple in the real world. As indicated previously, the pump can run briefly to recharge the pressure in the water line, and the pump may only run intermittently when the water flow is low, due to the actions of the accumulator. Additionally when people are using a tap, especially when filling a sink, they may turn it off and on a number of times until they get what they want. This is not a show-stopper, but it does mean that the control circuit has to be a bit smarter than simply powering up the Inverter when the hot water pump runs and turning it off as soon as it stops.