stratification -vs- GPM - need some opinions

[bigburner]

I am considering lowering the GPM that circulates threw my boiler, there is hydraulic separation from the rest of the system. My goal is to rise the water temperature. it's 1,200 gals and it's set to move 30 GPM threw the boiler. Got a circuit setter, so adjustment isn't an issue. I realize that you don't get something for nothing, I am curious if anyone has had an issue with this situation and by reducing the GPM were able to rise the temperature of the discharge. and see an advantage of the hotter water, IE; bigger splits,small pumps or what ever. This year it seams like I got plenty of warm water and not enough hot water!! It's the third year and I keep messing with it to get it where it should be IMO

 

[Nofossil]

A schematic of your system would help, but I think you're on the right track. Reducing flow should definitely raise the outlet temp. A little bit of hot water is often more useful than a lot of warm water.

 

[bigburner]

May give it a whirl tomorrow. I tried drawing my system on Taco's soft ware couple times over the years, I am great at picking components but suck at connecting the lines. It's a pretty simple design, but lots of it

 

[kabbott]

I use a variable speed control on my boiler loop and reduce flow to hold the outlet temp to a setpoint. When my tank is cold the outlet temp
is a Little low and my baseboard is not very responsive when trying to heat the house and the tank. As the tank temp rises the outlet will
exceed the setpoint and at that point the pump runs at 100% and the temp will climb... not a problem. Works very well and I do not have to
cycle my tank pump on/off to keep outlet temp high enough for the baseboard.

My system is P/S with hydraulic separator as well

 

[jebatty]

...reducing the GPM were able to rise the temperature of the discharge. and see an advantage of the hotter water...

Generally yes, but I found it gets more complicated, depending on your system. Mine is 1000 gal pressurized storage, Tarm Solo 40, 140,000 btuh., Grundfos 15-58 on boiler/storage loop. At low storage return temps (90 to about 120F), I keep the circ on Lo, return water protection stays around 145F (balancing valve opened to maintain this temp), boiler output 160-165F. As storage return temp rises above 120F, boiler output temp rises, return water protection temp rises. This is where the complication sets in. My tank stratifies very well, which means as bottom of tank return to boiler starts to rise, the water column above already is very hot, and the bottom of tank rise is rapid. So at about storage return 130F I increase the 15-58 to Hi and substantially close down the balancing valve on return water protection (still maintain at about 150F minimum). I need this extra flow through the boiler to take the full output. This also is where I need to be a bit careful about how much wood is in the boiler, because I want the boiler to burn out without idling. With bottom of tank at about 130F, top of tank will be about 180F, and if the boiler has pretty much burned down to high coals, I can add about 20 lbs more wood, tank will top off at 190F top to near bottom and about 180F at the very bottom, no idling, boiler burns out.

The ideal carefree system would include more automatic control over boiler return water protection (no manual adjustment) and automatic adjustment on the boiler circ to increase flow as return temp (or boiler output) rises. Right now I don't want to make the additional investment in valves, circs and controls to achieve this level of automation. It's not very difficult to make the manual adjustments, just have to be around to do it. And with my system, which so far this year has seen temps in the -10F to +20F range, I still only have to fire once every 2-3 days, and the inconvenience is minor.

 

[Singed Eyebrows]

I am considering lowering the GPM that circulates threw my boiler, there is hydraulic separation from the rest of the system. My goal is to rise the water temperature. it's 1,200 gals and it's set to move 30 GPM threw the boiler. Got a circuit setter, so adjustment isn't an issue. I realize that you don't get something for nothing, I am curious if anyone has had an issue with this situation and by reducing the GPM were able to rise the temperature of the discharge. and see an advantage of the hotter water, IE; bigger splits,small pumps or what ever. This year it seams like I got plenty of warm water and not enough hot water!! It's the third year and I keep messing with it to get it where it should be IMO

What temps are you talking about BB? I went from a 72C in my Ladomatt to 78C & there is at least a 10C difference in output temp. I run this to 90C & set the fan to shut off at this, although it seldom shuts off & stays at 88C. There has been a big difference in the hotter water, more stored BTUs, better gasification. The different thermostat reduced the GPM to raise temps. I balance this with large splits so the boiler does not cycle( stays right at 88C), if it cycles output is reduced, Randy PS, wouldn't a big return mixer(Danfoss 2") solve the problems of hot water.

 

[Blevesque]

Please see link! It's a good read! Brian

http://www.fiainc.com/documents/5-09Canwatermovetoofast.pdf

 

[Nofossil]

Please see link! It's a good read! Brian

http://www.fiainc.com/documents/5-09Canwatermovetoofast.pdf

The author is right about flow rate and baseboards. If you only have one heat source and you're using it to transfer heat to a room, faster flow rates will transfer (marginally) more heat at the cost of more pumping energy. Storage is a whole different issue. With storage, you want to maintain the highest possible level of stratification. The goal is not simply transferring heat - it's transferring usable energy into storage. Slower flow rates will accomplish that.

 

[in hot water]

In a big, wide open wood boiler it may not be an issue, but most boiler manufacturere will specify a delta t range that is acceptable thru the boiler. Some boiler manufactureres will even give a list of circulators, of various brands, that are required to get the appropriate flow rate.

A boiler, like a solar collector will be more efficient with lower return temperatures, but you need to watch the minimun return temperature to prevent condensing. Unless you have a condensing boiler that is designed to run below dewpoint.

Maybe a condensing,gasifing wood boiler is what we need! Gas, LP and now fuel oil condensors are on the market. Condense the flue gas and scrub some additional btus. A PVC vented wood boiler would be a unique looking appliance.

hr

 

[bigburner]

"Maybe a condensing,gasifing wood boiler is what we need!" Funny you mentioned that, I have a 24 inch Dia stack & .05 is the static The velocity per tube is very low [130 +/- 9 ft long x 3.5 inch dia tubes], and the stack temp is max about 250F. The boiler and vent connector stay dry, but I have a nice condensing chimney, the water runs down inside the concrete base and freezes. couple times a season I clean it out. some day I plan to insulate it, but it's 1/4 thick so got a few years before it has a hole in it. On a reload it smokes for a few minutes, then steam for maybe 10 more minutes. then nothing that is visible. This thing may not be a true gaser, but it burns hotter then anything I have ever seen. 2800F in the top of the burn chamber with a hot fire.

 

[jebatty]

This thing may not be a true gaser, but it burns hotter then anything I have ever seen. 2800F in the top of the burn chamber with a hot fire.

Do you think you might be a little optimistic? Iron melts at just under 2800F.

 

[bigburner]

Just going by what my Fluke says, by the way what temperature does fire brick melt at?? How hot is the flame on a down draft gaser?? My guess about 2800F-- IE one of reasons for the refractory, and those don't have the hard to get condensation chimney option.

 

[Singed Eyebrows]

Just going by what my Fluke says, by the way what temperature does fire brick melt at?? How hot is the flame on a down draft gaser?? My guess about 2800F-- IE one of reasons for the refractory, and those don't have the hard to get condensation chimney option.

1800 to 2000 on a downdraft gasser. I don't doubt your 2800 observation as the Energy Mate boiler was capable of these temps in the center of the flue pipe!, Randy

 

[stee6043]

If you have time on your hands and use the wood burner as an excuse to drink a beer or two - this question is most interesting. I personally adjust my 3 speed pump at least twice each night when I have the time. I run my Grundfos on medium when I'm starting my fire and the tank return is in the 135-145 range. After an hour or two of burning I'll usually kick it up to high. When I throw in my second and final full load for the night I turn the pump back down to medium. At this point my tank returns are usually mid 150's. Lower speed over night means I'll get less mixing when the fire dies, tank returns are above 170, and the pump is still running. I don't currently want to buy a differential setpoint controller so unfortunately the pump runs until I leave for work in the morning and shut the boiler off. At this point my tanks are usually mid 170's top to bottom because they have been mixing all night.

So that's my story of manual adjustment....It works very well for me until I can save up enough disposable cabbage to buy some fancier controls.