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basic plan to connect solar to small pumpHe is the guy that has a bunch of solar panels that he got for cheap, just sitting in the back yard doing nothing.   Hesitant to buy Inverters, Charge Controllers, Batteries.  Trying to figure out what to do with them.

He came up with a great idea for his situation.    His idea goes something like this:

He has Nat Gas water heater.

Instead of buying big electric to plug PV into, buy small POU water heater (10 gallons or whatever).  Then install small recirc pump to cycle water through the gas heater.
The small POU electric heater becomes a sort of PV heat exchanger.

To his idea I would add a mixing valve so that more hot water can be stored above the Gas thermostat set point and a timer so the recirc pump only runs during the day.

#======================================

My extension of his idea is to use a 50 gal (or whatever) gas heater and a 50 gal (or whatever) electric and then with the recirc pump and mixing valve the storage capacity is like doubled or something.

-Dave
gas at night
solar in day
Me:
The water heater manufacturers are working on all this stuff... with electronics...
Their offering will be narrow... and complicated... without any resource except online phone registration and interface after you buy product ...

Cost to the consumer: personal intrusion and lost privacy... expensive to buy and repair.
I like the idea of using gas water heater timer at night, and solar in day.
Dang you provoke more ideas for internet content than can be illustrated and posted..
surge/ advantage DIYCarrington event redux, or some other EMP thingy, Lightning or just something as simple as a power surge.

Manufacturers recommend a surge protector for things like modern computerized washer dryers.  The electronics board is  half a grand to replace.  To have someone come out and replace it in the sticks another half grand.   Best to just buy new and have free ship and install.
problem with gas whme:
Only problem I see with gas water heater it that the thermostat is part of the gas control valve...
The thermostat is single-use,.... and if it trips... then *$150 gas control valve has to be replaced.
There is no interface with outside source of temperature.
solve gas water heater problem
180 degree eco
Is 190 ECO standard for all of the gas valves?
195 on intellivent

http://www.whirlpoolwaterheaters.com/learn-more/gas-water-heaters/how-gas-water-heaters-work/

"An energy cut off (ECO) switch is mounted inside the probe attached to the back of the gas valve and extends inside the water heater. The ECO functions as a high limit switch. If water temperature inside the tank reaches about 190F, the ECO disables the water heater. The entire gas valve must be replaced if this happens."
electric eco 150Me

Electric thermostat is usually 170-180 .... I think.... keeping it above the TP release temperature.
Maybe 150 is correct... but all thermostat calibrations are approximate... 150 would explain why ECO trips yet TP has not released water... which is common occurance.
two circulation pumps

I was thinking about two two circulation pump ideas some more today.  Both the small POU electric with gas heater and the mid size electric with gas heater would require a mixing valve if there is a circulation pump in the design.

There also has to be a scheme to not turn on the circulation pump unless the water in the electric tank is at or above the gas thermostat setting or the circulation will only serve to pump cold water into the gas heater, then the gas heater will turn on a burn up gas to heat that cold water.  Not exactly what I was looking for.

Also,
   The additional storage provided by the GAS water heater is limited to the temperature increase from the gas thermostat setting (lets say 120F) and the electric thermostat setting (lets say 150F).
That only gives 30F storage ability from the PV array.  

My monster 105 gallon stores energy from 60F to 150F, which is a rise of 90F, about 25KWh of storage.  The entire tank can be at 60F and if I need a little hot water I run my controller timer for 1H and the top is toasty hot in one hour.

Maybe these two new ideas are not very practical except for a very small system.    Gas water heater doesn't make a very good solar storage device.  Electric is way better, and it has the flexibility of multiple elements (top/bottom) to heat from the top instead of heating from the bottom like you get with gas heater..

Maybe something can be done with a timer on the gas side to heat the water up to usable temp before use and leave it off otherwise.  complicated.
gas water heater timer figured into equationme
Let me feed shards of data into the idea machine ... and wait for results !!

We can get 2 different control points from ordinary 2-element electric water heater.
http://waterheatertimer.org/images/Water-heater-element-wiring-led.jpg

They make gas water heater timer that toggles gas valve from vacation (50 degrees) to 135 degrees.
But I think the control is problematic since it resets to regular temperature when power is stopped.
http://waterheatertimer.org/Jeff-Davis-gas-water-heater-timer.html
http://waterheatertimer.org/Hibernator-gas-water-heater-timer.html

I always wondered if ordinary electric water heater thermostat could be installed onto the inner tank of gas water heater and provide some type of electrical control... for example turn off power to recirculation pump... we would cut through outer shell on gas water heater... and epoxy small clip to steel tank that holds thermostat... drill 3/4" hole to run conduit connection and wires  ...  then cover thermostat with insulation and add salvaged cover off electric water heater from recycle center.

Obviously the big manufacturers are installing thermistors in place of thermostats... but the circuit board interface for tiny thermistor voltage becomes problematic for DIY

2) Problem with the gas water heater timer:  only works with old style gas thermostat... and there are only two settings... vacation and 135.
You can add any 120 volt module into outlet located on top of unit... so adding relay would be easy install.

3) We could control gas water heater timer with thermostat located on electric water heater
With your thermostat sensor mod on the gas heater and the gas heater timer that goes from 50F to 135 you could argue that you have the ability to make that 50F to 135F timer into a 50F to whatever temperature (up to 135F of course).

That could have applications for people that dont want 135F as their ON set point.
heat pumpme
quote from me Speaking of water heaters. Seems like you could build miniature heat pump water heaters for the kitchen that would be able to sync up thermally with the fridge and synergize. The waste product from one is the feedstock for the other. That's brilliant. I've got a relatively small kitchen myself but you could tuck a smartly sized square water heater in there somewhere. They'd be great for L shaped kitchens where the ergonomics of the corner space make storage a hassle.
http://www.greentechmedia.com/articles/read/whirlpool-launches-the-wi-fi-smart-appliance

88 cent per month energy house;
http://waterheatertimer.org/pdf/House-design-with-low-cost-energy.pdf
small tank
pump heat to gas water heater

*****************

I was doing more thinking about the logistics of the small electric tank acting as a heat exchanger pumping in PV power for a larger gas powered tank.   The one with the recirc pump.  

The ideal scenario is to have both the electric and gas tank cold at the start of the day so its ready to accept the PV power from the array. 

Electric tank has a thermostat and ECO. 

Recirculation pump turns on when the electric thermostat reaches satisfied set point.   Turns off when cools off.  This effect transfers heat from the small electric heater to the gas tank away from the electric tanks element.

Gas tank has thermostat+ECO mod to top of the tank so it turns the entire system off (PV array disconnect using high amp DC relay) when that thermostat is satisfied. 



Not sure at this point if gas heater upper thermo satified should override the recirc pump and turn it off.  Im thinking NO at this point.


If either ECO trip it disconnects the PV array via the DC relay.
ECO trip means something has gone wrong. So it goes into the failsafe condition and stays there until manual intervention with ECOs reset.

Gas "timer" / control valve also needed to let the user to fire up the gas heat manually.   The manual over ride timer ability goes along way for user acceptability.  Warm water is fine for washing hands, pots & pans, feed to dishwasher, cloths washer, etc.   ....

.....   Its the cold/cool/luke warm shower part that is not going to be popular/dangerous with Legonella.    With temperature awareness of what is going on in the gas heater (Like I have with my water heater) its easy for the user to determine if they should fire up the gas for 15min, 30min or an hour before they have their shower.

But like I said the idea thing is to minimize gas use and let the PV do its job.  Also low temp in tank minimizes standby loss when heated with gas.  Its like tankless efficiency (with respect to standby loss) but not using a tankless (of course).

Mixing valves are a big plus in any PV solar system.

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