markviii wrote:Exactly what are you trying to correct?
Let me give you the full history, than we can discuss the best possible course of action.
My house was built in 1929, thereabouts (interestingly, it looks like it was going to be part of a very large development, the 'Wynn James Estates', but the depression hit and only 5 of the planned homes ended up being built). It's a structural brick home, with a framed second story. There are 26! windows in a house with a 32x24' footprint, but they have aluminum storms on them which means I have zero drafts. At some point, insulation was blown into the upper floor and the attic, so the home is reasonably well insulated for it's age.
I've replaced my old GE oil burner with a new LL 110K dual fuel boiler. The GE, which apparently was a 'Cadillac' boiler for it's time, looks to have been installed sometime in the 1950's. It also appears to have been tied into an existing two pipe gravity feed system, origins unknown. The mains in the basement are 2 inch, with 3/4 inch feeds and returns to the radiators, of which there are ten, 5 per floor. Frankly, were it not for the price of oil, the old system worked extremely well, was very reliable and could probably have kept running (with maintanence) until I died.
However, oil prices being what they are, I've converted over to coal. I've tied into the old system using 1 inch black iron for my feed and return, but using the bulk of the old mains to send the hot water up to the radiators. The issue this is presenting is that there is soooo much water that needs to be heated that the cycle times on the new boiler are pretty long. In oil mode, at 165k btu (approx), it took ~1 hour, 45 minutes for the circulator to start running without shutdown, it coal mode 9at 110kbtu) that extends out to 2 hours. The delta on the feed and return is as high as 100degrees, depending on how long it's been since the call for heat has gone out.
I learned a new term this week; 'thermal shock'. So in trying to figure out how to prevent that, I came across this thread. Sting's explanation on how to balance the system seems to solve two issues that I might have, that of dumping too much cold water into the system, and running the entire system more efficiently. So right now, I'm trying to work through the details on how to best accomplish that, starting with a system that only has one circulator hooked up. Running with the feed valve too far open allows too much of a delta to develop on supply and return. Running with it to restricted could potentially, I say potentially, not allow the dump zone to clear the heat from the boiler in time to keep the fire going in the grate.
Now, here's the second issue. For the record, I'm sure that these are resolvable, but it's fun to work through them (at least for me).
For some reason (probably because the damn aquastat display is upside down....that's not something someone can fix?) my low limit was set at 130f (HL-180f). I didn't notice this as a problem until this week. However, I did do some charting of burn times (I timed it from cirulator off, until the LL tripped the circulator again, then the circulator run time) at this temp to determine how long it would take for the system to come up to full circulation. The numbers were pretty linear, and I'll be I have a pretty straight line graph, but they were all done between the temperatures of 100f (low side with return) to 135f (max temp the boiler hit before the blending of the return water started dropping the temp). This was charted with all the valves on the supply and return wide open, and the boiler on max burn. All the radiators in the system came up to temp, not evenly, but by the time the 2 hours was up every radiator had warmed up and was putting out heat.
So last nite I changed my LL to 155f. Than, to start to balance the system, I restricted flow on the supply side of the boiler. In concept, for keeping the return blended better, this was working very well. I could run the system with the circulator going full out for hours at a time. The house came up to temperature, but very unevenly. In fact, I had two dead radiators (one of them being the bathroom, of course). In fact, al the radiators that were getting the most heat were in rooms I would need it the least.
I was able to close valves and start to re-direct flow to the radiators that were not getting heat, so this isn't a long term problem. However, I was surprised by the cycle time that the boiler had at the higher temperature settings (much longer than 2 hours) and how much less responsive the system was overall (heat concentrating in a few radiators).
So, that's what I'm doing. One question, based on limited testing so far, would be is it uncommon for different output temperatures to have a dramatic effect on how the heat gets distributed into the system? I've turned my HL to 165 and my LL to 145 to run some experiments today, but atm I'm changing too many variables at once without having enough knowledge of what might be happening. It could be that the restriction of the supply is causing the flow to favor a few radiartors over the others? Or it could be the water temp?
I understand, both for condensing and DHW, I want to run the temperature on the boiler higher. But if condensing is not an issue because of the solid fuel (thermal shock is apparently not an issue either, however better safe than sorry) would it be ok to run the boiler at say, 150HL and 130LL?
Next summer, I'm planning on ripping out the old 2 inch mains and going with 1 inch for the supply and return. By then, I'll have read Sting's books so that I can design the system as efficiently as possible. So this is a situation that I'm facing for just this winter.
But it's my new toy, and it's a puzzle, so it's fun to talk about.