The attack of the 1000 gallon hydraulic separator!

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DaveBP

Minister of Fire
May 25, 2008
1,156
SW Maine
The recent thread on hydraulic separators made me realize that the propane tank storage system I'm designing might be just that, an oversized hydro separator.

I'm building a house that's very well insulated and almost airtight. Very low heating load and 250 sq. ft. of Low-E glass facing SSW on a hill.I have a new Tarm Solo 40 that will always be putting out more heat than the house will be calling for, even on the coldest, windiest nights. The Solo 30 might have been more appropriate but the 40 is in the basement so there I am. So my situation is different than most and what I'm thinking about doing won't work for many of us.

I came up with a couple 500 gallon propane tanks and started watching very closely all the various schemes for directing boiler water to the tanks and then switching valves manually, electrically or thermostatically back and forth and I don't know what else to take heat to the house and so on. With Nofossil's 'Simplest' sticky for inspiration I wondered if the boiler and storage couldn't be coupled together even more closely so the boiler always fed into the storage tank. I wanted to come up with a way to connect the heating loads of the house so they always drew from the tank too but that when the boiler was firing the supply water could go directly to the loads 'through' the tank. I keep coming back to a 2" pipe welded through the top of the tank; boiler connected to one end and the heating loads to the other end. Inside the tank this pipe would be swiss-cheesed with lots of holes or slots facing up to the top to promote stratification. A corresponding pipe would be mirror-imaged across the bottom for the return lines. If the boiler is supplying more than the house is calling for it charges the tanks. If the house is calling for more flow than the boiler is supplying then the loads are supplied by the tank. If the flows are about equal, the supply water will come into the tank and flow right across to the loads in the house. The returns flows would cross the bottom in a similar way back to the boiler.

So I have now worked into Siegenthaler's book to where I understand the basics of primary/secondary distribution. And now I think that my little scheme might help things by decoupling the boiler circulator circuit from the rest of the system so that the various loads coming in and out and all that changing head in the system won't affect the boiler circuit itself.

And isn't this just what hydraulic seperators are about?

Was it Hot Rod that suggested that a hydro seperator/buffer tank combo would be perfect for low mass boilers? So why would an even bigger one not be better for a gassifier?
I've seen european schematics that seemed to suggest this might be done over there but the connection details are too simplified to know if that is what they are doing.

The biggest issue for this kind of simplest system that I see is the flow through the boiler when it is not running but the house is calling and drawing from the tank. Pretty much the same issue as Nofossil's system. If the flow resistance through the boiler circuit is a lot more than the large perforated pipes through the tank then this might be trivial but it won't be zero. A motorized ball valve of some sort in the boiler supply line to the tank would stop that flow if it became a problem.

I'm not trying to get my system running this winter season so I have lots of time to learn and improve my system design. This forum has become one of my top 2 or 3 reasons for the invention of the internet. I hope some of you pros and amateur hydronics experts out there might give me your opinions on this way of looking at pressurized storage.
Anybody out there doing this. What problems? What would you do differently next time?

Again, this might only be appropriate for people with low load houses that will never need more than a fraction of the boiler output. I don't have the intuitive understanding of BTU flow that a lot of you have from much experience.

Appreciate any and all input.
 
If you could safely mount one of those LP tanks on end you would have one heck of a separator. An excellent spot for air removal, the mother of all sediment traps and have a nice stratification vessel.

The circ used on the boiler loop and the "load" side would have intergral check valves. I doubt you would get any cross over with that much tank diameter, even with different head circs?

The first tank could be a separator, the second could be modified into a "super" storage tank. This link shows some of the high tech tank designs common on the other side of the pond.

You could wrap some copper coils around the outside at different levels, like the Rheem Solaraide. Low for solar or wood input, mid for DHW preheat, top coil for highest temperature loads. It would be a bit easier to install external coils, than trying to cram coils into a already built tank. Not ideal HX but simple, easy to install and service, etc.

www.preheat.org/fileadmin/preheat/d...bo_Heat_storage_for_solar_heating_systems.pdf


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DaveBP said:
I keep coming back to a 2" pipe welded through the top of the tank; boiler connected to one end and the heating loads to the other end. Inside the tank this pipe would be swiss-cheesed with lots of holes or slots facing up to the top to promote stratification. A corresponding pipe would be mirror-imaged across the bottom for the return lines. If the boiler is supplying more than the house is calling for it charges the tanks. If the house is calling for more flow than the boiler is supplying then the loads are supplied by the tank. If the flows are about equal, the supply water will come into the tank and flow right across to the loads in the house. The returns flows would cross the bottom in a similar way back to the boiler.
....

The biggest issue for this kind of simplest system that I see is the flow through the boiler when it is not running but the house is calling and drawing from the tank. Pretty much the same issue as Nofossil's system. If the flow resistance through the boiler circuit is a lot more than the large perforated pipes through the tank then this might be trivial but it won't be zero. A motorized ball valve of some sort in the boiler supply line to the tank would stop that flow if it became a problem.

Hydraulically, you're talking about exactly what I'm intending in the simplest storage design. The key idea is that zones are supplied directly without having to heat storage first, but excess flow from the boiler goes automatically to storage.

I think the secret is to use large enough diameter plumbing in and near the tank so that the flow velocity is low enough to avoid kinetic effects.

If there is NO flow related pressure drop between the top and bottom of the storage, then there will be no inclination for ghost flow.
 
I have a homebuilt boiler and presure tank setup. My tank has two outlets on top and one at the bttom. The supply pipe leaves the boiler and goes across the two top openings. When the boiler is hot and the house calls for heat hot water goes though pipe to load. When load slows or stops it thermosiphens out the bottom of tank through boiler and back in through the first opening. The return lines from floor return to boiler. if heat is called for and fire is out water will be drawn through boiler then to tank. it will drop into first openig and warmer water will come out second opening. with a hot fire you can send heat directly to house and charge tank at the same time. my system has several shortcomings that money would solve but I am very happy with pipe scheme.
 
A weighted flow check would take care of ghost flows in the boiler.

Yeah, and that's what I would do (and may end up doing) except for one other thing I want to do.

I'm eyeing those loading units that Termovar and Laddomat make. The ones with the boiler circulator, thermostatic mixing valve for return protection and some isolation valves and thermometers all rolled into one casting. On the european websites they mention that with the versions that have a very low head check valve intergral to the casting they can thermosiphon when the power fails or if the circulator fails and act as an emergency heat dump. I spoke to tech support at Tarm (Bioheat) and they haven't up until now stocked the models with the "backflow preventer" as they call it because they are intended for pressurized storage, but now that they are offering pressure tanks they will be bringing them in. They have not yet tested them to see if they can thermosiphon well enough to replace the usual Automag/gravity dump. I will continue to pester them to see if they will. If they do work as an emergency dump obviously the less head between the boiler and the tank the better.

Luckily, I'm not trying to get my system together for this heating season, so I have time to watch developments.
 
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