CoalisCoolxWarm wrote:Most likely you have reached "critical mass" with your system and heat loads.
Coal stokers don't like "recovery" heating, they like "steady" heating. Once you've gotten enough heat into your zones that some are satisfied and don't need to such out every last BTU of the water that flows within 10 feet of it like a giant black hole...then BTUs can get to the next section and some might even make it back to the boiler, LOL.
That is one main advantage of proper zoning. Not only can you deliver Where and When you deliver BTUs to the exact place that is needed at any given time, you can control HOW MUCH heat (BTUs) go to a zone at any given time.
For example, say a given load is on a zone and needs to be heated by 20*. Well, you can either throw 'x' number of BTUs at it in an hour, or '1/2 x' over 2 hrs. Either way works, but what happens when your boiler can only make '3x' and you have 4 zones all calling for 'x'?
You are calling for X times 4 zones = 4x load, but the boiler can only make 3x, so each zone can LOSE heat and start increasing from X to 'X+1' then 'X+2', etc. You can see how the problem starts to snowball pretty rapidly over a few hours.
But if you have zones, they can all get their 1/2x max when all zones are calling for heat, then when the first (branch off the supply loop) is satisfied, the others can get 3/4X, then when the next is satisfied, the last gets a full X. It may only take 1/3x to maintain the zone after it us up to temp.
Now the above is NOT a perfect example. In reality the upstream zones usually get higher temp water, but the closely spaced tees like I've used help balance and limit excessive BTU draws per zone. That helps maintain a higher primary loop and boiler temp, which provides more heat to the zones and is less stress on the boiler.
But...zone "can" increase the recovery time of a zone. Hence the "steady heat" preference of a coal boiler. You don't have to heat the entire boiler and loop full of water before you can provide heat to the zones. Therefore, you can provide smaller amounts of heat over longer periods of time, which can result in a much lower average load- especially since "more zones" means even more of a chance of staggering the demand.
This is why many marginal capacity systems tend to spiral downward under extreme loads- like last year's multiple days of -30's. In a zoned system, you could "cheat" by prioritizing which zone needed heat "now", temporarily turn off the other zones, and crank up the aquastat on the boiler. Once that zone was satisfied, move to turn on the next one, and so on.
Eventually, that really cold scenario would result in lower zone max temps and end up in the same boat, but in most cases it can buy us up to a week. Most of those extreme temps don't last longer than that- or we can supplement with propane or whatever. Many (most?) of us have backup heat sources of propane, oil, wood, etc that can be called upon in those uncommon and extreme times.
Glad you are FINALLY getting some satisfactory HEAT out of your system! Hope the info I've posted is helpful for your next evolution.
This makes perfect sense and the lack of multiple zones is what was killing me at first. I can't figure out why it is working so well now but I'm just going to keep it the way it as and get working on other projects!!!! Finally I am free from this! (pic below)