storage in two locations with one boiler

[jdboy9]

I have three buildings I want to heat, one with boiler heat already(barn), one forced air(house), other nothing(garage) Total heating sq/ft around 8,000 between the three buildings. I would like to locate the boiler in the garage with storage and heat the garage off the storage tanks alone(if possible) and the house detached from the garage has no space for storage but having it in the garage would work fine and just run a line to the heat exchanger in the furnace from the garage storage. I have space in the barn for more storage and would like to put it in, then heat the barn off that. I feel that having the storage in the barn is just a waste and better off just locating it all next to the boiler, but my thought was also to try and distribute the storage for heating purposes as well as storage. I would have to imagine if I had all the storage in the garage I would need to insulate it some to keep from loosing too much to the garage.

I realize this is confusing, even is to me and I have been running it around in my head for awhile and just need some input to help my decisions. I realize I'm going to need a large system for this and I didn't include storage sizes because honestly I haven't gotten that far. I would just like to know if the theory of storage in two places works?

 

[stee6043]

8,000 sq.ft is a big load for wood heating. You're going to need substantial amounts of wood if you intend to heat the entire space full time.

The easiest way to seperate storage would be to simply plumb them in series. The first one in line gets hot first and then on to the second one. Downside is system response time.

But let's back up - why do you think you need storage? I think most "very large" boilers would be running near full output all the time to keep up with 8,000 square feet. If you're never idling the boiler you'll rarely take advantage of storage. I think you should start with a heat loss estimate and see what you're really dealing with. You may find storage to be innefective based on your loads compared to most boiler outputs.

 

[WoodNotOil]

IMO storage tanks should not double as radiators as you are suggesting. The purpose of storage is to keep the boiler from idling and allow the stored heat to take over when the fire goes out. I would locate the storage all in one place and make sure that the system is plumbed so that heat can go directly to zones when the boiler is firing, then to storage if the zones don't need it, and finally zones come from storage if the fire is out. The best use of storage during the heating season is to oversize the boiler a bit so that you have the heat to spare for storage and then you don't have to fire as often. You will have a hard time over sizing a boiler with an 8000 sq. ft. heat load. So, storage would more than likely be used in the shoulder season to prevent idling and during the summer for DHW. Start with a heat load calc and we can make suggestions from there on sizes of boilers and storage.

 

[jdboy9]

Right I agree the space I'm heating is a bit large, but then again not all will be heated at the same time. I have a lot of figuring to do before I go any farther with it, just wanted to know peoples inputs on the storage ideas.

They do make boilers capable of heating that large of footage so I'm not too worried about that aspect of it. Over sizing it is another story. If I was heating all 8,000 at once I would most likely be around to feed the burner. I guess I should have clarified that a bit more.

I agree locating the storage in one area is probably the way to go. The only reason i was hoping for storage is to heat the house during the day without a fire going while I'm at work and maintain at least above freezing to 50ish in the barn and garage until needed otherwise.

2000 gallons of storage....500,000 btu boiler....yea maybe too much Like I said still in the figuring stages

 

[RobC]

I'm heating 3000sq ft with 200,000 btu tarm and 1000 g of storage. Above 25f I do 1 full burn 4 hours to charge storage and satisfy heat demands in the evening. Below 25 I need to add another 1/2 load or more depending. I bet you aren't too far off with 500,000 boiler and 2000 g of storage or 3000 g. As long as the boiler has some place to dump heat your good. If your boiler is to small you'll be feeding it for ever and never get the BTU output to charge the storage. Plus if you want to use the shop at a warmer temp you will have heat in storage to start with and bring the boiler on line while your at work.
Charging 2 tanks can be done with some solar controllers. Controller will charge 1 tank and then go to second tank. Keeping all the tanks together would be the simplest and probably the least expensive to install.
Rob

 

[jdboy9]

I would use solar if that lovely lady mother nature would keep the dang clouds away during the winter.

I went to a greenhouse locally where they are using a biomass gasifier and I forget how many btus it puts out but it was two stories tall and 20x50 square including all the conveyor belts and whatnot. Maybe I should look into that boiler, it heats about 5 acres under glass with cow crap.

I don't care anymore how much this all costs I will figure out how to pay for it somehow...I just can't take paying the propane guys thousands every year and by the looks of it I don't think prices will be coming down anytime soon.

Thanks for every ones input so far

 

[leaddog]

Looks like a good fit for a garn.
leaddog

 

[Nofossil]

One consideration is that if there's a long distance between buildings you can end up with a lot of loss to the ground during the time that hot water is circulating through the buried lines.

In most systems with storage, you'll spend a lot more hours heating from storage than from the boiler. If that's the case, there's an advantage to locating storage at the load - there's no flow through the buried pipes during the time you're heating from storage.

Also, with long lines you'll get a slug of cold water when you turn on the circulator. When heating storage from the boiler, flow is pretty much continuous so the 'cold slug' only happens once at the beginning of the heating cycle. When heating the loads from storage, there's often a lot of cycling on and off especially when it's warmer out. You'll get a big slug of cold water every time a load calls for heat. This is a particularly nasty problem when you're heating an indirect DHW tank from storage that's a long way off - you actually end up drawing heat out of the DHW tank at first, as the cold water slug passes through.

In my case, I average 7 hours per day heating from the boiler and 17 hours per day heating from storage. I guess I'm a fan of putting storage near the loads when possible.

 

[RobC]

Good point nofossil. First thing that came to my mind with a BIG boiler was BIG pipe size. That could get cost prohibitive quick doing long runs underground.
Any plot plan of building locations ?
Did like the Garn idea....
Rob

 

[joecool85]

You could always do a boiler in the garage for the house and garage, then a wood stove in the barn if you only need it hot when you are out there, no big deal.

 

[jdboy9]

nofossil very nice points indeed

robc,
sorry no plot plans but the garage and house are right next to each other with the barn about 150 feet away from them.

The garn was a thought, still might be.

The nice thing with storage is that it can be charged from a large boiler and then all branch circuits could be downsized to whatever is needed, at least that was my thought process on it.

joecool85, wood burner in the barn is a last resort only because its more of a finished barn for woodworking with three stories instead of a classic animal barn. Heating the three stories is best done with the water heat that is currently being utilized in it.

 

[RobC]

No expert here but isn't the Garn unpressurized ? With your forced air system could you go unpressurized to house and garage and then do whatever was necessary at the barn. I had a OWB to forced air, radiant and DHW years ago and it ran no pressure fine. The problem comes when you go into other units that will rust or have to get to 2nd and 3rd floors.
The parts to plumb up storage, the storage, controls, insulation etc... add up $$$$. The Garn has a price tag attached but everything is in one package. Simplicity, especially if you could go with out a heat exchanger. Same with the barn. Maybe don't tie into existing boiler but do a self contained blower & fan coil unit so you don't need to add a HX out there either.
I looked quick at the Garn site and they don't seemed concerned about thermal shock because of the mass of the unit.
Ha! I'm not a Garn sales man either....... Maybe you can search in Garn in the forum I know guys have them....
Good luck Rob.