reset curve as a step function?

CC.Rob_2

I see what you mean, but I'm not sure it applies. The supply sensor is seeing the water after it leaves the boiler, downstream of the injection pump. It's seeing supply temps go up (and come down when the 260 hits the autodiff high limit of the moment), but it shouldn't be affected by what the internal circ is doing at lower outdoor temps any more than at higher outdoor temps.

As I understand it, the vs3000 is basically varying speed to ensure the boiler is protected. It definitely knows nothing about the outdoor temp. As the internal boiler temp rises, the pump speeds up to get more of that hot water into circulation (pun intended...).

CC.Rob_2

reset curve as a step function?

This is my first season with a tekmar 260 doing full ODR on a Revolution. Two zones of fin-tube. Outdoor design temp 5F. Supply temp at design 175F. Indoor temp 68F. Back in the fall, the tekmar was clearly learning. Differential was pretty tight. Starting in mid-October, once or twice each day I noted the supply target temp (aka BOIL TARGET) and outdoor temperature, and plotted it. Those are the green circles on the attached plot. In December, when we finally started seeing some colder temps, I noticed that for a given temp, the tekmar had reduced the target supply temp by 3-4 F. Basically, it had established a new curve. At that time, I also began to note the differential, and my unrecorded observations suggested it had widened the differential to about 20F with both zones calling. In Oct-Nov, I think it was using about 12-15F or so, but never recorded any of that.

We’ve had a lot of time with temps >=20F from Nov to early Jan, so the control has long exposure to demand at these temps.

Recently, we finally had a good run of outdoor temps below 20F. I have noticed that the supply targets took a big jump up. The “curve” now has a pretty significant step in it between ~18-15F. Performance-wise, this has bumped up the emitter output such that what used to be nearly continuous circulation now will satisfy the stats.

For a few days, we actually got close to design conditions, briefly. At 7F, the supply target was 179F and the differential was 14F with both zones calling.

All of this has me wondering what the control is thinking. I fit a line to the temps >=20F, and a linear regression has an r^2 of 0.99, and the regression line passes very close to (but a bit higher than) the programmed 175F at 5F. I would think the control would simply stick with that. Instead, it’s got this 5-6F step that overestimates the needed supply temp. Given the stats are satisfying easily at these higher temps, I can’t figure why the step up would be necessary.

Anybody know what the logic behind this might be? Only thing I can figure is that the control needs more time at these lower temps in order to convince itself that the step up is not necessary, much like it did during Oct-Nov.

Any insight would be most appreciated.

Key to plot:

tt (Dec-Present): BOIL TARGET temps the control has been calculating

d-lo: low temp of auto-differential (typically two zones calling)

d-hi: hi temp of auto-differential (typically two zones calling)

tt (Oct-Nov): BOIL TARGET temps the control was calculating for its first ~6 weeks of operation.

Unknown

if you're running autodifferential, that would affect the temperature it shoots for as it shifts the boiler firing differential.. I *believe* it's trying to maintain your target temp as an average temp, with the differential half over and half under that. So you can get a 5 degree rise in SWT by the differential jumping from 10 to 20, for example.

I'm not positive about that, but it's a thought.

Uni R_3

Battling Controls?

The Revolution's internal VS300 injection controller might be confusing the Tekmar 260 because the sensor is after the P/S injection circuit.

With the injection circuit changing its parameters as temperatures drop and the Tekmar learning, but also having certain expectations, it could become confused. The 260 was designed to have a boiler sensor so that it know what the boiler is doing directly. Instead, the injection circuit does things differently as teh temps drop.

CC.Rob_2

agree

I agree. The question then, I guess, is why it thinks a tighter differential is necessary. Rate of rise and fall at the supply sensor, I assume. But when the whole system gets heated up, I would think a larger differential would lead to longer on and off times, hence less cycling and greater efficiency.

Unknown

well, if it's going to be below target temperature for too long, it will probably tighten up the differential specifically so you don't come up short at the emitter..? Or, maybe it's trying to run a lower supply temp.

hard to say, they pack a lot of smarts into those controllers

CC.Rob_2

indeed

That's what's perplexing. There's too much emitter output, if anything. Generally speaking, at OT's >=20F, the reset curve results in about a 0.75-1F/hr temp rise (e.g., morning recovery from 66F night setback to 68F daytime temp takes ~3 hr). At the "stepped up" supply targets and tighter differential, it takes a lot less time and we're "blasting" (in a highly relative sense) a lot of excess heat. I'd think the 260 would want to strive for the lowest possible target temp and widest practical differential? Seems like that's what it did in Oct-Nov, which makes me wonder if it just needs more time exposure to learn what it can do at lower outdoor temps. When initially set up, I told it "175F at 5F" (which is itself a likely 5-8F overestimate). You'd think that would figure into its thinking. Probably does, but it's likely a lot smarter than me when it comes to figuring out how to get there.

CC.Rob_3

contact?

Is there anyone from tekmar on the board these days, or can someone suggest a contact at tekmar? I'd like to appease my curiosity. Thanks.