How is this thread two years dead? It seems like a pretty important topic for wood boiler design. Although there are some good bits of info on this thread, for the most part it seems to have derailed into a discussion about indirect DHW heaters and heat exchangers. I’d really like to hear some good arguments on pressurized vs. non-pressurized heat storage systems. One particular aspect that I have not seen addressed anywhere is whether or not non-pressurized heat storage tanks are prone to cause or contribute to moisture problems in the building in which they are located. This is just one example of what I’m sure are many as yet unaddressed topics related to pressurized vs. non-pressurized heat storage.
pressurized vs. non-pressurized storage
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Burning Alaska, I would not say that unpressurized systems are PRONE to add moisture to the room, but it is a possibility where it is not with a pressurized system.
Incidentally, in the two years since this thread was started, we have begun carrying reverse indirect water heaters that have about three times the heat exchange surface area of a traditional indirect and so work well at low supply temps (as from storage). We have found these to be an excellent match with pressurized thermal storage and especially in a low temp heating system where you would like to be able to draw tank temps down to 110. In the past, with a traditional indirect, you would have to maintain higher tank temps in order to make decent volumes of hot water - in other words, domestic hot water production was the limiting factor, not space heating. Chris
Incidentally, in the two years since this thread was started, we have begun carrying reverse indirect water heaters that have about three times the heat exchange surface area of a traditional indirect and so work well at low supply temps (as from storage). We have found these to be an excellent match with pressurized thermal storage and especially in a low temp heating system where you would like to be able to draw tank temps down to 110. In the past, with a traditional indirect, you would have to maintain higher tank temps in order to make decent volumes of hot water - in other words, domestic hot water production was the limiting factor, not space heating. Chris
maple1
Minister of Fire
What would the brand/model of that heater be?
(For those in other market areas...).
That is one feature that made me decide against an indirect here - the bigger one was I couldn't find one with electric elements for backup DHW heating. I'm always eyeing the future - these electric tanks only last so long....
(For those in other market areas...).
That is one feature that made me decide against an indirect here - the bigger one was I couldn't find one with electric elements for backup DHW heating. I'm always eyeing the future - these electric tanks only last so long....
What’s “reverse” about a reverse indirect water heater? Is it a separate heat exchanger unit for the storage tank, or storage tank and hx in one (in which case, what’s the difference from a “regular” indirect?)? Can it only be used with pressurized storage, or can it also be used with non-pressurized?
Thanks
reverse indirect: instead of running hot boiler water through a heat exchanger inside a 40 gallon (typical) tank filled with domestic water, a reverse indirect runs boiler water through the 40 gallon vessel and the domestic hot water runs through the coil. In other words, the boiler water and domestic water are on opposite sides of the heat exchanger - or reversed - compared to traditional indirect. In addition to larger heat exchange surface area, these tanks typically have larger supply and return ports allowing for higher btu input. Typical indirect would have 3/4" ports whereas the reverse indirect might have 1 1/4".
Wow - the IS an old thread! It's great to see new and innovative products and ideas. More for us crazy folk to tinker with.
I'm an increasing fan of s-l-o-w heat transfer for DHW. It doesn't matter if it takes a long time to transfer heat into DHW as long as you can keep ahead of demand. Traditional 'bang-bang' systems let DHW run down almost to cold, then have to heat it back up REALLY fast so that you don't get a cold shower. If you can instead just thermosiphon a couple thousand BTU per hour as needed and keep it 'topped off', you'll be fine.
I'm an increasing fan of s-l-o-w heat transfer for DHW. It doesn't matter if it takes a long time to transfer heat into DHW as long as you can keep ahead of demand. Traditional 'bang-bang' systems let DHW run down almost to cold, then have to heat it back up REALLY fast so that you don't get a cold shower. If you can instead just thermosiphon a couple thousand BTU per hour as needed and keep it 'topped off', you'll be fine.
maple1
Minister of Fire
That's what I'm doing with my sidearm and 80 gallon electric tank.
It's almost time though to get back at that project & finish it right - I need to do some more insulating, and put in a thermal switch and maybe a check valve to stop reverse flow when my storage gets too low.
It's almost time though to get back at that project & finish it right - I need to do some more insulating, and put in a thermal switch and maybe a check valve to stop reverse flow when my storage gets too low.
Here is my plan. Build a sidearm similar to this one.
(broken link removed to http://www.ebay.com/itm/HIGH-OUTPUT-Side-Arm-Heat-Exchanger-Outdoor-Furnace-Boiler-Stove-Sweat-/170880879835?pt=LH_DefaultDomain_0&hash=item27c94b4cdb#ht_1420wt_1093)
It's only 24" long but has 7 smaller copper tubes inside of the 1.5" shell. I would try this one for $85 but I don't like how close the drinking water gets to the boiler water and the chance of contamination if a solder joint fails. Picture a 1.5" shell with two 1.5"x1"x1.5" tees on the ends, then end caps on both ends with 7 holes drilled through the caps. The 3/8" tubes would extend through the caps on both ends and connect to a 3/4" manifold with seven 3/8" ports for the DHW connections to my 80 gal electric water heater. Any kind of leak whether it be boiler or DHW would easily be visible and would have almost no chance of drinking water contamination. The heat transfer should be about 1.75 times that of the typical old style 48" sidearm by my calculations. Also, placing it at the bottom 2 foot of the water heater should greatly improve the thermosiphon action when compared to the old style because of the elevation difference. Right?
Instead of a 7 port manifold on each end (which I don't believe already exists) it might be cheaper to add 2 more endcaps with 7 holes turned the other way an inch or so away from the other caps and then reduce this down from 1.5" to 3/4" to connect the DHW side. Sketch on this to come later.
(broken link removed to http://www.ebay.com/itm/HIGH-OUTPUT-Side-Arm-Heat-Exchanger-Outdoor-Furnace-Boiler-Stove-Sweat-/170880879835?pt=LH_DefaultDomain_0&hash=item27c94b4cdb#ht_1420wt_1093)
It's only 24" long but has 7 smaller copper tubes inside of the 1.5" shell. I would try this one for $85 but I don't like how close the drinking water gets to the boiler water and the chance of contamination if a solder joint fails. Picture a 1.5" shell with two 1.5"x1"x1.5" tees on the ends, then end caps on both ends with 7 holes drilled through the caps. The 3/8" tubes would extend through the caps on both ends and connect to a 3/4" manifold with seven 3/8" ports for the DHW connections to my 80 gal electric water heater. Any kind of leak whether it be boiler or DHW would easily be visible and would have almost no chance of drinking water contamination. The heat transfer should be about 1.75 times that of the typical old style 48" sidearm by my calculations. Also, placing it at the bottom 2 foot of the water heater should greatly improve the thermosiphon action when compared to the old style because of the elevation difference. Right?
Instead of a 7 port manifold on each end (which I don't believe already exists) it might be cheaper to add 2 more endcaps with 7 holes turned the other way an inch or so away from the other caps and then reduce this down from 1.5" to 3/4" to connect the DHW side. Sketch on this to come later.
maple1
Minister of Fire
That's the sidearm I'm using. And I have it situated just above the bottom inlet of my electric tank. The second time, that is - I first had it at the top & it didn't work so good. Mine works very good - but as I noted above I think it'll transfer heat the other way just as good if your storage gets low on temps. Which mine is doing now once in while now that we're creeping into shoulder season.
Although I make my living manufacturing coiled DHW hx's, I would like to add that if you want to produce a sidearm hx, a single pass one, without any joints in the boiler stream would work reasonably well.
It would take longer to heat the tank, but a little more time for a simpler, safer hx is no big deal.
BTW, if the eBay hx did leak, it would over-pressurize the boiler side and the potential of cross contamination is low, because your boiler PR valve would lift.
It would take longer to heat the tank, but a little more time for a simpler, safer hx is no big deal.
BTW, if the eBay hx did leak, it would over-pressurize the boiler side and the potential of cross contamination is low, because your boiler PR valve would lift.
You're right. The water pressure would be way more than the pr blowoff. I may still look at making my own. Going to get a mixing valve too. Someone posted a link awhile back for cheap simple differential controller board that I might add as well.
Nofossil, first off that is an awesome website
I read through the heat storage part and it said you don't pull water from the tank correct? What do you do if your zones are calling for heat and also the tank needs heat? Can you do both at once or does the boiler heat the tank only?
Erin
I read through the heat storage part and it said you don't pull water from the tank correct? What do you do if your zones are calling for heat and also the tank needs heat? Can you do both at once or does the boiler heat the tank only?Erin
The water in storage stays there and never moves. I built a simple little control system that prioritizes heat transfer ;-)
- If the boiler has heat available and DHW is cold, it heats up DHW to a usable level first.
- If any of the space heating zones need heat, they're satisfied next.
- The hot tub gets attention once the space heating zones are satisfied.
- Next, the DHW tank is heated up to 160
. - Finally, heat is dumped to storage.
In my case my dhw is just a coil running through my storage. Furnace just automatically heats storage and radiant pump draws the water from the hot side, so it'll get heat before the storage. Essentially, storage furnace and radiant are all in parallel with each other.
Found this drawing in a Swedish forum
http://www.byggahus.se/forum/attachment.php?attachmentid=6452&d=1171210146
It non presurized.
http://www.byggahus.se/forum/attachment.php?attachmentid=6452&d=1171210146
It non presurized.
Not in everyone's house, although mine is probably a rare case. My domestic water pressure is only 20 psi, not enough to set off my boiler PR valve.
We can get it higher if we want to turn on the pump but I hate the wasted electricity just to get higher pressure. Our water is gravity fed from a spring way up on the hill behind our house.
maple1
Minister of Fire
Even 20psi could be more than boiler system pressure.
My boiler system maxes out at 15psi when full hot. 8-10 when cold. Domestic goes from 25-35, or so.
My boiler system maxes out at 15psi when full hot. 8-10 when cold. Domestic goes from 25-35, or so.
Yeah, but the blow off valve I'd probably at 30psi.
I've got a 40-60 pressure switch on my well. That would do it for sure.
I've got a 40-60 pressure switch on my well. That would do it for sure.
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