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TT PE110 longer run times (10 Posts)
TT PE110 longer run timesI have a Triangle Tube PE110 nat gas boiler in my house. 100 plus year house with cast iron radiators one zone. The boiler is piped P/S with a Grundfos alpha pump set on lowest speed for main zone second and third zone available for future zones. Boiler runs with the outdoor reset control. What is the best way to get the boiler to run longer with lowest possible firing rate when there is a call for heat? I believe the contractor never changed the outdoor reset control from factory settings. This is the fifth winter and with the very cold weather the CI radiators have never been hotter that this year because when it gets very cold outside the boiler is sending out higher water temp to heat the radiators. If the heating curve was set for sending out 160 Deg max water temp when coldest weather is outside would this make for longer run times at lower firing rates? Would this improve system efficiency?
Is it short cyclingWhat are your current cycle times?
I have had very good luck with the taco bumble bee circulators, using delta T instead of P..
Can you let us know a little more about your system? .
To get the longest run times,To get the longest run times, use the lowest supply temperatures you can get, consistent with being able to achieve the temperatures you want. This involves setting your outdoor reset curve correctly.
I have a radiant slab at grade. My design temperature (outside) is 14F, but this year it got down to just under 3F a couple of times. With my 1150 square foot Cape Cod here in New Jersey, and trying for 69F inside, I supply 76F water to the slab until it gets down to 50F outside. I then let the supply temperature to increase in a straight line until it gets to 0F outside and the supply temperature is 128F.
With that, the run times get shorter and shorter as the outdoor temperature increases. but when it is under 50F outside, I get run times of 10 to 18 hours sometimes. I could squeeze it a little bit more but then it responds to changes in outdoor temperature too slowly. As it is, I cannot get the indoor temperature over 70F by changing the thermostat setting because the supply temperature is not high enough.
There is no secret, really. Just weeks of boring set and test. Because with my slab, it takes about 24 hours to really stabilize the heating again after making a temperature change. (So forget about setbacks).
I am trying to do the same thingbut not only are you tweaking outdoor reset but you also have to factor in the boiler pump vs system pumps for my system at least. So even if your tstat is still calling, you may reach set point quickly.
If all of my zones are calling, the boiler is fine but if one tstat gets satisfied, the burner can not modulate down fast enough and hits its setpoint and shuts down.
I also have pulse width modulating tstat for my radiant heated slabs that also can affect burn times, the closer to the setting, the shorter the burn times like 10-12 minutes.
How long are your burn times and how much delay are you running for your burner?This post was edited by an admin on March 5, 2014 8:33 PM.
trying to do the same thing"I am trying to do the same thing
but not only are you tweaking outdoor reset but you also have to factor
in the boiler pump vs system pumps for my system at least. So even if
your tstat is still calling, you may reach set point quickly."
If you reach the set point quickly, your supply temperature is too high. You want it to be just a tiny bit higher than what is required to maintain the temperature. So you adjust the reset curve accordingly. If you cannot do that, it is likely that your boiler is oversized.
"If all of my zones are calling, the boiler is fine but if one tstat gets
satisfied, the burner can not modulate down fast enough and hits its
setpoint and shuts down. "
How long does it take to modulate down? Mine will do that in well under two minutes. Is it a question as to how fast it will modulate? Or a question of whether it will modulate down far enough no matter how much time it is given?
"I also have pulse width modulating tstat for my radiant heated slabs
that also can affect burn times, the closer to the setting, the shorter
the burn times like 10-12 minutes."
For radiant slabs, it seems to me the best thermostat is a simple on-off one like the old round mercury-filled Honeywell ones. but they are not the only ones.
"How long are your burn times and how much delay are you running for your burner?"
Today, and is is not terribly cold outside (25F), my radiant slab zone has been calling for heat for 9 hours 24 minutes since midnight. Chances are it fired continuously for that time, but I did not go out to the garage, where the boiler is, to watch it the whole time. When I do watch it, it tends to run continuously when the zone is calling for heat. (It is a different story when only my small baseboard zone calls for heat, because the boiler will modulate down only to 16,000 BTU/hr and that zone needs only 6250 BTU/ hour when it is 14F below the design temperature. So my boiler is way oversized for that one zone. Even in that zone, though, it promptly modulates down to the lower limit and wanders up to the upper limit, about 4 to 6 cycles per hour, depending on outside temperature.
Tuning ODR parametersis far easier if you remove the thermostat from the equation before you start. Raise the setpoint on the stat to 85ºF or so and leave it there until you can maintain a consistent indoor temp using just the ODR settings. Then drop the setpoint to 2º-4º above your desired space temp as a high limit control.
If you intend to use the stat for space temp control going forward, a PWM stat helps (as mentioned above) but you should also raise the ODR curve a couple degrees at each end so the stat has something to work with.This post was edited by an admin on March 6, 2014 12:28 PM.
Is it a Proven Factthat having your system always running is the most efficient way to heat a space? A lot of people seem hung up on trying to reach this goal, but is it the way for every modcon install to work for long, or short term dollar savings?
Mod/con always runninggenerally produces the most stable indoor temps, and minimizes thermal stress on both the boiler and the system. Since it is heating with the lowest possible water temps, it also maximizes combustion efficiency.
Minimal setbacks (of a degree or three) seem to work OK, espeically if they are done via the supply temp rather than by turning off the boiler. The best answer is ODR with indoor feedback, which is unfortunately somewhat rare here in the US.
If You Underset the Temperatureof the supply at any point, you risk having a system that never catches up, thus always running, right? Therefore, every system has to be run on supply water that is at least a little hotter than actual BTU demand to prevent this. It just seems unpractical to try and hit the 101% mark, at all heating points thru out the course of any given heating day, if not impossible. I think for most of us, reasonable run times of 1/2 an hour or so, are much more realistic.
BTUsPlot ODR curve with emitter output and house demand on the same graph, preferable per zone. See how she overlays and tweak away, i.e. shift curve as much as you want. This is pretty much the same as setting the stat the way SWEI is saying.