Basic Storage

[chuck172]

I'm awaiting delivery of my new Tarm Solo 40. Had not planned on storage this year but re-thinking. I'm thinking 1000 gal, a plate HX, (5 x 12 x 30 plate) Possibly a STSS Storage Tank.
Thanks to Jim who is successfully using the HX in this boiler.
Now comes the basics, I guess the HX will have 4 tappings, Wood boiler in wood boiler out- Heats the Tank water. Oil boiler in oil boiler out- provides the boiler with hot water for DHW and hydronic heat. All this in a small unit?
Having never seen an STSS tank I can assume the inside will be something like an above ground swimming pool. How would I support this HX?
Where would I place the HX in the tank?
I'll be piping the oil boiler in parallel with the tarm, coming off the 1 1/4 copper supply and return I'll be cutting in tees, what size should I feed the HX?
What additional controls and pumps will I need?
Thanks,

 

[Eric Johnson]

The flat plate hx should be located outside the tank, with pipes going in to dip tubes. Yes, there are four tappings on a flate plate hx. You need to have pump serving the hx below the water line (outside the tank but below the water line), preferably with a volume of water above it to provide a prime and enough pressure to keep the pump from being damaged by cavitation. I think one-inch pipe should work with a Solo 40.

 

[chuck172]

Sorry, I never realized the HX is installed outside the tank. How does it work, I'm now guessing tank water circulates through the HX that is heated by the wood boiler?

 

[DenaliChuck]

Based on my understanding, one flat plate HX serves the connection between one heat source and one heat receiver (tank or house). The four tappings are boiler in - boiler out - tank in - tank out. This way the boiler fluid doesn't exchange with the tank fluid.

In your case you'd need two HX; one for the wood boiler to tank and one for the tank to house supply. The oil boiler ideally would not be plumbed to the tank.

DC

 

[Eric Johnson]

I think he could get away with just one. A flat plate works both ways, so when it's not adding heat to the tank on the one side, it's extracting it from the other. Dip tube placement in the tank gets a little tricky, mainly because the location of the ends of the tubes determines what it's most efficient at--adding or subtracting heat from the tank.

 

[chuck172]

Are the four HX tappings as follows:
wood boiler in
wood boiler out

Storage tank in
Storage tank out

I assume the storage tank in and out tappings are the (dip tubes) that enter the tank and intake and discharge at specific levels.

The entire hx is mounted outside the tank.

Am I correct so far?

 

[DenaliChuck]

Eric

Any idea if this might set up a slow current in the tank by inputting hot or cool water midway in the tank? I'd think there would be some fluid migration up during the tank heating cycle, and down during the house heating cycle. This wouldn't be good for stratification...

For the price of the setup, a few hundred extra dollars seems small compared to the increased efficiency of having the dip tubes in the best places and to minimize the chances of messing with the stratification of the tank.

Chuck172

Based on my understanding, I'd say your inputs and outputs are correct. For your tank taps you want to pull cool water from the bottom of the tank, heat it with the boiler water, and put it back into the top of the tank. This would maximize stratification and efficiency of heat transfer from the boiler fluid to the tank fluid (the greater the temp differential between the fluids, the more efficient the heat transfer).

The HX to the house would be opposite: Pull hot water from the top, heat the house fluid, and return it to the bottom. Again, this would maximize efficiency and keep the stratification.

Can anyone poke holes in my understanding?

 

[free75degrees]

Dip tube placement in the tank gets a little tricky, mainly because the location of the ends of the tubes determines what it's most efficient at--adding or subtracting heat from the tank.

When a circulator pump is off, does it prevent flow in the opposite direction? If not, could you have 2 circulator pumps aimed in opposite directions so that you could charge the tank going into the top, then draw from the tank out of the top?

 

[chuck172]

Burning Chunk, So HX#2 would be, in my situation, feeding the oil boiler, which in turn supplies my 50gal. superstore hot water tank. So to be clear I would need 2 Heat exchangers, one to heat the storage tank and the other to heat the oil boiler. Am I correct?

 

[DenaliChuck]

172: Yes, this is my understanding and my plan for installing my system.

However, can you plumb the superstore directly from HX#2 and bypass the oil boiler? From what I've read here, running through the oil boiler works, but is not efficient.

You might need to provide a thermostatic mixing valve on the DHW output from the superstore since, for example, heating the superstore with 180* water from the top of the tank would make for some VERY hot DHW. These are examples others have discussed on this board: (broken link removed)

DenaliChuck

 

[chuck172]

I'd like to use this system not only for domestic hot water, but for my entire hot water heating system. Bypassing the boiler would only get me domestic hot water, correct?

 

[chuck172]

jebatty- Do you have two plate hx's on your system, it seems I'm following your lead?

 

[DenaliChuck]

Depends on how you're plumbed...I have a primary - secondary system so putting the HX#2 to the primary loop puts tank heat to the whole house.

 

[chuck172]

I will have both boilers piped parallel. I need to heat the oil boiler.