water heater switchgear question

[pvdude]

Planning for the replacement of the 30 year old electric water heater.
Old unit works fine on the solar, uses 6kw for about an hour to heat 80 gallons.
I have it on a timer, heating elements turn on once per day, about Noon.
80 gallons is plenty for one day of our use.
Considered replacing w/ a “hybrid”, heat-pump water heater.
Not doing that, would expect the technology to have a very short life ie:
“warranty period only” Not spending $2-3K every 2-3 years on a WH.

Bought a Bradford-White 50 gallon old-tech electric heater, to be installed if/when the ancient AO Smith gives up.
(It may last longer than I will….)
The Bradford-White is “simultaneous operation”, as opposed to the old AO smith “non-simultaneous”.
This means that the Bradford-White will power up both heating elements simultaneously, rather than one or the other.
I expect to see about 9-10kw load from the Bradford -White, but only for 10-15 minutes, vs an hour for the old one, one time each day.
The PV and solar will handle that fine, as long as I am careful about what else is running on the inverters while the WH is on.

My question is: The old WH uses one single 30A 240V circuit.
I have that circuit connected through a Square-D 30A double pole, double throw, manual transfer switch.
This allows the WH to be powered by the grid, when necessary.

The new one requires two separate 30A 240V circuits. (One for the top element, one for the bottom)
I have a spare Square-D 4 pole 60A double-throw transfer switch I want to use for the new WH.
It will switch the two 30A WH elements between the solar and the grid, so the WH can be powered by the grid when required.
Any problems with this approach?

 

[efficientPV]

Never heard of a water heater that used upper and lower heater elements at the same time. They usually switch from top to bottom. Often people just rewire and run bottom one on solar.

 

[Supervstech]

Planning for the replacement of the 30 year old electric water heater.
Old unit works fine on the solar, uses 6kw for about an hour to heat 80 gallons.
I have it on a timer, heating elements turn on once per day, about Noon.
80 gallons is plenty for one day of our use.
Considered replacing w/ a “hybrid”, heat-pump water heater.
Not doing that, would expect the technology to have a very short life ie:
“warranty period only” Not spending $2-3K every 2-3 years on a WH.

Bought a Bradford-White 50 gallon old-tech electric heater, to be installed if/when the ancient AO Smith gives up.
(It may last longer than I will….)
The Bradford-White is “simultaneous operation”, as opposed to the old AO smith “non-simultaneous”.
This means that the Bradford-White will power up both heating elements simultaneously, rather than one or the other.
I expect to see about 9-10kw load from the Bradford -White, but only for 10-15 minutes, vs an hour for the old one, one time each day.
The PV and solar will handle that fine, as long as I am careful about what else is running on the inverters while the WH is on.

My question is: The old WH uses one single 30A 240V circuit.
I have that circuit connected through a Square-D 30A double pole, double throw, manual transfer switch.
This allows the WH to be powered by the grid, when necessary.

The new one requires two separate 30A 240V circuits. (One for the top element, one for the bottom)
I have a spare Square-D 4 pole 60A double-throw transfer switch I want to use for the new WH.
It will switch the two 30A WH elements between the solar and the grid, so the WH can be powered by the grid when required.
Any problems with this approach?

If the tank isn’t cold, the upper element likely won’t operate 99% of the time. The hottest water will be at the top of the tank, keeping the thermostat from operating.

 

[Hedges]

Power one element from grid and other from PV?

 

[Steve777]

Just curious, why if the B-W heater has 1.6x the power draw as the old AO you think it will take only 1/4 the time to heat up? This should be pretty linear, 2x the power in heats the water in 1/2 the time, etc. Should take about 1/1.6 = 63% of the time, but use roughly the same total energy.

Certainly should work, but other than getting your hot water more quickly (and of course getting you a new tank), isn't going to save you much energy. The idea of running the lower element of the B-W tank off your solar system, perhaps as a dump load, could lead to savings. Especially if your typical hot water use is low enough to live with just the upper element on cloudy days.