Storage tank - series or parallel connection?

[SteveJ]

For all of those out there using storage tanks...

Do you connect your storage tank in series or parallel with your wood boiler and why?

How do you deliver heat to DHW or your house before going to storage? What controls do you use to set priority?

Is there an advantage to having a storage tank when house is off-grid?

Thanks,
Steve

 

[Eric Johnson]

Most people have a big coil in series that they pump water through both ways, depending on whether they're trying to store or recover heat.

I'm going with a two-heat exchanger strategy. Basically I have an hx for heat storage and a separate one for heat recovery. When the house calls for heat, a pump circulates water between the house zones and the heat recovery hx in the tank. Meanwhile, the other hx is busy stashing heat from the wood boiler. That's a separate pump. I will also have a bypass that allows me to go directly from the wood boiler into the house zones when I need to heat the house up more quickly.

The advantage to this approach is that each heat exchanger is optimized for its desired function, and they work independently of each other. The downside is that it's more expensive.

I can't tell you how any of this works yet, because I don't have it all set up. But I've put a lot of time, thought, money and work into it, so I'm optimistic.

A number of other members here have very successful one-coil tank setups. Hopefully they'll chime in with some details.

 

[Nofossil]

I would be one of those other members, chiming in. I use a single coil for storing and retrieving heat from the storage tank. I have an additional coil for domestic hot water preheat.

Essentially, my oil boiler, wood boiler, and storage tank are plumbed as three parallel heat sources, each with their own circulator. Only one is active at a time. The storage tank also has a zone valve that allows it to act as an additional zone when I want to dump heat to it. In that mode, the flow is backwards (top to bottom). I have a a more detailed explanation on my web site.

 

[SteveJ]

Eric,


I have followed most of your tank saga and see you started with flat plate exchanger and switched to the coils due to mixing versus stratification - correct?


nofossil,

I have gone through your web site for about the third time - geez! Are you a master plumber and electrician?

Is your house totally off grid? I ask because in one of your posts you state that you only have one pump going in your system and you have to be able to power by battery.

Also, I have been using your scratchpad.xls spreadsheet for doing calculation with my radiant floor heating and domestic water heating. What is the fudge factor of 11 in cell H44?

For your storage tank, what is the total copper run for the boiler supply - you state 50' coil with 40"x60" multipipe section top and bottom but what is the total flow path and flow rate?

Thanks so much - it is great getting information from experts that have working systems.

Thanks,
Steve

 

[Eric Johnson]

I started with the flat plate idea and abandoned it because I had another use for the flat plate and I wasn't convinced that it would work the way I want it to. So I embarked on the heat exchanger saga, which has been a real learning process and a lot of fun. I'm not charting new ground, but I will be using an hx that I designed for the tank I have. I just finished making the eighth header assembly today. So, now it's just a matter of getting the rest of the fittings together and then assembling it in the tank and hooking both units up to the system. I'll post a pic of the whole thing when I get it assembled.

It may not work, but it won't be for lack of effort, however misdirected at times it may have been.

The new boiler, by the way, works great. During the recent brief cold snap we were able to keep both the house and the greenhouse at the desired temp (hot) with no real effort. And no smoke.

 

[Nofossil]

Eric,


I have followed most of your tank saga and see you started with flat plate exchanger and switched to the coils due to mixing versus stratification - correct?


nofossil,

I have gone through your web site for about the third time - geez! Are you a master plumber and electrician?

As a close examination of my solder joints and wiring will show, I'm a long way from 'master' status. I'm noy afraid to try things, though, and I've learned a lot from my mistakes over the years.

Is your house totally off grid? I ask because in one of your posts you state that you only have one pump going in your system and you have to be able to power by battery.

I'm nowhere near being off the grid. I am at the end of a dead-end dirt road, though, and I want to be able to deal with prolonged power outages. We can run a generator a couple of times per day to pump water and keep the refrigerator cold, but I don't want to have to run it to get heat.

Also, I have been using your scratchpad.xls spreadsheet for doing calculation with my radiant floor heating and domestic water heating. What is the fudge factor of 11 in cell H44?

The spreadsheet has to solve a series of equations for multiple variables. The 'fudge factor' is a dimesionless constant that has to be adjusted to minimize the error in cell I44. I use the 'solver' add-in to do it for me automagically, but you can adjust it by hand.

For your storage tank, what is the total copper run for the boiler supply - you state 50' coil with 40"x60" multipipe section top and bottom but what is the total flow path and flow rate?

The boiler / baseboard exchanger is a 50' coil of 3/4" copper with a rectangular array of 1/2" parallel pipes top and bottom - you can see them in the tank photos. The rectangular array is 60" long and 40" wide, with 5 1/2" x 60" copper pipes and a 3/4" x 40" header on each end.