What are the options for heat storage?

[Flame Job]

This is my first post, but I have been lurking for about a month or more. What a great site you have.

Here is my situation. I am planning on beginning construction of my single family home this spring. Based on a lot of reading, talking, and thinking, I have decided to incorporate a wood gasification boiler and whole house radiant heat into the project. Though I am still comparing various boilers, they all seem to vary from one another only relatively slightly. No so with heat storage.

My what a gambit. From buying a completely prepackaged system like the OPES-1 from Tarm, all the way to snagging a used dairy farm tank off of ebay and figuring out how to get it shipped. So what are people using. And more importantly, why?

From what I have determined, for me, heat storage will become inevitable. I would rather tackle it now, during design and construction. Right now, all I have are pretty pieces of paper with lines drawn on them. So what are the better options, given cost and the fact that, literally, the house can be built around the heat storage? What would you do if you were doing it all over again, and from scratch?

Cost is probably the biggest single factor for me. Swallowing the cost of the boiler with promises of the eventual payback has taken me some time, but I am there. Adding to that 40%...50%...60%...for heat storage may force me to rethink the entire premise.

Your opinions and perspectives are greatly appreciated. Thank you.

 

[Nofossil]

Cost is a major factor, and tanks are large and heavy - hard to ship. In part the best solution may be based heavily on what's available locally. I got an 880 gallon stainless tank for $400 from a local scrap dealer.

If I had it to do over, I'd spend more time and consider a pressurized storage tank (or two), built into the house - perhaps into a wall of the boiler room. I'd also have a walkout door in the boiler room with a better designed adjacent deck with wood storage underneath.

 

[Flame Job]

Thanks for your reply, nofossil.
Can you or anyone else point me to a good prior discussion of pressurized vs. nonpressurized storage? I think I need to learn more about the pros and cons of these two systems in order to make an informed choice. Why did you go with nonpressurized storage?
Building it into the walls sounds intriguing, but how would this be done? Does anyone here have any experiences with this? I guess I always picutred having some version of a large tank sitting in the middle of my basement utility room.
It sounds like a common option for pressurized storage is propane tanks. How do people insulate them?
Thanks again.

 

[muleman51]

If I had it to do over, I would go with a Garn. You will end up spending the same money, have 100 times the frustration if you piece it together. Seriously consider placing your boiler out of the house, get the mess and smoke where it belongs, outside. I have an adobe now. It is outside but to make it work properly I am going to need storage and a draft inducer and spend easily the cost of the boiler over again.

 

[termite]

discussion of pressurized vs. nonpressurized storage? I think I need to learn more about the pros and cons of these two systems

I'm no expert but I'll give it a shot.

Pros:
No chemical additives needed
No evaporation
No efficiency loss through heat exchangers/coils

Cons:
Big expansion tanks are expensive

I don't think you have to spend the same amount a Garn costs to set up a modularized system. I have a little less than $10K in my system complete, boiler room included. I build a fire once a day. Not a big fire, just enough to get the tank back up to 165 on the bottom. Even when we had several days of near zero weather at night I still just built one fire in the evening and topped the tank off.
If the Garn performed better than my system I would be surprised.

I paid $300 for the tank at a salvage yard. I insulated the heck out of it and walled it off in my boiler room. If you want to see what I did look at:
https://www.hearth.com/talk/threads/12887/
I've done some re-plumbing on the boiler loop but the pictures still give you a good idea of what I have.

 

[Nofossil]

I'm with Termite, but I'll add an extra 'con' for pressurized storage: You can't easily add additional heat sources and/or heat loads. For instance, I have a domestic hot water preheat coil and a solar panel coil in my nonpressurized tank. It would be harder to get equivalent functionality with a pressurized tank.

However, the improved efficiency in getting heat in and out of the tank for its primary heating function is much better with pressurized.

Someone talked about using an 80 gallon hot water heater as an expansion tank.

My ideal setup would be two 500 gallon propane tanks, one above the other, built into the basement - perhaps in a wall that divides the boiler room from the rest of the house. Of course, I'd insulate the living death out of it, but I'd make the wall panels removable for service.

 

[Flame Job]

Thank you all for your replies. As far as keeping the mess out of the house, my plans at this point are to have the boiler in a small room off the garage (elevated 18" per code). That way, the wood, smoke, etc, never even comes into the house. The heat storage is another matter. I had envisioned having the tank inside the house, in the basement, in the same utility room that will house the standby propane boiler and other utilities. It makes for a run of about 50' from boiler to storage, but it will all be through heated space.

I had been looking at Tarm, Greenwood, EKO, etc, and somehow Garn has slipped past me. Interesting concept: an all-in-one integrated solution. I guess I will have to crunch the numbers and compare Garn to modular systems.

Thanks, Termite, for the quick primer on pressure. My very rough preliminary calculations call for storage of about 600 gallons. Would this require a big, expensive expansion tank?

The question I am really beginning to mull over is whether this will all be worth it for my application. I am planning on building a 2400 sq ft highly insulated energy efficient home with floor radiant throughout. Counting the garage and basement, I have about 3500 sq ft of floor to heat. If $10-12,000 is a realistic figure for getting this all done properly...wow. I'm 45 years old. I will be buying my wood cut, split and delivered. I may not recover the cost of this system in my lifetime. I will need to make my boiler room wheelchair accessible if I even want to try to break even.

I know. The Middle East may blow any year. $100 for a barrel of oil may seem like a screamin deal in 2015. I am having doubts...

 

[termite]

an extra 'con' for pressurized storage: You can't easily add additional heat sources and/or heat loads.

nofossil:
I would agree with you if the tank was functioning as the primary loop in the system. I have a primary loop running from the boiler room to the house. In the boiler room the boiler can feed heat to it and the tank can extract or inject heat. All it takes for additional sources or loads is a set of closely spaced tees and a circulator. I'm getting by without any circulators in the house. I made a copper manifold and split it with a globe valve to force flow through the different heat loads. Each heat load flow is further balanced by ball valves.

 

[Nofossil]

nofossil:
I would agree with you if the tank was functioning as the primary loop in the system. I have a primary loop running from the boiler room to the house. In the boiler room the boiler can feed heat to it and the tank can extract or inject heat. All it takes for additional sources or loads is a set of closely spaced tees and a circulator. I'm getting by without any circulators in the house. I made a copper manifold and split it with a globe valve to force flow through the different heat loads. Each heat load flow is further balanced by ball valves.

You describe exactly what would be required with a pressurized tank. Not terribly complicated, but compare to the alternative:

In my installation, I have a DHW preheat coil in the tank that heats the cold well water before it goes into the DHW tank. It requires no sensors, no circulator pump, no controls.

I also have solar panels with their own coil in the tank. They heat by thermosiphoning. Again, no sensors, no circulator, and no controls.

It's not painfully difficult to reproduce that type of functionality, but it's definitely more complicated in a pressurized tank than in an open tank like mine. If I had a pressurized tank, I think I'd experiment with large sidearm heat exchangers right next to the tank.

 

[termite]

Point well taken on the solar collectors. I am going to implement solar collection someday. You are right in that a pressurized tank (without glycol) present problems there.
The DHW is taken care of with a sidearm on the HWH in the house (no additional circulator).
As another con for pressurized storage I would have to mention the scarcity of large pressure vessels. Had I not lucked out on the 1200 gallon tank I would have taken the dual 500 gallon propane tank route thus adding more complexity.