Author Topic: Will I break my hot water heater?  (Read 2725 times)

Offline mangyhyena

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Will I break my hot water heater?
« on: September 20, 2011, 11:28:14 AM »
I have plans to add passive solar air and water heating to my home.  My question is about using my hot water heater as a solar batch heater.  I'm not talking about building an external solar batch heater, then circulating water from my electric hot water heater through the batch heater and back, but heating the electric hot water heater itself with solar.  I'll explain my situation.

There is a door on the outside of my house that opens to a small closet.  In that closet sits my electric hot water heater.  Our water heater can be accessed only from that outside door.  The closet is on the side of my house that gets the most sun exposure.  The closet is big enough for maybe 3 adults to squeeze into.  With the hot water heater in there, no more than one adult could fit in there and that adult would be cramped when the door shut.

My thought is to put insulation on the walls & ceiling inside the closet, put a shiny film on the insulated walls, and paint the electric hot water heater black.  I would put a glass door inside to let sunlight in when the regular door is open.  In essence, that closet with the electric hot water heater in it would become a big solar batch heater.

Will I ruin my electric hot water heater if I let the sun heat it?  I would think the closet will heat up to 140 degrees F or so in full sun.  Is that going to damage the hot water heater?

I figured that I could open the outside door on sunny days, then close it at night.  I don't know if adding something to hold heat, like black rocks or sand, in the closet would help radiate collected solar heat from the day into the night, but I'd be able to add that later to see if it works.  Right now, I need to know if I'll damage my hot water heater by getting the closet that hot.

Anyone know if I can safely do this without damaging my electric hot water heater?

Offline Truik

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Re: Will I break my hot water heater?
« Reply #1 on: September 20, 2011, 10:14:08 PM »
I can only guess about any potential damage (the electrical components outside the tank would be of a concern to me but I'm no expert) but one thing that comes to mind is the insulation on the inside of the tank cover. If you were to actually do this, would it be far more efficient to remove the inner insulation and maybe even the tank cover itself to allow the solar radiation to heat the water in the tank?

And if you did, you would then have to relocate or reroute the outer electrical components anyway, right?

(Sorry if this isn't a helpful reponse. Just kinda thinking out loud.)

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Offline NWBowhunter

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Re: Will I break my hot water heater?
« Reply #2 on: September 20, 2011, 10:54:16 PM »
The way you describe this you'd be working against the waterheaters built in insulation. I think I would build a black box at the entrance to the closet and pipe the inlet side of the water heater through the box at the bottom the pipe would then serpentine back and forth from side to side creating a tremendous amount of surface area to absorb heat. The out would be at the top and pipe into the cold side of the hotwater heater. This would preheat the water probably to the point that the water heater would not need to run at all.  It would be your insulated storage vessel.

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Offline d0j0w0

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Re: Will I break my hot water heater?
« Reply #3 on: September 20, 2011, 11:50:31 PM »
I think the thermostat for the hot water tank might prevent the heating element from turning on.  They kind of hang out of the tank a bit. 

I also think NWBowhunter has the right idea about creating a heat exchanger on the outside of the tank.  This would maximize the solar gain and still allow the hot water tank to do its job overnight when the sun is not shining.

Radiator cores can be purchased brand new and plumbed into a system like this.  But may not be suitable for potable water.

Solar heat exchangers are available for purchase.  I'm suggesting using a pre-made system used for roof top solar water heaters and adapting that to your system within the closet.

I suggest looking at conventional solar setups and see how they work, in a passive solar system they use a series of black tanks heated by the sun.  These systems are tested and proven to be effective.  Active solar water heaters use a heat exchanger set up like I'm talking about.  I think either system would help maximize the solar benefit in your setup

During the "winter months"  sun angles may not be optimal for full time use.  I do think your system will work.  Check the prices on hot water tank replacement parts, the heater rods are not to expensive and the thermostat is the only other thing that can break.  If those are cheap I say have a go at it.

Sorry if this post sounds conflicted; I like your idea; but there is more than one way to skin a cat.

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Offline Perfesser

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Re: Will I break my hot water heater?
« Reply #4 on: September 21, 2011, 10:01:09 AM »
Ideally you would keep your insulated tank as just that, insulated storage. The most efficient way to introduce solar heat is to plumb a collector in as a thermosiphon system. No pump or playing with valves. The collector is sort of an extension of the storage tank where the coldest water collects. Once heated it becomes less dense and moves in to the tank, replaced by the cooler water from the tank bottom. The downside is that the top of the collector has to be at least a foot below the bottom of the tank.
 

Good diagram here: http://www.zeroenergydesign.com/Passive%20Solar%20Heating.html
Scroll down near the bottom to Inexpensive Passive Solar Hot Water Heaters
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Offline mxitman

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Re: Will I break my hot water heater?
« Reply #5 on: September 21, 2011, 06:18:07 PM »
As a Commercial HVAC Mechanic i've had plenty of experience with water heaters, solar collectors etc. With that said, I'll try and answer your questions;

Q:Will I ruin my electric hot water heater if I let the sun heat it?
A: Probably not, but the design for the outside of the heater (electrical components) are mostly rated for 125 Deg F max temp, if the temp is up to 140-160...shouldn't be a major issue. They might even be 175 Deg F, some are stamped if you want to check.

Q: From someone else;I think the thermostat for the hot water tank might prevent the heating element from turning on.

A: No problem there, the sensing bulb is in the tank itself just the switch is on the outside of the tank.

You didn't say if your electric water heater is a natural vent style, no powered fan for venting? If it is just a standard heater then you shouldn't have an issue. With the fan you would shorten the motor's life with that high temp in  the area.

If you are going to do that, i would remove the outside shell of the heater and remove the insulation. Maybe even paint the tank black but this will expose all the wiring which will make if dangerous.

I personally would do a simple pre-heater, you don't necessarily need to run a circ pump if you don't want to, a basic pre heater would be cheap to construct...could even put it on the door and run some braided flex hoses at the door hinge. You run your cold water through that first then to your water heater, the more capacity you have the more efficient it will be.

If you started with a glass door you could build it on the backside (inside) of the door, simply box it it and paint it black. I plan on building a simple pre-heater using my old water tank as a storage tank, I just put in a tankless a few weeks back. I'm simply boxing in the tank, paint everything black and pipe it into my inlet for the water heater. Add a couple bypass and drain valves and your good to go.
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Offline mangyhyena

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Re: Will I break my hot water heater?
« Reply #6 on: September 21, 2011, 06:21:33 PM »
mxitman, thank you very, very much for the info.  You just changed the whole design for my closet.  I'll put a large radiator behind the glass.  The radiator will be as big as the glass door.  Might be able to sandwich the radiator between two sheets of glass.

This will be perfect.  It'll let metake advantage of that closet without risking damage to my hot water heater.  Should require less work as well.

Again, thanks.  I was posting a longer response as you were posting.  Made me use the edit to change the whole thing. ;D
« Last Edit: September 21, 2011, 06:31:58 PM by mangyhyena »

Offline vardaman

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Re: Will I break my hot water heater?
« Reply #7 on: September 26, 2011, 11:18:37 PM »
Everyone's response was sort of predicated on there being constant hot and sunny weather. Where do you live?
Open loop systems only work for environments that only get a couple of freezes per year or less, South Florida, Hawaii, etc. If you route your incoming water through a radiator on a cold day then the water will just get colder. And what freeze protection do you have in place? Closed loop systems work well in cold weather because they do not circulate potable water through the collector and sensors tell the controller not to run the pump when the collector is colder than the water in the tank. Your first idea was actually the best because you are raising the ambient temperature in the w/h room. Most of the tank's heat loss, or standby loss, is due to convection to the surrounding cooler air. The closer the air temp is to the water temp in the tank the slower the rate of loss will be. Even on a cold day the added insulation in the room will keep the room warmer and lessen the rate of heat loss. This is the whole concept behind water heater blankets. Don't ever remove the insulation from your water heater unless you want your electric bill to go higher.

Offline LdMorgan

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Re: Will I break my hot water heater?
« Reply #8 on: September 27, 2011, 02:24:52 AM »
Putting the entire electric water heater inside a solar collector would indeed require peeling all the exterior insulation off. But it isn't really practical because the temps could easily hit 170 degrees F, and that would slag the plastic parts of the heater, and maybe even the insulation on the wiring.

That's why I had to plumb my system in with metal--PVC might have melted out.

The amount of heat you can collect will be limited to what goes in the open doorway.

If you want a tank collector (my pref) use an old-fashioned galvanized tank from a water well. If you want a flat plate, make your own from copper pipe & Aluminum sheet.

Put auto water heater hoses on the flat plate collector and make it the door (normally closed), with another door on it (normally open during the day).

That way you can have your collector and your doorway too.

I don't recommend old auto radiators because they are usually crudded up and you don't want to be drinking the stuff that's inside them. Plus they tend to corrode if they aren't full of antifreeze.

With any preheater, you'll get all the heat you collect. It makes no difference (electricity-wise) whether it goes into the water heater as a short shot of very hot water (flat plate), or a longer shot of very warm water (tank).

The electricity saved will be the same either way.

If you go the flat plate collector route, you'll probably need to install a tempering valve to prevent getting unexpected shots of scalding water. A hot shot of (say) 2 gallons of 170-degree water going in the top of the water heater and straight to your shower head could hurt ya pretty bad. And kids even worse.

Even if the hot shot was only thirty seconds long.

With a tank, what would be going in to your water heater would be a longer run of not-as-hot water. Say up to 40 gals of water at 90-110 degrees max. temp.

Don't get too hypnotized by the idea of thermosiphoning. Stand the collector up, glass it in, and run the water line from top of it to the bottom of the water heater.

Ordinary flow will carry the preheated water into the water heater where it will rise naturally.

You'll usually be using the solar hot water mostly during the day, anyway. Probably about as fast as it gets warmed.

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Offline mangyhyena

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Re: Will I break my hot water heater?
« Reply #9 on: September 28, 2011, 01:37:11 PM »
Vardaman, I'm trying to cut out the main problem with solar batch heaters in freezing temps by installing the setup in the closet instead of in a box sitting outside.  What protection does it have from freezing temps?  My home's heat will protect it from freezing, same as my indoor plumbing.  When the door is shut, the freezing temps are outside and this setup is inside.  I'll be using a second glass "door" inside the regular main door.  When the main door is open on sunny days, the sun comes through the glass to heat the water.  When the sun goes down, the main door is closed, preventing the water from freezing.  On cloudy days, the main door remains closed.  Nothing about this is predicated on always having sunny days or never having freezing temps.

If I set up the batch heater between the glass and the hot water heater, it shouldn't get too hot in the closet, at least, not hot enough to damage anything.

I was thinking I could set the radiator up with two incoming pipes, one from the regular water fill line so any water put in to refill the hot water heater comes in hot from the radiator.  The other line could be used to circulate the water in the hot water heater through the radiator and back to help maintain heat during sunny days.  Seems like that setup would act both as a water pre-heater and a solar heater to maintain the temperature in the electric water heater without using electricity to do the heating.

Still thinking this through, but it still seems doable.  Mainly, I like that it can operate during the winter without having to worry about the water freezing.  Batch heaters usually get drained and shut down during winters due to freezing issues in northern regions.  This setup can be used simply by opening the outer door on sunny days and be protected from freezing when the sun is not out by closing the outer door.

In any case, I'm going to go for it.  Thanks for all the input.  I'll post pics when it's done.

Offline vardaman

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Re: Will I break my hot water heater?
« Reply #10 on: September 28, 2011, 03:32:42 PM »
Hyena, I'm glad you are thinking about freeze protection, it's one of the most important aspects of solar hot water systems. The Golden Rule of freeze protection is it should only rely on the laws of physics to work. i.e. Gravity (drainback, draindown), anti-freeze glycol. ICS/Batch heaters rely on a large thermal masses to prevent freezing but pipes that connect to them are still susceptible to freezing conditions.

Remember, many times freezing conditions are also accompanied by power outages. So no freeze protection scheme should be dependent on electricity. Attic pipes can burst in a hurry during freezes, pipes in slabs or crawls spaces maybe not as fast.

Unless you live in the tropics ICS or batch water heaters are best when all of your hot water use is in the evening. They can lose all of their heat gain overnight especially in crystal clear night environments like Las Vegas, even though it's a hot climate. If you are going to manually close a solid door everyday then you might have less of an issue.

It sounds like you intend to add an additional tank into the room with the existing w/h as a batch heater. I'm not totally clear on how you are routing your piping with the pre-heat/radiator arrangement. If you could post or email a sketch it would be helpful. Another strategy employed with passive systems is to put the electric water heater on timer so that it's off through most of the day. Have it set to come back on in the evening.

Hope this helps!

Offline mangyhyena

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Re: Will I break my hot water heater?
« Reply #11 on: September 28, 2011, 08:44:40 PM »
All the feedback really helped me figure this out.

My house is heated via propane furnace, fed by a big tank out back, so a power outage will not leave us cold.  A propane generator is on my hit list this year as well.  After that, nickel iron deep cycle batteries will be purchased as funds allow till I've got myself a big battery bank.  Solar panels and a wood gasifier after that and I've got my home energy needs licked.

With all the sun exposure this place has, a very large solar air heater is also in my plans for supplemental winter heating.  It'll be the can column setup, 4' high and as long as our house is.  I'll post about it soon.  Like the closet, I'll be able to open and close it.  When closed, you won't even know it's there.

I've been studying alternative energy for years.  I'm finally in a position to put that knowledge to use in my life.  Exciting times ahead.

Offline vardaman

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Re: Will I break my hot water heater?
« Reply #12 on: September 29, 2011, 08:18:29 AM »
I have a gas furnace too, but it requires electricity to function.(i.e. ignition/blower)

Good luck! Keep us posted.

Offline Dangerous Dan

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Re: Will I break my hot water heater?
« Reply #13 on: October 05, 2011, 05:00:21 PM »
Sorry it took me so long to respond to this post I saw it a long time ago and didnt reply then.  I am an engineer in the water heating industry and am currently working on some solar projects for our company. 

If this were my set up here is what I would do. 
-Purchase second water heater,(doesnt need to work just hold water)  Strip as much insulation off it as physically possible( a wire brush or pressure washer does a good job but makes a huge mess)  I would use a water heater because they are designed for heating water.  The inlet has a tube attached to the fitting sticking out of the tank that takes the incoming cold water and sends it down to the bottom of the tank.  The outlet pulls water off the very top of the tank where it is at its hottest.
-paint this second heater mat black and position it for the most sun exposure.
-plumb it inline with the orginal heater
-Insulate the crap out of the orginal heater.  Focus on the top.  Insulation is your friend.
-Don't forget relief valves. 


Basically this system preheats the incoming water and requires a minimal ammount of energy to get it up to temp.  Insulate the crap out of your pipes and fixtures and turn the thermostat down as low as you want.  Rememeber insulation is your friend.  If you have the room inside this keeps everything inside and you don't have to worry about freezing.

Offline mangyhyena

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Re: Will I break my hot water heater?
« Reply #14 on: October 05, 2011, 06:30:11 PM »
Thank you, Dangerous Dan.  I'll have to do some measurements to see if I can make room for the second hot water heater.  It sounds like a good setup for my circumstances.