OK..I'll pick and choose from all the stuff above to try to get at the problem with the least amount of typing..
I installed a new LL110 boiler (coal/oil), (110,000 btu net on coal), along side my wood boiler las Spring....I re-did all the plumbing at the boilers so that it has a primary/secondary set up (1" copper). The boilers can be run in series, parallel or individual..so I have a primary loop fed by 2 boilers...all per Mr. Holohan in his "Pumping Away" and "Primary Seconday Plumbing" made easy. (per the advise of Sting...very good educational read)
Each boiler loop has its own pump..the primary loop has its own circulator...and supplying my 4 zone supply manifold there is another circulator, which I refer to as the 'system pump'. All of the pumps are Taco 007's. Of the 4 heat circuits, which are 3/4" copper, 2 go to individual hydro-air coils, 1 in the attic, 1 in the basement. 1 is 4 ton, the other is 2.5 ton or 3 ton. 1 zone feeds an indirect 40 gal hw tank, and the 4th zone feeds the basement zone which is baseboard heat. I installed a new Taco SVC406 zone valve controller, my zone valves are HW on the supply side..some had issues..I either replaced the powered head or gutted the valve body and replaced the actual valve as needed.
All had been well since the install last Spring..I havent burned a drop of oil since. Used about 18 lbs/coal/day for HW...When the first real cold spell hit this year, I noticed that my delta T was way down..the boiler H/L was as high as 170/190...water would leave the primary loop at 175-180, and return at about 110...even if just one hydro-air zone was calling...even with the prim/sec set up, this was killing the boiler water temps, always knocking it down to the LL and really never recovering...my first thought was that the boiler was sized too small..I did several things and monitored a lot!..
I covered every spec of copper with 1" insulation, I choked back on the ball valve (@50 %) to the boiler to allow water to linger in it longer and give it a bit of extra time to recover...I tried the same thing with ball valves on the supply and return lines to/from the manifolds...I prioritized the hot water so that all 4 zones would never be calling...
Even with the boiler temp. getting the *censored* kicked out of it, the hot water zone and the 2 hydro air zones were satisfied..the basement never was...and the odd thing was that my coal usage was not excessive! I averaged out to needing about 40k/hr in Jan.
I did one more thing that helped out the most in terms of helping to keep the boiler temps from going into free fall:
When I did the re-vamp, I plumbed in, on the primary loop, a HW L6006a high/low aquastat ..why? at the time just because I had it, and thought it might be of use..well it was.
Basically I use that to be a stop gap method...I have it wired so that IT controls the system pump..I have it set about 15* higher than the boiler set points, with a 5* dif.
Sooo..now, when there is a call for heat, as long as the boiler is at temp., its pump will push water into the loop..BUT, the control on the loop will not energize the system pump untill it is happy..that gives the coal a bit more time to build up a head of steam, if u will...on the flip side, when the too-cold water returns to the primary, the same control will turn off the system pump sooner than the boilers' pump..so it makes the sytem pump turn on after the boilers', and shut off before...I guess this in effect made the primary loop 'the boiler' per say..It really helped in keeping the the boiler temps from going into free fall.
ok..phew, u with me? ..thought I had it solved!..well..I did solve the boiler temp issue...BUT...the basement zone would still not make temp., even on a mild day with all other zones shut down. I was having water leave the primary loop at 180 and see the return water temp, measured after the return manifold, but before the primary loop, was/is 85-90!
Now the odd thing I noticed was that the boiler water temp in this scenario repeatededly climbed all the way to its HH of 190, and would kick off...with 85* water comming back into the primary, AND the primary loop temp retained a consistent 175* or so....hmmm...return pipe temp for the zone was barely warm to the touch...I thought air!..I power purged the troubled zone...It helped a little, but didn't fix it..so it occurred to me that this is NOT a boiler issue after all, this is a flow issue...the water flow must be returning at barely a bit more than a trickle into the primary loop for it to have such little effect on temp...
The odd thing is, before I did the prime/sec loop, this same system pump supplied the same zone and satisfied it with a 100k oil boiler...
Why? My assumption is, that with the new set up, and the supply lines now getting fed by a 'tee' and a pump on the primary loop, probably 50% or less head is now available to the system pump/heat zones...and for this one troubled zone, it probably was just enough to push it past the tipping point.
So I am begining to conclude that I need a substantially larger system pump. I just measured all the footage of copper pipe, and counted up all the 90's and 45's on that zone, and measured the elements. I was astounded.. ( I did not install this zone!..
I came up with the following: Total length of 3/4 inch copper pipe: 284 ft, of which sits (first in line) 11 ft of HO element, and then another 34 ft of regular element..the return pipes loop back over the elements..
Number of 90's: 40
Number of 45's: 13
So if I treat every 90 as 2 ft pipe resistance, and every 45 as 1 ft, and add it to the actaul measured length of pipe I get 377 ft of pipe resistance!...being driven by a 1/25th hp Taco 007...
So this has been a snap shot of what was, what I have done, what is and what I conclude...
From here, I am looking first, for 1.an opinion of what I have concluded 2. with the given set up as described, and the mix of heating loads, what should I target for a delta T ( even with the other zones satisfied, the delta T of 70* or so has got to be too much) 3. If I am on the right track here, what should I aim for pertaining to a new Taco system
pump? (Taco IS in RI btw!..like to support the local biz)..for instance Taco 0011? what should I need for head/gpm..etc. NOTE: I have been in contact with Yanche too, and plugged my #'s into his Yanches tool box, but I can not plot my resulting equation on a graph to find an intersection of needed gpm... 4. How will greater flow affect my 2 fan coil unit operation? I am thinking that with a bigger pump, the water will be zipping thru them faster, less heat will be extracted per minute, resulting in a lower detla T ( Is that correct?)..If so, doesn't that mean that, sure, the boilers job will be made easier, BUT wont the fan coil units have to run longer to extract the right amout of btu's?...while using $.15/kwh electricity?...
..kind of sounds like 'choose your poison'...quite a balancing act...
Well..there you have it..sorry this is so lenghty, but I figured I'd put it all out there at once rather than playing pink pong back and forth with questions and answers!
Any help, opinions, info, feed back is greatly appreciated!