# On solar hot water via PVs and hot-water heat pumps

(1) Hi Hal:
The Geyser is 60dBA according to my radio shack meter at 3ft away from the back/fan side. But it also makes a much longer 2-sec rumble when it first starts up. Across the room it is 50 dBA.

(2) Hi Marc:
> Eric [sic], how do you have the Geyser piped – through the cold water dip tube?

hot water from the geyser circulates back to a T in the cold water supply to the marathon

colder water returning to the geyser comes from the bottom of the marathon.

This is as suggested for marathons in the geyser 6000-3.0 manual on pg 16

> And what are your solar calcs?

We upsized our PV from 200W panels to 230W (6KW->6.9) so 0.9 peak KW was a \$5400 expense and gets us approximately 0.9*1200 = 1100KWh a year to use for hot water heating.

We use ~26 gallons of hot water per day according to my meter. Assuming heating from 50F to 120F that is 8.3lbs/gal * 26gal * 70F * 365days = 5.5 million BTUs/year => 1611 KWh/year. But… that is assuming straight resistance and not the HW heat pump. So… taking that into account… the geyser is “free” in the summer when the AC is on (and I’m not sure how the math works in the winter with geyser+extra basement heating… but even if it’s COP=1 we are still doing well in a annual/net sense vs the 1100KWh from the PVs.

I welcome match corrections of course!

> Do you have gallons and kWh measured into the tank, including > the resistance elements? Note that my set-up gives up the
> lower element.

We keep the resistance elements off at the breaker except when we have a predicted perfect storm of 3+ kid baths coming up.

I haven’t connected the flow meter to a hobo yet — just manually record the numbers once in a while. We have an eMonitor tracking the KWh of the geyser, but of course the basement also needs extra heat (from our mitsu air-source heat pump) in the winter because of it.

And I often leave the kids bath water to cool off before draining the tub.

Erik

Filed under erik-green, solar