Simplest Pressurized with Hydraulic Separator - System Design

[churchillrow]

After a long regression to lurking, finishing renovations and wondering if I ever would hook up my BioMass I'm back.

Here is my situation

2 500 gal tanks stacked horizontally, welded up to be a hydraulic separator
1 BioMass 40
3 Zones Radiant
2 Zone Radiators
Electric hot water which I'd either like to hook up with a side arm or by immersing a copper coil in my tanks using a "manport" with two threaded fitting in it I had put in the tanks.

I've attached a lightly modified version of Simplest Pressurized and I am wondering If there is anything different I can/should do with the Circs or anything else because of the hydraulic separator.
(maybe I don't need a Load Circ?)


Also: I will be using an electric boiler as backup and I'm wondering if it makes sense to run it through the tanks or if I should should I bypass them somehow. The scenario I'm trying to avoid would be coming back after a weekend away with the tanks warmed by expensive electricity.

Thanks In Advance for your help

Augie

 

[Clarkbug]

Also a lurker/newbie here, but I can provide my input if its worth anything to you.

What you could do is arrange it so that the flow rates into/out of your separator are almost equal from the supply and the load side. This way the hot water going into your tanks at the top would be pulled out again immediately, and you wouldnt have much heat rejected to storage. Then you would need the boiler to shut down when there was not a zone load. This would be different than how you would control the wood boiler, so it does complicate matters some.

You could also pipe the electric boiler so that it is attached to the load side directly (the right hand side of your diagram) and only fires when there is a zone load. That would also help eliminate it charging your storage tanks.

I would keep the load circ rather than trying to run the system with just one on the boiler.

 

[churchillrow]

What you could do is arrange it so that the flow rates into/out of your separator are almost equal from the supply and the load side. This way the hot water going into your tanks at the top would be pulled out again immediately, and you wouldnt have much heat rejected to storage. Then you would need the boiler to shut down when there was not a zone load. This would be different than how you would control the wood boiler, so it does complicate matters some.
.

How would this be accomplished? A pair of variable speed pumps?. I think your second suggestion of putting the electric boiler after the separator makes a lot of sense. Any downside to this?

 

[Nofossil]

I don't see the wood boiler....

One modification that I'd consider would be moving the electric boiler just to the right of the load circulator. In that case you wouldn't run the load circ at all when heating with electric, and storage would be out of the loop.

 

[Clarkbug]

How would this be accomplished? A pair of variable speed pumps?. I think your second suggestion of putting the electric boiler after the separator makes a lot of sense. Any downside to this?

It would really depend quite a bit on the layout and design of your system. Variable speed pumps are going to be quite expensive, and probably arent the best option. The ideal way would be to have the same size circulators on both the boiler side and the load side, and closely match the pressure drops. Tweaking could be done with a globe valve or circuit setter. (But again, these can get expensive)

I would follow with NoFossil has suggested, and move the electric boiler so you arent heating storage, or at least would only be doing so in a very minimal fashion. The only downside would be that you would have to re-charge your storage temp when you got back to your house for the weekend.

 

[DaveBP]

The whole purpose of using a hydraulic separator is so you DON'T have to match the boiler circulator and the load circulator.

The two circulators may not run at the same flows when optimized to the changing loads of boiler and heat load requirements. With the loads 'separated' they don't interfere with one another.

I assume when you say your storage tank is welded as a hydraulic separator the hot (in and out) and the cold (in and out) pipes are not connected inside the tank as shown in your schematic. Unless they are riddled with lots of good sized holes.

 

[Clarkbug]

I agree entirely Dave.

I was just trying to think of the scenario where as little storage as possible was charged while using the electric boiler. But I didnt do a very good job of explaining what my head was thinking....

 

[joe117]

Clarkbug, I'm leaning towards the same setup. I have the same concerns as you with heating the storage with electric. Which electric boiler did/are you planning on purchasing?

 

[ewdudley]

I agree entirely Dave.

I was just trying to think of the scenario where as little storage as possible was charged while using the electric boiler. But I didnt do a very good job of explaining what my head was thinking....

We've got a fossil fuel boiler parallel to a wood boiler that feeds into the manifold at the top of storage similar to the drawing here. What we did was to put a Ranco aquastat at the top of storage that tells the fossil fuel boiler when to run. Plus there's a timer that extends any call for heat at the top of storage by a programmable amount to limit short cycling, a nice enhancement but not necessary.

On the load side there's a couple ways that could be used to insure that hot water is 'used up' before returning to storage so as to minimize mixing in storage.

One way you'll see in the Tarm schematics is to put a mixing valve in a diverting configuration so that hot water returning from the loads is diverted back around again if it is not cool enough to return to storage.

Another is a primary-secondary configuration on the load side. This has the advantage in a radiator-plus-radiant system where the lower-temperature radiant loads can draw from downstream of the high-temperature radiators.

And yet another is to place a hydraulic separator on the load side.

--ewd

 

[Clarkbug]

Clarkbug, I'm leaning towards the same setup. I have the same concerns as you with heating the storage with electric. Which electric boiler did/are you planning on purchasing?

I am actually not looking to go with an electric boiler at all. Most of my lurking here has been to learn about putting in an indoor wood gasifier. I currently have an oil fired boiler, but am looking to get out from under the rising cost of oil.

Im thinking of installing a system similar to what ewdudley has installed, with an aquastat off of the storage that would enable/disable the oil boiler. Currently I am leaning towards the idea of the Varmebaronen boilers with the associated storage tanks. This would function the same as the hydrauilc separator as mentioned, and then would allow the load side to run as needed.

Lots more for me to learn about ways to skin this cat, so to speak.

 

[Piker]

With the right controls, you can just heat the top of the tank when the wood boiler is cold and the electric boiler is active. IF the tanks are vertical, and have a relatively small cross section that makes the volume of water at the top of the tank small, this could work ok... but I'm for putting the electric boiler on the other side of the hydraulic separator/storage tank.

cheers