Which comes first, Storage or Load?

[HeatFarmer]

So after looking at a dizzying array of diagrams and reading countless theories & methods I am still stumped as to how best to plumb my Eko 60 in an efficient and cost-effective manner for my system.
My loads are going to be a flat panel radiator zone, two separate one loop slab zones, and the storage tank. I really only want to use one coil in the storage tank to charge it and draw heat back off for the loads when the boiler isn't being fired. I'm pretty sure I saw this diagram mapped out somewhere here, but can't find it any more.

SO back to my question.... do I charge the storage tank and then draw off for the load, or can I hit the loads off of the boiler & charge the tank at the same time and....???? Or am I stressing over nothing because I have 20 projects up in the air, winter is closing in & I'm behind the 8-ball on everything and I don't want to wake up to find the dog dish frozen to the kitchen floor again.......

 

[HeatFarmer]

Let's not worry at this time that I will be drawing DWH exclusively out of the storage tank as well...... & no I won't be using anything else during the summer. If It really becomes bothersome with firing the boiler once a week or being too hot, I will use the Rinnai gas on-demand we have now. But it is old & needs work to keep the pilot lit and I am trying to wean ourselves off of fossil fuel & electricity for heat & water as much as possible. For what my Eko system is costing me I could have continued being cold, burning our wood stoves full bore & minimally using propane heat for another 5 or 6 years.....my decision to go wood-boiler only means I am 100% committed to using it (within limitations of house & budget) for as much heat/dhw as possible without a back up.... We do not leave home for more than 1 day. The storage tank should take care of that anyway.... Probably another reason I find many of ht diagrams and pictures on this sight confusing...they all contain some sort of redundant fossil fuel system to cob up the works.......

 

[HeatFarmer]

Based on a PM...some more information about my system....sorry for not including it, but I didn't want to be too redundant.....


My Eko60 is 100ft away from my storage tank. The boiler is in a room in an attached barn. The storage is in the cellar. Because of the elevations of the house the floor of the boiler room is roughly the height of where the top of the storage tank will sit 100ft away in the cellar. The 7 of the panel rads will be on the first floor of the house above the storage tank. One will be on the second floor in the bath. The DHW loop drawn from a HX in the storage tank will also be used in the house above the tank....will probably need a recirc pump on this loop, but not sure, we have excellent water pressure.

The only load not near the storage tank will be the two radiant slabs. These 2 single loop zones originate out in the boiler room and need to be able to pull heat from the storage tank to keep the slabs and associated shallow foundations above freezing. For the most part these slabs will be set on the cool side, with temps brought up for extended work periods when I am in the shop. I'm not sure how best/ cheapest to control these 2 zones....two single one loop manifolds? No manifolds, but some other way to connect & bleed air & control temps?

I am feeling so out of my depths!!

 

[benjamin]

I've read most of the background on your plans, and I have to echo everybody else's advice, go pressurized if at all possible. If you have unpressurized storage like you describe, you'll be losing temp by transferring the heat into the storage and then losing temp transferring the heat out of storage. If you have enough radiators and/or insulation it will work fine and you'll never know the difference, but if you're marginal in the radiator and/or insulation departments you won't be happy with how short the storage lasts between firings.

I hate to muddy the waters at this point by adding other possibilities, but it may be worth skipping the storage, at least for now. Cast iron radiators were used with solid fuel boilers in old houses because they were the storage, and it worked pretty well. The fire burns hot for a while and heats the building up, then the coals can "idle" without the problems of damping down a big fire. If you can find an old building being demolished/updated you can usually get all the radiators you need for scrap price + labor to remove them.

For DHW put in a few used electric water heaters, a heat exchanger (mine is 20' of 3/4" copper inside of 1") a DHW circulator pump and controls. Then you're only losing heat from the DHW itself, not a larger volume of storage water at a higher temperature.

Also, since you're already in compromising mode, forget about storing water to heat a workshop slab. You'll be in there firing the boiler whenever you need heat anyway.

 

[stee6043]

Without actually seeing how you plan to plumb this I'd say that typically plumbing your loads first, storage second, is better. If you start a fire one cold morning with cold storage you will certainly want to heat the house first before worrying about brining all of your storage up to useable temps.

 

[ewdudley]

Based on a PM...some more information about my system....sorry for not including it, but I didn't want to be too redundant.....


My Eko60 is 100ft away from my storage tank. The boiler is in a room in an attached barn. The storage is in the cellar. Because of the elevations of the house the floor of the boiler room is roughly the height of where the top of the storage tank will sit 100ft away in the cellar. The 7 of the panel rads will be on the first floor of the house above the storage tank. One will be on the second floor in the bath.

The main boiler loop goes straight to storage. As soon as there is a pint and a half of hot water in the top of storage it will be available to feed loads, so going to storage first does not materially delay when you can start heating after you start a fire. Need a check valve somewhere in the boiler-to-storage loop to prevent reverse thermo siphon when boiler not running.

Since all of your loads are radiant you have a big advantage in sizing the pipe from boiler to storage. Since your return temperatures will be 120 degF or lower you can size according to a 50 or 60 degF deltaT as opposed a traditional rule-of-thumb 20 degF deltaT, so you can transport two or three times the btu per hour per gpm.

Study the taco link:

http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

which is cited in the useful tidbits sticky.

At 25000 to 30000 btu per gpm you only need 8 gpm or so, easily achieved with 200 ft round-trip of nominal 1.25" PEX, conceivably nominal 1.0" would work.

The DHW loop drawn from a HX in the storage tank will also be used in the house above the tank....will probably need a recirc pump on this loop, but not sure, we have excellent water pressure.

Do whatever it takes to have pressurized storage. Have a look at hunderliggers and others tanks that have a fixture for a DHW 'tankless coil' inserted into the storage tank. No pump, no controls, just hot water. A custom rectangular tank with internal bars to accommodate pressure might be a lot less expensive than you would think, find a fabricator and ask.

The only load not near the storage tank will be the two radiant slabs. These 2 single loop zones originate out in the boiler room and need to be able to pull heat from the storage tank to keep the slabs and associated shallow foundations above freezing. For the most part these slabs will be set on the cool side, with temps brought up for extended work periods when I am in the shop. I'm not sure how best/ cheapest to control these 2 zones....two single one loop manifolds? No manifolds, but some other way to connect & bleed air & control temps?

The near boiler loads can pull from the line that goes to storage, just make sure the check valve is not between storage and the tee. Assuming you will have a Danfoss or similar mixing valve the the mixing valve will prevent parallel flow through the boiler when the boiler is off-line, and thus the shop load will pull from storage.

--ewd

 

[hobbyheater]

So after looking at a dizzying array of diagrams and reading countless theories & methods I am still stumped as to how best to plumb my Eko 60 in an efficient and cost-effective manner for my system.
My loads are going to be a flat panel radiator zone, two separate one loop slab zones, and the storage tank. I really only want to use one coil in the storage tank to charge it and draw heat back off for the loads when the boiler isn't being fired. I'm pretty sure I saw this diagram mapped out somewhere here, but can't find it any more.

SO back to my question.... do I charge the storage tank and then draw off for the load, or can I hit the loads off of the boiler & charge the tank at the same time and....???? Or am I stressing over nothing because I have 20 projects up in the air, winter is closing in & I'm behind the 8-ball on everything and I don't want to wake up to find the dog dish frozen to the kitchen floor again.......

 

[hobbyheater]

Heatfarmer.
I have used heat storage (1000 imp. gallons) for 30 years - 27 of those years with a Jetstream boiler. The Jetstream and storage share the same water unpressurized with a open ended expansion 10.5 feet above the boiler giving about 2.5 to 3.5 lbs of psi in the boiler heat exchanger, with no corrosion problems. Our local water quality is excellent with little mineral content. Also the system is plumbed all copper and black steel; a third metal in the system would cause corrosion. The storage tank has two internal heat exchangers; one for domestic supply and the other for baseboard heat. Our back up boiler is now electric but when our back up was oil fired, it also heated the tank at considerable saving as there was no stand by time for the oil boiler. On the electrical side this is fairly simple. It requires an aquastat higher up in the storage tank to turn the boiler on and off requiring no change to the boilers controls If your tank is well insulated to minimize heat loss, this can be a very simple and trouble free arrangement. In the summer months we go about 10-14 days between firings for domestic supply. Your Eko 60 in the summer time would likely not need a full load to bring the storage tank up to temperature .
A sub note; we took out the oil boiler because we used it so little, our furnace oil was stating to grow algae.

For insulating the storage tank, we first wrapped in the tank in foil back insulation you can see on the Jetstream heat exchanger with the foil side in. Next we put one layer of 2 ft. X 4 ft. X 2 inches thick compressed insulation and used aluminum banding to pull it tight. We repeated this process two more times while staggering the joints of the three layers. Heat lost from this tank is 1%.
Allan

 

[in hot water]

The more options you want the more complex, and expensive the piping and controls become. It might be nice to bypass large storage volume and go directly to the loads.

Or with a 50- 120 gallon hydro separator/ buffer tanks connected to the boiler, then from that to the storage, Like the huffdaddy system posted nearby.. Here is a conceptual drawing from John Siegenthaler, that may be in the next Caleffi I-dronics 10 issue. While this shows an un-pressurized storage the same concept for bypassing would apply to a pressurized storage.

A few important details, the backup boiler, whatever it may be, never heats the storage. The boilers never flow thru one another.

You would need a back up source for DHW if the tank temperature is too low, or cold.

The wood boiler must have return temperature protection when it connects to a large load like the storage. The same would apply if the back up boiler was a non condensing type and the loads being fed were large mass, like concrete slabs.

Two pumps, plus the load pump, not show, make this work. It does require multiple 3 way zone valves instead of multiple pumps, but it is a fairly clean and easy piping.

hr

 

[ewdudley]

The more options you want the more complex, and expensive the piping and controls become. It might be nice to bypass large storage volume and go directly to the loads.

I have suggest a rare disagreement with you, HotRod.

The OP is doing pressurized storage, and the best and simplest is to go from wood boiler to storage first. Since hot water rises so very nicely, any hot water arriving at the top of storage is available as soon and as directly as you please for loads. So the boiler loop has one goal: deliver hot water to the top of storage, which is the correct function and is easy to control. There really is no other way to do it with pressurized storage.

Then pull from storage to the hydraulic separator if heat is available in storage, else pump hot water from fossil fuel boiler to hydraulic separator.

 

[henfruit]

If you are running with storage and charging the tank and the house calls for heat and the 2nd pump starts to pull the water from tank/ boiler won't the water bypass the tank and go right to the oil boiler and to the heating circuit's?

 

[hobbyheater]

reply to "In hot water" A few important details, the backup boiler, whatever it may be, never heats the storage. The boilers never flow thru one another

I agree: boilers should never flow through one another; been there done that. Having the oil back up heating the storage tank can work successfully.
The history: our 1000 gallon storage tank is a 5/8" riveted plate steel boiler with the tubes removed. It sits on concrete saddles; the bottom of the tank being 42" off the floor so the original airtight type wood boiler could circulate on gravity with no pump .
The oil boiler was a cast iron slant fin Hydro Therm, weighing 295 lbs with a total water capacity of 3 1/2 gallons with a tankless coil for demand hot water. The boiler had to maintain a water temperature of 170 to 185 degrees. A Hobbs meter was attached to the boiler and it was found that the boiler would fire for 3.5 hours every 24 hours with no load so over a week, this represented 24.5 hours. To raise the storage tank 145 to 185 degrees, the boiler would run 3.6 hour three to four times a week representing a good savings even in the days of 45 cents a gallon of furnace oil!
On the plumbing side, the oil boiler and wood boiler both had separate feeds to the storage tank. The boilers were below the bottom of the storage tank so once they cooled, the water would stratify, eliminating stack loss.
In 2004, we removed the oil boiler and installed an electric back up, and no, it does not feed to the storage tank .
Did enjoy your input.

Allan

 

[stee6043]

The more options you want the more complex, and expensive the piping and controls become. It might be nice to bypass large storage volume and go directly to the loads.

I have suggest a rare disagreement with you, HotRod.

The OP is doing pressurized storage, and the best and simplest is to go from wood boiler to storage first. Since hot water rises so very nicely, any hot water arriving at the top of storage is available as soon and as directly as you please for loads. So the boiler loop has one goal: deliver hot water to the top of storage, which is the correct function and is easy to control. There really is no other way to do it with pressurized storage.

Then pull from storage to the hydraulic separator if heat is available in storage, else pump hot water from fossil fuel boiler to hydraulic separator.

I would disagree, EW. In many setups (mine included) when we "bypass" storage (by plumbing the loads first) my system return is also bypassing storage. As such I can generate significantly more flow through my loads because return temps will immediately be above 140. Whereas if I were to send this flow through storage first and sip off the top of my tank the returns temps will be a LONG way from 140. As such my Danfoss is in full force, and my loads are receiving only a fraction of the flow they need to operate effectively.

You can't consider only supply side temps when thinking about pressurized storage. System return temps impact flow significantly when properly maintaining boiler return temps with a Danfoss or other mixing valve.

 

[ewdudley]

In many setups (mine included) when we "bypass" storage (by plumbing the loads first) my system return is also bypassing storage. As such I can generate significantly more flow through my loads because return temps will immediately be above 140. Whereas if I were to send this flow through storage first and sip off the top of my tank the returns temps will be a LONG way from 140. As such my Danfoss is in full force, and my loads are receiving only a fraction of the flow they need to operate effectively.

You can't consider only supply side temps when thinking about pressurized storage. System return temps impact flow significantly when properly maintaining boiler return temps with a Danfoss or other mixing valve.

You need to come up with a reason that the tanks would be filled with water that is cooler than normal system return temperature. In a normal burn cycle this cannot be the case.

If you went away for a couple days and recirculated storage down to some temperature substantially below normal return temperature, then yes, there would be some advantage in the short term to having the ability to capture system return water instead of letting it go to the bottom of storage.

If adding complexity to the system in order to accommodate this type of situation is worthwhile to you, then for you it is the correct design. Speaking for myself and anyone else who may not much care about such an abnormal situation, the added complexity would not be worth it.

--ewd

 

[stee6043]

Abnormal? Ha. My bottom tank temp drops below 140 several time per week under normal circumstances. And the plumbing is far from complex. Flexibility is what I designed for. And ultimately this is the whole point of storage, is it not? I just think your advice in this case is a touch limiting. Just my opinion.

 

[ewdudley]

Abnormal? Ha. My bottom tank temp drops below 140 several time per week under normal circumstances. And the plumbing is far from complex. Flexibility is what I designed for. And ultimately this is the whole point of storage, is it not? I just think your advice in this case is a touch limiting. Just my opinion.

No, my claim is that is impossible for your storage tank to be filled with water that is at a lower temperature than normal system return temperature, not 140 degF, unless of course you have one of those systems that is always mixed, all the time. If your storage tank is at 95 degF and your system return temperature is at 95 degF, then it doesn't matter if you draw from storage or draw from system return, the Danfoss temperature has nothing to do with it.

 

[in hot water]

This a classic example why every system should be designed to the owners needs, wants, and desires. Not to forget budget.

When I get home from a week on the road the boiler is cold and the first load I want satisfied ASAP is my DHW. The only other DHW heat is solar. So I want full flow, full output going to my DHW, coil in tank, load. My tank has a 1-1/2" coil so it can take all the output my 40 EKO can muster.

Next, if the shop is below 50F, I want full output going to the slab. After those loads are satisfied I'll start charging the 500 gallon. No reason to flow into that tank, take a small hit on piping and insulation losses when I can go directly from boiler to priority loads.

If you tend your boiler on a daily basis and never see a wide temperature swing, then flowing into the tank concurrently with the load would be fine.

hr

 

[ewdudley]

When I get home from a week on the road the boiler is cold and the first load I want satisfied ASAP is my DHW. The only other DHW heat is solar. So I want full flow, full output going to my DHW, coil in tank, load. My tank has a 1-1/2" coil so it can take all the output my 40 EKO can muster.

With pressurized storage I have no difficulty sending all boiler output to the highest priority load despite the fact that water arrives at the top of storage before it can go anywhere else.

Sounds like your experience with indirect unpressurized storage is not relevant to my experience with direct pressurized storage.

 

[HeatFarmer]

Thanks all who responded! It has been very educational.
Now to bump this thread with a related question.

1st a note...... My house & setup will not fit a pressurized system of tanks of any practical configuration. Ain't gonna happen without HUGE expense. I have, however, bought a nifty 1100gal heat bank from americansolartechnics.com/ which I hope to be installing soon. In this tank I will be placing my DHW coil and a 150,000btu heating coil. There will be no secondary system. I am baffled by the huge numbers of posts which make it seem that the gasser is a back-up to the oil furnace..... The EKO will be my primary and ONLY source of heat, other than the wood stoves in this house. There just ain't a point--or money leftover after putting in this system--to have anything else, except perhaps a solar system to bump the storage up during the summer for DHW......

Now on to the question. From what I gather, I should plumb the secondary loads--using closely spaced tees--off of the primary loop, before it gets to the storage. These secondary loads would be plumbed on the out-bound feed from the boiler., not the return line. This seems all well and good while the boiler is firing and its circa. pump is running and the storage is being charged. But what happens when my storage tops out at max-temp--whatever it is I can get it too close to 200ºF--and the boiler and circ pump shut down? I can't quite get my head around what happens to the secondary loops when the primary circ pump on the boiler is off. Do they draw the flow through the off pump to retrieve heat from storage? Or is there some other way I need to plumb for this? What happens when my Danfoss closes down below 140ºF on the return line....theoretically I can draw my storage down to 120º and still feed my loops and DHW with no problem before I need to fire up the boiler again.....

Here's a plan of my proposed system plumbing......

 

[maple1]

I have no experience with this type of thing, but - would you maybe need two separate exhangers and loops? One loop with exhanger & EKO (to heat the water), another loop with exchanger & loads (to heat your zones from the water)? Another thought is having two circ pumps, the first would flow as shown, the second would run the flow in the opposite direction when the first circ is cut from the EKO fire being out (EDIT: maybe helped with a checkvalve or two somewhere...).

 

[ewdudley]

Or is there some other way I need to plumb for this? What happens when my Danfoss closes down below 140ºF on the return line....theoretically I can draw my storage down to 120º and still feed my loops and DHW with no problem before I need to fire up the boiler again.....

Here's a plan of my proposed system plumbing......

Perhaps study the Tarm open-storage reference designs:

http://www.woodboilers.com/admin/uploads/public/WoodBoilerPlumbingSchematic0111Web.pdf

There's one or more open tank systems with no fossil fuel boiler. Once you understand everything they do and why, then you'll be in good shape to either adapt one of their designs or improve upon them.

-ewd

 

[HeatFarmer]

I have no experience with this type of thing, but - would you maybe need two separate exhangers and loops? One loop with exhanger & EKO (to heat the water), another loop with exchanger & loads (to heat your zones from the water)? Another thought is having two circ pumps, the first would flow as shown, the second would run the flow in the opposite direction when the first circ is cut from the EKO fire being out (EDIT: maybe helped with a checkvalve or two somewhere...).

This is how I first envisioned doing the thing.....However, it adds greatly to the cost & creates further places for things to go wrong. I also read somewhere that it isn't as efficient.....

 

[HeatFarmer]

Or is there some other way I need to plumb for this? What happens when my Danfoss closes down below 140ºF on the return line....theoretically I can draw my storage down to 120º and still feed my loops and DHW with no problem before I need to fire up the boiler again.....

Here's a plan of my proposed system plumbing......

Perhaps study the Tarm open-storage reference designs:

http://www.woodboilers.com/admin/uploads/public/WoodBoilerPlumbingSchematic0111Web.pdf

There's one or more open tank systems with no fossil fuel boiler. Once you understand everything they do and why, then you'll be in good shape to either adapt one of their designs or improve upon them.

-ewd

Eliot,

I have studied designs D, E & F before I drew my design. I didn't think there was much of a functional difference between theirs and mine....just that mine is much simpler & I need to add some check valves. However, it does seem that they are treating the storage as a secondary loop, which I was not. I'll delve into it a bit more. Thanks.

 

[ewdudley]

I didn't think there was much of a functional difference between theirs and mine....just that mine is much simpler & I need to add some check valves. However, it does seem that they are treating the storage as a secondary loop, which I was not. I'll delve into it a bit more.

It looks like you can simplify from the generic Tarm because your system is pure low temperature emitters with mixed input, which means you can return directly to the cold side without the TV-2 diverter, loop, and pump.

What do you think of simply dropping the load returns all the way down to the cold side without the closely spaced tees? I believe the Danfoss would close the C-to-M mixer port when the boiler is off line, so you wouldn't have to worry about pulling parallel cold flow through the boiler when it's off line.

Also, it looks like the return from the overheat loop was mistakenly placed on the wrong side of the Danfoss and pump.

[edit:] And another thing, maybe run the numbers and see if a higher-head lower-flow pump like a 008 or a 15-42 or a 15-58 might give more gpm for the same power on the slab loops.

--ewd

 

[HeatFarmer]

What do you think of simply dropping the load returns all the way down to the cold side without the closely spaced tees? I believe the Danfoss would close the C-to-M mixer port when the boiler is off line, so you wouldn't have to worry about pulling parallel cold flow through the boiler when it's off line.

Hmm....again this is heading back to my initial intuition. I added the closely spaced tees based on info from here and other sources as "the" way to go in a system like this......might be worth a re-think.

Also, it looks like the return from the overheat loop was mistakenly placed on the wrong side of the Danfoss and pump.

AH! you caught my error. I noticed it as soon as I hit "submit post"......almost added a disclaimer!

[edit:] And another thing, maybe run the numbers and see if a higher-head lower-flow pump like a 008 or a 15-42 or a 15-58 might give more gpm for the same power on the slab loops.

--ewd

My slab runs are 3/4" and are quite small--only 200 feet each--I figured, for the amount they are run--which is mainly to keep the slabs above 40º at the very least--the 007 would be sufficient. Since it is on it's way we will find out!