PB105 Observations

[AndrewChurchill]

Last night I thought I'd check out how well my PB handles a call for heat from my DHW.

I'm using the OAT and I have the upper limit set at 180 and the lower limit set to 140. The outside temp when I was watching the boiler was 30 and the temp of the boiler before the call for heat was 150 (right were it should be based on the outdoor temp).

I have my DHW set on a timer so I know when it's going to call for heat. At 6:00 the DHW called for heat and I saw the temp gauge on the boiler start to drop. There was already a fire going so when the boiler hit 145 the auger kicked in and the temp leveled off at 140 and stayed there until the call for heat from the DHW stopped at 6:30.

The feed rate was set at 5 and about 15 minutes into my observation I decided to drop the feed rate to 4 to see what would happen. The temp stayed steady at 140. Once the DHW stopped calling for heat the boiler temp rose back up to 150.\

I'm wondering if the PB tries to maintain the minimum temp during a large call for heat rather than trying to get back up to the max boiler temp?

I'm going to raise my minimum temp to 150 and see what happens.

I'm thinking that since the PB was able to maintain 140 on the #4 feed rate it should have been able to raise the temp when it was set at 5, but the boiler decided that it was happy maintaining the minimum boiler temp.

 

[Wayne64SS]

I would love to contribute to this thread... however my plumbing is a mess right now and i fear it is severely inefficient the way it is. Right now IF there is a fire burning (low fire) and there is a call for heat (tested today) it pulls the boiler down about 35deg... so from 180 down to about 145 150... I went upstairs after it went back to high flow and seemed to be holding steady at those temps... If there is no fire it will drop to at least 130 before the fire picks up and starts to pick up the temp. Feed rate on 4. I'm not sure if I should increase this? .... I have dip 1 in the on position and dips 2 through 4 in the off position. Any ways I can increase the efficiency?

Also I came home today to a boiler with no fire a blinking status light 5. Had pellets in it. I originally had dips 1 and 2 up but put #2 down to get more pellets in pot during ignition. Also I cleaned the burn pot... its the first time I gave it a good thorough cleaning since I've had it... I noticed there was alot of hard soot or ash in the burn pot built up along the sides and bottom near the feeder. Could this be the cause of my no start?

 

[AndrewChurchill]

Yesterday morning I set my low limit to 145 and last night I watched the boiler again when there was a call for heat from my DHW zone and the boiler dropped from 160 to 145 and stayed there until the DHW zone stopped calling for heat.

I'm going to set the lower limit to 150 tonight and do some more watching.

I'm noticing that if there's a call from heat from any or all three of my heating zones the boiler is easily maintaining the Hi temp the OAT is recommending.

Wayne, I have been cleaning my burn pot twice a week to get rid of the ash and carbon that builds up in the burn pot. During the warmer months if I didn't do this I would get the dreaded 5 blink syndrome. However, now that it's colder and I'm leaving the boiler on 24/7 I haven't had any problems with re ignition so I may back off to cleaning the burn pot once a week.

 

[nmerrill]

Andrew,
Be aware that if the boiler is just maintaining 140F, that the return water to the boiler will be well below that (120?) depending on the drop induced by the load -
Return temps that low *can* cause condensation of the flue gasses inside the boiler that will cause corrosion and a short life of our $$ toys.
This is the reason there are so many methods of "boiler protection" that have been used in the boiler world.
This is a "problem" I have been watching with my PB105 since I first fired it. They suffer from significant lag under initial call for heat and then take time to recover temp during the load.
Thus my thoughts about keeping the feed rate maxed - hotter initial fire to reduce the time the boiler runs in low temps.


Nat
Vt

 

[AndrewChurchill]

According to their manual the PB is designed to withstand lower return temps. I've checked the secondary ash chamber I don't believe the PB is condensing based on what I've observed.

So far my PB seems to be keeping up with the regular calls for heat with no problem. I've had all three heating zones call for heat with no fire in the burn pot and the temp only dropped about 10 degrees F before the PB fired up and within 10 minutes after ignition it was back up to the upper temp limit.

The only time I see the PB drop below the max temp is when my DHW calls for heat and this is only for 1/2 hour in the evening and two hours in the AM. Unfortunately, I haven't had two hours to watch how it does during the DHW call for heat in the AM.

 

[nmerrill]

Yea, i've read that too.
I also have not seen any direct evidence of condensing either.
I'm curious what your zones are - baseboard, floor, or radiator?

 

[AndrewChurchill]

In my first post I mentioned that decreasing the feed rate from 5 to 4 made no difference in decreasing the boiler temp during the DHW call for heat.

My conclusion is since the boiler temp didn't drop when I lowered the feed rate to 4 the PB wasn't using all of the fuel it could have when it was set at 5, thus the fuzzy logic of the control board somehow determines what the boiler temp should be when under a large load. I don't think in my case that if I had set the feed rate to 6 the temp would have increased.

I am going to keep experimenting though.

 

[AndrewChurchill]

My zones are all baseboard. I'm heating 2000 sq ft.

 

[nmerrill]

I noted that you said that - that is interesting.
I do think that the initial fire is larger when the feed rate is higher - it may well slow down after that based on its calculations to maintain some determined temp.
I just re-hooked up the OAT sensor last night and need to get some observations in to see how it runs differently.
Looks like next week will be a good cold spell for observin' the fire

I'm surprised that you see such little temp drops when you get calls for heat from the baseboard. Do you do any thermostat setback, and is the response the same say first run in the morning?

 

[AndrewChurchill]

I use programmable t-stats. and basically when we're not home during the day all the t-stats turn down to 55 and I've got them programmed to bring the temps up to 72 when we are going to be home.

So in the late afternoon (3:00 PM) 2 zones turn from 55 to 72 and then at 8:00 PM they turn back down to 60 until 4:00 AM then all three zones turn back up to 72 until 6:30 AM.

I checked my boiler temp this morning at 5:30 shortly before I left for work. All three zones were still calling for heat as well at the DHW and the boiler temp was at 145 which is what my minimum temp was set for.

Some day if I wake up before 4:00 AM I will go down to the basement and see how the boiler reacts. My suspicion is it will respond similarly to what it does in the evening.

 

[Sting]

could it be as simple as the load and the input leveled(s) at 140?

 

[AndrewChurchill]

Sting that's possible. It was interesting that reducing the feed rate from 5 to 4 didn't make a difference.

However, based on this morning's observations I think you might be correct.

This morning I got up before my heating zones called for heat. My minimum temp was 150 and that's what the boiler was holding at when I got downstairs. There was no fire in the burn pot and at 6:00 three zones called for heat at the same time. The temp started to drop slowly and by the time the PB ignited the temp had only dropped 7 degrees. Within 10 minutes of ignition the PB temp had gone back to 150 and was holding steady.

I watched for about 15 minutes to make sure things were stable and then I went upstairs and turned on the timer for the DHW and went back downstairs to watch. The temp dropped to 140 and stabilized at that temp. Then I turned the feed rate up to 6 and within 15 minutes the temp climbed up to 150 and stabilized.

I've decided to keep the feed rate set at 6. It makes sense to me to allow the PB to have all the fuel it needs and I feel the control board logic does a good job of not giving the PB more fuel than it needs.

As I was watching the fire I noticed that when the PB was set at 4 the fire was a good size and it stayed relatively close to the burn pot, but when I turned the feed rate up to 6 the fire rose to the top of the boiler and then stretched all the way to the far end of the boiler.

 

[Sting]

Aint this fun!

Sounds like your applinace is working just fine

You may need a bit more of a degree day load --- more than the DHW load you are using to continue you experiments but it sounds like you on top of it

later when the loads are working the appliance lets look at and adjust the Delta t of each loop and then retest your experiment.

Kind Regards
Sting

 

[AndrewChurchill]

Sting, what is the Delta T and how do you adjust it?

 

[nmerrill]

Andrew, delta T is the change (delta) in the temperature of the water between leaving the distribution point (boiler, or manifolds) and returning from the emitters, or load (baseboards in your case).
The delta T is essentially a measure of how the loads are performing and is influenced by the temperature differential the loads "see", the flow rate of the circulating water, etc.
There are ideal dT's for different emitters.
I think baseboards typically shoot for 20F DT, right Sting?

 

[AndrewChurchill]

OK, but how do you adjust it? I'm using zones valves instead of circulators.