updating Heathkit solar system from 1980

[guzzirider]

I am remodeling our retirement place in Durango CO. It came with Heathkit ( remember them build your own stereo) domestic hot water system that still works well. I currently have 4 flat panels that heat up a 120 Gal storage tank which feeds 2} 50 gal elec hot water heaters. The system produces a lot of hot water. I put down radiant heat in the floor up stairs to run off the solar. I need to build / buy a 300 gals plus storage tank for the radiant heat. the storage tank will be heated by the return line on the existing 120 gal tank. I am doing this because the radiant can operate at a lower temp.

my questions??

1) source for a 300 gal tank I can assemble on site with components fitting through an entry door ( solar is in down stairs work shop behind garage

2) if I build a tank I will have to have a heat exchanger to get heat transferred into the tank but do I need a heat exchanger to pull hot water out of the storage tank.( second closed loop) ? Or can I just pump the hot water off the upper portion of the tank and feed returned cool water to bottom of tank ( kind of like a regular water heater). Why do I need another mass of coils as a second heat exchanger?

Thanks learning

[PNPmacnab]

Never knew Heathkit offered this. Think you are stuck with water heaters if it has to go thru a door. Can't imagine it working that well unless you have a really good control system to move the heat efficiently.

[LucMan]

You can build your own tank with wood framing, rigid insulation, and rubber roofing for a liner. Use 1/2 soft copper tubing to make your own HX suspended in your tank.

[inetdog]

The main drawback of using the water directly from the thermal mass tank is that you would have to design that tank to be pressurized or else provide a pump to deliver the hot water from the tank on demand.

[guzzirider]

Thanks for the input

One option I have found for a possible tank it residential fire sprinkler tank they fit through doorways, Made of Roto Molded Plastic I would have to insulate it.

Follow up questions for storage /heat exchanger.

1)The above mentioned storage tank has 16" round plastic screw lid opening. Will that be a big enough diameter for 1/2 HE coil??
2) copper VS Pex tubing coil,,, cost is obvious but does Pex work ok for 1/4 the $$
3) how much tubing should be in the coil? Is there a difference based on material...I ask this because home brewing supply places sell copper chiller coils for reasonable prices but they are not that long of tubing.
4) I would be using this as a low temp tank for radiant heat/ The waterwill be heated by the return line after the domestic water is heated. Using the tank without a second HE. I would suck water off the top 6" of the tank to feed two separate zones of radiant using one pump per zone. Will the regular solar system pumps do this? taco pumps

[J.P.M.]

You can build your own tank with wood framing, rigid insulation, and rubber roofing for a liner. Use 1/2 soft copper tubing to make your own HX suspended in your tank.

Just don't try to pressurize it.

[LucMan]

The copper comes in 60' coils from any plumbing supply house. You should be able to bend it around a piece of sono tube.

[J.P.M.]

The copper comes in 60' coils from any plumbing supply house. You should be able to bend it around a piece of sono tube.

If I understand what you're writing correctly, the heat transfer will be about non measurable doing that. If anything is done with copper tubing, it'll need direct contact w/the tank fluid to be of any use.

Also, to do it properly and have some hope of success, the HX surface area (whatever form it winds up taking) needs to be sized to the expected load(s).

[peakbagger]

Look up American Solartechics in Searsport Maine. Talk to Tom and he can recommend a cost effective tank solution. The suggestion for homemade tank is not going to work for most systems as most "rubber" liners are not designed for elevated immersion services. Most plastic tanks also do not do well with elevated temps.

[LucMan]

If I understand what you're writing correctly, the heat transfer will be about non measurable doing that. If anything is done with copper tubing, it'll need direct contact w/the tank fluid to be of any use.

Also, to do it properly and have some hope of success, the HX surface area (whatever form it winds up taking) needs to be sized to the expected load(s).

You really misunderstood what I was trying to say!
The sonotube or a 5 gallon bucket or what ever circular object would just be used to form the copper into a spiral heat exchanger of the required size to fit into the opening on the tank. I will leave bracing the spiral and HX btu out put design to the builder. I don't have the time nor desire to spoon feed DIYers in their science projects, just offering some simple advice the rest can be gleamed from web if one so desires.

[LucMan]

Look up American Solartechics in Searsport Maine. Talk to Tom and he can recommend a cost effective tank solution. The suggestion for homemade tank is not going to work for most systems as most "rubber" liners are not designed for elevated immersion services. Most plastic tanks also do not do well with elevated temps.

Rubber roofing does just fine with med temp HW. It is a low cost solution to a storage problem and has been used extensively in home built storage tanks. Is it a 20 year solution? No, either is a steel tank for that matter. The low cost and ease of construction in limited space can solve numerous problems. Would I use it? Of course not, I don't build super low cost solar systems for customers because I would have to stand 100% behind the install and filing insurance claims is not something I'm interested in doing.

Here is another option http://jlmercer.com/ used tanks.

[J.P.M.]

You really misunderstood what I was trying to say!
The sonotube or a 5 gallon bucket or what ever circular object would just be used to form the copper into a spiral heat exchanger of the required size to fit into the opening on the tank. I will leave bracing the spiral and HX btu out put design to the builder. I don't have the time nor desire to spoon feed DIYers in their science projects, just offering some simple advice the rest can be gleamed from web if one so desires.

Understood.

[peakbagger]

Rubber roofing does just fine with med temp HW. It is a low cost solution to a storage problem and has been used extensively in home built storage tanks. Is it a 20 year solution? No, either is a steel tank for that matter. The low cost and ease of construction in limited space can solve numerous problems. Would I use it? Of course not, I don't build super low cost solar systems for customers because I would have to stand 100% behind the install and filing insurance claims is not something I'm interested in doing.

Here is another option http://jlmercer.com/ used tanks.

Easy to make guesses with someone else's system.

Given the location, flat panels can put out 160 to 170 degrees which is not a medium temp system. That is above the recommended working temp for standalone plastic tanks which usually are limited to 140 F. EPDM is not rated for immersion service at elevated temps, sure it may last for some limited period but plan on a good floor drain for when it starts leaking. The elevated temp "boils" breaks down the EPDM and its gets stiff and eventually cracks.

The reason I recommended American Solartechnics is the owner has built more non metallic tanks for solar heating that anyone on this site and probably in the country. He has been working on affordable solar hot water systems for years and has real long term experience with materials used in the systems. He also sells coils and custom tank liners made with materials that will hold up for those folks who build a tank and then discover their chosen liner failed.

[guzzirider]

Thank you for the input.

The system really works very well for being installed in 1980 I replaced the panel / heat exchanger circulating pump last fall and the heat exchanger / storage tank pump mid winter. I provides almost all our domestic hot water storing 120 gals of hot water. I currently have the panels 3/4 covered with a roll up shade and still get 135 degree stored water.
I will be heating my radiant heat storage tank with the line returning to the heat exchanger, so it will be lower temp water in the 90-125 degree range. I think a rotomolded plastic tank will handle that temp.
I did email Tom in ME and they no longer make the collapsible / soft sided tank. I will contact him again about a heat exchanger

We get 300 plus days of sunshine in SW Colo and the sun is quite strong at 7400' with blue skies. If solar won't work here?????

I was trying to get an idea on how much of a copper coil would be adequate for heat transfer

The possible negatives if I use water directly from the thermal mass tank. Would I need different self priming pumps? would all the storage water have to be distilled water?

Thank you