# Tweaking the BioWin's Buffer Tank



## velvetfoot (Nov 5, 2014)

I've been tweaking the buffer tank's upper and lower temperature settings to try to get the most heat I can into the tank, and allow the most use of the tank.  The BioWin's max internal and external setpoints are 176, but that can be overshot by some undetermined amount as the unit modulates down.  

The tank controller I put together is latching, (thanks again, ewdudley), and the sensors are at the top and a little above the return opening at the bottom.  With settings of 150/168 (top/bottom), I was able to eventually get a final reading of 181/174, with a boiler temp if 186.  This was after the heat call from the tank was stopped, the circ pump run on 'purge' for 10 minutes, and the boiler shut down and in stand by.  There was no call for heat from the zones, which is a big factor.

For the next cycle, I changed the settings to 145/170.  Even if the controller doesn't initially see 170 before the boiler shuts down, it will after the boiler pump runs for a while in shutdown and then the pump will shut down after that 10 minutes I mentioned before.  The issue could be if there are heat loads during that time with the boiler shutting down.  Then, the controller might not see that temperature, and the pump would continue running until the boiler starts again on its own.  We'll see how that works.

The fact that there's virtually no heat load is a factor now.

The boiler is protected by a thermomix valve and the boiler pump won't run unless its temp is above 130.

Any ideas/suggestions?  I don't want to fly too close to the sun.


----------



## maple1 (Nov 5, 2014)

There's a bit of a catch-22 with storage tanks, in that the more heat you get into them the more potential there is for increased stand by losses from them. That might turn out to be negligible if the tank is very well insulated - or of no consequence if the tanks are in the heated space. It could be more of a factor if heating for DHW only in the summer.


----------



## velvetfoot (Nov 5, 2014)

Well, I am spending more time in the basement nowadays.


----------



## harttj (Nov 6, 2014)

I'm surprised you need a buffer tank. With a modulating pellet boiler seems it would not be needed. How many gallons does the boiler hold?


Seems adding storage defeats some of the benefits.


----------



## ewdudley (Nov 6, 2014)

harttj said:


> I'm surprised you need a buffer tank. With a modulating pellet boiler seems it would not be needed. How many gallons does the boiler hold?
> 
> 
> Seems adding storage defeats some of the benefits.


Exactly.  I believe heaterman offered a technique for setting the aquastats that would encourage the pellet boiler to operate continuously under modulation as the boiler was designed to do.


----------



## maple1 (Nov 6, 2014)

Would the storage tank acting as a hydraulic separator though add some benefits back in, and allow more opportunity for modulation?

Interesting stuff.


----------



## ewdudley (Nov 6, 2014)

maple1 said:


> Would the storage tank acting as a hydraulic separator though add some benefits back in, and allow more opportunity for modulation?
> 
> Interesting stuff.


Seems to me you would want to circulate constantly through the buffer from the pellet boiler side in order to keep the changes in load as gradual as possible so that the pellet boiler can modulate smoothly in response to longer term changes in load.

As opposed to setting up a buffer for an oil buffer where you would want to let the buffer stratify so as to minimize short cycling.


----------



## velvetfoot (Nov 6, 2014)

harttj said:


> I'm surprised you need a buffer tank. With a modulating pellet boiler seems it would not be needed. How many gallons does the boiler hold?


Ideally, that could be true.  The buffer tank serves double duty as a water heater: 11 gallons for dhw are in a 1.5" corrugated stainless coil and 108 gallons are buffer.  The other thing is, it's shoulder season now and there's not that much of a load.  I can see reduced load in the winter too because I have a wood insert that I'll use, but maybe not as much as before, with a good feature that the upstairs will now be heated better.  I think those factors argue for a buffer tank here.



ewdudley said:


> Exactly.  I believe heaterman offered a technique for setting the aquastats that would encourage the pellet boiler to operate continuously under modulation as the boiler was designed to do.


Yes, I'm experimenting with different settings.  Hence the topic.  Getting the tank as hot as possible is probably generally good, despite standby loss.  The emitters are baseboard, so they like warmer water.  If I use heaterman's technique of lowering the external temp and keeping internal temp at max, I'm thinking the water temperature available from the boiler when directly heating the zones off the top of the tank will be less than the max of 176.  Maybe less high a tank temperature achieved?  The big plus is that when it is modulating down low like that, it's available for instant heat, and as long as it's firing to heat up the tank, it's ready to heat up a zone, and will run longer. It takes maybe 20 minutes for it to start churning out meaningful heat.  20 minutes for the buffer tank might not cut it when there's a shower or cold temperatures involved.  (A reason to bump up the boiler min. temp.)



maple1 said:


> Would the storage tank acting as a hydraulic separator though add some benefits back in, and allow more opportunity for modulation?


I'm not totally clear on what a hydraulic separator is, but as I said, as long as the buffer tank is being heated, the more opportunity for the boiler to directly heat the zones, doing its modulation thing.

I really don't know what the best way to operate the system is.  Maybe different settings for different times of year as well.  Throw in the wood insert, and...


----------



## velvetfoot (Nov 6, 2014)

ewdudley said:


> Seems to me you would want to circulate constantly through the buffer from the pellet boiler side in order to keep the changes in load as gradual as possible so that the pellet boiler can modulate smoothly in response to longer term changes in load.
> 
> As opposed to setting up a buffer for an oil buffer where you would want to let the buffer stratify so as to minimize short cycling.



That's interesting.  Froling brags about the stratifying qualities of this tank and expounds how it's a perfect match for their P4 pellet boiler.
This whole subject is interesting to me, anyway, and I can tweak things and experiment without really hurting anything.  
I'm thinking along the same lines as well:  it takes a good while before the pellet boiler comes up to temp, and if the buffer tank is set too low, it'll only put a small dent in the heating requirements when the boiler is warming up from standby.


----------



## mustash29 (Nov 6, 2014)

If your boiler is on the left, and your loads on the right, a buffer / hyd separator is in the middle.  It acts as buffer volume and also as a pri / sec piping concept.

http://www.taco-hvac.com/www.epa.gov/hydraulic_separator/index.html


----------



## mustash29 (Nov 6, 2014)

http://www.seekcg.com/wp-content/uploads/2013/02/MayJunepg38.40hires.pdf


----------



## mustash29 (Nov 6, 2014)

http://ctashrae.org/images/meeting/101112/hydronic_systems___dinner_session_presentation.pdf


----------



## velvetfoot (Nov 6, 2014)

Hear is a nice writeup from Tarm:
http://blog.woodboilers.com/2013/05...013/05/using-pellet-boilers-with-thermal.html


----------



## mustash29 (Nov 6, 2014)

Very nice article.


----------



## velvetfoot (Nov 7, 2014)

I moved the top sensor 1/3 of the way down the tank and changed the settings to 150 top/ 172 bottom.
It's good to have more heat to work with when the zones or dhw kick in.
The tank got to 179/172 at stop, and 180/176 after 10 minute heat purge.


----------



## Deering (Nov 9, 2014)

I think a big part of the challenge you're having is the small amount of water you have in your DHW loop (11 gallons, right?).  Once you deplete that 11 gallons, you have to rely on the thermal storage tank for all of your DHW.  That forces you to keep the big thermal storage tank at a high temp, if I'm understanding your challenge.  Ultimately this turns out to have a high lifecycle cost due to lowered system efficiency.

The simplest, but maybe most capital expensive, solution is to install an indirect water heater.  On my system I have a 35 gallon system that has an integral heat exchange loop inside it.  You could accomplish the same with an electric water heater and a flat plate heat exchanger, cheaper, but that adds another pump to the system.  Plumb it as another zone in your system with its own zone valve or circulator.  Then the indirect is your shower 'buffer' - you have enough HW for lots of showers and the thermal storage can be allowed to drop to a lower temp, with lower standby losses, and optimizing boiler modulation.  It will still reheat the DHW tank, but perhaps at a slower rate.  Think of it as adding more thermal mass to your system, allowing your boiler to cycle even longer at low modulation.

The downside with allowing your thermal storage to drop to a lower temperature is that the water supplied to your baseboards when there's a call for heat might be lower than desired for awhile.  But that just means that the room heats up a bit more slowly until the boiler can catch up.  Usually that's not as objectionable as a cold shower.  If you have programmable thermostats for some spaces, you could program them to come on 15 minutes earlier. 

The cheaper option would be to install low-flow shower heads.  I tried out a 1.5 gpm Niagara head (available through Amazon for under $10) and I have to say that the quality of the shower experience was much better than I expected.  I'd recommend starting with that.


----------



## velvetfoot (Nov 9, 2014)

This is interesting.  Our shower heads are low flow and there hasn't been any shortage of heat for the shower even when the tank gets below 130.  I have the zone and boiler pumps set so they don't run under 130.  The thing I didn't like was what I thought was the slow return from  setback.  I changed the setback return to a half hour earlier so then the heat is on for a half hour before I get up.  Depending on how much energy is in the tank, it'll warm up the zones while the boiler starts.

I do have an indirect tank from the oil boiler, and I guess I could experiment with running that as well, but I already have that big well insulated tank with the coil in it too, and I'm leaning to not experimenting for a while, lol.

The other thing is, while it does store heat, it's nothing like a big boy tank like the wood burners use.


----------



## ewdudley (Nov 9, 2014)

Deering said:


> The simplest, but maybe most capital expensive, solution is to install an indirect water heater.


OP has a well insulated reverse indirect already.


----------



## Deering (Nov 9, 2014)

OP?  I have an Amtrol on my system.


----------



## ewdudley (Nov 9, 2014)

(OP. Short for Original Poster, i.e., @velvetfoot)


----------



## Deering (Nov 9, 2014)

velvetfoot said:


> This is interesting.  Our shower heads are low flow and there hasn't been any shortage of heat for the shower even when the tank gets below 130.  I have the zone and boiler pumps set so they don't run under 130.  The thing I didn't like was what I thought was the slow return from  setback.  I changed the setback return to a half hour earlier so then the heat is on for a half hour before I get up.  Depending on how much energy is in the tank, it'll warm up the zones while the boiler starts.



I get you now.  Sorry for my misunderstanding above.  First cup of coffee...  Sounds like you're well on your way to tweaking the timing of the components.


----------



## velvetfoot (Nov 9, 2014)

I do have the  (Amtrol) indirect tank just sitting there though.  I could maybe add a pipe or two and use it as a buffer tank for the cold well water, before it's heated.


----------



## Deering (Nov 12, 2014)

Does the circulator between your boiler and pump run continuously as long as the tank is above 130, even if the boiler has been off for a substantial time?


----------



## velvetfoot (Nov 12, 2014)

Deering said:


> Does the circulator between your boiler and pump run continuously as long as the tank is above 130, even if the boiler has been off for a substantial time?


Not as planned.  If there is no call for heat, the boiler pump does not run.  I currently have the tank to start at 145, I think.  However, if the boiler turns itself off because the internal temperature setting has been reached, then there still is a call for heat, and the boiler pump would run; I'm trying to avoid this.


----------



## Deering (Nov 12, 2014)

In my case, after the boiler shuts down, it's designed to keep the circulator pump running until the internal boiler temp reaches 130.  The idea being to pull the last remaining bit of heat out of the boiler.  But if my thermal storage tank's lower temperature was 145, the boiler circ would just keep running and running because the boiler would never reach 130.  I couldn't figure any way to change that.  I have one of the older Windhagers.  I think the newer ones were supposed to have a feature to set them up for thermal storage tanks, but mine didn't.  Does yours?

The problem with this is that the boiler loses heat due to the big flue pipe running in it.  And it can't be as well insulated as the storage tank, just due to all the necessary penetrations for pipes, augers and whatnot.  So in essence it become another radiator that stays on continuously, or at least until it cools my tank down to below 130.

So how I got around that was by installing a time delay relay into the pump circuit.  I have it actuated by the fan motor circuit.  It runs for 10 minutes after the fan motor shuts off at shutdown.  This pulls most of the heat out of the boiler, but doesn't drain my tank.  A 20 minute relay would be better, but this is what I had, and the savings would be marginal.  

The risk from a relay failure is fairly minor.  If the pump shuts off the boiler would quickly reach its setpoint and turn off.  Worst case scenario, the pressure relief would open.  If the fan fails and stops, combustion quickly stops anyway.


----------



## velvetfoot (Nov 12, 2014)

This is very interesting to me.

I think I have an even earlier model; it was a demo from one of the first batch that came over to the US.  It doesn't have a feature to control the boiler circ pump; I had to rig my own.  In addition to the controller that doesn't let the boiler pump run when the boiler temperature is not greater than 130,  I installed a relay that runs the pump for 10 minutes after there is no more call for heat by the tank. (You're right, 20 minutes would be better).  

I like your fan motor ploy.  I was thinking the same thing, but didn't know where to tap.  The other thing I was going to do with the information that the boiler is shut down (fan not running) is start the backup oil boiler if there is a call for heat at the same time, with a time delay.  The thing is, if the boiler shut down on internal temperature instead of by the tank's controller being satisfied, the fan would also shut down, and then the oil boiler would come on.  My current arrangement is the second stage of the Ranco controller that controls the pump for condensation (130) controls the kickoff of the oil boiler by turning it on if the pellet boiler is less than 120 for 20 minutes when there is a call for heat.  It takes a while for the pellet boiler to get that cool, which I figure is safe and it seems to hit 120 in 20 minutes when the pellet boiler fires up from cold.  

I don't know if this is helpful, but the thermowell in the boiler can hold another sensor, easily, which is where I've got one.


----------



## Deering (Nov 12, 2014)

I like it!

I suppose you could always just have the pump run so long as the boiler is warmer than the tank lower temp, down to 130.  Not sure how that would integrate with your oil boiler arrangement. 

Seems to me you'd just want to make sure you power the pump from the boiler's 120V bus so you're not energizing the boiler when you think you have the power shut off.  Might just want to have an electrician scope that one out before you throw the switch.


----------



## velvetfoot (Nov 12, 2014)

Deering said:


> I suppose you could always just have the pump run so long as the boiler is warmer than the tank lower temp, down to 130.  Not sure how that would integrate with your oil boiler arrangement.


I like that idea. I could finagle some settings and see what running the pump for a while would do.  A zone that turned on would affect things and might push cooler water to the zone?  Also, there'd be less stratification with the pump running.  I'm thinking of running the pump until the tank temps stabilize after turnoff and turning off the pump and see what happens with the boiler temp; what i've seen so far is that the boiler temp goes up over the top tank temp after it's stopped after ten minutes.



Deering said:


> Seems to me you'd just want to make sure you power the pump from the boiler's 120V bus so you're not energizing the boiler when you think you have the power shut off.  Might just want to have an electrician scope that one out before you throw the switch.


The pellet boiler pump is powered from the the pellet boiler circuit.  I have an on-off switch wired in for each pump which is useful once in a while.


----------



## PassionForFire&Water (Nov 12, 2014)

There should be a 10 minute post purge time delay installed.
After 10 minutes the boiler pump stops


----------



## velvetfoot (Nov 12, 2014)

That's the way it is now.  Do you think there's anything to be gained with a longer run time to extract some more heat?


----------



## PassionForFire&Water (Nov 13, 2014)

the 10 minute post purge is now standard on all BioWINs and can not be changed.
I assume Windhager tested this and came to the conclusion that this is the most optimum post purge time.


----------



## heaterman (Nov 13, 2014)

velvetfoot said:


> That's the way it is now.  Do you think there's anything to be gained with a longer run time to extract some more heat?



In 10 minutes time the boiler and tank temp will equalize so there is nothing more that can be transferred.


----------



## velvetfoot (Nov 13, 2014)

That's sort of not what I've been seeing.

I wonder if I should turn up my boiler pump?  It's been on 3 (of 7).  

The zone pumps are on pretty low, and I will tweak them if I need to when it gets cold.
I'm not sure what to do about the boiler pump though.  I figure it'll transfer the heat from the boiler to the tank quicker and maybe I'll get a fuller heat load on the tank.
I turned it up to 7 this cycle and will see what happens.


----------



## velvetfoot (Nov 13, 2014)

What's interesting is that the baseboards are getting warm even with no zone pumps running.  As I recall, this happened before.  There's no zone pumps and it must push some water up to the zones as well as going through the tank, though all the near boiler pipe is 1.25".  I'll turn it back down again.


----------



## Deering (Nov 13, 2014)

10 minutes comes pretty close to equalizing temps between my boiler and the tank.  15 or 20 would probably be a little better.  But what would really be the cat's meow would be to run the pump for 10 minutes, shut it off, wait for 30 minutes for the tank to stratify to allow cooler water to settle to the bottom/pump intake, then run the pump for another 5-10 minutes.  After stratifying, my lower tank is often 15-20 degrees cooler than the boiler, say 150 vs the boiler's 170.  I wanna suck every BTU outa that boiler that I can.

Velvet, could your zones be getting heat due to thermal siphoning?  Do they warm up even when the boiler circulator is off?  The hotter your tank is, the more pronounced that effect would be.  With your tank as a hydraulic separator, they shouldn't see any effect from the boiler pump.  A way to test this would be to valve them off while the boiler is running, then open them right after it stops and monitor the baseboards.


----------



## velvetfoot (Nov 13, 2014)

No, they don't warm up when the boiler pump is off.


----------



## Deering (Nov 13, 2014)

Hmmm.  That shouldn't be happening.  The water is going to take the easiest path back to the pump, and that's definitely through the tank.  Unless there's some baffling or something inside the tank restricting flow through it...hmmm


----------



## velvetfoot (Nov 13, 2014)

That's a good point, there is baffling in the tank, at least that's what the mfr. claims!  I'll just turn it down some.


----------



## Deering (Nov 14, 2014)

Out of curiosity, what speed are you running your boiler/tank circulator?  You have a Caleffi, right?  I just slowed mine down to the slowest setting and it seems like I'm getting longer run times.  Maybe because the stratification is not being as disrupted by a high-speed jet of water.


----------



## velvetfoot (Nov 15, 2014)

No, I have some B&G Ecocirc Varios for all the pumps.  I currently have it on 3 of 7.  No ghost flows.  I notice way better stratification on extraction when the boiler pump isn't running.  Charging, even on 3, the best I can do is something like 180 top and 174 bottom, after a ten minute purge and no zone pumps running.  If a zone pump runs and the boiler pump is still running with the boiler off, you can see the boiler heat going directly to the zone.  The bottom of the tank cools rapidly when heat extraction takes place, with the top remaing hot.


----------



## Deering (Nov 15, 2014)

velvetfoot said:


> I don't know if this is helpful, but the thermowell in the boiler can hold another sensor, easily, which is where I've got one.



Say, where is that thermowell located?

I just had an issue this morning where I woke to my boiler sitting idle while my tank was down to 145 and the electric backup boiler was running.  Nothing wrong with the pellet boiler.  It just had an internal temp of 177, well above its max setpoint of 167, so it wasn't going to start until it cooled off below 167.  Those darn Windhagers are pretty well insulated, so it might have taken another hour to cool while my electric handled the morning heating load.  Not the arrangement I was hoping for when I installed a pellet boiler. 

This goes back to our conversation about how long the pump should run post purge to extract heat - 10 minutes just isn't enough.  

I'd like to figure out a way to have the boiler pump run whenever the top of the tank is warmer than the boiler.  To do that I need a sensor in the boiler.  Will need to figure out how to use the differential between the two temps to control a relay in the pump circuit.  Seems like you might benefit from the same arrangement.  Any ideas?


----------



## velvetfoot (Nov 15, 2014)

Deering said:


> Say, where is that thermowell located?


It's behind a panel in the back; the boiler sensor is in there and you can follow the wire.

The main thing is that the tank temp setpoint wasn't satisfied.  In your control scheme, the boiler pump shuts down 10 minutes after the boiler goes to standby because of the internal max.  In my scheme, the boiler pump would keep on running because the pump is keyed into the call for heat by the tank, which still hasn't been satisfied.  

The boiler has internal and external setpoints.  I don't quite understand what your settings are, like, what the 167?  Internal, external, both?

Again, I think the main thing is that the tank temp setpoint wasn't satisfied.  Perhaps you're cutting things a little too close.

What emitters do you have?  I have baseboard, so I'd have a tendency for higher temps.  I try to charge my tank to as high a temp as I can.


----------



## Deering (Nov 15, 2014)

Both internal and external setpoints on my boiler are set to their max - 167.  That's the Euro limit on the older Windhagers - the newer imports have a higher max for typical U.S. setups. (176?).  I have my tank upper limit set at around 175 - the boiler will modulate above its 167 setting (why, I don't understand) - I've seen it as high as 183.  

I have baseboards so higher temps are desired.  In order to keep the boiler max temp below 167, I'd have to set my tank limits at around 160 or lower, which would not be suitable for my distribution system.  

I like your approach.  So you have a relay on the pump circuit.  How are you powering the low voltage side of the relay?  You're connecting the aquastat to a different terminal in the boiler - one that remains energized regardless of the boiler's internal temp?  How does the boiler know there's a call for heat then?


----------



## velvetfoot (Nov 15, 2014)

Are you sure about that?  Did you go into the parameters menu to check?  My boiler was originally set at 167.  I thought I had an old one but both can be set to 176.

I went with 120 volt Rancos, mostly.  The boiler has nothing to do with it.  The call for heat comes from the tank, if the pellet boiler can it will start up, and the boiler pump will run only if the boiler temp is above 130.


----------



## ewdudley (Nov 15, 2014)

Here's my control scheme for feeding a buffer tank with a solid fuel modulating boiler.  It's coal boiler but I believe the constraints and goals are the same.

I use an aquastat near the bottom of the buffer to generate a call for heat (T-T) to the boiler.  During the shoulder seasons I set it to minimum return temperature, 140 degF or whatever.  Then I set the boiler supply temperature to whatever it takes to keep the house warm, starting at 150 degF in the fall and increasing to 180 degF as the season progresses.  Then if the system starts to fall behind I start to raise the tank lower aquastat setpoint up from 140 degF.

If the return flow from loads can bring the bottom of the buffer below return temperature minimum then need another aquastat to disable load pumps until bottom of buffer recovers above boiler return temperature minimum.  (In my case the control is simplified because I'm using a Taco 5000 series mixing valve to maintain minimum boiler return temperature, so no need to disable load flows if bottom of buffer tank goes below boiler return temperature minimum.)


----------



## Deering (Nov 15, 2014)

velvetfoot said:


> Are you sure about that? Did you go into the parameters menu to check? My boiler was originally set at 167. I thought I had an old one but both can be set to 176.



Yeah, pretty sure.  Been in parameters a bunch of times.  It's 167 max.  Your boiler must be a bit newer than mine. They made the switch shortly after I bought mine.  I just need to add more baseboard or some panel radiators.



velvetfoot said:


> The boiler has nothing to do with it.



Then what are you using the sensor in the boiler temp well for?  Or are you just saying that there's room for a second one?  



ewdudley said:


> I use an aquastat near the bottom of the buffer to generate a call for heat (T-T) to the boiler.



Maybe I'll just use the lower aquastat to control tank temp like you do, and use the upper to control the pump and see how that works out.  I think the lower stat is going to dominate the tank control scheme anyway.  If the upper stat falls below 167, it turns the pump on.  The lower stat won't let the tank fall below 130 or so to protect the boiler during startup.  Besides, I have a Caleffi 281 Thermobloc circ pump to provide redundant protection.  The worst that can happen is that the pump runs for awhile with an idle boiler until the lower stat starts to call for heat.


----------



## velvetfoot (Nov 15, 2014)

Deering said:


> Then what are you using the sensor in the boiler temp well for?  Or are you just saying that there's room for a second one?


That two stage Ranco senses boiler temperature for boiler protection, temp not less than 130 for running the boiler pump, as well as for when the oil backup comes on, temp <120 with a heat call for more than 20 minutes.


----------



## velvetfoot (Dec 20, 2014)

More observations.
With an internal setpoint of 176, the BioWin shuts itself down after spending a fair amount of time at 181.
When a load comes on when charging the tank, the boiler temps drops, and not the tank, showing that the boiler is satisfying the load, as it should.
I am thinking now that arranging the controls so that the boiler runs until it shuts off by itself would be best, to more fully charge the tank and avoid situations that keep the boiler pump running.  The pump will still run for 10 minutes after shutdown, and not under 130.  With the more energetic, non-modulating nature of the oil boiler, this same philosophy may or may not work.


----------



## bdud (Dec 20, 2014)

I have a Honeywell L4006B humidistat on the output pipe from the boiler. This turns on at a set temp and is wired to a separate input on my controller. I use this to control how long the circulation stays on for the buffer tank. I have not timed how long the pump stays on for, it depends on the temp sensed on the boiler outlet pipe, the buffer tank ultimately gets to a higher temp than the boiler turn off temp.


----------



## velvetfoot (Dec 20, 2014)

bdud said:


> humidistat


  I know you mean aquastat.
So, if I understand it right, the boiler turns itself off based on its internal temperature setting, and then, after that event, the aquastat on the boiler supply pipe keeps the pump running until it (drops?) to a certain point?


----------



## bdud (Dec 20, 2014)

Yep, aquastat.
The sensor for turning off the boiler is on the buffer tank, and then, after that event, the aquastat on the boiler supply pipe keeps the pump running until it (drops?) to a certain point.


----------



## velvetfoot (Dec 20, 2014)

Can you tell me where on the tank sensor and aquastat are located?
I really have a hankering to have the boiler turn itself off rather than a tank sensor.


----------



## bdud (Dec 20, 2014)

A picture of my aquastat that controls my pump for the buffer tank.






A picture of the aquastat controlling the boiler on and off.




I took out the original mechanical aquastat and put this one in. This one seems more precise, with an easy to see display. The probe is in the stock location where the old aquastat's  probe was installed, maybe 2/3rds up from the bottom of the tank.
I have the boiler temp set at 167 and the buffer tank is at 170. If there is a call for heat on any of the zones and the boiler is on, the buffer tank does not reach the 170, hopefully running more economically rather than the boiler having to keep powering itself up.
I had considered rewiring so if any zone was on the boiler would not turn off, but this works well.
Might need some more tweaking in the colder temps. 

I am not sure what you mean by "I really have a hankering to have the boiler turn itself off rather than a tank sensor."
If there are no zones calling for heat and the buffer tank is up to temp, not sure what you want to achieve.


----------



## velvetfoot (Dec 23, 2014)

Thanks.


bdud said:


> I am not sure what you mean by "I really have a hankering to have the boiler turn itself off rather than a tank sensor."



I just did it.  I changed the wiring so that the heat demand from the tank is turned on by a temperature controller with a sensor 1/3 of the way from the top, and turned off when the boiler draft fan stops.  The heat demand is kept going by a relay that gets its signal from the running draft fan.  The tank got to 179 top and 176 bottom.  The guesswork is eliminated and the heat transferred is maxed.  

As a side benefit, the heat purge on shutdown timer can be eliminated, because the pump continues to run throughout the burnout stage, which is about 10 minutes, I think.  Although I didn't time it yet, the tank's top and bottom temps were the same 179/176 after running 10 minutes after the end of burnout, so I think that running the pump through the burnout phase does the trick.

The oil backup is also simplified, and a timer eliminated, because it is wired to come on if the 1/3 from top tank temp is somewhat less than the temp triggering the pellet boiler and the pellet draft fan is off.  It will also stay running until its built in aquastat is satisfied.

What stays the same is the pellet boiler pump won't run unless the boiler temp is above 130, and the zone pumps won't run unless the tank top is above 130.

Deering noted a situation where his backup boiler came on because the tank sensor temp was below that of the boiler while it was in standby.  I'm hoping that's not a problem for me, but I can always lower the oil boiler's kickoff temp.


----------



## velvetfoot (Dec 24, 2014)

Well, I tested it, and everything seems to work!  Anyway, everything seems to work!  The backup oil boiler came on with the tank top -1/3 Ranco set at a little less than the pellet sensor and stopped with the boiler aquastat, the pellet boiler came on and stopped in a similar manner.  Pellet boiler pump ran throughout the burnout stage (which was at least 13 minutes-I think I caught it near the start when I went downstairs, lol).  Pellet boiler pump and zone pumps do not run at less than 130.  Another side benefit is that the setup is a lot more compact with fewer stuff.  I believe my tweaking has come to an end!

I should note that during my testing the Froling Energy Tank top sensor got below 130, as I recall, and was providing good hot water for the shower.

Here is what the new setup looks like.


----------

