Ideas for solar hot water tank???

We got an incredible deal on an incredible house, but primarily because the luxury bathrooms got gutted including the hot water heaters. My wife heard cold water was good for hair and skin, but after 2 weeks of only cold water showers, I say screw this, so it's time to build a solar hot water heater. At this point anything above just cold will be like a luxury shower for us.

We get no freezing weather, so a thermosyphon is the name of the game. The collector part will be a snap, as will supporting any size tank I want. If I go gravity fed, then a large tank is also a snap, but my concern is plumbing the cold water, since at the end of full sunny days the water may be too hot and need cold added. How would low gravity pressure combine with municipal water pressure cold side work? Due to the simplicity I'd prefer gravity fed...maybe a 2nd tank for the cold also gravity feeding the shower plumbing is the answer.

If gravity fed won't work then I need something cheap for a tank that can handle municipal water pressure. Old hot water tanks are probably hard to find, so I'm open to all suggestions.

John

If you are going to use city water to feed the tank, won't you simply have pressure in that tank, equal to the cold water supply ?? Then, you won't have conflicting pressures. Can you find something like metal SS beer kegs in San Jose ?? Plumbing up an alternate tank won't be difficult, for use as hot water tank.

There are new tanks, so, you have electric backup when the rainy days set in. I HAVE seen old tanks, sitting in scrap yards, as I tour the country in the Petri Dishes.

As a rough rule of thumb figure 4.3psig for every 10 ft of head, ie liquid level above your delivery point. Then measure the pressure of your municipal source at the tap. If its within a 10 to 1 ratio ( pipe pressure to head pressure) you should be ok controlling it with a standard valve. Anything higher and you might need to insert an orifice to induce a pressure drop to get in a better range. If you need to do that, post your pressures and I'll calculate you an orifice diameter.

Sorry about the US units...but it's what I keep in my head for statics and plant stuff.

Harold,
I can pick up a 300-500 circular tank with a flat bottom and smaller diameter flat top for under $100 new....some glass reinforced plastic that I've seen on some rooftops as water heater tanks and I looked up a couple of years ago and could handle the temps. No way those are good for much more than just the pressure of gravity with the flat top and bottom, but the price and the ease of just using a toilet float valve to keep full sure is appealing.

GMuseless,
That's just what I was looking for, and being from the US, those units are fine. I think 10ft may be right around the number, so I'm in the ballpark. As far as orfice, wouldn't a valve on the cold water side handle that part?

Now a quick question about plumbing. Despite an abundance of fresh water here, muni water is getting a bit pricey AFAIC, so until I rig rain collection too, I'd keep the piping to the kids side (water hogs) somewhat restricted. For when the wife and I want some luxury though, or just short spurts like power rinsing or whatever, would it help my gravity feed hot side by using larger diameter pipe to the shower, or does the flow restriction at the shower itself provide an overall controller so nothing above say 1/2" or 3/4" cpvc help? Should I go with metal pipe in case my hot water gets closer to boiling point?

Now you're getting fancy. A valve should give decent modulation if your supply isn't much over 50psig. Now, remember standard plumbing is designed for those supply pressures. You're working with a much lower pressure, so you need to account for losses, etc. Another rule of thumb: 3/4" inch pipe will have 1/4 of the losses of 1/2" pipe. Take a look here for a better assessment: http://www.engineeringtoolbox.com/pressure-loss-plastic-pipes-d_404.html

water weighs 8lbs/gallon so 500 gallons is like a chevy suburban, on your roof?

my 125 gallon solar storage tank made a dent in the concrete floor, you cannot put that much weight overhead, especially in earthquake territory. jmho.

I don't know about fancy, but I don't want to go to the trouble and end up with plenty of hot water but just drips in terms of flow. I've never lived where water isn't abundant, so those flow restrictors always come out of the shower massage. Cold water shower or low flow shower would be a hard choice for me, so thanks for confirming that I want big pipe on the hot water side.

This is going to be fun, and it needs to be a down and dirty project. Now that my move is essentially complete, I've got to get back to building some bikes. My high efficiency 2 speed hubbie is screaming to try a mid-drive rig, and there's my 200 mile on a charge mountain climbing ebike to finish up and test too. I need about three 20 year old clones of myself with remote on/off switching, so I can get everything done, but put them on ice after the work day is done to keep them out of trouble.

John

dnmun said:

water weighs 8lbs/gallon so 500 gallons is like a chevy suburban, on your roof?

my 125 gallon solar storage tank made a dent in the concrete floor, you cannot put that much weight overhead, especially in earthquake territory. jmho.

Click to expand...

I appreciate the concern, and I may have been overstating the size, but I seem to recall eyeballing tanks that were 500 and 750 liters, but I abandoned the idea at our old house due to no structure to support a good size tank up high enough. This new house was built by some renown german architect for his wife, and is a couple of decades old and is the first house I've been in here with no cracks from quakes. All of the main walls are thick concrete that extend up above the roof line, a bit difficult to explain, but the structure is more like a commercial building and built to withstand a serious earthquake. I've got a couple of good corners to choose from to support a water tank.

There's also some decorative concrete corners that may be high enough too which already have some huge clay planters that must weigh a few hundred pounds each. Now that I think about it maybe I can empty the dirt out of those, and hide 2 or more tanks in those.

Going gravity fed opens up some nice options as far as hiding a big water tank, including just welding a rectangular one out of steel to fit right on the exposed concrete structure and look like part of the house once painted. Now I need to price steel and an appropriate maintenance free coating.

Just sayin, the showers we had in 'Nam, were aircraft drop fuel tanks. They were about 2 feet above our heads, and, had the large round shower heads, with the trip valve. We got plenty wet, and had sufficient force to wash off the mud and other debris. Unless you need the driving force for a water massage, gravity alone is very sufficient.

I'm trying to get our system working solar as well.

Here is a drain back DIY system design I am fond of. The tank design is particularly well suited to custom applications,for instance if you need to engineer for lb/sq. ft. roof loading you can design a shallow, wide base tank. There are a few of these in use from what I have been able to find, but high temperatures (extremes) could cause premature liner failure, I believe that is addressed in the design notes - you can engineer a dump load easily enough. You would need to adapt this to a gravity/thermosyphon if that is the route you want to take, but it might be something to consider. This site has all sorts of decent technical DIY projects of the sort, maybe something else will be of use to you there,

http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm

small pumps will get the water from storage up to the collectors on the roof. then drain back into the tank. use another pump off the hot side of this non pressurized solar storage tank and plumb that directly to the appliance. if you need line pressure cool water to temper then just use a regular mixing valve to add enuff cool water to temper.

use a regular hot water tank for storage, and buy the biggest and add insulation, solar panels in the states have been dirt cheap for decades. i bot a bunch on CL over the years for less than scrap metal prices. maybe you can find some there, but i gotta feeling they are valued more down there than in the states. good panels are a lifetime investment.

for the pumps you could use your solar PV panel to run the circulating pump during the day when the pump would be needed. and it only takes 30 watts or so for the small inline circulating pumps which would give you enuff pressure to move the water.

http://homepower.com/view/?file=HP58_pg30_Bocci

thermosiphon systems may be cheap, but you don't get much from them. for the piping away from the box, don't use copper pipe, use PEX tubing instead since it won't lose heat as fast and is so much cheaper than copper tubing. since this is thermosiphon it has to use the double insulating layers of glass, which will fog up if not thermopane, and two layers instead of one reduces thermal input.

drainback in the northern states is best, the system i built uses drainback but it is two stage with heat exchanger from the glycol in the panels in a nonpressured drainback tank to the pressured domestic water loop back to the tank.

i use PEX for everything anymore.

I know that you probably want to have a very low budget for this, but have you looked into evacuated tube solar collectors. The ones I am thinking of have no fluid in the tubes. The heat is collected and then stored in a manifold using a phase change medium. You could put up one small one on the roof outside the bathroom, run one pex up and one pex down, a safety relief valve and you're in. Phase change medium stores heat at a constant temp. Small storage is there. It would probably be expensive to ship but you wouldn't have to use all the tubes that would fit in the manifold.

I did a project once on alternative sources of energy in 8th grade!!
so that instantly makes me the most qualified person on this page to comment, don't listen to any of these noobs
^ jk jk i do not want anyone coming to my house with pitch forks

But you may want to get a tank (like the one used for a water heater) 50 gallons should be good, then you want to put a pipe thats connected to a solar panel outside and have that same pipe go through the solar panel and back to the tank. You would need a pump to take the water from the tank and make it go to the panel.

I did a pretty terrible job explaining it but here is a pic for you
http://www.energysavers.gov/images/active_closed_loop_solar_wa.gif

note: you do not actually need a solar panel to heat the water as it passes, just something really dark.

I had ideas about that after I got rid of natural gas. Most of what I found online is gone now.

http://www.builditsolar.com/Projects/WaterHeating/FSECFS36Batch11349.pdf

This one notes you can't use it in a pressurized system, but as Harold said, gravity from above is good. I don't know if there's a physical problem of going with a normal tank with solar heating it. http://www.thesietch.org/projects/solarthermalpanel2/index.htm My gas water heater was on the south side of the house and I'd considered just finding a way to heat that up. Instead I wound up with a 120 volt 19 gallon electric which is all I really need. Light enough to carry under one arm when I brought it home.

Here's a hybrid approach I've considered I could add to mine and would work in the pressurized system.. The batch collector is on the roof, it feeds the little tank which only needs enough electricity to keep it from cooling. http://www.squidoo.com/solarhotwaterbuild Note they have the link to buy the setup ready made. http://www.siliconsolar.com/solar-hot-water-products.html

This morning I wake up interested in figuring out a method to use a non-pressurized tank and collector that feeds into a pressurized line....something along the lines of a scuba regulator working in reverse. I guess I should get out and scrounge some kind of reasonable size tank that can handle line pressure instead of trying to dream up the impossible.

I don't see any reason for a nonpressurized tank feeding the pressure system. The water has to come from the pressurized system, right?

Run a line to wherever you want to heat it, then that feeds into the house.

Water heater I built over my homemade Propane tank wood furnace. See how it's plumbed and just enclose it in an insulated box. House pressure will move the hot water into the house. Just insulate the lines out of the box to the house.

As we received our truckload of stuff tonight at work, I checked the trashcans for packing material to ship something, and look what I found:




I don't have any time to do anything with it yet, but this is the key thing I was missing to attempt a solar water heater--storage. I may have to repair it, as there is hardwater corrosion at the base, probably from a leak, but that should be relatively easy (maybe time consuming).

However, if the electric part works and the tank is intact (not sure how to tell yet, until I attempt to fill it), I may well just swap it for my gas heater that is actually in service, and turn off the gas--that would save me $20 or so a month in fees just to keep the gas on (depending on the season, as it is more expensive in winter, naturally).

Then I could use the gas heater for storage of the solar-heated water, and then only use the electric heater for times that there isn't enough insolation to heat the water.

Or, more practically...I can just turn off the gas anyway, shutoff and drain the gas heater and let it sit unused as-is. Then connect the electric heater up to the AC power, with a breaker/switch so I only turn that on if there isnt' enough insolation to heat the water.



My original placement idea to minimize impact on the house (rental) was to place the tank itself either on or just beside and below the edge of the nearly-flat roof of the back room, and place the solar heating water "coils" above it's level (on standoffs above the shingles if necessary), so they can gravity feed down into the tank, so I don't have to leave the system pressurized to work (this means I don't have to worry about a rupture in any of my hacked-together stuff flooding the house :lol: ).

The tank would then gravity feed down into the bathroom window, so I don't have to make any holes in the house. Almost all of my hot water usage is for showers anyway, and the rest is for washing dishes and other things in the kitchen sink (on the other side of the wall from the bathroom), with just a little bit for clothes washing every couple of weeks or less often.


The solar heating method I haven't decided on. If I had two tanks I would use one in a reflective trough, and have it feed the other as insulated storage. Since I don't, then either the single tank has to be heater and storage, which is going to mean having to manually go up and cover it with insulation as it gets out of direct sunlight for heating, so it stays hot longer, or I need to use piping to contain the water to be heated.


The former means it's easy to get the water in the tank, as it's already there. The latter means I need a way to get the colder water out of the tank and into the heating piping, and the hotter water into the tank out of the heating piping. I have some washing machine solenoid Y-valves that can be used to switch water flow around and merge piping together, and I also have the washing machine pulley-powered water pumps, easily driven from various motor possibilities if necessary.


Piping to heat the water in...about all I have for that is some old PVC pipe that has seen some better days, and large-size water pipe. I'm not sure if it's usable for supplying water, or if it was meant for drainage only. I'd love to use copper pipe but I dont' have any (except one small coil of 1/2" tubing, which may be even smaller diameter than that). I also have a bunch of EMT conduit but I figure it would be a really bad idea to use that for water.


Anyway, that's my pondering for the moment, with more to come as I have time. Sketches too, if I get time for that. Pics of the materials I have available, if I can dig them out.

pressure test it before you put high pressure water in it. in fact you may want to turn off the water to your house while you are gone from the house for a period of time until you can be certain it will not rupture on you. electric water heaters last for up to 30 years, and gas water heaters go in as little as 5 years, but if you are not home when they blow out, the damage it does is severe. in fact outside of fire, nothing is worse damaging than a ruptured water pipe or water heater because it usually happens when you are not home and the flooding is extensive.

more likely that someone decided to replace the tank rather than buy an element, or for a larger one or even converted to gas for cheaper water heating.

you can verify the element continuity with an ohmeter.

Perfect, PERFECT. Now, you can do a show and tell.

First thing is to strip it down. It all comes apart really easy. The insulation may be stuck to the tank, but, it's not a problem. Do NOT remove any E parts.

Once stripped down, look for a "track" where the leak ?? might be coming from. Usually, a leak will be in the seam, where a dab of flux from welding, has plugged a pin hole. Later on, it just can't hold pressure. I have done over 2 dozen of these tanks. Most had the same problem leak, but not all. If it is in the side or bottom, a gooped up sheet metal screw will work fine. Of course a Mig welder will do you just fine, also, BUT, you could damage the epoxy-glass lining inside the tank, so, think before you act.


If you can find a leak, hook a garden hose to the inlet and fill the tank. THEN, cap off the outlet and let the house pressure pressurize the tank. IF it eventually leaks, you get a fine mist or pisser. DO NOT pressurize with air. IF it blows, you COULD have consequences. Tanks are filled with water to test them, so they do not blow. PERIOD.

If there is no leak, you are golden. 8)

Scrounge around for a standard glass sliding door. It is perfect for a solar "Breadbox". While looking and asking around, open or remove the bottom drain pipe, so you can use a wire coat hanger, or, cut a piece of E conduit, on a long sloping cut, to use as a scoop and scrape out the lime deposit from heating the water. You MIGHT be lucky and only have a small or no buildup. This is why E heaters go bad. The lime from the water gets deposited on the elements and they can not get water cooled, so they burn out. They also get to slough off some of the lime coating on the element, until you get a large deposit build up in the tank, which will insulate the lower element and cause IT to burn out.

You will need to run a hose to one upper nipple, to flush the crap out the bottom hole. That's why it might be better to remove that drain pipe.

After the tank is clean and leak free, check continuity on both elements, to see if they are shorted-grounded to the tank. If not, you are more golden. Leave all the E hookup in place. You can use it later, if needed, on rainy ?? days. You lay the tank on it's side, with the elements on the bottom side. When you hook up the tank, the elements work just as well as upright tank. THIS DOES WORK. I have built more than 6 horizontal systems, and hung the tank between the floor joints in the basement of houses.

IF an element is bad, buy a new one, that is DOUBLED BACK on itself. It will look like someone has taken the long loop and bent it in half. This is even better than the straight type. It's shorter, so, it works equally as well in a horizontal system.

Now, you can scrounge pieces of 2 X 4 to build a box. If you have other ideas, that's fine. If you want to build the breadbox design. Let me know if you want some ideas.

The most important thing is to keep the tank lower than your other tank, inside the house, so hot water can rise and heat the water inside the house, as you are not using hot water, or, you need to plumb a hot water pump into the system.

Here's all the technical info you'll ever need. Copper is expensive these days, if using PEX, you only need to make it a little bigger to have the same effect.

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm

John in CR said:

Now a quick question about plumbing. Despite an abundance of fresh water here, muni water is getting a bit pricey AFAIC, so until I rig rain collection too

Click to expand...

Hi John
This guy and his wife has water collection down. They drink ,water and shower with it. I collect water in a 500 gallon tank for watering and don't shower or drink it. I have 500 square ft of roof and 1 inch of rain will fill the tank. I have a small pump for watering. For pretreatment of water he uses a settling tank and I would string filter it at least for showering. I assume you have solar to run pumps. The link to his system is listed below.
http://www.geopathfinder.com/9566.html

I read about a guy who collected rainwater from his roof gutters. he had to keep cleaning out the settling barrel from leaves and debris, so he rigged up a diversion flapper. when it starts raining, the first few minutes it flows out onto the ground, some of the rain is channeled to a cup, and when its almost full the weight of the water in it causes the flap to trip and the water goes into the barrel.

There's a very small hole in the cup so after it stops raining, the water drains out of it, and the mechanism trips back to the original line-up.