water tank as a radiator

Hi
I have to heat a small room.
I got an old solar/electricity water heater with a solar panel and I peeled the insulation.
I painted the tank and it now standing at the room corner.
I got a little pump and now the idea is to put the solar panel on the roof and have a free eco energy.
Here we have 3-4 freezing nights a year and a hot summer.
How can I plump everything so the solar panel will not explode nor from freezing and nor from over boiling?
A link to something similar will be helpful.
thanks! sorry about my bad English..

http://www.solarhotwater-systems.com/

These links may help. You can build wall or ceiling panel radiators with pex very cost effectively, feed heated water to manufactured low temp convector/radiators or un-insulate the tank and put fins and a sleeve on it like people do for diy solar hot air to water and blow air through it.

You could just strip the insulation and let it radiate, but if it is a high performance storage tank, and if you want storage and control, id run a solar pump and a heated liquid pump for distribution.

Drainback will provide simplicity, freeze protection and thermal expansion protection.

A closed loop requires, temp/pressure relief, an expansion tank and antifreeze, generally.

Oops, i guess it would be good to know what other parts you have and what type of system it was. There are a few bits that will be present or not present, depending.  And i see you already peeled the tank. A reminder to me to not try to "help" when i am distracted!

It may already be a drainback type system, or maybe not... a photo of the whole bag-o-cats would be fun.

The temp sensor indicating "tank" or storage temp could be your new room thermostat sensor, and i would place it as you would a  room thermostat. Hopefully a controller came with the equipment. If the control has a high limit, that will be your room temp adjustment, if not an in-line thermostat or hvac thermostat, power supply and relay can interrupt the pump so you dont sweat.

Alternatively, let it go hot, but you will not want it to operate when there is insufficient heat at the collector, and lose your heat.

If you only have 4-5 freezing nights per year, then the simplest solution is just to pump water through the panel on those days.  Granted the water in you tank will get colder, but it will keep the panel from freezing and is a small price to pay for those few nights.

Drain back systems work when designed properly, but they require a much more powerful (and expensive) pump and it might not be worth it for the few times it's needed.  If you already have a suitable pump, then definitely go with drain back.  But if you don't then wasting some warm water a few nights per year is probably more economical.

Peter VanDerWal wrote:If you only have 4-5 freezing nights per year, then the simplest solution is just to pump water through the panel on those days.  Granted the water in you tank will get colder, but it will keep the panel from freezing and is a small price to pay for those few nights.

Drain back systems work when designed properly, but they require a much more powerful (and expensive) pump and it might not be worth it for the few times it's needed.  If you already have a suitable pump, then definitely go with drain back.  But if you don't then wasting some warm water a few nights per year is probably more economical.

Nice. It could work. We do not know the required level of (usually maximum in the north) freeze protection, but its fun to throw it out there anyway.
I would be wary, in a freezing or near freezing climate, especially if not running antifreeze or drainback control, or of bypassing or switching a thermal controller to "on" and walking away. Also, what if you are away or intend to be away from home, or if you intended to switch off your control, but failed to do so before your tank was depleted of sufficient heat to run at freezing ambient temps without solar gain.

The surface temps can be 10 or more degrees cooler than ambient air and freezing conditions can persist into the daylight hours... without solar gain for days. This is a major concearn at or below 0 deg/f, especially at 15 or 20 below. Additionally, the coldest days are when you want the heat and if your tank depletes to say 30 or 40 degrees it could be several days before heat is available again and might be out of use for a week or more depending on sun, but, that also depends on storage tank and collector size, building envelope, etc. You can dump a 120 gallon tank into space heat for most homes or large rooms rapidly, so depending on how it is used or operated, it will probably be a near daylight only heater, rather than the way i usually think, which would be on demand or on call and several cycles worth of storage. Still, dumping it into a building more or less uncontrolled would be gain and im not desparaging the concept.  

The pv-direct differential thermal controllers cannot pump fluid when the sun is not strong enough to keep it from freezing. In effect the water will not be in the collector, even if the control failed in the on mode, or if the switch were left "on" for whatever reason. Antifreeze works excellent, but i do not like to rely on it or be responsible for its disposal and eventual release into the environment, even the "non toxic" variety, which breaks down, but still has additives for anti-corrosion and thermal characteristics, acid buffer, etc.
These details justify the expense of extra power (80w-250w pv, possibly more... depending) and medium or high head pump (same price as a good circulator, unless you have one or the other already) in my case.

I love designing because it always depends! I do have to quit designing or troubleshooting out of thin air, these things without full details, though i cant figure out why i enjoy performing all the wrong tree barking or dead horse beating on these. Its kind of like cross word puzzles, but way more interesting to me.

Thanks permies... my wife gives me "the look" all the time and the people with the cool solar thermal system living its second or third life as a hot stripper, or stripped hottie or whatever, wont even send a photo!

So, ill rag chew and bench race with Peter over the whole thing, which neither of us know enough about! These really are great forums.  

Hmm, I hadn't considered that the pumps might be powered solely by a PV array.

Many (most?) differential solar controllers include a freeze protection setting that will circulate water through the panels when the panel temp drops below some preset temp, but obviously you need some form of power for this to work at night (batteries or grid-tie)

Anyway, you're absolutely right, the devil is in the details.  So far all we know for sure is that Shilo lives in a fairly warm area (near the 34th parallel) with a tank and solar panel of unknown sizes, a 'small' room and a 'little' pump.

I suspect Shilo has picked up a used solar water heating system and I'm guessing the pump came with the system.  If that's the case, then given the location, it's very likely that the system was originally designed as an open-loop direct system, most likely with a differential controller as described above. If Shilo has the controller (unknown) and if it still works, then setting the jumper/switch to enable freeze protection is the simplest solution.  If the controller isn't available, it's possible to build one for less than $10 from an Arduino Nano, a relay module, and a couple thermistors (assuming they can program an Arduino or know someone that can).
Of course now the assumptions are getting stacked up pretty high.

If anyone is interested I could post the necessary code for an Arduino.  I use something similar in my solar space heater.  Mine uses hot air not water, but it would be trivial to add the freeze protection code.

Hi evrybody
Sory abaut my dissapiring, I had a problem login.
Your words and links are very helpfull to me.
The dryback concept is new for me and I like it.
I will rty to attach pics of my stuff-
That the type of tank and collector that common here.
I can choose if the solar collector will contain pipes from copper or from galvanized steel (called scadual).
The tank have no spiral tube inside. Just 2 pipes that enter the bottom. One tall and one short.

Here is my tank in the corner of my room

Here is the pump I bout

And the pumps' papers

Solar Panels (Electric)      =  $1/W and 150W/m2 x4hr
Solar Collector (Thermal) =  $1/W and 300W/m2 x4hr
So other than Solar Panels taking up twice the amount of space on your roof for the same amount of Energy there isn't any difference

Solar Panel (Electric)
1) Can provide the same amount of Heat/Energy if connected directly to a Heating Element.
2) Can provide 3x the amount of Heat if connect to a heat pump (phase change/compressor)
3) Can send excess Energy to the rest of the house electrical system


So to answer you question you will need some type of thermometer-switch that will turn off once the temp gets to 180F
Here is one on Amazon: https://www.amazon.com/WILLHI-Temperature-Controller-Thermostat-Improved/dp/B00V4TJR00/

Im dont asking abaut electric solar panel at all

Shilo, are you in Palestine?

I cannot read the specification for gallons per minute (or litres), ill look it up. You will want to pump fluid to your collector at a rate of .5 to 1 gallon per minute maximum for a 4x8 collector depending on its efficiency and tilt, orientation, etc.  I am guessing the lowest speed available will be suitable. You are looking to get a 10 deg.F rise in temp between the collector feed and return, 20 deg.F  max. This indicates efficiency.

There is a pipe plug on the top of your tank, visable in the photo. That is the place to plumb a over-temerature/ over pressure relief valve. They are common and there should have been one on the tank when it was a water heater. It looks like a 90° fitting with a lever for manual operation. It would likely have had a stem pointing to the floor. You can re-build/ replace that device and place a 1-2 gallon container under it or send it out the wall and point it downward. Make it long enough inside to avoid conducting its heat away and freezing (probably not an issue for you) linked example below.

It is not needed for drainback.

Ther are also over pressure valves for boilers that do not include overtemp, some are adjustable.

https://www.homedepot.com/p/Rheem-PROTECH-3-1-4-in-Standard-Shank-Water-Heater-Temperature-and-Pressure-Relief-Valve-SP12574/205651345

A simple line voltage snap disk (around 10$, preferrably an adjustable one, can control your pump, it goes as close to the collector output manifold as possible, you can tuck it in against the pipe leaving the collector, wedged in the grommet that it passes out of the box or tight against the pipe, just outside. Insulate it well, but do try for contact with the metal of the plumbing. It can also be placed high inside the box.

This is not as efficient as a differential controller and tank and collector sensor array, but is quite workable if controls are hard to come by.

You will want some way of monitoring temps, mercury type thermometers, aquarium temp indicators (the lcd tape kind) cooking probes, non contact types, your hands or other.

Your system may be able to survive mild freeze overnight, if it will thermosyphon in its present arrangment. Feel the pipe feeding (foot of collector usually) the collector in the middle of the night on a cool night. If it is good and warm, it is thermosyphoning. You are losing heat also, though.

The above scenario is unlikely and is also a risk, Peter was good to suggest running the pump at night on freezing nights, but it is also only as reliable as the operator. Controllers mostly do not have this function anymore, as even that is not reliable enough to risk expensive collectors on.

Drainback is likely the best option, it does not require exotic and toxic fluids and gravity is most reliable.

To drain back, the plumbing simply is arranged to drain. The collector outlet is high corner and the inlet low corner. A slight off level, one inch or so over 4 feet width (side to side) produces the high corner. You will want a "T" fitting and a short stalk pointing straight upward. Make it long enough so that when the pump turns on, no fluid spills out. This could be from a couple inches to a foot, depending, insulate it.
You could install a vaccum breaker. You could easily build one. It will keep heat better and avoid a gangly pipe up top.

Fill the tank just to the top. The over pressure valve could be located low. This will keep it wet and free of heavy deposits of minerals. Test the valve often to keep it free and check that it opens easily.

Do you have access to a controller?

Ok, i found your pump. Cubic meters per hour!!! Good thing for calculators.

The maximum hight that water will flow is 6 meters to the top of the collector plumbing, unless it is being operated full to the top.

That circulator will move fluid at a high rate if run full to the top. Too much for a single collector of 4'x 10', even on low setting.

5 meters and a pump setting of medium or high looks ok, max 4 litres per minute. You can experiment with a stalk of plumbing or a hose at different heights to establish this or place a valve inline and adjust it to get a low flow rate. It could wander over time if there are minerals present.

The pipe returning to the tank can be taller like an upside down "U" or right side up as "h" because of the vaccum break if it is used. The whole collector could be raised, but it depends.

If your collector is small, like the ones in the photo, go lesser, like 2 liters per minute and maintain minimum 10 deg.F/ maximum 20 deg.F between feed and return.

There is a range specification on square meters collector area and flow rate. Ill try to post it. Otherwise or correctly, rather the temperature differental is still the target.

You can message me on "purple moosages" and i will help you make it work with what you have, can make or buy.

One thing, the tree grew through your friends chair! And i did learn a new trick... is that fiberglass used to seal the pipe? I know packing is packing, but would have never tried it. Bentonite clay can be added, it is very similar to what we use, as i do not like to handle or have teflon tape or putty in contact with water, for health reasons.

Hi!
Thank you very very much!!!
Yes I'm in palstine. (33-34 parallel)
I'm deside to make it drain back
Am I realy need a controler or anything? I planed to just operate it manualy. 10 dolars are not a problem but I want to keep it simple and I don't want the controller will cancel my plans to oprate the system at sumer nights too.
If it is draiback, do I need the over pressure/temprature/vacum stuff?
The pipes conectors are seeled with natural flux. It's better then teflon because it get bigger when it get wet.
the bottom of the collector is 2.8M above the bottom of the tank.

Manual is fine. To help others, the pump can be dc powered. Then you would use twice as many solar watts to run direct, no controller. The solar panel direct, will operate with about 80% efficiency or accuracy of heat recovery control.

The temp/pressure relief is the safety in a closed system. The temp/pressure relief will operate properly with water service pressure to the tank. Without it, only the pressure relief will operate as intended. Your installs should source boiler type pressure relief, adjustable or fixed pressure. It will not stop the pump.

In a drainback, you will only need a vent to outside or other suitable place for overpressure safety. It has to remain clear, the water heater pressure relief should still be left in place unless you can ensure safety.

Controllers will generally have a high limit and will not run past that temp, 120 deg. F -200+ They stop operating when there is no heat in the collector and ensure that most heat is scavenged.

250 deg. F to 325 deg. F or higher is possible.

The snap disc is a simple way to automate your pump. But, if you are the controller you can run all kinds of testing for best effect in your installation. Fun stuff.

At 28º paralel, and no freeze at all, I have the same sort of idea (dropped burning wood for burrying wood)....
Here are the differences:

- I do not have the material, so I can still choose what to buy.
- I do not think to have the water heater in the room but behind a central wall, and use conduction, and do a WMH! A Water Mass Heater!
- As I will have to heat the water 10 meters above, I think to change the water everyday. I can use it for watering, why not morning shower...

Will the 100ºc max heat be enough to heat a mass?
I don't mind grey days, I am super insulated.
Thanks!

Shilo, what else is the tank plumbed to do? Is the electric heat still operable? A sketch would be useful.

Your pressure relief is kind of tricky. It can be at the top of the collector or one will occur there from vaccum breaker operation. I dont know how the thing is arranged compared to when it was manufactured.

If the hot water outlet (collector return) is a tall stalk inside or will otherwise allow some room, your vent (overpressure) can be above that point. It would be great if it was on top of the tank there and then to a catch can.

Having the collector high enough to fully drain back is important and collectors with parallel risers work fine on their sides.

A sketch of the collector.
It is only metal pipes

The tank.
In the midel an electric heater with thermostat 50-90 cellsius.

Thoughts..

the tank was solar/electric combo.
I don't like the thought about relief inside my bedroom. prefer it on the roof.
Isn't an open vent the best pressure relief?

Yes, an open vent is going to be best. The pressure relief on these are usually located outside on a closed and pressurized collector loop type system.

A pressure relief safety device is a failsafe for pressurized systems or a second safety for an open vented system where it is possible that ice, debris or other obstruction could close the vent.

I like your layout and i was trying to cover it all. Its why i said as long 'as you can ensure safety' as a caution.

I wouldnt worry as long as diameter is ample and obstruction can be avoided without constant tending.

A discharge from overpressure caused by your collector heat would likely be a seep or cough and not a blast, i worry when 5-6kw are being delivered by thermostat control.

A vent in the room would not cause an issue other than humidity (slight) if you are boiling. I use a plastic cap that fits loosely ontop of the vent/fill tube of our thermal storage vat, to stop steam and retain heat and water.

How does it work? Im sure the folk here would also like to hear about your experience of its function.

It looks nice.

Well done for someone asking questions of how to do it! I hope it works well and that it promotes the adoption of more of them.