Carry Barrel Solar Hot Water

           

 

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A low cost solar hot water heat storage project like this takes an hour to build and can pay for itself in one season. We'd all like to save the environment, but saving money is also important. The cylindrical ribbed design of the carry barrel is made from a tough polyethylene material imbedded with reinforcing fibers that holds 60 gallons of solar heated water without a problem. The low cost of the barrel + the low cost of the polyethylene heat exchange tube make a cost effective solar hot water storage tank possible. The commonly available materials may be purchased for less than $60 and the assembly takes less than one hour.

A conventional CLOSED LOOP solar hot water tanks like the one illustrated on the left could have a price tag in excess of $1000

If you're a Do-it-Yourselfer you can build your own OPEN LOOP heat storage tank like the one illustrated below for less than $100. The problem with most Green People with good intentions is that they never get started because the projects are too expensive or because they take too long. The carry barrel solar hot water system is a quick, easy project designed to help people get started. 

If you have an OPEN LOOP drain back collector design  and you need an inexpensive storage tank to test your theories the carry barrel is ideal. It saves time, money and energy.










You'll need a 100' coil of polyethylene to wrap around inside the tank. I recommend allowing yourself plenty of room. Long plastic tubes have a mind of their own. They are not very cooperative so you should stretch the the polyethylene across the full length of a lawn before pressing it into the barrel. When you're done drill a few holes under the top lip of the barrel and snake the the tube through the holes.

It's important to keep keep the top rim of the barrel smooth and free from pipes and tubes because we'll need to install a solid poly foam lid to keep the heat in the barrel where it belongs.








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The heat exchange rate from the solar heated water into the domestic hot water heating system will be largely determined by the surface area of the tube exposed to the heated water inside the barrel. A 100'  3/4" coil has a surface are of about 25 square feet, but not all of this surface area is directly exposed to the water in the tank so that PVC spacers may be used to increase the surfaces exposed. The increase in heat exchange efficiency may not be worth the extra $10 worth of materials, or the time involved in the installation but it's something to think about.










To make the PVC spacer support fixture you'll need:

One  .5"x 10' PVC pipe
Four .5" PVC 90* elbows
One  .5" PVC cross

The PVC pipe is cut into four 10" lengths and four 20" lengths... a little longer or a little shorter will still work.

The cross support pops together like this with four elbows pressed into the four ends. PVC cement is unnecessary. The only purpose of the cross support is to hold the the 2" long PVC spacers in place while the polyethylene coil is pressed inside the barrel.


Without the cross support to hold the spacers in place the spacers will slip around as you press in the coil and drive you nuts... so if you decide to use spacers to increase the heat transfer efficiency use a cross support... BUT before dropping in the cross support spacer assembly drill a hole in the carry barrel for the outlet spigot.











A 1.25" circular saw  can be used to drill the output spigot hole. This is about the largest hole you'll be able to drill into the carry barrel because of the proximity of ridges between the hole.

2.5" holes may be drilled in commercial plastic drums and rubber boots may be used to form a waterproof seal.

For this drum we'll use a 7/8" heater hose to form a waterproof connection because the outside diameter of a 7/8" heater hose is 1.25".

The carry barrel spigot is made from a heater hose, a 3/4" polyethylene tube sleeve and and adaptor. This one inch adaptor will eventually be connected to a drain back pump.

The finished spigot will look like this. Notice the bulge where the heater hose rides up on the polyethylene sleeve. This bulge is what makes the waterproof seal possible and this also allows for the easy insertion of the spigot into the barrel. In the good old days wooden spigots were pressed into beer barrels. Today spigots like this may be used for solar applications.

It's a good idea to drill the hole in the barrel before pressing the polyethylene coil in... BUT hold off on pressing the spigot in place since the insertion of the spigot will make the insertion of the heat exchange coil more difficult. The spacer jig is optional as is this spigot for the pump. if you are squeamish about drilling a hole in your carry barrel you may install a siphon tube from the top of the barrel... BUT the spigot in the barrel is better. Your pump will always be primed and run smoothly with a direct connection to the carry barrel spigot.

 

Anyhow!  Congratulations on the completion of the the carry barrel solar heat storage system.  All you have to do now is build an insulated enclosure for the storage tank. A 2x6 frame packed with R19 fiberglass insulation would work or you could get away a 2x4 frame packed with solid insulation. I'll leave the details up to you. You'll also need a a solid foam insulated lid for the top of the carry barrel and 3/4" connectors to the polyethylene tube. I recommend crimp connectors or shark bite connectors. You may decide to use PEX rather than polyethylene. 

 

PEX (Cross Linked Polyethylene) is tougher than regular polyethylene. It can handle higher pressures at higher temperatures, but PEX is about 2x more expensive than regular poly and it normally has a thicker walled construction which means the heat transfer rate through the PEX will be less.

Since the heat transfer coil will only be used to transfer heated water from a barrel I do not expect that it will get hot enough or soft enough to cause a problem under household water pressure conditions.

Most plumbing problems occur at the junctions so be sure your connections can handle the pressure. The cold tap water should enter at the bottom of the coil and exit at the top to maximize the heat transfer process.







  


If you do decide to use this heat storage method to to preheat the water for your domestic hot water heater let me know what you discover and please send some pictures. Any article submissions with illustrations would be greatly appreciated. 

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