Is stratification necessary?

[kuribo]

I recently purchased a Econoburn 200 indoor boiler which I plan to put in a purpose built outbuilding 50 feet from my home. I want to run the supply and return lines underground to my basement where I hope to put two 500 gallon propane tanks. I will only be heating my floors via the embedded pex tubing (no baseboard, radiators, etc.). I have read conflicting reports here about the need to obtain stratification in the storage tanks....seems if the system only uses low temp emitters such as the pex I have, stratification is not necessary. It would be a real pain to stack these tanks in my basement and I would rather not if it will not be advantageous. Any opinions?

 

[ewdudley]

I recently purchased a Econoburn 200 indoor boiler which I plan to put in a purpose built outbuilding 50 feet from my home. I want to run the supply and return lines underground to my basement where I hope to put two 500 gallon propane tanks. I will only be heating my floors via the embedded pex tubing (no baseboard, radiators, etc.). I have read conflicting reports here about the need to obtain stratification in the storage tanks....seems if the system only uses low temp emitters such as the pex I have, stratification is not necessary. It would be a real pain to stack these tanks in my basement and I would rather not if it will not be advantageous. Any opinions?

As you suggest, for low temperature loads stratification is not such a big deal. But even with both tanks at the same level they can be stratified in parallel at the same level horizontal same as standing side-by-side vertical.

Since you will be mixing temperature down to supply the loads, you will automatically have nice low return temperatures to the tanks and it would be best to supply fittings or plumb in dip tubes to send low temperature return water to the bottom of the tanks to maintain stratification.

This may not matter so much for supplying radiant loads, but your ability to transfer output from the boiler over distance to the storage tanks will be greatly enhanced if you can pull the coolest water possible on the return side. Since your low temperature system can provide nice low return temperatures you would want to take advantage of that by maintaining stratification.

Also if you plan to provide DHW from storage, the more stratification the better. The slickest way is to immerse a tankless coil in the top of a storage tank. During summer you could just charge one tank for DHW.

--ewd

 

[kuribo]

Thank you so much for the excellent advice...

I am assuming it would be a good idea to plumb the tanks in parallel so one can be shut down in the summer if the other is supply DHW?

Also, any advice in sizing my supply and return lines to the boiler? The boiler is rated at 200,000 btu/hr, the run to the house is 50-60 feet or so each way. The boiler will be physically about 10 feet above the storage tanks. I am assuming I will need a tempering valve (landomat (SP?) at the boiler to mix the low temp return with hot boiler supply water.....Normally I see these lines sized with a 20 degree delta T....Am I correct in assuming I can use a much larger delta T due to the low return temps?

Thanks again for any help offered...

 

[goosegunner]

I charge to the top of a 1000 gallon horizontal propane tank and draw off the bottom. The stratification is amazing to witness when you feel the tank and watch the return temps.

I have forced air coil so return temps cause some mixing but tank still stays stratified. With your low temp emitters I would think it would work even better.

Check with Taxidermist I think his tanks are at the same level.

Your biggest obstacle will be using large enough pipe to move the btus to storage. Calculate this carefully.

With that I would use less than 200,000 btus in your calculations. I have a Econoburn 200 and have not come close to 200k. Maybe more like 130-180. I have not figured out why yet. Might be wood burn rate or moisture. I use red oak and it is 15-20% but it does burn slower. When I used softwood this summer Boiler climbed faster but burn time way less.

gg

 

[taxidermist]

My tanks are end to end I just used the same length pipe to charge and draw off my tanks. I have perfect stratification. I charge the tanks in the top and draw off top to my heat loads and return to boiler off the bottom. As for the undergroung 1 1 min I installed 1 in and should have at least installed 1 1 does it work yes but I could use a way smaller pump if I went bigger pex.



Rob

 

[ewdudley]

I am assuming it would be a good idea to plumb the tanks in parallel so one can be shut down in the summer if the other is supply DHW?

I was just thinking parallel would be simple and effective for achieving stratification. If you chose to switch to one tank in summer for DHW then it might be easier to isolate one tank if you went parallel, now that you mention it, but it seems like parallel or serial could work out just fine.

Also, any advice in sizing my supply and return lines to the boiler? The boiler is rated at 200,000 btu/hr, the run to the house is 50-60 feet or so each way.

Who knows what they mean by 200000 btu per hour, could be gross fuel consumption rate like with oil boilers, could simply mean that the 200000 btu per hour unit is bigger than the same manufacturer's 150000 btu per hour unit. There have been forum members who have made solid measurements of heat outputs on the order of 75% of the brochure number, so for design purposes I would say plan on moving at least 150000 btu per hour and no more than 200000 btu per hour.

A good reference for sizing the lines would be that Taco guide in the 'useful tidbits' stickie:

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

Short answer, with a Taco 008 driving 6 gpm through 100 feet round trip of one inch PEX with a temperature delta of 70 degF you'd be up over 200000 btu per hour easily. But if you're burying the lines may as well go with 1.25 inch even if you know it's bigger than you need.

The boiler will be physically about 10 feet above the storage tanks. I am assuming I will need a tempering valve laddomat at the boiler to mix the low temp return with hot boiler supply water.....Normally I see these lines sized with a 20 degree delta T....Am I correct in assuming I can use a much larger delta T due to the low return temps?

I believe you are correct on all points. DeltaT is the key. If you can get big deltaT with low-temperature emitters and decent tank stratification then your flow rates go way down, just like lowering amperage when running 440 VAC instead of 120 VAC.

If you are pumping to storage at only 6-10 gpm, then connecting directly to the boiler through a Laddomat might not work right. I'm pretty sure the Laddomat and Thermovar pumps have flatter curves that are intended for connecting to adjacent storage. I'm thinking instead of trying to feed storage with the boiler supply, loop it straight back to the Laddomat and then tap into that line with closely spaced tees to feed storage with a separate high-head steep-curve pump like an 008 or a 15-58. That way the deltaT though the boiler wouldn't get huge due to inadequate flow.

 

[goosegunner]

I had a Grundfos 15-58 on my Econoburn 200 connected to my 1-1/2" copper going to my tank 20' away. With my piping I figured that I was flowing 11gpm. The boiler temp would gradually climb and then drop to low fan. My Danfoss H port does not close so as tank return rises the 15-58 was not moving enough water.

I have installed a Grundfos 26-99 with a calculated flow of 18gpm on Medium speed. It will now run steady without dropping to low fan. It has created another issue which is cold start modulation. Pump turns on at 170 and with cold return the 18gpm will pull the boiler down to pump off at 165 once or twice before it gets good and hot.

The Higher flow rate also charges the tank differently, and not really better for my forced air heat. The 18 gpm with a Delta T of 20-25 charges the tank up to about 170 top to bottom before it gains much more on the top. When I was moving 11 gpm with the higher delta T of 30-35 it would get 180+ on top and then work its way down.

Still trying to figure this thing out.

gg

 

[jebatty]

I have installed a Grundfos 26-99 with a calculated flow of 18gpm on Medium speed. It will now run steady without dropping to low fan. It has created another issue which is cold start modulation. Pump turns on at 170 and with cold return the 18gpm will pull the boiler down to pump off at 165 once or twice before it gets good and hot.

Greetings and Happy New Year! A solution would be to install the two circs in parallel. Use the 15-58 on start-up and until boiler output rises close to the point of low fan, then an electronic aquastat that switches on the 26-99 to get extra water flow at the hot end. Perhaps a 2-5F differential, something like "on" at 180, "off" at 175, or whatever does the trick. If the aquastat is SPDT it could be wired with the NC pole to the 15-58 and the other pole to the 26-99, that way it would switch between the two.

 

[jebatty]

I use the Tarm solely to heat 1000 gal storage, horizontal tank, Taco 007, tank fittings are within 6' feet of the boiler. The tank is commonly charged to 185-190F top to bottom. I then draw from the top of tank and return to the bottom of tank to feed the radiant in-floor, using a mixing valve to mix down radiant supply to 100F. The flow rate to radiant computes to about 37,500 btuh (2.5+/- gpm, supply 100F, return 70F, delta-T=30). No DHW.

In this situation stratification is irrelevant for heating purposes but is important when the boiler is charging the tank to maintain cool return water to the boiler as long as possible.

But when using a mixing valve to supply 100F to radiant and tank supply is much hotter than 100F, the return from the mixing valve to the tank also is much hotter than 100F, and since this return is going to the bottom of the tank, mixing of the tank occurs, and can occur to the point that the tank is fully mixed. Again, this is not relevant for the radiant.

If stratification is important, such as for DHW or non-radiant supply zones, then it would be desirable to plumb the return from radiant to some mid-point in the tank to reduce tank mixing.

 

[goosegunner]

I have installed a Grundfos 26-99 with a calculated flow of 18gpm on Medium speed. It will now run steady without dropping to low fan. It has created another issue which is cold start modulation. Pump turns on at 170 and with cold return the 18gpm will pull the boiler down to pump off at 165 once or twice before it gets good and hot.

Greetings and Happy New Year! A solution would be to install the two circs in parallel. Use the 15-58 on start-up and until boiler output rises close to the point of low fan, then an electronic aquastat that switches on the 26-99 to get extra water flow at the hot end. Perhaps a 2-5F differential, something like "on" at 180, "off" at 175, or whatever does the trick. If the aquastat is SPDT it could be wired with the NC pole to the 15-58 and the other pole to the 26-99, that way it would switch between the two.

I have considered doing that. I thought I would leave the main boiler circ wired as is. Then add a 15-58 controlled by an aqua stat 185 on 180 off. It would keep my Econoburn from going into low fan at 190 when using setpoint of 195.

It would also work as a overheat back up if main circ failed.

If controlled by aqustat I could also shut down main circ with flue temp/fan. If boiler temp climbed to 185 the second circ would kick in.

My main problem is figuring the best way to plumb in the second circ in parallel? I know I can T into 1 1/2" coming off boiler but,

Do I tie back into 1-1/2" going to tank? Or run a new line to tank?

gg

 

[jebatty]

I think 1-1/2" can handle the volume just fine. Here is a very simplified drawing to start from.

 

[goosegunner]

My circ is on the supply side but I get what you are saying. Seems like a fair bit if restriction with side port t's and additional 90's.

I was thinking I could leave my exsistence plumbing and tie in the second circ before and after somehow. That way the majority of the burn I would have less restrictive piping through original path.

gg

 

[jebatty]

You could leave your primary circ "in-line" and add T's to put the secondary circ off to the side in parallel so that the extra flow restriction likely will mainly affect the secondary circ.

 

[2.beans]

My tanks are end to end I just used the same length pipe to charge and draw off my tanks. I have perfect stratification. I charge the tanks in the top and draw off top to my heat loads and return to boiler off the bottom. As for the undergroung 1 1 min I installed 1 in and should have at least installed 1 1 does it work yes but I could use a way smaller pump if I went bigger pex.



Rob

how far is your boiler from storage?