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Old 10-24-10, 08:29 PM   #1
Patrick
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Default Alternative Energy Water Heater in Series?

Now that I have my hybrid heat pump water heater installed I'm thinking about putting the old water heater in series before the hybrid and heating that water with alternative energy sources.

So the water flow would go from the water softener into the old (modified) heater, then into the hybrid water heater, then into the house. The idea being that water heated by the old heater doesn't need to be heated by the hybrid and therefore won't use any power I have to buy from the grid.

I was thinking of buying two 500W 12V elements and installing them in place of the original 220V elements. I would then power one element with a wind turbine and the other with some PV panels. Do the members see any problems with this plan? Thanks.

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Old 10-24-10, 11:06 PM   #2
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my understanding is that the 12V elements can be quite expensive. Other then that the idea would work and I've heard of quite a few home built wind turbines using water heaters to dump their excess power when their batteries are full.

if you're looking into water heating though solar to preheat the water in the tank will be far more efficient both power and cost wise then solar electric or wind to electricity then to heat
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Old 10-25-10, 12:31 AM   #3
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Heat pump water heaters have a hard time getting water heated those last few degrees, that is why they are limited to 130 degrees and sometimes use resistance elements to get that last little bit of heat in there so I would say to turn down the temp of the heat pump water heater and use it as the pre-heater, or just run the heat pump water heater off solar, it would be a larger investment but it would be cheaper then buying enough PV to run a resistive element.
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Old 10-25-10, 09:17 AM   #4
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Thanks for the replies. I don't really want to mess with solar hot water (due to complexities and aesthetics at my location) but would like to get into PV and wind (I just won a HAWT on Ebay!).

Does anyone know what would happen if I hooked up 12V to a 220V resistive heating element? I'm wondering if I can just use the old elements I already have. Thanks.
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Old 10-25-10, 09:24 AM   #5
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Quote:
Originally Posted by Ryland View Post
Heat pump water heaters have a hard time getting water heated those last few degrees, that is why they are limited to 130 degrees and sometimes use resistance elements to get that last little bit of heat in there so I would say to turn down the temp of the heat pump water heater and use it as the pre-heater, or just run the heat pump water heater off solar, it would be a larger investment but it would be cheaper then buying enough PV to run a resistive element.
If I put the heat pump as the preheater and it's night and calm (no wind), won't the water in the second heater get cold, causing us to have to run the water until the hot flows through from the heat pump - about 50 gallons worth? Seems like that would take a long time. I guess I could insulate the heck out of the second heater to keep the heat in there.

The heat pump is 220V. To run it off solar PV I would need a lot of panels and a large inverter.

Last edited by Patrick; 10-25-10 at 09:27 AM..
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Old 10-27-10, 11:11 AM   #6
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Quote:
Originally Posted by Ryland View Post
Heat pump water heaters have a hard time getting water heated those last few degrees, that is why they are limited to 130 degrees...
It's true, the last few degrees will drag your efficiency down.

I have a tankless water heater and I run it at about 110-115. I adjust it so that when I take a shower, I use all heated water, and don't mix in any cold. My reasons are to reduce scaling, but I have found that I can get along just fine with lower water temps.

I think you'd do well to reduce your water temp in your hybrid heater. Better efficiency.

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Old 10-28-10, 08:56 AM   #7
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Pre-heating your water is a good idea, but not cheap..I'm using 500w of PV to add some BTUs to my hot water..

http://ecorenovator.org/forum/solar-...eat-water.html

http://ecorenovator.org/forum/projec...r-project.html

It might work pretty well on an old hot water heater that has good insulation.
My system is leaky, sending heat up the flue, which you don't have..

Some cheap thin-film panels could work for you at higher voltages,
so you may not need to invest in 12v elements..
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Old 10-28-10, 02:29 PM   #8
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Quote:
Originally Posted by Patrick View Post
If I put the heat pump as the preheater and it's night and calm (no wind), won't the water in the second heater get cold, causing us to have to run the water until the hot flows through from the heat pump - about 50 gallons worth? Seems like that would take a long time. I guess I could insulate the heck out of the second heater to keep the heat in there.

The heat pump is 220V. To run it off solar PV I would need a lot of panels and a large inverter.
Your 2nd water tank would be a normal hot water heater that would bump up the temp and keep it there, so yes if it was calm and at night it might run a little more, or you could have it on a timer and not run it at night at all unless you take alot of late night showers or do other things that call for alot of hot water late at night.
as for needing more PV and a large inverter to run the heat pump... look at the specs of the heap pump, something like 500 watts? that is a pretty small inverter, look at the specs on yearly energy use and realize that those specs are for heating water to 130F and what I'm talking about is heating it to maybe 110F or so and at that point you could almost get away with a small under counter 5 gallon tank style water heater to bump the water temp up the last 10-20 degrees as you use it.
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Old 10-28-10, 04:40 PM   #9
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Quote:
Originally Posted by Xringer View Post
Pre-heating your water is a good idea, but not cheap..I'm using 500w of PV to add some BTUs to my hot water..

http://ecorenovator.org/forum/solar-...eat-water.html

http://ecorenovator.org/forum/projec...r-project.html

It might work pretty well on an old hot water heater that has good insulation.
My system is leaky, sending heat up the flue, which you don't have..

Some cheap thin-film panels could work for you at higher voltages,
so you may not need to invest in 12v elements..
Xringer, thanks for the reply. Since you seem to be into electrical a lot, do you have any idea if I can connect 12V DC to a 220V AC heating element (the submerged one in the tank)? Or could I connect a higher voltage DC to the 220V AC element?
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Old 10-28-10, 06:00 PM   #10
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A 3500 watt heater / 220 volts = 16 amps.. Means the heating element will warm up
and drift to a resistance of about 13.75 ohms..

12vdc / 13.75 = 0.9 amps.. Or, about 10.5 watts of heating.. Not good enough..

Now, if you had about 600watts of PV, and wanted to deliver it into a load
resistance of 14 ohms, you could use about 6.5 amps at 91 volts...

Anyways, you need to match your load to your PV power source..

~~~

If you have one of these, (or a few of these wired in parallel),
Micromorph Tandem Thin Film Solar Module 130w, Micromorph Tandem Thin Film Solar Panel 130w

Spec:
* Pmax: 130W
* Vmp: 101V

101 volts at the max power point (doing 1.3A) means you need a load
resistance of 77.7 ohms, if you wanted that 130w..


Just remember, any time you start using DC over 48 volts, you can get shocked.
Just one mistake with a 101v panel could KILL you..

Holding your VOM lead tips with your thumbs and forefingers
to measure the panel output, will (even in weak sunshine) stop your heart..


On the plus side, (pun intended) you can use smaller diameter wire at these voltages..
And not suffer big line losses.. That's why I'm using 70volts these days..

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