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54067323

join:2012-09-25
Tuscaloosa, AL

2 recommendations

Free Hot Water From The Sun. And It Works Too. ;-)

On sunny days that is, finally completed the installation of a solar DHW system, the system is a combination of a standard roof mount copper under glass DHW solar heater combined with a modified 40 gallon storage tank with a shaft-less magnetically driven 120 volt circulator pump.




The 40 gallon electric heater was modified by disconnecting and removing the electric controls, the dip tube and the T&P valve, then it was with the control lids left off floated within a hardy-board wrapped rectangular enclosure, the space between the enclosure and the tank was back-filled with a two part expanding polyurethane foam, encasing the tank in a closed cellular foam, increasing the existing tanks insulation thickness by a minimum of two inches on the sides and 3+ inches on the bottom and top. The foam also insulates the tank from external moisture allowing me to install the storage tank outside versus inside of the home adjacent to my shop where it is out of the way and out of sight.




From the storage tank the hot (160 degree+) flows through a tempering valve which mixes it with cold water to reduce the temperature to a safer 120 degrees and also minimizes the amount of stored water that is sent to the tankless water heater in the home.




The pump is operated by a standard differential controller that reads the temperature of the water in the panel and compares that temperature to the water stored within the tank, as long as the collector is a few degrees higher the controller powers up the pump once they get close it shuts down.

As for performance, we no longer use any electricity for evening hot water use including a few showers and running the dishwasher and still have 95+ degree water in the tank in the morning lowering the amount of power used as the tankless cranks back on the amount of power it pulls as the input water temperature rises.

This is what it looks like on the TED. At 17:12:15 you can see a sharp drop in usage, that is the A/C being turned off for the test, at 17:12:45 I turn on the master bath shower nice and hot and the usage spikes up to about 15Kw at about 12 seconds the heated water from the storage tank meets the tankless heater and as that water temperature rises the tankless powers down, a small second spike can be seen just after that and that was the result of the tempering valve over-cooling the 160 degree water down to below 120 for a short period of time.




tschmidt
Premium,MVM
join:2000-11-12
Milford, NH
kudos:9
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2 recommendations

Thanks for sharing.

I'm a big fan of alternate energy solutions and domestic water heating is the low hanging fruit. Much faster ROI then generating electricity and simple to install. IMHO water heating should be the first green energy project, then move on the electricity second.

In the summer we heat water with a batch heater in our attached greenhouse:
»www.tschmidt.com/writings/Greenh···tion.pdf

In the winter the wood stove acts as a preheater:
»www.tschmidt.com/writings/2ndgen···ller.pdf

Overview of the entire water system:
»www.tschmidt.com/writings/SolarW···ater.pdf

/tom


scooper

join:2000-07-11
Youngsville, NC
kudos:2
reply to 54067323

Question - what are you using for your tankless water heater ? And how much power does it use ?

I'm using an EEMAX EX95T for my kitchen hot water, but I'm using a conventional electric 40 gallon tank water heater for showers / laundry, etc.



pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast
reply to 54067323

Very nice.
I agree with Tom that solar hot water should be the first option for alternate energy in a home. Electric solar has a really poor ROI when compared to solar hot water.

I do not see a TP valve in your PID? Is there one? Is freezing an issue for your climate like it would be in the NorthEast?
--
The difference between genius and stupidity is that genius has its limits.


TheMG
Premium
join:2007-09-04
Canada
kudos:3
Reviews:
·NorthWest Tel
reply to 54067323

Commercial versions of these things are VERY common in certain countries, you see them on almost every rooftop. Oftentimes the tank is mounted on top of the panel itself, and the water is circulated by natural convection so it does not necessitate an electric pump.

I'm actually quite surprised that solar water heaters aren't more common in the southern US where there is more than enough solar energy and warm weather for systems like this to be effective. There's really no excuse, they should be on everyone's houses. Compared to photovoltaic panels, these water heaters are much cheaper and they pay for themselves much quicker.

If I lived in a warmer climate I'd definitely be installing a system like this, but at my current geographical location in Canada, such a system simply would not work for most of the year.



54067323

join:2012-09-25
Tuscaloosa, AL

1 edit
reply to pende_tim

said by pende_tim:

Very nice.

Thanks

I agree with Tom that solar hot water should be the first option for alternate energy in a home. Electric solar has a really poor ROI when compared to solar hot water.

Not counting labor, I have about $600 tied up in this system, the panel was obtained used off of CL for $75, the Little Giant pump was bought new for $150 and the heater for about the same again off of CL from a guy who had a two car garage full of them NIB, the rest was the copper tubing (my lord has copper gone through the roof) and insulating foam..

I do not see a TP valve in your PID? Is there one? Is freezing an issue for your climate like it would be in the NorthEast?

It’s up on the panel. Pardon the mess I used way too much flux on that inch and a quarter copper and we also spilled some PVC cement as well…




54067323

join:2012-09-25
Tuscaloosa, AL
reply to TheMG

said by TheMG:

If I lived in a warmer climate I'd definitely be installing a system like this, but at my current geographical location in Canada, such a system simply would not work for most of the year.

This is down in Gulf Shores Alabama and as of now this is where I stand hot water wise.




The upper reading is the panel and the lower reading is the storage tank and since there the panel is less than 8 degrees higher the pump is off is indicated by the LED being out.

Haven't had the time to label the controller yet.


intok

join:2012-03-15
reply to 54067323

Another way I've seen this done is building a mirror box around a water heater tank thats been painted black and had the insulation and burner assembly taken off and being topped off some triple pane glass to keep the heat in.

Though I've only seen this setup at a campsite shower.


Beezel

join:2008-12-15
Las Vegas, NV
reply to 54067323

Those are common here in Vegas. They are worth it.



leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET
reply to 54067323

How do you handle excessive heat from the rooftop (besides the T&P valve) ?

Long time ago I participated in a school project on this subject and we ran into issues when the home made solar collector was far more powerful then anticipated and turned from a water heater into a steam generator (we didn't get a chance to solve those issues, the project was shut down as "too dangerous for school kids"). A lot of effort had gotten into making it as efficient as possible

Ideally a T&P valve should only be a second line of defense and not being utilized in normal operation. With a gas or electric powered water heater you would turn the heat off if it gets too hot but you can't easily turn off the sun (one of our ideas was to use either pressure or temperature to close aluminum blinds that would reflect most of the sun light and allow the collector to cool down).
--
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Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom

1 recommendation

said by leibold:

How do you handle excessive heat from the rooftop (besides the T&P valve) ?

Long time ago I participated in a school project on this subject and we ran into issues when the home made solar collector was far more powerful then anticipated and turned from a water heater into a steam generator (we didn't get a chance to solve those issues, the project was shut down as "too dangerous for school kids"). A lot of effort had gotten into making it as efficient as possible

Ideally a T&P valve should only be a second line of defense and not being utilized in normal operation. With a gas or electric powered water heater you would turn the heat off if it gets too hot but you can't easily turn off the sun (one of our ideas was to use either pressure or temperature to close aluminum blinds that would reflect most of the sun light and allow the collector to cool down).

The 40 gallon electric heater was modified by disconnecting and removing the electric controls, the dip tube and the T&P valve

The OP is operating a closed vessel with absolutely no safety devices installed on it. As you experienced with your "steam generator" school project this is taking quite a risk.

averagedude

join:2002-01-30
San Diego, CA
Reviews:
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1 recommendation

reply to leibold

said by leibold:

How do you handle excessive heat from the rooftop (besides the T&P valve) ?

Long time ago I participated in a school project on this subject and we ran into issues when the home made solar collector was far more powerful then anticipated and turned from a water heater into a steam generator (we didn't get a chance to solve those issues, the project was shut down as "too dangerous for school kids"). A lot of effort had gotten into making it as efficient as possible

Ideally a T&P valve should only be a second line of defense and not being utilized in normal operation. With a gas or electric powered water heater you would turn the heat off if it gets too hot but you can't easily turn off the sun (one of our ideas was to use either pressure or temperature to close aluminum blinds that would reflect most of the sun light and allow the collector to cool down).

Over temp, and boiling of water can and does occur in panels when there is no demand and the water sits in the panel on hot days.

Some manufactures suggest using a 3-way valve that circulates the excessive hot water in a copper line in the shade - thus bleeding off just enough heat to stop the panel water from boiling.

Other systems use a "drain back" system that only pumps/circulates water in the panel when a mini-control system senses the need for heating the storage vessel. Water can't boil if it is not in the panel. IMO for small residential systems, drain back systems are the most fool proof systems. With these you don't have to worry about circulating hot water during the winter to stop the panels from freezing.

IMO (and others) PVC should never be used for T&P blow off. PVC is rated for 140 deg F at best. The water/steam at the T&P discharge could be greater that 212* F thus causing the PVC to fail.

There are plenty of web sites (google) that can help out with making the system safer.

In the 1970's lots of people tried DIY water solar panels...some ended up with catastrophic fails.

I am not trying to be a wet blanket on solar installations.
I am all for them...if they are done safely.


Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom

said by averagedude:

Over temp, and boiling of water can and does occur in panels when there is no demand and the water sits in the panel on hot days.

Some manufactures suggest using a 3-way valve that circulates the excessive hot water in a copper line in the shade - thus bleeding off just enough heat to stop the panel water from boiling.

Other systems use a "drain back" system that only pumps/circulates water in the panel when a mini-control system senses the need for heating the storage vessel. Water can't boil if it is not in the panel. IMO for small residential systems, drain back systems are the most fool proof systems. With these you don't have to worry about circulating hot water during the winter to stop the panels from freezing.

IMO (and others) PVC should never be used for T&P blow off. PVC is rated for 140 deg F at best. The water/steam at the T&P discharge could be greater that 212* F thus causing the PVC to fail.

There are plenty of web sites (google) that can help out with making the system safer.

In the 1970's lots of people tried DIY water solar panels...some ended up with catastrophic fails.

I am not trying to be a wet blanket on solar installations.
I am all for them...if they are done safely.

OP removed the T&P valve eliminating that safety device. IMO a very dangerous situation given that overtemp and boiling water can occur.


54067323

join:2012-09-25
Tuscaloosa, AL

1 edit
reply to leibold

said by leibold:

How do you handle excessive heat from the rooftop (besides the T&P valve) ?

The T&P is all there is and that actually meets code, but in reality what really happens is the efficiency of the panels insulation drops as the water temperature increases over ambient, eventually to a point where the panel ceases heating water over the already stored water temperature and this happens at around 180 +/- a few degrees with a 95 or so ambient.

Do keep in mind, these types of panels are rather crude with only a single 3/4 inch sheet of closed cell insulation between the copper collector and the aluminum sheet metal bottom.

Now if the pump failed to run, then I could see the T&P opening under temperature before a boil-off.

I might lose a little hot water, but hey the rain gutter will be clean.


54067323

join:2012-09-25
Tuscaloosa, AL
reply to Jack_in_VA

said by Jack_in_VA:

The OP is operating a closed vessel with absolutely no safety devices installed on it. As you experienced with your "steam generator" school project this is taking quite a risk.

Nope that is incorrect, there is, as required by code a T&P on the collector, a T&P is not required on the storage tank unless it is also a heater and with the thermostats removed and the elements disconnected, my storage tank is no longer considered a heater, hence the reason I could remove the T&P and use it for the collector.


54067323

join:2012-09-25
Tuscaloosa, AL
reply to averagedude

said by averagedude:

IMO (and others) PVC should never be used for T&P blow off. PVC is rated for 140 deg F at best. The water/steam at the T&P discharge could be greater that 212* F thus causing the PVC to fail.

Good point, I will swap out the PVC drain with copper this weekend, after I installed it I realized the white PVC on the roof looks tacky anyhow. I was trying to save a few bucks going with PVC, but considering your information and the fact copper will darken and not look so bad in time it's going to be done.

Thanks


tschmidt
Premium,MVM
join:2000-11-12
Milford, NH
kudos:9
Reviews:
·G4 Communications
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said by 54067323:

after I installed it I realized the white PVC on the roof looks tacky anyhow. I was trying to save a few bucks going with PVC,

Not to mention that in a few years it will also become pretty brittle from UV exposure.

/tom


54067323

join:2012-09-25
Tuscaloosa, AL

said by tschmidt:

Not to mention that in a few years it will also become pretty brittle from UV exposure.

/tom

One more nail in the coffin for the ugly PVC drain.


54067323

join:2012-09-25
Tuscaloosa, AL

1 edit

1 recommendation

reply to tschmidt

said by tschmidt:

Thanks for sharing.

I'm a big fan of alternate energy solutions and domestic water heating is the low hanging fruit. Much faster ROI then generating electricity and simple to install. IMHO water heating should be the first green energy project, then move on the electricity second. /tom

Your greenhouse and the automation is over the top amazing, I love the simplicity of the design based upon what it can do, I am truly quite envious.


tschmidt
Premium,MVM
join:2000-11-12
Milford, NH
kudos:9
Reviews:
·G4 Communications
·Fairpoint Commun..
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said by 54067323:

Your greenhouse and the automation is over the top amazing,

Thanks - I'm really happy with the way the greenhouse and 2nd gen wood stove controller turned out. Fun projects.

Not sure what to do next, electronically.

/tom


JustBurnt

@rr.com
reply to 54067323

How much electric does the circulator pump cost for this "free" hot water? How about the Tankless?



54067323

join:2012-09-25
Tuscaloosa, AL

1 edit

said by JustBurnt :

How much electric does the circulator pump cost for this "free" hot water? How about the Tankless?

Re-read the thread, the answer is already there.

Then again, maybe I misread your question.

The Little Giant circulator pump itself cost me $150, it in turn draws 105 watts of power when running, which the cost of operating is offset by the time the shower heats up.

As for ROI, I will break even on this installation in less than two years based upon the data I am currently collecting from the TED.