Which tankless as backup?

Glen

here's the system - Greenwood boiler with 1000 gal buffer, 4500 sf roth panels, Rheem tankless (lpg) for domestic, PV & wind, diesel backup (yes completely off grid). Client would like tankless as backup if time away depletes storage. System piping design stolen from HR (thanks). So it boils down to backup selection - any thoughts? System fluid will be treated for inhibitor only. Backup would be for freeze protection only.

bruce_21

Is this a separate tankless for the back-up heat or the one now set for domestic? If its designed as the same unit be sure to use a flat plate heat exchanger to isolate the domestic water from the heating water to eliminate any Legionaires bacteria issues.

Glen

Hmmm -

the client has been talking about something separate - but isolation with FP would work.

kpc_23

considering it would...

be off grid.. Boch makes a tankless that works of of a hydro generated spark and is nat. draft. no power needed.

ChrisHoskin

tankless backup

Regarding the hydro-ignition unit from Bosch, kpc is correct in saying that the unit itself does not require electricity. However, as with any tankless, the unit requires water flow and pressure to run so unless this home is on city water, they will need electricity for pumps to make this run.

If your intention is to re-circ between the 1000 gallon tank and the tankless, the hyro-ignition unit from Bosch may not be a good choice because (last I knew) it is only flow modulating and not thermostatically modulating. In other words, the water heater assumes that any incoming water is 50 degrees F and fires accordingly. I would recommend making sure the unit that you choose is thermostatically modulating - when I was last selling tankless water heaters, a couple of the Japanese units were thermostatically modulating and I would bet that Bosch has at least one available now too. Hope this helps. Chris

Glen

while off grid -

if the wind/PV is not sufficient to charge the batteries then a genset starts. All of this cleverly controlled and from what I see - will be very reliable. Even without the HO there. So yes - we are using circs to zone the backup. Current tankless is a Rheem - which I believe is temp modulating.