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Posts: 2
Reply with quote  #1 
Hello everybody!

I need your advice and expertise.

I'm planning to create solar heating for my home (163 square meters) with radiant heating and DHW. I will collect most heat during spring, summer, and autumn and put it in the big storage in the basement under my house. The planing temperature that I wish to achieve is a minimum of 180 Fahrenheit, but it will be best if I could achieve a minimum temperature of 200 Fahrenheit.

Now there are few options for me to do create this tank and connect to it and I need your help to chose which option is the best:

The first option is to create a very good insulated big storage heat tank in these dimensions: Length 4.8 meters, wide 1.9 meters and height 1.95 meters (these are dimensions of the tank from inside of the tank where is water). It is about 18 square meters of hot water (18000 liters of water or 4755 gallons).

The type of tank would be something like in this video from David Poz (but in these bigger dimensions): 

he second option for creating a big tank is that I use multiple 55 gallons drums (barrels). I have enough space to connect three drums like in this video: 
 but with very good insulation from outside. So in this one small isolated tank created from three drums, I will have 165 gallons of water.
I calculate that I need to create 30 of these small tanks to have the same amount of water as in the big tank. I'm planning to connect them something like in John Canvian method of modular heat storage: 
Or there is a better method for both of these tanks? Or maybe even the third method?
The second part of my question is which is the best method to extract heat from that storage?

The first option here is to use two plate heat exchanger like this one
 (one for radiant heating, another for DHW)

The second option for creating a heat exchanger is to put some pipes inside of the tank and to create two separate loops, one for radiant heating and one for DHW, something like this David Poz video: 
. The control for these two heat exchanger of how much heat needs to be extracted will be through three way (port) valve like this one id David Poz video: 

nd there is also an option to use the first method for radiant heating and second for DHW.

Or there is another one method?

It is a long text but my wish is to describe to you as much as I can so you can give me good advice and help to make a choice which way is best to store heat and which way is the best to use and extract that heat.

Thank you for all your help in advance.


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Posts: 3,030
Reply with quote  #2 
Hi Antegtvn, welcome to the forum. What you propose is a great idea, BUT...

It's been discussed. Personally I doubt it would be cost-effective. Have you calculated the amount of insulation required to get the R-value you'll need to retain that much heat for that long, and the cost, if it's even possible?

To that add the cost of the collectors you'll need to capture and maintain the heat, and the pumping system.

Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay

Posts: 2
Reply with quote  #3 
The calculation has been done. It is done by a construction engineer who did such a system in his own house. I'm just copying his job. :-)

I will put the translated article: https://translate.google.hr/translate?hl=hr&tab=rT1&authuser=0&sl=hr&tl=en&u=https%3A%2F%2Fliving.vecernji.hr%2Fnekretnine%2Frjesenje-za-stednju-solarnom-energijom-grije-160-kvadrata-910054

About costs: I'm planning to put heat pipe solar panels. They will be connected with this tank with drain-back system. The cost for them will be around 3000$ (with all included to make the solar system to work)

The cost of the big tank will be around 2000 - 2500 $.

If I create lots of small tanks the cost for one is around 70 - 80$, so when you calculate it is almost the same amount of money as a big one.

Even if I wish to heat home with firewood (which is the cheapest method in my country) I have calculated that I will get money back in four years. I also forget to mention that this is the price for materials ( I will create the system by my self with help from all of you :-) ).

Insulation for the big tank will be made like in David Pozz tank + extra layers of stone wool.

The insulation for the small tank will be made from lots of stone wood and I'm planning to put drums in the wooden box also with insulation.

But the main questions for me remains, what type of tank to create and best way to extract heat without using to much collected heat in that tank?


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Posts: 3,030
Reply with quote  #4 
The cascade system has some advantages but a single big tank would have less surface area per unit mass and therefore should be more efficient. However the bigger the tank is, the more surface area and the more heat loss that will have to be made up by more input (solar collectors). Somewhere there is a sweet spot but no I don't know where that spot is, it will vary with conditions.

Having the system in your basement is beneficial as the "lost" heat still helps to heat your home.

The coil-in-tank heat exchanger will only require one pump, this should be simpler than the separate flat-plate unit which will require two, one for each liquid.

How many total Btus/Kwh do you figure you will need to heat your home? The size of your tank equates to about 20 tons of water or about 4 million btus /1170 kwh of usable heat storage (less losses). The longer you store this heat and the higher the temperature differential the greater your losses will be. Have you calculated how much insulation you will need in terms of R value? "Lots of stone wool" does not cut it, you need a value. You need to insulate about 44 sq meters of surface. That's going to be a lot of rock wool.

May I suggest you put your question to one or more of the universities in your country. It would be an interesting project for them and you should get a lot of useful information back.

Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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