Non-Pressurized Storage; HX Coil vs Dip Tubes

Aranyic

Burning Hunk
Sep 3, 2015
130
Ohio
Ok, I had pretty well shifted my train of thought to doing an OWB when I finally got some honest input from the wife. Up until now, it's been "it doesn't really matter to me" which I know is never true. I was thinking she would prefer a less invasive to the house direction; if I picked the wrong one however I would invariably hear about it for years on and off. We were cleaning the basement this past week and she finally said that that she would prefer keeping it out of sight and having the chimney on the far side of the house vs an OWB unit and hopefully use less wood.

That puts me back towards the Vedolux v37 which is fine and running the chimney. One of the basement windows will turn into a wood chute of sorts with a bin underneath. None of those a huge issue. The hurdle I've got is a 30" doorway at the top of a flight of stairs. Trying to get enough tanks down there and arranged for the amount of storage I would like seems tough and expensive.

I'm really looking the direction of an American solartechnics 1100 gallon. There's a spot between some posts that's 89.5" wide which would fit it just perfect in between and it would fall between the boiler and the furnace. This leads me to how to get heat in and out of the tank. I could do a 150k btu coil from them for the boiler side and 100k btu coil for the furnace side. My concern is how much of the tank will be usable; will the heat really make it down the bottom and draw off the bottom on the reverse side?

The other alternative I see which I can do about $500 cheaper I think would be 2 70 plate heat exchangers and dip tubes. In my mind, the dip tubes would allow me to deposit into the top and draw off the bottom better to utilize the entire tank? The piece I'm having trouble wrapping my mind around is how do I control those pumps and have them turn on and off with the correct pieces? The pump on the tank side of the HX plate would need to run whenever the boiler pump is running. Can it be run straight back to the boiler and tied in right where the circulator for it is? Or is there an additional controller that I would need to power it? I'm thinking there are 2 additional switches I need? One on the boiler side that if there's power to the boiler pump it turns on; when the boiler pump turns off it turns off. The second on the furnace side that would be tied into an additional thermostat upstairs. When it calls for heat it would power the pump on both sides of the plate HX and the furnace blower?

Am I thinking correctly and if so what have people used? Also is there a specific pump that works well for the tank side of the plate HX? I am thinking stainless for sure based off what I read because that side is open. The boiler and furnace side of the plate HX could be cast because they would be closed?
 

maple1

Minister of Fire
Sep 15, 2011
10,091
Nova Scotia
Not sure I'm totally grasping your concept and not sure I've heard of someone doing that.

I am picturing airlock issues on the tank side circs? They need some pressure at inlets, not sure how that is done with dip tubes and an open tank?
 

Aranyic

Burning Hunk
Sep 3, 2015
130
Ohio
Maybe it can't be done then? But here's what I was envisioning; I know I've seen diagrams with dip tubes but I guess those could have been pressurized vessels? Pumps probably are not in the correct spots but I wanted to at least show the quantity. Left side would be pushing hot into the top and drawing cold off the bottom (Boiler Side) and right would be pulling hot off the top and pushing return/warm into the bottom on furnace side. Both portions on the outside of the plate HX are pressurized and then the ones attached to the tank open circulating water.
Plate HX and nonPress Concept.jpeg
 

maple1

Minister of Fire
Sep 15, 2011
10,091
Nova Scotia
Could just be me but I can't see that working. I am picturing that if you do get the storage side circs pumping, when they shut off they will drain back & be airlocked when they try to start again. The only dip tube stuff I have seen is with pressurized storage.

Tom at AS should be able to set you all up, he knows his stuff.

EDIT: I am also not sure but I think you can do this with just one coil. Is used for both loads and charging. Not sure the ins & outs but lots of others do. And Tom can make you a custom sized tank for your space. Or you can, and just get him to make you the liner for it.
 
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Aranyic

Burning Hunk
Sep 3, 2015
130
Ohio
I've got an email into him I figure I'll hear back soon. Just trying to figure out how to best utilize the full height of the tank.
 

3fordasho

Minister of Fire
Jul 20, 2007
829
South Central Minnesota
Look at Tom's (American Solartechnics) drop in coil heat exchanger - you should be able to get by with half the pumps, no plate exchangers and everything pressurized except the water in the 1100 gallon tank. I've seen plumbing diagrams from Tarm biomass that will get you in the right direction.
 
Either hx will work. Coils tend to be simpler, given there is no need for another circulator.
The tank side loops to plant hx usually maintain their prime as long as the ends in the tank are submerged.
We have done it both ways.
 

Chris Hoskin

TarmSalesGuy
Aug 29, 2008
558
Lyme, NH
www.tarmbiomass.com
The set up you have shown puts the thermal storage between the wood boiler and the heating load. This means that there will be a lag when you get useful energy to the hydro-coil when you re-heat the tank. In other words if your tank is down to 130 degrees, it will be a while before you can get hot water temps flowing to the hydro-coil even if/when the wood boiler is running at 175+. This would be a big deal if you had a low-temp heating system (radiant floor), but with a hydro-coil it is something to be aware of.
 

TCaldwell

Minister of Fire
The non pressurized concept will work, If there no potential air leakage such as a can vent. It’s the same concept of the finger on the top of the straw, leave it on and the water stays, take it off and the water runs out.
 

Karl_northwind

Minister of Fire
Feb 13, 2012
515
Central Wi.
at the very least, if you keep the unpressurized circulators down near the floor, (and use stainless) you won't have issues with air locking. I have a setup like that for a drainback solar system on one of tom's tanks at my place and it's run for 7? years without a hiccup. also I used non-stainless pumps, but that's another story. for priming I placed a hose bib below the circulator and ball valves so I can force water from a hose over the hump into the tank and then up thru the circulator. do that for a few seconds each way, and then turn it on, and let it run for 5 min to get any air out.

also, you don't need a heat exchanger on the furnace coil side. just pump tank water, assuming they're close enough etc that pressure isn't needed.

you could certainly do the furnace coil in the boiler piping for fast response, but if you keep your water temps up a bit (1100 gallons is a lot of storage) you'll probably be fine. most air coils are larger than the house needs for most situations. YMMV.