Homemade heatwell

Discussion in 'Alternative Energy' started by Dahc, Apr 22, 2006.

  1. Dahc

    Dahc Don't Tase me, bro!?!

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    How would you build it?

    I have wanted to begin building a solar hot water heater for a while but the only place I have to store the water is the 30 gallon HWH in my mobil home which we use now.

    I need to build a heat well to store the hot water before I actually build the collector(s). The collector will be something similar to what's here:

    [​IMG]

    It's just a simple copper pipe assembly in a frame. I will most likely paint this black. There will be more than one of these and each one will be about 2'x4' and preferably on a pivot to change the angle to capture more energy from direct sunlight.

    What I can't decide on is how to build the heat well. Since I live in a mobile home, I know that a factory made heat well is not an option. They are too expensive for us and I want to make one that holds at least 100 gallons of hot water but really want one around 150-200 gallons. 150 gallons could last us 5-7 days with a little conservation. That way, we'ld have hot water even thru several days without direct sunlight.

    The idea I'm considering at the moment is getting a large, verticle standing polyethylene tank, pouring a 4" thick slab with 6" or more of flat styrofoam panels on top of the slab to rest the tank on. Then, build a strong wooden stick frame around the tank and use A/B spray foam (expanding) to fill up the wooden frame. Once the foam expands fully, a long saw would be used to trim off the excess from the four flat sides. If you have ever seen the guys that come and spray foam new housing for insulation, they spray the foam between two studs and once it expands, they rest the saw (hand saw) on the two studs and run it downward to trim off the foam and then have a flat surface to be covered in drywall, wall board... etc... This how it would be done and then it could be protected by coating the whole thing in fiberglass or some other type of housing.

    New tanks can be found for a little more than a buck a gallon, so we'll call it $150 for a new 150 gal tank plus around $80-$100 for shipping. I would also need someone with spray foam equipement to apply it on the tank. I have no idea how much that would cost, then, the cost of whatever I covered the foam with as a housing.

    But let's change the equation a bit. Let's say we have a budget of around $300 for just the heat well. That pretty much rules out brand new materials and services. So, using $300 as a highend target for complete cost of a finished heat well mounted on a slab that will hold 150 gallons of hot water. How would YOU do it?

    Please give all ideas, even if they sound stupid at first. There's no telling what ideas will work and whose ideas can be used and whose can't.

    Don't be scared, give it a shot.
     
  2. SouthernThunder

    SouthernThunder Well-Known Member

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    Your heat well will be resisting temperature change to equal the outside temps. There are a few things you can do to reduce this.

    First I would dig down below the frost line to where the ground temperature is constant. Not sure where you live, but this figure is generally the average of both your summer and winter temp averages. This is about 67 degrees here in oklahoma. (probably a lot hotter than that nowday tho.)

    This will keep your well working through the winter without freezing or loosing too much heat. The main drawback is that it will make it less efficient on those hot summer days when the outside air is very hot.

    Second, to help it retain heat even better you need to build it with something that will have a significant thermal mass. This will help resist night time temp changes and carry your hot water on into the the early morning when you probably need it most.

    Since we're on a serious budget I would suggest ferrocement. To make a 150 gallon tank you should be well under $300.

    Last I would look at insulating the tank. This can be tricky if you are doing the cement in ground. I would probably use polystyrene panels because they are fairly cheap and easy to work with. If you could sandwich them in between some cement that would be just great. Just remember you want the majority of the cement (thermal mass) on the inside of the tank in contact with the water.

    Best of luck with whatever you decide to do. :)
     

  3. caballoviejo

    caballoviejo Well-Known Member

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    I plan to put my "heat well" inside a glassed lean-to on the southwest side of my metal bldg. I will hook about five 55 gallon drums together with the water flow out of the first in the series going out the bottom and to the top of the next. I may use old hot water heater tanks. The barrels will be painted black, as well as everthilng inside but the glass. My collectors consist of 1/2 or 3/4" copper tubing with aluminum vanes. All painted black.

    I may put one-way thermal film on the inside of the glass, or a panel of foam insulation on the outside for a cover removable on cold sunless days.
     
  4. BobK

    BobK Well-Known Member

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    Will the 'heat well' be in an area large enough for a greenhouse? The setup sounds perfect for a 55-gal drum bench to bottom-heat germinating pots.
     
  5. Windy in Kansas

    Windy in Kansas In Remembrance

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    caballoviejo will you have a problem using dissimilar metals, i.e. copper and aluminum? Dissimilar metals are often a corrosion concern.

    Dahc I am wondering if you shouldn't figure out some sort of absorber plate and fasten the copper tubing to it for better heat gain?

    When painting the tubing remember you want a thin layer of paint as a thick one will prevent some heat transfer.

    Have any of you considered using several rolls of 1/4" copper tubing, unfolding the layers of coils as it comes from the box to expose more sun catching surface, manifolding it in a heat box and pumping water through it using a very low wattage, low volume pump?

    I think it typically comes in 100 foot rolls and the last I priced was $23. That would be a lot of exposed surface if two or more rolls were used.

    I don't know how much copper pipe and fittings you will be using, but you might consider this $223.41 purchased alternative--- http://kingsolar.com/catalog/mfg/aet/ap-2101c.html
     
  6. caballoviejo

    caballoviejo Well-Known Member

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    Windy,

    13 years ago my father-in-law gave me the straight copper tubing with the aluminum vanes. Cost me nothing. I must have 100 or more feet of them. They look like they were commecially designed heat exchangers. Heat pumps and I guess airconditioners mix copper and aluminum in the coils. I've forgotten but I think you need the presence of salts to get the electrolysis between different metals.

    Your roll of copper tubing seems a good idea. I've seen people use pvc pipe as a collector. Probably not the best heat exchanger but cheap and you can afford the inefficiency.

    BobK,

    What I'm planning is very much like a lean-to greenhouse on the side of the building. However, on a clear day, even in winter, I can see inside temps of 130 F plus. Sure, I could ventilate but I'm really after the heat buildup and trapping in the water and floor thermal mass. I would undoubtedly burn up plants without ventilation. Plus I want it dry, dry inside - no algal buildup, no condensation on glass, floor or containers. If I can crown in enough drums and store enough heat I'll consider a venting (in winter) to inside heated space above a certain temp. we're in a cooling climate and the payout is not like it can be elsewhere, however, preheating well water, even in summer, does save money.
     
  7. Dahc

    Dahc Don't Tase me, bro!?!

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    Yes, that's the idea. The assembly will be in a shallow box type frame about 4'x2'. It doesn't have to be 2'x4' but to me, that sounds like an easy size to install on whatever I build as a base. I have access to several washer and dryer bodies. I was considering cutting them up and piecing the metal in for the back of the frame. The collector assembly can be mounted on that and everything painted black.

    Yes, I have considered that. Both 1/4" and 1/2" tubing too. I just need to find or come up with some figures on wether or not it will be more effective. Overall, it's cheaper because you don't have to sweat in or buy any pipe joints. It'll be a lot of sweating in with an assembly made of straight sticks. With tubing, everything can be done with compression fittings. Just wrenches.

    This is a good idea for a collector. I bet I could make one these a lot cheaper.

    I worry about metal 55 gallon drums and hot water heaters though. I have both on the property. Most of the paints used on the insides of the drums is not trustable for cooking, showering or washing dishes. I have also torn apart several hot water heaters that were other folks junk. I didn't have much good luck finding inner tanks without many layers of minerals or that had not rusted. They're great if they haven't had much use.

    The one in my house will keep water hot for about 3 days without more cold water coming in. We only run the thing for 3 hours in the early morning hours (2-5am) and have hot water all day. That's for two people.


    Southernthunder, I'm in south central Georgia. The temps get as high as 110 in the summer and their is not much of a frost line although it's recommended to bury your water pipe at least 3" deep. I think it would be more efficient above ground and insulated. It wont be used for anything other than hot water. No home heating or anything like that.

    I have a hydroponics system with a 250 gal reservoir and burying it is how I cool the nutrient solution. Being underground would definetly make it non-efficient.
     
  8. SouthernThunder

    SouthernThunder Well-Known Member

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    Ditto that.