Hot water & short trip water buffer

Hot water & short trip water buffer

As it was time to add some luxury to the living unit. Hot water was on the to-do list this week.

As our water consumption merely exists of use water for eating, drinking and personal hygiene. There is no need for a 30-40 liter energy and space consuming hot water boiler to take long showers with three persons. Therefore a 3 liter 24VDC 400W Elgena boiler is installed directly under the kitchen sink. This small boiler will mainly be operated over the solar energy surplus or can be manually overridden in case it is needed.

Our battery state is constantly monitored by the Victron BMS 702. Standard these are normally programmed that an alarm contact closes when the battery voltage drops below a certain set value (factory value 50%).

The mode of this relay however can also be inverted. Meaning that it closes once the battery voltage reaches a certain programmed high voltage threshold value. Indicating the battery is full. Normally this voltage threshold would trigger the MPPT algorithm to provide a lower amperage output than the solar panels potentially could deliver at that point in time. As it regulates from bulk phase to absorption and finally float.

The inverted alarm signal will now switch a high amperage relay, increasing again the demand from the MPPT to its max at that moment to heat up the water in case the internal boiler thermostat demands so. In this way we are fully harvesting the solar energy and not straining the battery unnecessary with unloading cycles to make up hot water. Once the demand decreases again the MPPT wil resume absorption and float phase again depending on the programmed values.

When we drive the truck, the 55A alternator is coupled to the living unit via a Citrix 120CT smart relay. Once the starter battery is topped off again, it senses the increased voltage level and automatically connects the living unit battery in parallel. Now again the same will happen automatically for the power supply to the boiler. As the BMV will see the increase in voltage (if not already there). The whole play of signals and relais switching starts again. The whole control is automagically over the voltage sense of the board system.

A second item installed is a 22 liter water canister if we only set off for a short(er) weekend or trip. Having to fill up the big water tank on board is not always convenient. The possibility of filling and connecting a 22 liter canister therefore eases the operation of collecting water practically at any faucet location. And balances the water inventory to the actual use case for these shorter trips.

A 3-way valves makes the selection of main tank or canister / main tank fill. Self closing Gardena couplings should make it a 'spill free' operation. In all situations water passes the combined PureOne carbon & micro filter at least once. When filling the main tank and when using water from either the main tank or the canister.