Pellet Boiler Cycle Monitoring

[velvetfoot]

I spent a few hours in the basement and noted various temperatures and boiler output.
Boiler is a 15kw Windhager, some load-2 degree setback recovery on one zone and 1 degree on the other. Outside temp was 24-29. 109 gallon buffer tank.
Boiler set temp: 176 Boiler external temp: 156

I have been thinking of adding a 3-way mixing valve on the tank to keep the tank isolated as much as possible and keeping boiler output low when not actually need. Now, I'm not sure it is really necessary. An hour and a half in, boiler output drops like a stone and stays there for the rest of the 5 hour run time. Bear in mind, the external temp is set at 156 and while the circ pumps cycled, it's not that cold out.

Legend:
Blr: Boiler temp
In: Return from tank to ThermoMix mix valve
Out: Return to boiler (mixed)
Top: Top of tank
Bot: Bot of tank
%: Boiler output

 

[velvetfoot]

Here is another one I just did. Only 2.5 hours long. Probably not as much zones plus I started the wood insert.

 

[Tennman]

VF, What product are you using to collect this data and are you using EXCEL to plot? I've been considering how to minimize pellet consumption by linking storage setpoint with outside air temp. The average water temp going to our WTA HX can go down as outside temp goes up. For us 50F days are pretty common during the winter months so mean storage temp can be reduced and still keep the home comfortable. Not sure what that device is but some type of smart controller that allows me to program storage temp as a function of outside temp. I'm sure there's some type of controller that can do this to replace my simple A419 controller, but no idea what it is. Probably should start a thread, but regardless still interested in how your collecting this data.

 

[velvetfoot]

I spent hours in the basement, or made a trip down every 15 minutes and collected manually. I use OpenOffice: it's free.

I think you're looking at an outdoor reset control. I forgot your control setup. Maybe something like this: http://www.supplyhouse.com/Tekmar-256-Boiler-Control-One-Stage-Boiler-4150000-p
That'd be for the tank.

If you want to use a shunt to mix down the water in the tank for the wta hx, that's another thing. It's been talked about a lot here lately. You'd need a proportional mixing valve with a suitable controller with outdoor reset. That would provide water temperature that adjusts to outdoor temperature. That wouldn't do anything for mean tank temperatures though.

Thinking out loud here, even though your boiler is large, it still starts and stops at will and modulates down to 30%, unlike a wood boiler. If it was relatively cold, it could maybe even heat the house without a tank. I'm not sure of your piping layout, but I think if I were you I'd want to have as little hot water inventory as possible when running the pellet boiler. Like maybe only keep the upper part of the tank hot somehow. Maybe put a sensor a certain distance from the top and have it control turn on and off. It'd depend on how stratified your tank is when loading I imagine. You want to have a nice run of maybe a couple of hours minimum, but not heat the whole tank and then just let it sit there and lose heat, even though it's well insulated.

 

[Kristen]

Not sure what that device is but some type of smart controller that allows me to program storage temp as a function of outside temp

Just in case it helps with Googling, over here I have seen them called "weather compensation control"

 

[Tennman]

Copy, collected manually. At the moment the BioWIN is being controlled much like you described and working wonderfully. The TC for the A419 is attached at mid-tank and set to turn on the boiler at 130F and shut down at 150F charging storage to about 175F top and 135F bottom after the boiler run. This is very comfortable for our home but for 60F days like today there's no need to have as much energy "inventory" as you so well put it. Unfortunately I have no idea how long it runs to recharge and is highly dependent on the home's demand. Kristen, I'll google weather compensation control. I figured there had to be some controller out there. Will be researching data collection systems. Thx guys.

 

[velvetfoot]

Then, I think you should check out that link I posted. I bought that model for my oil boiler a while ago, so I'm familiar with how it works. Not that expensive.

 

[Sparky978]

Then, I think you should check out that link I posted. I bought that model for my oil boiler a while ago, so I'm familiar with how it works. Not that expensive.

Will that outdoor reset work with the Biowin?

 

[velvetfoot]

I was just talking of the tank.
I don't think Windhager offers an outdoor reset on its US version.

 

[velvetfoot]

Here is another one I did earlier today. It was tank charging only.
I would hope to keep it more at 30% with a mixing valve in front of the tank set higher than the external target temp.

 

[Tennman]

VF, Thanks for the tip on the Tekmar. Called their tech support to see if it works with the A419 or replaces it. But it appears to be the link to the outside air temp I'm looking for. The other limitation of the A419 is it only has a 20F max differential. With as much storage as we have instead of a 130-150F setpoints it would be nice to have 120-150F resulting in fewer but longer firings. But to be honest I don't know if less frequent/longer duration firings are more efficient. I believe fewer startups are less stressing on the boiler, but that's based on nothing but intuition.

Sparky, Yes, it appears the Tekmar 256 is programmable to have a variable ON setpoint as a function of outside air. On our BioWIN there are two terminals for external control that just require an closed/open state to control the boiler. I'm getting the impression from VF and others you guys are controlling your BioWINs based on the water in temp? Ours is being controlled solely by an external control based on the mid-storage tank temp. Which by the way is working wonderfully, but since I enjoy it, I'm confident I can save pellets by shifting the boiler ON/OFF setpoints as a function of outside air since our temps can range very significantly where we live. If we were at the NY or MA latitudes where the fluctuations from a mean temp is far smaller I doubt there would be much benefit. Fun stuff.

 

[velvetfoot]

I'm getting the impression from VF and others you guys are controlling your BioWINs based on the water in temp?

Willfully controlling it is just a concept at this point, , but it seems to happen with lower boiler external temp setting and the boiler protection valve.

The other limitation of the A419 is it only has a 20F max differential.

I think the Ranco controller has a 30F max differential. Not too expensive.

 

[Sparky978]

Sparky, Yes, it appears the Tekmar 256 is programmable to have a variable ON setpoint as a function of outside air. On our BioWIN there are two terminals for external control that just require an closed/open state to control the boiler. I'm getting the impression from VF and others you guys are controlling your BioWINs based on the water in temp? Ours is being controlled solely by an external control based on the mid-storage tank temp. Which by the way is working wonderfully, but since I enjoy it, I'm confident I can save pellets by shifting the boiler ON/OFF setpoints as a function of outside air since our temps can range very significantly where we live. If we were at the NY or MA latitudes where the fluctuations from a mean temp is far smaller I doubt there would be much benefit. Fun stuff.

I was just talking of the tank.
I don't think Windhager offers an outdoor reset on its US version.

If I have this right. Even though Windhager doesn't offer outdoor reset it seems that with 256 we could have our controllers A419 or Ranco send a call signal to the 256 then the 256 would start the boiler depending on outdoor air temp and water temp. Where would you put the water temp sensor?

 

[__dan]

My thought is that 100 gal "buffer" DHW indirect Energy Tank is not there to extend your firing time. It is too small for that, so taking it out of the picture has no foreseeable effect, in my opinion. It is only big enough to absorb the excess heat of the Windhager's shutdown sequence, the burning off and purging of the remaining fuel, heat, flue gas, when the boiler is commanded off. And to extend DHW production without calling the boiler on from the off state. This is the intended function of the present system.

The reference design would be to convert to primary / secondary loops. The primary is straight boiler water including only the boiler and the DHW Energy tank. I would stop calling it a buffer tank.

The secondary is your heat emitter distribution loop temp, The mixing valve or injection pump goes between them using closely spaced tees and an OAT reset controller to set the distribution HW by OAT reset, which is a good proxy for demand. This change will move you closer to a constant flow system, maintaining a constant lower load on the boiler and extending its run time, making its firing rate turn down, modulating fire feature, work basically all the time.

I would advise not touching it until you understand this alternate and can choose between the two. Clearly, this choice will save you money and achieve what you want to do, extend your boiler run time in its low fire range. Why take a working system and modify it several more times in a non standard way. Promote, employ, best practice and take pride in your heat making.

 

[__dan]

I took another look at the graphs you posted and I'm starting to see what you tried to convey. It looks like the high fire time from a cold start is only 30 to 40 minutes and the boiler starts to turn down very quickly, spending 60% to 75% of its time at its lowest fire output. I don't see how you could expect any improvement on that. That's a very state of the art, very sophisticated equipment package.

OAT reset of the emitter loops may improve the comfort level, reducing any squeaking from expansion contraction of the rads as they go on and off, reducing any temp differentials in the house as the heat spreads out more evenly as the heat is always on at a lower temp. Since it's an expensive adder, it would not be standard in most installs using convention high water temp emitters. The lowest cost option would be the most popular.

For the boiler, the graphs are already showing what a state of the art system should be doing. Far more than 85% of the other boilers in your town. Only a gas condensing rated boiler could do better. If the house needs windows, insulation, siding, that may be next.

 

[velvetfoot]

If I have this right. Even though Windhager doesn't offer outdoor reset it seems that with 256 we could have our controllers A419 or Ranco send a call signal to the 256 then the 256 would start the boiler depending on outdoor air temp and water temp. Where would you put the water temp sensor?

I don't know. You and I have small buffer tanks, while Tennman has a thousand gallons. I think for us, we could use the reset controller to change the temperature that the boiler comes on, figuring you might need more heat on cold days when zones are calling and the boiler is starting up and getting up to temperature. I, for one, would continue to try to get as much heat into that buffer that I could, and not shut down the boiler before I did. Now for Tennman, I don't know.

To my way of thinking, it takes about an hour and twenty minutes to get to 30% modulation. That last tank-only run, took 2.5 hours total. I figure, in that case as an example, heating only the distribution loop and the boiler, it could get up to 160 or so rather quickly, where the boiler would be at 30%, and would stay there as loop temperature got to 176 or so where it would stay as the diverting valve would keep it there as the tank slowly got charged up-at 30%. This would stretch out run time and give the boiler an opportunity satisfy a zone calling during that time.

Now, if I moved the boiler external temp to 176 from 156, there would be less modulating going on during the trip to 176 in the loop before it started to bleed some to the tank, and would be more vigorous in satisfying multiple calling zones, say from a setback in cold weather. The Windhager can't OAT boiler temp.

As far as OAT distribution, my current set up and way of thinking, is to tap the zones off the boiler supply first-give the zones first crack at the boiler's hot water. It's called a two-pipe setup, I believe. The water is untempered since they are high temp emitters. It would be pretty easy to deliver mixed water with a four-pipe system, delivering all the hot water to the tank and running the tempered water out to the zones from there. I'm not sure it would be worth the trade offs such as quick zone response, setback recovery. I still use a wood stove, so that's in the mix-most times it's on, sometimes it's not, it's hot, it's warm, it's cold, etc. Plus, I like to use a setback at night, and timely recovery is necessary. I have the thermostat differential at .5, so that keeps it tight. I do not like the creaks though.

 

[__dan]

This:

http://tekmarcontrols.com/support/tekmarglossary/33-support/glossary/193-variable-speed-output.html

with this:

http://tekmarcontrols.com/products/hvac-systems/361.html

Two separate loops with a two pipe bridge. The bridge connects to the loops at each end with closely spaced tees. Because of the flow differences at the transition points, the closely spaced tees take the place of a hydraulic separator. This control is made to work with a standard 007, not made for an ECM circ.

You cannot OAT reset the boiler unless it is a condensate rated boiler (modern gas appliance). You are already at 160 F setpoint HWS so there is no space to go with a lower HW temp. The boiler is looking for 140 F return water and a 10 degree F differential from return to supply. Your range to vary is only 160 to 180 or almost nothing, nothing if fixed 160 works all the time.

Note this. Your boiler HWS is already set as low as it can go without condensing the flue gas and making a very hard to clean mess.

http://tekmarcontrols.com/solutions/browsesolutions/energy-savings.html

The distribution loop in reset however, will have a range of 90 to 140 F and depending on how low you dial it down, your typical emitter temp will be 110 F or so (and on much longer). It will work with convection baseboards, just adjust up the operating temp to suit.

Setback: Add an isolating relay to the indoor setback stat and open the tank to boiler call for heat circuit in setback. No need for DHW when you are in setback. Adjust the setback recovery time earlier so it has completed recovery at your waking time. When you want heat first thing in the morning, the boiler should be off and hot, resting, after having fired hard to recover from setback. Ditto for the tank, it will probably be at its hottest temp of the day at your waking time if setback recovery time has started early enough.