solar water heater

homerramirezhomerramirez Solar Expert Posts: 102 ✭✭
Hi guys, I live in north central Tx. and I'm looking to minimize our water heating bill, is there any brand of solar water heater for home use that you would recomend? , I do not want to mount it on my roof because I have solar panels on it , I have a large yard facing south with no shade, or do you guys belive that colud be easier to build it my self, users will be my self, wife and 2 early teen kids....any sugestions are apreciated:D

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,090 admin
    Re: solar water heater

    Solar Guppy has used Solarroofs.com for a couple projects over the years and found them to be very nice and great for the do-it-yourselfer.

    I keep thinking about doing some sort of solar hot water with them--but I have not bit the bullet yet.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: solar water heater

    Here is a simple flat plate collector that I have built. Pretty simple, pretty cheap, in Texas should give lots of hot water. If you don't get enough hot water, add a second one,,,the pump and controller are the biggest cost and don't have to be duplicated. No reason you can't mount it on a fence, leaned up to a wall or what ever.

    http://forum.solar-electric.com/showthread.php?t=3950&highlight=flat+plate+collector

    Tony
  • homerramirezhomerramirez Solar Expert Posts: 102 ✭✭
    Re: solar water heater

    Thanks for the time guys, I was thinking about building it myself but with the price of copper and brass check valves buying it could be an option, is there any web site that shows a simple way to do it?, fitting together 250 ft. of 1/2 copper pipe is not that hard but he did not showed the finished proyect, is there any schematics and how the controlled is installed on the sys.?

    Thanks again for your time.:D
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: solar water heater

    I can't provide a picture because I'm not there but I can describe it a bit better. (one of these days I'll figure out how to draw and attach line drawings!)
    I built the collector out of lengths of 1/2" copper tubing. I used 180 degree elbows so it goes in one continuous loop. You could just as well build it with manifold system with tees. When I built it I assumed that the water should go in a continuous loop (this was years ago) but if you use a manifold it would likely be a bit more efficient.

    Start with getting 2 patio door glass units, of either 28x76 or 34x76. These can be had used for almost nothing from glass shops because when one pane breaks the whole unit is replaced leaving one piece for scrap. You should pay no more than $5-10 each for these. Putting two of these glass panels end to end will give you the total length of the system. (152") Then frame a box out of 2x4 lumber (treated if you wish) and put a bottom on the box of treated plywood if you can find it. Line the bottom of the box with 2" of thermax or blue or pink styrofoam. Then get a couple of pieces of scrap steel from the scrap dealer, cut to the interior size of the box. (3/16" or thicker,, the thinker the better for the mass). Using several small pieces makes getting them on a roof easier. Drop the steel into the box on top of the foam. Paint the steel with high temperature barbecue paint.

    Solder up the copper pipe, leaving a stub for a boiler drain, or a automatic sprinkler drain at the low point(s) Once the copper is soldered up, stub it through the side of the box where ever you wish to enter and exit the water pipes. Paint the copper with the same paint. The sensors are nothing but thermisters. These are simple two wire variable resisters. Place one in the box, on the pipes at the place where you would expect it to be the hottest,,near the top, but it really doesn't matter. Send the wire leads out the box.

    Place the glass on top of the frame, securing it with several angle iron or aluminum angle pieces. It is a good idea to put a piece of industrial rubber between all surfaces of the glass and the angles so that when the glass expands it has a place to expand without breaking.

    The house plumbing is pretty simple. If you have an existing hot water tank, you will need to find a spot for another one. If you are adding a demand gas unit you can use your existing water heater as the pre-heat tank. Let's assume that you are going to use your existing tank. First, remove the drain valve from the bottom of the tank, (assuming you have turned off and drained the tank and killed the power or gas!!!) and thread in a nipple and then a tee. On one side of the tee replace the boiler drain so that you can still drain the tank. On the other side of the tee, add another nipple. On this nipple attach the pump. I used a simple grunfos hydronic pump that draws ~7 watts and circs about 1 gpm. The outlet side of this pump should be plumbed to the cold side of the collector. The outlet side of the collector should be plumbed into the cold inlet of the water heater, along with a tee from the cold water supply for the water heater. The hot side of the water heater then feeds the demand water heater or the conventional water heater.

    The second thermistor sensor mounts on the water pipe near the pump. The controller mounts on the wall near the tank. The sensors are wired with simple low voltage door bell or t-stat wire.

    So here is how the system works: When the temperature sensors detect a difference between outlet of the tank, and the inside of the collector, the pump turns on. When the temperature difference drops to less than the set temperature, the pump shuts off. When you call for hot water in the house, it simply flows out of the tank into the conventional or demand water heater. Over the course of the day, the water keeps circulating through the collector adding to the heat in the tank.

    A couple of items to note. The controller will turn on when the collector temperature drops below any given set temperature to keep warm water in the collector to prevent it from freezing. As I said before, this one has not frozen after several days of 7f with 40 mph winds. If you live in a very cold climate you have to consider a glycol system that add several layers of complexity, Or you may just choose to drain the system during the really cold times.

    Used water heaters are a dime a dozen on Craigs list. If you pay more than ~$20 for a good one you are paying too much.

    I built this system with a bunch of valving so that I could bypass the collector with a turn of a couple of valves, or by pass the preheat tank with the turn of a couple of others.

    These days PEX has made plumbing so easy that any one can do pretty good plumbing. If however you are going to use PEX for the piping to the collector be sure to buy the type of PEX for hydronic heat systems. It seems that some of the PEX tubing does a number on cast iron impellers of pumps.

    The 200' of tubing picks makes over 50 gallons of 135f water in the summer. In reasonable winter sun it picks up about 5f an hour. 135f seems to be about the limit, at least in this climate.

    If you have other questions I'll try to answer them. I'm sure there are way more efficient systems out there,, perhaps using 1/4 tubing would add efficiency, but I am very happy with the way this project worked.

    Tony

    PS Remember to install a pressure relief valve in both the tank, as well as for the collector. I wouldn't expect the water to get that hot, but unused for several days t might. Also, insulate all the piping leading to and from the collector both to prevent freezing, but to cut losses as well. Avoid the cheap home depot type pipe insulation, try to find high r-value tundra type foam.
  • homerramirezhomerramirez Solar Expert Posts: 102 ✭✭
    Re: solar water heater

    Thanks for your advise and valuable time.;)
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